METHOD AND TOOL FOR JOINING OF METALS OR METAL ALLOYS BY COLD WELDING

Abstract: A method to perform cold welding, e.g. in metals or alloys of different kinds is peculiar in that the surfaces which are to be cold welded are slided over each other at the same time as swarf is removed from each surface in such a way that the freshly produced metal surfaces which are to be welded together mainly do not come in contact with air. The whole process occurs in a sliding movement and a good welding takes place without use of inert gases or vacuum.

Description: METHOD AND TOOL FOR JOINING OF METALS OR METAL ALLOYS BY COLD WELDING The invention relates to a method for joining two or more parts made out of metals or metal alloys, perhaps of dissimilar kinds, by cold welding, where the parts have mating surfaces having a straight line generatrix, where a skiving of the surfaces is performed first and subsequent¬ ly the surfaces are brought into mutual contact while a normal force is exerted between them. An inconvenience existing in cold welding is that the parts have to be cleaned carefully immediately before the joining. Moreover, cold welding requires large material deformations. A method has been described aimed to solve this problem, where a previous machining of the surfaces to be joined together is performed in a vacuum chamber, where also the cold welding is carried out. It has also been tried to let the remaining gas in the vacuum chamber be an inert gas. It has been experienced that one can ob¬ tain good results in this way but it is obviously diffi¬ cult to perform the machining as well as the cold welding in a vacuum chamber. Such a method has been described by W.C. Sherwood and D.R. Milner in a paper in "Journal of the Institute of Metals" Vol 97, 1969. From a paper written by Robert J. Russell in "Materials Engineering" 3-75, page 48-50 it is furthermore known to place a metal inlay under pressure by rolling into a groo¬ ve in a metallic part, having the groove been skived out immediately before, in such way that the freshly machined surface has been in contact with air only for a short ti- me. This method is however confined to joining of strip shaped parts . Furthermore, from the description of US-patent no. 3 768 718, a method and tool for cold welding is known to be performed as butt welding of massive metal wire ends, whe¬ reby the two ends are first sheared across, then brought together under a pressure load, and then are pressed together again and again in such a way to make the material flow to such an extent that a ring of excess ma- terial is formed around the welding zone. This ring con¬ tains, among other things, the contaminants which might have been present on the surfaces that have been brought together, while the material which is present in the wel¬ ding zone must be totally clean and never has been in con- tact with air, this being due to the flow which the mate¬ rial has been submitted to. The ring is subsequently cut of and the weld is perfect and consisting as mentioned of pure material. This method is confined to welding metals having the same hardness. _, Common for the known methods is that one has clearly rea¬ lized the necessicity that the surfaces which are to be cold welded must be very clean and preferably not have been in contact with air for too long time. The peculiarity of the method of the present invention consists in that skiving of at least one of the surfaces to be joined, and preferably of both surfaces, is carried out by a movement of the surfaces having a component in the direction of a generatrix, and that the same movement brings the surfaces further in mutual sliding contact, using the sliding movement to cover at least one surface and preferably both surfaces, in such manner that they do not come in contact with air. In this way, a simple method has been demonstrated by which one, to a great extent, can avoid that clean metal surfaces come into contact with air, and it has been experienced that perfect welds can be obtained in this way. According to the present invention, a normal force can be applied to the welding surface before the final position is reached. By having the two newly exposed surfaces pressed together, one can further improve the welding, since investigations have shown that even a short time contact between air and the fresh metal surfaces can decrease the quality of the weld. It is therefore also clear that one can achieve, in some cases, a better weld quality if, according to the present invention, during the skiving one makes use of one or more methods known to improve a weld, e.g. heat, electric current or inert gas perhaps by carrying out a subsequent heat treatment. As known, cold welding is often used to join metals or me¬ tal alloys of different kinds, in which case one of the parts will often have higher hardness than the other part or parts. In such a case, according to the present invention, the part having the highest hardness can be used for skiving the other part or parts, i.e. the part which has the highest hardness is used as a tool. By so doing, the method is simplified. If one needs to fasten a stud, insert or rivet into a hole, according to the present invention one can easily apply the method described letting the stud have higher hardness than the material where the hole is present, pla¬ cing an external skiving tool over the hole, pressing the stud through the skiving tool and further down into the hole, and letting the stud obtain a section which is sligthly larger than the hole section, i.e. a somewhat larger diameter if the parts are of circular shape, and letting the stud receive a sharp edge all around its end, and pressing or striking on the stud at the end and con¬ temporaneously exerting a resistance on the material sur¬ rounding the hole in order to provide circular stresses around the hole. An advantageous embodiment of the present method is cha¬ racterised by letting the stud have a height which is slightly larger than the height of the hole. By so doing one can achieve in a simple way a tight pressing and a perfect weld. If one, according to the present invention, lets the hole pass through two or more sheets which are lying one over the other, and during the operation holds them in this po¬ sition, it is possible to obtain a riveting of the sheets. Thus a method is actually shown for riveting with a rivet without protuberances, e.g. having no rivet head. It is indeed doubtful whether one should call this machine ele¬ ment a rivet, since a riveting in the pure sense of the term is not performed, but just a pressing or striking. Finally, according to the present invention, stud and hole can be circular-cylindrical, naturally obtaining in this way an embodiment which is easy to establish. The present invention relates also to a tool to perform the method and this tool is characterised by means for fastening each of the parts and means to bring the parts against each other or along each other in the direction of a generatrix. One embodiment of this tool is characterised by means for producing a normal force in the welding zone. Another embodiment is characterised by a skiving edge having a clearance angle which is mainly equal to 0. With this tool it is possible to keep the freshly machined surface covered by the tool itself, in such way that the surface can slide from a position of contact with the tool directly to another position of contact with the surface which it is to be welded to. It shall however be emphasized that the method will also work even if, for a short time, there has been access for the oxygen of the air. Speed and time therefore play a predominant role. Finally, the tool can be characterised by the fact that the skiving edge has the shape of a ring, perhaps a split ring. Such a tool is very simple in its design. It is also easy to manufacture and is finally easy to work with. One can in such way imagine riveting performed using headless rivets. A further development of this tool is characterised by consisting of a block provided with a through hole to gui¬ de the stud, and having at one end of the hole a circular skiving edge and at the opposite end of the hole a guide edge and between these edges a cavity for accomodating ex¬ cess material, e.g. swarf, if desired provided with chan¬ nels for swarf disposal, and the other end of the hole be¬ ing designed to accomodate a punch. Finally, the tool can be characterized by the fact that the punch is removable and the opposite end with the guide edge for the stud, i.e. the end at which the punch is ac¬ ting, is designed as a sliding ring, e.g. of plastic, which in the starting position embraces the punch as well as the stud in the region where these are positioned against each other and which is guided concentrically a- round punch and stud. By so doing a preferred embodiment is shown whereby in a simple way after the welding it is possible to remove the circular swarf which has been ski¬ ved off. The present invention is explained in more details in con¬ junction with the accompanying drawings, wherein Fig. 1 shows two block shaped parts in start position before a welding. Fig. 2 the two parts in final position after welding, Fig. 3 a section in a portion of a sheet with a welded insert or stud. Fig. 4 a section of a tool in starting position for welding of an insert or stud as shown in fig. 3, Fig. 5 this tool in final position, Fig. 6 a section in a portion of a sheet wherein a busting has been welded, Fig. 7 a section in a portion of two sheets which are joined by a welded stud, Fig. 8 the same, but where the stud is hollow or has the shape of a bushing, Fig. 9 a section in the end of a tube with a welded flange, Fig. 10 a section in a tool to produce this tube end with flange. Fig. 11 a section in a tool for welding together strips or ribbons, Fig. 12 another tool for joining together sheets or strip shaped parts, e.g. electrical cables, in front sectional view along the line XII-XII in fig. 13, and Fig. 13 this tool seen from the side. fig. 1 are shown two metallic parts 1 and 2, where the In fig. 1 are shown two metallic parts 1 and 2, where the first part 1 is provided on the upper side with a skiving tool 3 covering the whole width, while the second part 2 is provided in similar way on the lower side with a skiv- ing tool 4. The cutting edges 5 and 6 are engaging each other, since the clearance angle is zero. The cutting edge 5 is positioned somewhat below the end surface 7 on part 1. When parts 1 and 2 are now moved sidewards with respect to each other as shown by the arrows 8 and 9, the cutting tools 3 and 4 will skive a chip from the end surfaces over the whole width at the same time as the cutting tools will cover the fresh surfaces, until these will slide over each other and cover in this way each other, as shown in fig. 2, where also two chips 10 and 11 are shown. If one thereafter presses the parts 1 and 2 against each other, as shown by the arrows 12 and 13, a cold weld is produced between the end surfaces. It is actually known that cold welding can produce welds between different metals or metal alloys. The same is valid using the method according to the present invention, which furthermore gives welds of very high quality. Fig. 3 shows a section in a metal sheet 14 wherein a cir¬ cular insert or stud 15 is welded, using the method according to the present invention. Such a metal sheet can be produced by using a tool 17, as shown in fig. 4 and 5. In fig. 4, the tool is shown in a starting position, where it has been aligned over the center of hole 16 in the sheet 14, which is laying on a base 14a. The tool 17 consist of a block which is provided with a through hole for aligning the stud 15a, having at the top a cylindrical guide wall 18 for the stud 15a and a punch 19 while being provided at the bottom with a cutting edge 20 with a clearance angle equal to zero. This cutting edge 20 has eventually a diameter which is slightly less than the diameter of the stud 15a and sligthly larger than the diameter of the hole 16. Actually, the tool is made of a material which is harder than the material of which is made the stud 15a. This material is on the other hand harder than the material of which is made the sheet 14. The height of the stud 15a is furthermore larger than the thickness of the sheet 14. The means of centering are not shown since they can be of any known kind. The same is valid for the fastening means which fasten the sheet 14 to the base 14a. On the contrary, it is important that the base is provided with an air hole 16a or that another kind of bleeding is established, e.g. by a hole through the stud. When the punch 19 is activated, the outer portion of the cylindric surface on the stud 15a will be skived off du- ring the downward movement. When the stud 15a comes into contact with the sheet 14, its diameter will still be slightly larger than the diameter of the hole 16 of the sheet 14 and, since the stud 15a has a higher hardness than the sheet 14, the continuing downward movement will result in skiving of the cylindrical surface of the hole 16, at the same time as the skived surfaces slide in di¬ rect contact to each other, in such way that both surfaces at no time have been uncovered or exposed, having in this way not been in contact with air. Further downward move- ment of the punch 19 will lead to the end position shown in fig. 5, where the diameter of hole 16 has increased be¬ cause the stud 15a had a larger height than the heigth of the hole 16. In this way, circular stresses have arised around the hole, which by due dimensioning can provide the pressure which is required to obtain a cold weld. It should be emphasized that it is important, at the same ti¬ me as a downward force is exerted on the punch in the fi¬ nal step, also to exert a resistance on sheet 14, e.g. by pressing the tool downward as shown by the arrows A and B. By so doing, the circular stresses required are obtained, and undesired deformation around the hole is avoided. For the same purpose, the surface of the tool can be provided with slots or grooves. At the bottom side of the sheet 14 will a ring 21 of chips be present, which may be removed by grinding or milling. One can also imagine a circular slot in the base designed for reception of the ring 21 which consists of swarf material. This ring will appear as a bulb which can be removed easily. In the tool 17, a ring 22 of loose swarf will be present. If desired the tool can be designed with outlet slots for the swarf. Finally, one can imagine that the mentioned centering of tool 17 rela- tive to hole 16 in sheet 14 is performed by providing the stud 15a with a downwards pointing protuberance which fits into the hole 16 in its original size. Fig. 6 shows a sheet 23 wherein a bushing 24 of another material has been welded. Such a sheet can be produced by using the tool shown in fig. 4 and 5, provided there is used a mandrel which fills out the hole in the bushing. Fig. 7 shows two sheets 25 and 26 laying upon each other, wherein a stud 27 has been welded, in the same way as in fig. 3, and which in this way actually keeps the two sheets together as a rivet would have done it. In this way, a new method for joining sheets has been shown, where no protuberances are present as when rivets are used. This can be of importance e.g. in aircraft designing. Fig. 8 shows a construction where two sheets 28 and 29 are held together by a bushing or a blind rivet for the pro¬ duction of which the same is valid as for the construction relative to fig. 6. Fig. 9 shows a construction where a tube end 31 is welded to a flange 32 of another and thicker material. Fig. 10 shows a tool for producing such a tube end with flange. The tool consists of a tool 33 as the one shown in fig. 4 and 5. Moreover are used a jaw 34, a mandrel 35 and a holder 36 with a hole 37 to accomodate the mandrel 35. The holder 36 is provided with a collar 38 to center the flange 32..The tool works in principle as the tool accor¬ ding to fig. 4 and 5. It should be pointed out, however, that if the tube end 31 is of a softer material than the flange 32, as it often will be the case if a hard flange is joined to a soft tube, it will be necessary to insert a ring on the mandrel 35 from below. This ring shall have the same inner and outer diameter as the tube 31 and a hardness which is higher than the hardness of the flange 32 and lower than the hardness of the tool 33. This ring is not shown on the drawing but it could e.g. fill the ring shaped cavity 39 which has in the main a quadratic section. This ring can also be imagined to be soldered to the tube end 31. Fig. 11 shows a section in a tool for joining together strips or ribbons, e.g. bimetallic strips, where a skiving tool 40 having in the main a triangular section is kept stationary, while a strip 41 is moved along one of the sides in the triangle and another strip 42 is moved along another side in the triangle in such way to produce skiving at the two corners of the triangle of the two surfaces on strips 41 and 42, which run together at the third corner 43 of the triangle. The movement is produced by continuously exerting a pull on the two strips 41 and 42 and the compression is obtained by using pressure surfaces 44 and 45 at the outer side of strips 41 and 42 along the two sides of the triangle. These pressure surfaces could be replaced by rolls, entirely or in part. Also, pushing instead of pulling can be envisaged, to produce the movement. Fig. 12 and 13 shall be considered together. The tool con- sists of a block 46, in which upper part is mounted a punch 47 guided for vertical movement in a through hole 48, which at the bottom runs out in a horisontal opening 49 . The position shown is a starting position where the punch 47 rests on a stud 50, which is cylindrical and which is to be pressed down into a hole 51 going trough four strips 52-55 which are to be joined together, and where the hole 51 is centered relatively to the punch 47. The punch 47 is designed at the top with a shoulder 56 which is supported by a pressure spring 57, which at the lower end is supported by another shoulder 58 in block 46. In the region where the punch 47 and the stud 50 are in mutual contact, a sliding plastic ring 59 is placed, embracing the upper part of the stud 50 and the lower part of the punch 47, respectively. At the lower end of the upper part of block 46 is mounted a skiving ring 60 having a hole 61 that has a diameter which is slightly less than the diameter of the stud 50 but slightly larger than the diameter of the hole 51 in the strips 52-55. In the lower part of block 46 is mounted an anvil 62 provided with air channels 63, 64 and 65. The anvil 62 is provided at its upper face with circular protuberances 66 to increase friction. Similar protuberances 67 are present on the bot¬ tom face of the skiving ring 60. The punch 47 is also pro¬ vided with an air groove 71. The tool works in the way that when the stud 50 has been pressed down into the hole 51, after a layer of its cy¬ lindrical surface has been skived off by the skiving ring 60 and after the stud 50, under the downward movement in the hole 51, has skived this latter internally before reaching the final position where cold welding takes pla- ce, on the punch 47 under the plastic ring 59 will be pre¬ sent a chip having the shape of a ring 68 as shown at the left top in fig. 13, where the punch has been taken out for removal of the ring 68 and of the plastic ring 59 in a specially made slot 69 having a slip off edge 70 providing the slipping off of the two rings 59 and 69 when the punch is pulled upward after it has been inserted from the side. After the punch 47 has been cleaned in this way, it can be mounted again in the tool together with a new plastic ring. A common hydraulic press, not shown here, can be used for the pressing operation. It shall be emphasised that, since speed plays a major role, it will be advanta- geous if the press works at a high speed. As it appears from the described embodiments of the inven¬ tion, there will be many possible areas of application for the invention, as well as there will be broad ranges for the machining which takes place before the surfaces to be cold welded are brought together. It can be the case of a regular cutting as explained according to fig. 1 and 2. It can also be the case of a peeling or an extrusion proper, if the conditions are of such kind that no real chip is formed. The important fact is of course to perform a treatment which results in formation of fresh metal sur¬ faces and that these surfaces in a sliding movement be kept covered until they, again in a sliding movement, are brought into mutual contact. In the explanation of the invention, general workshop pro¬ cedures as e.g. holding and centering have not been trea¬ ted in details. Using the method, in principle two possi¬ bilities exist for controlling the force which is necessa- ry to achieve a good weld. One can actually regulate the force by direct force measurement, e.g. by a hydraulic sy¬ stem of any known kind. Alternatively, one can also con¬ trol the force by dimensioning of the different parts with tolerances and predetermined strokes, i.e. obtaining a control by pure geometrical magnitudes. The use of the term "stud" througout the whole description must be understood broadly, since it can be the case of an insert, part of an insert, a bushing or a rivet like part. Also, the invention is not confined to through holes as shown in the examples. It will be possible to fasten the mentioned bushings and studs in a completely similar manner in blind holes. When it is stated, in claim 1, that the mutual movement of surfaces must have a component in the direction of a generatrix, this is due to the fact that the movement of the stud into the hole could be also imagined being performed as a helical movement.

Claims: C A I M S 1. Method for joining two or more parts of metal or metal alloys, perhaps of dissimilar kinds, by cold welding, where the parts have mating surfaces having a straight li¬ ne generatrix, where a skiving of the surfaces is perfor¬ med first and subsequently the surfaces are brought into mutual contact while a normal force is exerted between them, c h a r a c t e r i s e d by performing the skiv- ing of at least one of the surfaces and preferably of both surfaces by a movement of the surfaces having a component in the direction of the generatrix and by bringing with the same movement the surfaces further in sliding mutual contact using the sliding movement to cover at least one surface and preferably both surfaces. 2. Method according to claim 1, c h a r a c t e r i ¬ s e d by exerting a normal force on the contact surface already before the final position has been reached. 3. Method according to claim 1 or 2, c h a r a c t e ¬ r i s e d by the use, during the skiving, of one or more means known per se for improving a weld, e.g. heat, electrical current or inert gas, perhaps by performning a subsequent heat treatment. 4. Method according to claim 1, 2 or 3 and where one of the parts to be joined show a higher hardness than the o- ther part or parts, c h a r a c t e r i s e d by the use of the part having the highest hardness to skive the other part or parts, i.e. the part having the highest hardness is used as one of the tools. 5. Method according to claim 4 to fasten a stud into a hole, where the stud in the main is to fill out the hole, c h a r a c t e r i s e d by letting the stud have higher hardness than the material wherein the hole is placed. placing an external skiving tool over the hole, pressing the stud through the skiving tool and down into the hole, letting the stud receive a slightly larger section than the hole, i.e. a slightly larger diameter if both parts are circular, and letting the stud receive a sharp edge all the way round, and thereafter pressing or striking the stud and at the same time exerting a resistance on the ma¬ terial lying around the hole. 6. Method according to claim 5, c h a r a c t e r i ¬ s e by letting the stud have a height which is slightly larger than the height of the hole. 7. Method according to claim 5 or 6, c h a r a c t e - r i s e d by letting the hole pass through two or more overlaying sheets, holding the sheets in this position du¬ ring the operation. 8. Method according to claim 5, 6 or 7, c h a r a c - t e r i s e d by letting stud and hole be circular- cylindrical. 9. Tool according to claim 1 for joining two or more parts of metal or metal alloys, perhaps of dissimilar kinds, by cold welding, where the parts have mating surfa¬ ces having a straight line generatrix, where a skiving of the surfaces is performed first and subsequently the sur¬ faces are brought into mutual contact while a normal force is exerted between them, c h a r a c t e r i s e d by means to hold each part and means to bring the parts tow¬ ards or along each other in the direction of the genera¬ trix. 10. Tool according to claim 9, c h a r a c t e r i s e d by means to produce a normal force in the contact surface. 11. Tool according to claim 9 or 10, c h a r a σ t e - r i s e d by a skiving edge having a clearance angle which in the main is equal to zero. 12. Tool according to claim 9 to perform the method ac- cording to claim 8, c h a r a c t e r i s e d by the skiving edge having the shape of a ring, perhaps a split ring. 13. Tool according to claim 12, c h a r a c t e r i s e d by its consisting of a block provided with a through hole to guide the stud, and having at one end of the hole a circular skiving edge and at the opposite end of the hole a guide edge and between these edges a cavity for accomodating excess material, e.g. swarf, if desirede provided with channels for swarf disposal, and the other end of the hole being designed to accomodate a punch. 14. Tool according to claim 13, c h a r a c t e r i ¬ s e d by the punch being removable and the opposite end with the guide edge for the stud, i.e. the end at which the punch is acting, being designed as a sliding ring, e.g. of plastic, which in the starting position is embracing the punch as well as the stud in the region where these are mounted against each other and which is guided concentrically around punch and stud.

Inventors: DE CHIFFRE LEONARDO, DE CHIFFRE, LEONARDO
Applicants: CHIFFRE LEONARDO DE, DE CHIFFRE, LEONARDO
Application year: 1987
Main classification: B23K20
IPC codes: B23K20