US 3719536 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
6, 1973 L. M. RHEENGOLD ETAL 3,719,536
MECHANOCHEMICAL SHEET METAL BLANKING SYSTEM Filed Feb. 12, 1971 4 Sheets-Sheet 1 i Q g mu-l llnmj 5P 0 Q INVENTORS LAWRENCE M. RHEINGOLD MILTON BERLIN 13y LOUIS DELAUO ALFR SCHIERWAGEN swan March 6, 1973 RHEENGOLD ET AL 3,719 536 MECHANOCHEMICAL SHEET METAL BLANKING SYSTEM Filed Feb. 12, 1971 I 4 Sheets-Sheet 2 INVI'J'V'I LAWRE M. RHI LD MILTON ERLIN HY LOUIS ALIO LFRED IERWAGEN MECHANOCHEMICAL SHEET METAL BLANKING SYSTEM Filed Feb. 12, 1971 March 6, 1973 RHEINGQLD ETAL 4 Sheets-Sheet 3 March 6, 1973 RHEWGOLD ETAL 3,719,536
MECHANOCHEMICAL SHEET METAL BLANKiNG SYSTEM Filed Feb. 12, 1971 4 Sheets-Sheet &
FIG. /9 FIGZO F I G. 2 Z
INVI'JN 'I'ORS LAWRENCE M. RHEINCDLD MILTON BERLIN HY LOUI$ DILALIO ALFRED CH WAGEN fl L11;
3,719,536 Patented Mar. 6, 1973 US. Cl. 156--6 14 Claims ABSTRACT OF THE DISCLOSURE A system of blanking sheet metal by using a punch and die to partially stamp 21 part out of sheet metal stock in a fashion such that a considerable portion of the thickness of the part protrudes from the stock but the remainder is retained therein, being separated from the stock by a peripheral shear crack or fault zone. Preferably at least some portions of the part and stock have a coating or layer of an etch resistant material. The openinc in the stock from which the part was partially punched out is freshly exposed unprotected metal. Subseouently, the stock and part are etched. The etching fluid attacks the metal at the exposed portion of the opening and in the peripheral shear crack (fault zone) to loosen the hold of the stock on the part. The part finally is released from the stock. Etch resistant material may be applied to the die-facing side of the stock and part after the partial punching operation has been completed and may be a subsequent second application of such material, the first being prior to the punching step. Such an after-punching etch resist coating can be used to retain the part in the stock when the part is loosened by etching so that the part will be held to the stock until such etch resistant coating is removed. The etching step, in addition to loosening the part from the stock, desirably eliminates the burr which conventionally is present on the punch-facing side of the part so that the part does not have to be deburred in a subsequent step. An etching step may be practiced to deburr a completely stamped out part by protecting all surfaces of the part except in the region adjacent the burr.
CROSS-REFERENCE TO RELATED APPLICATIONS This application is an improvement over the method disclosed and claimed in application Ser. No. 664,881, filed Aug. 31, 1967, now US. Pat. No. 3,563,819 on Feb. 16, 1971, for Mechanochemical Sheet Metal Blanking System, over the apparatus disclosed and claimed in application Ser. No. 73,883 filed Sept. 21, 1970 for Mechanochemical Sheet Metal Blanking System, and over the article disclosed and claimed in application Ser. No. 82,973 filed Oct. 22, 1970, for Mechanochemical Sheet Metal Blanking System.
BACKGROUND OF THE INVENTION (1) Field of the invention A system of blanking sheet metal by partially stamping a part out of sheet metal stock so that a peripheral shear crack or fault zone separates the retained portion of the part from the stock, chemically attacking the walls of the opening left in the stock and also the walls of the shear crack or fault zone and releasing the part.
(2) Description of the prior art There are presently two categories of forming parts from sheet metal. One of these is a mechanical system and the other is a chemical system. Each system has advantages and disadvantages which markedly separate it from the other.
In the mechanical system it is conventional to provide a male punch and a female die. The punch matches the die, except that there usually is a slight clearance around the punch when the punch is nested in the die. The amount of clearance depends upon the required tolerance for the part and also depends upon the type of finish required for the edges of the part. The clearance may vary from a positive clearance to a zero clearance and even to a slightly negative clearance.
The punch is made by metal removing operations which usually are quite precise, the precision depending upon, inter alia, permissive variations in the part to be blanked out, e.g., such variations as edge finish, tolerance and the nature and degree of the burr. The precision in manufacturing the punch and die also is governed by the number of parts to be made with the tool, the thickness of the stock from which the part is to be formed and the metallurgical constitution of the stock.
Similarly, precision metal removing operations are required in the formation of the female die. customarily, the female die is in the form of an opening which extends completely through a metal member inasmuch as in a standard blank-stamping operation the part, after severance from the stock, is pushed completely through the female die and is discharged from the upper or under face thereof.
It is also usual to provide strippers for disengagement of the blanked-out part from the tip of the punch after the stamping operation and for similar disengagement of the stock from the sides of the punch.
Due to the cost of labor and equipment involved in the production of a punch and die, such a system is employed principally where a run of a large number of pieces is contemplated. A commonly accepted point is 100,000 pieces as a minimum; that is to say, if less than 100,000 pieces are to be made the manufacturer usually will look for a system other than a mechanical system for forming the parts. Where special problems exist which are best solved by using a punch and die for blanking out the parts and which have poor solutions with other methods of manufacture, a punch and die system is used for even smaller production runs, for instance, as low as 100. One such problem is that, frequently, specified tolerances are quite tight, that is to say, small, and cannot be met by anything other than a punch and die system.
A punch and die can be quite costly to manufacture. Initial die cost for a typical part which is small but which has some degree of complexity such, for instance, as a typical lead frame (a frame used to supply terminal connections to an integrated circuit) is $25,000. The time required to make a punch and die is quite lengthy and typically runs to about 4 to 8 months. Of course, once a punch and die is made, it can be operated with relatively high speed and is relatively inexpensive to use. For example, with the same lead frame whose typical die cost is $25,000 the per-piece cost of the parts is in the range of $.02 each. However, it is the considerable length of the toolmakers time and the initial high cost of the punch and die which restrict the use of such System for anything but extended runs unless other factors are involved. It will be understood that the price of about $.02 each mentioned above for a typical lead frame is not typical for punching out simple parts as, for example, washers.
The mechanical system can typically blank out from to 300 parts per minute at an average cost for the blanking operation in the range of 1 /2 mils.
Another disadvantage of the mechanical system, aside from those of lengthy tooling time and high tool costs, is that with the mechanical system the parts produced almost invariably have a peripheral burr on the corner that originally faced the punch. The size of the burr will vary with the type of part, the condition of the punch and die, the thickness and composition of the metal stock, the speed of operation of the punch and die, and the punch and die clearance. However, the presence of a burr persists, being inherent in a punch and die blanking step. Depending upon the use of the part, the burr may have to be removed. Various procedures are employed for this purpose such as tumbling, grinding, wirebrushing, scraping, filing, chemical action and electrolytic action. These represent a considerable additional cost as well as additional factory space, additional labor and additional through-time in the factory.
A further drawback of the mechanical system is that the punches and dies must be sharp, failing which the parts blanked out therewith experience edge deformation, do not hold to specified tolerances and have increasingly larger burrs. This can be overcome by regrinding the punch and die which obviously requires additional time for removing the punch and die and regrinding the same, or, if some of the down time is to be avoided, the provision of extra sets of punches and dies.
For psychological reasons many companies, and these even include the large companies which should not be affected by such reasons, do not like to place stamping die orders if they can help it. Using as an example the lead frame mentioned earlier for which the stamping die cost is in the order of $25,000, it is understandable why a company is reluctant to make an investment of this size. Sometimes, despite the best intentions on the part of the forecasters, sales fail to meet market projections or the engineering department decides to make a change, and the dies become obsolete. Hence, the companies often resort to less costly production methods, i.e. to methods other than the punch and die system, and these other methods will, as will be pointed out hereinafter, have different drawbacks although the initial cost is lower. It frequently is the case that a company cannot project the usage of a large number of parts, say, one million parts or over, in order to justify the purchase of a costly stamping die. As a result, such a company might place a succession of small orders, the aggregate of which would have warranted the purchase of a punch and die system over the life span of the part. Such orders are placed for production by initially less costly systems, but the end result is that the per-piece cost of the parts over the usage life of the part is very high.
A basic punch and die operates by placing sheet metal stock on top of the die and then moving the punch toward the die. The punch stamps a blank of predetermined shape out of the stock by pushing the blank through the die. When the punch first engages the stock it embosses the stock, that is to say, it indents a depression on the punch side of the stock and, by a step that at least includes shearing, raises a boss on the die side of the stock which boss enters the die opening. The punch continues through the die pushing the part out ahead of it until the punch clears the lower face of the die whereupon the part which has now left the die is discharged, being stripped from the face of the punch if it adheres thereto.
During the initial portion of the punching operation when the boss-embossing step is being effected the part is within the stock, being at some stage of the operation separated from the stock by a shear crack or fault zone which extends peripherally around the part. It will be seen later that this shear crack, i.e. fault zone, is used in the practice of the present invention.
The chemical system forms a blank by partially coating at least one surface of the stock with a resist, i.e. a material that is not attacked by the particular chemical etch n to be emp y d, which et a w ll attack th metal of the stock. The resist coating is in the shape of the part to be made. For instance, assume that the part to be made is a washer, then the coating is in the form of a flat annulus which will leave exposed on the inside of the annulus a surface of the stock in the shape of the hole that ultimately is to be present in the washer and will leave uncoated on the outside of the annulus a zone having an inner circular edge in the shape that the circumference of the washer ultimately is to assume. Thereafter, the surface of the stock bearing the resist is exposed to a chemical etchant which erodes the uncoated area of the stock and does not affect the protected area. The etch erodes through the thickness of the stock and finally leaves free the part to be blanked out. In some chemical systems the other face of the stock may be fully coated with the resist. In other systems it may be coated partially in registry with the coatings on the first-named side and, When the stock is etched, the chemical attack will erode the uncoated areas on both sides of the stock in order to speed up the etching time and to improve accuracy of configuration.
As a practical matter, the chemical system is restricted to parts made from thin stock because of the time involved in etching through the unprotected part of the stock, because of the cost involved in replenishing chemicals in the solution, and because dimensional tolerances and accuracy of configuration become progressively more difficult to control with increasing thickness of stock. Chemical blanking has one marked advantage. It does not require the expensive and time-consuming fabrication of metal punches and dies. The chemical dies, if they may be so denominated, are far cheaper and simpler to make than mechanical dies. They usually are nothing but printing plates or rubber stamps which apply the resist coating in substantially the correct shape on the metal stock. The printing plates can be made photographically, so that extremely complex shapes can be fabricated at a low cost. Also, the protective resist can be produced by direct photochemical methods in situ on the sheet metal stock, this system being used, by way of example, in the production of integrated circuit lead frames and is conducive to the formation of highly involved shapes. Additionally, the shape of the part can be repeated in multiple, so that many parts can be chemically blanked out in one operation. But, as a practical matter, chemical erosion is expensive and time-consuming. The average cost of making a lead frame such as the typical lead frame mentioned above is in the area of $.06 as compared to the $.02 cost for the production of the same part with a punch and die. Of course, the higher per-piece cost involved with the chemical system is offset by the lower price of the socalled dies (the graphic or art work) used in the chemical system.
It has been found as a rule of thumb that the chemical system is best employed where the total number of parts made in a run is up to about 100,000 and that the mechanical system is best used when there are more than 100,000 parts to a run. Naturally, there is an overlapping area in which the decision will be made pursuant to the judgment of management taking into account all the advantages and disadvantages of both systems. Nevertheless, in general, each of these two methods operates in its own field and tends to be exclusive of the other. Each has many advantages and each has many disadvantages.
Among the drawbacks of the chemical system, aside from its slow speed, are corrosion and undercutting of the blanked out parts and the restriction of the system for efiicient operation to very thin sheet metal stock, usually not more than Also, with the chemical system it is difficult to maintain uniformity and close tolerance of the parts, particularly where a printing-type step is employed, as in the production of integrated circuit parts. Poor resist applications may leave etch inclusions on lead frame legs which create a continuous problem in semiconductor manufacturing. This problem neces- S t s co siderable ins ection time and results in high reject rates for completed units. Furthermore, the edges of an etched part are usually not well defined and certainly never as well defined as a part made by the mechanical system. On the other hand, a part produced by the chemical system has no burrs. Indeed, it is a defect of the chemical system that it has a poor edge squareness because the etch undercuts the resist. Where etching is conducted on both sides simultaneously a condition similar to a burr occurs where the undesired lateral etching which is greatest at each surface of the part meets in the center to leave a fin. A substantial advantage of the chemical system is that turn-around time, which is the time between receiving a firm order and starting the production of the parts, is quite short, typically being about 2 weeks compared to the 4 to 8 months for the punch and die system.
It will be appreciated from the foregoing that the initial costs and the per-piece costs for either the mechanical or chemical systems can be readily determined and, therefore, the decision to use either system is generally based on the economics of the parts to be made. However, both processes advantages and disadvantages are also factors in the final choice of system selected.
SUMMARY OF THE INVENTION (1) Purposes of the invention It is an object of the present invention to provide a novel mechanochemical sheet metal blanking system.
It is another object of the invention to provide a mechanochemical system of the character described which has a greater versatility than either the mechanical system or chemical system and which, therefore, can be used over a wider range in the number of parts run, such, for example, as from about 10,000 or less up rather than from about 100,000 or less up as with the mechanical system, to an unrestricted upper limit rather than a commercial upper limit of about 100,000 as with the chemical system.
It is another object of the invention to provide a mechanochemical system of the character described which can be economically employed for a wider range of jobs than either of the two previous systems.
It is another object of the invention to provide a mechanochemical system of the character described employing dies which are of a more rudimentary and, therefore, less expensive, character than the dies employed in the mechanical system and in which the parts may be run through the mechanical section of the mechanochemical system more rapidly than through a mechanical blanking system.
It is another object of the invention to provide a mechanochemical system of the character described in which the die work entailed in making the die is considerably reduced as compared to the mechanical system.
It is another object of the invention to provide a mechanochemical system of the character described employing an erosion step which is usually carried out more quickly than the erosion step of the chemical blanking system.
It is another object of the invention to provide a mechanochemical system of the character described which in the chemical section of the system removes the burrs formed in the mechanical section of the system.
It is another object of the invention to provide a mechanochemical system of the character described which enables parts to be blanked with ease and minimal operational steps from soft to hard and from thin to thick stock.
It is another object of the invention to provide a mechanochemical system of the character described in which the edges of the stock can have a fine, i.e. excellent, finish Which in most respects is as good as the finish obtained with the mechanical system and in some instances better, and which furthermore, can obtain a finish much better than that secured with the chemical system.
'It is another object of the invention to provide a mechanochemical system of the character described where in both corner edges of the part, that is to say, the corner edge adjacent the punch side and the corner edge adjacent the die side, have desirable contours, a desirable contour generally being one in which the face of the part is essentially square to the edge but is not sharp, i.e. is slightly chamfered.
It is another object of the invention to provide a chemical system constituting an improved method of removing the burr at the punch side of a part and leaving this edge of the part in a desirable configuration without deteriorating the condition of the remainder of the edge of the part by lowering the quality of the finish, reducing the definition of the edge or increasing the tolerance of the part.
Other objects of the invention in part will be apparent and in part will be pointed out hereinafter.
(2) Brief description of the invention The present invention provides a hybrid system including certain steps and equipment taken from a mechanical system and certain steps and equipment taken from a chemical system, the steps and equipment being so blended as to retain the advantages of both systems and to minimize the disadvantages of each in the metal blanking field.
In carrying out the present invention sheet metal stock is subjected to a punch and die operation which causes a part to be boss-embossed in the stock by an action that at least includes shearing; that is to say, the part is punched out of the stock for a predominant portion of the thickness of the part, not more than 20% and preferably in the region of 5%, being retained in engagement with the stock. Indeed, the part may be so far pushed out of the stock that the top surface of the part is below the bottom surface of the stock but the upstanding peripheral burr of the part still engages the opening in the stock formed by punching out the part so that the part is still captively retained by the stock. Thereafter the stock and part are subjected to an etching fluid. This fluid attacks the exposed wall of the opening left by the part and also attacks the walls of the shear crack (fault zone) peripherally surrounding the part. The attack on the Walls of the shear crack performs two functions; first, it enlarges the crack (fault zone) to the point that the part is ready to be removed from the stock and, indeed, can fall from it under a slight push or by gravity, and second, it totally or substantially removes the peripheral burr and usually a portion of the part beneath the burr so that the part now is chamfered at the punchfacing side of the part, the chamfer on the other side, i.e. the die-facing side, having been created as a roll-over edge which is inherent in the stamping of the part and is created when the lower surface of the part first entered the die opening.
Preferably, at least certain portions of the stock and/ or the part are protected during the etching step. The protectron may be by way of an applied coating such, for instance, as an etch resist coating, or the protection may be afforded chemically as by forming an etch resist compound of the metal stock at a surface region thereof. Another mode of protecting the stock and/or part faces is by the application of a thin ceramic layer or by plating as with a metal, e.g. gold, which will resist the etching fluid. Obviously, different plating metals can be employed, the one selected being one which is not attacked by the etching liquid which will attack the metal of the stock. A still different method of protecting the surfaces of the part and/or stock is to apply a layer of an etch resistant film, e.g. a synthetic plastic film, which can be bonded as with heat or pressure or with the use of adhesives or by application in liquid form with subsequent evaporation of a volatile solvent or cooling to leave a film deposit.
Such etch resist coating or layer can be applied to one or both surfaces of the stock prior to the boss-embossing step. If it is only applied to one surface of the stock it preferably Will be that surface to which the etching fluid is directed during the erosion step if the etching fluid is only directed to one surface. Furthermore, the application of the etch resist coating or layer may be in part practiced after the boss-embossing step. For example, the etch resist material can be applied to the punch-facing side of the stock before boss-embossing and then applied only to the die-facing side of the part, but not the stock, after bossembossing, inasmuch as it is not necessary to protect the die-facing side of the scrap, the only advantages therein being lengthening the life of the etching fluid, minimizing the amount of metal to be recovered from the etching bath if such recovery is practiced, minimizing ecological pollution and increasing somewhat the weight of solid scrap recovery.
In another form of the invention all of the part which protrudes from the die-facing side of the stock, this including not only the die-facing surface of the part but also the edges of the part which protrude from the stock, may be covered by the etch resist material, and this form of the invention is a highly preferred form because it preserves the shape and finish of so much of the part as has been pushed out of the stock, thus better holding tolerance and better maintaining the excellent finish of the edge of the stock which was obtained by the punch and die section of the mechanochemical system. Furthermore, with this arrangement the attack (as to the part) is limited to only so much of the part as faces and engages the stock across the crack (fault zone) and the immediately adjacent portion of the part and, in so doing, creates a chamfer around the periphery of the part which originally faced the punch. A still further advantage of this arrangement is that even after the erosion has proceeded to an extent sufficient to destroy metal-to-metal engagement between the part and the stock, the part still is held to the stock by the etch resist material which not only covers the portion of the edge of the part that protrudes from the stock but also extends over to at least a portion of the underface of the stock so that this etch resist material functions as a bridge that now holds the part to the stock enabling the part and stock to be unitarily handled if so desired. Thus, the stock with etch resist attached part can be conveyed from the etching zone to a flushing zone and/or neutralization zone where the corrosive action of the etch is nullified. The part will continue to remain with the stock until the etch resist is removed as by the application of a solvent for the etch resist material.
The etch resist material can cover the upper face of the part and be applied thereto either before or after the part is boss-embossed in the stock. When applied after the boss-embossing step it is contemplated that the etch resist material need not cover the entire upper face of the part, particularly if it is desirable for some reason to maintain at least some portion or portions of the upper face of the part in the virgin state in which it existed prior to etching, while it may be desired to expose other portions to the etching fluid.
In another embodiment of the invention the stock with boss-embossed part may be affixed to a substrate, eg a substrate of insulating material, as by bonding, and then the stock and part subjected to the etching fluid. This will leave the part affixed to the substrate and facilitates the handling of tiny fragile parts by keeping them integral with the stock up to the time that they are bonded to the substrate, after which the stock is physically removed. Such arrangement is useful in the preparation of circuit boards where the part constitutes an electrically conductive portion of the circuit board.
In still another form of the invention which presently is considered less desirable, the part may be fully punched out of the stock and then restored to the opening left in the stock, the degree of restoration being within the range previously indicated, which is to say, not more than 20% of the thickness of the stock and preferably in the range of about 5% of the thickness of the stock, and even down to retention of the stock only by the raised peripheral burr on the surface of the part that faces the punch, after which the etching step is effected.
The invention also embraces the full detachment of the part from the stock without its subsequent restoration into the opening in the stock, and in providing an etch resist coating around all the part except the narrow edge zones of the part adjacent the surface of the part that faced the punch, the part subsequently being subjected to an etching fluid which, in attacking the exposed metal of the part, is restricted in its action to this narrow zone and thus only removes the burr and chamfers the aforesaid surface of the part.
BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings in which are shown various possible embodiments of the invention,
FIG. 1 is a side elevational schematic view of equipment employed for carrying out the present invention;
FIG. 1A is a side elevational schematic view of an alternate equipment used at the etching station;
FIG. 2 is an enlarged fragmentary sectional view through the sheet metal stock after the upper and lower surfaces of the stock have been coated with an etch resist;
FIG. 3 is a highly enlarged fragmentary sectional view through the stock at the punching station, the stock being illustrated at the termination of a punch stroke;
MG. 4 is a highly enlarged fragmentary sectional view through the stock subsequent to the punching operation and after a further application of etch resist material to the undersurface of the stock and part but before the etching operation;
FIG. 5 is a still more enlarged fragmentary sectional view through the stock after the etching operation, the dotted lines indicating the condition of the stock and part prior to etching;
FIG. 6 is a view similar to FIG. 5 of the part separated from the stock and with the etch resist removed;
FIGS. 7, 8 and 9 are views similar to FIG. 5, but illustrating different configurations of corner edges at the punch-facing surface of the parts;
FIG. 10 is a view similar to FIG. 5, but in which prior to the etching operation neither the stock nor the part has had a resist material applied thereto, the etching liquid being directed toward the punch-facing and diefacing surfaces of the part and stock and the opening in the stock;
FIG. 11 is a view similar to FIG. 5, but in which the punch-facing surfaces of the part and the stock have had a resist material applied thereto prior to the boss-embossing step and the etching step, the etching liquid being directed toward the punch-facing surface of the part and the opening in the stock;
FIG. 12 is a view similar to FIG. 5, but in which the die-facing surfaces of the part and stock have had a resist material applied thereto prior to the boss-embossing step and the etching step, the etching liquid being directed toward the punch-facing surface of the part and the opening in the stock;
FIG. 13 is a view similar to FIG. 5, but in which the punch-facing and die-facing surfaces of the part and stock have had a resist material applied thereto prior to the boss-embossing step and etching step without a further application of resist material to the die-facing surfaces of the stock and part, the etching liquid being directed toward the punch-facing surface of the part, the same surface of the stock and the side edge of the part;
FIG. 14 is a view similar to FIG. 11, but in which a resist material is applied to the punch-facing side of the stock and part prior to the boss-embossing step and to the die-facing surface of the part after the boss-embossing step, the etching liquid being directed toward the punchfacing surface of the part and the opening in the stock;
FIG. 15 is a view similar to FIG. 10, but in which a resist material is applied to the punch-facing surface of the part after the boss-embossing step, the etching liquid being directed toward the punch-facing surface of the part and the opening in the stock;
FIG. 16 is a view similar to FIG. 15, but in which a resist material is applied only to a preselected area of the punch-facing surface of the part, which area is less than the entire said surface;
FIG. 17 is a fragmentary top view of the part, the same being taken substantially along the line 17-17 of FIG. 16;
FIG. 18 is a view similar to FIG. 5, but in which a resist material in the form of plating is applied to the punchfacing surfaces of the part and stock prior to the bossembossing step and a resist material is applied to the diefacing surfaces of the part and stock and to the side edge of the part after the boss-embossing step, the etching liquid being directed toward the punch-facing surface of the part, the same surface of the stock and the opening in the stock;
FIG. 19 is a view similar to FIG. 18, but in which the resist material applied to the punch-facing surfaces of the part and stock prior to the boss-embossing step is a film adhered to these surfaces;
FIG. 20 is a view similar to FIG. 4 in which the punchfacing surfaces of the part and stock have had a resist material applied thereto prior to the boss-embossing step, the part and stock, and being shown prior to an etching step;
FIG. 21 shows the stock and part of FIG. 20 applied to a substrate to which the die-facing surface of the part is secured, said view being taken after an etching liquid has been directed toward the punch-facing surface of the part and the opening in the stock; and
FIG. 22 is a fragmentary sectional view through a fully punched out part that has had applied thereto a resist material over the punch-facing surface of the part, the die-facing surface of the part and the side edge of the part, except for a narrow zone adjacent the burr at the punch-facing corner edge of the part, the part subsequent- 1y having been etched at the non-resist-protected zone to remove the burr.
DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, the present invention is carried out by first performing on sheet metal stock a mechanical punching operation which substantially but not entirely displaces the part from the stock, thus leaving a boss-embossed part which protrudes from the die-facing side of the stock an amount which is equal to a predominant portion of the thickness of the stock, the part being separated from the stock by a shear crack, i.e. fault zone, running around the periphery of the part and being retained in the stock by metal-to-metal engagement. Thereafter the part and stock are subjected to chemical erosion that attacks the walls of the opening in the stock left by a partially ejected part and also attacks the walls of the shear crack. As will be explained in detail below, portions of the stock and/ or part preferably are protected by an etch resist during the etching operation, which resist may be applied before or after or before and after the mechanical punching operation. If desired, and this frequently is the case, the resist is removed from the part.
Referring now in detail to the drawings, and more particularly to FIGS. 1-6, the reference numeral 30 denotes a mechanochemical sheet metal blanking system embodying the present invention, the same constituting several pieces of mechanical equipment which are schematically illustrated in FIG. 1. The system is fed with sheet metal stock 32 taken from any suitable source of supply, such, for instance, as a coil 34 of sheet metal stock.
Literally any kind of sheet metal stock can be employed which is capable of being eroded by chemical etching. One frequently used metal is iron. Other typical metals are copper, brass, bronze, silver, aluminum, precious metal alloys, steel, zinc plated steel, tin plated steel and steel alloys of all constitutions. Certain of these metals as is will known, are rather soft and/or have good electrical conductivity and/or have a coefiicient of expansion which matches that of glass and materials having different ones of these characteristics will be employed where the parts to be made have electrical uses, such, for instance, as lead frames and metal parts of circuit boards.
The thickness of the stock is not critical and typically the stock can be extremely thin, for example, 0.001", there being no limit to the upper range of stock thickness. Anything that can be punched with a punch and die is within the scope of the invention. Thus, the invention can be practiced with sheet metal in the plate range, this being a mil designation for sheet. metal stock having a minimum thickness of about A. The thickness is not critical because, as will be apparent from the foregoing brief description of the invention, the part is first almost fully ejected from the stock so that the amount of metal to be etched away in order to free the part from the stock is quite small, even where heavy stock is used in practicing the invention. The actual thickness of the sheet metal stock selected will be the same as that of the thickness of the part to be blanked.
The stock preferably is degreased and cleaned so as to form a good bond with the etch resist coating,
In the event that the heavy stock is used, it will be drawn from a flat rather than a coiled source of supply.
The stock is intermittently advanced into the system by any suitable means, such, for instance, as a pair of intermittently actuated feed rolls 36.
The stock is fed from the coil 34 to a coating station 3d at which an etch resist coherent coating is applied to both faces of the stock. Conventional coating equipment is employed. This may constitute equipment such as a brush applicator, a dip applicator, a spray applicator or a roller applicator. A roller applicator has been illustrated. The applicators lay down an etch resist coating on both broad faces of the stock, specifically on the top face and on the bottom face.
Although at this point the apparatus will be described with respect to the application of an etch resist coating in liquid form which subsequently solidifies into a film, it should be mentioned that the etch resist coating can be of many types and, indeed, it is possible to purchase stock with pre-applied coatings. By way of illustration, instead of using etch resist materials applied in liquid form that set and/or harden to solid form, the etch resist coating may constitute a metal plating, for instance, a plating of gold which is resistant to almost all types of etches, or a plating of a material which is not attacked by the etching fluid which is used to attack the stock itself. For instance, the etch resist coating may be a layer of lead which, in general, will resist most fluids that will etch iron or steel or copper or brass or aluminum, which are the materials most commonly employed for the stock. The etch resist coating, if of metal, can be applied by plating. Any kind of plating can be used, examples thereof being dip plating in a bath of the fused metal, or electroplating, or electroless plating, or sputter deposition, or vacuum deposition, or flame or plasma spraying. A metal coating can also be applied by cladding.
Another type of etch resist coating which can be used is of the ceramic type. Such coatings are refractory and tend to be fragile. However, they usually will sufficiently retain their coherency during the subsequent punching operation to an extent sufficient to protect the surfaces of the part involved. Ceramic type coatings include various types of glass or clay which may be applied in particulate form and subsequently fused under heat which renders the particles fluent to an extent that they liquify and coalesce to form a coherent layer which will bond to the surfaces of the stock and harden upon cooling.
Still another type of etch resist. coating is an in situ chemically formed coating as, for instance, an oxide film.
1 1 Thus, for instance, with aluminum the surfaces can be anodized, i.e. electrochemically oxidized. Such sheet stock can be purchased already anodized and it, therefore, would not be necessary to form such a coating at or adjacent the site that punching is carried out.
It is also within the scope of the invention to provide an etch resist coating by means of the application of a preformed film or sheet, such, for instance, as a foil sheet or a paper sheet or a plastic sheet. These may be bonded to the surfaces of the stock by an adhesive or by application of heat and pressure assuming that the film or sheet has a surface which is capable of being fused under heat and pressure and which in that condition is adherent to metal stock and will remain adherent upon cooling and the removal of pressure. It is known, likewise, that stock may be purchased with such coatings so that these, too, can be emplaced at a location remote from the punching station.
Reverting now to the description of the apparatus shown in FIG. 1 which details the application of an etch resist coherent coating in liquid form that is subsequently solidifiable under ambient room conditions, the roller applicators 36 shown constitute ink" fountains 40, one of which is above and the other of which is below the path of travel of the sheet metal stock 32 through the coating station 38. Rotating transfer rollers 42 withdraw the liquid resist material from the fountains 4t and supply this material to applicator rollers, one of which lightly engages the top surface of the sheet metal stock and the other of which lightly engages the bottom surface of fountain and is solid at room temperature and ambient conditions or after curing or cooling or baking. Etch resist solid material can be rendered liquid by the addition thereto of a suitable volatile solvent in which the material is either dissolved or dispersed or can be liquifiable by heating, being, in effect, thermoplastic. By way of example, a suitable etch resist material is pitch, asphalt or wax which are solid at room temperature and can be easily liquified by heating. For this purpose, the fountains are provided with electrical heaters 48. The resist material also is characterized by its ability to bond well to the exposed surfaces of the sheet metal stock. Pitch, asphalt and wax have this characteristic. Another material which is suitable for use as an etch resist is a synthetic resin, for example, nitrocellulose dissolved in a volatile organic solvent such as acetone or toluene. Essentially, any type of synthetic resin can be used, examples of other resins being polyesters, a butadiene-styrene copolymer, and polyvinyl alcohol. If desired, a photosensitive resin may also be employed, such, for instance, as a solution of a polyvinyl cinnamate, this being rendered etch resistant upon exposure to light. The same type of apparatus can be employed where the etch resist constitutes particulate material that is solid at room temperatures and is rendered fluent upon the application of heat, examples thereof being clay and glass frits.
After leaving the coating station 38 the sheet metal stock carries on its top and bottom surfaces a thin coherent film of still-liquid etch resist material which, in the example being described, is liquid pitch, asphalt or wax or a synthetic resin dissolved or dispersed in a volatile liquid.
This material is now hardened at a setting station 50. Construction of the setting station will, as is well known in the chemical milling system, depend on the nature of the etch resist material employed. Some materials are quick-setting and will set without any special equipment at the setting station. For example, the volatile solvent employed may evaporate so quickly that the setting station simply may constitute a span long enough to permit the solvent to evaporate. Similarly, the setting station, with 12' pitch, asphalt or wax used as the etch resist material, may constitute a span long enough to allow these materials to cool and harden at ambient temperature. Furthermore, if the etch resist material is a thermosetting material, it will cure to hard form quickly without any ancillary equipment at the setting station.
However, using thermoplastic materials or materials including volatile solvents as applied, since space fre quently is at a premium, it is preferable to additionally include at the setting station 50 means for accelerating the hardening of the etch resist material. Such means may constitute a cool stream of air where a heat-liquified resist material is employed. If the material is liquified by the presence of a volatile solvent, an accelerating means may assume the form of heat-applying means such as is illustrated, for example, a bank of heat lamps 52 the radiant energy from which plays on the sheet metal stock. The resist material may be set chemically as noted above, using a thermosetting material. Examples of such materials are aldehyde condensation products, illustration of which are phenol formaldehyde and urea formaldehyde. Another example of a chemically-setting material which can be be formulated to set rapidly is a two-component epoxy resin system.
When the sheet material leaves the settling station 50 it has a cross-sectional configuration which is shown to an enlarged scale in FIG. 2 wherein the reference numeral 32 denotes the sheet metal stock, the reference numeral 54 denotes the top etch resist coating, and the reference numeral 56 denotes the bottom etch resist coating. In an example, the sheet metal stock has a thickness of 0.005 and the two resist coatings have a thickness of about 0.002 each. Heavier resist coatings may be em ployed. Generally speaking, the resist coating is not made thicker than about 0.005" because there is no particular advantage in using additional thicknesses of resist coating since they ultimately are discarded and the coating merely has to be thick enough to protect the underlyiing substrate from erosion by the etching fluid. In FIG. 2 the showing of the thickness ratios is proportional to the dimensions given above. However, in the subsequent figures the showing of the thicknesses of the etch, the stock and the part are only given for purposes of illustration and are not necessarily to scale, because to show the stock in a thickness which is truly proportional to the thickness of the etch coating might require illustrating either the etch resist coating so thin that it is barely visible or the stock thickness so thick that it appears to be grotesque.
After leaving the setting station 50 the coated sheet metal stock 32 passes to a punching station 58. At this station a boss-embossing step is performed upon the coated sheet metal stock with the use of a punch and a female die. For this purpose there may be employed at the punching station a power press 6% as illustrated in FIG. 1, or, if higher speeds are desired, a pair of mating boss-embossing rolls can be employed.
The punching equipment, as shown, the power press, is so adjusted that, as previously explained, the punch performs a boss-embossing step which almost but not completely ejects the part from the stock so that the part protrudes from the stock into the die and the part is separated from the stock by a peripheral shear crack (fault zone) and held in the stock by metal-to-metal engagement of the walls of the crack or fault zone. The amount of protrusion should be at least equal to a predominant fraction of the thickness of the stock so that the portion of the part remaining in the stock and held captive by engagement with the walls of the opening of the stock surrounding the part is less than half the thickness of the stock. The thickness of the part left in the stock at the termination of the punching operation should not exceed about 20% of the thickness of the part and preferably should he in the order of 5%, or less, of the thickness of the part. Indeed, because a peripheral burr is formed on the punch-facing surface of the part, which burr engages the side walls of the opening formed in the stock by the part, the part may be ejected from the stock at the termination of the punching operation a distance equal to the thickness of the stock or even slightly in excess of the thickness of the stock inasmuch as the engagement of the upstanding peripheral burr with the side walls of the opening in the stock will sufiice to retain the part in the stock. It is possible while practicing the invention, although this is not presently preferred, even to fully eject the part with its peripheral burr from the stock and then to push the part part-way back into the stock, e.g. to the extent that the burr catches in the opening or, preferably, no more than of the thickness of the part re-engages the opening of the stock or even up to about 20% of the thickness of the part re-engaging the stock.
The stroke of the punch is adjusted to effect the foregoing extent of punching, i.e. the substantial but not total protrusion of the part from the stock. The ensuring protuberance of the part is sometimes hereinafter referred to as a boss, and the opening in the stock which is partially plugged by the upper portion of the formed part is sometimes hereinafter referred to as a depression or embos'sment. Thus, when the punch is retracted the part to be blanked, although separated from the stock by a peripheral shear crack or fault zone, is still retained within the opening in the stock.
FIG. 3 shows the condition of the punch, the stock, the part and the die at the termination of the boss-embossing step but before the punch has been retracted. The reference numeral 62 denotes the punch, the reference numeral 64 denotes the female cavity, and the reference numeral 66 denotes the part to be blanked out.
At the end of the boss-embossing step illustrated in this figure, the punch has descended into the stock and, in so doing, has substantially ejected the part 66 from the stock 32 for about 95% of the thickness of the stock so that about 5% of the thickness of the part remains within the opening 68 left in the stock by formation of the part.
The reference numeral 70 denotes the peripheral shear crack or fault zone surrounding the part and separating that portion of the part remaining in the stock from the stock. It will be seen that the portion 72 of the part to be blanked (the boss) protrudes from the surface of the stock facing the die 74 in which the cavity 64 is provided.
Attention is called to the lower peripheral corner edge 76 of the part. This corner constitutes a short-radiused fillet which is characteristic of the die-facing surface of a punched part. Such fillet is known as a roll-over edge which is the result of the entry of the part into the die cavity 64 at the start of the punching step. The radius of the fillet will depend upon many factors, such, for example, as the thickness of the stock, the metallurgical composition of the stock, the punch-die clearance and the condition of the die. This roll-over edge constitutes a smooth edge for the part which is considered highly desirable due to the absence of any burr. The various parameters are sometimes so selected that the radius of the roll-over edge is 'sufiiciently short for the type of usage for which the part is to be put. Thus, if the part is a rough part such as a washer, no particular care need be paid to the shortness of the radius because this edge performs no function; in other words, it need not be shortradiused or essentially sharp. In many applications it is not even desirable to have an extremely short radius as when the part is to be fitted into an opening in the machine where the chamfer of the roll-over edge acts as a pilot guide. Conversely, in other applications the radius should be extremely short so that the aforesaid corner edge is almost sharp and this is obtainable by having a die which is ground to provide a sharp entry corner, by using small clearances or, indeed, even negative clearances between the punch and die, by, if practicable, having stock as thin as possible, and by selecting the metallurgical composition within the acceptable specifications for the part to be less ductile than might otherwise be chosen.
Attention also is drawn to the side edge 78 of the part 66 which is the portion of the part between the top and bottom surfaces thereof (the punch-facing and the diefacing surfaces). This side edge is an edge which is characteristic of a punch-formed side edge. It is, in general, a fine edge such as is obtained by coining or extrusion, such edge being characteristic of the punching operation where a negative clearance is employed; and where a small positive punch and die clearance is utilized the side edge is burnished by sliding engagement of this edge with walls of the cavity 64. Such side edge is entirely different from the side edge obtained with the chemical system wherein the entire side edge is eroded with the erosion greater near the surface at which etching commences or greater at both surfaces if the stock is etched from both sides concurrently. Where the stock is etched from only one side, the side edge is tapered, i.e. flared downwardly away from the side where etching starts, the erosion undercutting the resist even where protective filming agents are incorporated in the etching composition.
Attention also is directed to the peripheral burr 80 which extends upwardly (toward the punch) on the corner of the surface of the part that faces the punch. This burr is characteristic of a punched out part, being a thin fin of metal which is formed as the part is pushed through the stock by the punch. The presence of this burr is a decided disadvantage of punched out parts and it is conventional practice to treat punched out parts to remove the burr as by tumbling, grinding, wire-brushing, scraping or filing, all of which entail considerable additional labor and time and which, even after they have been performed, leave an undesirable finish on this punch-facing corner edge of the part.
It also has been proposed to remove the burr chemically by submersing the part after being punched out, unprotected, in a chemical etching liquid. However, this method is unsatisfactory for several reasons, one being the additional time and labor and another being deterioration of the part. The etch attacks all surfaces of the part and thus lowers the definition of the edge, requires the acceptance of increased tolerances because of the attack on the side edge and deteriorates the finish of the side edge which has been obtained by the punching operation.
It will be observed that as the part is being punched out the top coating 54 of resist material remains in place on the top surface of the part 66. It has been found that this top resist coating does not noticeably interfere with the punching operation. Preferably, the material used for the top resist coating is sufficiently flexible to remain coherent during the punching operation. However, even if the coating fractures somewhat it will still substantially protect the top surface of the part during the etching erosion step subsequently to be described.
The punch 62 is of completely conventional construction. It is made by metal removing operations to match the desired configuration of the part to be blanked. It is fabricated from a tough, strong, hard or hardened hardenable material, such, for instance, as tool steel. Its lower surface is fiat and optionally may be coated with a film of good release properties, e.g. silicone. Optionally, although the same is not needed, it may include stripping pints (not shown). Its bottom corners are square.
The shape of the female die cavity 64 matches the shape of the punch 62, as is usual, there being positive clearance between the punch and cavity, i.e. the cavity generally is slightly larger around than the punch. As has been indicated previously, a negative clearance may be employed. Such a negative clearance is far easier to use in the present invention than in a conventional punching operation because, as has been pointed out heretofore, the punch does not enter the die cavity. In conventional punch and die practice the female die cavity is an opening extending all the way through the die which is a metal member or a composite of metal members so as to permit the part being blanked to be discharged through the metal member or composite.
Contrariwise, in the female die cavity 64 pursant to the present invention the same is in the form of a cavity having a bottom, or, phrased differently, the cavity does not extend all the way through the die. Thereby the female die cavity 64 of the instant invention can be manufactured quickly and at a lower cost than the cavity of a conventional female die since it is not necessary to cut all the Way through the female die member. The die cavity can be made rapidly and economically by simple tooling operations such as electric discharge erosion (an EDM machine) or by electrochemical machining (an Anocut machine). In the EDM machine an electrode in the shape of the punch is approached to a metal block and by electrodischarge action sinks into the block reproducing its shape with a controllable desired clearance between the electrode and the cavity. If the punch/cavity fit is to be an interference fit, e.g. negative clearance, the EDM electrode is made somewhat smaller in cross-section than the punch. Inasmuch as the cavity 64 is quite shallow it can be formed quickly, expeditiously and economically. In a typical prior art punch and die the depth of the cavity almost always was in excess of the thickness of the stock, usually considerably in excess. However, in the present invention the cavity need not be much deeper than 95% or 100% of the thickness of the stock. The cavity only has to be deep enough to accommodate the amount of the part which protrudes from the stock. Thus, these cavities can be made quite simply and rapidly, e.g. by methods such as described or by older tooling methods such as milling or grinding.
Desirably, a stripping means is included to assist in lifting the part out of the die cavity when the punch is retracted. Any well-know type of stripping means can be utilized. Thus, stripping may be performed by introducing air under pressure into the bottom of the cavity each time that the punch is raised. Alternatively, stripping pins can be employed which are arranged to function at the time the punch is lifted or which can be spring loaded to bias the part upwardly when the punch is retracted from the stock. As shown herein, the stripping means is in the form of a resilient block 82 positioned at the bottom of the cavity.
Optionally, a conventional stripping means may be provided to strip the stock from the punch if desired or necessary.
Because the part is captured by the opening in the stock at the time the punch is retracted, when the part is lifted out of the cavity the stock is lifted along with it. The part and the stock are at this time functionally integral insofar as joint movement is concerned. This enables better control to be exercised over the part; that is to say, if it is desired to move the part, as it will be for the completion of the system of this invention, the parts are not moved individually but are simply moved by moving the stock.
The appearance of the stock and the part after retraction of the punch is illustrated in FIG. 4 where, for convenience, the punch and the female die have not been shown.
The feed of the stock is halted during the puching operation if the part to be blanked is large and if a stamping press is employed. It is contemplated that the stock feed may be steady rather than intermittent where the part to be blanked is small or where roll dies are employed instead of a stamping press.
As the stock emerges from the punching station it constitutes a continuous strip of scrap carrying within openings the part 66 (actually, many parts) ultimately to be obtained, the part at this time being retained in the opening at the peripheral shear crack (fault Zone). It is pointed out that at this time the shear crack or fault zone between the part and the stock is bare; that is to say, it has no resist coating. The resist coating 54 and the resist coating 56 are at this time present only at the top surfaces of the stock and part and the lower surfaces of the stock and part. There is no resist coating at this time on (a) that portion of the side wall of the opening 68 which is not plugged by the part 66, (b) the side edge of the part 66 which protrudes below the stock, and (c) the side wall of the opening 68 and the side edge of the part 66 which face one another across the shear crack or fault zone 70. In the operation of the present system as is being described, the top and bottom surfaces of the part to be blanked are coated with etch resist material prior to the etch erosion step. This coating is inherent because the etch resist material was applied to the top and bottom surfaces of the stock 32 prior to punching by the top and bottom applicators at the coating station 38.
After leaving the punching station in the form of the invention here being described and which is the presently preferred form, the stock 32 with the partially punched out parts 66 carried thereby is introduced to a second coating station 84 located beyond the punching station 58 so that the boss-embossed stock passes through the second coating station after leaving the punching station. At the second coating station an applicator is provided below the stock (on the part protruding side). Such applicator includes an ink fountain 86 in which a liquid form of a hardenable etch resistant material is disposed. A rotating transfer roller 88 withdraws the fluid etch resist material from the ink fountain and supplies it to an applicator roller 90 directly below the stock. The applicator roller is sufliciently resilient to contact all of the exposed surfaces of the part and the stock. Thereby it will apply a second etch resist coating 92 which is shown in FIG. 4.
This second etch resist coating is not present as the stock leaves the punching station although, for convenience, FIG. 4 has been referred to hereinabove as illustrative of the condition of the stock and part as they left the punching station. The second etch resist coating is applied over the bottom resist coating 56 which already is present on the bottom surface of the stock and the bottom surface of the part, this being an incident to but not a feature of the present invention. More importantly, the second etch resist coating 92 covers the side edge of the protruding portion of the part exposed below the stock and forms a bridge, as it were, between the portion of the coating covering such side edge and the etch resist coating on the undersurface of the stock whereby, as later will be pointed out, when the etch erosion step is completed and the part is no longer physically held in the opening by the close fit between the part and the side wall of the opening, the part nevertheless will remain attached to the stock by virtue of such bridge and, upon removal of the bridge, the part will fall out of the stock or be pushed out of the stock by application of a very light force. This second coating operation is sometimes referred to as a re-coat operation and, depending upon the etch resistant material employed, may either be a physically separate second coat or may blend into or integrate with the first coat 56 at the bottom of the stock and at the bottom of the part.
If the dimension of the protrusion of the part from the bottom surface of the stock is significant, for example, more than a few hundredths of an inch, so that an elastic applicator 90 will not suflice to fully coat the side edge of the part, the re-coating can be performed in other manners, as for instance, by spray or brush coating.
A second setting station 94 follows the second coating station and, as shown, consists of a bank of heat lamps 96.
The boss-embossed strip of sheet metal with the part 66 having its upper and lower surfaces and exposed protruding side edge protected by etch resist coatings, with the upper and lower surface of the stock protected by etch resist coatings, but with the side wall of the opening 68 bare and with the top edge of the crack 70 exposed, is now subjected to an etch erosion step. This step consists of treating the stock with the contained parts to an etch material, e.g. to an etching liquid.
The etching liquid employed is a suitable one for etching the metal of which the stock is composed. By Way of example, a water solution of ferric chloride may be employed if the sheet metal stock is copper, stainless steel, steel or an alloy thereof, nickel, magnesium or aluminum. The solution is of 30 to 51 Baum and the free hydrochloric acid is from about 0.3% to about 0.6%. Another etchant solution which can be used for copper sheet metal stock is a mixture of chromic acid and sulfuric acid with about to 20% of chromic acid and about 20% to 40% of sulfuric acid, the balance being water. Other etch erosion solutions which are useful for copper are a mixture of ammonium bicarbonate, ammonium hydroxide and sodium chlorite as described in U.S.L.P. No. 3,231,503; a mixture of ammonium persulfate and mercuric chloride; and a water solution of cupric chloride. Dilute nitric acid is a useful etch erosion solution for zinc and magnesium sheet metal stock. For aluminum stock another etch erosion solution is a dilute water solution of sodium hydroxide and sodium carbonate with glucose as an additive. Etch erosion solutions are well known to the art, being widely used for chemical milling.
The etch erosion liquid is applied to the stock with the contained parts in any suitable fashion, such, for example, as brushing, roller application or immersion, the last-named being illustrated. A conventional spray etching machine also is excellent for this purpose and is illustrated in FIG. 1A. To accomplish immersion treatment the stock with the contained parts is led by a roller 98 into a tank 100 where the stock forms a reach 102 below the surfaces of the erosion (etching) liquid 104 in the tank. The stock leaves the tank by passage over a roller 106. The stock is treated with the etch erosion liquid for a predetermined period of time which is a function of the length of the reach 102, the average speed of feed of the stock, the concentration of the etchant, the activity of the etchant, the metallurgical composition of the stock and the height of the shear crack or fault zone 70 (the height of the part inclusive of the burr 80 held captive within the opening 68). This time is so selected that the surfaces defining the peripheral shear crack (fault zone) 70 around the part will be eroded to such an extent that retaining engagement between the part and the stock is completely broken or is greatly lessened. During the treatment with the etch erosion liquid said liquid attacks the side wall of the opening 68 as is indicated by the solid line configuration of said side wall in FIG. 5. The dotted lines in said figure illustrate the configuration of the part and opening prior to etching.
FIG. 1A illustrates an alternate piece of equipment that can be used at the etching station. The same is a closed tank 100 with admittance and exit ports A and E between which the boss-embossed stock travels from roller 98 to roller 106. Said stock is etched by etching liquid emitted from upper and lower spray nozzles 101 supplied with etching liquid under pressure from a pump 103 that draws etching liquid from the bottom of the tank and forces it into manifolds 105 from which the nozzles 101 extend.
The etch erosion liquid attacks the fault zone and erodes the side edge of the part facing the shear crack. It is assisted in this respect by the erosion of the side wall of the opening 68 below the part which is consequent upon erosion of said side wall above the part. In other words, the shear crack or fault zone is widened, the widening being greater near the top edge of said crack. These portions of the stock and part are attacked by the etch erosion liquid because such surfaces are bare, being unprotected by etch resist coatings thereon. The lateral attack on the side edge of the stock immediately adjacent the surface thereof which previously faced the punch erodes the burr 70 and leaves an unburred corner edge, the specific configuration of which will vary with different factors as will be pointed out below. However, in
1 general, in addition to removing the burr, this punchfacing corner edge of the part is chamfered usually concavely as seen in FIGS. 5 and 6 by etch erosion of the part under the burr.
However, at this moment the part is not yet freed from the stock and is held thereto by the second etch resist coating 92 and, in particular, the bridge formed by said coating between that portion of the coating overlying the said side edge of the part and that portion of the coating overlying the bottom surface of the stock or the resist coating 56 on the bottom surface of the stock.
It will be observed that the etch erosion liquid does not attack, in this form of the invention, the side edge 78 of the part and, therefore, this edge retains its original desirable finish and definition which are imparted during the punching operation.
After leaving the tank 102 the strip of sheet metal is led over a roller 108 to a second tank 110 containing a quenching liquid 112 which may be water or a neutralizing liquid. In the second tank the action of the etching liquid is stopped. The sheet metal strip is now led out of the second tank at which point it may be ready for industrial use or may be treated to one further step to ready the parts for industrial use.
Thus, the sheet metal strip which now has been mechanochemically treated can be re-coiled or strips thereof can be bundled and transported to a place where the parts are to be used. Here the strips can be fed into an assembly machine with the parts still carried by the strips and movable therewith. The parts in this case will be removed from the strip by the application of a treatment which will destroy the integrity of and remove at least the second coating 92 so that the part is freed from the stock. The first and second coatings may or may not remain in place, depending upon the desired usage. Thus, in some instances the coatings 54, 56 desirably may be retained- Such an example is anodized coatings which a manufacturer may wish to employ in the finished product. Obviously, if the coatings 54, 56 are to be removed they, too, can be taken off just prior to use at the point of assembly or earlier if the manufacturer so desires, to maintain the parts of a piece with the strip only for purposes of transportation and storage.
In accordance with the invention, the part that is retained by this second coating can be forced back partially or fully into the opening for retention by the stock and subsequently ejected for use.
Optionally, the parts can be removed in conjunction with the same equipment that is used to perform mechanochemical sheet metal blanking operation. This can be achieved by the useiof a third tank 114 into which the strip is led after the second tank and which contains a liquid that will, for instance, dissolve the second coating and, optionally, the top and bottom coatings 54, 56 as well. At this time the part will drop out of the stock under the influence of gravity or, if the part is still very lightly held in the stock, by tapping the part mechanically or vibrating or applying an air blast thereto. As the parts drop out of the stock they may either accumulate at the bottom of the third tank and subsequently be removed, or they may drop onto an ascending reach of a moving conveyor 116 which which they are delivered to suitable packing equipment or to a container for transportation to an assembly station.
By way of example, the liquid used to remove the two coatings 54, 56 and the second coating 92 is turpentine if these coatings are pitch, asphalt or wax, and acetone if the material is nitrocellulose. It will be observed that because of the second coating the dimensions of the part, and particularly the plan dimensions, are not altered by the erosion step because the lateral erosion only affects a tiny area at the upper peripheral corner edge 118 where the burr existed prior to etching.
The specific configuration of the corner edge 118 will vary as a function of sundry parameters such, for instance,
as the method and apparatus used for etching, the direction of impingement of the etching liquid, the type of etching liquid, the concentration of the etching liquid, the velocity of impingement of the etching liquid, the droplet size of the etching liquid, the temperature of the etching liquid, the metallurgical composition of the stock, the height of engagement between the stock and part, the type of resist material employed, the mode of application of the resist material, the placement of the resist material, the time of application of the resist material relative to the boss-embossing step, the method and apparatus used for the boss-embossing step, the punch and die clearance, the type and size of burr, and fluctuations in all of the foregoing, these sometimes being from moment to moment. In general, for most metals, for a run-of-the-mill punch and die and for application of the etching liquid from the punch-facing side of the stock and part, and with little regard for the other parameters, the configuration assumed by the punch-facing corner edge of the stock is somewhat concave as is best illustrated in FIGS. and 6. These figures and subsequent figures illustrating corner edge configurations are necessarily representative only and Will vary widely in shape and depart from the illustrated symmetry in actual practice.
Frequently, the juncture of the aforesaid concavity with the side edge of the part and with the punch-facing surface of the part is reasonably sharp and no fillet at these points is observable to the naked eye, although the presence of a rounded edge can be ascertained tactilely and under a lowpower microscope, e.g. X. However, often short-radius fillets can be seen at this juncture as shown in FIG. 9. FIG. 7 illustrates an ideal corner edge at the punch-facing surface of the part; this ideal is quite difficult to achieve as there is always a tendency for some erosion to occur at this corner edge and, indeed, for many conditions this configuration of the corner edge is not the most desired configuration and the chamfered edge of FIGS. 6 and 9 is more commercially acceptable. In FIG. 8 another type of configuration for the corner edge 118 which sometimes occurs is illustrated. This configuration tends to be present where the etching liquid is directed to the stock and part from the die-facing surfaces thereof and, indeed, quite frequently the corner edge 118 under these circumstances is even more rounded than illustrated in FIG. 8.
Due to the high speed operation of the punching step, which can perform as rapidly as 100 to 300 times a minute or even more rapidly if desired, and to the relatively short period of treatment with the etch erosion liquid, the new mechanochemical system is a very speedy method of blanking parts from sheet stock. Furthermore, because it is not necessary to make elaborate female dies, the punches and dies can be fabricated in a fraction of the time and at a considerably lower cost than the conventional mechanical system. Indeed, the turnaround time for the new system is approximately the same as that for a chemical milling system. Thereby the present system retains the high speed advantage of the mechanical system and the low cost die production advantages of the chemical blanking system. It also retains the advantage of high dimensional accuracy and fine side edge finishes of the mechanical blanking system and the burr-free advantage of the chemical system. It retains the chamfered roll-over die-facing corner edge of the mechanical system without deterioration and forms a punch-facing corner edge which, likewise, is chamfered and which is burr-free. It eliminates the undesirable undercutting and destruction of defintion and tolerances of the chemical system. It has the considerable advantage that its initial cost for tooling is almost as low as that of the chemical system. For example, for the typical lead frame to which reference heretofore was made where initial die cost for the mechanical system was in the area of $25,000 and where the initial art work for the chemical system was in the area of $200, the set-up cost of the present system would be in the area of $1,000. So far as the per-piece cost is concrned, with the mechanical tit system the per-piece price is in the order of $.02 and for the chemical sysem the per-piece cost is in the order of $.06 as has been mentioned before, by the present system the per-piece cost is in the order of $035. This is particularly significant taking into consideration the tendency of companies to improperly predict the total number of parts to be made. Instead of using the chemical system to save initial set-up costs, by using the present system the initial set-up cost may still be kept quite low and yet the per-piece cost is lower than for the chemical system, so that if the prediction has been inaccurate and the usage of the part is very high, the saving effected by initially using the system of the present invention becomes very large.
It will, of course, be apparent that using the present system the various etch resist coatings are imperforate, i.e. continuous over the area to be protected, inasmuch as entire areas are coated at one time and the definition of the part is by punching. There, therefore, is very little likelihood of any rejects either because of flaws in the coating caused by the presence of inclusions or improper printing as in the chemical method, or because of poor definition of the edges of the part, this constituting a further very substantial advantage over the chemical system.
In FIGS. 1018 there have been shown various combinations of direction of application of etching liquid and modes of application of resist material or even its absence on various surfaces and edges of the part and stock. As noted previously, the specific after-etching configurations and, indeed, the specific configuration of the before-etched burrs are merely representative and are not to be construed as a limitation upon the invention.
.It already has been noted that the preferred application of the resist material and the preferred direction of impingement of the etching liquid (always illustrated in the various figures by arrows and assuming a spray application rather than immersion or other techniques) is as has been described in detail above, particularly with respect to FIG. 5. Nevertheless, this preferred technique is not preferred for all applications of the invention because under some circumstances the metallurgical composition of the stock encourages the use of other techniques, or the thickness of the stock requires a different technique, or the particular use to which the part is employed may require a different technique, or a special type of corner edge may be desired which will call for a different technique. The techniques shown in said FIGS. 1018 are merely given by way of example and as illustrative of the wide range of techniques that can be employed within the scope of the present invention.
FIG. 10 illustrates the stock 32 and the part 66 as they appear after a boss-emboss and an etching operation, such condition being denoted in this and subsequent figures by dotted lines, the stock and part being shown in this and subsequent figures by solid lines as they appear after etching. Neither the stock nor the part in the technique illustrated in FIG. 10 have had resist material applied to any surfaces or edges thereof prior to etching. The etching liquid is directed, as indicated by the arrows, toward the punch-facing side of the stock 32 and part 66 and also toward the die-facing surfaces of the stock and part as well as the side edge 78 of the part and the opening in the stock. Because no areas of the punch and part have been protected by resist material all surfaces of the stock and part have been eroded. The erosion tends to maximize in the opening of the part forming the concave surface illustrated in FIG. 10 and the impingement of the etching liquid into the zone between the stock and part at the terminal portion of the etching step tends to round the junctures of the chamfered concave punch-facing corner edge of the part with the punch-facing surface and side edge of the part, this being the configuration illustrated in FIG. 9. Likewise the flow of etching liquid through the zone between the part and punch at the termination of the etching step tends to round out the lower corner edge of the opening as seen in FIG. 10 although this is of no importance. It also will be observed that the etching liquid tends to reduce all surfaces of the part so that this technique is usually not desired because it tends to deteriorate the fine surface finish of the bossed side edge of the part and also tends to deteriorate the definition of the configuration of the part, particularly when the stock and part are thin, and to cause the part to lose close tolerances.
In FIG. 11 a technique has been illustrated wherein prior to the boss-embossing step a coating 54- of resist material has been applied to the punch facing side of the stock 32 and the etching liquid has been directed toward this face of the stock and part as well as toward the opening 68 as indicated by the arrows. The result is the formation of a part 66 which is almost but not quite as good as that resulting from the use of the technique described with respect to FIGS. 1-5. The configuration of the punch-facing corner edge 118 is the same as that of FIGS. 5 and 6, it being reiterated the figures are only representations and that wide fluctuations from the illustrated contours occur in practice. As in the case of FIGS. 1-0 and 11 as well as FIGS. 1-5 the burr 80 has been removed by the etching step. However, toward the termination of the etching step some etching liquid tends to penetrate the zone between the part and stock and flow onto the side edge 78 of the part Where it can to some extent reduce the fine finish of said edge and, if care is not observed, slightly lessen a close tolerance of the part. The protection afforded by the resist material 54 in FIG. 11 to the erosion action of the etching liquid, which in this case is applied to the punch-facing surfaces of the stock and part, protects these surfaces of the stock and part. The side wall of the opening 68 in the stock needs no protection, and the burr 80 needs not protection; indeed, it is desired, as a rule, that it be removed. The removal of the burr, as previously pointed out in detail, is accomplished by the etching liquid which erodes the facing side walls of the shear crack.
In FIG. 12 there is shown a technique which is the same as that of FIGS. 5, and 11, except that in this instance there is no top resist coating 54 applied to the stock and part and, instead, a resist coating 56 is applied only to the undersurface of the stock and part. Here, too, the opening 68 in the stock tends to belly during the etching operation and there is a tendency to form a concave corner edge 118. The unprotected upper surface of the stock and part and the unprotected surface of the opening 68 likewise tend to be eroded by the etching liquid, as exaggeratedly indicated by the relative positions of the dotted and solid lines.
FIG. 13 illustrates a technique in which both top and bottom resist coatings 5d, 56 are applied to the stock and part prior to the boss-embossing step and in which the etching liquid is directed to the stock and part, as indicated by the arrows, toward the top of the stock and part and toward the side wall of the opening 68. The technique of this figure differs from that of FIG. 5, which it most closely resembles, by the omission of the recoating step and presence, therefore, of the second etch resist coating 92 as seen in FIG. 5. The ultimate configutions of the stock and part, therefore, are very much similar to those shown in FIG. 5. However, due to the absence of the second etch resist coating 92 there is nothing to retain the part in the stock if the etching is carried to the point that the part is completely freed from the opening in the stock.
FIG. 14 has a visual similarity to FIG. 13. It differs therefrom in that the stock has had a top resist coating 54 applied thereto which also appears on the part 66 after boss-embossing, but there is no bottom resist coating 56 applied to the stock. However, a bottom resist coating 120 is applied to the die-facing surface of the part. In this figure the etching liquid is directed toward the top surface of the stock and the part and the side Wall of the opening 68. The finished shape of the part after etching is essentially similar to that of part 66 in FIG. 13 inasmuch as the same surfaces of the part are protected by etching in the technique of FIG. 14 as are protected in the technique of FIG. 13, only the undersurface of the stock being unprotected and this not being extensively eroded because the etching liquid is applied from the top.
In FIG. 15 the technique illustrated is like that of FIG. 10, with the exception that an etch resist coating 122 is applied to the part 66 after the boss-embossing step for any reason desired. Hence, after the etching liquid has been directed to the stock and part in the direction of the top surface of the stock and part and the opening 68 in the stock, the part only will be etched in a fashion essentially similar to that illustrated in FIG. 5. The stock will be eroded at its top surface and there also will be a tendency to form a belly in the side Wall of the opening 68 in the stock. However, because the bottom and-side edge of the part 66 is not exposed for any lengthy period of time to the etching liquid which will only find its way to these surfaces indirectly and because of the protection to its upper surface afforded by the coating 122, the part tends to retain its original as-punched configuration except for removal or substantial removal of the burr to leave the deburred corner edge 118.
Under certain circumstances it is desirable to preserve the original surface of the part, a typical reason being to prevent the presence of chemical residues on a portion of the surface of the part which subsequently is to have other operations performed thereon that require a. clean surface, e.g. soldering, for instance, in connection with the attachment of a lead or terminal. At the same time it may not be necessary to protect other portions adjacent the protected portion of such surface or, indeed, it might even be desirable to erode such adjacent portions for electronic reasons such as to provide a mesa or to provide a sloped edge leading away from the etch portion. In order to form a part where such further structural or electronic advantages are present, the techniques illustrated in FIGS. 16 and 17 can be utilized. Pursuant thereto neither the top surface nor the bottom surface of the part (before boss-embossing) has applied thereto an etch resist coating such as the coatings 54, 56. However, preferably, before (but optionally after) the boss'embossing step the area of the top surface of the part 66 to be protected has applied thereto a predetermined area of etch resist coating 124, e.g. in the form of a circular area as can be: seen in FIG. 17. Etching liquid is directed toward the top of the part and stock and the opening 68 in the stock and erodes all, or substantially all, of the burr 80 and also the peripheral shear crack or fault zone 70. There is a tendency to form a belly in the side wall of the opening 68 and the top surface of the part unprotected by the coating 124 tends to erode and to blend into the corner edge 118. Due to the erosion of the unprotected portions of the top surface of the part, there is some tendency for the corner edge 1118 to be convex. However, this particular configuration will not invariably result since it also is a function of the specific direction, speed, temperature and concentration of the etching liquid. Due to the direction of application of the etching liquid, as indicated by the arrows, the tendency to attack the side edge and bottom surface of the part 66 is minimal.
Mention should be made that in all of the techniques described which do not employ a second coating on the part, if desired, the etch erosion liquid can be directed to the boss-embossed stock and part conveniently from the bottom as well as from the top, or from the bottom alone. It also is to be observed that the invention will function satisfactorily on stock that previously has been ornamented or configured so as to be out of flat.
As has been pointed out previously, the etch resist coatings can be in forms other than those described above, to wit, applied in the form of a subsequently hardenable liquid, and a technique employing a different type of etch resist coating is illustrated in FIG. 18. Here a coating 126, e.g. of gold or lead, is applied to the top surface of the part and to the top surface of the stock by plating, e.g. electroplating or cladding. The application conveniently is prior to the boss-embossing step. Another coating 128 of etch resist material is applied, e.g. in liquid form and subsequently hardenab'e, as by the re-coating step detailed at length in connection with FIG. 1 to the under-surfaces of the stock and part and to the side edge 78- of the part, this coating 128 forming a bridge between the part and stock, as does the coating 92 of FIG. 5, so as to hold the part to the stock after the etching operation. In the technique of this figure the etching liquid is directed toward the part and stock as indicated by the arrows, i.e. to the top surfaces of the part and stock and to the side wall of the opening 68 in the stock. There is, as usual, a tendency to inwardly belly the side wall of the opening 68 and to form a concave corner edge 118. Likewise, as in the case of the technique described with reference to FIGS. 1-5, the part is held to the stock even after the peripheral shear crack (fault zone) is eroded providing that the recoating 128 is sufiiciently strong so that the several parts that are boss-embossed and subsequently etched for removal in a single piece of stock remain eifectively unitary with the stock for purposes of common movement, e.g. for bundling, transportation and feed into an assembly machine. If the recoat 128 is thinner the part will be released upon completion of etch erosion. As in all of the cases previously mentioned, the etch erosion step tends to fully or substantially remove the burr.
The technique illustrated in FIG. 19 is essentially similar to that discussed with respect to FIG. 18, except that instead of using a plated layer of etch resist metal for the upper etch resist coating, there is employed a pre-formed film 130 of an etch resist material, eg lead foil or a synthetic plastic, that is inert to the etching liquid and which is secured to the upper surface of the stock before the boss-embossing step, e.g. by a layer of adhesive 132, or by heat and pressure-bonding in the event that it is a film of thermoplastic.
The present invention can be advantageously employed where plural and usually a very large number of parts are to be formed from stock 32 and are mounted, tag. on a substrate 134 (see FIG. 21), concurrently. This technique, for instance, is quite useful in connection with application of lead lines to a circuitboard of full, miniature or sub-miniature size. Referring to FIG. 20, a part 66 (only a single part is here shown, but it is to be understood that with this technique plural parts will be concurrently boss-embossed) is boss-embossed from stock 32 so as to protrude therefrom as shown in said figure. The upper surface of the stock and part are provided with an etch resist coating '54. No etch resist coating is provided on the under-surface of the stock and part. Preferably, the etch resist coating on the upper surface of the stock and part is provided prior to the bossembossing operation. After the boss-embossing operation the stock and part have the appearance shown in FIG. that is to say, most of the part protrudes from the bottom of the stock. However, the part is retained in the stock and there is a metal-to-metal engagement between the stock and part across the peripheral shear crack (fault zone). The stock is firmly engaged in the part, although the extent that the part protrudes from the stock may be quite substantial; indeed, somewhat in excess of the thickness of the stock, e.g. a few thousandths of an inch in excess.
Next, the undersurface of the part is provided with an adhesive film 136. It is within the scope of the invention for the undersurface of the stock to be provided with an adhesive which may be of the pressure-sensitive type or may be an activatable adhesive, e.g. activatable upon the addition of water or the application of heat, and such adhesive can be covered by a protective strippable layer which is stripped away from the stock and part after the boss-embossing operation. In any of these events, the undersurface, at least of the part, is provided with the adhesive film 136. At this time the part, actually all of the parts, carried by the stock, is applied to the upper surface of the substrate 134.
conventionally, the substrate can be a solid, usually rigid, sheet frequently having a high dielectric value, e.g. an electrically nonconductive thermosetting resin or any of the other materials commonly used as a substrate for circuitboards. If desired, the upper surface of the substrate may first be coated with an adhesive film and the parts 66 then applied to such film.
Regardless of which of the procedures above mentioned is used, at this time all of the parts will have been secured as by adhesion to the substrate. However, the stock 32 still is engaged to the parts.
To remove the stock the etching step described hereinabove is now practiced. Etching liquid is directed, as shown by the arrows, toward upper surfaces of the stock and part and toward the side wall of the opening 68 in the stock, ultimately eroding the surfaces of the metals of the part and stock which were in engagement to retain the part in the stock so that the stock now is freed from the parts as illustrated representatively in FIG. 21, whereupon the stock can be removed from the parts leaving all of the parts 66 in their proper mutual relationship secured on the circuitboard as defined by the mutual relationship of the parts created during the boss-embossing step.
Although the primary thrust of the invention resides in the sequential steps of boss-embossing and subsequent erosion with an etching liquid with the various sophistications detailed above, it also will be appreciated that, as a result of the practice of the invention, a very convenient, economical and efficient deburring operation is practiced. This is particularly true in connection with those techniques wherein the top surface, the bottom surface and the side edge of a part, indeed, all of the part with the exception of the zone at and near the burr, were protected, because in conjunction with such techniques only substantially all or all of the burr and, optionally, some portion of the burr-underlying portions of the part, were eroded so that the original finish of the top and bottom surfaces of the part were maintained as were the fine finish and definition and tolerance of the side edge. Indeed, the only change in the part pursuant to these techniques was the total or substantial elimination of the burr and the optional formation of a chamfer at the corner edge 118.
A technique embodying the application of the invention solely to the removal of burrs in the foregoing fashion is illustrated in FIG. 22. Here a part 138 is shown which has been formed by stamping and, therefore, is provided with the inherent peripheral burr 140 extending upwardly from the punch-facing surface of the part. This burr is shown in dotted lines in FIG. 22 for the same reason that dotted-line showings of the part and stock were employed in the preceding figures. The top surface of the part is provided with an etch resist coating 142, an etch resist coating 144 is also provided for the bottom surface of the part, and an etch resist coating 146 for the side edge of the part. Desirably, the etch resist coatings 144, 146 are continuous around the roll-over corner edge 76. However, the periphery of the top resist coating 142 terminates substantially at the base of the burr 140. It will be understood that, as in the previous figures, the burr 140 is quite exaggerated for purposes of illustration. This leaves exposed a portion of the burr 140, the portion which originally faced the punch. Moreover, the upper line of the side edge coating 146 of the part 138 similarly terminates slightly below the base line of the burr 1.40,
25 all of this relative positioning of the burr and coatings 144, 146 being exaggerated in FIG. 22 for the sake of clarity. A part coated as just described may be prepared in any suitable manner, for example, by the method described in connection with the first form of the invention (FIGS. 1-6) except for the etch erosion step shown in connection with FIGS. 5 and 6, the part instead being punched fully out of the stock.
Now with the part 138 thoroughly protected except at and adjacent the burr 140 (the part having been punched out of stock and separate therefrom), said part 138 is subjected to chemical milling, e.g. is immersed in an etching liquid, or is sprayed by an etching liquid, in the latter case the spray being directed toward the general area of the burr. As a result, the burr 140 is wholly or substantially removed and a portion of the metal below the burr likewise may be removed to leave a corner 148. The configuration of this corner will vary depending upon the etching technique employed. Although a concave configuration has been illustrated, the configuration may be almost flat or it may be concave.
It thus will be seen that there are provided methods and articles which achieve the various objects of the invention and which are well adapted to meet the conditions of practical use.
As various possible embodiments might be made of the above invention, and as various changes might be made in the embodiments above set forth, it is to be understood that all matter herein described or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
Having thus described the invention there is claimed as new and desired to be secured by Letters Patent:
1. A mechanochemical method of blanking sheet metal, said method comprising:
(A) punching sheet metal stock to boss-emboss a part therein to the extent that at least a predominant portion of the thickness of the part protrudes from the stock opposite the punch-facing surface thereof while the remainder of the part is retained therein, being separated from the stock by a peripheral Zone where metal of the part faces metal of the stock, and leaving an opening in the stock which is plugged by the part, said part having a peripheral burr thereon on the punch-facing corner edge thereof which extends into said opening, and
(B) then treating the stock and part with an etch erosion liquid which attacks the stock and part at least at the facing metal portions thereof to loosen the hold of the stock on the part and to at least substantially eliminate the burr.
2. A method as set forth in claim 1 wherein no more than about of the thickness of the part remains in the stock after the punching step.
3. A method as set forth in claim 1 wherein in the region of 5% of the thickness of the part remains in the stock after the punching step.
d. A method as set forth in claim 1 wherein at least the full thickness of the part protrudes from the stock after the punching step and the part is retained in the stock by engagement between the peripheral burr thereon and the opening in the stock.
5. A method as set forth in claim 1 wherein a resist layer is applied to at least one broad surface of the part before the stock and part are treated with the etch erosion liquid.
6. A method as set forth in claim 5 wherein the material of the resist layer is solvatable and whereinafter the treat- 26 ment of the stock and part with the etch erosion liquid the part is treated with a solvent for the resist layer so as to remove the same from the part.
7. A method as set forth in claim 5 wherein the resist layer is applied to both broad surfaces of the part before the stock and part are treated with the etch erosion liquid.
8. A method as set forth in claim 5 wherein the resist layer is a metal resistant to the etch erosion liquid.
9. A method as set forth in claim 1 wherein a resist layer is applied to the die-facing surface of the part, the protruding side edge of the part and at least the adjacent surface of the stock so as to form a bridge of resist material between the part and the stock, said resist layer being applied prior to treatment of the stock and part with the etch erosion liquid so that the bridge holds the part to the stock after the part is loosened.
10. A method as set forth in claim 1 wherein prior to the treatment of the stock and part with the etch erosion liquid the part is secured to a substrate and the stock is lifted off the part after the treatment of the stock and part when the etch erosion liquid has loosened the part.
11. A method as set forth in claim 1 wherein the etch erosion liquid etch erodes a chamf er at the punch-facing corner edge of the part.
12. A mechanochemical method of blanking sheet metal, said method comprising:
(A) punching sheet metal stock to boss-emboss a part therein to the extent that at least a portion of the thickness of the part protrudes from the stock opposite the punch-facing surface thereof while the remainder of the part is retained therein, being separated from the stock by a peripheral zone where metal of the part faces metal of the stock and leaving an opening in the stock which is plugged by the part,
(B) applying a resist layer to the die-facing surface of the part, the protruding side edge of the part and at least the adjacent surface of the stock so as to form a bridge of resist material between the part and the stock, and
(C) then treating the stock and part with an etch erosion liquid which attacks the stock and part at least at the facing metal portions thereof to loosen the hold of the stock on the part,
(D) said resist layer being applied prior to treatment of the stock and part with the etch erosion liquid so that the bridge holds the part to the stock after the part is loosened.
13, A method of deburring a sheet metal part having a peripheral burr on the punch-facing corner edge thereof, said method comprising applying to both broad surfaces and the side edge of the part, except at the burr, a resist layer and then treating the part with an etch erosion liquid which attacks the part at the burr to at least substantially eliminate the same.
14. A method as set forth in claim 13 wherein the etch erosion liquid etch erodes a chamf'er at the punch-facing corner edge of the part.
References Cited UNITED STATES PATENTS 3,330,032 7/1967 Bedell et al 29-598 3,177,104 4/1965 Miller 15614 2,739,047 3/1956 Snaz 156--6 X JACOB H. STEINBERG, Primary Examiner U.S. Cl. X.R.