Structural assembly of welded parts

Abstract

The invention relates to a structural component comprising two components welded to one another, a first component consisting of a casting material and a second component consisting of a hardened steel, both components being rotatable about an axis of rotation, at least one component being machined on a respective flange surface, according to the invention, the two parts are connected to each other in such a way that a circumferential weld groove between the two parts is defined when the two parts converge on the respective flange surfaces, into which weld groove an austenite melt connecting the two parts in a cohesive manner is introduced, the weld groove being formed asymmetrically between the two parts by removing material only from the flange surface of the second part, and the weld groove being formed asymmetrically between the two parts by removing material only from the flange surface of the second part. Or more material is removed from the flange surface of the second part in the width direction of the weld groove than from the flange surface of the first part, and an exhaust space is arranged in a stepped arrangement along the axial direction of the rotation axis and behind the weld groove, a release is provided in a further axial stepped arrangement along the axis of rotation and behind the exhaust space.

Description

TECHNICAL FIELD

[0001] The invention relates to a structural assembly for the welding of a first component composed of a cast material to a second component made of case-hardened steel, wherein at least one of the components is partially machined on a respective flange face before the welding, such that a circumferential weld preparation is formed between the first component and the second component when the two components meet on the respective flange faces, and the two components are welded to one another after the meeting with the supply of additional material and under the action of a welding beam. BACKGROUND

[0002] Such a structural assembly is employed in particular in the field of axle reduction gears of motor vehicles, which then consist of a differential housing which guides the balance wheels and a crown wheel which is fixed on the differential housing. On the basis of the fact that the connection between the crown wheel and the differential housing forms a highly stressed connection here and the crown wheel is usually made of case-hardened steel on account of the wear resistance, while the differential housing is made of cast steel as a cast component, a screw connection is usually prescribed in this field. Since on account of the high carbon content in the cast component, the welding of the two components leads to an increased risk of brittle fracture under the action of loads.

[0003] However, by employing modern welding methods, for example laser welding, it becomes possible to weld the components such that the joining faces of the components are melted only to a relatively small depth. In this modern welding method, therefore, only a relatively small amount of carbon is alloyed into the weld. Furthermore, an additional material is usually employed as a welding wire, which is usually in the form of a nickel-containing additional material, by means of which brittle tissue components are prevented from the solidifying weld, which additionally reduces the risk of crack formation and thus of brittle fracture. Furthermore, in some welding methods, the surfaces to be welded to one another are pretreated before the welding, such that the melting of the joining faces is positively influenced when welding.

[0004] A method for welding a first component composed of a cast material with a second component made of case-hardened steel is known from DE 10 2011 077 562 A1. Here, the first component is a differential housing of a motor vehicle's axle reduction gear, to which a crown wheel constituting the second component is connected in the context of the welding process. Both components here have a flange face each, onto which the two components converge in order to be positioned in a position to be welded. The flange face of the differential housing is here partly machined such that, when the flange faces converge, a circumferential weld gap between the crown wheel and the differential housing is defined therebetween. The two components are welded to one another with a supply of welding wire and under the action of a welding beam, at which time a melt of austenite is formed in the weld gap, which, when hardened, lockingly connects the two component materials to one another. The melt here is composed in such a way that, in particular, a connecting tab of a root region of the weld gap defined on the first component and a portion of the flange faces defining the flanking faces of the weld gap are melted by the welding beam, which, when solidified, produces a weld seam that lockingly connects the two component materials to one another. SUMMARY

[0005] Starting from the prior art described above, it is the task of the present application to provide a structural assembly by welding the two aforementioned components, which has a low risk of brittle fracture.

[0006] The task is solved by a structural assembly which comprises two mutually welded components, of which the first component is composed of cast material and the second component is composed of case-hardened steel, the components being rotatable about an axis of rotation, at least one of the two components being machined on a respective flange face in such a way that, when the two components meet on the respective flange faces, a circumferential weld gap is defined therebetween into which a melt of austenite for the material-locking connection of the two components is introduced, the weld gap being formed asymmetrically between the components in such a way that material is removed only from the flange face of the second component or in such a way that more material is removed from the flange face on the second component than from the flange face on the first component in the width direction of the weld gap, a venting space being additionally provided in a stepped arrangement in the axial direction along the axis of rotation A and behind the weld gap, and a release being provided in a further stepped arrangement in the axial direction along the axis of rotation A and behind the venting space. Here, the cast material is advantageously a differential gear housing for a drive train of a vehicle, which can have a classic internal combustion engine, a known hybrid drive or also an electric motor as drive device. The second component welded to the first component can be a crown wheel or also a cylindrical gear in order to be able to transmit torque from the drive device to the differential gear housing. If the two components, i.e. the differential gear housing and the crown wheel / cylindrical gear, are now welded to one another, strong stresses can occur in the respective flange faces since the weld contracts after cooling. In order to reduce such stresses on the respective flange faces, the respective flange faces are constructed as unstably as possible so that the stresses in the flange can be compensated by elastic deformation. It has proven here that the release behind the weld and the venting space in the stepped arrangement in the axial direction additionally destabilizes the flange and thus enables elastic deformation. Here, the release can be provided not only on the flange of the differential gear housing or on the flange of the crown wheel / cylindrical gear but also on both flanges.

[0007] In addition, the release can be realized by an axially extending material removal on one of the two flange faces or on both flange faces. This can advantageously be realized by a cutting method, for example turning.

[0008] Here, the axial extension (y) of the release can be 0.5 to 3 times the length of the weld.

[0009] Advantageously, the weld gap and the release are spaced equally or almost equally from the axis of rotation A.

[0010] In addition, the axial extension of the venting space can be between 3 mm and 5 mm.

[0011] The corresponding flange surfaces of the first component and / or the second component can also be processed in such a way that they form a respective portion of the U-shaped weld seam.

[0012] The corresponding flange surfaces of the first component and / or the second component can also be processed in such a way that they form a respective portion of the Y-shaped weld seam.

[0013] In this case, the first component may be a differential case of an axle reducer, to which the crown gear / spur gear forming the second component is welded.

[0014] Furthermore, the ventilation space can be formed by a respective circumferential undercut on each associated flange surface.

[0015] In this case, the weld groove between the two components can extend in a directional manner in the axial direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Other advantageous solutions of the present invention are obtained from the following description of preferred embodiments of the present invention with reference to the figures shown in the accompanying drawings.

[0017] Figure 1 A sectional view showing the assembly according to the invention according to a preferred embodiment of the invention;

[0018] Figure 2 Displayed on the Figure 1 Detailed drawings in the area of ​​weld grooves of structural components;

[0019] Figure 3 A detailed view of a weld groove showing an alternative embodiment of the present invention; and

[0020] Figure 4 A detailed view of a weld groove showing another alternative embodiment according to the present invention. DETAILED DESCRIPTION

[0021] Depend on Figure 1 A cross-sectional view of a component according to a preferred embodiment of the present invention is shown, which is an axle reduction gear 1 for a motor vehicle. Axle reduction gear 1 comprises a first component in the form of a differential case 2, which is made of a cast material, preferably cast steel in the form of gray cast iron, and accommodates further components of axle reduction gear 1, which are not described in detail here for the sake of clarity. As those skilled in the art will be aware, the differential case 2 carries two bevel balancing gears on the differential pins. These bevel balancing gears mesh with bevel axle gears of the axle shafts, which are oriented orthogonally to the bevel balancing gears. The rotational movement of the differential case 2 is transmitted either evenly to the two axle shafts or, in the case of compensating movements, unequally to the two axle shafts.

[0022] A second component in the form of a crown wheel or spur wheel 3 is mounted on the outer region of the differential housing 2, is made of case-hardened steel and is preferably shrink-fitted to the differential housing 2. The steel of the crown wheel / spur wheel 3 is in particular case-hardened steel which is carbonized in the edge region of the crown wheel / spur wheel 3 in the context of a case-hardening process in order to increase the welding resistance and the loadability in the edge region and at the same time to preserve a soft and tough core. Here, the crown wheel / spur wheel 3 is mounted to a flange face 5 of the differential housing 2 with a flange face 4 thereof. Here, the position of the crown wheel / spur wheel 3 on the differential housing 2 is defined by a stop 6 on the crown wheel / spur wheel 3 in cooperation with a step 7 on the differential housing 2.

[0023] In addition, the crown wheel / spur wheel 3 and the differential housing 2 are connected to one another in the region between the flange faces 4 and 5, which faces away from the stop 6, via a welded connection 8, which is oriented in the axial direction here. The welded connection 8 is constituted here by a melt, which is not further described at present due to generality, which materially connects the differential housing 2 and the crown wheel / spur wheel 3 to one another and is introduced into a surrounding weld seam groove 9. Here, the weld seam groove 9 is defined by the corresponding, before welding achieved machining of the flange face 5 of the differential housing 2 and the flange face 4 of the crown wheel / spur wheel 3, the exact configuration of which should now be set out in more detail with reference to the detail view in Figure 2 . The exhaust space 19 and the release 20 are also described in Figure 1 , but they should also be set out in more detail in the subsequent Figures 2-4 .

[0024] As is shown by Figure 2As can be seen, weld groove 9 is defined by the combination of a U-shaped weld portion on the flange surface 4 of the crown / spur gear 3 and a Y-shaped weld portion on the flange surface 5 of the differential case 2. The U-shaped weld portion on the flange surface 4 is larger in the width direction of weld groove 9 than the Y-shaped weld portion on the flange surface 5. Due to this design, the root region 10 of weld groove 9 is formed almost exclusively by the flange surface 4 of the crown / spur gear 3. As a result, during welding of the differential case 2 and the crown / spur gear 3, the weld beam melts almost exclusively the steel of the crown / spur gear 3 in the root region 10. The machining of the flange surface 4 is performed after the case hardening of the crown / spur gear 3, removing the hardened surface layer of the crown / spur gear 3 in the region of weld groove 9. Consequently, the weld beam melts the steel with a low carbon content in the root region 10. Preferably, the crown wheel / spur gear 3 and the differential case 2 are connected to one another within the scope of a laser welding method, so that the concentrated high-energy laser beam mainly melts the root area 10 of the weld groove 9 and thus also mainly melts the material of the crown wheel / spur gear 3, while a smaller melting of the material occurs on the flanks of the weld groove.

[0025] Furthermore, a gap 11 is formed in the area below the weld groove 9 , defined by an undercut 12 on the flange surface 5 and an undercut 13 on the flange surface 4 . Together with the weld groove 9 , the gap 11 forms a web 14 , which melts completely during welding and is formed almost exclusively by the surface of the crown / spur gear 3 located in this area. The gap 11 thus defines a weld seam formed by the melting of the web 14 and the flanking surfaces of the weld groove 9 , thereby additionally reducing the effects of notch stress concentrations in this area. Furthermore, excess additional material introduced as nickel-containing welding wire in the area where the crown / spur gear 3 is welded to the differential case 2 flows into the gap 11 , thus ensuring that no local weld bulges occur in the area of ​​the surface layer 15 . Finally, the gap 11 also serves to contain welding fumes, which are generated in part by the combustion of any contaminants present during the welding process.

[0026] Furthermore, by the share of the Y-shaped weld joint in the region of the flange face 5 of the differential housing 2, the following effect is achieved: The weld joint groove 9 is formed more widely in the region of the surface layer 15 in relation to the differential housing 2, so that in the region of the surface layer 15 and also along the flank faces of the weld joint groove 9 in relation to the flange face 5, less carbon-rich cast material is melted by the incoming welding beam. Thus, also in the region of the surface layer 15, less carbon is alloyed into the melt and thus also into the weld joint which is formed by the melt solidifying, which increases the toughness in this region. In addition, the solution of the share of the Y-shaped weld joint also generally allows a small amount of offset between the incoming welding beam and the weld joint groove 9, since by the thus increased opening area, at least one flank face area of the weld joint groove 9 is encountered by the welding beam when deviating from the root region 10.

[0027] In contrast, in relation to the crown wheel / pinion 3, by the share of the U-shaped weld joint, in addition to the already mentioned advantages of the main construction of the connecting web 14 which is formed from the low-carbon steel of the crown wheel / pinion 3, also the space in the root region 10 is increased, so that in addition to the melt, a greater share of additional material can also reach into this region. By this greater amount of additional material, the toughness of the welded joint is increased in the root region 10. In addition, in the Figure 2 The relief 20 is well visible in Figure 1 , which is provided here by means of the extension dimension on the crown wheel / pinion 3, and by which the flange face 5 of the crown wheel / pinion 3 is formed more unstably and thus also more elastically deformable, in order to reduce the stresses after the welding of the two flange faces 4 and 5 and thus the crack formation on the welded joint 8 (see

[0028] In addition, the detail of the weld joint groove 16 as Figure 3 an alternative solution is visible from Figure 2 . The difference from the solution explained above consists in that the flange face 5 of the differential housing 2 remains completely unprocessed in the region of the weld joint groove 16, so that the weld joint groove 16 is defined only by the machining of the flange face 4 of the crown wheel / pinion 3 in this region. Here, in relation to the flange face 4, as already in the preceding solution according to Figure 2 , the share of the U-shaped weld joint is formed by machining, so that the connecting web 14 is formed only by the surface of the crown wheel / pinion 3 in this region. The relief 20 is also formed alternatively in Figure 3 , since this is provided here on the flange face 4 of the differential housing 2. The advantages achieved by the relief 20 are here the same as already explained below under Figure 2 .

[0029] Finally, the detail of the weld joint groove 16 is also visible from Figure 4A further possibility for the weld groove 17 is visible. Unlike the embodiments described above, the weld groove 17 here consists of a share of a Y-shaped weld in terms of the flange face 4 of the crown gear / spur gear 3 and a share of a U-shaped weld in terms of the flange face 5 of the differential housing. Thus, in this case, the connecting web 18 is also partially composed of the material of the differential housing 2 in the root region 10 of the weld groove 17, so that upon melting of the connecting web 18, a higher carbon share of the carbon-rich casting material from the differential housing 2 is alloyed into the melt. As a result, the weld quality of the welded connection is then reduced compared to the embodiments described above. However, due to the lower strength of the casting material, the manufacturing method upon machining of the flange faces 4 and 5 can be simplified, since a higher machining speed is possible in terms of the differential housing 2 and a smaller load on the tool occurs. With regard to the release 20 in Figure 4 , it is necessary to mention that an alternative embodiment is chosen here which results from the embodiment in the combination of Figure 2 and 3 . Here, the release 20 is constructed such that material removal is achieved on both flange faces 4 and 5, so that the release 20 is composed of both flange faces.

[0030] Thus, by means of the welding method according to the invention, the weld quality can be improved since less carbon is alloyed into the weld. The method according to the invention is thus particularly suitable for manufacturing structural assemblies in the form of a shaft reducer 1, wherein high loads occur between the differential housing 2 and the crown gear / spur gear 3 in operation.

[0031] List of reference signs

[0032] 1 shaft reducer

[0033] 2 differential housing

[0034] 3 crown gear / spur gear

[0035] 4 flange face

[0036] 5 flange face

[0037] 6 stop

[0038] 7 step

[0039] 8 welded connection

[0040] 9 weld groove

[0041] 10 root region

[0042] 11 gap

[0043] 12 tool withdrawal groove

[0044] 13 tool withdrawal groove

[0045] 14 connecting piece

[0046] 15 surface layer

[0047] 16 weld bevel

[0048] 17 weld bevel

[0049] 18 connecting piece

[0050] 19 exhaust space

[0051] 20 release portion

[0052] x axial extension of the exhaust space

[0053] y axial extension of the release portion

[0054] t weld length

[0055] A rotation axis

Claims

1. A structural assembly comprising two mutually welded components, of which a first component is composed of cast material and a second component is composed of case-hardened steel, which components are rotatable about an axis of rotation A, at least one of the components being machined on a respective flange face (4, 5) in such a way that, when the components meet on the flange faces (4, 5), a circumferential weld preparation (9, 16, 17) is defined between them into which an austenitic melt for materially bonding the components is introduced, which weld preparation (9, 16, 17) is formed asymmetrically between the components in such a way that material is removed only from the flange face (4) of the second component or in such a way that more material is removed from the flange face (4) on the second component than from the flange face (5) on the first component in the width direction of the weld preparation (9, 17), and in addition an exhaust space (19) is provided behind the weld preparation (9, 16, 17) in a stepped arrangement in the axial direction along the axis of rotation A, characterized in that A release (20) is provided in an additional axial step-shaped arrangement along the axis of rotation A and behind the exhaust space (19).

2. The structural assembly of claim 1, wherein, The release (20) is realized by an axially extending material removal on one of the two flange faces (4, 5) or on both flange faces (4, 5).

3. The structural assembly of claim 2, wherein, The axial extension (y) of the release (20) is 0.5 to 3 times the length (t) of the weld seam.

4. The structural assembly of any one of claims 1 to 3, wherein, The weld bevels (9, 16, 17) and the release (20) are spaced equally or almost equally from the axis of rotation A.

5. The structural assembly of any one of claims 1 to 4, wherein, The axial extension (x) of the exhaust space (19) is between 3 mm and 5 mm.

6. The structural assembly of any one of claims 1 to 5, wherein, The respective flange face (4, 5) of the first part and / or the second part is machined such that it forms a respective share of a U-shaped weld seam.

7. The structural assembly of any one of claims 1 to 5, wherein, The respective flange face (4, 5) of the first part and / or the second part is machined such that it forms a respective share of a Y-shaped weld seam.

8. The structural assembly of any one of claims 1 to 7, wherein, The first part is a differential housing (2) of a shaft speed reducer (1), to which a crown / cylindrical gear (3) forming the second part is welded.

9. The structural assembly of any one of claims 1 to 5, wherein, The exhaust space (19) is formed by a respective one circumferential relief groove (12, 13) on the respective one assigned flange face (4, 5).

10. The structural assembly of any one of claims 1 to 9, wherein, The weld bevels (9, 16, 17) between the two parts extend directionally in the axial direction. The axial extension (y) of the release (20) is 0.5 to 3 times the length (t) of the weld seam. The axial extension (x) of the exhaust space (19) is between 3 mm and 5 mm. The respective flange face (4, 5) of the first part and / or the second part is machined such that it forms a respective share of a U-shaped weld seam. The respective flange face (4, 5) of the first part and / or the second part is machined such that it forms a respective share of a Y-shaped weld seam. The first part is a differential housing (2) of a shaft speed reducer (1), to which a crown / cylindrical gear (3) forming the second part is welded. The exhaust space (19) is formed by a respective one circumferential relief groove (12, 13) on the respective one assigned flange face (4, 5). The weld bevels (9, 16, 17) between the two parts extend directionally in the axial direction.

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