METHOD AND APPARATUS FOR WELDING THIN SHEETS

Abstract: The invention relates to a method and an apparatus for welding thin sheets, whereby thin sheets (34) and (35) are joined at the holes by fusing the sheets together by means of a rotating electrode (23) and electric current in protective gas. The sheets (34) and (35) are pressed together by means of copper rings (32) and (33) which also function as coolers and conduct the heat from the welding point and thus prevent changes in shape. The electrode (23) is adjusted to the right vertical position by a guide (9) and a jig (7), and it is locked to the position determined by the sheets (34) and (35) by means of a clamp (31).

Description: Method and apparatus for welding thin sheets The invention relates to a method and an apparatus for joining thin sheets at the circumferences of circular holes. In the method of the invention no filler metal is used, instead the joint is welded by fusing the thin sheets together. The welding apparatus of the method comprises a welding machine, a welding jig, a rotating welding head and necessary means for gas supply, and a power source. Electric welding methods for joining thin sheets are previously known. Such methods include e.g. spot and projection welding. In these methods the sheets are pressed against each other and a current is allowed to pass through the pressure point, whereby the melting of metal is sufficient for the joining. A disadvantage of spot welding is e.g. that the joints are spot-like. This means that e.g. water-proof or gas-proof seams, a prerequisite for pressure vessel or like e.g. heat- exchanger structures, cannot be made. The use of projection welding for joining the edges of circular holes requires expensive equipment. Further, as pressure vessels are concerned, the above methods do not usually provide a sufficiently even and strong joint. Welding and brazing methods using various filler metals, e.g. in the form of rods or strip, have been applied to joining the edges of holes in thin sheets. Even in these cases the cost of equipment and tools easily rises so that these methods cannot be used when small series are manufactured. The quality of the seam may also be inferior when filler metal is used. The seam becomes unequal in thickness and uneven. Additional problems may arise regarding penetration. Distortion of thin sheets in connection with welding is also a problem which is very difficult to control. Even with modern methods, joining thin sheets by welding has proved rather problematic in several cases. The lack of suitable equipment and methods has resulted e.g. in frequent use of mechanical joining means, such as screws, rivets or the like in joining thin sheets. The main problems in welding together thin sheets are changes caused by thermal stress, which change the shapes of the structures. Another major problem has been that in thin sheet work it is difficult to control the melt, which has resulted in low-quality and unsatisfactory seams. Exact allocation of heat has also been problematic in several welding methods. Wrong allocation of heat results in possible melting and sagging of metal, and therefore in an inferior seam. In methods being used, elimination of generated heat has not been sufficient, and therefore it has been necessary to limit e.g. the strength of the current very strictly. With the method and apparatus of the invention decisive improvement to the above problems and shortcomings is achieved. The method and apparatus of the invention are characterized by what is set forth in the attached claims. The main advantage of the method and apparatus of the invention may be considered to be its applicability to joining thin sheets at a hole irrespective of material. When thin sheets are joined by the method of the invention, they remain completely straight, and there are no changes caused by thermal stress. The seam produced by the method and apparatus is first-class and is suitable for use in e.g. pressure vessels. It is a further advantage that no filler metal is needed in the welding; an adequate quantity of the parent material is melted to ensure that the resulting seam is sufficiently strong. The seams of the invention do not sag, as excess heath is efficiently led off the welding area. On the basis of the above the resulting melting zone is so narrow that sagging problems do not occur. The apparatus and method of the invention may easily be automatized, and the method is particularly well adaptable to mass production. In the following the invention will be described in greater detail with reference to the accompanying drawings. Figure 1 is a side view of a welding machine. Figure 2 is a side view and a partial cross section of a welding head in the initial position. Figure 3 is a side view and a partial cross section of a welding head in the welding position. In Figure 1, numeral 1 refers to a welding machine. A leg of the welding machine is denoted by numeral 2 and a mobile clamp thereon by numeral 3. The clamp is connected to a platen 4. A shank of the platen is denoted by numeral 5 and a joint by numeral 6. A welding jig is denoted by numeral 7 and guides thereon by numerals 8 and 9. Numeral 10 denotes a welding head and numeral 11 a cooler. A fitting for incoming water for the cooler 11 is denoted by numeral 12 and a discharge fitting by numeral 13. Numeral 14 denotes a protective gas conduit and numeral 15 a vertical axle. A switch 16 and an electric motor 17 rotate the vertical axle 15. The welding head 10 is raised and lowered by means of a pneumatic cylinder 18 whose shank 19 is connected via a bar 20 to the axle 15 and the welding head 10. In Figures 2 and 3 the numeral 21 refers to a junction ring coupled to the cooler 11. The welding head 10 comprises a nozzle 22 with an electrode 23 in the middle, the location of the electrode being adjusted by a screw 24. A disciform part 25 is attached to the lower portion of the axle 15, and the part is connected to the axle 15 with a ball bearing 26. A round hole 27 has been milled to the jig 7 and the guide 9 has been fitted therein so that it rises and descends down to the jig level. The guide 9 comprises springs 28, placed in holes 29, to keep it in the upper position. The guide 9 comprises a recess 30 in the middle, the recess being of the size of the cylindrical member 25. The member 25 descends in the recess and simultaneously presses the guide 9 to the level of the jig 7. As the cylinder 25 is vertically lockable to axle 15 by means of a clamp 31, it may be used to adjust the vertical position for the electrode 23 of the welding head 10. The welding method of the invention is applied in the following manner. The holes in the sheets to be joined are placed one on the other by means of the guides 8 and 9. The vertical position of the electrode 23 of the welding head 10 is adjusted according to the seam between sheets 34 and 35. The cylindrical member 25, which positions the electrode 23, is aligned by means of the clamp 31. When the sheets 34 and 35 to be joined have been placed one on the other by means of the guides 8 and 9, at the holes, the cooler 11 is pressed by means of the pneumatic cylinder 18 against the jig 7. The welding head 10 inside the cooler glides in place, and the cylindrical member descends into the recess 30. The vertical position of the electrode 23 is at this time exactly between the sheets 34 and 35. Hereafter current is switched on to the electrode 23 and the axle 15 is rotated round, and simultaneously protective gas is supplied through the axle 15 via its inner part from the conduit 14, resulting in an oxygen-free state at the welding point, and the seam may be made. A copper ring is attached to the lower surface of the cooler 11. Similarly, the upper surface of the jig 7 comprises a copper ring 32, and the sheets 34 and 35 to be joined are between these cooling rings 32 and 33, pressed closely together. The heat generated in the welding is led into the copper cooling rings 33 and 32, and from there it is conducted by conduction into the cooler 11, thus enabling adequate prevention of sagging of the melt generated in the seam. Once the welding head 10 has rotated round about one turn, it may be lifted together with the cooling portion, and the welding seam is complete. Dissipation of heat generated in welding results ,in e.g. the welded pieces being immediately workable, and the heat remaining in them causes no changes in shape. It is clearly understood that the applications of the method of the invention are numerous. The method may be applied to joining various materials. The protective gases used in the welding may also vary. The apparatus used for implementing the method of the invention and its mechanisms may also vary quite widely. The cooler 11 may have a different type of physical form than is disclosed in the application. The shape of the welding head may also be modified within the scope of the inventive idea.

Claims: Claims 1. A method for welding superimposed thin sheets at the circumferences of circular holes without filler metal by melting the seam by means of an electrode with electric current, by protecting the melt from oxidation by means of protective gas or the like and by cooling the welding area by means of copper supports, c h a r a c t e r i z e d in that the sheets to be joined are pressed together by means of copper or corresponding annular supports situated round the circumferences of the holes to be welded, said supports preventing the changes caused by thermal stress and the sagging of melt metal, and leading the heat generated in welding off the welding area. 2. A welding apparatus for use in a method for « welding thin sheets, comprising a welding machine (1), a welding jig (7), a rotating welding head (10), gas means and a power source, c h a r a c t e r i z e d in that the cooler (11) of the welding seam is a double- casing cylinder with a copper ring (33) attached to its lower surface, that inside the double-casing of the cooler (11) circulates cooling material, liquid or the like, and that the said cooler (11) functions as a clamp for the copper rings (33) and (32), and is controlled by a cylinder (18) or the like. 3. An apparatus as claimed in claim 2, c h a r a c t e r i z e d in that to adjust an electrode (23) in the right vertical position in relation to sheets (34) and (35) to be joined, a rotating cylindrical member (25), adjustable vertically by means of a clamp (31), has been attached to the lower end of an axle (15) which rotates the electrode (23), said member (25) bearing on the base and walls of a recess (30) of a guide (9), which guide (9) bears on the base and walls of a hole (27) in the jig (7) during welding. 4. An apparatus as claimed in claim 2, c h a r a c t e r i z e d in that the axle (15) functions as a rotating member for the welding head ( 10) and as an input tube for protective gas. 5. An apparatus as claimed in claim 2, c h a r a c t e r i z e d in that the distance of the electrode (23) from the seam is adjusted by means of a screw (24), and that a nozzle (22) may be adjusted in the direction of the radius. 6. An apparatus as claimed in claim 2, c h a r a c t e r i z e d in that the guide (9) has been arranged to descend inside the jig (7) during welding and to rise by means of springs (28) in the initial position.

Inventors: PIRILA TIMO MAUNO, PIRILAE, TIMO, MAUNO
Applicants: PIRILAE TIMO MAUNO, VAHTERUS OY, PIRILAE, TIMO, MAUNO
Application year: 1995
Main classification: B23K37
IPC codes: B23K9, B23K11, B23K37