Method for measuring and machining a target outer contour of a workpiece by means of grinding
Patent Information
- Application Number
- PCT/DE2026/100181
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-02-19
- Filing Date
- 2026-02-16
- Publication Date
- 2026-08-27
Smart Images
Figure DE2026100181_27082026_PF_FP_ABST
Abstract
Description
[0001] Method for measuring and machining the outer contour of a workpiece by grinding
[0002] The invention relates to a method for measuring and machining a workpiece rotatably clamped in a machine tool having at least two electrically controllable steady rests, in particular a long shaft, which is machined at least partially on its outer surface by grinding, wherein the workpiece is supported with several electrically controllable steady rests.
[0003] Long, rod-shaped workpieces, when clamped between centers, not only sag due to their own weight but often also exhibit distortion from heat treatment, particularly hardening. To meet the high demands on machining accuracy, grinding requires consideration of additional influencing factors beyond the dynamic compliance behavior of the machine tool, compared to turning processes with geometrically defined cutting edges. These factors include the compliance of the grinding wheel in the contact zone, the deformation of the grinding wheel during the process due to dynamic wear, and the differing geometric engagement conditions between the tool and the workpiece.
[0004] For grinding extremely long, wavy workpieces, external cylindrical grinding between centers is typically used. In this process, the workpiece is held between a first center located on the workpiece headstock and a second center located on the opposite tailstock. The workpiece can be rotated either by the friction of the center on the workpiece headstock side, by separate drive points, or by a chuck with compensating jaws.
[0005] For this type of grinding between centers, it is particularly necessary with long and thin workpieces to support them at one or more points during grinding to achieve a sufficiently high-quality grinding result. This support is usually achieved using one or more steady rests, depending on the length of the workpiece. For this, it is necessary to grind the corresponding steady rest seats before the steady rests can be finally positioned against the workpiece. Grinding the steady rest seats requires additional time, which increases with the length of the workpieces, as several steady rest seats may be required. Various solutions are known from the prior art.DE 102015206565 A1 describes a method for external cylindrical grinding in which, during grinding, the shaft section to be ground is held between centers and additionally supported at the rotationally symmetrical sections by means of a support device. The current diameter values of the rotationally symmetrical sections of the shaft section are measured and these measured values are transmitted to a control device, which adjusts the support device according to the measured diameter values until the finished dimension of the shaft section is reached.
[0006] The principle of a method described in DE 102009059897 B4 is based on the fact that, during grinding, the grinding wheel and the steady rest together form a fixed assembly and that this assembly is moved relative to the round bar workpiece in its longitudinal direction. The grinding wheel always engages the unground round bar first. Furthermore, the described method includes in-process measurement and control of the ground diameter.
[0007] DE 102013226733 B4 describes a method for measuring and generating an external target contour of at least one area of a workpiece, in particular a crankshaft, in which an actual contour on the workpiece is measured, and the measured values are transmitted to the CNC control in such a way that any deviations from the target contour that may be present are corrected and the target contour of the respective workpiece area is adaptively ground on the basis of the measured values recorded for the respective measuring planes of a workpiece area.
[0008] A disadvantage of these solutions is that they are not sufficiently suitable, especially for extremely long components. As already mentioned, extremely long, rod-shaped workpieces, when clamped between centers, not only sag due to their own weight, but often also exhibit distortion from heat treatment, particularly hardening. Sag and distortion overlap and have a different effect on each individual workpiece, meaning that the steady rests provided for support must be reconfigured for each component.
[0009] The object of the invention is therefore to propose a method by which the setting up of steady rests, the grinding of steady rest seats, and the machining of the workpiece, in particular a long shaft, can be carried out both faster and thus more cost-effectively, as well as in an automated manner. According to the invention, this object is achieved, firstly, by determining an axial position with low concentricity error in a central area of the workpiece with respect to the rotational axis of the workpiece using a measuring system integrated into the machine tool.
[0010] At this axial position with low runout, a support kinematic system moves the workpiece in the X and Y directions using a first and a second actuator until a slight pressure build-up occurs, and then raises it to a defined height. The first and second actuators are positioned at a defined angle to each other. For example, an adjustable steady rest with linear actuators can be used as the support kinematic system. These linear actuators can be equipped with measuring probes and capable of supporting and manipulating the component in the X and Y directions. Raising the workpiece, particularly the shaft, creates a preload.
[0011] A first seat is then ground at one end of the workpiece. During this process, the actual workpiece diameter is measured using a measuring device integrated into the machine tool, which could be, for example, a mechanical measuring head. Alternatively, the diameter can also be determined using confocal chromatic sensors, laser scanners, optical micrometers, inductive sensors, or similar devices. The seat created in this manufacturing step serves as a reference surface.
[0012] Next, a second seat is ground at the other end of the workpiece, during which the actual workpiece diameter is also measured using a measuring device integrated into the machine tool – this measuring device can be the same as in the previous machining step or a separate measuring device. The second seat also serves as a reference surface.
[0013] Following this, the cylindricity of the workpiece is measured using machine-integrated measuring and evaluation devices, and subsequently, a cylinder error correction is performed. The cylinder error correction is preferably carried out by adjustment operations on an external clamping device, for example, a tailstock or a chuck.
[0014] Subsequently, a first steady rest seat is ground at one end of the workpiece, and a first electrically controlled steady rest is positioned at this seat. This steady rest seat is preferably ground at the nearest stable steady rest position. This position can, for example, be located at one end of the workpiece at the point where the seat was previously ground as a reference surface for cylinder error correction.
[0015] In a further step, a second steady rest seat is ground, and a second electrically controlled steady rest is attached to this seat. The second steady rest seat can, for example, be ground at the opposite end of the workpiece, at the same location where the second seat was previously ground as a reference surface for cylinder error correction.
[0016] Following the grinding of the first two steady rest seats and the positioning of the first two electrically controlled steady rests, further steady rest seats are ground and all subsequent electrically controlled steady rests are positioned. It is advantageous to begin this process close to one of the first two steady rest seats or steady rests, as the workpiece is most stable there. The number of additional steady rests depends, among other things, on the length-to-diameter ratio of the workpiece, the existing form deviation, and the associated support requirements. The steady rest seats are preferably ground to a defined target diameter. The actual diameter can be determined either manually or using in-process measurement, for example, with a measuring device integrated into the machine tool.A particularly advantageous design of the measuring technology ensures that the diameter is measured at the position of the grinding wheel or immediately next to it.
[0017] After all steady rest seats have been ground and all steady rests have been set, the entire workpiece is ground section by section to a defined target workpiece diameter, whereby the actual workpiece diameter is measured using a measuring device integrated into the machine tool, for which mechanical measuring heads, confocal chromatic sensors, laser scanners, optical micrometers, inductive sensors or similar devices can be used.
[0018] Following this, in a first step, the entire workpiece is ground to the target contours, with the electrically controlled steady rests being adjusted accordingly and the workpiece's axis of rotation being held in a defined position. In a second step, the workpiece's actual parameters are measured, and in a third step, the actual parameters are compared with the target parameters using evaluation and control units integrated into the machine tool control. All electrically controlled steady rests are then adjusted accordingly in the X and Y directions. The first, second, and third steps are repeated until the specified state of the workpiece is achieved. The parameters that are measured and evaluated can include, for example, the workpiece's deflection, diameter, and position, as well as its surface roughness.
[0019] In a second embodiment, the object of the invention is achieved by first grinding a first seat at one end of the workpiece, whereby the actual workpiece diameter is measured using a measuring device integrated into the machine tool, which may, for example, be a mechanical measuring head. Alternatively, the diameter can also be determined using confocal chromatic sensors, laser scanners, optical micrometers, inductive sensors, or similar devices. The seat produced by this manufacturing step serves as a reference surface.
[0020] Next, a second seat is ground at the other end of the workpiece, during which the actual workpiece diameter is again measured using a measuring device integrated into the machine tool. This measuring device can be the same as used in the previous machining step or a separate measuring device. This second seat also serves as a reference surface.
[0021] Following this, the cylindricity of the workpiece is measured using machine-integrated measuring and evaluation devices, and subsequently, a cylinder error correction is performed. The cylinder error correction is preferably carried out by adjustment operations on an external clamping device, for example, a tailstock or a chuck.
[0022] Subsequently, a first steady rest seat is ground at one end of the workpiece, and a first electrically controlled steady rest is positioned at this seat. This steady rest seat is preferably ground at the nearest stable steady rest position. This position can, for example, be located at one end of the workpiece at the point where the seat was previously ground as a reference surface for cylinder error correction.
[0023] In a further step, a second steady rest seat is ground, and a second electrically controlled steady rest is attached to this seat. The second steady rest seat can, for example, be ground at the opposite end of the workpiece, at the same location where the second seat was previously ground as a reference surface for cylinder error correction.
[0024] Following the grinding of the first two steady rest seats and the positioning of the first two electrically controlled steady rests, further steady rest seats are ground and all remaining electrically controlled steady rests are positioned. It is advantageous to begin close to one of the first two steady rest seats or steady rests, as the workpiece is most stable there. The number of additional steady rests depends, among other things, on the length-to-diameter ratio of the workpiece, the existing form deviation, and the associated support requirements. The steady rest seats are preferably ground to a defined target diameter. The actual diameter can be determined either manually or using in-process measurement, for example, with a measuring device integrated into the machine tool.A particularly advantageous design of the measuring technology ensures that the diameter is measured at the position of the grinding wheel or immediately next to it.
[0025] After all steady rest seats have been ground and all steady rests have been set, the entire workpiece is ground section by section to a defined target workpiece diameter, whereby the actual workpiece diameter is measured using a measuring device integrated into the machine tool, for which mechanical measuring heads, confocal chromatic sensors, laser scanners, optical micrometers, inductive sensors or similar devices can be used.
[0026] Following this, in a first step, the entire workpiece is ground to the target contours, with the electrically controlled steady rests being adjusted accordingly and the workpiece's axis of rotation being held in a defined position. In a second step, the workpiece's actual parameters are measured, and in a third step, the actual parameters are compared with the target parameters using evaluation and control units integrated into the machine tool control system. All electrically controlled steady rests are then adjusted accordingly in the X and Y directions. The first, second, and third steps are repeated until the workpiece reaches the specified state. The parameters that are measured and evaluated can include, for example, the workpiece's deflection, diameter, and position, as well as its surface roughness.
[0027] Further advantageous embodiments of the method are the subject of dependent claims.
[0028] The method according to the invention will now be explained with reference to the drawings. The drawings show
[0029] Fig. 1a an ideal workpiece,
[0030] Fig. 1b a workpiece with shape deviation due to sagging or dead weight, Fig. 1c a workpiece with shape deviation due to hardening distortion or pre-machining, Fig. 1d a workpiece with superposition of different shape deviations, Fig. 2 a workpiece arrangement according to claim 1 according to the method
[0031] Fig. 3 shows a workpiece arrangement according to claim 2.
[0032] Fig. 4 shows an arrangement for lifting the workpiece in X and Y,
[0033] Fig. 5a shows an arrangement for measuring the position of the workpiece in X and Y as well as its diameter; Fig. 5b shows an arrangement for measuring the position using combined measuring probes.
[0034] Fig. 5c showing the holding of a workpiece with a counter-holder and
[0035] Fig. 5d shows an arrangement for measurement with dial gauges.
[0036] Figures 1a to 1d show a long shaft 1, i.e., the type of workpiece for which the method according to the invention is particularly suitable, both without and with shape deviations due to various defect influences. During machining, the workpiece 1 rotates about an axis of rotation 3.
[0037] Fig. 1a shows an ideal starting workpiece 1 with a target diameter 10, which is to be achieved after completion of all steps of the method according to the invention. As the starting workpiece, the shaft 1 has an actual diameter 11, which includes a grinding allowance 8, the amount of which corresponds to the difference between the actual diameter 11 and the target diameter 10.
[0038] In reality, however, the initial workpieces 1 are subject to various defects, which are illustrated in Figs. 1b, 1c, and 1d. Fig. 1b shows a form deviation of the shaft 1 in the form of sag, caused by the shaft's own weight when clamped between centers, as is frequently used in the external cylindrical grinding of long shafts 1. The greater the ratio of workpiece length 12 to workpiece diameter 10, 11, the greater the sag.
[0039] The machining of shaft 1 by external cylindrical grinding is usually preceded by other manufacturing steps, of which heat treatments, for example hardening, are primarily responsible for form and dimensional errors in the initial workpieces 1 due to the associated heat input followed by cooling. Fig. 1c shows a shaft 1 with so-called hardening distortion, i.e., a multidimensional form deviation, which is particularly evident in relation to the axis of rotation 3 of the shaft 1.
[0040] In practice, the errors of sag and distortion often overlap, leading to a shape of the initial shaft 1 as shown in Fig. 1d. While shape deviations can be ignored or compensated for by increasing the grinding allowance 8 when machining short shafts 1, this is not possible for long shafts 1. To nevertheless produce dimensionally accurate shafts, steady rests 2.1, 2.2, 2.n are used, as shown in Figs. 2 and 3.
[0041] In the embodiment shown in Fig. 2, a support kinematic 2 and four steady rests 2.1, 2.2, 2.n are used to carry out the method according to claim 1 of the invention: First, a support kinematic 2 is positioned at a determined axial position with a small runout error 21 relative to the axis of rotation 3 of the workpiece 1. This support kinematic 2 can, for example, be a steady rest. In the embodiment shown in Fig. 2, the position with a small runout error 21 is positioned approximately in the middle of the workpiece length 12. With the aid of the support kinematic 2, the workpiece 1 is raised to a defined value in the X and Y directions (not shown here). Subsequently, seats 6 are ground to defined diameters 11 at both ends of the workpiece, which then serve as reference surfaces for measuring the cylindricity of the workpiece 1 and for subsequent cylindricity correction.
[0042] Figure 2 shows two successively ground bezel seats 7.1, 7.2 at the two outer ends of the workpiece 1, each with a bezel 2.1, 2.2 attached to it. The first bezel seat 7.1 is positioned next to one of the seats 6, and the second bezel seat 7.2 is in the position of the other seat 6. The bezel seats 7 can, in principle, be arranged independently of the position of the seats 6.
[0043] In the embodiment shown in Fig. 2, further steady rest seats 7.n with attached steady rests 2.n are arranged in the areas between the support kinematics 2 and the steady rest seats 7.1, 7.2 and steady rests 2.1, 2.2, respectively. The steady rests 2.1, 2.2, 2.n are positioned after the corresponding steady rest seat 7.1, 7.2, 7.n has been ground on the workpiece 1 with a grinding tool 13, whereby the workpiece diameter 11 is measured using a measuring device (not shown) integrated into the machine tool (not shown).
[0044] In the embodiment shown in Fig. 3, five steady rests 2.1, 2.2, 2.n are used to carry out the method according to claim 2 of the invention. First, seats 6 are ground to defined diameters 11 at both ends of the workpiece. These seats subsequently serve as reference surfaces for measuring the cylindricity of the workpiece 1 and for subsequent cylinder error correction. Fig. 3 shows two successively ground steady rest seats 7.1, 7.2 at an outer end of the workpiece 1, to each of which a steady rest 2.1, 2.2 is attached. The first steady rest seat 7.1 is positioned at the location of the seat 6. All steady rest seats 7 can, in principle, be arranged independently of the positions of the seats 6.
[0045] In the embodiment shown in Fig. 3, further steady rest seats 7.n with angled steady rests 2.n are arranged over the entire length 12 of the workpiece 1. The steady rests 2.1, 2.2, 2.n are positioned after the corresponding steady rest seat 7.1, 7.2, 7.n has been ground on the workpiece 1 with a grinding tool 13, whereby the workpiece diameter 11 is measured using a measuring device (not shown) integrated into the machine tool (not shown).
[0046] Figure 4 shows an arrangement for the defined lifting of the workpiece 1 in the X and Y directions. According to the invention, an axial position with a small runout error 21 (not shown here) relative to the rotational axis 3 of the workpiece 1 is first determined in a central area of the workpiece 1, shown here as section A-A, using a measuring system integrated into the machine tool (not shown here). At this axial position with a small runout error 21, the workpiece 1 is moved in the X and Y directions by a support kinematic 2 with a first actuator 4 and a second actuator 5 until a small pressure build-up occurs and is lifted to a defined value, wherein the first actuator 4 and the second actuator 5 are arranged at a defined angle α to each other. The X and Y positions of the workpiece 1 and of the rotational axis 3 of the workpiece 1, respectively, are determined using mechanical or optical measuring probes 18.
[0047] Figures 5a to 5d each show a sectional view (B-B) of a workpiece 1 held by a steady rest 2 with a steady rest body 14 between an upper quill 15.1 and a lower quill 15.2, and on which a grinding wheel 13 engages. The quills 15.1, 15.2 of the steady rest 2 are adjustable in the X-direction and the Y-direction, respectively. Furthermore, measuring arrangements that are advantageous for carrying out the method according to the invention are shown in each figure.
[0048] Figure 5a shows a measuring system 17 for measuring the position of the workpiece 1 in the X-direction, a measuring system 16 for measuring the position of the workpiece 1 in the Y-direction, and a measuring system 9 for determining the workpiece diameter 11. The measuring systems can be integrated into a tool holder (not shown) of the machine tool (not shown) or attached to separate holding devices (not shown). Figure 5b shows an arrangement with only one measuring device in the form of a single probe 18, particularly suitable for the sequential measurement of geometric parameters of the workpiece 1. The probe 18 can also be integrated into a tool holder (not shown) of the machine tool (not shown) or attached to separate holding devices (not shown).
[0049] Fig. 5c shows the same arrangement as Fig. 5b with the difference that the workpiece 1 is subjected to a force acting radially to the axis of rotation 3 of the workpiece by an additional counter support 19.
[0050] Figure 5d shows an arrangement with only one measuring device, here in the form of a dial gauge 20. The dial gauge 20 can be used to measure the runout when the workpiece 1 is rotating about the axis of rotation 3, or, when the workpiece 1 is stationary, for measuring, among other things, the surface geometry. Reference numeral list: 1 Workpiece; Shaft
[0051] 2 Support kinematics, bezel
[0052] 2.1 First bezel, pilot bezel
[0053] 2.2 second bezel
[0054] 2.n further bezel
[0055] 3. Rotation axis of the workpiece
[0056] 4 first actuator
[0057] 5 second actuator
[0058] 6 seats
[0059] 7 Lunette seat
[0060] 7.1 First lunette seat
[0061] 7.2 second lunette seat
[0062] 7. further lunette seat
[0063] 8 Grinding allowance
[0064] 9 Measuring device for workpiece diameter 10 Target diameter of the workpiece
[0065] 11 Actual diameter of the workpiece
[0066] 12 Length of the workpiece
[0067] 13 Grinding wheel; grinding tool
[0068] 14 lunette base bodies
[0069] 15.1 Upper quill; upper component holder
[0070] 15.2 lower quill; lower component holder
[0071] 16 measuring system in Y
[0072] 17 measuring systems in X
[0073] 18 individual measuring probes
[0074] 19 Counterholders
[0075] 20 dial gauge
[0076] 21 axial position with low runout error a angle
Claims
Patent claims 1. Method for measuring and machining a workpiece (1), in particular a long shaft (1), rotatably clamped in a machine tool having at least two electrically controllable steady rests (2), which is machined at least partially on its outer surface by grinding, wherein the workpiece (1) is supported by several electrically controllable steady rests (2), characterized in that that first, in a central area of the workpiece (1), an axial position with low runout error (21) is determined with respect to the rotational axis (3) of the workpiece (1) using a measuring system (16, 17, 18) integrated into the machine tool, that afterwards, at the axial position with low runout error (21) the workpiece (1) is approached in the X and Y directions with a first actuator (4) and a second actuator (5) up to a low pressure build-up and raised to a defined value, wherein the first actuator (4) and the second actuator (5) are arranged at a defined angle (a) to each other. that afterwards a first seat (6) is ground at one end of the workpiece (1), whereby a measurement of the actual workpiece diameter (11) is carried out using a measuring device (9, 16, 17, 18) integrated into the machine tool, that afterwards a second seat (6) is ground at the other end of the workpiece (1), whereby a measurement of the actual workpiece diameter (11) is carried out using a measuring device (9, 16, 17, 18) integrated into the machine tool, that subsequently, using machine-integrated measuring and evaluation devices, a measurement of the cylindricity of the workpiece (1) is carried out and a cylinder error correction is subsequently performed, that afterwards a first bezel seat (7.1) is ground at one end of the workpiece (1) and a first electrically controlled bezel (2.1) is attached to the first bezel seat (7.1), that afterwards a second bezel seat (7.2) is ground and a second electrically controlled bezel (2.2) is attached to the second bezel seat (7.2), that afterwards further bezel seats (7.n) are ground and all further electrically controlled bezels (2.n) are attached, that afterwards the entire workpiece (1) is ground section by section to a defined target workpiece diameter (10), whereby a measurement of the actual workpiece diameter (11) is carried out using a measuring device (9, 16, 17, 18) integrated into the machine tool, and that afterwards In a first step, the entire workpiece (1) is ground to target contours, whereby the electrically controlled steady rests (2.1, 2.2, 2.n) are adjusted accordingly and the rotation axis (3) of the workpiece (1) is held in a defined position. In a second step, the actual parameters of the workpiece (1) are measured. and in a third step, using evaluation and control devices integrated into the machine tool control, a comparison of the actual parameters with target parameters is carried out and all electrically controllable steady rests (2.1, 2.2, 2. n) are adjusted accordingly in the X and Y directions. wherein the first, second and third steps are repeated until the specified state of the workpiece (1) is reached.
2. Method for measuring and machining a workpiece (1), in particular a long shaft (1), rotatably clamped in a machine tool having at least two electrically controllable steady rests (2), which is machined at least partially on its outer surface by grinding, wherein the workpiece (1) is supported by several electrically controllable steady rests (2), characterized in that that a first seat (6) is ground at one end of the workpiece (1), whereby a measurement of the actual workpiece diameter (11) is carried out using a measuring device (9, 16, 17, 18) integrated into the machine tool, that afterwards a second seat (6) is ground at the other end of the workpiece (1), whereby a measurement of the actual workpiece diameter (11) is carried out using a measuring device (9, 16, 17, 18) integrated into the machine tool, that subsequently, using machine-integrated measuring and evaluation devices, a measurement of the cylindricity of the workpiece (1) is carried out and a cylinder error correction is subsequently performed, that afterwards a first bezel seat (7.1) is ground at one end of the workpiece (1) and a first electrically controlled bezel (2.1) is attached to the first bezel seat (7.1), that a second steady rest seat (7.2) is then ground and a second electrically controlled steady rest (2.2) is attached to the second steady rest seat (7.2), that further steady rest seats (7. n) are then ground to a defined target diameter (10) and all further electrically controlled steady rests (2.n) are attached, that the entire workpiece (1) is then ground section by section to a defined target workpiece diameter (10), whereby a measurement of the actual workpiece diameter (11) is carried out using a measuring device (9, 16, 17, 18) integrated into the machine tool, and that in a first step the entire workpiece (1) is ground to target contours, whereby the electrically controlled steady rests (2.1, 2.2, 2.n) are adjusted accordingly and the rotation axis (3) of the workpiece (1) is held in a defined position, In a second step, the actual parameters of the workpiece (1) are measured. and in a third step, using evaluation and control devices integrated into the machine tool control, a comparison of the actual parameters with target parameters is carried out and all electrically controllable steady rests (2.1, 2.2, 2. n) are adjusted accordingly in the X and Y directions. wherein the first, second and third steps are repeated until the specified state of the workpiece (1) is reached.
3. Method according to one of claims 1 or 2, characterized in that the workpiece, in particular a long shaft, is machined according to shape and dimensions.
4. Method according to one of claims 1 or 2, characterized in that the grinding is carried out with one or more grinding tools (13).
5. Method according to one of claims 1 or 2, characterized in that the workpiece (1) is rotatably mounted between two clamping devices positioned coaxially to the axis of rotation (3).
6. Method according to one of claims 1 or 2, characterized in that open or closed electrically controllable bezels (2.1, 2.2, 2.n) are used.
7. Method according to one of claims 1 or 2, characterized in that the grinding of the entire workpiece (1) to a defined target diameter (10) is carried out in several iteration loops.
8. Method according to one of claims 1 or 2, characterized in that the cylinder error correction is carried out by adjustment operations on the clamping means.