Method for welding two components together

Abstract

The invention relates to a method for welding two components (12, 14) in which a first component (12) is heated at least locally by applying a heat storage element (26), whereby the heat storage element (26) is not applied to the second component (14), and the components (12, 14) are placed against each other and welded together by forming a weld seam (24).

Description

[0001] The invention relates to a method for welding two components together.

[0002] DE 10 2013 009 208 A1 discloses a method for manufacturing a component in which two components are welded together by means of at least one weld seam. The weld seam is essentially rotationally symmetrical, and the areas of the components to be welded are preheated before welding by means of at least one heat treatment unit. The welding and preheating are carried out with essentially stationary units. During preheating and during welding, the components are rotated about a longitudinal axis of the component at the same rotational speed. The heat treatment unit is designed as a laser unit or as an electron beam unit.

[0003] The object of the present invention is to provide a solution which enables particularly simple welding of components while producing a particularly stable weld seam.

[0004] This problem is solved according to the invention by the subject matter of the independent claim. Further possible embodiments of the invention are disclosed in the dependent claims, the description, and the figures.

[0005] The invention relates to a method for welding two components together. In this method, a first component is heated at least locally by applying a heat storage element, while the heat storage element is not directly attached to the second component. By heating the first component with the heat storage element, a temperature difference between the first and second components can be achieved. Furthermore, the temperature development in the first component can be selectively influenced by the heat storage element attached to it. The method also provides for the components to be placed against each other and welded together, forming a weld seam. Heat storage devices are storage units for thermal energy. Distinctions can be made between sensible heat storage, latent heat storage, and thermochemical heat storage. Heat storage devices enable the generation of heat to be decoupled from its use over time.Using the heat storage unit to preheat the first component eliminates the need to integrate a preheating unit into a tool or welding system. In particular, the heat storage unit is designed for multiple reuses. Preheating the first component reduces residual stresses in the weld seam, resulting in a particularly strong weld.

[0006] In a possible further development of the invention, it is provided that the components are welded together using a laser beam. In laser beam welding, energy is supplied via a laser. Laser beam welding enables the components to be welded at a high welding speed, with a narrow and slender weld seam and low thermal distortion.

[0007] In particular, the process involves welding two components together that are made of different materials in the weld area. Specifically, the process welds materials that are difficult to weld together. Consequently, it can be challenging to achieve a precise process window for welding these dissimilar materials. Preheating the first component makes it easier to achieve this process window, resulting in a particularly strong weld that joins the two components.

[0008] In this context, it is particularly advantageous to weld the components together without a filler wire. This results in welding the components without any filler material. Because the components are welded without a filler wire, no additional material is introduced into the weld seam. The described process enables laser welding of the components without a filler wire, resulting in a particularly stable weld seam with very low residual stresses.

[0009] In a possible further development of the invention, the heat storage device is attached to the first component before welding, remains attached to the first component during welding, and is only removed from the first component when or after the first component has cooled down after welding. This means that heat input into the first component via the heat storage device is used to preheat the first component, the component is further heated or kept at temperature during welding by means of the heat storage device, and heat input into the first component via the heat storage device continues after welding while the weld is cooling. This slows down the cooling rate and / or curing rate of the weld, thereby keeping residual stresses in the weld seam particularly low.By applying the heat storage device both during preheating and during welding, as well as at least temporarily during cooling, the temperature development in the first component during the formation of the weld seam can be particularly well influenced by means of the heat storage device.

[0010] In a further possible embodiment of the invention, it is provided that the maximum temperature set by the heat storage device in the first component is below the tempering temperature of the first component. The tempering temperature is the holding temperature set to achieve the desired hardness. During tempering, two temperature ranges are observed that lead to embrittlement in the component, in particular 300 °C embrittlement and 500 °C embrittlement. By selecting the heat output provided by the heat storage device, and especially the temperature level provided by the heat storage device, such that the temperature of the first component is below its tempering temperature, it can be ensured that the change in the hardness of the first component as a result of the energy input from the heat storage device is particularly small.In particular, the heat storage system prevents the first component from becoming brittle due to excessive heat input. This ensures a particularly high level of stability for the first component during the process.

[0011] In a further possible embodiment of the invention, the heat storage unit is arranged, at least partially, within an opening of the first component and is thereby attached to the first component. The heat storage unit can encompass at least part of the opening of the first component, thus ensuring that the heat storage unit is held particularly securely to the first component. The risk of the heat storage unit unintentionally detaching from the component can therefore be minimized.

[0012] In a further possible embodiment of the invention, it is provided that the components are parts of an axle drive that are welded together. The first component is, in particular, a gear of the axle drive, and the second component serves as a differential housing of the axle drive. The first component is, in particular, a so-called final drive of the axle drive. The gear is, in particular, mounted on the outer circumference of the differential housing, with the components being welded together at a contact surface between the gear and the differential housing. The method thus enables the gear of the axle drive and the differential housing to be welded together using a laser beam without additional wire, thereby producing a particularly stable weld seam with particularly low residual stresses.

[0013] In this context, it may be particularly useful to radially support the heat storage unit at a bearing seat of the axle drive. This radial support at the bearing seat of the differential housing ensures the heat storage unit is centered. The risk of the heat storage unit, which rests against the gear, slipping during preheating, welding, or cooling, and potentially coming into contact with the second component, is significantly reduced by this radial support. If the heat storage unit were to slip off the first component and into contact with the second, the resulting heat generation in the components could lead to residual stresses in the weld seam. This can be prevented by radially supporting the heat storage unit.

[0014] In a further possible embodiment of the invention, the heat storage unit has an annular shape, the weld seam has a ring shape, and the heat storage unit and the weld seam are arranged radially around the outer circumference. Here, the heat storage unit, with its annular shape, and the weld seam, with its ring shape, are arranged concentrically to each other. Particularly in the embodiment of the first component as the gear, which is partially mounted on the outer circumference of the compensation housing and welded to it, the ring-shaped weld seam results from the contact of the inner side of the gear with the outer side of the compensation housing.Because the heat storage unit has a circular annular shape and is arranged radially around the outer circumference of the weld seam, the first component can be reliably preheated across its entire area adjacent to the weld seam. This allows for uniform preheating of the gear section that is welded to the compensating housing during the process. As a result, a similar, and in particular at least substantially the same, temperature difference between the first and second components can be achieved along the entire weld seam. Consequently, residual stresses in the resulting weld seam can be kept to a minimum.

[0015] In a further possible embodiment of the invention, the heat storage device is used to heat the first component, at least locally, to a temperature that is at least 15 °C, and in particular at least 20 °C, above the temperature of the second component. This means that the heat storage device establishes a temperature difference of at least 15 °C, and in particular at least 20 °C, between the first and second components, with the first component having the higher temperature compared to the second component. As a result, residual stresses in the weld seam can be reduced particularly effectively.

[0016] Further features of the invention may become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures themselves, can be used not only in the combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0017] The drawing shows in: Fig. 1. A schematic perspective view of an axle drive with a gear as the first component and a differential housing as the second component, which are welded together; and Fig. 2 a schematic front view of the axle drive according to Fig. 1.

[0018] In the figures, identical and functionally equivalent elements are provided with the same reference symbols.

[0019] In the Fig. 1 and Fig. Figure 2 shows an axle drive 10 for a motor vehicle in various illustrations. The axle drive 10 is designed to transmit drive power supplied by the motor vehicle's transmission to the drive shafts and drive wheels of the motor vehicle. The axle drive 10 comprises a gear 12, which can also be referred to as the final drive, and a differential housing 14. The differential housing 14 is supported by two bearing points 16 of the axle drive 10. The gear 12 has a web 18, via which an outer tooth 20 of the gear 12 is connected to a lip 22 arranged radially inside the web 18 and projecting radially from a radially inner edge of the web 18. The gear 12 is mounted radially outside the differential housing 14 in the axial direction A. This axial direction A runs parallel to an axis of rotation about which the gear 12 rotates during operation.

[0020] As in Fig. As can be seen particularly well in Figure 3, the compensating housing 14 and the gear 12 are welded together in the area of ​​the lip 22, creating a weld seam 24 between the gear 12 and the compensating housing 14. This weld seam 24 extends in an annular shape around the axis of rotation of the gear 12, with the axis of rotation at the center of the annulus. The gear 12 is welded to the compensating housing 14 as the first component using a laser device – and thus using a laser beam – without filler wire. In this case, the gear 12 comprises case-hardening steel, at least in the area of ​​the lip 22, and the compensating housing 14 comprises cast steel GJS 600-10, at least in the area where it is to be welded to the gear 12.In order to enable welding of the components with the formation of the weld seam 24 despite these different materials of the gear 12 and the compensating housing 14, whereby the weld seam 24 has particularly low residual stresses, it is provided that the gear 12 is preheated at least in some areas for welding.

[0021] A heat storage unit 26 is used to preheat at least part of the gear 12. This heat storage unit 26 can also be referred to as a heat pack. The heat storage unit 26 used is – as in Fig. 2 can be recognized - in this case, it is circular in shape. In Fig. For clarity, the heat storage element 26 is only partially shown in Figure 1. Here, the heat storage element 26 is applied to the web 18 in the axial direction A for preheating the gear 12. The heat storage element 26 is arranged radially surrounding the weld seam 24, with the weld seam 24, with its annular shape, and the heat storage element 26, with its circular annular shape, being arranged at least substantially concentrically to each other and to the axis of rotation. Thus, the lip 22, on which the weld seam 24 is to be produced, is preheated on one side by means of the heat storage element 26, which allows residual stresses in the gear 12 during welding and residual stresses in the weld seam 24 to be kept particularly low. The preheating of the gear 12 takes place, in particular, in a process step prior to welding.

[0022] Heat conduction from the gear 12 via the lip 22 to the compensating housing 14 can reduce the positive effect of preheating on residual stresses in the weld seam 24. Because the heat storage element 26 is used both for partial preheating of the gear 12 and is kept in contact with the gear 12 during welding to the compensating housing 14, a temperature difference between the lip 22 of the gear 12 and the compensating housing 14 can be maintained for a particularly long time, resulting in especially low residual stresses in the weld seam 24. In particular, it is provided that the heat storage element 26 is placed against the web 18 of the gear 12 before welding, remains against the web 18 during welding, and is only removed from the web 18 and from the gear 12 when or after the gear 12 has cooled down after welding.In particular, the heat storage device 26 heats the gear 12 at least locally to a temperature, especially in the area of ​​the lip 22, which is at least 15 °C, and in particular at least 20 °C, above the temperature of the compensating housing 14. The maximum temperature set by the heat storage device 26 in the gear 12 is below the tempering temperature of the gear 12.

[0023] To ensure particularly secure retention of the heat storage element 26 on the gear 12, it can be provided that the heat storage element 26 is inserted, at least partially, into at least one opening 28 of the web 18. In this case, the heat storage element 26 can extend through the opening 28 of the web 18 and engage behind it. As a result, particularly secure retention of the heat storage element 26 on the web 18 is achieved. By engaging behind the opening 28 of the web 18, the heat storage element 26 can be fixed in axial direction A. To ensure radial fixation of the heat storage element 26, it can be supported on its inner circumference by the lip 22 and / or on its outer circumference by the toothed rim 20 of the gear 12. Alternatively or additionally, the heat storage element 26 can be radially supported at a bearing seat of the axle drive 10.For this purpose, struts can protrude from the heat storage unit 26 in an axial direction, which can be placed against the respective bearing seat in order to fix the heat storage unit 26 in its position.

[0024] Laser welding of components offers advantages in terms of weight and packaging. However, laser welding is very complex to master, which is why it is often not used for axle drives. Preheating helps to reduce the complexity of laser welding and thus facilitates its implementation, particularly for axle drives.

[0025] Welding is the permanent joining of components using heat and / or pressure. In laser welding, a laser is used to melt material, thus creating a bond between the two welding partners. A common problem is that the weld seam contracts as it cools after welding. This can lead to high residual stresses, particularly circumferential, axial, and radial stresses, which can quickly cause cracks to form. This reduces the load-bearing capacity and can lead to weld failure, even without a load. The risk of this is higher the faster a hot weld area cools from an adjacent cold area. To prevent these cracks, the components to be welded can be preheated to a specific temperature before welding. One existing approach to achieving this is the use of inductors.These can be used, for example, in the form of a heating table, an inner field inductor, an outer field inductor, or a flexible inductor.

[0026] An example of the problem described above, involving the formation of cracks in a weld 24 without preheating, is the welding of the final drive to the differential housing 14 of an axle drive, particularly a differential. In this case, the weld 24 runs radially or axially. Without preheating, the weld 24 would contract upon cooling and pull on the cold final drive, resulting in the residual stresses described above.

[0027] While inductors offer a solution for preheating components, they have the disadvantage of being machine-bound and therefore requiring consideration during the initial plant design. Adding them after a plant is already built is a complex and costly process. In the component welding process, where the gear 12 is heated at least locally by contacting the heat storage element 26, the heat storage element 26 is not applied to the compensating housing 14, and the gear 12 and compensating housing 14 are placed together and welded by forming the weld seam 24, the heat storage element 26 is used to bring the gear 12 to the preheating temperature before welding.

[0028] The aim is to preheat the outer lip 22 of the gear 12 so that residual stresses after welding can be kept particularly low. To achieve this, the heat storage element 26 is used. Every temperature difference between the lip 22 of the gear 12 and the compensating housing 14 helps to reduce the residual stresses in the weld seam 24.

[0029] In Fig. Figure 1 shows only a portion of the heat storage element 26. This element is arranged in an annular shape around the axis of rotation. The heat storage element 26 is a heat source that is mounted on the gear 12 immediately before welding. The heat storage element 26 can be attached via at least one opening 28 in the web 18 or by being supported against a bearing seat. After a certain cooling period of the weld 24, the heat storage element 26 can be removed from the gear 12. The heat storage element 26 is thus used as a temporary manufacturing aid.

[0030] The heat storage unit 26 is particularly effective in counteracting the problem of cracks at the weld seam 24. Compared to inductors, the heat storage unit 26 is workpiece-resistant and can be retrofitted if a system layout no longer permits the use of an inductor. The heat storage unit 26 also eliminates the need to rotate the gear 12 and / or the compensating housing 14 during preheating.

[0031] Overall, the invention demonstrates how a preheating process can be implemented in laser welding, particularly without additional wire. Reference symbol list 10 axle gearboxes 12 gear 14 expansion tanks 16 storage location 18 Bridge 20 toothed ring 22 Lippe 24 weld seam 26 Heat storage 28 Opening A axial direction QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2013 009 208 A1

[0002]

Claims

[1] Method for welding two components (12, 14), in which - a first of the components (12) is heated at least locally by applying a heat accumulator (26), whereby the heat accumulator (26) is not applied to the second component (14), and - the components (12, 14) are placed against one another and welded together to form a weld seam (24). [2] Method according to claim 1, characterized by that the components (12, 14) are welded together by means of a laser beam. [3] Method according to claim 2, characterized by that the components (12, 14) are welded together without an additional wire. [4] Method according to one of the preceding claims, characterized bythat the heat accumulator (26) is applied to the first component (12) before welding, remains applied to the first component (12) during welding and is only removed from the first component (12) during or after the cooling of the first component (12) after welding. [5] Method according to one of the preceding claims, characterized by that a maximum temperature set by the heat accumulator (26) in the first component (12) is below a tempering temperature of the first component (12). [6] Method according to one of the preceding claims, characterized by that the heat accumulator (26) is arranged at least in part in at least one opening (28) of the first component (12) and is thereby fastened to the first component (12). [7] Method according to one of the preceding claims, characterized bythat parts of an axle transmission (10) are welded together as the components (12, 14), the first component being a gear (12) of the axle transmission (10) and the second component serving as a differential housing (14) of the axle transmission (10). [8] Method according to claim 7, characterized by that the heat accumulator (26) is radially supported on a bearing seat of the axle drive (14). [9] Method according to one of the preceding claims, characterized by that the heat accumulator (26) has a circular ring shape, the weld seam (24) has a ring shape and the heat accumulator (26) is arranged radially surrounding the outer circumference of the weld seam (24). [10] Method according to one of the preceding claims, characterized by that by means of the heat accumulator (26) the first component (12) is heated at least locally to a temperature which is at least 15 °C, in particular at least 20 °C, above the temperature of the second component (14).

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