US2460519A

US2460519A - Working of high tensile sheet metal

Info

Publication number: US2460519A
Application number: US596887A
Authority: US
Inventors: Lee L Marchant
Original assignee: Engineering & Res Corp
Current assignee: Engineering & Res Corp; ENGINEERING AND RESEARCH Corp
Priority date: 1945-05-31
Filing date: 1945-05-31
Publication date: 1949-02-01
Anticipated expiration: 1966-02-01

Description

Feb. 1, 1949. L L. MARCHANT WORKING OF HIGH TENSILE SHEET METAL Filed May 51, 1945 L155. L. MARCHANT Patented Feb. 1, 1949 UNITED STATES PATENT OFFICE WORKING OF HIGH TENSILE SHEET METAL Lee .L. Marchant, .Takoma Park, Md., assignor to Engineering and Research Corporation, Riverdale, Met, a corporation of Maryland Application May 31, 1945, Serial No. 596,887

v1 Claim. 1

'This 'invention relates to the dimpling, punching, shearing or other working of sheet metal and, more particularly, to the working of sheet metal of-such high tensile strength that it tends to rupture or crack when worked col-d. While the invention is applicable to any such working of high-tensile sheet metali't w'illbe described herein in connection with the dimpling of such sheet metal.

It has'zbeen found that if usual-and known dimplingrneans are utilized to dimple high-tensile sheetm'etal', such as magnesium or high tensile valuminum sheet, the metal surrounding the dimple will. crack and shatter when the pressure applied to the dimpling die is increased suiticiently to cause dimplingto take place. While it is known to reduce tensile strength by heating in order to permit working, such methods and means for eiTecting-this as are presently available are not useful where it is necessary to localize the heating or where rapid operation is necessary or desirable.

The present invention provides a method of, and means for, dimpling high-tensile metal sheet without causing such cracking and rupturing. In

the method according to the invention the dimpling die is forced against the sheet with a known available pressure which is insufficient to dimple the sheet while cold and is also insufficient to rupture or crack it. Simultaneously, the sheet is momentarily heated at and closely adjacent the area of contact of the die until the tensile strength of the sheet at such area of contact is decreased to a value at which it is equal to or slightly less than, the pressure applied to the sheet by the dimpling means, at which time the die will dimple the sheet. The heating is performed by the application of electric power to the sheet and in accordance with the invention more than sufficient power to effect the necessary heating is applied, whereby a very rapid increase in temperature at the area of contact is produced, thus localizing the heating and providing a very rapid operation.

In the drawings, in which similar reference numerals refer to like parts,

Fig. 1 is a partly diagrammatic, partly sectional view showing parts of a punching and riveting machine embodying the invention and showing the parts in their respective positions just prior to the dimpling and punching operation, and

Fig. 2 is a view showing the parts illustrated in Fig. 1 after completion of the dimpling and punching operation.

The high-tensile sheets with which the invention is particularly useful are those which, when dimpled cold, will crack and shatter about the dimple because of the'high tensile strength of the material. Each such material has a so-called critical range which is defined, for the pur poses of this application, as the temperature, or range temperature, at or below which the tensile strength of the material is such that cracking or shattering will occur when the sheet is dinipled and above which the tensile strength of the material is such that these undesirable effects are not produced. For the purposes of this application, the word cold will be understood to mean temperatures below this critical temperature or range.

In the drawings there are disclosed parts of a punching and riveting machine of known type and embodying means for carrying out my invention. The machine parts'comprise'a dimpling die 2 which is mounted on the lowerend of a vertical piston rod 4 which is movable vertically by a piston 6 mounted in a cylinder 3 to which fluid under pressure may be introduced or exhausted through pipes IG, [2 in order to move the dim pling die. Below the dimpling die is mounted an anvil 20 having an opening therethrough in which a punch 22 is mounted for vertical movement. These described parts are conventional and weilknown, being disclosed, for example, in my capending application Serial No. 535,134. In the operation of these known means, metal sheets 30 are placed on the anvil and the dimpling die is forced downwardly against them in order to simultaneously dimple and punch the sheets.

Means are provided by the invention for momentarily heating the sheets 30 during the application of the dimpling die thereto. Such means comprise an insulating member 49 which surrounds the anvil at the upper end thereof and supports a high-resistance contact member 62 which extends above the upper end of the insulating member and the anvil and is adapted to support the sheets 30. Electric energy is adapted to be supplied to the contact member 42 through a connecting device 44 and to the dimpling die 2 through connection 46.

In accordance with the invention cold sheets 30 of high-tensile sheet metal are laid on the upper end of the contact member 42 and the dimpling die is forced downwardly against the sheets with a force which is insufficient to dimple the sheets while cold and which is preferably approximately suilicient to dimple the sheet at the critical temperature or critical range of tema peratures. As this pressure is insufficient to cause dimpling the parts will remain in the positions shown in Fig. 1. Contact between the dimpling die and the sheets will, however, com-- plete the described electric circuit causing current to flow through the dimpling die, sheets and resistance member 42, and causing the sheets to become heated at and adjacent the area of contact of the dimpling die. In accordance with the invention the electric energy provided by this circuit closure is more than sufiicient to raise the temperature of the said localized area of the sheets to a value at which dimpling will take place without undesired rupture or shattering. The temperature of the sheets at this localized area will therefore be very rapidly increased and the tensile strength very rapidly decreased.

When the tensile strength is decreased by in-- crease in temperature, to a value at which the pressure applied to the 'dimpling die is suflicient to dimple the sheet the dimpling will occur, after which the immediate removal of the die 2 from the sheets will break the circuit and stop the heating. I have found that the surge of excess electric energy through the localized area of the sheets not only provides very rapid operation but restricts the heating to the area at and closely adjacent the point or area of contact between the dimpling die and the sheets. This permits the sheets to be held in the hand during the dimpling operation, although very high temperatures are produced at the dimpling area.

In the machine disclosed in the drawings, a punching operation is performed simultaneously with the dimpling. This isusual in punching and riveting machines of known types and is well within the spirit and scope of the invention.

While I have described and illustrated one method and means according to my invention, modifications in such method and means may occur to those skilled in the art, all of which may be made without departing in any way from the spirit and scope of the invention, for the limits of which reference must be had to the appended claim.

What is claimed is:

The method of working metal, which metal has such a high tensile strength that it tends to crack and shatter when worked cold, which consists in applying a working tool to the'metal with a pressure insufficient to Work it in the desired manner while cold but which is suficient to work it in the desired manner at a temperature of the metal just above the critical temperature thereof, and while maintaining such pressure applying to the metal at the area of contact of the working tool electric energy in amount more than sufflcient to cause the metal to be heated to a temperature at which the tensile strength is such that the pressure applied to the tool will cause the desired working.

LEE L. MARCHANT.

' of this patent:

UNITED STATES PATENTS Number Name Date 1,296,780 Dyer Mar. 11, 1919 1,333,036 Robertson et al. Mar. 9, 1920 1,658,056 Phelps et a1 Feb. 7, 1928 1,670,699 Weed May 22, 1928 1,848,905 Rabezzand Mar. 8, 1932 1,870,987 Drake Aug. 9, 1932 2,066,791 McBain Jan. 5, 1937 FOREIGN PATENTS Number Country Date 245,232 Great Britain Jan. 7, 1926 375,882 Italy Oct. 25, 1939