DE102024103319A1 - Method and device for producing a planar or cylindrical surface on a coated workpiece and cutting insert of a turning tool - Google Patents

Abstract

The invention relates to a device and a method for producing a planar or cylindrical surface (206) on a coated workpiece (200) using a cutting insert (102) of a turning tool (100), comprising the steps of providing the workpiece (200) which is provided with a coating (202) comprising a carbide with a binder that binds the carbide, or an abrasion-resistant metal alloy, and applying the cutting insert (102) to a surface (204) of the workpiece (200) while the workpiece (200) rotates and while the cutting insert (102) rotates, whereby the planar or cylindrical surface (206) is formed on the workpiece (200). The invention also relates to a cutting insert (102).

Description

The invention relates to a method for producing a planar surface on a coated workpiece. The invention also relates to a device for carrying out the method and a cutting insert for use on a lathe.

The present invention relates to the production of pre-coated workpieces, in particular to the machining of pre-coated brake discs or brake drums whose flat surfaces (friction surfaces) are coated. Typically, these coated brake discs or workpieces comprise a coating comprising a hard material, an abrasion-resistant material, e.g., a carbide bonded by a binder, or an abrasion-resistant alloy with chromium and nickel (e.g., acid-resistant stainless steel, V4A). This coating forms a material layer produced by laser, flame, plasma, or spraying processes. The binder of the hard material layer typically comprises a stainless steel composite mass. Pre-coated brake discs are currently re-faced by grinding, honing, or lapping. When grinding such pre-coated workpieces or brake discs, the problem arises that no suitable grinding wheel is available on the market that is reliably suitable for both grinding the carbide and the binder in order to economically and flatten the surface of the workpiece. Furthermore, grinding brings with it the problem of increased generation of fine dust. Furthermore, grinding is not carried out dry, but with the addition of a cooling fluid, which requires additional drying and cleaning steps on the workpiece.

It is therefore the object of the present invention to provide an improved method for producing a planar surface or cylindrical surface on a coated workpiece, a corresponding device and a cutting plate which take into account the disadvantages mentioned above.

This object is achieved by a method having the features of claim 1, by a device having the features of claim 8 and by a cutting plate having the features of claim 9. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

1. a) Bereitstellen des Werkstücks, das mit einer Beschichtung versehen ist, die insbesondere eine verschleißfeste Oberfläche, insbesondere einen Hartstoff, beispielsweise ein Carbid mit einem das Carbid bindenden Binder, oder eine abrassionsbeständige Metalllegierung umfasst,
2. b) Ansetzen der Schneidplatte an einer Oberfläche des Werkstücks, während das Werkstück rotiert und während die Schneidplatte rotiert, wobei die planare oder zylindrische Oberfläche am Werkstück ausgeformt wird.

The method according to the invention provides for turning, in particular planar machining, of the surface of the workpiece using a lathe. Thus, a method for producing a planar surface on a coated workpiece using a cutting insert of a turning tool is provided, comprising the following steps:

1. a) providing the workpiece which is provided with a coating which comprises in particular a wear-resistant surface, in particular a hard material, for example a carbide with a binder binding the carbide, or an abrasion-resistant metal alloy,
2. b) Applying the cutting insert to a surface of the workpiece while the workpiece is rotating and while the cutting insert is rotating, whereby the planar or cylindrical surface is formed on the workpiece.

The cutting insert is thus used to machine the workpiece's coating flat or cylindrically by turning, which generates significantly less dust than surface machining by grinding, honing, or lapping. To reduce wear on the cutting insert and thus extend the service life of the turning tool, the method according to the invention not only rotates the workpiece but also the cutting insert. This cutting insert has a cutting edge and is rotationally symmetrical.

A particularly abrasion-resistant coating on the workpiece can be achieved if the carbide is selected from the group comprising titanium carbide, tantalum carbide, tungsten carbide, chromium carbide, oxide compounds, and cementite. This has proven particularly advantageous in the production of coated brake discs or coated brake drums.

The binder is preferably made of stainless steel or a stainless steel alloy, which results in a secure bond between the base material of the workpiece, e.g. gray cast iron, and the coating, the carbide.

For reliable surface machining, it has proven advantageous for the rotating cutting insert to comprise a cutting material made of synthetic diamond. Due to the hardness of synthetic diamond, a cutting insert formed in this way is particularly well suited for machining workpieces coated with a composite of carbide and a binder.

In one embodiment, it has proven advantageous if the synthetic diamond is formed as a polycrystalline diamond (PCD) which Preferably, the diamond particles have an average particle size of 30 micrometers (µm) to 50 µm, but alternatively preferably 80 µm to 120 µm, wherein the diamond particles are bound by a binder material. Typically, the binder material of the PCD particles is formed in the form of a metal or ceramic matrix.

Alternatively, a self-grown, synthetic diamond can be used, namely a grown laboratory diamond, which is formed, for example, as a CVD diamond (CVD for “chemical vapor deposition”) or an HPHT diamond (HPHT for “high pressure high temperature”).

It has been found that machining coatings containing carbide causes significant wear on the cutting edge, leading to blunting of the cutting edge of the insert. To reduce this wear, it has proven advantageous to coat the synthetic diamond with a protective layer to minimize wear on the insert.

The protective layer is preferably deposited from the physical vapor phase, i.e., using a PVD process (PVD for "physical vapor deposition"), wherein the protective layer in particular has a coating selected from the group comprising titanium-silicon-nitrogen (TiSiN), aluminum-titanium-nitrogen (AlTiN), aluminum-titanium-silicon-nitrogen (AlTiSiN), aluminum-titanium-chromium-nitrogen (AlTiCrN), aluminum-titanium-chromium-nitrogen (AlCrSiN), and aluminum-titanium-chromium-silicon-nitrogen (AlTiCrSiN). In the production of coated brake discs, a coating of the synthetic diamond of the cutting insert formed from aluminum-titanium-silicon-nitrogen (AlTiSiN) has proven particularly preferred.

The protective layer increases the temperature resistance of the synthetic diamond (PCD or CVD) and its binder, as the diamond does not decompose or dissolve even at temperatures of approximately 600 degrees Celsius, which would otherwise dull the cutting edge. Furthermore, the protective layer protects the individual diamond particles from air and oxygen (and thus from chemical wear).

In order to provide additional thermal protection for the cutting insert, it is advantageous if the protective layer is supplemented with boron or boron nitride.

The protective layer preferably has a layer thickness of between 0.1 µm and 8.0 µm, in particular between 0.2 µm and 1.5 µm.

If a laboratory diamond (CVD diamond or HPHT diamond) is used as an alternative for the cutting insert, it has been found that the protective coating described above does not adhere very well. For this reason, it is advantageous to first apply an adhesion-promoting layer before depositing the protective layer itself using the PVD process.

It has proven advantageous to apply minimal cooling lubrication to the cutting insert and/or the workpiece during turning in step b). This ensures that after facing the coated workpiece, especially after facing the coated brake disc, only a very small amount of fluid remains on the surface, making a subsequent drying step obsolete or requiring less effort.

In this context, it is also advantageous to use isopropanol, acetone, or ethanol for minimum-quantity cooling. These substances provide reliable cooling during turning, and evaporative cooling even occurs during machining, providing an additional cooling effect. Furthermore, these substances evaporate very quickly, completely eliminating the need for a subsequent drying step for the surface-machined or cylindrical workpiece. These substances also have the property of cleaning the workpiece, particularly due to their degreasing properties. The surface-machined workpiece is therefore directly available for subsequent painting, without the need for unnecessary additional intermediate steps.

It has proven advantageous to remove between 0.05 mm and 0.3 mm from the workpiece in step b), as this reliably produces a planar surface.

The uniform temperature development during machining and also the dimensional accuracy are beneficial if the rotational speed of the cutting insert and/or the rotational speed of the rotating workpiece is adjusted depending on the distance of the cutting insert from a rotational axis for the rotation of the workpiece, in particular in such a way that a lower rotational speed is set when the cutting insert is at a greater distance, and that a higher rotational speed is set compared to the lower rotational speed when the cutting insert is at a shorter distance from the rotational axis than the greater distance. In this way, a constant circumferential speed or constant cutting speed.

Reliable surface finishing can be achieved by positioning the cutting insert with its cutting edge at an angle of between 3 degrees and 13 degrees, particularly at an angle of between 5 degrees and 11 degrees, and preferably at an angle of 7 degrees, relative to the workpiece surface. This also provides an axis of rotation for the cutting insert's rotational movement through the corresponding angles relative to the horizontal or relative to the workpiece surface.

The advantages, advantageous embodiments and effects explained in connection with the method according to the invention apply equally to the device according to the invention.

The device according to the invention for carrying out the method comprises a base plate to which a drive unit is attached, the output of which is connected to a cutting insert in a torque-transmitting manner. The cutting insert can also be driven directly via the drive on a turret of the lathe, in particular using one or more intermediate gears. The base plate is preferably attached to or in a lathe with a base holder for quick changeover.

In order to be able to adjust the clearance angle of the cutting plate, it has proven advantageous if the base plate can be fixed with respect to the base holder in a predetermined angular range, which is preferably between 2 degrees and 11 degrees, in particular 7 degrees.

The advantages, configurations and technical effects explained in connection with the method according to the invention and the device according to the invention apply equally to the cutting plate according to the invention.

The cutting insert according to the invention comprises a cutting material formed from a synthetic diamond.

The synthetic diamond is preferably formed as a polycrystalline diamond (PCD), which in particular comprises diamond particles having an average particle diameter of between 30 micrometers (µm) and 50 µm, preferably of substantially 80-120 µm, which are bound by a binder material.

Alternatively, the synthetic diamond can also be formed as a grown laboratory diamond (CVD diamond or HPHT diamond).

Diamond has a low temperature resistance and decomposes at approximately 600 degrees Celsius, especially in the presence of oxygen (atmospheric oxygen). In other words, the diamond then decomposes into CO2, which also causes the diamond grains themselves to decompose. Therefore, it is advantageous for the synthetic diamond to be coated with a protective layer to minimize wear. The protective layer forms a diffusion barrier for atmospheric oxygen and protects the binder and the PCD matrix from chemical wear. The protective layer also acts as an insulator, blocking heat from entering the cutting insert.

Preferably, the protective layer was deposited from the physical gas phase (PVD process) or from the chemical gas phase (CVD process), wherein the protective layer in particular has an application selected from the group comprising titanium-silicon-nitrogen (TiSiN), aluminum-titanium-nitrogen (AlTiN), aluminum-titanium-silicon-nitrogen (AlTiSiN), aluminum-titanium-chromium-nitrogen (AlTiCrN), aluminum-chromium-silicon-nitrogen (AlCrSiN), aluminum-titanium-chromium-silicon-nitrogen (AlTiCrSiN).

To increase the temperature resistance of the protective layer, it has proven advantageous to supplement the protective layer with boron. The protective layer preferably has a layer thickness of between 0.1 µm and 8.0 µm, in particular between 0.2 µm and 1.5 µm.

In the case of a synthetic diamond formed as a lab-grown diamond, the protective layer is applied to an adhesion promoter layer (preferably a titanium or chromium layer). Such an adhesion promoter ensures that the protective layer can be reliably deposited using the PVD or CVD process and adheres to the lab-grown diamond.

The features and feature combinations mentioned above in the description, as well as the features and feature combinations mentioned below in the description of the figures and/or shown alone in the figures, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also to be considered encompassed and disclosed by the invention that are not explicitly shown or explained in the figures, but which emerge and can be produced from the explained embodiments through separate feature combinations.

• 1 eine schematisch illustrierte Seitenansicht des Verfahrens, welches mit einem Drehwerkzeug ausgeführt wird, dessen Schneidplatte an ein beschichtetes Werkstück angesetzt ist;
• 2 eine perspektivische Ansicht auf das Drehwerkzeug aus 1;
• 3 eine Frontalansicht auf das Drehwerkzeug aus 1;
• 4 eine schematische Schnittansicht durch eine Schneidplatte die mit einem polykristallinen Diamant (PKD) gebildet ist; und
• 5 eine schematische Schnittansicht durch eine Schneidplatte die mit einem gewachsenen Labordiamanten (CVD-Diamant) gebildet ist.

Further advantages, features, and details of the invention will become apparent from the claims, the following description of preferred embodiments, and the drawings. These show:

• 1 a schematically illustrated side view of the process carried out with a turning tool whose cutting insert is applied to a coated workpiece;
• 2 a perspective view of the turning tool 1 ;
• 3 a front view of the turning tool 1 ;
• 4 a schematic sectional view through a cutting insert formed with a polycrystalline diamond (PCD); and
• 5 a schematic sectional view through a cutting plate formed with a grown laboratory diamond (CVD diamond).

In the 1 to 3 Parts of a lathe are shown. The turning tool 100 can be seen, which comprises a cutting insert 102 that can be driven in rotation by means of a drive unit 120, here in the form of an electric motor, or by means of a drive on the tool holder (tool turret). In the present case, two opposing (mirrored) and in particular coupled turning tools 100 with cutting inserts 102 are shown, by means of which two flat surfaces can be machined simultaneously. In this way, the machining forces support each other. The machining quality is improved and vibrations are minimized. The respective drive unit 120 preferably applies a torque of 5 Newton meters (Nm) up to 0.5 Nm and in particular achieves speeds of up to 8000 revolutions per minute. The drive unit 120 is coupled to a gear unit 124 via a flange 122. In this case, the gear unit 124 can be arranged rotated in 90-degree increments relative to the drive unit 120. The gear unit preferably has a gear ratio of between 10 to 1 (10:1) and 30 to 1 (30:1), in particular a gear ratio of 20 to 1 (20:1). Instead of the drive units 120 shown, the rotational drive of the cutting insert 102 can also be effected via the tool holder 130 of the turning tool 100.

Adjacent to the gear unit 124 is a cutting insert holder 126, on which the cutting insert 102 is rotatably mounted. The cutting insert holder 126 is connected, in particular in one piece, to a base plate 112, which in turn is screwed to a base holder 110. The base holder 110 forms, for example, a link in a quick-change interface of the lathe. In addition to the cutting insert 102 on the turning tool 100, a workpiece 200 to be machined, in particular a brake disc, can also be driven by the lathe in rotation about a rotation axis 208.

From the 2 and 3 It can be seen that the base plate 112, which is connected to the cutting insert holder 126 in a rotationally fixed manner, has a plurality of elongated holes 128, so that the base plate 112 can be fixed at different angular positions relative to the base holder 110. The base plate 112 can be fixed relative to the base holder 110 in a predetermined angular range, which is between 20 degrees and 50 degrees, in this case in particular 40 degrees. This design allows a clearance angle to be set for the cutting insert 102. Two different clearance angles can be considered here: Firstly, the clearance angle in the axial direction to the workpiece, which is determined by the design of the cutting insert holder 126 and the base plate 112 and the design of the insert seat. Second, there is the clearance angle in the feed direction, which can be adjusted by rotating the base plate 112 on the adapter plate 110. This angle should always be positive, otherwise a cutting edge 118 of the cutting plate 102 will "press" in the feed direction. The higher the feed, the larger the radial clearance angle should be, otherwise the cutting edge 118 will press.

In this case, the cutting insert holder 126 is additionally assigned a minimum-quantity cooling lubrication unit (not shown in detail) to provide minimum-quantity cooling lubrication during machining of the workpiece 200. This unit is operated, in particular, with ethanol, since ethanol dries particularly quickly and also has improved cleaning properties; for example, it dissolves grease and removes dirt.

In 4 A cross-sectional view of a first variant of a cutting insert 102 of the turning tool 100 is shown. The cutting insert 102 has a through-bore 108 so that the cutting insert can be fixed to the output of the drive unit 120 or to the output of the gear unit 124 in a rotationally fixed manner, in a torque-transmitting manner. The cutting insert 102 comprises a cutting material formed from a synthetic diamond. The synthetic diamond is formed as a polycrystalline diamond (PCD), which in particular comprises diamond particles 114 with an average particle diameter of between 80 µm and 150 µm, preferably from 80 µm to 120 µm, in particular substantially 120 µm, which are bound by a binder material 116. The binder material 116 is in particular a metal matrix or a ceramic matrix. Since the binder material Since the cutting insert 116 is not particularly temperature-resistant and decomposes at temperatures of approximately 600 degrees Celsius, a protective layer 104 is additionally provided. This protective layer 104 serves to minimize wear on the cutting insert 102.

The protective layer 104 was deposited from the physical vapor phase (PVD process), although a CVD process is also possible. In this case, the protective layer 104 comprises a coating of aluminum-titanium-silicon-nitrogen (AlTiSiN). In addition, the protective layer 104 is supplemented with boron, which further increases its temperature resistance. The protective layer has a layer thickness of 0.1 µm to 8.0 µm, in particular between 0.2 µm and 1.5 µm.

In 5 A second variant of the cutting insert 102 is shown, which is also formed with a synthetic diamond. A grown laboratory diamond is used here; for example, a CVD diamond or an HPHT diamond. Here, too, a through-bore 108 is provided for rotationally securing the cutting insert 102 to the output of the drive unit 120 or to the output of the gear unit 124. Since it has been found that the protective layer 104 is difficult to deposit on laboratory diamonds using a PVD (or CVD) process, an additional adhesion-promoting layer 106 is provided to promote this adhesion. The adhesion-promoting layer 106 thus acts like an adhesive.

The workpiece 200 is surface machined by turning using one of the two cutting inserts 102 explained above.

1. a) Bereitstellen des Werkstücks 200, das mit einer Beschichtung 202 versehen ist, die insbesondere eine verschleißfeste Oberfläche, insbesondere einen Hartstoff, beispielsweise ein Carbid mit einem das Carbid bindenden Binder, oder eine abrassionsbeständige Metalllegierung umfasst,
2. b) Ansetzen der Schneidplatte 102 an einer Oberfläche 204 des Werkstücks 200, während das Werkstück 200 rotiert und während die Schneidplatte 102 rotiert, wobei die planare oder zylindrische Oberfläche 206 am Werkstück 200 ausgeformt wird.

Based on 1 The method for producing a planar surface 206 on a coated workpiece 200 using a cutting insert 102 of the turning tool 100 is illustrated. The method comprises, in particular, the following steps:

1. a) Providing the workpiece 200, which is provided with a coating 202, which in particular comprises a wear-resistant surface, in particular a hard material, for example a carbide with a binder that binds the carbide, or an abrasion-resistant metal alloy,
2. b) Applying the cutting insert 102 to a surface 204 of the workpiece 200 while the workpiece 200 is rotating and while the cutting insert 102 is rotating, whereby the planar or cylindrical surface 206 is formed on the workpiece 200.

The carbide of the coating 202 on the workpiece 200 is selected from the group comprising titanium carbide, tantalum carbide, tungsten carbide, chromium carbide, oxide compounds, and cementite. The binder consists of stainless steel or a stainless steel alloy.

When machining the surface 204 of the workpiece 200, i.e., in order to obtain the planar or cylindrical surface 206, the drive unit 120 and, if applicable, also the unit for rotating the workpiece 200 are controlled accordingly.

For a particularly good, flat or cylindrical result, the rotational speed of the cutting plate 102 and/or the rotational speed of the rotating workpiece 200 is adjusted depending on the distance of the cutting plate 102 from the rotational axis 208 for the rotation of the workpiece 200. In the present case, the respective rotational speed is adjusted such that a lower rotational speed is adjusted when the cutting plate 102 is at a greater distance, and such that a higher rotational speed is adjusted compared to the lower rotational speed when the cutting plate 102 is at a shorter distance from the rotational axis 208 than the greater distance.

In this way, in step b) the workpiece 200 is turned from 0.05 mm to 0.3 mm.

The present invention ultimately offers the advantage that the workpiece 200 already coated with a hard material layer no longer needs to be ground, but can be surface-machined or cylindrically shaped by turning. This reduces the amount of fine dust generated and eliminates additional steps for post-processing the workpiece 200. For example, the workpiece no longer needs to be cleaned and dried due to the reduced amount of lubricant used during turning. By coating the cutting insert 102 with the protective layer 104, the service life of the cutting insert 102 can also be drastically increased. The running time of the processing machine until the cutting insert needs to be changed can thus be significantly increased compared to turning processes in which the cutting inserts 102 are not driven.

LIST OF REFERENCE SYMBOLS

100

Fixture / turning tool

102

Cutting plate

104

protective layer

106

Adhesion layer / adhesive

108

Through hole

110

Base holder

112

Base plate

114

diamond particles

116

Binder material

118

cutting edge

120

Drive unit / electric motor / pneumatic drive

122

Flange (drive unit)

124

Gear unit

126

Cutting insert holder

128

slot

130

Tool holder

200

workpiece

202

Coating

204

Surface (untreated)

206

Surface (machined) / planar surface

208

rotation axis

Claims (14)

A method for producing a planar or cylindrical surface (206) on a coated workpiece (200) using a cutting insert (102) of a turning tool (100), comprising the steps of: a) providing the workpiece (200) provided with a coating (202) comprising a carbide, in particular a metal-like carbide, with a binder that binds the carbide, or an abrasion-resistant metal alloy, and b) applying the cutting insert (102) to a surface (204) of the workpiece (200) while the workpiece (200) rotates and while the cutting insert (102) rotates, whereby the planar or cylindrical surface (206) is formed on the workpiece (200). Procedure according to Claim 1 , characterized in that the rotating cutting plate (102) comprises a cutting material formed from a synthetic diamond which comprises a protective layer (104) for minimizing wear. Procedure according to Claim 1 or 2 , characterized in that a minimum quantity cooling lubrication takes place during the turning in step b). Procedure according to Claim 3 , characterized in that isopropanol, acetone or ethanol is used for the minimum quantity cooling lubrication. Procedure according to one of the Claims 1 until 4 , characterized in that in step b) the workpiece (200) is turned off by 0.05 millimeters to 0.3 millimeters. Procedure according to one of the Claims 1 until 5 , characterized in that the rotational speed of the cutting plate (102) and/or the rotational speed of the rotating workpiece (200) is set as a function of the distance of the cutting plate (102) from a rotational axis (208) for the rotation of the workpiece (200), in particular in such a way that a lower rotational speed is set when the cutting plate (102) is at a greater distance, and that a higher rotational speed than the lower rotational speed is set when the cutting plate (102) is at a shorter distance from the rotational axis (208) than the greater distance. Procedure according to one of the Claims 1 until 6 , characterized in that the cutting plate (102) is placed with its cutting edge (118) at an angle of between 3 degrees and 13 degrees, in particular at an angle of between 5 degrees and 11 degrees, preferably at an angle of 7 degrees, relative to the surface (204) of the workpiece (200). Device (100) for carrying out the method according to one of the Claims 1 until 7 , comprising a base plate (110) to which a drive unit (120) is fastened, the output of which is connected to a cutting plate (102) in a torque-transmitting manner. Cutting plate (102) for a method according to one of the Claims 1 until 7 or for a device (100) according to Claim 8 , which comprises a cutting material formed from a synthetic diamond. Cutting plate (102) according to Claim 9 , characterized in that the synthetic diamond is formed as a polycrystalline diamond (PCD), which preferably comprises diamond particles (114) with an average particle diameter of between 30 micrometers and 150 micrometers, preferably from 80 micrometers to 120 micrometers, in particular substantially 120 micrometers, which are bound by a binder material (116). Cutting plate (102) according to Claim 9 , characterized in that the synthetic diamond is formed as a grown laboratory diamond (CVD diamond or HPHT diamond). Cutting plate (102) according to one of the Claims 9 until 11 , characterized in that the synthetic diamond is provided with a protective layer (104) to minimize wear. Cutting plate (102) according to Claim 12 , characterized in that the protective layer (104) was deposited from the physical vapor phase (PVD) or from the chemical vapor phase (CVD), wherein the protective layer (102) in particular has an application selected from the group comprising titanium-silicon-nitrogen (TiSiN), aluminum-titanium-nitrogen (AlTiN), aluminum-titanium-silicon-nitrogen (AlTiSiN), aluminum-titanium-chromium-nitrogen (AlTiCrN), aluminum-chromium-silicon-nitrogen (AlCrSiN), aluminum-titanium-chromium-silicon-nitrogen (AlTiCrSiN). Cutting plate (102) according to Claim 13 , characterized in that the protective layer (104) in the case of a synthetic diamond formed as a laboratory diamond is applied to an adhesion-promoting layer (106).