CA1051230A - High speed room temperature seam bonding of metal sheets - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved method of cold pressure welding a cover member to the edge of a hollow tubular member, with both mem-bers consisting of cold pressure weldable metal. The method comprises outwardly bending the end portions of the members to provide frusto-conical interfitting flanges. The cylindrical member is placed in a die wherein the die supports the flange on the cylindrical member. The cover member is mounted on a circular punch wherein the punch supports the flange on the cover member. The punch is positioned concentric with the die.
A metallic interlay is placed between the faying surfaces of the members. The flanges and the interlay comprise the weld assembly. The punch is axially displaced relative to the die to compress the weld assembly thereby creating an intense inter-facial flow conducive to bonding of the members in a solid phase welding bond.

Description

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The present invention relates to pressur~ welding and more paxticularly, to cold pressure weldin~.
It is already known to join a pair of metal members, such as sheets, plates etc. capable of being cold pressure welded by a lap joint by applying pressure to the superposed members substantially at right angles to the interface or w~ld area through the use of suitably shaped impression tools or dieg. As a result of the applied pressure, metal is caused to ~ow outwardly from under the pressure appIying die surfaces or weld area, thereby causing a merging or intimate union of the adjoining metals equivalent to a solid phase welding bond at that area.
In a method of the above character, the metal flow varies within substantial limits at different points of the usual strip-like or rectangular weld area, being greater a~
the edges of the strip or longer sides of the rectangular weld area and being reduced towards the center on account cf the greater impedance offered to the flow of the metal from the center towards the edges of the area. As a result, substantial welding pressure becomes necessary to insure a sufficient metal flow over the entire weld area condu_tive to efficient cold pressure welding, the pressure required being furthermore dependent upon the degree of hardness of ductility of the metals being welded. This, in turn, results in a substantial deformation or distortion of the parts of members being welded at and adjacent to the weld spot or area. Commonly, thic~ness reductions in the memkers to be joined, of 6~/o or more of each member are required to insure efficient welding. This thinning seriously r~

`- 105123~
weakens the weld area. Furthermore, practical limitations imposed by the necessity of applying sufficient pressure may result in unacceptably low bonding speeds.
Among the objects of the present in~ention is the provision of an improved method of and means for joining a pair of pressure weldable metal members by a lap joint which substantially overcomes the aforementioned and related difficulties and shortcomings, which will afford a more uniform metal flow and, in turn, a more efficient weld over the entire weld area, and which can be carried out easily and reliably while involving a minimum of rejects or defective welds.
With the aforementioned objects in view, the invention involves generally the provision of means for and an improved method of welding a pair of pressure weldable metal members which comprises essentially positioning a sacrificial metal interlay between the faying surfaces to be bonde~ and compressing the assembly until the interlay is properly spread over the faying surfaces. The interlay has a cross-section designed to produce a highly differential flow when subjected to external compressive loads. This differential 10w causes shear movement between the interlay and the faying surfaces which effects the weld.

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10~123~
Besides many other applications, the invention has special advantages in attaching a cover to a hollow cylindrical member such as welding a lid to a can by cold pressure weldinq. Thus, the edge of a can of allIminum or other cold weldable metal is flared outwardly to provide a flat flange of small radial width. A lid having a surface which fits on the flange is placed on top of the can and the lid is welded to the flange by suitable cold pressure welding tools which make a ring weld. The surfaces to be welded together are previously cleaned to remove the oxide film and other surface contamination and to provide clean metal surfaces at the interface to be welded. If the projecting weld is undesirable, this can be dressed down by forcing the whole can top downwards through a die, the weld area then lying close up against the side of the can.
The invention will ~e better ~nderstood from the following detailed description taken in conjunction with the accompanying drawings, forming part of this specifi~ation . and wherein:
Figure 1 shows partly in section, a tool setup for welding a lid to a can in accordance with the in~ention, Figure 2 shows, partly in section, a tool setup for weldiny the side seam of a can and Figures 3a-3f show, in cross-sectional views, several interlay configurations.
Like reference characters identify likè parts in the different views of the drawings.

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Referring to Figure 1, there is shown a can 1 and lid 2, both of pressure weldable metal. The can is of circular or any other section and has a bottom la attached by a c~ouble lap seam lb or any other method.
An outwardly directed frusto-conical flange ld has been formed in the free extremity of the can wall lc and a mating comp~ementary flange 2a has been formed in the lid 2.
The can 1 is held in a die 3, wherein the die base 3a is adapted to grip the can bottom seam lb to prevent radial displacement of the can 1, while the die sidewalls 3b provide support for the can flange ld.
The die 3, which is mounted on the platen of a hydraulic press or the like, may comprise a single piece or may be assembled from component pieces as an aid to tool fabrication.
A co-operating punch 4 is also mounted in the press such that it moves rectilinearly and coaxially with respect to the can 1. The punch is adapted to hold the lid 2 while su?porting the lid flange 2a.
11 In operation, the faying surfaces S of the can flange ld and the lid flange 2a are cleaned, using a rotary steel wire brush or the li~e, and a metal interlay 6 is placed ther~between to form a weld assembly. The punch 4 is then brou'ght d~wn under pressure, co~mpressing the assembly and causing the interlay 6 to deform and ^
spread over the faying surfaces 5, thereby welding the assembly in a solid phase bond.
Referring to Figure 2, there is shown a sheet 7 of pressure weldable metal, bent to form a hollow cylinder. The sheet 7 is constrained between concentric circular male 8 and female ~ dies with the axial edges 10 overlapping: the overlap being exposed by an opening 11 in the fe~ale die 9. The dies 8 and 9 are mounted on the platen of a hydraulic press or the like.
A co-operating punch 4 is also mounted on the press such th~t it moves rectilinearly and r~dially with respect to the cylindrically formed sheet 7.
In operation, the faying surfa~es 5 of the sheet axial edges 10 are cleaned, using a rotary steel wire brush or the lilce, and a metal interlay 6 is placed there~tween to form a weld assembly. The punch 4 is then brought down under pressure, compressing the assembly and, causing the interlay 6 to deform and spread over the faying surfaces 5 thereby welding the assembly in a solid phase bond.
The interlay 6 has a cross-section which results in a highly differential flow when subjected to external compressive loads, the ratio of the rate of deformation measured along one axis to the rate-of deformation measured along a perpendicular axis preferably being in the range i of 5:1 to 30:1, with the highest ratio being most preferably.
Although the mechanism is not fully understood, it apoears that the differential rates of flow between the interlay ~
and the two faying surfaces 5 produce an intense intèrfacial or shear flow. This shear flow serves to scrape off any oxide coating which may have formed on the faying surfaces 5 after the preweld cleaning (the presence of oxygen in the atmosphere causes these oxides to begin forming immediately after the cleaning) and whi~h would tend to reduce the quality~

1051 23~) of a cold pressure weld. The flow further serves to ca~se intense localized facial heating. Further heating results from the pr~ssure exerted on the weld assembly. The heat, the pressure and the intimate contact between the faying surfaces 5 and th~ interlay 6 all combine to produce the desired weld.
The desired differential in the shear flow rates is dependent upon the relative hardness of the interlay 6 and the base metal, the desired degree of thickness reduction of the base metal, and the surface condition of the interlay 6 and the faying surfaces 5.
The desired differential may vary during the course of effecting the ~eld. For example, it may be desirable to initially have a relatively low shear differential to scrape off any oxide coa~ing on the interlay 6 or the f~ying surfaces 5, followed by a relatively high differential to effect the weld. Further, it may be desirable to have different shear flow differentials at the two faying surfaces 5 if the underlying base metals are of different hardness.
It i~ therefore, necessary to choose an interlay 6 configured to provide the desired time/location pattern of she~r flow differential.
Figures 3a-3f illustrate some of the possible interlay 6 cross-sections, including round, oval, ~ia~ond with depressions at opposing corners, arrow-head and rectangular with asymmetrically placed void. These sections, when compressed between two fa~ing surfaces 5, will produce the desired highly differential flow, each, however, producing a different pattern of f~low O~;~ Z3~) differential. Improperly designed cross-sections, such as -~imple rectangles, undergo thickness reduction without -~uch differential flow. Instead, the interlay material merely extrudes in the unrestrained directions.
The pressure necessary to effect the weld is dependent upon the shear resistance of the interlay 6 and the faying surfaces 5. Preliminary results indicate that a pressure of about 15~h of the surface stress of the interlay material is sufficient, provided that this pressure produces contact stresses at the points of contact between the interlay 6 and the faying surfaces S sufficient to cause some localized flowing of the base metal underlying the surfaces 5.
The interlay 6 is preferably softer than the base metal. When the interlay hardness is eq~al to or gre~ter than that of the base metal, the interlay 6 does not spread over the faying surfaces 5, but, rather, cuts into the base metal. The proper hardness for the interlay 6 must be determined experimentally and largely depends upon the desired thickness reduction in the base metal, the minimum reduction occurring when the interlay 6 is very soft as compared to the base metal. Experimental results indicate that an optimum weld is achieved when the interlay thickness has been reduced by 65-99%. This may be accompanied by a thickness reduction in the base metal of about 5%. The interlay 6 may also be formed of a soft filler metal 6a with several fine wires 6b of a stronger, harder metal disposed therein (see Figure 3f).
The presence of these wires 6b increases the differential flow of the interlay 6 during the deformation process and .

;

. 10~23~) -elevates the shear resistance of the accomplished bond.
Thus, the strength characteristics of the bond may be talored through proper orientation of the wires 6b.
Preliminary results indicate that this process permits cold pressure bonding at speeds of 10 feet per second.
While the invention has beén described herein with specific reference to cold pressure welding, i.e.
welding at room temperature or without the use Oc any appreciable amount of external heat, it will be understood that some heat may be applied to the members being welded provided, however, that welding is essentially effected 2S
a result of the he~t and pressure-induced plastic flow , of the metal, to effect merging or intimate welding at the interfaces in the manner described. The additional heat may be supplied by either heating the pressure welding tools, or the members to be welded may be heated either before or during welding.
In the foregoing the invention has been described ; 20 by reference to a few illustrative tools and methods. It is to be understood, however, that variations and ~odifications of both the described tools and method steps, as well as the substitution of equivalent to~ls and steps, may be made without departing from the broad scope and spirit of the invention as set forth in the appended claim~.
; The specification and drawings are accordingly to be regarded in an illustrative rather than in a limiting senge.
The application is a division of Canadian Patent Application Ser. No. 240,945 filed December 3, 1975.

Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of cold pressure welding a cover member to the edge of a hollow tubular member, both said members con-sisting of cold pressure weldable metal, comprising outwardly bending the end portions of said members to provide frusto-conical interfitting flanges, placing said cylindrical member in a die wherein said die supports said flange on said cylin-drical member, mounting said cover member on a circular punch wherein said punch supports said flange on said cover member, said punch being concentric with said die, placing a metallic interlay between the faying surfaces of said members, said flanges and said interlay comprising a weld assembly, and axially displacing said punch relative to said die to compress said weld assembly thereby creating an intense interfacial flow conducive to bonding of said members in a solid phase welding bond.

2, In a method according to claim 1, wherein said inter-lay is of cross-section such as to deform at substantially dif-ferent rates, as measured along mutually perpendicular axes, consequent to said compression of said assembly.

3. In a method according to claim 2, wherein the maximum hardness of said interlay is equal to the hardness of said mem-bers to be joined.

4. A method of cold pressure welding a lapped side-seam to form a hollow tube from a preformed sheet of cold pressure weldable metal, comprising placing said preformed sheet between mating male and female dies such that the axial edges of said sheet overlap, said female die having an opening exposing said overlap, placing a metal interlay between the faying surfaces of said edges, said edges and said interlay comprising a weld assembly, and compressing said weld assembly between said male die and a punch, said punch acting through said opening in said female die, said compression creating an intense interfacial flow conducive to bonding of said edges in a solid phase welding bond,

5, In a method according to claim 4, wherein said inter-lay is of cross-section such as to deform at substantially dif-ferent rates, as measured along mutually perpendicular axes, consequent to said compression of said assembly.

6. In a method according to claim 5, wherein the maximum hardness of said interlay is equal to the hardness of said edges to be joined,