A METHOD OF ACCURATELY JOINING TOGETHER TWO SHEET SECTIONS

Abstract: By a method for accurately joining together two sheet sections (1, 2) along edges (3, 4) thereof having complementary shapes, the edge of at least one sheet section is formed by means of a numerically controlled machine with the sheet section fixed in a fixture by moving a cutting member relative to the sheet section according to a predetermined path or curve. The complementary edges (3, 4) of the two sheet sections are then made to abut each other. The two sheet sections are subsequently welded together in a numerically controlled machine, said one sheet section being fixedly retained in said fixture and the knowledge of the path used during cutting is used to determine the path of the welding means at the welding of the sheet sections. The complementary edges (3, 4) are arranged in at least one projecting area (5) on a first sheet section (1) and the complementary areas have interlocking shapes, preferably trapezoidal, for preventing a mutual displacement of the sheet sections at least in directions parallel to the surfaces thereof.

Description: Title: A method of accurately joining together two sheet sections Technical Field The invention relates to a method of accurately joining together two sheet sections along edges of said sheets having complementary shapes, and wherein the edge of at least one she t section is formed by means of a numeri¬ cally controlled machine with the sheet section fixed in a fixture by moving a cutting member relative to the sheet section according to a predetermined path, where¬ after complementary edges of said two sheet sections are made to abut each other and the two sheet sections are welded together in a numerically controlled machine, said one sheet section being fixedly retained in said fixture and the knowlegde of the path used during cut¬ ting is used to determine the path of the welding means at the welding of the sheet sections . Backgrond Art In the fabrication of motor vehicles a method of the above type is known, whereby a trimming of the edge of a first sheet section is carried out in a numerically con¬ trolled laser cutting/welding machine, said first sheet section being fixedly retained i..ι a fixture, whereafter a second sheet section, which is also fixed in the said fixture, is cut along an edge and the two edges are brought into abutment for a subsequent welding together of the sheet sections. The fixture used at said method is very strong and comparativel ' complicated construc¬ tion. German patent No. 1.119.057 discloses joining of two metal strips by forming a dovetailed protrusion in the first strip and forming a complementary tab in the se¬ cond strip, which are subsequently brought into engage¬ ment with each other. The two sections are then con¬ nected by means of welding, for instance by resistance spot welding. The object is to hold the ends of the two strips together to form a coherent strip at a subsequent processing thereof. Finally, from US-A 3,091,844 it is known to provide the ends of strips of metal with complementary dovetailed protrusions and tabs for keeping the strips together during a subsequent compression of the joint and in a subsequent processing in a roller. Thus, no accurate joining of sheet parts is disclosed. Disclosure of Invention The object of the invention is to provide a method of the type stated in the introduction enabling an accurate weld joint of sheet sections by means of more simple fixtures than hitherto. The method according to the invention is characterised in that the complementary edges are arranged in at least one projecting area on one sheet section and in a com¬ plementary area on the other sheet section, and the two complementary areas have interlocking shapes for preven¬ ting mutual displacement of the sheet sections at least in directions parallel to the surfaces thereof in the joint area. Due to the accurate geometrical interlock¬ ing, the stress produced by the heat during welding are absorbed by the inter-gripping areas of the sheet sec¬ tions. As the sheet sections thus merely are to be con— trolled transversely to their surface, much simpler and thinner fixtures may be used than hitherto. At the same time, the accurate geometrical interlocking ensures that a minimal and accurate joint gap is maintained between the sections. As a result, very smooth welds are ob¬ tained without the use of filler materials. Consequent¬ ly, most advantageously only minimal or no further machining of weld seam is necessary. In order to obtain a weld seam requiring very little or no further machin¬ ing, the sheet sections have to be cut out with such an accuracy that the width of the gap between the comple¬ mentary edges does not exceed 0.2 mm and preferably are less than 0.1 mm. To obtain such tolerances it is advan¬ tageous to carry out machining in a combined laser cut¬ ting and welding machine. It is, however, evident that also other cutting and welding methods having the re¬ quired accuracy may be used, such as plasma cutting and water jet cutting. Beside laser welding other welding methods may be used, such as electron beam welding and plasma welding. According to the invention the edge faces or cut faces of the edges may be arranged on mutually complementary cylinderical faces, whereby the sheet section are brought into engagement by a movement along the axis the cylindrical faces, in which directi.on no geometrical interlocking of the two sheet sections will take place. According to another embodiment of the invention, when the sheet sections are plane in the joint area the edge faces may advantageously be perpendicular to the surface of the sheet sections in the joint area. This embodiment provides many possibilities of variation, as regards the method of production of the other sheet section, as this for instance may be punched. Moreover, according to the invention the angle of the edge faces relative to the surfaces of the sheet sec¬ tions may vary complementarily to each other along the edges. When the angle of the edge face is not perpen¬ dicular to the surfaces of the sheet sections, the de¬ viations from perpendicular may advantageously be appro¬ priately minor ones, whereby the subsequent welding (for instance laser welding) may be carried out by means of a beam essentially perpendicular to the surface by means of a single run. The most advantageous width of the beam should thus be taken into consideration when selecting the deviations from perpendicular. Furthermore, in this connection the angle of the edge faces may according to the invention vary relative to the surface of the sheet sections with appropriate minor positive and negative deviations from perpendicular en¬ abling the edges of the two sheet sections to engage in— terlockingly. As a result, by selecting the appropriate size and position of the positive and negative devia¬ tions from perpendicular along the egdes of the sheet sections, a complete fixation of the sheet sections re¬ lative to each other in a direction perpendicular to the surfaces thereof in the joint ar.ea is obtained. The use of- a fixture for positioning of the two section relative to each other during welding may thereby be avoided, at least theoretically. Moreover, according to the invention, the projecting area may be T—shaped or trapezoidal. In practice, this embodiment has produced very advantageous results . In this connection, according to the invention the edge portion of the projecting trapezoidal area corresponding to the long base line of the trapezoidal portion may have an egde face forming a positive angle relative to the surface of the sheet section, while the edge portion of the sheet section forming an extension of the short base line of the trapezoid may have an edge face forming a negative angle relative to the surface of the sheet section or vice versa. As a result, it is possible by means of a pivot movement about a line intermediate the lines corresponding to the two base lines of the trape- zoid to bring the sheet section into interlocking enga¬ gement, whereafter merely a mutual fixation of the sheet sections against being pivot in the opposite direction of the engagement movement is necessary to hold the sec¬ tion together accurately. Finally, according to the invention the edge portion of the projecting trapezoidal area corresponding to the long base line of the trapezoidal portion may have an edge face having portions of both a positive and a nega¬ tive angle relative to the surface of the sheet section, and the edge portion forming an extension of the short base line of the trapezoid may likewise have an edge face having portions of both a positive and a negative angle relative to the surface of the sheet section. This embodiment is particularly advantageous as regards an approximately completely fixation of the two sheet sec¬ tions relative to each other. Brief Description of the Drawings The invention is described in greater detail in the fol¬ lowing with reference to accompanying drawings, in which Fig. 1 is a top view of a first joint of two sheet sec¬ tions obtained by means of the method according to the invention, Fig. 2 is a top view of a second joint obtained by means of the method according to the invention, Figs. 2a-c are sectional views along the lines AA , BB , and CC in Fig . 2 , Fig. 3 is a top view of a third joint of two sheet sec¬ tions obtained by means of the method according to the invention, Fig. 4 illustrates how the two sheet sections forming the joint of Fig. 3 are brought into engagement with each other, and Fig. 5 is a top view of an example of weld of two sheet sections obtained by means of the method according to the invention. Best Mode for Carrying Out the Invention The following explanation of the method according to the invention is based on a joint of two sheet sections which at least in their joint area are plane in order to make the explanation and illustration of the provided joints more simple. Furthermore, it is presumed that the e-thod is carried out out by means of a numerically con¬ trolled (CNC controlled) laser cutting/welding machine, it being implicit that as previously mentioned other methods may be used for the cutting and welding provided that these are carried out by means of numerical con¬ trol. With reference to Fig. 1, the edge (3) of a first sec¬ tion (1) is cut by means of a numerically controlled laser cutting/welding machine, the section (1) being fixedly retained in a fixture (not shown) . A second sheet section (2) is then made having an edge (4) corre¬ sponding to the edge -(3), that is to say it is comple¬ mentary to said edge. The cutting of the edge (4) on the sheet section (2) may be carried out by means of any known method. The edge (3) of the first sheet section (1) is cut according to such a path that the sheet sec¬ tion (1) is provided with at least one T-shaped or tra¬ pezoidal projecting area (5) . Consequently, the second sheet section (2) has a complementary area. Furthermore, the edges (3,4) of the sheet sections (1,2) are cut in such manner that the edge faces thereof are perpen¬ dicular to the surface of the sheet sections (1,2) and complementary to each other. The thus completely complementary edge portions of the sheets are made to engage each other with abutting edge faces by a movement perpendicular to the surface of the paper shown in Fig. 1. Due to the interlocking shape of the edges, any mutual displacement of the sheet sections (1,2) in the common plane thereof is prevented, when the edges (3,4) have been brought into engagement with each other, whereby only a fixation of the sheet section (2) relative to the sheet section (1) is necessary in the mentioned direction perpendicular to the surface of the paper. Subsequent to such a fixation of the sheet sec¬ tion (2) relative to the sheet section (1) , the two sheet sections (1,2) are welded together, the sheet sec¬ tion (1) still being fixedly retained in the fixture used for cutting the edge (3) . The welding may be car- ried out by moving a welding member along the same path used for cutting the edge (3) , the tool offset, however, being taken into consideration. By carrying out the wel¬ ding in the same setup as during cutting and by taking the path used at the cutting into consideration, a very accurate weld of a high quality is obtained. As illustrated in Fig. 5, alternatively to using exactly the same path (including the tool offset) at the welding as at the cutting, three runs may be used during the welding. At the first run or passage PI a wave-shaped weld is produced, whereby the edge portions of the tra¬ pezoidal projection (5) forming the faces (7,8) of the trapezoid, is welded together with the complementary edge portions (9,10) of the sheet section (2). At the second run or passage P2 the edge portions (15) on pro¬ jecting trapezoidal area (5) of the sheet section (1) corresponding to the long base line of the trapezoid are welded together with the complementary edge portions (16) of the second sheet section (12) . At the third run or passage P3 the edge portions (11,12) of the sheet section 81) forming an extension of the short base line of the trapezoid are welded together with the complemen¬ tary edge portions (13,14) of the complementary edge of the sheet section (2). By using all of the three runs or passages P1-P3 a com¬ plete welding of the abutting edges (3,4) of the two sheet sections (1,2) is obtained, as shown by means of the dotted line in Fig. 5. The use of the mentioned three runs is advantageous in that sharp turns in the welding path are avoided, and in some cases a higher welding rate may be obtained. If the distance between the welding paths P2 and P3 is small, that is to say that the height of the trapezoidal projection is low, the wave—shaped run PI may be omitted. Fig. 2 illustrates an alternative joint made by means of a method according to the invention. At this joint the sheet sections (21,22) are provided with edges (23,24), in a top view having a shape corresponding to the edges shown in Fig. 1. However, the inclination of the edge faces of the edges (23,24) of the sheet sections (21,22) varies along the edges (23,24) , when seen relative to the surface of the sheets. The trapezoidal projection (25) of the sheet section (22) is provided with an edge area (38) at the edge (35) corresponding to the long base line of the trapezoid, in which edge area the edge face of the sheet section (22) forms an angle (αl) of more than 90° with the surface (39) of the sheet sec¬ tion, as shown in Fig. 2a, and an edge area, wherein the edge face (40) forms an angle (α2) of less than 90° , as shown in Fig. 2c. In an area between said two edge face areas (38, 40) a transition area (41) is provided, whe¬ rein the edge face is perpendicular to the surface (39= of the sheet section. Expressed differently, in the edge portion corresponding to the long base line (35) of the trapezoidal projection (25) the sheet section (21) is thus provided with an edge face area (38) , wherein the edge face extends be¬ neath the second sheet section (22) (Fig. 2a) , an area, wherein the edge face (41) is perpendicular to the sur¬ face (39) of the sheet section (21) (Fig. 2b) , and an edge face area (40) , wherein the edge face (42) of the second section (22) extends beneath the first sheet sec¬ tion (21) (Fig. 2c) . The angles αl and α2 are such that the sheet sections (21, 23) by being pressed together on the surface (39) , that is to say perpendicular to the surface of the paper in Fig. 2, may be brought into engagement with each other by means of a snap effect in said areas having varying edge face angles. As suggested in Fig. 2 areas having varying edge face angles may be provided in the edge areas of the sheet sections (21,22) corresponding to an extension of the short base line of the trapezoidal projection (25) . This embodiment is shown in Fig. 2 by means of dotted lines in said areas . The edge areas having varying edge face angles enable a complete interlocking and fixation of the two sheet sections relative to each other without the use of further fixtures. The joining principle shown may thus per se be used for joining or holding together sheet sections, or as in the present case be used for accurate fixation of the sheet sections prior to a subsequent finishing of the joint by means of welding (in this case laser beam welding). Figs. 3 and 4 illustrate a further embodiment of joining together two sheet sections (51,52) along the edges (53, 54) provided with a shape as shown in Figs. 1 and 2, the sheet section (51) being provided with an essentially trapezoidal projection (55) and the sheet section (52) being provided with a complementary area. The joint illustrated in Fig. 3 differs from the pre¬ viously mentioned joints by the sheet section (51) in the area corresponding to the long base line of the tra¬ pezoidal projection (55) being provided with an edge area (65) , wherein the edge face forms an angle of more than 90° with the surface of the sheet section (51), that is to say that the edge face extends beneath the surface (70) of the sheet section (52) in the area (65) . Correspondingly, in the areas (61,62) corresponding to an extension of short base line of the trapezoidal pro¬ jection (55) the sheet section (51) is provided with edge face areas , wherein the edge face forms an angle of less than 90° with the surface (69) of the sheet section (51) , that is to say the complementary edge face areas (63,64) of the sheet section (52) extend beneath the sheet section (51) . This is illustrated by means of the dotted line in Fig. 3, showing the corner between the lower surface of the sheet sections and the edge faces, the fully drawn line shows the corner between the upper surface (69,70) of the sheet sections and the edge fa¬ ces . Fig. 4 illustrates how the two sheet sections (51,52) is brought into mutual engagement by the projection (55) of the sheet section (51) being brought into engagement with the complementary area of the sheet section (52) in the direction of the arrow shown in A, and then pivoting the sheet section (51) relative to the sheet section (52) , as shown by means of the arrow in B, whereby the sheet section (51) is brought into the same plane as the sheet section (52) , as illustrated in C of Fig. 4 corre- sponding to the illustration of Fig. 3. Subsequent to engagement, the two sheet sections (51,52) can only be disengaged by being pivoted and displaced in the opposite direction of the direction shown in A to C of Fig. 4. The engagement or joint is thus self-locking in relation to a load in the first direction perpendicu¬ lar to the plane of the sheets, that is to say in a di¬ rection from beneath and upwards in illustration C of Fig. 4 and in a direction upwards of the surface of the paper in Fig . 3. Thre method according to the invention may be used for joining sections of a plurality of various sheet mate¬ rials, such metal and in particular steel sheets, and of various thickness, in particular thin sheets. The use of a C0 2 laser is considered particularly advan- tageous carrying out the method according to the inven¬ tion. A laser of 1 to 3 kw is perferred for producing sheet parts of a thichness of up to 2 to 4 mm.

Claims: Claims 1. A method of accurately joining two sheet sections together (1, 2 ; 21 , 22 ; 51, 52) along edges (3 , ; 23 , 24; 53 , 54) of said sheet sections having complementary shapes , and wherein the edge of at least one sheet section is formed by means of a numerically controlled machine with the sheet section fixed in a fixture by moving a cutting member relative to the sheet section according to a pre¬ determined path or curve, whereafter the complementary edges of the two sheet sections are made to abut each other and the two sheet sections (1, 2 ; 21, 22 ; 51, 52) are welded together in a numerically controlled machine, said one sheet section being fixedly retained in said fixture and the knowlegde of the path used during cut— ting is used to determine the path of the welding means during welding of the sheet sections c h a r a c t e ¬ r i s d in that the complementary edges (3,4; 23, 24; 53,54) are arranged in at least one projecting area (5; 25; 55) on one sheet section and in a complementary area on the other sheet section, and the two complementary areas have interlocking shapes for preventing mutually displacement of the sheet sections (1,2;21,22; 51,52) at least in directions parallel to the surfaces thereof in the joint area. 2. A method as claimed in claim 1, c h a r a c t e ¬ r i s e d in that the edge face or cut face of the edges (3,4) are arranged on mutually complementary cy- linderical aces . 3. A method as claimed in claim 2, c h a r a c t e — r i s e d in that the edge faces are perpendicular to the surfaces of the sheet sections (1,2) in the joint area. 4. A method as claimed in claim 1, c h a r a c t e ¬ r i s e d in that the angle (αl, α2) of the edge faces (38,41, 40) relative to the surfaces (39; 60,70) of the sheet sections varies complementary to each other along the edges (23 , 24 ; 53 , 54) . 5. A method as claimed in claim 4, c h a r a c t e ¬ r i s e d in that the angle (αl, α2) of the edge face relative to the surface (39) of the sheet sections va¬ ries with appropriate minor positive and negative devia- tions from perpendicular enabling the edges (23,24) of the two sheet sections (21,22) to engage interlockingly . 6. A method as claimed in one or more of the preceed- ing claims . c h a r a c t e r i s e d in that the pro¬ jecting area (5,25,55) is T-shaped or trapezoidal. 7. A method as claimed in claims 4 or 6, c h a r a c¬ t e r i s e d in that the edge portion (65) of the pro¬ jecting trapezoidal area (55) corresponding to the long base line of the trapezoidal portion is provided with an edge face forming a positive angle relative to the sur— face (69) of the ' sheet section, while the egde portion (61, 62) of the sheet, section forming an extension of the short base line of the trapezoid is provided with an edge face forming a negative angle relative to the sur¬ face (69) of the sheet section or vice versa. 8. A method as claimed in claim 5 or 6, c h a r a c ¬ t e r i s e d in that the edge portion (35) of the pro¬ jecting trapezoidal area (25) corresponding to the long base line of the trapezoidal portion is provided with an edge face having portions (38) of both a positive and a negative (40) angle (αl, α2) relative to the surface (39) of the sheet section, and the edge portion (31,32) forming an extension of the short base line of the tra-

Inventors: OLSEN FLEMMING, OLSEN, FLEMMING
Applicants: INST PRODUKTUDVIKLING, INSTITUTTET FOR PRODUKTUDVIKLING
Application year: 1993
Main classification: B23K33
IPC codes: B23K26, B23K33