Laser welding process for joining a non-sintered material with a sintered material and composite body produced thereby

Description

[0001] The invention relates to a laser welding method for joining a non-sintered material with a sintered material.

[0002] Laser welding processes are primarily used for welding components that require high welding speeds, a narrow and slender weld seam, and minimal thermal distortion. This process, also known as laser beam welding, is generally performed without filler metal. A major advantage of laser-welded components is the lower, more concentrated energy input into the workpiece compared to other welding processes.

[0003] However, joining carbon-containing components using a laser welding process is problematic. Sintered materials, especially those with a high carbon content, cannot currently be welded to non-sintered materials using laser beam welding. Applying or coupling a laser beam into the sintered material leads to structural changes and even local destruction of the microstructure due to its material properties, i.e., porosity, carbon content, unavoidable impurities, and the energy density introduced by the laser beam. Furthermore, the carbon index of carbon-containing sintered materials often exceeds the permissible limit or guideline value for a stable hardness profile within the welded joint to prevent cracks.

[0004] Nevertheless, the known prior art at least mentions that non-sintered materials and sintered materials can be joined or bonded using the laser welding process, but does not describe this in detail. However, a concrete solution to the problems cited when coupling a laser beam into a sintered steel component is not known. Examples include the publications DE 102004038681 A1, DE 102016220830 A1, and DE 102017119264 B4. Further prior art is described in DE 1971230 A1 and EP 0940214 B1.

[0005] The object of the invention is therefore to provide a laser welding method as mentioned above for joining a non-sintered material with a sintered material, as well as a composite body resulting from this method and the use of a laser welding method for joining a non-sintered material with a sintered material.

[0006] According to one aspect, the object is achieved by a laser welding method for joining a non-sintered material to a sintered material, which has the following steps: providing a first component made of a non-sintered material, providing a second component made of a sintered material, arranging the first component and the second component along a contact plane to produce a joint, applying a laser beam to a first joining region of the first component in the region of the joint to melt the first joining region to a melt, melting a second joining region of the second component in the region of the joint by means of the melt of the first joining region, and cooling the joint.

[0007] Advantageous embodiments are specified in the subclaims and independent claims.

[0008] The sintered material in the second joining area is thus melted by the melt of the non-sintered material from the first joining area. The laser beam is applied directly to or coupled into an edge area of ​​the non-sintered material. This is why it is referred to in this context as indirect laser welding. The laser welding process according to the invention has the advantage of easily creating a stable welded joint between a non-sintered material and a sintered material that is suitable for large-scale production. In particular, for many applications, welding is now possible instead of screwing. This leads to a significant reduction in material and manufacturing costs. In addition, the laser welding process can be used very flexibly for different geometries of the components to be joined, which in turn significantly reduces process and / or manufacturing costs.

[0009] Sintered metals often exhibit so-called barrier layers, such as martensite structures. Martensite is a metastable structure that forms diffusion-free and athermally through cooperative shear movement from an initial structure, in this case the sintered material, and leads to particularly high strength and hardness. A barrier layer therefore generally has a positive effect on the material properties of a sintered metal or second component, but complicates joining or bonding with the non-sintered material or the first component. Removing the barrier layer facilitates and accelerates the joining of the non-sintered material and the sintered material.

[0010] For better understanding, the terms contact plane, joint and joining area should be explained in more detail at this point. The contact plane refers to a virtual surface to which the two components to be joined are placed in order to be welded together. Thus, during a welding process, the first component is arranged on one side and the second component on the other or opposite side of the contact plane. The two components lie against each other, at least in sections. As already mentioned, the two components form or create a joint. The joint is understood to be an abutting edge that runs along outer edge sections of the two components where the components lie against each other.An outer edge section of one component can either rest on an outer surface of the other component that extends beyond its outer edge, or it can be flush with an outer edge section of the other component. Two joining areas run along the joint, more precisely the first joining area of ​​the first component and the second joining area of ​​the second component. The joining area is the part or section of a component that is directly involved in the welding process. In the case of the first component made of the non-sintered material, it is the part that is converted into a melt when the laser beam is applied. In the case of the second component made of the sintered material, it is the part that is melted by means of the melt of the first joining area, whereby the two joining areas are fused or joined together.

[0011] In an advantageous embodiment, the laser beam is aligned parallel to the contact plane during application. The laser beam is preferably also directed frontally or at the end face onto the first joining area of ​​the first component. This allows the laser beam to develop its maximum effect and achieve a high penetration depth. With this alignment of the laser beam, a maximum penetration depth and increased strength of the weld seam can be achieved. This type of alignment of the laser beam is particularly suitable in the case of a joint in which the outer edge sections of the two components are flush with one another. The risk of inadvertently applying the laser beam to the second component made of sintered material is thus reduced.

[0012] According to a preferred embodiment, the laser beam is aligned at an angle α to the contact plane during application, wherein the angle α is a maximum of 45°, in particular a maximum of 30°, in particular a maximum of 15°. The greater the penetration depth into the joint, the greater the strength of the weld. A deviation of the angle α from 0° can be provided, for example if the first joining area cannot be reached with a laser beam aligned parallel to the contact plane due to structural conditions or if no parallel weld root is formed and the penetration depth would therefore be reduced. Up to a maximum angle of 45°, however, the laser beam can still have a sufficient effect to melt the joining area of ​​the first component.Such an angled alignment of the laser beam is particularly suitable when the outer edge section of one component to be joined rests on an outer surface of the other component that extends beyond its outer edge. This either minimizes the risk of the laser beam being directed onto the second component or makes it possible to apply the laser beam to the first joining area in the first place.

[0013] In a further advantageous embodiment, the laser beam is applied using a continuous or pulsed laser beam. Whether a continuous or pulsed welding process is advantageous depends, for example, on the geometry, but also on the thermal conductivity of the non-sintered material.

[0014] Continuous laser welding is an uninterrupted welding process and is particularly suitable for welding thick components as well as refractory metals such as titanium, chromium and tungsten.

[0015] In pulsed laser welding, the energy is delivered at limited time intervals. Each laser pulse is followed by a short pause during which the previously generated molten metal can cool. This process, also known as precision welding, is particularly suitable for thin-walled workpieces, such as light and thin metals, for joining components with very different geometries, and for difficult-to-weld materials. It prevents the components from deforming or melting more than desired.

[0016] According to the invention, the application is advantageously carried out using laser beam MIG / MAG hybrid welding. The laser beam MIG / MAG hybrid process, or laser beam MIG / MAG hybrid welding, combines a laser beam with a MIG / MAG welding process in a common process zone (MIG = gas metal arc welding). This utilizes the advantages of both processes. Very deep penetrations with good flank bonding are achieved. This creates a very narrow heat-affected zone with little distortion. The process allows for very high welding speeds, which leads to lower energy per unit length. The main reason for the high cost-effectiveness lies in reduced weld preparation. Entire work steps can be eliminated.

[0017] In a preferred embodiment, the first component is provided by a steel component, and the second component is provided by a carbon-containing sintered steel component. Providing such a combination is particularly suitable for manufacturing a camshaft adjuster—usually designed as a hydraulic phase adjuster or pivoting motor. Specifically, this embodiment is suitable for welding a steel end cover to a carbon-containing sintered steel stator. Conversely, the laser welding process results in significant material and thus cost savings when manufacturing the camshaft adjuster, particularly compared to previously used screw connections.

[0018] According to a further preferred embodiment, the first component is provided by means of a circular disk-shaped component, and the laser beam is applied from the radial outside onto the first joining region and guided around at least one of the components on a circular path parallel to the contact plane. Alternatively, or in combination, it is also possible to permanently install a laser device providing the laser beam and rotate the components such that the relative movement between the laser beam and the components is the same as when the laser beam or the laser device is guided around the at least one component on the circular path. This variation of the method steps is also particularly suitable for welding an end cover to a stator in the manufacture of a camshaft adjuster.

[0019] A composite body comprising a first component made of a non-sintered material and a second component made of a sintered material can be produced according to a method according to the preceding embodiments. The composite body offers similar advantages to the method according to the invention.

[0020] The sintered material of the second joining area is thus melted using the melt of the non-sintered material from the first joining area. The laser beam is applied directly to or coupled into an edge area of ​​the non-sintered material. Consequently, even difficult-to-join material pairings that have different properties or are used for different purposes can be welded together.

[0021] Preferably, the first component is circular disk-shaped. Thus, the first component has, for example, the shape of the end cover on the stator of a camshaft adjuster. A circular design of the first component enables or facilitates a uniform application of the laser beam from the radial outside onto the first joining area, while the laser device is guided in a circular path around the first component.

[0022] Furthermore, the first component is preferably designed as a cover, in particular as a stator cover on a camshaft adjuster. The stator cover corresponds to the end cover for the stator on the camshaft adjuster. The second component is preferably designed as a stator, in particular as a stator of a camshaft adjuster.

[0023] In connection with these two embodiments, the particular suitability of the laser welding process for producing a camshaft adjuster should be emphasized again. The stator of the camshaft adjuster is designed, for example, with teeth for a chain drive. In order to ensure the hardness necessary to support a chain, the stator is preferably made of a hardenable sintered material. A laser-welded connection between this sintered material and a stator cover made of a non-sintered material is possible in a particularly good form using the laser welding process according to the invention. The stator cover, on the other hand, can be made of an easily weldable steel. For example, this is a stamped steel sheet with a thickness of less than 6 mm or preferably less than 3 mm.

[0024] In an advantageous embodiment, the sintered material is a sintered metal, preferably a sintered steel. Sintered metal is ideally suited for components that require multiple machining processes, have complex geometries, and / or integrate multiple subcomponents into a new component, as is the case with the stator, for example.

[0025] In a particularly preferred embodiment, the sintered metal has a carbon content, preferably between 0.3 and 0.9 percent, in particular between 0.5 and 0.8 percent, in particular 0.6 percent. With increasing carbon content, steel, and in particular sintered steel, can be hardened more effectively. At the same time, a material with the lowest possible carbon content is best suited for the laser welding process in order to reduce residual material stresses. A corresponding optimum is 0.6 percent carbon content in order to provide a sufficiently hardenable material, which can also be used for the laser welding process according to the invention. Furthermore, the non-sintered material is preferably a metal, preferably steel. Such a non-sintered material is stable and particularly easy to process and / or join using laser welding.

[0026] According to the invention, the non-sintered material also advantageously has the lowest possible carbon content, in particular a carbon content of no more than 0.2 percent, and thus reduced residual material stress. For example, the steel has a carbon content of approximately 0.02 percent and a manganese content of approximately 0.2 percent. This ensures good weldability.

[0027] An aspect not belonging to the invention is the use of a laser welding method for joining a non-sintered material to a sintered material. A laser beam is applied to a first joining region of the non-sintered material in the region of a joint to melt the first joining region into a melt, and a second joining region of the second component in the region of the joint is melted using the melt of the first joining region. The use of the laser welding method and the following embodiments for using this method bring similar advantages to the laser welding method according to the invention and / or the composite body described here.

[0028] The sintered material in the second joining area is melted using the melt of the non-sintered material in the first joining area. For this purpose, the laser beam is applied directly to or coupled into an edge area of ​​the non-sintered material. This process is therefore referred to as indirect laser welding. The use of the laser welding process offers the advantage of easily creating a stable welded joint between a non-sintered material and a sintered material that is suitable for large-scale production.

[0029] In particular, welding instead of screwing is now possible for many applications. This leads to a significant reduction in material and manufacturing costs. Furthermore, the laser welding process is very flexible and can be used for various geometries of the components to be joined, which in turn significantly reduces process and / or manufacturing costs. The laser beam is applied directly to an edge area of ​​the non-sintered material or coupled into it. The use of the laser welding process enables a welded connection between a non-sintered material and a sintered material. Consequently, even difficult-to-join material pairings that have different properties or are used for different purposes can be welded together.

[0030] According to a preferred embodiment, the first component and the second component are arranged along a contact plane to create a joint. When using the laser welding process, the laser beam is aligned parallel to the contact plane. This allows the laser beam to develop its maximum effect and achieve a high penetration depth. With this alignment of the laser beam, a maximum penetration depth and strength of the weld seam can be achieved. This alignment of the laser beam is particularly suitable in the case of a joint in which the outer edge sections of the two components are flush with one another. The risk of inadvertently applying the laser beam to the second component made of sintered material is thus reduced.

[0031] In an alternative embodiment, when using the laser welding process, a laser beam is aligned at an angle α to the contact plane, wherein the angle α is a maximum of 45°, in particular a maximum of 30°, in particular a maximum of 15°. A deviation of the angle α from 0° can be provided, for example if the first joining area cannot be reached with a laser beam aligned parallel to the contact plane due to structural conditions or if no parallel weld root is formed and thus the penetration depth would be reduced. Up to a maximum angle of 45°, however, the laser beam can still exert a sufficient effect to melt the joining area of ​​the first component. Such an angled alignment of the laser beam is particularly suitable if the outer edge section of one component to be joined rests on an outer surface of the other component that extends beyond its outer edge.This either minimizes the risk of applying the laser beam to the second component or makes it possible to apply the laser beam to the first joining area in the first place.

[0032] In a further advantageous embodiment, continuous and / or pulsed laser welding is used when using the laser welding process.

[0033] Whether a continuous or pulsed welding process is advantageous depends, for example, on the geometry, but also on the thermal conductivity of the non-sintered material. Continuous laser welding is an uninterrupted welding process and is particularly suitable for welding thick components, as well as refractory metals such as titanium, chromium, and tungsten. In pulsed laser welding, on the other hand, the energy is delivered at limited time intervals. After each laser pulse, there is a short pause in which the previously generated melt can cool. This prevents the components from deforming or melting more than desired.

[0034] When using the laser welding process, it is advantageous to use a laser beam-GMAW hybrid welding process. The laser beam-GMAW hybrid process, or laser beam-GMAW hybrid welding, combines a laser beam with a GMAW welding process in a common process zone (GMAW = metal inert gas welding). This utilizes the advantages of both processes. Very deep penetrations with good flank bonding are achieved. This creates a very narrow heat-affected zone with little distortion. The process allows for very high welding speeds, which leads to lower energy per unit length. The main reason for the high cost-effectiveness lies in reduced weld preparation. Entire work steps can be eliminated.

[0035] Further advantages of the invention will become apparent from the description and the drawings.

[0036] The invention is explained in more detail below with reference to the exemplary embodiments illustrated in the drawings. In the drawings: Fig. 1 a cross-section of a first embodiment of a composite body produced by the method according to the invention before the application of a laser beam; Fig. 2 a cross-section of the composite body Fig. 1 during the application of a laser beam; Fig. 3 a perspective view of a second embodiment of a composite body produced by the method according to the invention during the application of a laser beam; and Fig. 4 a flow chart of the method according to the invention.

[0037] The Fig. 1 shows a cross-section of a first embodiment of a composite body 1 according to the invention before the application of a laser beam 11. The composite body 1 is in an early phase of a method according to the invention for its production or of a laser welding method according to the invention for joining a non-sintered material and a sintered material. The first component 2 consists of a non-sintered material and the second component 3 consists of a sintered material. In addition, Fig. 1 a laser device 4, which is arranged directed toward the first component 2. The components 2, 3 are located on opposite sides of a contact plane 5, along which they are arranged and thus applied to one another. The first component 2 has a first joining area 6. The second component 3 has a second joining area 7.

[0038] The joining regions 6, 7 are each arranged at the ends of the components 2, 3 facing the laser device 4. The components 2, 3 are arranged along the contact plane 5, and a joint 8 is created by means of the joining regions 6, 7. The joint 8 is arranged along a butt edge. The butt edge runs where the components 2, 3 are flush with one another on the contact plane 5. The joining regions 6, 7 can furthermore each have a groove 9, 10. Specifically, in the exemplary embodiment shown, the first joining region 6 has a first groove 9 and the second joining region 7 has a second groove 10. The grooves 9, 10 are arranged opposite one another and define a common cavity. The functions of the grooves 9, 10 will be discussed in the following description. Fig. 2 received.

[0039] The Fig. 2 shows a cross section of the composite body 1 according to the invention from Fig. 1 during the application of a laser beam 11. Compared to Fig. 1 The composite body 1 is shown in an advanced phase of the process for its production. As in Fig. 1 Here, too, the components 2, 3 with their joining areas 6, 7 and grooves 9, 10 can be seen. Furthermore, Fig. 2 The laser device 4 and the contact plane 5 are shown again. However, the components 2, 3 are now arranged on the contact surface 5 and thus lie directly against one another, whereby the joint 8 is created. In addition, the laser device 4 is activated in this phase of the process, shown with a laser beam 11 directed at the first component 2 or its joining region 6. Specifically, the process step of applying the laser beam 11 to the first joining region 6 of the first component 2 in the region of the joining joint 8 in order to melt the first joining region 6 into a melt is shown here. A subsequent or resulting process step is the melting of the second joining region 7 of the second component 3 in the region of the joining joint 8 using the melt of the first joining region 6. This creates an essentially circumferential weld seam.

[0040] The grooves 9, 10 are embedded in the respective components 2, 3 and arranged at the common contact plane 5 and at least partially parallel to the joint 8. Since the two grooves 9, 10 are directly opposite each other at the contact plane 5, they form a common cavity. The stress on the weld seam can be reduced because, during operation of the composite body 1, pressure can be kept away from the weld root and diverted into the surrounding base material.

[0041] It is also possible to provide a first or second groove 9, 10, which is embedded in the first and / or second component and runs at least partially parallel to the joint, for gas pressure equalization. This can, for example, achieve the advantage that the melt is less influenced by the diffusion of gases that arise, thereby further increasing or stabilizing the strength. Furthermore, the flow of the melt into the groove can provide improved shear strength of the joint. Furthermore, stresses during the joining process can be significantly reduced, further improving the quality of the welded joint.

[0042] Furthermore, only one of the grooves 9, 10 can be provided, i.e. either only the first groove 9 or only the second groove 10. The joining of the components 2, 3 without any groove is also part of the invention.

[0043] When applied to the first joining area 6, the laser beam 11 is aligned at an angle α to the contact plane 5. Specifically, the angle α here is 15°. Optimally, the laser beam 11 is aligned parallel to the contact plane 5 or with α = 0°, as the laser beam 11 can then achieve its maximum effect and penetration depth. However, the angle α can be up to 45° to achieve a sufficient effect of the laser beam 11. Three-dimensional stress and heat dissipation states must be avoided.

[0044] The Fig. 3 shows a perspective view of a second embodiment of the composite body 1 according to the invention during the application of a laser beam 11. The composite body 1 is shown in this second embodiment as part of a camshaft adjuster. The composite body is in the - in Fig. 2 illustrated - advanced stage of the process for its production. As shown in Fig. 2 The first component 2 and the second component 3 can be seen, which abut one another along the joint 8. The first component 2 is designed as a circular disk-shaped stator cover and is made of a steel with a low carbon content. The second component 3 is designed as a stator of the camshaft adjuster and is made of a sintered steel with a carbon content of 0.6 percent. The selected carbon content of 0.6 percent ensures sufficient hardenability of the sintered steel of the second component 3, but at the same time still enables the components 2, 3 to be joined using the laser welding process according to the invention.

[0045] In addition, here in Fig. 3 The laser device 4 with the laser beam 11 is again shown. When applying the laser beam 11, in this embodiment, the laser beam 11, and thus also the laser device 4, are guided on a circular path 12 around the first component 2 or the stator cover. The laser beam 11 is directed onto the first component 2 or applied to it from the radial outside.

[0046] However, the invention is not limited to a circular weld seam. Thus, the first component 2 can have a shape that deviates from a circular shape, among other things to prevent the component 2 from swelling. For example, the component 2 can be cloverleaf-shaped, so that the circumferential weld seam runs along multiple radii and partially radially. It is also conceivable to provide multiple circumferential weld seams that run separately from one another.

[0047] For simplification, Fig. 3 Some details (such as contact plane and joining areas) have been omitted. However, the corresponding explanations regarding the Figuren 1 und 2 .

[0048] The Fig. 4shows a flowchart of the method according to the invention. After providing a first component 2 made of a non-sintered material and providing a second component 3 made of a sintered material, the method comprises the first step of arranging 100 the first component 2 and the second component 3 along a contact plane 5 to create a joint 8. In a second step, the method comprises applying 200 a laser beam 11 to a first joining region 6 of the first component 2 in the region of the joint 8 to melt the first joining region 6 into a melt. In the subsequent method step, a second joining region 7 of the second component 3 in the region of the joint 8 is melted 300 using the melt of the first joining region 6, and in the final step, the cooling 400 of the joint 8 takes place.

Claims

1. Laser welding method for joining a non-sintered material with a sintered material, comprising the following steps: - providing a first component (2) made of a non-sintered material, providing a second component (3) made of a sintered material, - arranging (100) the first component (2) and the second component (3) along a contact plane (5) to create a joint (8), - applying (200) a laser beam (11) to a first joining region (6) of the first component (2) in the region of the joint (8) in order to melt the first joining region (6) into a molten mass, and - cooling (400) the joint (8), characterized by - melting (300) a second joining region (7) of the second component (3) in the region of the joint (8) by means of the molten mass of the first joining region (6).

2. The method according to claim 1, characterized in that the laser beam (11) is aligned parallely to the contact plane (5) during application.

3. The method according to claim 1, characterized in that the laser beam (11) is aligned at an angle a to the contact plane (5) during application, wherein the angle a is at most 45°, in particular at most 30°, in particular at most 15°.

4. The method according to one of the preceding claims, characterized in that the laser beam (11) is applied by means of a continuous or a pulsed laser beam (11).

5. The method according to one of the preceding claims, characterized in that the application is carried out by means of laser beam MSG hybrid welding.

6. The method according to one of the preceding claims, characterized in that the first component (2) is provided by means of a component made of steel and the second component (3) is provided by means of a component made of a carbon-containing sintered steel.

7. The method according to one of the preceding claims, characterized in that the first component (2) is provided by means of a component in the form of a circular disk, and the application of the laser beam (11) is carried out radially from outside onto the first joining region (6) and guided on a circular path (12) parallel to the contact plane (5) around at least one of the components (2, 3).