Method for coating a brake disc made of grey cast iron or steel

Abstract

The present invention relates to a method for coating a brake disc (1) made of gray cast iron or steel, wherein the brake disc (1) has a substrate (10) and at least one disc-shaped body (11) extending radially from there perpendicular to an axis of rotation (D) of the brake disc (1), the disc-shaped body having a face (11a) whose normal is parallel to the axis of rotation (D). The disc-shaped body (11) defines the outer diameter (d1) of the brake disc (1), wherein the outer diameter (d1) has a radially external allowance (Ü1) relative to the theoretical outer diameter (d2). In laser surfacing, a coating (B) is applied to the face (11a) of the disc-shaped body (11) by means of a tool (13), which consists of a first layer (B1) made of high-quality steel applied to the face (11a) of the disc-shaped body (11) and at least one second layer (B2) applied to the first layer (B1), the second layer being a composite material made of an iron alloy matrix with embedded hard particles. According to the present invention, a coating (B) is performed without first performing a machining process to reduce the outer diameter (d1) of the brake disc (1) to the theoretical outer diameter (d2).

Description

Technical Field

[0001] The present invention relates to a method for coating brake discs made of gray cast iron or steel. Background Technology

[0002] The coating of brake discs should aim to significantly reduce fine dust emissions generated during vehicle braking and thereby minimize the environmental impact. In testing, such brake discs have historically been manufactured in the following manner: the delivered brake disc (blank) is first machined to a predetermined finished or theoretical size in terms of its outer diameter. Then, coating is applied to one or more sides of the disc. Here, a layer of high-quality steel is first applied, followed by a layer of a composite material consisting of an iron alloy matrix with embedded hard particles. Both layers are applied to the respective substrates by means of laser overlay welding.

[0003] During coating, a tool (which aims not only the coating material but also the laser beam at the substrate to be coated) is moved radially across the substrate. If the tool is moved radially from the inside out, it is advanced to the outer diameter of the brake disc when the first layer is applied. Correspondingly, the application of the second layer is also achieved by advancing the tool to the outer diameter of the brake disc.

[0004] The tests revealed that this method generates heat buildup in the edge areas of the brake disc. This is associated with a strong localized temperature rise, which leads to a decrease in the coating quality in the edge areas.

[0005] A method for manufacturing brake discs for vehicles is known from document US 10 274 ​​032 B2. The method first involves heating the brake disc and then immersing it in a molten metal alloy, such as an aluminum or zinc alloy. The metal layer applied to the entire brake disc functions not only as an adhesive but also as a corrosion protectant. Next, the brake disc is machined to the required theoretical dimensions. Finally, a hard metal powder, which may contain tungsten carbide or titanium carbide, is applied to the friction surface of the brake disc using high-speed flame spraying. Summary of the Invention

[0006] The purpose of this invention is to provide a method for coating brake discs made of gray cast iron or steel, which can improve the coating quality of the brake discs.

[0007] This objective is achieved by the method according to the invention. Advantageous constructions or improvements of the invention can be found in the description.

[0008] This invention relates to a method for coating a brake disc made of gray cast iron or steel. The brake disc to be coated has a substrate and at least one disc-shaped body extending radially from there perpendicular to the axis of rotation of the brake disc. This disc-shaped body has a surface whose normal is parallel to the axis of rotation. Here, the disc-shaped body defines the outer diameter of the brake disc. This outer diameter has a radially external allowance relative to the theoretical outer diameter. A coating is applied to the surface of the disc-shaped body using a tool in laser overlay welding. This coating consists of a first layer made of high-quality steel applied to the surface of the disc-shaped body and at least one second layer applied to the first layer, the second layer being a composite material composed of an iron alloy matrix with embedded hard particles. Subsequently, in the assembled state of the brake disc in a motor vehicle, the second layer provides a friction surface for abutting the brake pads.

[0009] The high-quality steel is preferably austenitic or ferritic high-quality steel. For example, it is conceivable that the first layer is made of austenitic chromium-nickel-molybdenum steel, having material properties such as those corresponding to material 1.4404 according to standard EN10027-2 or material 316L according to standard AISI. However, depending on the material properties of the brake disc, alternatively, and which has proven advantageous, it is conceivable that the first layer is made of ferritic high-quality steel, having material properties such as those corresponding to material 1.4016 according to standard DIN EN 10027-2 or material 430L according to standard AISI.

[0010] The second layer has an iron alloy matrix, preferably composed of the aforementioned material 316L or 430L. The hard particles are preferably composed of an alloy of titanium carbide and ferrochrome (TiC-FeCr) or solely of titanium carbide or tungsten carbide.

[0011] The present invention now proposes to perform a coating without prior processing that reduces the outer diameter of the brake disc to the theoretical outer diameter.

[0012] In principle, the pre-processing of the brake disc and the machining of its outer diameter are not excluded from the beginning, as long as the outer diameter of the brake disc is not reduced to the theoretical outer diameter through the machining process.

[0013] This method provides the prerequisite for significantly improving the coating quality of the brake disc, especially in its outer edge areas. By not ending the coating in the outer edge areas, significant heat buildup and localized temperature increases occur there. This thus avoids carburization of the first layer and bonding defects.

[0014] According to an improvement, a brake disc with a radial external margin in the range of about 1.5 mm to about 5.0 mm, preferably in the range of about 2.0 mm to about 3.0 mm, and particularly preferably with a radial external margin in the horizontal range of about 2.5 mm is used.

[0015] It has been shown that choosing such a margin allows for a very good trade-off between available process improvements and material costs.

[0016] According to a construction scheme conceived in this invention, when applying a coating by laser welding, the tool is moved radially such a distance on the corresponding substrate to be coated that the outer diameter of the laser beam generated by the tool is exactly adjacent to the outer diameter of the brake disc. In other words, the laser beam, or the laser spot generated on the substrate, does not exceed the outer diameter of the brake disc.

[0017] This method prevents the laser beam from uncontrollably reaching the coating equipment components in the edge area of ​​the brake disc. This also prevents the equipment from being damaged by a high-energy laser beam.

[0018] According to another improved approach, the second layer is processed by grinding. Laser welding creates a very hard, carbonized, and rough surface on the second layer. Such a surface can damage the brake pads during braking. Grinding, especially utilizing the diamond-set portion of the grinding tool, produces suitable surface properties.

[0019] According to a highly advantageous construction scheme, the disc-shaped body is machined by turning before or after grinding, thereby reducing its outer diameter to the theoretical outer diameter. Turning the outer diameter to the theoretical size occurs, in any case, after the cladding of the disc-shaped body. This yields several positive effects: • It removes so-called spatter during the coating process. Spatter is understood as the radially adjacent area of ​​the brake disc to the coated surface (friction surface) where heated hard particles impact and remain attached or melt into the surface during the application of the second layer via laser welding. Removing spatter improves the paintability of the surface adjacent to the coating after applying a corrosion protectant. • It allows for the addition of chamfering in the transition area at the edge of the friction surface (the transition from the disc-shaped body with gray cast iron or steel to the coating). This positively impacts the notch effect. Furthermore, it facilitates the paintability of this transition area by applying corrosion protectants.

[0020] One proposed improvement involves using a brake disc in which the base is connected to the disc body via a grooved recess. Here, the inner diameter of the disc body has a radial internal allowance relative to a theoretical inner diameter. This allowance can be in the range of approximately 1.5 to 5 mm, preferably in the range of 2 to 3 mm.

[0021] This method offers the following advantages: it significantly improves the coating quality of the brake disc, particularly in the inner edge regions. Specifically, it ensures the coating does not terminate in the edge areas (the transition between the friction surface and the groove), resulting in minimal heat buildup and localized temperature increases.

[0022] To reduce spatter in the recessed area during coating application, the coating tool is moved radially across the substrate to be coated during laser welding so far that the outer diameter of the resulting laser beam is just adjacent to the inner diameter of the disc. In other words, the laser beam, or the laser spot thus generated on the substrate, does not extend beyond the inner diameter of the disc.

[0023] Finally, an improvement to the method further involves machining the disc-shaped body by turning before or after grinding, thereby increasing its inner diameter to the theoretical inner diameter. This removes any spatter that might still be present in the grooved recesses, which in turn facilitates the application of corrosion protectants.

[0024] It should be noted that during the turning process, the entire groove area is advantageously machined out, thereby machining not only the splashes but also the allowance present in the area to the theoretical dimensions. Attached Figure Description

[0025] Preferred embodiments of the invention are shown in the accompanying drawings and will be described in more detail in the following description with reference to the drawings. Further features and advantages of the invention are also illustrated therein. The same reference numerals refer to the same, similar, or functionally identical components in different drawings. Corresponding or similar features and advantages are achieved herein, even if not described or referenced repeatedly thereto. The drawings are not, or at least not always, drawn to scale. Scale or distances may be exaggerated in some drawings to more clearly highlight the features of the embodiments.

[0026] Indicatively: Figure 1 A blank of the brake disc is shown, as it is used in this method. Figure 2 The illustration shows the method as the tool moves radially from the inside out until it reaches the outer edge region of the brake disc. Figure 3 The illustration shows the method as the tool moves radially from the outside in until it reaches the inner edge region of the disc-shaped body of the brake disc, and... Figure 4 The illustration shows a possible process for machining a coated brake disc. Detailed Implementation

[0027] exist Figure 1 The blank of brake disc 1 is shown, which serves as the starting point for this method. Brake disc 1 is made of gray cast iron. It has a hub-shaped base 10. A disc-shaped body 11 extends radially from the base 10. For reasons of symmetry, only half of brake disc 1 is shown, both vertically and horizontally.

[0028] The base 10 is used to secure the brake disc 1 to the wheel frame of a motor vehicle (not shown). The base 10 is connected to the disc-shaped body 11 via a grooved recess 12 (which serves as a heat balance groove). The disc-shaped body 11 has a surface 11a, the normal of which is parallel to the axis of rotation D of the brake disc 1. Since only half of the brake disc 1 is shown horizontally, there is another surface of the disc-shaped body 11 opposite to surface 11a. The method described below also applies to this surface.

[0029] Brake disc 1 has an outer diameter d1. Furthermore, the theoretical outer diameter d2 is shown in dashed lines. The blank of brake disc 1 has a allowance Ü1 in terms of its theoretical outer diameter.

[0030] Furthermore, the disc-shaped body 11 has an inner diameter d3. The theoretical inner diameter d4 is also shown in dashed lines. The blank of the brake disc 1 therefore also has a margin Ü2 in terms of the theoretical inner diameter of the disc-shaped body 11.

[0031] The radial external allowance Ü1 is in the range of about 1.5 mm to about 5.0 mm. Preferably, it is in the range of about 2.0 mm to about 3.0 mm. Particularly preferably, a brake disc 1 with a radial external allowance Ü1 at a level of about 2.5 mm is used. The radial internal allowance Ü2 can also be in the range of about 1.5 mm to about 5.0 mm, preferably in the range of about 2.0 mm to about 3.0 mm.

[0032] The blank of the brake disc 1 is now coated in laser overlay welding, wherein the surface 11a of the disc body 11 is provided with a coating consisting of two layers.

[0033] exist Figure 2 The diagram illustrates one stage of the coating process, in which surface 11a is coated using tool 13. A laser beam 14 (to which the coating material is also supplied (not shown)) is aligned with the corresponding substrate using tool 13. In this embodiment, tool 13 preferably moves radially from the inside out at a feed rate V (see dashed illustration). Here, a first layer B1 is first applied to surface 11a.

[0034] The first layer B1 is made of high-quality steel. It is preferably austenitic or ferritic high-quality steel. For example, it is conceivable that the first layer is made of austenitic chromium-nickel-molybdenum steel, having material properties such as those corresponding to material 1.4404 according to standard EN10027-2 or material 316L according to standard AISI. However, depending on the material properties of the brake disc, alternatively, and having proven advantageous, it is conceivable that the first layer is made of ferritic high-quality steel, having material properties such as those corresponding to material 1.4016 according to standard DIN EN 10027-2 or material 430L according to standard AISI.

[0035] Furthermore, the tool 13 is shown at the end of the first layer B1 coating surface 11a. It can be seen here that the tool 13 is moved only so far outward radially that the outer diameter dL of the laser beam 14 and the laser spot thus produced are exactly adjacent to the outer diameter d1 of the brake disc 1. This effectively prevents the laser beam 14 from uncontrollably reaching other parts and causing damage there. Furthermore, this also reduces spatter.

[0036] Accordingly, the process proceeds immediately afterward as the first layer B1 is coated with the second layer B2 (indicated by dashed lines). Here, the coating tool 13 also travels radially from the inside out. The coating B is formed by the first layer B1 and the second layer B2.

[0037] The second layer, B2, has an iron alloy matrix, which is also preferably composed of the aforementioned materials 316L or 430L. The hard particles are preferably composed of an alloy of titanium carbide and ferrochrome (TiC-FeCr) or even solely of titanium carbide or tungsten carbide.

[0038] When the second layer B2 is applied, the tool 13 moves radially outward only so far that the outer diameter dL of the laser beam 14 and the laser spot thus generated therefrom are exactly adjacent to the outer diameter d1 of the brake disc 1.

[0039] Furthermore, it can be identified that the thicknesses of the layers B1 and B2 in the region of the laser beam 14 continuously decrease until the outer diameter d2. Due to the allowance Ü1, this region of the coating B, with its reduced thickness, lies only radially outside the desired theoretical outer diameter d2. In this way, this does not adversely affect the quality of the coating B in the "working area" following the brake disc 1. On the contrary, the thickness of the coating B can be continuously maintained until the theoretical outer diameter d2.

[0040] exist Figure 3 An embodiment is shown in which the tool 13 moves radially from the outside to the inside at a feed rate V (indicated by dashed lines) when applying the coating B. It can be seen here that the tool 13 is made to travel only such a distance at the end of the coating process that the outer diameter dL of the laser beam 14 and, therefore, the laser spot it produces, are just adjacent to, but not beyond, the inner diameter d3 of the disk 11. A related advantage is that significantly less spatter reaches the grooved region 12.

[0041] It can also be observed that the thickness of layers B1 and B2 continuously decreases within the region of laser beam 14. Due to the allowance Ü2, this region of the coating B, with its reduced thickness, lies only radially outside the desired theoretical inner diameter d4. In this way, this also does not adversely affect the quality of the coating B in the subsequent "working area" of the brake disc 1. Therefore, the thickness of the coating B can be continuously maintained up to the theoretical inner diameter d4.

[0042] exist Figure 4 The diagram shows how the brake disc 1 with coating B can be further processed: Therefore, it is advisable to process the second layer B2 by grinding using a suitable grinding tool WZ1. Grinding can process the very hard, rough, and carbon-deposited surface of the second layer B2 to a surface quality suitable for contact with the brake pads.

[0043] Before or after grinding, the coated brake disc 1 can be subjected to a turning process. Here, the outer diameter d1 can be turned to the theoretical outer diameter d2 using a turning tool WZ2. This removes any spatter that may be present in the area of ​​the outer diameter d1. Immediately afterward, a chamfer F1 (indicated by dashed lines) can be machined in the transition area from the disc body 11 to the coating B.

[0044] In the region of inner diameter d3, the inner diameter d3 can be machined to the theoretical inner diameter d4 using turning tool WZ3. Here, it is preferable to machine out most of the region of the groove-shaped recess 12. This can remove any splashes that may exist in the region of the groove-shaped recess 12. Immediately thereafter, a chamfer F2 (indicated by dashed lines) can be machined immediately in the transition region from the disc-shaped body 11 to the cladding B.

[0045] By chamfering F1 and F2, the notch effect at these locations can be reduced and the applicability of corrosion protectants can be improved.

[0046] List of reference numerals 1. Brake disc 10 Matrix 11. Discoid body 11a face 12 grooved recesses 13 Tools 14 Laser beams B Coating B1 First Floor B2 Second Floor d1 Outer diameter d2 Theoretical outer diameter d3 inner diameter d4 Theoretical inner diameter dL laser beam outer diameter D. Rotation axis F1, F2 chamfer V feed rate Ü1 Balance Ü2 Balance WZ1 Grinding Tools WZ2 turning tools WZ3 turning tool.

Claims

1. A method for coating a brake disc (1) made of gray cast iron or steel, wherein, The brake disc (1) has a base (10) and at least one disc-shaped body (11) extending radially from its axis of rotation (D) perpendicular to the brake disc (1), the disc-shaped body having a face (11a) whose normal is parallel to the axis of rotation (D), wherein the disc-shaped body (11) defines the outer diameter (d1) of the brake disc (1) and the outer diameter (d1) has a radially external allowance (Ü1) relative to the theoretical outer diameter (d2), wherein a cladding (B) is applied to the disc by means of a tool (13) during laser welding. On the surface (11a) of the disc (11), the coating consists of a first layer (B1) made of high-quality steel applied to the surface (11a) of the disc (11) and at least one second layer (B2) applied to the first layer (B1), the second layer being a composite material made of an iron alloy matrix with embedded hard particles, characterized in that the coating (B) is performed without prior processing to reduce the outer diameter (d1) of the brake disc (1) to the theoretical outer diameter (d2).

2. The method according to claim 1, characterized in that, A brake disc (1) is used with a radial external allowance (Ü1) in the range of 1.5 mm to 5.0 mm, preferably in the range of 2.0 mm to 3.0 mm, and particularly preferably with a radial external allowance (Ü1) in the horizontal range of 2.5 mm.

3. The method according to any one of the preceding claims, characterized in that, When applying the coating (B) by laser welding, the tool (13) is moved radially such a distance on the corresponding substrate to be coated that the outer diameter (dL) of the laser beam (14) generated by the tool (13) is exactly adjacent to the outer diameter (d1) of the brake disc (1).

4. The method according to any one of the preceding claims, characterized in that, The second layer (B2) is processed by grinding.

5. The method according to the preceding claim, characterized in that, The disc (11) is machined by turning before or after the grinding and thereby reduces its outer diameter (d1) to the theoretical outer diameter (d2).

6. The method according to any one of the preceding claims, characterized in that, The following brake disc (1) is used, wherein the base (10) is connected to the disc body (11) via a groove (12), wherein the inner diameter (d3) of the disc body (11) has a radial internal margin (Ü2) relative to the theoretical inner diameter (d4).

7. The method according to the preceding claim, characterized in that, When applying the coating (B) by laser welding, the tool (13) is moved radially such a distance on the corresponding substrate to be coated that the outer diameter (dL) of the laser beam (14) generated by the tool (13) is exactly adjacent to the inner diameter (d3) of the disc (11).

8. The method according to any one of claims 6 and 7, characterized in that, The disc (11) is machined by turning before or after grinding, thereby increasing its inner diameter (d3) to the theoretical inner diameter (d4).

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