US 3060564 A
Description (OCR text may contain errors)
Oct. 30, 1962 J. S. CORRAL TITANIUM FORMING METHOD AND MEANS Original Filed May 27, 1955 4 Sheets-Sheet 1 INVENTOR. JOSEPH S. CORRAL ATTORNEY Get. 30, 1962 J. s. CORRAL TITANIUM FORMING METHOD AND MEANS 4 Sheets-Sheet 2 Original Filed May 27, 1955 INVENTOR.
JOSEPH S CORRAL ATTORNEY 00L 1962 J. 5. CORRAL TITANIUM FORMING METHOD AND MEANS 4 Sheets-Sheet 5 Original Filed May 27, 1955 N On Oct. 1962 J. 5. CORRAL TITANIUM FORMING METHOD AND MEANS 4 Sheets-Sheet -4 Original Filed May 27, 1955 INVENTOR. JOSEPH 5. 00mm.
||1\ KIN E E E W \\\T u n w H w h. 5 mm M m m .n m ml ifw H \m m an I ow U n m mm 1 wn mm mm & y/,// 2 d W Jv ATTORNEY art 3,050,564 Patented Oct. 30, 1962 3,060,564 TITANIUM FORMING METHUD AND MEANS Joseph S. Corral, Los Angeies, Calif, assignor to North American Aviation, Inc. Continuation of application Ser. No. 511,573, May 27, 1955. This application July 14, 1958, Ser. No. 748,540 6 Claims. (Cl. 29-5522) This invention pertains to forming of titanium and more particularly to imparting a closely held contour to a titanium workpiece without difliculty from spring back. This application is a continuation of my copending application, Serial No. 511,573, now abandoned.
From a production standpoint titanium has proved to be one of the most diflicult metals for forming which has yet come into such usage. For example, when a titanium workpiece has been given the general contour desired for a completed part, subsequent stress relieving of the workpiece causes severe warpage requiring further work on the part to bring it to the shape necessary for its intended purpose. Warpage may also occur from other causes and during forming operations. Because of the nature of titanium it is not permissible on assembly to bend a warped part into shape to any appreciable degree and then hold it in place by means of fasteners. It is also deleterious to the properties of the titanium part to pound it into the desired contour because this induces cold working and attendant harmful effects for the titanium. Thus when a part has been stress relieved and seriously warped out of shape there has been virtually no means of giving the part its desired shape without harm to the workpiece, short of laborious and time consuming work.
By the teachings of this invention the above reviewed difliculties are overcome and a part may be given an exact contour without harmful eflect on the workpiece or expenditure of excessive time and effort. This is accomplished by a special forming means which includes metals of diifering thermal coeflicients of expansion, to be heated together with the titanium part, so as to exert a force against the part at the elevated temperature. This force provides a creep forming action which gives the workpiece an exact contour.
Accordingly, it is an object of this invention to form titanium to an accurately held contour. Another object of this invention is to form titanium rapidly, with inexpensive equipment and without harmful effects on the titanium part. A further object of this invention is to form titanium by means of metal elements of diflerent thermal coeflicients of expansion to provide a forming force while the titanium is in a formable temperature range. Another object of this invention is to form and stress relieve titanium simultaneously. These and other objects will become apparent from the following detailed descrip tion taken in connection with the accompanying drawings in which FIG. 1 is a perspective view of a typical workpiece to be formed by the provisions of this invention;
FIG. 2 is an exploded perspective View of the forming device of this invention;
FIG. 3 is a top plan view of the device of FIG. 2 in an assembled relationship;
FIG. 4 is a sectional view taken along line 4-4 of FIG. 3;
FIG. 5 is a sectional view of an assembled workpiece .and jig in an oven for a forming operation;
FIG. 6 is an enlarged detail view illustrating the forming action which takes place by the provisions of this invention;
FIG. 7 is an exploded perspective view illustrating a modified force block;
P16. 8 is a perspective view of a workpiece having two flanges to be formed in accordance with the teachings of this invention; and
FIG. 9 is a sectional view similar to FIG. 4 but illustrating the modification for simultaneously forming a two-flanged part.
The titanium forming according to this invention may take place either before or after a titanium workpiece has been stress relieved. A typical part to be formed according to the teachings of this invention is workpiece 1 of titanium or titanium alloy sheet shown in FIG. 1. This workpiece includes a principal surface 2 and a flange 3 projecting therefrom. Normally for the use of this invention the workpiece has been partially formed but does not have the exact shape required for a finished part. Thus, for example, workpiece 1 may have been stress relieved and may be severely warped so that surfaces 2 and 3 do not approach the necessary degree of flatness or trueness to the contour to which they are to be formed. The angle between flange 3 and surface 2 may be at something other than degrees. The workpiece, therefore, is not usable as a part until these deficiencies have been alleviated.
An exploded view of the device which is used to impart the desired contour to workpiece 1 may be seen in FIG. 2. This includes first a base member 4 which is preferably of relatively heavy steel construction. Supported on the base and attached thereto is a die member 6 which in turn is adapted to receive and support workpiece 1. Accordingly upper surface 7 of the die corresponds to the desired contour for principal surface 2 of the workpiece, while vertical surface 8 corresponds to the contour which is to be imparted to flange 3'. Surface 8 is disposed at 90 degrees relative to surface 7 in accordance with the predetermined angular relationship for surfaces 2 and 3 of the finished part.
A force block 10 of aluminum is adapted to rest on the base adjacent die 6. Vertical surface 11 of force block 10 corresponds generally to the contour to be given the outer surface of flange 2. The force block is relatively wide and dimensioned to fit loosely between the die and outer flange 13 of the base member, and may be positioned generally by locating pin 12. The assembled relationship can best be seen by reference to FIGS. 3 and 4.- Generally it is preferred to provide a steel strip 14 disposed along the outer edge 15 of the force block between this edge and flange 13.
When workpiece 1 is disposed on die 6 with the flange 2 alongside surface 8 of the die, force block 10 is urged against flange 2 by means of wedges 18 which fit between strip 14 and flange 13 of the base. These wedges are driven in sufliciently to bring surface 11 of the force block into firm engagement with the outer surface of flange 2 of the workpiece. However, this force will usually be insufficient to bend the flange in a manner which will remove the warpage and distortions which have been imparted thereto. Even if it did so the flange would spring back as soon as released because it would not have been permanently given the contour of the die. The relationship of the force block to the workpiece is illustrated in the enlarged showing of FIG. 6 Where the initial position of force block engaging the flange may be seen in solid lines. As may be seen in this FIGURE the bottom portion of the flange is warped so as to stand out from surface 8 of the die despite the fact that the force block firmly engages the outer edges of the flange because of the force of the wedges thereagainst.
When the workpiece is so engaged by the force block and the die the top portion thereof, that is portion 2 of the workpiece, is likewise clamped in position. To this end, a plate 20, which may be of aluminum of appreciable thickness and formed to generally the contour of the die, is disposed over the workpiece having been aligned by means of pins 21 fitting in openings 22 in plate 20. Bars 24 are disposed over plate each of these bars being provided with two notches 25 in one side thereof. The bars are received within tabs 27 and 23 which are suitably fixed to the base such as by welding. The notches 25 receive the upper portion of tabs when the bars are in place in this manner, and wedges 30 are driven between the bars and the top of plate 20. In this manner the workpiece is firmly gripped and urged against the die.
The entire assembly is then inserted in an oven 31 as shown in FIG. 5. This may be an ordinary gas-fired oven having burners 32 and flue 33. The jig assembly is located in chamber 34 above the burners, closed off by door 35. The temperature within the oven chamber 34 is maintained at a temperature generally in the range of from 700 F. to 1050 F. For a typical example the assembly is maintained in an oven at 800 F. for a period of two hours. When the assembly is brought to such a temperature the aluminum force block 10, having a higher coeflicient of thermal expansion than steel base 4, will expand relative to the base between flange 13 of the base and flange 3 of the workpiece. This exerts a force against the workpiece so as to urge the flange into intimate contact with surface 8 of the die. This may be seen by the position illustrated in phantom in FIG. 6. Note that the aluminum force block has grown in size relative to the base due to the elevation in temperature so that it assumes a position causing the flange to intimately engage surface 8 of the die. At the same time aluminum plate 20 will expand sufficiently to urge surface 3 of the workpiece into intimate contact with upper surface 7 of the die.
When in this temperature range the aluminum reaches a semiplastic state so that any irregularities or inconsistencies between the surface 11 of the force block and the die are compensated for. Thus, it is not necessary to hold surface 11 to an exact contour and it is even pos sible to form aluminum block 10 by casting it against die 6, giving surface 11 approximately the same configuration as surface 8 of the die without compensating for the thickness of the flange of the workpiece.
The temperature range from 700 F. to 1050 F. is within the stress relieving range of the titanium part. The resistance of the titanium to forming is lowered at this temperature and it will more readily retain a contour which is imparted to it. Thus when force block 10 and plate 20 bear against the titanium workpiece with a relatively high force by virtue of the expansion of these members, the titanium will yield so as to intimately engage the die and after a period of time will be permanently given the contour of the die even upon subsequent cooling. This is in effect a creep forming of the titanium workpiece at an elevated temperature.
After the specified period at the elevated temperature the assembly is removed from the oven and allowed to air cool. It is possible to disassemble the elements even at the higher temperature without losing the contour or physical properties of the titanium workpiece. At around 500 the parts may be quenched. It will be found that the titanium workpiece is given exactly the contour desired and no spring back will be encountered.
The exact temperature to which the workpiece is raised and the time which it is maintained at the temperature will vary with the size and shape of the part. Obviously a thicker part will require longer in an oven and perhaps a higher oven temperature in order to achieve a thorough heating. Thus in many cases a workpiece may be maintained at as much as 1000 F. for an hour and a half. The maximum time for which any appreciable forming which will impart a permanent contour to the titanium workpiece is for most examples at around thirty minutes. The workpiece may be maintained at the elevated temperature for long periods of time without damage to the part but, of course, the minimum time is preferred from a production standpoint.
It is obvious that it would be as feasible to simultaneously form and stress relieve the workpiece as it is to first stress relieve and then form by the device of this invention. In many instances it is merely more convenient to run large batches of parts through a big oven for a brief stress relieving period followed by forming in the manner described on individual jigs for longer periods of time.
When the forming arrangement of FIGS. 2-4 is used over a period of time a problem is encountered arising from a gradual distortion of the aluminum force block 10. After repeated beatings the tendency is for the aluminum block to become thicker vertically and to form a lip extending beyond the upper edge of surface 11 of the block. This can prevent the force block from obtaintaining uniform contact with the workpiece and may result in failure to give the workpiece the exact contour of the die.
One way of correcting this is to merely machine otf the top of the force block when the distortion has reached harmful proportions. Another way, preferred for longer production runs, is to construct the force block as shown in FIG. 7. Here a steel facing 10a is provided to fit between an aluminum force block 10b and the workpiece. The facing member may be separate from aluminum force block 10b, and is provided with a vertical surface 11a corresponding to surface 11 of all-aluminum block 10 previously described. The forming action is the same as before except that aluminum block 10a exerts the forming force through the steel facing and not directly. Vertical growth of aluminum block 10b or the formation of a projecting lip will have no detrimental effect because the aluminum engages only the steel facing. The aluminum block may be rectangular and therefore easily replaced. However, this modification requires considerably more time in providing the reacting surface to urge the workpiece against the die. The steel facing will not become soft in the temperature range to which the assembly is subjected. Therefore the contour of surface of steel facing must be closely fitted to a contour cornplementary to the desired shape of the workpiece.
The teachings of this invention may be employed for forming workpieces having contours other than that illustrated for workpiece 1. Another example of a part adaptable for forming by this method and means may be seen in FIG. 8. Part 36 illustrated in this figure has a portion 37 provided with flanges 38 and 39 projecting therefrom. The arrangement for forming workpiece 36 is substantially the same as the arrangement for workpiece 1 and may be seen in sectional form in FIG. 9. However, in this instance the two flanges are formed simultaneously so that it is necessary to employ a pair of force blocks 40 and 41 disposed on either side of a die member 42. Surfaces 43 and 44 of die member 42 correspond to the contour desired for the flanges of the workpiece, while surface 45 is the desired contour for portion 37 of the workpiece. Wedges 46 and 47 react through strips 48 and 49 and against flanges 50 and 51 of the base 52 to urge force blocks 40 and 41 against the flanges of the workpiece. At the same time a cover plate 53, similar to cover plate 20, is provided over the top of the die and urged downwardly against the workpiece by wedges 54 beneath cross bars 55. Again the workpiece will be inserted within an oven and held at temperature for the prescribed period of time.
It should be emphasized that parts of many other shapes, with or without flanges, may be formed according to the teachings of this invention, and that these examples are merely illustrative of the basic principles of the invention.
It is possible to use materials other than aluminum and steel for the various portions of the device of this invention but these two metals are preferred for certain reasons. Obviously these materials are readily available and low in cost, while providing a sufficiently wide difference in coefiicients of expansion to permit the necessary force to be exerted by the aluminum against the workpiece. tAluminum has the relatively high coefiicient of thermal expansion of .0000129, while the value for steel is about half at .00000628. Another factor is that the aluminum will attain a semi-plastic condition at the temperature to which the assembly is raised in the oven. This means that there is never a danger from exerting an excessive force against the workpiece such as would cause damage to the fixture itself. As the aluminum becomes more plastic at the elevated temperature it will tend to be distorted to the sides and to the top thereby relieving to some extent the force exerted against the die. At the same time despite this movement of the aluminum at temperature there will be an adequate forming force exerted to maintain the titanium in intimate contact with the die.
This means that the dimension for the width of the force block is not critical so long as it is wide enough to permit a sufiicient movement of the aluminum to cause the titanium part to contact the die on all portions thereof. The stroke required for the force block will vary with the workpiece to be formed and the amount of warpage encountered. For a typical example of a part such as illustrated the width of the block at its narrowest portion may be in the neighborhood of eight inches, which will give over ,4, inch stroke for the block.
It can be seen from the foregoing that I have provided an improved forming method and means particularly adaptable for use with titanium parts. According to the provisions of this invention a workpiece may be simultaneously formed and stress relieved, or formed following stress relieving, in such a manner as to eliminate all warpage and other distortion and provide the workpiece with an exact contour. This is accomplished by means of a simple fixture arrangement employing dissimilar metals, heated to provide a force on the titainium while the latter is in its stress relieving range.
The foregoing detailed description is to be clearly understood as given by way of illustration and example only, the spirit and scope of this invention being limited only by the appended claims.
1. The method of forming a contoured part comprising the steps of imposing forces on a workpiece such as to urge said workpiece to the contour of a completed part, such forces being below the room temperature yield strength of the material of said workpiece, raising the temperature of said workpiece throughout while said forces are so imposed thereon to a temperature suflicient to lower the creep resistance thereof, maintaining said workpiece so subjected to forces and heat for a period of time sufficient to allow relaxation of internal resisting stresses and cause the same to assume the contour of a completed part, and then releasing said workpiece whereby the same retains the contour imparted thereto.
2. The method of providing a contoured titanium part comprising the steps of forming die means defining a contour to be given such a part, engaging a titanium workpiece by said die means and urging the same against said workpiece with a force insufiicient to cause said workpiece to assume the contour of said die means at the time of such engagement, heating said die means, and said workpiece to the range of from 700 F. to 1050 F., maintaining said heated workpiece in said temperature range to lower the internal resistance thereof so that said die means cause said workpiece to assume permanently the contour defined thereby, and subsequently releasing and removing said workpiece from said die means.
3. The method of providing a contoured metal part comprising the steps of forming dies defining a contour to be given such a part, engaging a metal workpiece by said dies and urging said dies against said workpiece with a force insuflicient to cause said workpiece to assume the contour of said die means at the time of said engagement, heating said dies and said workpiece to the neighborhood of 1000 F., maintaining said workpiece and said dies at an elevated temperature with said force substantially constant for a period of time sufiicient to lower the creep resistance of said workpiece so that said dies cause said workpiece to assume the contour defined thereby, and subsequently releasing and removing said workpiece from said dies.
4. The method of shaping a workpiece to a predetermined contour comprising the steps of forming die means having a shape complementary to that of a finished part, urging said die means into engagement with said workpiece with a force below the room temperature yield strength of said workpiece, heating said workpiece while so engaged to a temperature high enough to lower the creep resistance of said workpiece and below a temperature at which the properties of said workpiece would be substantially diminished, maintaining said workpiece so engaged and heated for a period of time sufficient to allow relaxation of internal resisting stresses in said workpiece and permit said forces of said die means to conform said workpiece to the contour thereof, and then releasing said workpiece whereby the same retains the contour of said die means.
5. The method of shaping a workpiece to a contour comprising the steps of forming die means to a shape complementary to that desired for a finished part, heating said die means and said workpiece to a temperature corresponding to that at which the resisting stresses of the workpiece will be materially diminished, simultaneously urging said die means against said workpiece so as to impose a stress in said workpiece below the room temperature yield strength thereof, maintaining the temperature of said workpiece so engaged by said die means for a period of time sufficient to permit relaxation of internal resisting stresses in said workpiece so that said die means conform said workpiece to the contour thereof, and subsequently releasing said workpiece from said die means.
6. The method of providing a contoured part comprising the steps of providing die means having a contour complementary to the contour to be given a finished part, gripping a workpiece by said die means with a force below that which will cause said workpiece to assume the contour of said die means upon such engagement, heating said die means and said workpiece, maintaining the temperature of said part so engaged by said heated die means for a period of time while preventing by said die means at least some of the expansion of said workpiece that would occur from such an increase in temperature, and to conform said workpiece to the exact contour of said die means, and subsequently releasing said workpiece from said die means.
References Cited in the file of this patent UNITED STATES PATENTS 1,621,095 Utter Mar. 15, 1927 1,695,239 Norton Dec. 11, 1928 2,424,878 Crook July 29, 1947 2,527,983 Brown et al Oct. 31, 1950 2,687,762 Faber Aug. 31, 1954 2,724,669 Quirolo et a1 Nov. 22, 1955 2,737,224 Jones Mar. 6, 1956