Method for producing a braking element, and braking element

Abstract

The invention relates to a method for producing a braking element and to a braking element. The aim of the invention consists in providing an inexpensive, material-saving, and simple method for producing a braking element. The invention additionally relates to a braking element which is weight-optimized and has an improved protection against wear and corrosion. This is achieved by a method for producing a baking element which consists of a metal main part made of a cast material, having at least one disc-shaped or annular friction surface, wherein the cast metal main part has a microstructure, a defective bainitic structure, and a cast surface layer which forms the cast surface; for the metal part, the cast surface layer is at least partly removed at least in the region of the provided friction surface using a first machining process, a wear- and / or corrosion-protection layer is then arranged at least on the defective bainitic structure, and at least the surface of the wear- and / or corrosion-protection layer can subsequently be modified by means of a second mechanical machining process.

Description

[0001] Method for producing a brake body and brake body

[0002] The present invention relates to the field of automotive engineering and industrial plant engineering and concerns a method for producing a brake body, which can be designed, for example, in the form of a brake disc or brake drum, and a brake body produced according to this method. The brake body produced according to the invention can be used, for example, in motor vehicles or as a braking system for industrial brakes or in wind turbines.

[0003] In addition to the base body, brake bodies can be designed with special cooling structures to dissipate the frictional heat generated during the braking process.

[0004] Conventional brake discs are designed as solid non-ventilated or internally ventilated brake discs and can be made of a metallic or ceramic material.

[0005] Conventional brake drums are of solid construction, sometimes also equipped with cooling structures on the outside of the drum and can be made of a metallic or ceramic material.

[0006] To reduce particulate matter emissions, brake bodies can also be provided with a housing.

[0007] Brake bodies have several functional areas. For example, brake bodies are mounted on the front and rear axles of motor vehicles and have a contact surface that is in contact with the wheel rim on the one hand and the wheel hub on the other. The entire brake body is connected via the contact surface using wheel bolts.

[0008] In addition, brake bodies have areas with friction surfaces through which the braking effect is realized in interaction with rubbing brake pads.

[0009] Brake bodies are currently treated with either short-term corrosion protection near the friction surfaces or long-term corrosion protection near the cooling structures. Short-term corrosion protection only protects the brake disc against corrosion for a short period of time and is worn away during the first braking applications, for example, after a vehicle is delivered. In addition, the friction surfaces have a wear-reducing coating, which, in conjunction with the brake pads, achieves the braking effect.

[0010] Various processes are known from the state of the art for manufacturing brake discs and protecting them from corrosion and wear.

[0011] DE 10 2009 003 161 A1 discloses a coated light metal disc, in particular a brake disc, comprising a support disc, in particular made of a thermally resistant light metal alloy, and a heat-insulating friction layer made of a metal alloy containing nanocrystals. The light metal base body is coated by thermal spraying of a mechanically resistant metal alloy, forming nanoparticles in the sprayed layer.

[0012] From DE 102 03 507 A1 a brake disc for a vehicle is known, comprising a base body made of a metallic material, in particular grey cast iron, which has at least one friction surface with a coating made of a hard material, wherein the base body has a removed material thickness under the coating in a direction parallel to the axis of the brake disc, wherein the base body has a material thickness removed in a direction parallel to the axis of the brake disc by approximately the layer thickness of the coating, or up to + / - 20% more or less, preferably + / - 10%, based on the layer thickness of the coating.

[0013] From DE 100 56 161 A1 a brake disc and method for its production are known, in which a brake disc body made of a cast iron material is provided with a metallic, non-ceramic coating at least in sections and at least on one of its axial outer surfaces.

[0014] To prepare the contact surface of the base body to be coated, the existing oxide layer or other contaminants are removed from the contact surface and the contact surface is roughened by irradiation with fine particles to increase the adhesion of the wear layer. The wear layer is then sprayed onto the contact surface of the base body using flame, arc, or plasma injection molding processes.

[0015] Also known from WO 2012 156 114 A1 is a brake disc and a method for producing a brake disc, in which a brake disc has a base body with at least one contact surface to which a wear layer is applied. To bond the wear layer to the base body, the at least one contact surface of the base body is pretreated. The at least one pretreated contact surface of the base body has a surface topography modified by laser radiation with at least one predetermined parameter in order to improve the positive adhesion between the wear layer and the base body.

[0016] The known manufacturing processes have the significant disadvantage that a large amount of material must be taken into account during the casting of the brake disc. This ensures that after the initial mechanical machining of the friction surfaces, which is usually carried out by turning, a minimum thickness of the disc-like friction surfaces to be coated, consisting exclusively of the basic structure on the friction band surface, is guaranteed. This machining allowance, which is present as chip volume after turning and can be described as the infeed of the machining tools, can amount to up to several millimeters, depending on the shape and position tolerances achieved during the casting process. Therefore, the known manufacturing processes are cost-intensive and complex, as a high proportion of material waste is generated by the mechanical machining of the base body to prepare it for coating with a wear and / or corrosion protection layer.

[0017] Another disadvantage is that known brake bodies are heavy, which, for example, results in increased environmental pollution due to increased vehicle fuel consumption. The object of the present invention is to provide a manufacturing method for a brake body that is cost-effective, uses less material, and is simple. Furthermore, the object of the invention is to provide a brake body that is weight-optimized and offers improved wear and corrosion protection.

[0018] The problem is solved by the invention defined in the patent claims. Advantageous embodiments are the subject of the dependent claims, whereby the invention also includes combinations of the individual dependent claims in the sense of an AND connection, as long as they are not mutually exclusive.

[0019] The object is achieved by a method for producing a brake body which consists of a metallic base body made of a cast material which has at least one disc-like or ring-like friction surface, wherein the cast metallic base body has a basic structure, an intermediate structure with defects and a cast skin layer forming the cast surface, wherein in the metallic body at least in the region of the intended friction surface the cast skin layer is at least partially removed by a first machining operation, then a wear and / or corrosion protection layer is arranged at least on the intermediate structure with defects, wherein subsequently at least the surface of the wear and / or corrosion protection layer can be modified by a second mechanical machining operation.

[0020] It is advantageous if at least parts of the cast skin layer are removed by grinding, laser radiation, abrasive processes and / or chemical processes.

[0021] In an advantageous embodiment of the process, the casting skin layer is completely removed.

[0022] It is also advantageous if the initial machining process produces a graded thickness of the friction surfaces. It is also advantageous if at least the surface of the defect-affected intermediate structure is machined using laser radiation before coating.

[0023] It is also advantageous if the wear and / or corrosion protection layer is arranged in one or more layers.

[0024] In an advantageous embodiment of the method, a graded layer thickness and / or material composition of the wear and / or corrosion protection layer is arranged.

[0025] It can also advantageously be provided that the wear and / or corrosion protection layer is produced by means of direct metal deposition (DMD), direct energy deposition (DED), thermal spraying, plasma nitriding, plasma nitrocarburizing, thermochemical processes and / or with the possible use of technical gases.

[0026] It is further advantageous if the coating of the wear and / or corrosion protection layer is carried out with at least one hard metal, metal alloy, metal matrix with embedded carbides and / or oxide ceramics or a combination material of carbides and / or oxide ceramics.

[0027] It is also advantageous if a metallic buffer layer is arranged before coating the wear and / or corrosion protection layer.

[0028] It is also advantageous if at least the load-bearing cooling structures of the brake body are coated with an Al-based corrosion protection layer and subsequently heat-treated.

[0029] The brake body produced according to the method according to the invention has at least one metallic base body made of a cast material with at least one disc-like or ring-shaped friction surface, wherein the cast metallic base body has at least one basic structure, a defective intermediate structure and a cast skin layer, wherein a wear and / or corrosion protection layer is arranged at least on the surface of the defective intermediate structure, and wherein at least the friction surface has a joining zone which is formed at least from the wear and / or corrosion protection layer and the defective intermediate structure.

[0030] In an advantageous embodiment of the brake body, the wear and / or corrosion protection layer is arranged on the defective intermediate structure and the cast skin layer, wherein the surface portion of the cast skin layer present on the friction surface amounts to up to 90%.

[0031] Also advantageously, the wear and / or corrosion protection layer is arranged in a material-to-material manner by means of a thermal coating process.

[0032] Advantageously, the layer thickness of the wear and / or corrosion protection layer and at least the intermediate structure containing defects is graded.

[0033] In addition, it can advantageously be provided that the wear and / or corrosion protection layer is formed in one layer or in multiple layers.

[0034] In an advantageous embodiment of the brake body, the layer thickness of the wear and / or corrosion protection layer is 50 pm to 200 pm for a single-layer coating or 125 pm to 250 pm for a two-layer coating.

[0035] Also advantageously, at least the cooling structures are coated with an Al-based corrosion protection layer.

[0036] Furthermore, it can advantageously be provided that the friction surfaces have a graduated thickness and / or a graduated material composition of the wear and / or corrosion protection layer. The solution according to the invention provides a method for producing a brake body that is cost-effective, material-saving, and simple. Furthermore, a brake body is provided that is weight-optimized and has improved wear and corrosion protection.

[0037] Due to the casting process and the cooling behavior of the cast blank of a brake body, a metallic base body is present which, in the case of metallic cast blanks made of steel or grey cast iron, essentially has three different areas.

[0038] The first area is the casting skin edge zone. According to the invention, a casting skin edge zone is defined as a limited area on the casting surface that, depending on the material, may exhibit various defects and deviations from the basic structure inside the casting. In this casting skin edge zone of the casting, a casting skin layer is present. This layer forms during solidification of the melt due to direct contact with the casting mold and the associated increased cooling rate. It has a fine-crystalline structure.

[0039] Beneath the casting skin layer, but within the casting skin edge zone, there is a cast structure, which according to the invention is to be understood as a flawed intermediate structure. This intermediate structure contains undesirable defects within the structure. These can be non-metallic inclusions, gases, or transformations in microscopic or macroscopic dimensions. Non-metallic inclusions should also be understood as graphite inclusions in degenerate forms in gray cast iron materials. Ordered forms of graphite include, for example, lamellar graphite or spheroidal graphite, which according to the invention are explicitly not to be understood as degenerate forms of graphite.

[0040] A basic structure is formed inside the metallic base body that exhibits the properties of the desired base material. The key features of the basic structure are that, in contrast to the intermediate structure, there are essentially no defects and a substantially homogeneous microstructure. In an advantageous embodiment of the brake body, the basic structure can be composed of an ordered graphite arrangement in the form of flake graphite or spheroidal graphite, which enables particularly cost-effective material use and economical processing of the metallic base body.

[0041] It is known from the prior art that after the casting process, the metallic base body, particularly in the area of ​​the disc-like friction surface in brake discs or the annular friction surface in brake drums, has a layer thickness of 0.05 mm to 0.2 mm. Furthermore, it is known that the casting skin layer and the imperfect intermediate structure must be completely removed from the cast blank in order to prepare the base structure area for subsequent coating with a wear and / or corrosion protection layer or to market it as a conventional uncoated brake disc.

[0042] The method according to the invention provides a metallic base body made of a cast material in which a smaller amount of steel or iron cast material is used, since according to the invention, after the casting of the metallic base body, the casting skin edge zone is machined in a first machining step and only the casting skin layer is at least partially removed in order to arrange a wear and / or corrosion protection layer at least on the intermediate structure with defects.

[0043] In the context of the invention, at least partial removal of the cast skin layer is to be understood as meaning that in any case areas of the intermediate structure containing defects are freed from the cast skin layer, whereby after the mechanical processing of the friction surfaces the surface proportion of the cast skin layer can be up to 90%.

[0044] The first machining step can advantageously be performed by grinding, laser irradiation, abrasive processes, and / or chemical processes. In particular, grinding the metal base body, in contrast to the conventional removal of the cast skin layer by turning with a cutting tool, enables a homogeneous surface with greater dimensional accuracy and improved axial runout of the brake body, so that the desired target geometry of the surface to be coated is achieved during the first machining step. The precise grinding of the friction band surfaces of the base body also results in an increased uniform layer thickness of the wear and / or corrosion protection layer and a reduction in chip volume during finishing.

[0045] A further advantage is that grinding partially down to the imperfect intermediate structure results in significantly lower tool wear, as this avoids unwanted vibrations and tool impact during machining in the area of ​​the imperfect intermediate structure, unlike the conventional multi-stage turning of the surface. The advantageous effects of grinding are further complemented by the fact that the material is only machined down to the imperfect intermediate structure, meaning the tool is subjected to less stress than with turning due to the irregular material properties and existing imperfections in the structure. Furthermore, the high precision of mechanical machining by grinding reduces the infeed dimensions for finishing, as any resulting shape deviations need to be infed to a lesser extent.This reduces the cycle time, reduces the chip volume and increases the process capability of the mechanical finishing.

[0046] In a particularly advantageous embodiment of the process, the cast base body can be manufactured with such a high manufacturing accuracy that the first step of mechanical machining of the friction surfaces and / or contact surfaces can be greatly simplified or even eliminated entirely.

[0047] After the first machining step, at least the surface of the friction surface, which essentially consists of a flawed intermediate structure, is coated with a wear and / or corrosion protection layer using a coating process. By coating the surface of the flawed intermediate structure with the wear and / or corrosion protection layer, at least the area of ​​the friction surface has a joining zone formed at least from the wear and / or corrosion protection layer and the flawed intermediate structure. According to the state of the art, cooling structures are dimensioned with an oxidation allowance in the form of a material addition, since oxidation reactions reduce the strength of the material during daily use of the brake body. This applies both to the ventilation bars between the friction surfaces of an internally ventilated brake disc and to the cooling structures of a brake drum.

[0048] In an advantageous embodiment of the method and the brake body, it can be provided that at least the cooling structures are coated with a permanently effective and firmly bonded corrosion protection layer. The coating of at least the cooling structures can particularly advantageously be carried out with an Al-based corrosion protection layer, and the corrosion protection layer can be incorporated into at least the material of the ventilation bars through a final heat treatment using diffusion processes.

[0049] By coating the cooling structures and the subsequent heat treatment, it is possible to provide long-lasting protection against corrosion for the material structures forming the cooling structures, which eliminates the need for oxidation additives in the design of the cooling structures and thus saves raw material.

[0050] A particularly good material bond between the material of the metallic base body and the material of the wear and / or corrosion protection layer can be achieved if the wear and / or corrosion protection layer is produced by means of a thermal coating process, particularly advantageously by means of direct metal deposition (DMD), direct energy deposition (DED), thermal spraying, plasma nitriding, plasma nitrocarburizing and / or a thermochemical process and with the possible use of technical gases.

[0051] Due to the existing differences in heat generation in different zones of the friction surface and in heat dissipation through different zones of the cooling structures and contact surfaces, different thermocyclic loads and deformations result in the area of ​​the friction surfaces. With a disc-shaped friction surface geometry in brake discs, this is further driven by the resulting different relative speeds between the lining and the friction band, which are at different distances from the rotational axis.

[0052] In a particularly advantageous embodiment of the method, to improve the thermal balance in the brake body, a graded geometry is created during the initial mechanical machining of the friction surface, which is then used to create a graded layer thickness during the coating process. This enables improved heat conduction and thus a more even heat distribution within the brake body to compensate for varying heat developments at the respective periphery of the friction surface. As a result, the heat flow within the metallic base body is homogenized across the entire friction surface.

[0053] In order to achieve an optimized heat balance within the friction surface, it may also be provided that a graded layer thickness and / or material composition of the friction surface is provided.

[0054] In order to achieve a standardized and improved surface quality, it can advantageously be provided that after the first processing and before coating the wear and / or corrosion protection layer, at least the surface of the defective intermediate structure is at least partially improved by means of laser irradiation.

[0055] Laser irradiation of the friction surface has the significant advantage of reducing defects and surface contamination, such as existing graphite pockets or grinding residues. Furthermore, the reduction of near-surface carbon increases the available iron content in the coating bonding zone and reduces the uneven alloying of carbon. The surface improvement makes it possible to achieve high coating and bonding quality even with a single coating using a coating process, due to the increased bonding metal content on the prepared friction belt surface.

[0056] With a thermal coating applied directly to the surface of the defect-affected intermediate structure, a particularly thin wear and / or corrosion protection layer can be provided, which leads to a significant reduction in the material required for the brake disc during the casting process of the metallic base body. Thus, the wear and / or corrosion protection layer of the friction surface can advantageously have a layer thickness of 50 μm to 200 μm for a single-layer coating and 125 μm to 250 μm for a two-layer coating.

[0057] The friction surface can be coated with the wear and / or corrosion protection layer using at least one cemented carbide, a metal alloy, a metal matrix with embedded carbides and / or oxide ceramics, or a combination of carbide and oxide ceramics. Especially with carbide materials, materials adapted to the load spectrum acting within the wear and / or corrosion protection coating can be used. For example, it is conceivable that mixed carbides and cermets could be used, which offer advantages, for example, with regard to their thermal expansion in the metal matrix composite and the associated reduction of crack structures and residual stresses, their good thermal oxidation resistance, their advantageous wettability compared to the matrix material, and their improved processing with thermal coating processes.

[0058] In order to improve the material bonding of the wear and / or corrosion protection layer, it can be provided that a metallic buffer layer is arranged before the wear and / or corrosion protection layer is coated.

[0059] The technical advantages of the manufacturing method according to the invention and the brake body produced thereby are, in summary, that - the simple machining and removal of the cast skin layer enables a direct coating on the friction band surface of the defective intermediate structure and / or partial cast skin layer, thereby realising a reduction in the chip volume,

[0060] - a reduction in material usage is made possible,

[0061] - the thermal resistance between the metallic base body and the wear and / or corrosion protection layer is adapted to the thermocyclic load spectrum,

[0062] - the required material addition for oxidation and / or wear can be reduced or completely eliminated,

[0063] - the performance of the brake body is increased and its comfort behavior is improved,

[0064] - a smaller allowance can be taken into account during the casting process of the metallic base body, thus saving costs through lower material usage,

[0065] - the thermal coating process enables an improved material bonding of the wear and / or corrosion protection layer, and

[0066] - the second mechanical processing for surface modification improves the friction belt surface and can be realized more efficiently.

[0067] The invention is explained in more detail below using an exemplary embodiment.

[0068] Example

[0069] An internally ventilated brake disc for a mid-size passenger car, manufactured using a casting process, is provided with a hardness of 190–230 HV [3] in the area of ​​the lamellar base structure. The brake disc consists of a metallic base body made of gray cast iron and has two opposing friction surfaces as well as a contact surface for attaching the brake disc to a rotating axle. The two friction surfaces are connected by ventilation webs. After the metallic base body is removed from the casting mold, it is clamped centrally via the formed ventilation channels using workpiece clamping devices, and the intended contact surface is machined.

[0070] Subsequently, the existing casting skin layer is essentially completely removed by grinding on both sides of the friction belt, down to the imperfect intermediate structure, which is a cast structure with a disordered graphite arrangement. The surface partially freed of the casting skin layer, which shows a cast structure with a disordered graphite arrangement and areas with a remaining casting skin layer, is irradiated with a CO2 laser for surface standardization, and the surface is almost completely cleaned of grinding process and graphite residues.The brake disc is then fed into a thermal coating system, preheated inductively to 185 + / - 5°C, measured on the surface to be coated, and a first corrosion protection layer made of a 316L stainless steel alloy is coated on the surface area intended as the friction surface by laser deposition welding under a locally generated argon protective gas atmosphere, and a material-fit connection is created between the surface area of ​​the cast structure with a disordered graphite arrangement, individual surface areas with a cast skin layer and the stainless steel alloy.

[0071] In a second coating process, a second layer consisting of a 430L stainless steel alloy with TiC hard material particles embedded in the metal matrix is ​​applied to the first layer by means of laser deposition welding.

[0072] To create an improved surface topography, the resulting wear and corrosion protection layer is then machined and modified in a second mechanical processing step by grinding. No mechanical processing of the surfaces is performed in the area of ​​the ventilation channels. The structures of the ventilation channels are coated with an AISi-12 alloy using LBD spraying and subsequently heat-treated.

[0073] The friction surfaces have a composite hardness of 500-750 HV

[0010] and long-term wear and corrosion protection.

[0074] With the manufacturing process according to the invention, the casting material to be used is reduced by 2.9 kg and the weight of the brake disc by 1.1 kg compared to known conventional internally ventilated brake discs, based on a brake disc with a total friction band area of ​​approximately 1000cm 2 reduced.

Claims

Patent claims 1. A method for producing a brake body which consists of a metallic base body made of a cast material which has at least one disc-like or ring-like friction surface, wherein the cast metallic base body has a basic structure, an intermediate structure with defects and a cast skin layer forming the cast surface, wherein in the metallic body at least in the region of the intended friction surface the cast skin layer is at least partially removed by a first machining step, then a wear and / or corrosion protection layer is arranged at least on the intermediate structure with defects, wherein subsequently at least the surface of the wear and / or corrosion protection layer can be modified by a second mechanical machining step.

2. Method according to claim 1, in which at least parts of the casting skin layer are removed by means of grinding, laser radiation, abrasive processes and / or chemical processes.

3. A method according to claim 1 or 2, wherein the casting skin layer is completely removed.

4. Method according to claim 1, wherein the first machining produces a graded thickness of the friction surfaces.

5. A method according to claim 1, wherein at least the surface of the defect-affected intermediate structure is treated by means of Laser radiation is used.

6. Method according to claim 1, wherein the wear and / or corrosion protection layer is arranged in one or more layers.

7. Method according to claim 1 or 4, wherein a graded layer thickness and / or material composition of the wear and / or corrosion protection layer is arranged.

8. The method according to claim 1, wherein the wear and / or corrosion protection layer is produced by means of direct metal deposition (DMD), direct energy deposition (DED), thermal spraying, plasma nitriding, plasma nitrocarburizing, thermochemical processes and / or with the possible use of technical gases.

9. Method according to claim 1, wherein the coating of the wear and / or corrosion protection layer is carried out with at least one hard metal, metal alloy, metal matrix with embedded carbides and / or oxide ceramics or a combination material of carbides and / or oxide ceramics.

10. The method according to claim 1, wherein a metallic buffer layer is arranged before coating the wear and / or corrosion protection layer.

11. The method according to claim 1, wherein at least the load-bearing cooling structures of the brake body are coated with an Al-based corrosion protection layer and subsequently heat-treated.

12. Brake body, manufactured according to at least one of the preceding claims 1 to 11, which has at least one metallic base body made of a cast material with at least one disc-like or ring-shaped friction surface, wherein the cast metallic base body has at least one basic structure, a defective intermediate structure and a cast skin layer, wherein a wear and / or corrosion protection layer is arranged at least on the surface of the defective intermediate structure, and wherein at least the friction surface has a joining zone which is formed at least from the wear and / or corrosion protection layer and the defective intermediate structure.

13. Brake body according to claim 12, wherein the wear and / or corrosion protection layer is arranged on the defective intermediate structure and the cast skin layer, wherein the surface portion of the cast skin layer present on the friction surface is up to 90%.

14. Brake body according to claim 12, wherein the wear and / or corrosion protection layer is arranged in a materially bonded manner by means of a thermal coating process.

15. Brake body according to claim 12, wherein the layer thickness of the wear and / or corrosion protection layer and at least the intermediate structure with defects is graded.

16. Brake body according to claim 12, wherein the wear and / or corrosion protection layer is formed in a single layer or in multiple layers.

17. Brake body according to claim 12, wherein the layer thickness of the wear and / or corrosion protection layer is 50 pm to 200 pm for a single-layer coating or 125 pm to 250 pm for a two-layer coating.

18. Brake body according to claim 12, wherein at least the cooling structures are coated with an Al-based corrosion protection layer.

19. Brake body according to claim 12, in which a graded thickness of the friction surfaces and / or a graded material composition of the wear and / or corrosion protection layer is present.