US 3914972 A
The female die in a sheet metal brake is fitted with TEFLON inserts at critical points in the die, which inserts permit the sheet metal to move relative to these inserts without exhibiting the usual tendency to mar the associated surface of the sheet metal. The inserts are preferably circular in cross section, having active segments which engage the metal workpiece during the forming process. The female die defines semi-circular cavities for rotatably receiving these cylindrical inserts or rods, and this configuration assures that the wear of the rods occurs uniformly around the periphery thereof, these rods being adapted to rotate incrementally during each forming operation of the associated male member so as to present an adjacent segment of the periphery of the TEFLON rod to the next succeeding workpiece.
Claims available in
Description (OCR text may contain errors)
[ 51 Oct. 28, 1975 TOOLING FOR SHEET METAL FORMING APPARATUS  Inventors: Richard N. Gillette, East Hartford;
Robert H. Sand, Canton, both of Conn.
 Assignee: The Vulcan Radiator Company,-
22 Filed: June 4, 1973 21 Appl. No.: 366,632
 US. Cl. 72/212; 72/380; 72/386  Int. Cl. B21D 9/08  Field of Search 72/380, 386, 212, 213; 29/132, 110
 References Cited UNITED STATES PATENTS 419,156 1/1890 McGiehan 72/212 600,699 3/1898 Weber l 72/213 1,552,416 9/1925 Bingham... 72/213 2,669,891 2/1954 Ware 72/213 2,908,315 10/1959 Hellwig.. 72/213 3,500,679 3/1970 Smith 72/212 3,613,427 10/1971 Haddon 72/212 FOREIGN PATENTS OR APPLICATIONS 68,127 3/1969 Germany OTHER PUBLICATIONS Cast Nylon Tooling-Better Than Metals?, Tool &
Mfg. Engineer; Vol. 49, No. 6, Pgs. 78-80; 12/1962; C. W. Dames, .lr.
Primary ExaminerC. W. Lanham Assistant Examiner-James R. Duzan Attorney, Agent, or FirmMcCormick, Paulding & Huber  ABSTRACT The female die in a sheet metal brake is fitted with TEFLON inserts at critical points in the die, which inserts permit the sheet metal to move relative to these inserts without exhibiting the usual tendency to mar the associated surface of the sheet metal. The inserts are preferably circular in cross section, having active segments which engage the metal workpiece during the forming process. The female die defines semicircular cavities for rotatably receiving these cylindrical inserts or rods, and this configuration assures that the wear of the rods occurs uniformly around the periphery thereof, these rods being adapted to rotate incrementally during each forming operation of the associated male member so as to present an adjacent segment of the periphery of the TEFLON rod to the next succeeding workpiece.
3 Claims, 5 Drawing Figures US. Patent' Oct.28, 1975 Sheet1of2 3,914,972
SUMMARY OF THE INVENTION This invention relates to metal forming, and deals more particularly with a die construction which has application to the bending of sheet metal, one surface of which sheet metal must not be marred or scored. This requirement is one which has become quite significant in the forming of polished aluminum, and also in the forming of vinyl clad sheet metal. The present invention may, therefore, be applied to cold forming sheet metal with at least one surface which must not be marred. A female die is provided for engaging this particular surface of the sheet metal workpiece when the invention is utilized in a conventional sheet metal brake. However, the invention might also be adapted for use in a forming process where the workpiece is rolled or otherwise formed.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view partly in section showing a sheet metal workpiece in place between the mating male and female die members.
FIG. 2 shows the female die without the workpiece or the male die associatedtherewith.
FIG. 3 shows the female die with the workpiece prior to being formed, and with the male die being spaced from the female die.
FIG. 4 shows the apparatus of FIG. 1, and
FIG. 5 shows the configuration of the resulting workpiece after having been formed in an apparatus of the present invention.
DETAILED DESCRIPTION Turning now to the drawings in greater detail, FIG. 1 shows a male die of conventional construction being fabricated from steel and adapted to engage one surface of a sheet metal workpiece W and to form the workpiece into the desired shape dictated by the cooperating surfaces of a mating female die member 12 associated therewith.
FIG. 2 shows the female die in vertical cross section as including a steel block 14 having a clearance cavity 16 formed in the block for the purpose of receiving the male die 10.
The female die 12 further includes spaced lands 18 and 20 which cooperate to define the boundaries of the clearance cavity 16, and which lands receive the workpiece W as best shown in FIG. 3, prior to the forming operation. These lands 18 and 20 are preferably not fabricated from the same material as is the block 14, namely from steel, but are instead fabricated from an anti-friction material such as a synthetic thermoplastic material selected from the fluorocarbon group which includes polytetrafluoroethylene (PTFE), tetrafluoroethylene (TFE) and trifluorochloroethylene (Kel-F) sold under the tradename TEFLON or the like.
In further accordance with the present invention these spaced lands of synthetic thermoplastic material are provided with a circular outer contour or periphery and are free to rotate in cavities defined for this purpose in the female die 12. As best shown in FIG. 1 each of these lands are defined by longitudinally extending rod members 18 and 20 each of which is rotatably received in the female die but can be removed for replacement or repare by means of the screws indicated a generally at 22, 22. Thus, the semi-circular cavities 24 and 26 which rotatably receive the rods 18 and 20 are defined in part in the body portion 14 of the female die and in part by longitudinally extending retaining strips 28v and 30 respectively. As so constructed and arranged the frictional forces exerted on these TEFLON rods 18 and 20 during the forming operation depicted in the FIG. 3 and FIG. 4 views will cause limited angular rotation of the rods as indicated generally at 32 and 34 in FIG. 4. This limited rotational movement of these rods precludes excessive wearing being caused to the rods at any one segment of their periphery, and assures that an anti-friction surface will be presented to the underside of the sheet metal workpiece W during the entire forming process. The clearance cavity 16 of the female die 12 is such that the underside S of the workpiece W never contacts it during this forming process. Thus, the workpiece W and more particularly its non-mar surface S never contacts the metal componets of the die construction, and instead always contacts only the TEF- LON rods 18 and 20 during the forming operation.
The advantages to the foregoing die construction will be readily apparent to those familiar with the art of forming sheet metal. While these advantages can be realized in adapting a die of the type shown in the drawings to a sheet metal brake of conventional construction, these advantages will be particularly apparent when the workpiece has one surface in particular which must not be marred or scored by the die. More particularly, this die has particular advantage in the art of forming sheet metal enclosures of the type used in the heating and ventilating industry where these sheet metal components are fabricated from a vinyl clad material or from a polished relatively soft aluminum material. However, the advantages to the present invention can also be applied to the forming of any metal components and might be well adapted for use in the forming of prepainted or precoated sheet metal workpieces.
1. An apparatus for bending sheet metal panels with a non-mar front surface and comprising:
a. elongated male die means for impacting the rear surface of the panel,
b. a female die means engageable with the non-mar front surface,
c. said female die means having a rigid body portion defining a clearance cavity for the panel portion to be bent and spaced lands extending longitudinally on either side of said cavity,
(17 at least one of said elongated lands being more particularly defined by a longitudinally extending member of synthetic material selected from the thermoplastic fluorocarbon group which includes polytetrafluoroethylene (PTFE), tetrafluoroethylene (TFE) and trifluorochloroethylene, and
e. said synthetic member having a circular cross section and being mounted in a semi-circular cavity defined by said rigid body portion so that said synthetic member is free to rotate during the bending of such sheet metal panel.
2. The apparatus of claim 1 wherein said female die means includes a second synthetic member of circular cross section mounted in a second semi-circular cavity associated with the other of said spaced lands in said rigid body portion, said second synthetic member also selected from the fluorocarbon group which includes polytetrafluoroethylene (PTFE), tetrafluoroethylene attached to said cavity defining body portion and coop- (TFE) and mfluorochloroethylene' erating therewith to define and circular cavities to re- 3. The apparatus of claim 2 wherein said female die means further includes a rigid retaining strip for each of said synthetic members, said strips being removably 5 strict said members to rotational movement.