US2771851A - Sheet metal forming die means - Google Patents

Description

Nov. 27, 1956 c. P. MOGREGOR 2,771,851

SHEET METAL FORMING DIE .MEIANS Filed May 20, 1954 3 Sheets-Sheet 1 l9" w l -26 E54 Nov. 27, 1956 P. MCGREGOR 2 77 SHEET METAL FORMING DIE MEANS Filed May 20, 1954 Sheet 2 F'g.- E

INVENTOR. CLIFTON I? McGREeoR Agent Nov. 27, 1956 c. P. MCGREGOR ,3

SHEET METAL FORMING DIE MEANS Filed May 20, 1954 3 Sheets-Sheet 3 Utlit SHEET-METAL FORMING DIE MEANS Clifton P. McGregor, North Hollywood, Calif., assignor to Lockheed Aircraft Corporation, Burbank, Calif.

Application May 20, 1954, Serial No. 431,090

Claims.- (Cl. 11346) This invention relates to the shaping or forming of sheet material such as sheet metal, and the like,'and re-' latesmore'particularly to dies for drawing or forming such materials.

In the aircraft industry and related industries, many sheet material parts are shaped or formed by die sets. A'great many ofsuch parts have heretofore been formed in dies used in expensive, complicated double action draw presses, the double action presses' being necessary.

to prevent or reduce the development of wrinkles in the marginal or flange regions of the blank-orpart as well as in-the major regions thereof. Although attempts have been made to control the flow or draw of the material into the cavity of conventional drop hammer dies bythe simpler, less costly drop hammer dies and drop' hammers in carrying out-many-of the sheet material forming operations.

It is a general object of the present invention to provide low cost sheet material forming diesadapted to be used in drop hammers to form sheet'material parts of the classes or types that have heretofore been, as a general rule, formed in the more expensive draw dies which required the use of complicated, double action draw presses.

Another object of the invention is to providedrop hammer die means of the character referred to that effectively control the flow of metal of the blank or partduring the drawing or forming operation or operations'to prevent the development of wrinkles in the part. In accordance with the invention, distributed, equal or controlled pressure is exerted on the marginal areas, which may or may not be of substantial extent, of the blank or part during the forming action and this controlled pressure governs the flow of the metal into the die cavity to prevent the development of wrinkles in the part.

Another object of the invention is to provide die means of this kind thatcan be designed and constructed to form parts of different sizes, configurations and depth of draw.

It is another object of the invention to provide drop" hammer dies of the character referred to that may be inexpensively produced from inexpensive readily available materials.

It is a further object of the invention to provide drop hammer die means that may, if desired, incorporate trimming or blanking means to effectively trim the part while being securely clamped against displacement.

Other objectives and features of the invention will bcome apparent from the following detailed description of States Patent 2,771,851 Patented Nov. 27, 1956 typical preferred embodiments thereof throughout' which descriptionreferenceis made to the accompanying drawings' in which':

Figure 1 is a perspective view of a'female die of the invention;

Figure 2 is a fragmentary vertical sectional view of a die set of the invention'prior to the initial forming stage;

Figure 3 is a view similar to Fig. 2 showing the punch and associated parts in the position assumed at the end of the first forming stage;

Figure 4 is a" similar view showing the parts prior to the second stage forming operation;

Figure 5 is a similar vertical sectional view showing the parts in the positions assumed at the end of the second stage forming operation;

Figured is-a vertical sectional view" illustrating the punch andassociated-pa-rts in -the'positions assumed at the end of the final forming stage;

Figure-6A is a pe'rspective'view ofa pair-of therubber pads; and

Figure 7 is a vertical sectional view of another form of die set'of the" invention incorporating blanking or trimming means.

The die apparatusor die setof the invention illustrated in Figures 1 to6A inclusive of the drawings'includes'a die '10,*a-punch'11 carried by the drop hammer head 'H,

a clamping ring1 2' ass'ociated'with the punch, and yield ing pad means 13*arran'ged'between the head H and the ring'12.'

The'die '10is the relatively stationary member or element of the die setand is secured on the bed of the drop hammer, not shown. Ithas been foundmost practical to construct the die "10 of Kirksite although the die may be formed of any selected or suitable material. The

upper oractiveface14of the die 10 may be of any shape, depending upon the intended configuration to be given the part-'P. In the 'drawings'the die face '14 is curved or concave and has'acavity' 15'into which the part is to be drawn'or formed. Theparticular die 10 illustrated' hasanupstanding rim'ld'around its face 14and the inner surface 17 of this-rimslopes or flares outwardly and upwardly.

The punch 11 is secured to 'the underside of the drop hammer head H to move or travel therewith and its lower portionisdesigned to'conform 'with' the die cavity 15. As illustratd'in the drawings, the'side walls of the cavity 15flare orslope upwardlyandoutwardly and the side surfaces of the punch" 11 are correspondingly inclined; In most cases'it may be preferred to construct the punch 11"of Kirksite," orthe like; although other suitable materials may be used for this purpose. In'this connection it may be" notedthat the die 10 and punch 11 are constructed' of substantiallyunyielding materials. The lower face and lower portion of the punch 11 are shaped to mate with the' die 10' and more particularly with the cavity 15 with suitable clearance, provision being' made for the thickness of theblank or part P which is to be formed between them. The sides 18 of the punch 11 preferably slope'upwardlyand outwardly for the purpose which will la'terbecome apparent. I

The clamping ring 12 is provided to exert a sufficient downward pressureon the flange or marginal portion 19 of the blank or part P to prevent the formation or developm'ent'of wrinkles in the part as it ispushed or drawn into eryof the'punch 11. The'upper end'of the ring '12 is" preferably flat'to be parallel with the'lower face of the hammer head H. The lower face 20 of the ring 12 is shaped to mate with the face 14ofthedie 1t and-in the case illustrated, is curved'or convex to be substantially concentricwith theupper-die-face." The lower end of'th'e' ring 12 has a reentry or groove 21 for receiving the rim 16 of the die 10, this groove being shaped to conform with the rim with working clearance. The inner surface 22 of the ring 12 flares or slopes upwardly and outwardly at substantially the same angle as the side 18 of the punch 11 so that when the punch moves downwardly these surfaces 18 and 22 cooperate to centralize the ring with respect to the punch. The ring 12 is arranged to have relative vertical movement with respect to the punch 11. Means is provided for limiting this relative movement, this means including two or more spaced pins 23 projecting horizontally inward from the ring and received in vertical slots 24 in the punch 11. The pins 23 and slots 24 are related so that the ring 12 is raised with the punch when the hammer head 11 is raised, the ring assuming a position such as shown in Figure 2 and when the punch 11 is moved downwardly the ring 12 is adapted to move down to first engage the flange 19 of the blank or part P to be thereby held against further downward movement while the punch continues downwardly to draw the blank or part into the die cavity 15.

In accordance with the invention, the clamping ring 12 is formed of a material that is yielding or compressible. I have found it most practical to construct the clamping ring 12 of a thermo plastic, such as cellulose acetate, cellulose butyrate, or combinations or blends thereof. The clamping ring 12 preferably has a Shore hardness on the A scale of between 80 and 100. When the ring 12 is to be constructed of a thermo plastic such as above described, it may be expeditiously and inexpensively produced by being cast directly to the punch 11, it being desirable to arrange a sheet of metal, plastic, or the like, around the punch prior to the pouring of the plastic and to employ a parting agent such as a high temperature wax. The ring 12, when constructed of cellulose acetate, cellulose butyrate, or blends thereof is found to be self-lubricating and to act or press on the flange 19 of the part P to control the metal flow without binding or galling. In many cases it may be found desirable to provide the lower face 20 of the ring 12 with a holding ridge or head 25 and the top face 14 of the die with a companion or mating groove 26, the bead and groove cooperating to assist in gripping or anchoring the flange 19 adjacent its outer margin during the drawing or forming operations. It will be observed that the ring 12 is somewhat shorter in the vertical direction than the punch 11, to leave a space above the ring to receive the yielding pads 13.

The pads 13 are arranged between the underside of the hammer head H and theupper end of the ring 12 to transmit downward movement and force from the head to the ring. While the pads 13 may be constructed of any selected yielding or compressible material, I have found it practical to construct them of rubber. The pads 13 preferably have a Shore hardness of from 50 to 60 on the A scale. It is preferred to employ sectional pads 13 to facilitate their installation and removal. Thus, as shown in Figure 6A there may be two substantially C- shaped pads 13 arranged in end to end relation to form an assembly capable of surrounding the upper portion of the punch 11. The thickness of the yielding pads 13 is determined by the nature of the forming or drawing operation to be performed and pads of dilferent thicknesses. will often be used during successive phases of the forming operations. Thus it will be noted that the pads 13 employed during the first or initial forming operation are thicker than the pads 13 shown in Figure 4 and used during the second or successive stage of the operations. It will be observed in Figures 2 and 4 that the pads 13 and 13 are proportioned so that their inner and outer margins or peripheries are spaced from the adjacent peripheries of the clamping ring 12, thus leaving ample space for the yielding rings to flow or distort laterally.

In performing certain drawing or forming operations it may be desirable to face the active lower portion of the punch 11 with a hard, or relatively hard material such as a steel or hard plastic to assist the drawing action. Furthermore, in carrying out certain forming operations where the finished part is to have a special or peculiar configuration, metal shims may be installed either above or below the pads 13 or 13 in certain regions of the assembly or the pads 13 may vary in initial thickness. However, as it is usually unnecessary to resort to either the hard facing of the punch, the use of shims or pads of unequal thickness, such details have been omitted from the present disclosure.

In employing the die means of the invention the punch 11, clamping ring 12 and pads 13 are assembled under the hammer head H as shown in Figure 2 of the drawings, and the blank or part P is arranged in position on the upper face 14 of the die 10. The drop hammer head H is then lowered or dropped to cause the punch 11 and die 10 to cooperate in forming the part P. During the sudden downward movement of the punch 11 the clamping ring 12 is the first to engage the flange or marginal region 19 of the part P to clamp the same against the top face 14 of the die 10. The pads 13 are compressed at this time to exert or transmit the required clamping pressure through the ring 12 to the marginal area of the part P. The punch 11 of course engages and pushes the intermediate portion of the part P into the die cavity 15 to draw or form the same. The ring 12, being formed of a yielding material, is vertically compressible during the drawing or forming operation to allow and control the radial slippage or flow of the flange area 19 of the part P. Being constructed of a yielding material the clamping ring 12 exerts a uniform or equal pressure resembling an hydraulic pressure throughout the extent of the flange area 19 of the part P to prevent the initiation or forming of wrinkles in either this flange area or the axially drawn portion of the part P. In this connection, it may be noted that where the configuration of the finished part P is such that an increased or varied clamping pressure be exerted or transmitted by the clamping ring 12, either the pads 13 may be of increased thickness at a given region or given regions and/ or metal shims may be installed either above or below the pads at such regions. Even in such instances the yielding material clamping ring 12 pressed downwardly against the flange area 19 of the part P by the head H through the medium of the yielding pads 13, applies or exerts a distributed clamping pressure that has been found to prevent the initiation of wrinkles in the part P. It is believed that this action of the yielding material clamping ring 12 results, at least in part, from the yielding action of the ring in controlling the radial flow of the metal of the part P.

In a typical forming operation the initial phase or stage described above will only partially form the part P to the die cavity 15. If this is true, the hammer head H is raised and the first yielding pads 13 are removed to be replaced by the somewhat thinner pads 13. For example, in a given job the thickness of the first pads 13 may be substantially the same as the depth of the die cavity 15 while the thickness of the second pads 13* may be equal to, say, one-half or one-third of the depth of the die cavity 15. With the second pads 13 in place the hammer H is again lowered to carry out the second phase of the forming. Here, again, the clamping ring 12 is the first element to contact the blank or part P and the ring exerts a somewhat yielding clamping pressure on the flange to control the draw or forming.

of the metal when the punch 11 contacts the same to push or draw it into the die cavity 15. This clamping action inhibits or prevents-the formation of wrinkles in the part P. A second or third forming operation, such as just described, may suffice to completely form the part P. Figure 6 of the drawings illustrates the parts in the position assumed during a final forming phase in which the yielding pads 13 and 13 have been omitted so that the head H directly transmits'the downward force to the yielding clamping ring 12. As shown 5 in Figure 6, the punchll has firitiHyz-formed-the part P to the die cavity 15.

Figure 7 illustrates a blanking or trimming die means incorporating the features of the-invention? In"-- this case there is'a die 30'of Kirksite, or the likeyhaving a cavity 35 andanupper face 39 surrounded by" an upstandingrim'36. In this embodiment of the inventionthe mating-punch'may be formed of two -se'c'ti'ons 40and 41, separated by a trimming'collar or blad42. Although this blade 42 may not-be' annular or continuous, it will be assumed that'it is of such a configuration. The lower faces of the punch" sections 40 and 41 are shaped to mate with the cavity 35--and face 39- of the die 30 to cooperate therewith in shaping orlforming the blank B. The punch sections 40"ar1d 41"are'pfeferably formed of a relatively yielding or compressible material such as cellulose acetate, cellulose butyrate, or a blend of the same.

A second or outer blanking or trimming blade 44 surrounds the outer punch section 41. The two spaced trimming blades 42 and 44 are secured to a plate 45 of steel, or the like, secured to the underside of the hammer head H. The lower ends or edges of the blades 42 and 44 have broad beveled or tapered faces and protrude beyond the lower face of the punch 40-41 to cooperate with abrupt vertical shoulders 46 and 47 respectively of the die 30. Inclined faces 60 extend from the lower ends of the shoulders 46 and 47. The trimming blades 42 and 44 may be formed of mild steel, or the like, and their active lower ends may be faced with layers 48 and 49 respectively of a hard material such as a fiberglas fabric laminated with a hard epoxy resin binder. When the hammer head H is lowered or dropped these hard-faced blades 42 and 44 cooperate with the shoulders 46 and 47 of the die 30 to shear or cut through the blank B and thus trim the same.

The die assembly of Figure 7 further includes a clamping ring 32 around the outer trimming blade 44, the lower end of this ring 32 is shaped to mate with the face 39 and rim 36 of the die 30 so as to clamp the flange or marginal area of the formed blank B against the die. The clamping ring 32 is formed of a yielding or somewhat compressible material such as cellulose acetate or cellulose butyrate so as -to exert a substantially uniform or distributed clamping pressure on the blank B. The punch sections 40 and 41 and the clamping ring 32 may be formed of a thermo plastic such as just described having a Shore hardness of from 80 to 100 on the A scale. One or more pads or layers 51 of yieldable compressible material, such as perforated rubber, are arranged between the mounting plate 45 and the upper ends of the punch sections 40 and 41 and the clamping ring 32. These pads 51 preferably have a Shore hardness of from 50 to 60 on the A scale and yield or compress to a considerable extent in transmitting the downward forces from the plate 45 to the punch and clamping ring.

It has been found that in the operation of the trimming die means shown in Figure 7 the yielding material clamp ring 32 exerts a distributed controlled clamping pressure on the marginal or flange portion of the blank or part B during operation. In Figure 7, the yieldable punch sections 40 and 41 and ring 32 being formed of yieldable material and being backed up by the pads 51 serve to clamp against the blank B and hold it tightly against the die at both sides of each trimming blade 42 and 44. Further, the extensive or broad tapered faces 60 adjacent the abrupt shoulders 47 and the tapered ends of the blades 42 and 44 serve to assist in holding the part or blank against movement during the trimming operation.

It is to be understood that the particular forming die means illustrated in the accompanying drawings are typical of the invention and are capable of considerable variation and modification to adapt them for the drawingior forming of blanks orparts ;of different materials and of special or different configurations; While I have described the die means employed in a drop hammer, it may be used in a double action press-Yin which case the pads=13 and 13 and the pins 23 are preferably incombination; a diehaving a' cavity and a surface around thecavity adapted-to,- support a sheet material part, an actuating hammer movable toward the die, a-

punch on the hammer movable against the part to draw the same into the cavity, a ring of compressible material around the punch and engageable with the portion of the part resting on said surface, the material of the ring having a Shore hardness of between and on the A scale, and yieldable means engaged between the hammer and the ring transmitting said movement of the hammer :to the ring to cause the ring to clamp said portion against said surface prior to and during the engagement of the punch with the part to control said drawing of the part.

2. Die means for forming sheet material comprising, in combination, a die having a cavity and a surface around the cavity adapted to support a sheet material part, an actuating hammer movable toward the die, a punch on the hammer movable against the part to draw the same into the cavity, a ring around the punch engageable with the portion of the part resting on said surface and constructed of a thermo plastic having a Shore hardness of between 80 and 100 on the A scale, means connecting the ring with the punch for limited axial movement with respect thereto, and yieldable pad means engaged between the hammer and ring transmitting said movement of the hammer to the ring to cause the ring to clamp said portion against said surface prior to and during the engagement of the punch with the part to prevent wrinkling of said portion.

3. Die means for forming sheet material comprising, in combination, a die having a cavity and a surface around the cavity adapted to support a sheet material part, an actuating hammer movable toward the die, a punch on the hammer movable against the part to draw the same into the cavity, a ring around the punch engageable with the portion of the part resting on said surface and constructed of a cellulose acetate having a Shore hardness of between 80 and 100 on the A scale,.means connecting the ring with the punch for limited axial movement with respect thereto, and yieldable pad means engaged between the hammer and ring transmitting said movement of the hammer to the ring to cause the ring to clamp said portion against said surface prior to and during the engagement of the punch with the part to prevent wrinkling of said portion.

4. Die means for forming sheet material comprising, in combination, a die having a cavity and a surface around the cavity adapted to support a sheet material part, an actuating hammer movable toward the die, a punch on the hammer movable against the part to draw the same into the cavity, a ring around the punch engageable with the portion of the part resting on said surface and constructed of a cellulose butyrate having a Shore hardness of between 80 and 100 on the A scale, means connecting the ring with the punch for limited axial movement with respect thereto, and yieldable pad means engaged between the hammer and ring transmitting said movement of the hammer to the ring to cause the ring to clamp said portion against said surface prior to and during the en- 7 gagement of the punch with the part to prevent wrinkling of said portion.

5. Die means for forming sheet material comprising, in combination a die having a cavity and a surface around the cavity adapted to support a sheet material part, an actuating hammer movable toward the die, a punch on the hammer movable against the part to draw the same into the cavity, a ring around the punch engageable with the portion of the part resting on said surface and constructed of a cellulose acetate having a Shore hardness of between 80 and 100 on the A scale, means connecting the ring with the punch for limited axial movement with respect thereto, and yieldable rubber pad means engaged between the hammer and ring transmitting said movement of the hammer to the ring to cause the ring to clamp said portion against said surface prior to and during the engagement of the punch with the part to prevent wrinkling of said portion.

References Cited in the file of this patent UNITED STATES PATENTS Norton Sept. 20, 1892 Asche Sept. 17, 1901 Moran Jan. 28, 1941 Frey June 8, 1943 Egli Nov. 13, 1945 Bruderlin June 24, 1947 Ames Apr. 27, 1948 Ledel June 20, 1950 FOREIGN PATENTS Germany Sept. 19, 1933 Switzerland June 16, 1941

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