Method for the high-precision grinding of workpieces, and grinding machine for carrying out the method

Abstract

Using the method according to the invention and the grinding machine provided for carrying out the method, high-precision workpieces (1) are ground, wherein a workpiece headstock (3) having a workpiece spindle (2) is clamped in for grinding the workpiece (1), and the workpiece (1) is ground by means of an HF grinding spindle (5) with a grinding wheel (6) clamped thereon, (1) and, after corresponding wear of the grinding wheel (6) or of the grinding lining (13), the grinding wheel (6) is dressed by means of a dressing unit (7). According to the invention, the dressing unit (7) dresses the grinding wheel (6) by means of a dressing wheel (9) which is clamped and driven on an HF dressing spindle (8). The components of the dressing unit (7) are at least partially made of CFRP material and are designed in such a way that the dressing spindle (8) almost completely prevents the thermal expansion of the CFRP components by means of targeted heat conduction and achieves a significantly higher vibration damping and rigidity behaviour compared with steel. By means of the CFRP components, a respective spindle (5, 8) is designed to be free of thermal expansion and to damp vibrations to a high degree.

Description

[0001] Applicant: Erwin Junker Maschinenfabrik GmbH F / LE / ch / si / sd Our reference: J86270PCT

[0002] METHOD FOR HIGH-PRECISION GRINDING OF WORKPIECES AND GRINDING MACHINE FOR PERFORMING THE METHOD

[0003] The invention relates to a method for high-precision grinding of workpieces according to the preamble of claim 1 and to a grinding machine for carrying out the method according to the preamble of claim 5.

[0004] The demands placed on workpieces produced by grinding are constantly increasing, so the demands on their production and on the grinding machines used to manufacture high-precision workpieces are also increasing.

[0005] The present invention relates to improving the quality of grinding results by further improving the grinding wheels, dressing tools, and workpiece-bearing motor spindles. Recently, efforts have been made to improve machine designs to achieve further improved and higher-precision workpieces, particularly with regard to grinding spindles. These grinding spindles operate at very high speeds, which, while enabling high-quality grinding results, also significantly increases the demands on the design of such spindles. This includes appropriate bearings, as the speeds for such grinding spindles, in the sense of so-called high-frequency grinding spindles, reach speeds between 8,000 rpm and 1000 rpm. -1 and 10,000 min' 1 with a target duration of up to 30,000 minutes -1are designed for high grinding performance. Since high grinding forces are exerted on the grinding spindle by the grinding wheel to achieve high grinding speeds, the input of heat energy into the grinding spindle, including drive-related heat energy, is a crucial factor influencing design modifications. These modifications and improvements to the grinding spindles focus on the increasing trend of incorporating fiber-reinforced plastics, at least partially, into the spindles. This allows for the use of essential components and complete grinding spindles—commonly referred to as motor spindles—which largely prevent, or at least significantly reduce, heat-induced expansion that can lead to defective grinding results.These optimizations of the described motor spindles are applied exclusively to grinding spindles in the prior art. The prevailing opinion is that improving the fundamental design and the use of CFRP materials in grinding spindles is beneficial. This is intended to reduce errors that, despite the highest precision in manufacturing and design, are transferred to the workpiece and thus negatively impact grinding quality. Grinding spindles operate at the highest speeds and have the greatest structural and functional influence on the entire manufacturing process of high-precision ground workpieces. When motor spindles are mentioned in the prior art, this term refers to grinding spindles, based on the understanding that improved design of grinding spindles is most likely to lead to further improvements in the quality of the workpieces being ground.

[0006] German patent application DE 10 2019 203 078 A1 describes a motor spindle primarily used for milling, in which fiber-reinforced plastic materials replace previously used steel parts. This known motor spindle incorporates components made of various CFRP materials, with at least two different CFRP materials being used to influence thermal conductivity, stiffness, and / or coefficient of thermal expansion in order to improve the milling result. Through targeted, property-specific adaptation of certain areas or components of such a known motor spindle, which operates in speed ranges from over 30,000 rpm up to 60,000 rpm, the following improvements are achieved:Operating at 000 revolutions per minute, numerous advantages arise, such as improved vibration damping and higher dynamic stiffness, resulting from the targeted selection of special CFRP plastic materials, thus providing the rigid bearing required for these extremely high speeds. The heat transfer from each inner bearing ring to a central area is specifically controlled via a spacer sleeve.

[0007] German patent DE 10 2017 120 523 A1 describes a motor spindle designed as a grinding spindle sleeve, in which a grinding wheel can be mounted on a cone. In this known motor spindle, the weight of the entire motor spindle is reduced through the use of CFRP components, such as the housing, bearing shields, grinding wheel, spacer sleeve, rotor carrier, and cover cap, thereby achieving higher precision in the manufactured workpieces.

[0008] Similarly, DE 10 2013 109 947 A1 describes a motor spindle suitable for lathes and grinding machines, which is a grinding spindle and in which at least some of its components are made of CFRP materials, thus improving the quality of the ground workpieces. DE 19 726 341 A1 describes another motor spindle in which components made of CFRP materials are also incorporated. The use of CFRP material, which, for example, surrounds the rotor of this shaft base material, enables extremely high peripheral speeds of 150 m / s and spindle shaft speeds of up to 150,000 rpm. -1 achieved. These high speeds allow for high grinding performance and also lead to improvements in the grinding accuracy of the ground workpieces.

[0009] German patent DE 40 09461 A1 describes a spindle made entirely of CFRP material, which is used in a machining center, for example, a drilling machine or a milling machine. The spindle with its CFRP components also allows it to be used as a grinding spindle. It is pointed out that steel spindles do not achieve the required workpiece accuracies, and therefore the use of CFRP components in the spindle leads to a further improvement in the quality and thus the grinding result of the ground workpiece.

[0010] EP 3 069 848 B1 describes a method for forming a fiber-reinforced composite structure, which is manufactured as a CFRP sleeve and is intended to encase a metallic mandrel. This describes a manufacturing process for components that can be produced using CFRP material for defined components of a motor spindle, i.e., a grinding spindle.

[0011] Finally, EP 2 725 392 B1 describes a spindle device that consists partly of metal and partly of CFRP materials. The known spindle is a high-speed spindle with a tool holder on which, for example, a grinding wheel can be mounted. A cylindrical element made of CFRP material encases the spindle shafts, thus preventing the transfer of heat introduced into the spindle to, for example, the bearings. This allows the known motor spindle to perform the drive task of, for example, a grinding wheel on a workpiece with greater accuracy. In the known motor spindles according to the prior art described above, the advantages of using CFRP material for selected components of drilling or milling spindles are utilized, thereby improving the manufacturing result compared to motor spindles made entirely of steel.These improvements in the design of motor spindles are aimed at grinding, drilling, or milling operations. While the combination of steel and CFRP components for such spindles has improved the quality of the manufactured workpieces, the requirements in grinding technology exceed the accuracies achievable with this approach for various applications.

[0012] The object of the present invention is therefore to adapt, in addition to the grinding spindles, other elements of the basic machine structure in such a way as to further improve the achievable accuracy and repeatable precision of the ground workpieces.

[0013] This problem is solved by a method having the features of claim 1 and by a grinding machine for carrying out the method having the features of claim 5. Advantageous embodiments are defined in the respective dependent claims.

[0014] According to the invention, the required high process reliability of the manufactured ground workpieces is achieved by transferring the advantages of CFRP components – namely, suppressing thermal expansion, reducing weight, reducing or optimizing dynamic vibration behavior, increasing damping properties, and improving stability – to other assemblies, in addition to using CFRP components in grinding spindles. Surprisingly, it has been shown that dressing plays a significant role in the process reliability of grinding workpiece production by dressing the grinding wheels on their grinding surface in defined cycles. This is based on the surprising finding that the grinding result can be further improved by performing the dressing process even more flawlessly.One problem with dressing, related to the high speeds used in grinding wheel dressing, is the so-called micro-ripple, also known as chatter or short weaviness behavior. This is where the invention comes in, which focuses on a holistic system approach. In this approach, not only the grinding spindle but also the dressing spindle is redesigned to transfer the experience gained in improving process reliability with grinding spindles that also incorporate CFRP components to the dressing units. By considering the entire system, which includes at least the grinding spindle and the dressing spindle, a significant improvement in the accuracy of the ground workpieces can be achieved.The overall system approach considers at least the constructive improvement and modification of the grinding spindle and dressing unit to meet the high quality requirements for the workpieces being ground. Further significant advantages from improved grinding wheel dressing allow for higher grinding wheel performance with the same or improved grinding quality on the workpieces. This increased grinding performance leads to reduced grinding times and thus to a reduction in unit costs per workpiece.

[0015] Ideally, the workpiece spindle should also be considered in the overall system analysis. This allows for a comprehensive process that considers the grinding, workpiece drive, and dressing processes. Optimizing the designs through material combinations of steel and CFRP, or by constructing the spindles entirely from CFRP, can achieve improved FFT (short weaviness) properties as a grinding result on the workpiece, potentially even eliminating the need for finishing altogether. Extending the overall system analysis, i.e.,The identical design for the grinding spindle, dressing unit, and workpiece spindle offers the further advantage that even the workpiece spindle, which under this new design is designed for a significantly higher speed range, can be fitted with a dressing wheel that operates advantageously at even higher speeds. This allows grinding wheels designed for even higher cutting speeds to be dressed. In this improved version, this eliminates the need for a separate dressing unit for dressing the grinding tool.

[0016] It is understood that the invention, which focuses on the overall system and includes dressing, contributes significantly to improving the quality of the grinding result. Thus, dressing is preferably performed at least partially concurrently with the main grinding process, for example, in centerless grinding. This means that dressing and grinding can be carried out at least partially in one operation.

[0017] It should be mentioned in this context that, so far, no consideration has been given to extending the design of known grinding spindles, which are at least partially made of CFRP materials, to a dressing unit. This is because, firstly, dressing times are typically significantly shorter compared to grinding process times. Therefore, it has not been considered that a further improved dressing unit could have a considerable impact on the accuracy of workpieces requiring high-precision grinding, nor that the properties that can be improved by combining steel and CFRP or using pure CFRP spindles could also be applied to dressing units.It has now been surprisingly revealed that the short weaviness introduced into the tool during dressing can be caused by high-frequency vibrations, which can occur at the extremely high speeds mentioned above. This leads to quality defects in the grinding contour due to the reduced short weaviness or FFT (Functional Face-Time) properties, negatively impacting high-precision grinding results. It has now been shown that these negative effects on the grinding result can be reduced by using modified dressing units, provided the design of the dressing units is adapted to the design of grinding spindles with CFRP (carbon fiber reinforced polymer) components, even if the cost of such dressing units is then higher than that of previously known, so-called standard steel dressing units.Furthermore, conventional, unmodified dressing units require more frequent dressing of the grinding wheel, reducing its service life between dressings. Therefore, using components of the dressing unit made at least partially of CFRP materials can significantly improve the grinding result, making the higher costs due to the more complex design of the dressing unit unavoidable for achieving such high-precision grinding results.

[0018] According to the invention, the workpieces are ground with high precision. The workpiece is clamped for grinding by means of a workpiece spindle stock, which carries a workpiece spindle. This excludes grinding the workpiece using a grinding wheel mounted on a high-frequency grinding spindle. Since the abrasive grains of the grinding wheel wear down with increasing use and thus deviate from the original contour used to grind the desired contour on the workpiece, it is necessary to dress the grinding wheel at defined intervals. The dressing of the grinding wheel is carried out by means of a dressing unit, which has a high-frequency dressing spindle. A dressing disc is arranged on the dressing spindle, by means of which the actual dressing process of the outer surface on the circumference and / or the flat surfaces of the grinding wheel's abrasive coating is carried out.The dressing unit incorporates components made at least partially of CFRP material, which are arranged and positioned within the dressing spindle in such a way that heat conduction is effectively dissipated by the CFRP components. This is achieved by virtually eliminating thermal expansion of the components, at least in predetermined areas. Furthermore, the CFRP components made of this type of CFRP material exhibit significantly improved vibration damping and stiffness characteristics for the entire dressing spindle. It has also been observed that the dressing process takes longer, particularly when dressing profiled grinding wheels, than when dressing a smooth circumferential surface of the grinding wheel in the simplest case. The longer the dressing process takes, the more economical and positively impactful the accuracy of the workpiece being ground will be when modifying the dressing unit.By incorporating CFRP components to minimize energy input into the dressing spindle and thus significantly improve the accuracy of the dressed grinding wheel surface, the dressing unit contributes, particularly during extended dressing processes, to a substantial improvement in the accuracy of the workpiece surfaces being ground. In other words, the influence of the dressing unit on the accuracy of the ground workpiece becomes even more pronounced during longer dressing cycles. Such positive effects occur, for example, when the time required for dressing, and therefore the overall machining time, increases.

[0019] The dressing unit, equipped with CFRP components, can handle even higher power from the high-frequency dressing spindle without material expansion negatively impacting the dressing process. The use of CFRP components ensures that the introduced heat is directed only to specific areas of the high-frequency dressing spindle, while other areas are protected from heat input. This significantly minimizes, if not completely eliminates, heat-induced material expansion compared to conventional steel designs. The design of the dressing unit, i.e., its modification, has been implemented in such a way that material expansion resulting from the introduction of heat energy approaches zero.Furthermore, the CFRP components of the dressing unit offer a decisive advantage and positive influence on high-precision grinding results for the workpiece being ground, particularly regarding stiffness and vibration resistance. The increased stiffness achieved through the use of CFRP for certain selected components enhances dimensional stability and improves vibration resistance, resulting in an improved surface finish during grinding. This significantly reduces or even eliminates chatter and other short circuits. Consequently, in many cases, subsequent finishing of bearing seats can even be omitted.

[0020] Preferably, the dressing disc of the dressing unit is designed as a diamond dressing wheel.

[0021] If the basic design of the dressing spindle of the dressing unit is approximated to that of the HF grinding spindle or implemented analogously, a modular design can be achieved and costs can be saved overall, despite a certain complication of the design of the dressing unit.

[0022] To further enhance the advantages of spindles incorporating CFRP components, such a dressing unit can preferably be combined with a high-frequency grinding spindle mounted on a grinding spindle headstock. This spindle, also equipped with CFRP components, features a suitable grinding wheel for the desired grinding task on the workpiece. This fully utilizes the advantages of the spindle design, whether constructed entirely of CFRP or with steel and CFRP components. During grinding, the spindle can be operated with minimal thermal expansion and significantly improved vibration damping and stiffness compared to steel. This allows grinding and dressing to be performed as a unified process with at least mutual speed synchronization.These improvements also allow for grinding at further increased cutting speeds and thus further increased grinding performance, which translates into shorter grinding times and therefore reduced unit costs per workpiece. It is understood that grinding spindles and dressing spindles constructed in this way offer the advantages that the CFRP components provide for the grinding spindle and, according to the invention, for the dressing spindle. Thus, the combination of a dressing unit and a grinding spindle, each equipped with CFRP components or made entirely of CFRP material, contributes to highly precise ground workpieces. Preferably, the workpiece spindle is also constructed in the same manner as previously described for a grinding spindle and a dressing unit.

[0023] If the workpiece spindle has a corresponding design and is also equipped with CFRP components, the positive properties that improve the quality of the ground workpieces can be achieved even more effectively across the entire system. Overall design costs decrease if the individual spindles—i.e., grinding spindle, workpiece spindle, and dressing unit or dressing spindle—are modular and similarly designed, thus at least partially offsetting the higher costs resulting from the more complex design of the respective spindles.If all three spindles listed here, required for high-precision grinding, are given this basic design with CFRP components, then surprisingly, the overall accuracy of the workpiece can be significantly improved compared to conventional grinding methods using grinding spindles, which at best only partially incorporate such a design. However, unlike conventional methods, these conventional methods do not involve a comprehensive analysis or optimization of the entire spindle system with corresponding coordination between components. The fundamental design principle, when applied to the workpiece spindle, offers the advantage that even when heat is introduced into the clamped workpiece, it is dissipated to such an extent that heat input into the workpiece spindle, and from there into the workpiece holder or even into the workpiece itself, is prevented.If the basic design of the workpiece spindle corresponds to that of the grinding spindle or the dressing spindle, then it is also possible to keep the workpiece essentially free of thermal expansion, thus enabling higher accuracy of the workpiece during both grinding and dressing. In this preferred embodiment, grinding, clamping, and dressing of the workpiece are therefore carried out as a single, unified process with at least mutual speed coordination.

[0024] Preferably, the grinding wheel is dressed using a dressing wheel, which, in terms of its design, is preferably based on a construction similar to the grinding spindle and is clamped onto the workpiece spindle. This naturally presupposes that the workpiece spindle operates in a similar speed range and has a similar design with regard to the CFRP components used.

[0025] According to a second aspect of the invention, a grinding machine for carrying out the method is provided and comprises a grinding spindle stock with a high-frequency grinding spindle carrying a grinding wheel, a workpiece spindle stock with a workpiece spindle by means of which the workpiece to be ground can be clamped, and a dressing spindle unit with a dressing spindle carrying a dressing tool, in particular a dressing wheel. According to the invention, the dressing spindle, in contrast to the basic structure known in the prior art made of steel and similar materials, is provided with CFRP components at the points where heat is introduced into the spindle. This allows the CFRP components to dissipate heat in a controlled manner, thus virtually eliminating thermal expansion of the other components of the dressing spindle. As a result, the dressing spindle enables the dressing process to be free of thermal expansion and with greater vibration damping than steel.Furthermore, it has become apparent that, especially with more complex grinding wheel contours, which require correspondingly longer dressing times, greater attention must be paid to the design of the dressing spindle. This is necessary because the forces and energy input into the dressing spindle, which ultimately performs the dressing process, affect the accuracy of the dressing process of the grinding wheel's profile or surface. The longer the dressing process lasts, and thus the longer the corresponding heat is introduced into the spindle, the stronger this effect becomes. With conventional steel dressing spindles, this can result in significant thermal expansion, leading to dressing errors and subsequently to corresponding grinding defects.The present invention addresses this by adapting the basic structure of the dressing spindle to that of the grinding spindle, thereby increasing the accuracy of the manufactured workpiece. In other words, the complexity of the dressing spindle's design is matched to that of the grinding spindle. Therefore, preferably both the dressing spindle and the grinding spindle are equipped with corresponding CFRP components.

[0026] An even better embodiment for the overall assessment is one in which, in addition to the dressing unit and the high-frequency grinding spindle, the workpiece spindle is also constructed analogously to the grinding and dressing spindles. Its functionality is then adapted to the basic design of the grinding and dressing spindles with regard to the inclusion of appropriate CFRP components, so that the dressing tool, in particular the dressing disc or dressing wheel, is mounted on the workpiece spindle. The dressing disc on the tool spindle thus performs the dressing process. This ensures that the workpiece can be held with virtually no thermal expansion and, through the use of CFRP components, the tool spindle is more vibration-damping than steel.

[0027] Preferably, the grinding spindle shaft of the grinding spindle and the dressing spindle shaft of the dressing spindle are encased by a CFRP hollow shaft in order to prevent heat energy introduced into the respective spindle shaft from being introduced or distributed throughout the entire spindle body.

[0028] For high-precision grinding, it is also important that the grinding spindle is properly balanced. Preferably, the grinding spindle has an integrated balancing system in its nose. This can also be provided for the dressing spindle, so that it too is balanced, thus enabling improved operation and the resulting quality of the workpiece being ground. An advantage for the basic design and overall consideration of the spindle assembly, which ultimately also reduces costs, is that the CFRP components of the grinding spindle, the dressing spindle, and the tool spindle are essentially structurally uniform and compatible with each other.Preferably the dressing tool, in particular the dressing disc, has a diameter in the range of 100 - 180 mm, with a grinding wheel diameter of preferably 300 - 600 mm and with a speed range of the dressing tool in the range of 8,000 - 20,000 min. -1 Preferably, the speed range and diameter range of the workpiece spindle also lie within the range of the dressing parameters for the dressing tool.

[0029] In summary, the core of the invention is that achieving high-precision grinding results depends not only on the grinding process itself, but also on optimizing the design of the grinding spindle. This process is only one aspect of the overall system under consideration. The inventive element lies in considering the entire system of all spindles used, so that all factors influencing the quality of the ground tool surface can be taken into account, thereby achieving significantly higher grinding precision.

[0030] Further details of the invention will now be described with reference to exemplary embodiments and the drawing. The drawing shows:

[0031] Figure 1 shows an HF dressing spindle unit with CFRP hollow shaft;

[0032] Figure 2 shows an HF grinding spindle unit with CFRP hollow shaft;

[0033] Figure 3 shows a dressing tool in the form of a diamond wheel during the dressing action on the grinding wheel's circumferential surface;

[0034] Figure 4 shows a dressing tool in the form of a pot-shaped diamond dressing wheel for dressing the grinding wheel on its circumference and on its side surfaces;

[0035] Figure 5 shows a dressing tool in the form of a diamond wheel mounted on the workpiece spindle;

[0036] Figure 6 Dressing tools for centerless grinding;

[0037] Figure 7 shows a dressing tool during the dressing of a profiled grinding wheel assembly; Figure 8 shows the dressing of a profiled grinding wheel according to a first embodiment;

[0038] Figure 9 shows the dressing of a profiled grinding wheel according to a second embodiment; and

[0039] Figure 10 shows a simplified representation of a grinding machine setup with a clamped workpiece and a separate dressing device.

[0040] Figure 1 shows the basic structure of a dressing unit 7, which, in addition to the commonly used steel components, includes a CFRP component in the form of a CFRP hollow shaft 12. The basic structure of this dressing spindle 8 corresponds to the structure of a grinding spindle 5, as shown in Figure 2. A dressing spindle shaft 10 is driven by a so-called high-frequency motor 19 with stator and rotor. The dressing spindle shaft 10 is supported on both sides of the motor 19 (or drive motor) by means of a first bearing assembly 16 designed as a fixed bearing and a second bearing assembly 17 designed as a floating bearing, so that even at high speeds, this dressing spindle shaft 10 ensures very precise centering. The motor 19 and the bearings 16 and 17 of the dressing spindle 8 (or dressing unit 7) are enclosed by a spindle housing 18.The stator of motor 19 is supported in the housing 18, whereas the rotor of motor 19 surrounds the dressing spindle shaft 10, at least in the area of ​​the motor 19. A CFRP hollow shaft 12 is provided between the rotor of motor 19 and the dressing spindle shaft 10. This CFRP hollow shaft 10 can also extend over a larger longitudinal area than that of motor 19. In terms of thermal insulation, the CFRP hollow shaft 12 provides insulation, contributes to vibration damping, and, in addition to the two bearing packages 16 and 17, stabilizes the running of the dressing spindle shaft 10. As a result, the heat generated by the HF motor 19 is no longer directly introduced into the dressing spindle shaft 10, but is ultimately dissipated to the outside towards the spindle housing 18, so that thermal expansion caused by heat introduction is significantly reduced, if not completely avoided, by the CFRP hollow shaft 12 or other CFRP components.These thermal expansions would otherwise lead to dressing errors in the profile or grinding surface to be dressed on the grinding wheel 6 by the dressing tool 9, in the form of a dressing disc or dressing wheel, preferably a diamond wheel. All running errors are transferred to the dressing disc, so that the dressing disc also creates errors in the profiling of the grinding wheel 6. For this reason, it is important to avoid any thermal expansion-related deformations, especially of the dressing spindle shaft 10. The more effectively these thermal expansions are avoided, the more precise the running of the dressing spindle 10 and thus also the dressing process itself, which is ultimately performed by the dressing disc, will be.Previous dressing units 7 were constructed from steel components because the prevailing approach was based on the assumption that the dressing process constituted only a small portion of the actual grinding process, thus significantly reducing the impact of any running errors in the dressing spindle 10 due to heat input. The basic design of the dressing unit 7, as intended for grinding spindles, therefore corresponds to that of grinding spindles.

[0041] Such a basic structure of a grinding spindle 5, also with a CFRP hollow shaft 12, is shown in Figure 2. It can be seen that the grinding spindle shaft 14 is supported on both sides of the area in which the high-frequency motor 19 with stator and rotor drives the grinding spindle shaft 14 by a first bearing assembly 16 in the form of a fixed bearing and a second bearing assembly 17 in the form of a floating bearing. These bearings 16, 17, as well as the high-frequency motor 19, are housed in a spindle casing 18. Normally, the rotor of the motor 19 sits on the grinding spindle shaft 14. However, it has been shown that the drive motor 19 introduces a considerable amount of energy in the form of heat into the grinding spindle shaft 14.

[0042] The actual grinding process is the machining operation that normally takes the most time. During this time, grinding is carried out over a relatively long period, so that the heat energy introduced into the grinding spindle 5 by the motor 19 leads to a thermally induced deformation of this grinding spindle shaft 14. This deformation causes a displacement of the grinding wheel 6, which is mounted on the grinding spindle shaft 14 by means of a flange cover. As the grinding wheel engages the tool being ground, the thermal expansion, combined with the movement of the grinding surface 13, leads to grinding defects. To minimize or completely eliminate the heat input from the motor 19 into the grinding spindle shaft 14, the CFRP hollow shaft 12 is provided.The combination of steel components and CFRP hollow shafts, as well as other CFRP components such as stop discs or similar items (not shown in Figure 2), significantly reduces or completely prevents heat input into the grinding spindle shaft 14. This ensures highly precise operation of the grinding spindle shaft 14 and, consequently, the grinding wheel 6, without the heat-induced displacement that would otherwise occur. Therefore, the combination of steel and CFRP materials offers a considerable improvement in grinding accuracy. It is understood that it is also possible to manufacture the respective grinding spindles entirely from CFRP material. Figure 3 shows a dressing tool 9 in the form of a diamond wheel, which is mounted on the dressing spindle 8 of the dressing unit 7 and is engaged with the grinding surface 13 for the purpose of dressing it.The dressing of the grinding surface 13 of the grinding wheel 6, which is mounted on a high-frequency grinding spindle 5, is achieved by either moving the dressing unit 7 along the circumferential surface of the grinding surface 13 of the grinding wheel 6 in the Z-direction or by moving the grinding wheel relative to the dressing unit 7 along the Z-axis. Depending on the duration of use, the grinding surface 13 gradually wears down, so that the grinding wheel 6 and the dressing unit 7 must be moved relative to each other in the X-direction to compensate for the wear from the grinding process and to ensure that the grinding contour of the grinding surface 13 on the grinding wheel 6 can reliably perform the grinding task with regard to its surface quality or surface profiling.

[0043] Figure 4 shows, according to a further embodiment, a grinding wheel 6 with a corresponding grinding surface 13 mounted on a high-frequency grinding spindle 5, and a dressing spindle 8 of a dressing unit 7, which carries a dressing wheel in the form of a diamond wheel 9. The diamond wheel 9 is designed as a conical cup wheel with which the circumferential surface of the grinding surface 13 of the grinding wheel 6 can be dressed by a relative movement of the grinding wheel 6 and the dressing unit 7 in the Z-direction. Due to the conical cup shape of the diamond grinding wheel 9, flat surfaces of the grinding surface 13 of the grinding wheel 6 can also be dressed by adjusting the dressing unit 7 along the X-axis. However, it is also possible for the grinding wheel 6 to be used for dressing purposes, i.e.,To compensate for the wear of the grinding surface 13 during the actual grinding process, the grinding wheel 6 performs a corresponding movement along the X-axis. It is understood that a relative movement between the dressing unit 7 and the grinding wheel 6 is essential, so that both the grinding wheel 6 and the dressing unit 7 can be moved in the X-direction to properly dress the grinding wheel 6 on its grinding surface 13.

[0044] Figure 5 shows a dressing tool 9, in the form of a diamond wheel, mounted on the workpiece spindle 2. A workpiece 1 is clamped on centers 21 between the workpiece spindle stock 3 and a tailstock 20. In this setup, the surface of the workpiece 1 is ground using the grinding wheel 6 and the abrasive coating 13 located on the circumference of the grinding wheel 6. The grinding wheel 6 is mounted on the grinding spindle stock 4 and driven accordingly, as usual. For grinding purposes, the grinding wheel 6 is moved towards the workpiece 1 in the X-axis direction and then moved across the surface of the workpiece 1 in the Z-direction.Depending on the duration of use of the grinding wheel 6, the grinding surface 13 wears down. To maintain high-quality and precise dimensions of the workpiece 1, this surface is regularly dressed using the dressing wheel 9. For this purpose, the workpiece spindle 3, together with the tailstock 20 and the workpiece 1 clamped between the centers 21, can be moved in the Z-direction until the dressing wheel 9 engages with the grinding surface 13 of the grinding wheel for the purpose of dressing.

[0045] 6. To achieve an improved dressing process, normally no workpiece is clamped between the centers of the workpiece headstock and the tailstock during dressing. This allows the required spindle speeds to be reliably achieved during the dressing process, independent of workpiece geometries and without their influence. It is also possible for the grinding spindle 5, with the grinding wheel 6 mounted on it, to perform the dressing in the Z-direction with the appropriate feed in the X-axis required for dressing. The advantage of mounting a dressing wheel 9 on the workpiece headstock is that a complete dressing unit is available.

[0046] 7 is then no longer required. In order to achieve an overall advantageous modular design and a complete coordination of all spindle systems with regard to a high-precision quality of the workpiece 1 to be ground, the workpiece spindle 2 can or should expediently have a similar or essentially analogous basic design as has been shown and described for the dressing unit 7 in Figure 1 and the grinding spindle 5 according to Figure 2.

[0047] Figure 6 shows the use of a dressing unit 7 according to the invention in centerless grinding. In accordance with the usual basic setup, centerless grinding involves a grinding wheel 6 with an abrasive coating (not shown separately), which is mounted on a high-frequency grinding spindle 5 and rotated by it. Figure 6 shows a regulating wheel 22 at the bottom, which is mounted on and driven by a regulating spindle 24. It is understood that the regulating spindle 24 preferably also has the same design as the dressing unit 7 or dressing spindle 8 and the grinding spindle 5 for the purpose of an overall modular and fundamentally identical structure, and can achieve overall coordination of the spindle units with each other. A grinding gap is provided between the grinding wheel 6 and the regulating wheel 22, in which the workpiece 1 to be ground, mounted on a support bar (not shown), is located.For this purpose, grinding wheel 6 and regulating wheel 22 are moved towards each other so that their outer surfaces engage the workpiece surface in opposite directions. To achieve this grinding task, grinding wheel 6 performs a feed along the X1 axis, while regulating wheel 22 is also fed in opposite directions to grinding wheel 6 by a feed or adjustment along the X2 axis to absorb the grinding forces. To enable both grinding wheel 6 and regulating wheel 22 to be dressed after appropriate grinding operations and depending on surface wear, a dressing unit 7.1 for grinding wheel 6 and a dressing unit 7.2 for regulating wheel 22 are provided on the side facing away from the workpiece 1. The dressing units 7.1 and 7.2 are designed for dressing along a W1 axis and a W2 axis, respectively.The W2 axis and, in the sense of a feed towards the element to be dressed (grinding wheel 6, regulating wheel 22), can be adjusted along a U1 axis or U2 axis. The internal structure of the dressing unit 7.1 corresponds to that shown and described in Figure 1.

[0048] Figure 7 shows another embodiment in which the dressing tool 9, as a diamond dressing wheel 9, performs a dressing of the grinding surface 13 on a grinding wheel pack 23 with the dressing spindle 8. This dressing process thus refers to a dressing process on profiled grinding wheels, which here are combined into a grinding wheel pack 23 consisting of four grinding wheels. The grinding wheel pack 23 is clamped on the high-frequency grinding spindle 5, so that all individual grinding wheels of the grinding wheel pack 23 to be dressed can be dressed one after the other by moving the diamond dressing wheel, designed as a dressing tool 9, either only in the Z direction along the circumferential surface of the corresponding grinding wheel of the grinding wheel pack 23, or, in the case of appropriately profiled and inclined circumferential surfaces of the grinding surface 13, by moving it in both the Z and X directions.It is understood that the movements in the Z-direction and X-direction are relative movements between the spindle 8 and the HF grinding spindle 5.

[0049] Figure 8 shows a further embodiment for dressing a profiled grinding wheel or its abrasive coating 13. According to the basic setup previously explained, particularly in Figures 1 and 2, a dressing spindle 8 is shown with a dressing wheel 9 mounted on it and driven by the spindle. The dressing wheel 9 is in the form of a conical, cup-shaped dressing tool. The grinding wheel 6 has a convex shape with a corresponding abrasive coating 13, which is to be dressed by means of the dressing tool 9. The dressing process is carried out by moving the grinding wheel 6 and the dressing spindle 8 relative to each other in the Z and X directions such that the dressing wheel 9, with its shown left engagement point, dresses the right half of the convex shape as depicted in the drawing, while, by corresponding offsetting of the dressing spindle 8, the dressing tool 9 is dressed with the right side, i.e., the right half.The right-hand injector of the dressing tool dresses the left half of the convex shape of the grinding surface of the profiled grinding wheel 6.

[0050] Figure 9 shows another embodiment of a profiled grinding wheel 6 in which the grinding surface 13 of the grinding wheel 6 has a convex shape on its left side, which transitions into a concave shape on its right side. The basic design of the dressing spindle 8 is analogous to that described above in Figure 8. In this case, the dressing wheel 9 uses its left side to dress the concave shape of the profile of the grinding wheel 6, while its right side dresses the convex shape of the grinding surface 13 of the grinding wheel 6. To ensure that the corresponding contours of the profiling of the grinding surface 13 of the grinding wheel 6 can be formed for dressing purposes, a relative movement of the grinding wheel 6 and the dressing spindle 8 in the Z and X directions is required, which, except for the shape of the profiling, corresponds to the embodiment shown in Figure 8.

[0051] Figure 10 shows a further advantageous embodiment of a grinding machine setup in a simplified representation, in which the dressing wheel 9 is not mounted on the workpiece spindle 2 as in Figure 5. In the setup shown, the diamond dressing wheel 9 is mounted on a separate dressing spindle 8. This has the advantage that the technical parameters of the high-frequency grinding spindle 5, the workpiece spindle 2, and the dressing spindle 8 can each be precisely tailored to the requirements of the grinding process. It goes without saying that, depending on the requirements, the components can also be equipped with the advantageous CFRP versions.

[0052] According to the present invention, preferably all four spindles—i.e., the dressing spindle, the grinding spindle, the workpiece spindle, and the control spindle—have an essentially identical basic structure, namely, they either consist of steel and CFRP components, by means of which highly precise and virtually error-free rotation of the respective spindles is achieved, or the entire spindle components consist of CFRP material. Due to the modular and essentially identical design of the respective spindles, a complete coordination of the spindles and / or the tools driven by the spindles can be achieved, thereby resulting in higher accuracy of the workpieces to be ground. Reference numeral list

[0053] 1 workpiece

[0054] 2 workpiece spindles

[0055] 3 Workpiece spindle stock

[0056] 4 grinding spindle stock

[0057] 5 HF grinding spindle

[0058] 6 grinding wheels

[0059] 7. Dressing unit

[0060] 7.1 Dressing unit grinding wheel

[0061] 7.2 Dressing unit control disc

[0062] 8 Dressing spindle

[0063] 9 Dressing disc / dressing tool

[0064] 10 Dressing spindle shaft

[0065] 12 CFRP hollow shaft

[0066] 13 Abrasive pad

[0067] 14 Grinding spindle shaft

[0068] 15 Flange covers

[0069] 16 fixed storage units / 1st storage package

[0070] 17 Lotlager / 2nd Lagerpaket

[0071] 18 spindle housings

[0072] 19 HF motor (stator and rotor)

[0073] 20 tailstock

[0074] 21 points for clamping

[0075] 22 Control disc

[0076] 23 grinding wheel package

[0077] 24 Control spindle

Claims

Applicant: Erwin Junker Maschinenfabrik GmbH F / LE / sd Our reference: J86270PCT PATENT CLAIMS 1. Method for high-precision grinding of workpieces, in which the workpiece (1) is clamped for grinding by means of a workpiece spindle stock (3) having a workpiece spindle (2) and is ground with a grinding wheel (6) by means of an HF grinding spindle (5) and the grinding wheel (6) is dressed by means of a dressing unit (7), characterized in that the dressing unit (7) dresses the grinding wheel (6) by means of an HF dressing spindle (8) having a dressing wheel (9), the components of which are at least partially made of CFRP material such that the dressing spindle (8) almost prevents the thermal expansion of the CFRP components by means of targeted heat conduction and achieves a significantly higher vibration damping and stiffness behavior compared to steel.

2. Method according to claim 1, characterized in that the grinding spindle (5) has at least partially CFRP components, by means of which the workpiece (1) is ground by means of the grinding wheel (6) with virtually no thermal expansion and with a significantly higher vibration damping and stiffness behavior compared to steel, wherein the grinding and dressing are carried out in the sense of a unified overall process with at least mutual speed coordination.

3. Method according to claim 1 or 2, characterized in that the workpiece spindle (2) has at least partially CFRP components, by means of which the workpiece (1) is held in the workpiece spindle (2) clamping the workpiece (1) by means of targeted heat conduction in the CFRP components, free from heat input, whereby a significantly higher vibration damping and stiffness behavior compared to steel is achieved and the grinding, dressing and clamping of the workpiece (1) is carried out in the sense of a unified overall process with at least mutual speed coordination.

4. Method according to one of claims 1 to 3, characterized in that the dressing of the grinding wheel (6) is carried out by a dressing wheel (9) mounted on the workpiece spindle (2).

5. Grinding machine for carrying out the method according to one of claims 1 to 4, characterized in that a grinding spindle stock (4) with an HF grinding spindle (5) carrying a grinding wheel (6), a workpiece spindle stock (3) with a workpiece spindle (2) for clamping the workpiece (1) and a dressing unit (7) with a dressing spindle (8) carrying a dressing tool (9) are provided, characterized in that at least the dressing spindle (8) has CFRP components which are virtually thermally expansion-free and vibration-damping than steel.

6. Grinding machine according to claim 5, characterized in that the HF grinding spindle (5) has such CFRP components that heat introduced into the HF grinding spindle (5) by means of a motor drive can be dissipated in such a way that the HF grinding spindle (5) is virtually expansion-free, wherein the CFRP components are more vibration-damping than steel.

7. Grinding machine according to claim 5 or 6, characterized in that the workpiece spindle (2) has such CFRP components that heat introduced into the workpiece spindle (2) by its motor drive is not or almost not introduced into a receiving of the workpiece (1) and also not into the workpiece (1), and thus the workpiece spindle (2) and also the workpiece (1) are kept almost free of thermal expansion, wherein the CFRP components of the workpiece spindle (2) are more vibration-damping than steel.

8. Grinding machine according to one of claims 5 to 7, characterized in that the grinding spindle shaft (14) of the grinding spindle (5) and the dressing spindle shaft (10) of the dressing spindle (8) are enclosed by a CFRP hollow shaft (12).

9. Grinding machine according to one of claims 5 to 8, characterized in that the grinding spindle (5) has a balancing system in its nose.

10. Grinding machine according to one of claims 5 to 9, characterized in that the dressing spindle (8) has a balancing system.

11. Grinding machine according to one of claims 6 to 10, characterized in that at least the CFRP components of the grinding spindle (5) and those of the dressing spindle (8) are modular and, including their number, structurally uniform and corresponding to one another.

12. Grinding machine according to one of claims 5 to 11, characterized in that the dressing tool (9) has a diameter in the range of 100 to 180 mm and the dressing of the grinding wheel (6) is carried out at a speed in the range of 8,000 to 20,000 min -1 This has been done.

13. Grinding machine according to one of claims 7 or 12, characterized in that the workpiece spindle (2) is designed such that a speed range and a diameter range are covered which correspond to the dressing parameters, and that the workpiece spindle (2) carries the dressing tool (9) for dressing the grinding wheel (6).

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