Device for processing a disc blank by grinding

Description

[0001] The invention relates to a device for machining a disc blank by grinding.

[0002] The present invention is particularly advantageous for the manufacture of brake discs. In principle, however, it is applicable to the manufacture of a broader group of products, especially annular, disc-like products. Without limiting the invention to this, it will be described in the following text preferably using the particularly valuable application example of a "brake disc".

[0003] A brake disc within the meaning of this document is a flat, essentially rotationally symmetrical structure which, in its intended use, is arranged on a rotating wheel and rotates with it. To brake the rotational movement, pressure is applied to both end faces eccentrically with respect to the axis of rotation by non-rotating brake shoes, so that a frictional force occurs between the brake disc and the brake shoes.

[0004] High-quality brake discs today typically consist of a composite of a metallic core and a coating made of a material with higher abrasion resistance than the core material. This coating is usually a composite material containing, among other substances, ceramic particles, metallic carbides, and / or very strong fibers. Compared to steel or cast iron, such brake disc coatings are inherently more abrasion-resistant, but very difficult to machine. Manufacturing a brake disc with such a coating involves a grinding process to remove material from the coating, creating surfaces whose dimensions and flatness meet the precision requirements for the intended friction surfaces of the brake discs.

[0005] In the most commonly used devices currently employed for machining the friction surfaces of brake disc end faces by grinding, the disc blank and two grinding wheels are driven to rotate around their respective axes. The two grinding wheels rotate around a common axis of rotation, which is aligned parallel to the axis of rotation of the disc blank. Each of the two grinding wheels engages with one of its two end faces against the other end face of the grinding wheel. Primarily due to the risk of overheating at the working surfaces, the achievable throughput of these devices is more limited than that of devices in which the grinding wheels are in contact with the disc blank being machined via their outer surface.

[0006] Documents US 4262452 A, DE 102019128522 A1, US 5607348 A, DE 2343949 A1, EP 0768147 A1 and US 2122978 A disclose devices for grinding rotating disc blanks using two rotating grinding wheels, in which the grinding wheels are in contact with an end face of the disc blank with their cylindrical surface. According to documents DE 102019128522 A1, US 5607348 A, DE 2343949 A1, EP 0768147 A1 and US 2122978 A, the axes of rotation of the grinding wheels are parallel to the plane of rotation of the disc blank.According to the remaining two documents, US 4262452 A and US 5607348 A, the axes of the grinding wheels are not parallel to the plane of rotation of the wheel blank being machined, but are inclined at a small acute angle to this plane, such that on the side of the grinding wheels facing the rotational axis of the wheel blank, the distance between the two rotational axes of the grinding wheels increases with increasing radial distance to the rotational axis of the wheel blank.

[0007] The objective of the present invention is to provide a device for grinding a disc blank using two rotating grinding wheels, in which the grinding wheels are in grinding contact with the cylindrical surface of an end face of the disc blank. Compared to the previously discussed devices of this type, the new device is intended to be improved in that it enables a higher throughput under comparable conditions.

[0008] The scope of protection is defined in claim 1.

[0009] The features according to the invention and their advantageous effect are illustrated with reference to a drawing. Fig. 1: Shows a highly stylized representation of a system according to the invention.

[0010] The illustrated device has the following features in common with devices according to the prior art: Both end faces of the disc blank 1 being processed are machined simultaneously. Two annular grinding wheels 2 are used for this purpose. These wheels are driven to rotate about their respective axes 3 and each wheel's cylindrical surface is in contact with one of the two end faces of the disc blank 1, grinding material from the contact surface. The disc blank 1 is also driven to rotate about its axis 4. With respect to this axis 4 of the disc blank 1, the two contact surfaces between the disc blank 1 and the two grinding wheels 2 lie on the same circumferential and radial coordinates.

[0011] The two grinding wheels 2 are each held by a device designated as a grinding spindle 5 and driven to rotate about their axis 3. In order to enable the grinding wheels 2 to be fed onto the workpiece 1, the two grinding spindles 5 are slidably mounted on a linear guide 6 parallel to the axis 4 of the workpiece 1.

[0012] By having the grinding wheels 2 contact the workpiece 1 with their cylindrical surfaces rather than their flat end faces, the contact areas can be kept very small – and narrowly linear – making it relatively easy to prevent overheating of the workpiece 1 and the grinding wheels 2. Since the two grinding wheels 2 press against the workpiece 1 from precisely opposite sides during grinding, the workpiece 1 is not subjected to bending stresses, or only minimally so, thus making it relatively easy to work without deformation, without vibration, and with high precision.

[0013] According to the further development according to the invention a), the axes 3 of the grinding wheels 2 are not parallel to the plane of rotation of the wheel blank 1 being machined, but are inclined at a small acute angle (less than 30°, typically about 5°) to this plane in such a way that on the side of the grinding wheels 2 of the axis 4 of the wheel blank 1, the distance between the two axes 3 of the grinding wheels 2 decreases with increasing distance to the axis 4.

[0014] Compared to an arrangement in which the axes of the grinding wheels 2 are aligned with respect to the plane of rotation of the workpiece 1, as in the prior art, this reduces space constraints, making it easier to use grinding wheels 2 with a very large diameter. The large diameter of the grinding wheels 2 increases the throughput of the device because, compared to using smaller diameter grinding wheels 2, the risk of overheating at the contact surfaces with the workpiece 1 is further reduced, and because the grinding wheels 2 require less frequent recalibration and replacement.

[0015] If the axis 3 of a grinding wheel 2 is inclined to the plane of rotation of the grinding wheel blank 1 being machined, then - as shown - the lateral surface of the grinding wheel 2 in question is not a circular cylindrical surface, but a truncated conical surface.

[0016] Optionally (not shown) it is also possible to arrange the axis 3 of only one of the two grinding wheels 2 at an angle to the plane of rotation of the wheel blank 1 being machined.

[0017] According to the further development of the invention (b), the two axes 3 of the grinding wheels 2 do not lie in a common plane perpendicular to the plane of rotation of the grinding wheel blank 1 being machined, but are pivoted by a few degrees (maximum 15°) in opposite directions with respect to such a plane. Thus, the two linear contact surfaces of the grinding wheels 2 with the grinding wheel blank 1 being machined are not parallel to each other, but slightly intersect when viewed from a direction parallel to the axis 4 of the grinding wheel blank 1. Therefore, the two lines in which the axes of rotation of the two grinding wheels lie do not intersect the axis 4 of the grinding wheel blank 1, but pass by it on radially opposite sides. Preferably, the distance to axis 4 is the same for both of these lines.(The distance between two lines that do not intersect and are not parallel to each other is equal to the length of the connecting line between the two lines that is perpendicular to both lines.)

[0018] The measure according to the further development b) of the invention ensures that sudden force loads on the grinding wheels 2, which are caused by thickness variations or by local variations in the stability of the wheel blank 1, are not as severe as if the contact surfaces of the two grinding wheels 2 were aligned parallel to each other. This avoids vibrations, eliminates the need for calibration procedures on the grinding wheels 2, and improves the service life of the grinding wheels 2.

[0019] According to a preferred embodiment of feature b, the two axes 3 of the two grinding wheels 2 are inclined equally in opposite directions relative to a plane in which the axis 4 of the wheel blank 1 lies, wherein preferably the centers of the two contact surfaces of the two grinding wheels 2 with the wheel blank also lie in said plane. This ensures the best possible balance of forces with respect to the forces exerted by the two grinding wheels 2 on the wheel blank 1 in its radial direction.

[0020] According to the further development c) of the invention, the device has two workpiece spindles 7, 8, both of which are arranged on a pivotable feed device 9. The pivotability of the feed device 9 allows either one or the other of the two workpiece spindles 7, 8 to be pivoted into the position in which the disc blank 1 mounted on it can be machined. Thus, if a disc blank 1 is currently being machined by the grinding wheels 2 on one workpiece spindle (7), a part 10 located on the second workpiece spindle (8), which was produced by grinding a disc blank 1 according to the invention, can be removed without any loss of time, and then another disc blank to be machined can be mounted. (The removal and mounting can typically be carried out by a robot or other automated device.)) The measure according to the further development c) thus ensures that the time for changing the workpieces hardly causes any breaks in the grinding processes.

[0021] According to a sketched, optional further development of feature c, a dressing unit 11 is also mounted on the feed device 9. This unit consists (as is known per se) of a dressing disc and a holding and drive unit that holds and rotates the disc. The dressing unit 11 serves to measure the working surfaces of the grinding wheels 2 after a defined number of work cycles and to recalibrate or sharpen them by removing material.

[0022] According to a further outlined development, which is optional with respect to feature c, the feed device 9 is displaceable by means of a further linear guide 12 perpendicular to the direction of the axis 4 of the disc blank 1 being machined. This also allows the workpiece spindles 7, 8 and the dressing unit 11, which may also be arranged thereon, to be displaced by means of the further linear guide 12 perpendicular to the direction of the axis 4 of the disc blank 1 being machined.

[0023] Beneficial effects that can be achieved with this include: Space constraints during the pivoting of the feed device 9 can be avoided. The position of the workpiece 1 relative to the grinding wheels 2 can be selected in another dimension. A relative oscillating movement between the grinding wheels 2 and the workpiece 1 can be set radially to the axis 4 of the workpiece 1. This improves the surface finish. It is also possible to process workpieces 1 where the width of the surface to be machined is greater than the engagement width (width of the outer surface) of the grinding wheels 2. The dressing unit 11 does not require its own displacement device for moving the dressing wheel along its axis of rotation.

[0024] If feature b according to the invention is implemented, slight movements of the grinding wheels 2 along the linear guides 6 must also occur during the movement of the dressing unit 11, which is engaged with the grinding wheels, along the linear guide 12. If no such additional movement were made, the cylindrical surfaces of the grinding wheels 2 would not assume the shape of a truncated conical surface (or a cylindrical surface if feature a is not implemented), but would be slightly concave when viewed from the direction of travel at a right angle to their respective axis 3.

Claims

1. Device for machining a disc blank (1) by grinding, wherein the disc blank (1) is a substantially flat and rotationally symmetrical structure and the device has a workpiece spindle (7) and two grinding spindles (5), wherein the workpiece spindle (7) is designed to hold the disc blank (1) and to move it in rotation about its axis (4), and wherein the two grinding spindles (5) are designed to each hold a circular grinding wheel (2) and to move it in rotation about its axis (3), wherein the grinding wheels (2) can each be brought into contact with their outer surface with a respective end face of the disc blank (1), wherein the two contact surfaces between the disc blank (1) and the two grinding wheels (2) lie on the same circumferential coordinate and on the same radial coordinate with respect to the axis (4) of the disc blank (1), characterised in that the two straight lines on which the axes (3) of the two grinding wheels (2) lie pass opposite sides of the axis (4) of the disc blank (1).

2. Device according to claim 1, characterised in that the two axes (3) of the two grinding wheels (2) are inclined in opposite directions by the same amount relative to a plane in which the axis (4) of the disc blank lies.

3. Device according to claim 1 or claim 2, characterised in that the two straight lines in which the axes of the two grinding spindles (5) lie are equidistant from the axis (4) of the disc blank (1).

4. Device according to one of claims 1 to 3, characterised in that the axis of rotation (3) of at least one of the two grinding wheels (2) is inclined at an acute angle of no more than 30° to the plane of rotation of the disc blank (1), wherein on the side of the grinding wheels (2) of the axis (4) of the disc blank (1) with increasing distance from the axis (4) of the disc blank (1), the distance between the two axes of rotation (3) of the grinding wheels (2) decreases.

5. Device according to claim 4, characterised in that the axes (3) of both grinding wheels (2) are aligned at an acute angle to the plane of rotation of the disc blank.

6. Device according to one of claims 1 to 5, characterised in that the device has two workpiece spindles (7, 8), each of which is designed to hold a disc blank (1) and drive it in rotation, wherein both workpiece spindles (7, 8) are arranged on a pivoting feed device (9) so that either one or the other of the two workpiece spindles (7, 8) can be pivoted into the position in which the disc blank (1) arranged on it can be machined.

7. Device according to claim 6, characterised in that the two workpiece spindles (7, 8) are rotated 180° relative to each other with respect to the pivot axis of the feed device (9).

8. Device according to claim 6 or 7, characterised in that the feed device (9) can be moved by a linear guide (12) parallel to the plane of rotation of the disc blank in the machining position.

9. Device according to one of claims 6 to 8, characterised in that a dressing unit (11) designed for calibrating the grinding wheels (2) is also arranged on the feed device (9).

10. Use of the device according to one of claims 1 to 9 for machining brake disc blanks.