US 3623278 A
Description (OCR text may contain errors)
NOV. 30, 1971 H, J, R Z 3,623,278
DEBURRING PROCESS Filed Dec. 3, 1969 INVENTOR HERMAN J. SCHWARTZ ATTORNEY United States Patent O DEBURRING PROCESS Herman J. Schwartz, Chicago, Ill., assignor to Teletype Corporation, Skokie, Il]. Filet! Dec. 3, 1969, 5er. No. 881,799 Int. Cl. B24b 1/00 U.S. Cl. 51-317 6 Claims ABSTRACT OF THE DISCLOSURE In a mass deburring process, the integrity of a corner of a workpiece is maintained by rotating a centrifugally maintained grittv abrasive wall in a first angular direction about the workpiece and rotating the workpiece in the wall such that the velocity of the corner is about at least as great as the velocity of the abrasive and in a second angular direction substantially opposite to said first angular direction.
BACKGROUND OF THE INVENTION The present invention relates to surface finishing. Particularly it relates to deburring piece parts in a mass production process.
It has been known to tumble, agitate or otherwise move metallic workpieces, such as small piece parts, in drum or barrel in the presence of a gritty abrasive to remove surface irregularities such as burrs and other projections. However, the heretofore known procedures are unsuitable for finishing a workpiece if there is a requirement to retain the integrity of a specific surface thereon because there is no known economical practice for protecting a selected surface from abrasion.
For example, in a known process for making a clutch, a metallic disc is stamped from a blank. Incident thereto burrs are raised on the surface of the disc which then is formed; and a corner is milled in the formed member. The sharpness of the corner is critical to clutch operation. Accordingly, no heretofore known mass abrading techniques can be used for deburring the dises. In consequence, a highly costly manual technique in which each disc is separately finished is required for burr removal and to insure retention of corner integritv.
It is an object of this invention to provide an improved finishing process.
It is another object of the invention to minimize the cost of finishing the surface of a workpiece having a region required to be unafiected by the finishing opera tion.
It is an additional object of the invention to provide a mass process for deburring metallic workpieces while maintaining the integrity of a sharp edge on each thereof.
It is a further object of the invention to eliminate the requirement for manual deburring of a workpiece in a finishing process in order to maintain the integrity of a sharp edge thereon.
SUMMARY OF THE INVENTION In accordance with the present invention, the foregoing objects are effected by rotating a workpiece relative a mass of an abrasive and arranging the workpiece in the mass such that during each rotational cycle a part of the workpiece sought to be protected is masked from abrasive impact by the bulk on the workpiece and will move away from an impacting course With the abrasive mass.
Considered from another aspect, the objects of the invention are achieved by coupling a wall of a gritty abrasive to a rotating container to rotate the abrasive. A workpiece is engaged and held at a fixed station in the wall as the abrasive rotates. A surface of the workpiece is rotated at a linear velocity at least about equal to the linear velocity of the abrasive in which the workpiece is engaged.
BRIEF DESCRIPTION OF THE DRAWINGS In the ensuing description reference is had to the accompanying drawings in which:
FIG. 1 is a side elevational view of apparatus for practicing a process embodying the present invention and FIG. 2 is a perspective view enlarged from, and taken in a plane al0ng line 22 of FIG. 1.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring now to FIG. 1, shown is a housing 9 which may be circular in cross section and has an upper opening 10. A sheet metal skirt serves as a base 11 adapted for rigidly supporting the housing above suitable flooring (not shown). An upwardly opening container, drum or barrel 12 concentric with the housing is arranged therein by any suitable means enabling rotation about a vertical axis. A vertically oriented drive shaft 14, which is journalled through the lower wall 16 of the housing 9, has an upper enlarged supporting end portion 17 centrally secured to the lower wall 18 of the drum. A pulley system 19 operably couples shaft 14 to the output shaft of a motor 20 which comprises prime mover means for rotating the drum.
A mass of a grinding medium such as a gritty abrasive 22 is disposed in drum 12. Motor 20 is adapted to rotate at a rate sufficient to generate a centrifugally maintained wall 24 of abrasive against the inner surface of the drum. In the illustrated embodiment the particles of abrasive 22 are vitrified molded angle cylinders or pellets of aluminum oxide by However, neither the specific composition nor the specific size of the pellets is critical in the invention. A load of abrasive sufficient to eteet the process in the exemplary drum comprises about 400 lbs.
In the illustrated process, the drum 12 has a diameter of 4 feet and is rotated at about 60 r.p.rn. The mass of the abrasive 22 is such that when rotated at said rate, the velocity of the abrasive at a circular grinding, abrading or finishing station 26, the character of which will be further clarified in ensuing description, is about 650 feet per minute.
A work holder 28 may, as illustrated, be one of a plurality of like members spaced about drum 12. It comprises an arm 30 which is rockably mounted above a pivot 32 to lower and raise a spindle 34 toward and away from station 26. The agency (mot shown) for rocking said arm may be any well-known means and is not limiting on the invention. A bracket 35 which is carried from the work proximate end of arm 30 adjustably carries a mounting cylinder 36. When operatively conditioned, the cylinder is secured by fastening means 38 at a generally vertical, though slightly tipped, orientation which can be selec tively adjusted within the limits of a slot 40 in bracket 35. A journalling sleeve 42, carried in cylinder 36, provides a bearing for a driveable shaft 44. Driving means comprising a motor 46 is drivingly coupled to shaft 44 through a drive transmission, which may be of known construction and include pulley belt 48. A chuck 50 is connected to the work proximate end of shaft 44 for rotation at the lower end portion of cylinder 36.
Spindle 34 is releasably secured in the chuck 50 by usual means for rotation with shaft 44 from which the spindle projects axially. The spindle is proportioned such that when in operable position, its lower end portion will engage in wall 24 and therein define an annulus comprising station 26 as abrasive is displaced. The exemplary spindle when operatively disposed is 1.75 feet from the center of rotation of drum 12.
According to the present invention, the surface of a plurality of workpieces 52 can be simultaneously abrasively finished by rotating them in wall 24 relative abrasive 22 at station 26. Abrasive dislodged or displaced by interaction therewith and any workpiece is returned to and reforms the wall by centrifugal force as drurn 12 rotates and thereby prevents cavitation. Each exemplary workpiece is a elutch dise fabricated of a chrome nickel alloy having an AISI designation of 4130 and is formed by stamping from a blank in consequence of which burrs, which will be removed during finishing, are raised on its surface. Following stamping, each dise is further formed to generate a pair of opposed outwardly opening recesses 54 and 56 and a pair of opposed corners 58 and 60; and then it is perimetrically ground to an outside diameter of about 2".
Thereafter, the corners 58 and 60 are contoured in a mil]. Subsequently, each dise is hardened by carburizing to a depth of about .003 inch. Each of the corners comprises a part or portion, the integrity of which it is desired to maintain during finishing. In accordance with the invention abrading association of the corners practically is prevented during finishing.
Each of the corners of a dise is defined by the jonction of the dise perimeter 59 and a respective wall of recesses 54 and 56. They are disposed in trailing association with dise bulks 62 and 64 in terms of angular dise direction (arrows 66 and 67) during finishing.
To the latter end a pair of dises 52 is fixed on spindle 34 in parallel planes normal to the spindle axis. The innermost dise is held against a fixed collar 68 and separated from an adjoining dise by a spacer 70. The assembly is secured by a nut mounted on the outer end portion of said spindle and forcing the proximate dise against said spacer.
In the illustrated embodiment, spindle 34 is driven at 1250 r.p.m. This rate imparts a linear velocity to the perimeter 59 of about 650 feet per minute, said velocity being about 25 feet per minute greater than the velocity of the abrasive at station 26. Moreover, the angular direction (66 and 67) of rotation of the spindle and the workpieces mounted thereon is substantially opposite to the angular direction (according to arrows 74 and 75 of rotation) of the abrading material which is disposed about station 26.
Ideally, the workpieces 52 are mounted such that cormers 58 and 60 are parallel to the axis of rotation of wall 24. Practically, in the exemplary equipment, this cannot be done economically; and an angle of between and from the vertical is imparted to spindle 44 to enable cylinder 36 to clear the abrasive in wall 24 during the process.
The aehievement of the process can be readily understood by referring to FIG. 2. There it is seen that during each cycle of disc 52 each corner.thereof, while moving in an opposite angular direction to the abrasive, will have: 1) a linear component of motion (according to arrow 66) which is opposite the linear component of motion (according to arrow 74) of the abrasive and (2) a linear component of motion (according to arrow 67 which is roughly the same as the linear component of motion (according to arrow 75 of the abrasive.
The concept elarifies by considering, for the moment, corner 58. In the phase (herein called the first phase) of the cycle shown in FIG. 2, the linear component of motion of said corner 58 is in a direction (arrow 66) which is substantially opposite to the direction (arrow 74) of the linear component of motion of the abrasive at station 26. Therefore, if it were not for the masking effect of bulk 62, corner 58 would corne into abrasive impact with the particles of abrasive 22 comprising wall 24. However, because it is masked during the first phase of each cycle, abrasion of corner 58 is prevented. On the other hand, when corner 58 is in the second phase of each cycle, that is, for example, when it occupies the position of corner 60 shown in FIG. 2, then the direction (arrow 67) of its linear component of motion is substantally the same as the direction (arrow 75) of the linear component of motion of abrasive 22. In the second phase of the cycle corner 58 is exposed without protection of the masking mass to the abrasive. However, because corner 58 is moving faster than wall 24, it moves away from the abrasive 22 to which it is exposed; and in consequence, though exposed, it does not become abraded.
During a short portion of each cycle, a corner sought to be protected will be neither masked nor have a linear component of velocity which is parallel and at least equal to the linear component of velocity of the abrasive. Accordingly, an abrasive effect on such corner is manifest. Integrity retention of the corner in this condition is proportional to the differential of the linear velocities of the abrasive and such corner. Praetically, under exemplary conditions, the undesired abrasion is inconsequential as the extent thereof falls within tolerable limits.
Though ideally, the relative rates of spindle 44 and shaft 14 are such that a workpiee 52 will move at least as fast as the abrasive 22 to avoid abrasive collision of a corner while in the second phase of each cycle, a suitable finishing result can be obtained if the velocity of the corner is less than or negative relative the velocity of the abrasive, provided total corner exposure is brief and abrasive impact is of low level. The limit of the range of tolerable negative velocity will, of course, vary according to many factors, for example, duration of exposure and grittiness of abrasive. However, it is intended that such negative speed of a workpiece within a tolerable limit at which integrity of an area or portion of the workpiece will be maintained following impact with the abrasive falls within the scope of a definition for velocity of about equal to the velocity of abrasive in which the workpiece is engaged.
Prior to the present invention one operator was required to work one hour to finish 50 exemplary work pieces. Employing the invention, the produetivity of the like worker has been inereased to 300 workpieces per hour.
As many changes could be conceived in the foregoing process, and as many changes could be made therein without departing from the spirit and scope of the claims, it is intended that all matter contained in the accompanying specification shall be considered as illustrative only and not in a limiting sense.
1. A process for abrasively finishing a workpiece having a bulk part while maintaining a surface part of the Workpiece in an unabraded condition and comprising the steps of:
rotating the workpiece including the bulk part and the surface part through a mass of abrasive;
rotating the abrasive mass about the workpiece while the workpiece is rotated; and
arranging the workpiece in the mass such that the surface part is masked from impact with the abrasive mass by said bulk part during only a portion of each rotational cycle and moves away from contact with the abrasive mass only during the remainder of such cycle.
2. A process according to claim 1 characterized in that the velocity of the surface partis greater than the velocity of the abrasive mass.
3. A process aecording to claim 2 characterized in that 5 6 the angular directions of rotation of the workpiece and the 6. A process according to claim 5 in which the linear abrasive mass are substantially opposite. velocity of the surface of the workpiece is greater than the 4. A process according to claim 1 wherein the surface linear velocity of the abrasive in the wall. partis a corner and is mounted in trailing relationship with said bulk part. 5 References Cited 5. A deburring process comprising the steps of: UNITED STATES PATENTS coupling a wall of a gritty abrasive against a rotating container for rotating the abrasive wall; 464,584 12/1891 Patterson et 5119 engaging and holding a workpiece at a fixed station in 2,218,353 10/1940 Gmenberg the wall as the container rotates; and 10 2,664,676 1/ 19 54 CuPPers rotating a surface of the Workpiece relative to a holder for the workpiece and at a linear velocity at least LESTER M'SWINGLE Pnmary Exammer about equal to the linear velocity of the abrasive in U S Cl XR which the workpiece is engaged and in an angular direction substantiafly opposite to the direction of 15 rotation of said wall.