US2980046A - Draw dies for multiple action press - Google Patents

Description

April 18, 1961 c. P. M GREGOR ETAL 2,989,046

DRAW DIES FOR MULTIPLE ACTION PRESS 3 Sheets-Sheet 1 Filed April 14, 1955 April 18, 196] Filed April 14, 1955 c. P. MCGREGOR ET AL 2,980,046

DRAW DIES FOR MULTIPLE ACTION PRESS 3 Sheets-Sheet 3 INVENTORS CL|FT\ON P. MCGREGOR WILLIAM H. RYON B 42. 'g d:a A gnt DRAW DIES FOR MULTIPLE ACTION PRESS Filed Apr. 14, 1955, Ser. No. 501,286 1 Claim. (Cl. 11349) This invention relates generally to multiple action metal forming presses and more particularly to draw dies for metal forming presses wherein a resilient material is secured to the face of the draw ring and punch for eliminating both the formation of wrinkles and the development of excessive shear stresses in sheet metal when being formed.

Conventional dies for multiple action presses are made of a solid, non-resilient metal such as Kirksite, lead, or steel. They require a considerable amount of hand tooling by highly skilled workmen and. hence, are expensive to produce. Also, the all metal dies are limited in their use because they are incapable of deflecting to control the drawing of sheet metal where there is a change in sheet thickness due to the forming of parts having corners or a curved configuration.

To obviate the deficiencies resent in conventional metal dies, much research has been carried on in the past with the primary purposes being to provide ways of building dies more economically and to provide greater control over the flow of metal during forming. Out of this research has come die configurations which will accommodate changes in metal thickness and die configurations which will suppress wrinkles but, heretofore, a die construction has not been found which will effectively accomplish both functions; that is, to accommodate changes in metal thickness as well as suppress wrinkles.

An object of this invention is to provide a die construction which will eifectively prevent the formation of wrinkles and at the same time accommodate variations in the thickness of the sheet material being formed.

Another object of this invention is to provide a draw ring for multiple action presses having a resilient pad secured to a stiff non-resilient base member for applying a holding force to the sheet metal being formed wherein the pad thickness allows a total deflection less than that required for wrinkles to develop in the part; the pad being sufiiciently stiff to allow applying the desired holding force to the sheet while maintaining sufiicient resiliency to exert a substantially uniform pressure thereon even though the latter may vary in thickness due to the flow of material during forming.

Another object of the invention is to provide a flexible metal wear plate between the resilient pad on the draw ring and the sheet metal being formed for increasing the life of the die.

Another object of this invention is to provide a punch for multiple action presses having a layer of resilient material secured to the face thereof for exerting a squeezing force on the sheet metal during the forming operation which elfectively causes the metal to flow rather than stretch while being forced into the desired shape.

Still another object of this invention is to provide dies for multiple action presses which are economical to produce and which require substantially no hand shaping for mating the punch and draw ring with the lower die member.

Further and other objects will become apparent from a reading of the following description especially when considered in combination with the accompanying drawing wherein like numerals refer to like parts.

In the drawing:

1 Figure 1 is a fragmentary side view of a typical multiple action press incorporating the die construction of this invention;

Figure 2 is a fragmentary cross-sectional view of the dies;

Figure 3 is an enlarged fragmentary cross-sectional view showing the relationship between the die members at the end of the forming stroke;

Figure 4 is a cross-sectional view illustrating a modified form of the invention wherein only the draw ring is provided with a resilient pad on theface thereof and wherein a flexible metal wear plate is secured to the resilient pad;

Figure 5 is a fragmentary cross-sectional view showing the relationship between the dies of Figure 4 at the final stage in the forming operation;

Figure 6 is a fragmentary cross-sectional view showing a further modification of the die construction of Figures 1 through 3; and

Figure 7 is a view taken on line 7-7 of Figure 4 showing a plain view of the punch and flexible metal wear plate.

A typical multiple action press utilizing the teachings of this invention is shown in Figure 1 wherein a frame 1 provides support for a lower die member 2, a punch 3 and a draw ring 4. A cavity 5 is formed in lower die member 2 which is shaped to produce an article from a ture 9 for guided movement toward and away from lower die member 2. The actuating force for raising and lowering punch 3 is obtained by any suitable means such as a hydraulic cylinder 10 as schematically indicated in Figure 1.

Draw ring 4 surrounds punch 3 and is similarly supported by frame 1 through suitable structure 11 for guided movement toward and away from the lower die member. Control over the movement of draw ring 4 is accomplished by means of independently actuatable hydraulic cylinders 12 whereby the draw ring may be low ered to exert a clamping action on sheet metal 6 prior to the lowering of punch 3.

Lower die member 2 may be of a composition type of construction as best shown in Figures 2 and 3 wherein the basic die material may be a low melting point metal such as Kirksite, lined with a layer 13 of non-resilient plastic material of a type which will adhere to the metal surface and which may be applied in the liquid state by the use of conventional mold or die casting techniques. A suitable material for this liner is a hard synthetic plastic such as an epoxy resin. By applying layer 13 to lower die member 2 in the liquid state the shape of die cavity 5 may be very accurately controlled, eliminating the necessity for hand finishing. The shaping of the Kirk:

site base metal need only be approximate since the dimensional errors after rough cutting the die may be easily corrected when applying layer 13. While this construction of lower die member 2 is not considered essential to this invention, the economy resulting from the use of such a composition mold is also obtained as an incidental benefit in the construction features of punch 3 and draw ring 4 as hereinafter described in detail.

Punch 3 as best shown in Figures 2 and 3 includes a. non-resilient metal base member 14 with a coating on the working face thereof of a resilient plastic material 15 which layer is normally not less than one-quarter nor more than one-half inch thick. This layer 15 of resilient material should exhibit a Shore durome'terhardness of between 55 and'SO so that forming pressures may be applied without completely compressing'the resilient material and thereby destroy its ability to further deflect. Any material for layer 15 having the above mentioned characteristics will be satisfactoryso long as it is of a type which will bond to base member 14. Synthetic plastics such as resilient epoxy resins are considered ideal for the purpose because they can be applied in liquid form by conventional die casting techniques to the face 8 ofpun'ch 3, howeverit should be understood that any type of resilient material could be used on the face of this die without departing from the teachings of the invention.

By employing a resilient layer on the face of the punch a slight mismatch with cavity in'lower die memher 2 will not prevent the dies from forming partsto close tolerances so long as the cavity dimensions are accurate. Also, parts may be formed with the same dies from sheet metal of various nominal thickness. Normally however, for good results the change in gage (thickness) should not exceed .032 of an inch.

An even greater benefit from the use of a resilient layer on punch 3 is obtained by extending the layer up the side of the punch as indicated at 16 and providing clearance between the punch and lower die which is less than the normal thickness of the metal being formed. By doing this, a wiping action may be obtained during the forming of sheet metal panel'6 whereby the sheet metal is squeezed between the lower die and the punch as the punch is moved downwardly and into cavity 5 of the lower die member. This effectively causes the sheet metal to be drawn into its final shape by the flow of metal rather than by simply stretching the sheet in tension. Thus, more critical drawing operations may be carried out without tearing the metal.

In order to draw sheet metal panel 6 without having wrinkles develop it is essential that a draw ring 4 be employed to restrain the flow of metal into the cavity. This drawing of sheet 6 into cavity 5 causes the sheet thickness to change. Where the sheet is drawn into a corner of the cavity the thickness will increase under the draw ring. Where the sheet is drawn around a convex curve in the cavity, the sheet thickness will decrease as compared with its original thickness. If this flowing of the metal which causes a change in thickness is not induced, wrinkles will be formed in the part and if a change in thickness does occur a non-resilient draw ring will obviously release its grip on the thinner portions of the sheet being formed and tighten up on the portions which increase the thickness and thereby introduce shear stresses which will result in tearing the metal. It is this change in the thickness of the sheet metal under the conventional draw ring during forming which limits the depth to which a part can be formed relative to a radius of curvature. A resilient draw ring will obviate the problem of maintaining a uniform holdingpressure on the sheet material, however, it is then diflicult to prevent the formation of wrinkles. In accordance with the teachings of this invention by limiting the maximum deflection of the draw ring to a value only slightly greater than necessary to compensate for variations in sheet thickness a substantially constant holding pressure may be obtained at the same time wrinkles are suppressed. Thus, the die construction of this invention utilizes a composition draw ring as most clearly shown in Figures 2 and 3 wherein a thin layer of resilient material in the form of a pad 17 is bonded to a draw ring base member 18 wherein the base member is a non-resilient and-unyielding material such as Kirksite, steel or other metal.

Resilient pad 17 forming a part of draw ring 4 should preferably possess a Shore 'durometer hardness between 55 and 80 whereby a suitable gripping 'force may be applied to sheet metal 6 without destroying the resiliency of the pad. Thus, a substantially uniform pressure may lbe exterted on the sheet of metal by the draw ring even when the thickness of the sheet metal changes during the forming operation. Also, the thickness of resilient pad 17 should, for normal operations, be no greater than one-half inch, but this will vary depending upon the required draw ring pressure, upon the average thickness of the sheet metal being formed and upon the shape of the part. As a design criteria it may be stated that the maximum deflection of the resilient pad 17, with the draw ring pressure applied should approximate the average thickness of the sheet material.

As previously described, draw ring 4 surrounds punch 3 and is movable toward and away from die 2 independently of the punch whereby the draw ring may be lowered to squeeze the sheet metal against the generally flat surface 7 bordering cavity 5 on die 2. This clamping or holding pressure must be exerted substantially uniformly and continuously around cavity 5 for proper forming. Due to the high forces involved in such metal forming operations it is highly desirable if not essential that the draw ring exert its holding force over a reasonably large area of the sheet and that such force be applied immediately adjacent the edge of the cavity in die 2 as shown in the drawing. Therefore, the working face 19 of draw ring is provided with a substantial width and is shaped to mate with the 'face 7 on die 2.

During the forming operation the sheet of metal 6 is drawn by the movement of punch 3 into cavity 5 against the action of draw ring 4 in squeezing the sheet. The friction between the draw ring surface and the sheet of metal in resisting such movement tends to pull resilient pad 17 into the cavity. This is effectively prevented however, by extending resilient pad 17 upwardly along the sides of the draw ring as shown at 20 in Figures 2 and 3.

Figures 4 and 5 illustrate a form of the invention wherein a thin metal wear plate 21 is bonded to resilient pad 17 on draw ring 4 to improve the wearing qualities of the draw ring and eliminate direct contact of pad 17 with the sheet of metal 6 to be formed. Wear plate 21 must be sufiiciently thin and flexible to allow resilient pad 17 to deflect and maintain a substantially uniform pressure on the sheet of metal during the forming operation. Normally, wear plate 21 is made of steel and is approximately 64 to thousandths of an inch thick for the majority of applications. To avoid excessive shearing stresses between wear plate 21 and resilient pad 17 as the sheet of metal 6 is being drawn into cavity 5, the Wear plate is formed as a continuous strip of metal as shown in Figure 7 whereby it will, by virtue of its configuration, resist any tendency to tear loose and slip into the cavity with the sheet metal. It is also essential that wear plate 21 be continuous and not segmented in order to prevent the development of wrinkles in the sheet metal since a segmented wear plate would not apply a uniform pressure continuously around cavity 5 as required for proper forming of the part.

Die member 22 and punch 23 in the configurations of Figures 4 and'S are shown as being of the more conventional type not utilizing a non-metallic liner as shown and described in Figures 1, 2 and 3. While the full benefits are not obtained with such a die construction it is clearly within the teachings of this invention to employ such an arrangement. The composition draw ring employing resilient pad 17 to maintain a uniform pressure on the sheet metal throughout the forming operation will still obtain results which are notably superior to those obtained with conventional multiple action press dies because the draw ring, in maintaining a substantially uniform pressure on the sheet metal, prevents wrinkles and the buildup of excessive shear stresses. The use of an all metal punch and diemember however, will not permit obtaining the squeezing action on the sheet metal during forming as is possible with a punch as described in connection with Figures 1 through 3.

A further modification of thedie construction is shown in Figure 6 wherein resilient pad 24 is secured to the face of lower die 26 including the draw ring seating-surface 25 rather than to the draw ring 27 and punch 28. This is also considered to be an obvious substitution which is within the teachings of this invention.

The actual forming operations with the dies described herein may be the same as with conventional multiple action dies wherein the sheet metal to be formed is first placed on the lower die member. After properly locating the sheet metal relative to the lower die member the draw ring is lowered to engage the sheet metal, squeezing the latter against the draw ring seating surface 7 on lower die member 2. While the desired load is being applied by the draw ring, punch 3 is forced downwardly, applying a forming pressure to the sheet. As punch 3 is lowered still further into cavity 5 of the lower die member 2, more and more of the sheet is drawn into the cavity by sliding relative to draw ring 4. By using a layer of flexible material as a liner for punch 3, as shown in Figures 1 through 3, a squeezing or wiping action may be applied to the sheet when being formed to help prevent tearing of the metal at the edge of the cavity Where the tensile loads on the sheet are the greatest. As the metal sheet is pulled into the cavity its thickness under the draw ring will vary depending upon the shape of the part being formed. As this thickness varies, the resilient pad 17 on draw ring 4 automatically adjusts itself to maintain a uniform holding pressure, preventing the development of excessive shear stresses. Also, because the maximum deformation of the resilient pad is limited to that which is necessary to compensate for variations in sheet thickness, wrinkles are prevented from developing.

The final stage of the forming operation is illustrated in Figures 3, 5 and 6 wherein the punch and sheet completely fill cavity 5 in the lower die member.

After forming the part, the punch and draw ring are retracted, allowing the part to be removed for trimming and other finishing operations. With the use of a conventional all metal punch and die member, as shown in Figures 4 and 5, there is no wiping action on the part as it is being drawn into the cavity. As a result, there is a tendency for the part to spring back or change its dimensions slightly when the forming pressures are removed. Where tolerances for the part are critical, this presents a difficult problem requiring a considerable amount of hand finish work on the dies to correct. By the use of the resilient layer on the face of the punch, spring back of the metal is avoided and, hence, so is the hand work required for production dies because of the wiping effect on the sheet as it is drawn into the lower die cavity.

While the invention has been shown and described herein in reasonable detail, it is to be understood that certain alterations, modifications and substitutionsmay be made to the instant disclosure without departing from the spirit and scope of the invention as defined by the appended claim.

We claim:

A multiple action press for forming parts from sheet metal comprising, a frame, a die member carried by said frame and having a cavity formed therein, said die member having a generally flat draw ring seating surface bordering said cavity, a punch movably carried by said frame, means carried by said frame and engaging said punch for controlling the movement thereof relative to said die cavity for forming a sheet of metal by drawing the sheet into the cavity, said punch having a liner of resilient material on the face and side thereof providing relative cross sectional dimensions between the punch and die which establishes a clearance between the sides of the die cavity and the punch which is less than the thickness of the sheet of metal for squeezing said sheet of metal between the punch and die member as it is drawn into the cavity, a draw ring surrounding said punch and movably carried by said frame, means carried by said frame and engaging said draw ring for controlling the movement thereof relative to the draw ring seating surface on said die member for applying a holding pressure on the sheet of metal being drawn into the cavity by said punch, a resilient pad of substantially uniform thickness between approximately one-quarter and one-half inch secured to said draw ring and arranged to transmit the draw ring pressure to the sheet of metal, said pad completely covering the face of said draw ring and extending to the edge of the die cavity, said pad having a hardness suflicient to exert the desired holding pressure on said sheet of metal-without completely collapsing whereby the pad may exert a positive pressure all around the punch even though the thickness of the metal may vary during forming, the maximum deflection of sm'd resilient pad being no greater than twice the normal thickness of said sheet of metal for suppressing wrinkles, and a thin, nonsegmented flat metal wear plate secured only to said pad for engaging the sheet metal, said wear plate generally mating with the face on the draw ring pad and being continuous whereby to resist being drawn into said cavity by said sheet metal and to present a smooth bearing surface for the resilient pad.

References Cited in the'file of this patent UNITED STATES PATENTS 405,618 Swift June 18, 1889 760,921 Rigby May 24, 1904 1,689,501 Rode Oct. 30, 1928 1,891,121 Thoreson Dec. 13, 1932 2,061,569 Zinser Oct. 8, 1935 2,230,043 Moran Jan. 28, 1941 2,321,075 Frey et al. June 8, 1943 2,327,177 Cross Aug. 17, 1943 2,388,838 Egli Nov. 13, 1945 2,649,067 Kranenberg Aug. 18, 1953 2,693,637 Peabody et al. Nov. 9, 1954 2,710,903 Seloff et al. June 14, 1955 8 2,836,530 Rees May 27, 1958 FOREIGN PATENTS 213,959 Switzerland June 16, 1941

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