DEVICE AND METHOD FOR GRINDING INTERNAL CONTOURS ON WORKPIECES

Abstract

A grinding machine 1 and a method for grinding internal contours 2 of bores in workpieces 3 using a grinding element 4 are described. The grinding element is designed as a grinding ring 5, which is mounted on both sides on drive shafts 6.1 and 6.2, and at least one of the drive shafts 6.1 and 6.2 drives the grinding element 4 rotationally. According to the method, the first drive shaft 6.1 is inserted into the interior of the workpiece, the grinding ring is inserted into the interior of the workpiece 3 from the free side and is temporarily fixed in place by the first drive shaft 6.1.

Description

[0001] The invention relates to a grinding machine and a method for grinding internal contours of bores in workpieces including threads according to the preamble of claim 1 and the preamble of claim 18.

[0002] When manufacturing spindles designed to cover longer travel distances, it is often necessary to grind internal contours in workpieces whose bore diameter is relatively small compared to the length of the internal bore, also known as the grinding depth. Such internal contours include, for example, internal threads, which require relatively high precision if they are to be suitable for high-precision adjustment distances. This is required, for instance, in robotics. If the grinding depths become quite large, meaning the travel distances to be achieved with the corresponding adjusting spindle are quite long, and if the bore diameters are quite small, necessitating the use of small-diameter grinding elements, the technological limits for grinding such long bores are quickly reached.These technological limits are often reached when the grinding depth, and thus the length of the internal contours to be ground, is several times the bore diameter. However, this issue is not limited to the internal grinding of bores, grooves, etc., but applies equally to the grinding of any internal contour. Grinding internal threads, in particular, presents technological difficulties, as the grinding element must be pivoted into the thread pitch to grind high-precision threads. Furthermore, the longer the internal thread to be ground, the longer the drive shafts for the grinding elements must be, the less stable the grinding element becomes, and the greater its tendency to vibrate, which is detrimental to the grinding accuracies typically required.If the grinding element were not pivoted into the thread pitch during thread grinding, profile distortions would occur, which in turn would negatively impact the accuracy achievable on the workpieces being ground. Larger pitch or multi-start threads generally require larger helix angles. However, grinding an internal thread with large helix angles is technically impossible without pivoting the grinding element into the large helix angle. The high pitches of such internal thread contours are particularly necessary when movements are to be achieved using spindle drives at relatively high, i.e., maximum, speeds. These requirements are further intensified when the threads to be ground are multi-start.The accuracy requirements dictated in particular by robotics, the requirements for smooth running, and the requirements for traverse speeds demand highly precise grinding results. In principle, it is known to swivel the grinding elements up to, for example, 10° when grinding internal threads, whereby the diameters of the internal threads to be ground range from 30 mm to less than 20 mm and are often also very long, i.e., exhibit a large grinding depth.

[0003] A company brochure from the Japanese firm MITSUI SEIKI describes an internal thread grinder. For the relatively small diameters required for grinding internal threads, a small grinding wheel with a corresponding thread pitch must be pivoted around the pitch angle relative to the longitudinal axis of a mandrel to which this small grinding wheel is attached. To accommodate different grinding tasks with varying thread diameters, mandrels of different thicknesses are provided for different diameter ranges. This necessitates changing the tools, including their drive shafts, whenever the grinding task changes. This increases effort, downtime, and costs.Overall, the described system is technically very complex. A one-sided bearing arrangement for the mandrels supporting the grinding wheel reduces rigidity, increases their tendency to vibrate, and thus impairs the precision of the grinding result. Grinding tasks, especially those performed internally with small diameters, are therefore subject to very limited space, which inherently imposes design limitations on corresponding manufacturing solutions. The compromises that must be made in the design of such pivoted or longitudinally inclined grinding wheels on the mandrels compromise accuracy and usually also grinding times, thus directly impacting the manufacturing costs of the workpiece.

[0004] A similar setup to the one previously described for the Japanese company MITSUI SEIK is also described in the company brochure of the Chinese company NODHA, which explicitly mentions internal thread grinders. There, a small grinding wheel, representing a grinding disc, is mounted on a mandrel and its axis of rotation is inclined relative to the longitudinal axis of the mandrel, which carries the small grinding wheel at its front end, with respect to the pitch of the internal thread to be ground. If other threads are to be ground, different tools must be used for each different thread pitch, which involves frequent tool changes. This not only increases downtime (i.e., non-operating time or idle time) but also raises costs due to the large number of tools required.

[0005] The invention is therefore based on the objective of providing a device and a method by which internal contours, particularly on small diameter bores, can be ground as single or multi-start threads, as grooves or internal surfaces in specific contours, even with relatively long internal threads, without increased vibrations impairing the grinding result, while simultaneously achieving short grinding times and low or moderate manufacturing costs for the workpiece to be ground.

[0006] This problem is solved according to the invention with a grinding machine having the features of claim 1 and with a method having the features of claim 18. Advantageous further developments are defined in the respective dependent claims.

[0007] According to the invention, the internal contours of the workpiece to be ground are ground using a grinding machine which has a grinding element in the form of a grinding ring. The grinding ring is supported on both sides, thus avoiding the harmful vibrations caused by single-sided support and, consequently, long support arms with lower rigidity due to their geometrical design, which carry such a grinding ring at one end. The grinding ring can therefore be held in the desired grinding position with significantly higher rigidity due to the double support, and a good, i.e., high-precision, grinding result on the internally ground contours, particularly of a thread, can be achieved without the occurrence of harmful dynamic vibrations.

[0008] Drive shafts engage the inner bore of the workpiece from both sides and support the slip ring at their respective facing front ends, the drive shaft heads. At least one of the drive shafts rotates the slip ring. Preferably, the slip ring itself can pivot to such an extent that a larger pivot angle for the pitch of the thread to be ground is achievable and reliably implemented. This is possible at least when the two drive shafts, with their axes of rotation, are offset by a defined amount parallel to each other from a mutually aligned position. With this offset, the drive shafts support the slip ring in different ways on each side.This is achieved by such that, through this offset, the slip ring can be brought into a desired inclined position when the axial pressure exerted on it by the drive shafts is applied.

[0009] According to the invention, the double-sided bearing of the grinding ring, which performs the grinding process of the internal thread, results in high machining accuracy of the thread inside the workpiece bore, regardless of the thread length within the workpiece bore, i.e., regardless of the grinding depth. Preferably, the stable inclination required for grinding threads can also be achieved by offsetting the two drive shafts relative to each other and applying corresponding axial pressure to at least one drive shaft on the grinding ring. Each offset dimension thus results in a defined inclination, so that, due to the continuously adjustable offset, the inclination of the grinding ring can also be continuously adjusted to achieve a defined thread pitch inside the workpiece.

[0010] The present invention is implemented on a grinding machine with a conventional design in a manner known per se. A grinding spindle stock is arranged on a machine stand, the grinding spindle stock supporting a grinding unit with a grinding spindle unit. Preferably, the movement of this unit is carried out on a cross slide. The cross slide incorporates the two CNC-controlled axes, namely the X and Z axes, each with its own drive, guide, and length measuring systems. At the front of the grinding machine, a workpiece spindle stock with a clamping device is provided, by means of which the workpieces are clamped in a central workpiece clamping position using a suitable chuck. The chuck is designed such that both ends of the workpiece are freely accessible, and the rotary drive of the workpiece spindle stock is also CNC-controlled.If threads are to be ground inside the bores of the workpieces, the CNC-controlled X, Z, and C axes must each be moved in interpolating mode. Additionally, a dressing device is usually provided on the grinding machine, which is used to dress the grinding wheel according to predetermined grinding intervals. This compensates for the grinding wheel wear caused by grinding and restores the required accuracy to the workpiece being ground.

[0011] Preferably, the slip ring comprises a base body and a grinding surface on its outer circumference. The base body has a relatively small thickness, at least in its central region, and carries a grinding surface on its outer circumference. This creates a concave relief on each side of the slip ring between the radially inward-facing undersides of the grinding surface and the base body. The respective drive shaft heads engage in these reliefs with their convex heads. The shape of the relief and the shape of the respective drive shaft heads are designed such that, when axial force is applied to the slip ring, both drive shafts support and rotate the slip ring via the reliefs.Preferably, the slip ring is tilted or inclined relative to the axis of rotation of the drive shafts by means of its axially parallel offset relative to each other. This pivots the slip ring into the helix angle of a thread to be ground, without compromising the slip ring's support on both sides. With this design, the slip ring is supported on both sides by the respective drive shaft, but is not mechanically screwed to the drive shaft ends, as is usually the case with grinding wheels on a grinding wheel spindle shaft. The slip ring and drive shafts are therefore decoupled from each other.By axially clamping the components against each other, the grinding ring is fixed in the required pivoted position to such an extent that safe grinding without the occurrence of vibrations, as is always the case with grinding elements supported on one side with relatively long mandrels, can be achieved.

[0012] It is also possible that the slip ring has a convex shape in the area of ​​the axis of rotation and concave shapes at the drive shaft ends. In any case, the slip ring and drive shaft ends are engaged with each other by positive locking and / or friction locking. In both embodiments, identical results are obtained with regard to the mounting of the slip ring and its drive by means of the drive shafts.

[0013] This interplay between the stepless offset of the drive shafts relative to each other along their longitudinal axes and the resulting stepless angular adjustment is particularly advantageous. The stepless offset and stepless adjustment of the pivot angle of the grinding ring ensures that different grinding tasks can be performed with one and the same grinding tool. This eliminates the need, as with the previously described prior art, to grind different tasks with different tools, which would increase the overall cost. The preferably stepless adjustment of the offset and pivot angle thus reduces the manufacturing costs of the workpieces, making series production of the workpieces on the grinding machine particularly feasible.

[0014] According to a further embodiment, the convexity of the drive shaft heads is designed such that they engage positively in the concavity of the relief cuts in the slip ring, allowing the slip ring to be fixed in the desired inclined position under axial preload for grinding. This means that the convex and crowned drive shaft heads engage in a concavity of the relief cut shaped according to their external form. With a corresponding longitudinal axis offset of the drive shaft heads, the slip ring is pivotally mounted so that it is fixed for grinding with respect to the thread to be achieved, i.e., its pitch.

[0015] According to another embodiment, the drive shaft heads are also convex and engage in the concavity of the relief cuts. This concavity of the relief cuts is, for example, conical, so that the drive shaft heads engage with the slip ring in a frictional manner. Thus, by means of an axial preload, the slip ring can, in this case as well, fix the slip ring in the desired inclined position for the purpose of thread grinding, with the drive shaft heads and the relief cuts that accommodate them engaging in a frictional manner.

[0016] According to another embodiment, the drive shafts can be manually adjusted with respect to their offset relative to each other. This manual adjustment to the desired pivot angle for achieving the corresponding thread pitch of the ground thread inside the workpiece is suitable when using grinding wheels that do not require dressing. However, if the grinding wheels used, i.e., the grinding ring, do require dressing, this is generally performed using a CNC axis, thus enabling automatic adjustment of the drive shaft offset and therefore the pivot angle. For dressing the grinding ring, an interpolating in-form dressing process is typically performed on a diamond wheel.Advantageously, the pivot angle should then be reset to 0° during dressing, after which the automatic pivoting to the desired helix angle can be set again once dressing is complete. However, it is also conceivable to dress the slip ring in the pivoted position.

[0017] To perform grinding, particularly of the threads inside the workpiece, it is possible for both drive shafts to be rotaryally driven, or alternatively, for at least one of the two drive shafts to be rotaryally driven. Especially for higher grinding capacities, it can be advantageous to drive both drive shafts rotaryally. They then rotate in the same direction and at the same speed. High-frequency grinding spindle units, which are speed-controlled, are typically used as the drive.

[0018] Preferably, the offset of the longitudinal axis of the drive shafts to each other in a vertical direction to the axis of rotation of the workpiece is adjustable.

[0019] To mount, temporarily secure, and position the grinding element (i.e., the slip ring) which is not clamped onto the drive shafts, at least one of the drive shafts must be axially movable to such an extent that it can be completely withdrawn from the workpiece. The slip ring can then be inserted into the workpiece up to the convexity of the drive shaft head, with the relief of the slip ring facing this head. The withdrawn drive shaft can then be axially retracted up to the respective relief with its drive shaft head, so that axial preload can fix the slip ring in the desired pivoted, i.e., angled, position according to the thread pitch.

[0020] For correspondingly long workpieces, which require relatively long drive shafts that also have a certain length outside the workpiece, it is preferably provided that the drive shafts are mounted on support steady rests outside the interior of the workpiece.

[0021] Furthermore, it is preferably provided that when grinding threads inside the workpiece, after the support steady rests have been loosened, a changing thread entry, as well as the thread itself and also the thread exit, are dimensionally corrected via an X-axis feed amount in order to compensate for certain errors between grinding without a steady rest and grinding with a steady rest.

[0022] This dimensional compensation with the X-axis can also be provided without a steady rest insert, since the grinding forces are not identical to those in the middle thread area, especially at the beginning and end of the thread.

[0023] Preferably, the workpiece is clamped in the workpiece spindle stock in such a way that it is clamped centrally by a chuck that is freely accessible from both sides.

[0024] According to yet another embodiment, at least one of the drive shafts is hollow. A vacuum can be applied through this bore or channel in this drive shaft, and after the convexity of the drive shaft head engages with the concavity of the slip ring, the slip ring is temporarily fixed to the drive shaft head by means of the vacuum. This temporary fixation remains in place until the other drive shaft also engages with its drive shaft head in the corresponding, adjacent cutout. At that point, the axial preload, combined with the appropriately set offset of the longitudinal axes of the drive shafts relative to each other, allows the slip ring to be fixed from this temporary fixation into the precise, inclined, desired final position required for grinding.

[0025] Furthermore, according to another embodiment, it is advantageous that the other drive shaft is also hollow and that cooling lubricant for grinding can be supplied to the grinding engagement area of ​​the slip ring via this internal bore. Within the drive shaft head, which is accommodated within the concavity in the relief of the slip ring, corresponding bores can be provided so that the cooling lubricant supplied inside the drive shaft can be guided directly to the bearing points of the drive shaft head in the side flanks of the relief of the slip ring, and, most importantly, the slip ring receives the appropriate cooling lubricant at the grinding contact point.

[0026] Preferably, the slip ring has a grinding surface bonded with CBN, electroplated, ceramic, resin, or metal, or coated with diamond, with the base body being made of partially hardened steel, heavy metal, or cemented carbide. It is important that such grinding surfaces can be used that have a long service life, which is particularly significant because the slip ring, used for grinding relatively small internal bores, has a small diameter and must achieve corresponding grinding performance at relatively high speeds. Therefore, grinding surfaces with extended service life are preferable. The base body being made of partially hardened steel, heavy metal, or cemented carbide is necessary so that the slip ring can withstand the high loads required to achieve the necessary high precision of the internal contours to be ground.

[0027] Preferably, the internal contours to be ground in the workpieces are grooves, inner surfaces of bores, and / or, in particular, single- or multi-start threads. The basic design, with its double bearing and the offset of the longitudinal axes of the drive shafts for adjusting the angle of the grinding ring, makes it possible to produce a wide variety of internal contours in workpieces using one and the same tool.

[0028] The invention also includes a design of the grinding machine such that the double-sided bearing of a grinding ring between the drive shaft ends is coupled with a design of the grinding spindle stock in which a fixed offset of the drive shafts relative to each other allows only a one-angle tilt. Such a machine is therefore referred to as a single-purpose machine, by means of which only one specific workpiece is produced, i.e., workpieces with the same tilt angle of the grinding ring are produced.

[0029] According to a second aspect of the invention, a method for grinding internal contours of small diameter and large length, including thread grinding, is described, wherein the internal contours are ground using an inclined grinding element. The grinding element is designed as a grinding ring and has recesses on both sides into which a drive shaft engages on the respective side to hold or support the grinding ring accordingly. At least one of the two drive shafts drives the grinding ring rotationally when an appropriate axial preload is applied. According to the invention, a first of the drive shafts is first inserted into the interior of the workpiece, followed by the insertion of the grinding ring from the free side of the workpiece into its interior, with the first drive shaft engaging in the recess with its drive shaft head in such a way that the grinding ring is initially held in place.A second drive shaft is then inserted into the inside of the workpiece from the free side. The second drive shaft then exerts axial pressure on the grinding ring with its drive shaft head. Preferably, the two drive shafts are offset parallel to each other with respect to their longitudinal axes before the second drive shaft is inserted, its drive shaft head being inserted into the recess of the grinding ring in such a way that the grinding ring is brought into the desired inclined position. The axial pressure or axial adjustment then fixes the grinding ring in this inclined position for internal grinding.

[0030] Preferably, the slip ring is fixed between the drive shaft heads, which engage in the respective recess from both sides and thus support the slip ring, without coupling or mechanical screwing, and is held in the desired position after axial pressure is applied to the slip ring by at least one drive shaft head, so that when the corresponding drive shaft or drive shafts are set in rotation, the inner contour is ground with the slip ring in its fixed inclined position.

[0031] Preferably, steady rests are provided in freely accessible areas of the two drive shafts, i.e., outside the bore of the workpiece, which support the respective drive shaft in these areas.

[0032] If dressing of the grinding ring is necessary, this is preferably carried out with steady rest support, whereby the grinding ring is pivoted back to a zero-degree angle relative to its axis of rotation during dressing, and after dressing is complete, the angle of inclination required for grinding the thread or the respective internal contour in the workpiece is set again. However, dressing can also preferably be carried out with the grinding ring in the pivoted position.

[0033] Preferably, the offset of the drive shafts relative to each other with respect to their longitudinal axes is automatically and continuously adjusted using a CNC axis. Since each set offset causes a corresponding tilt of the slip ring, the continuous offset of the drive shafts via a CNC axis also allows for the continuous pivoting of the slip ring into the thread pitch. Particularly in cases where the grinding surface is designed in such a way that dressing is not strictly necessary, the offset of the drive shafts relative to each other can be performed manually.

[0034] If the first drive shaft has been inserted into the interior of the workpiece and the slip ring is inserted into the interior up to the drive shaft head, the slip ring can be temporarily fixed to the drive shaft head of the first drive shaft by suction using the vacuum, since the first drive shaft is hollow and a vacuum is applied inside it.

[0035] According to a further embodiment, the second drive shaft, which also has a through-hole, is penetrated by a flexible shaft. At its end, which engages in the recess of the slip ring, this flexible shaft has a retaining element that engages positively with the slip ring, thus temporarily fixing it in place. This pre-aligns the slip ring in its desired inclined position. After applying the appropriate axial preload via the drive shaft, the slip ring is then tilted to the desired angle.

[0036] If the second drive shaft has a through-hole, then it is also possible that this through-hole is used to supply coolant lubricant to the grinding engagement area via the inside of the drive shaft.

[0037] The method according to the invention is also designed to provide that a slip ring is supported on both sides by means of a respective drive shaft, but the grinding spindle stock only provides a fixed offset of the drive shaft rotation axes relative to each other. The corresponding method is therefore simplified and intended as a single-purpose machine method for the production of only one specific workpiece, i.e., workpieces with the same slip ring skew angle.

[0038] Further details and possible applications of the present invention will now be explained in detail with reference to the accompanying drawing. The drawing shows: Fig. 1: the basic structure of a grinding machine according to the invention; Fig. 2: a principal partial representation of the front view of the grinding spindle stock of the grinding machine according to the invention; Fig. 3: a basic illustration of the clamping of the workpiece using a chuck with a longitudinal stop for axial fixation of the workpiece; Fig. 4: a basic representation of the clamping of a grinding element between two drive shafts for support on both sides by the drive shafts and their axially parallel offset according to a first embodiment of the grinding element; Fig. 5: a further embodiment according to the principle of clamping the grinding element according to the invention with a flexible shaft provided for clamping by a hollow drive shaft; Fig. 6: two detailed cutouts for friction-fit and form-fit and friction-fit grinding element mounts on the drive shaft heads; Fig. 7: a grinding element in the form of a slip ring according to the invention with a concave relief of the base body of the grinding element for receiving correspondingly designed drive shaft head ends according to the first embodiment of the invention; Fig. 8: a grinding element in the form of a grinding ring according to a second embodiment with convexly arranged projections of the base body of the grinding element; and Fig. 9: the embodiment according to Fig. 8 with axial offset of the drive shafts to achieve an inclination of the grinding element for grinding, for example, threads with adjustable pitch as an inner contour.

[0039] Fig. Figure 1 shows the basic structure of the grinding machine 1 according to the invention, with which the method according to the invention is also carried out. The simplified representation of the grinding machine 1, shown in the usual manner and therefore not shown separately, has a machine bed on which a grinding spindle stock 22 is arranged. Two drive shafts 6.1 and 6.2 can be driven by means of this spindle stock. A grinding element 4 is mounted between these drive shafts by exerting axial pressure on both drive shafts, i.e., the first drive shaft and the second drive shaft, which are hereinafter also referred to as one drive shaft and another drive shaft. The grinding element 4 is supported by the grinding spindle stock 22, which is usually preferably arranged on a cross slide with preferably CNC-controlled X, Z, and Y axes with their respective drive, guide, and length measuring systems.

[0040] Regarding the in Fig. In the top view shown in Figure 1, a workpiece spindle stock 17 with a clamping device designed as a chuck 18 for clamping workpieces 3 to be ground is provided in the lower part of the grinding machine, which is the front part in the side view. The chuck 18 provides a central clamping of the workpiece 3, in which, since internal contours 2 are to be ground according to the invention, both ends must be freely accessible. Such a workpiece 3 is shown mounted on the workpiece spindle stock 17 by the chuck 18, with an internal thread 16 being shown as the internal contour 2 of the workpiece 3 to be ground in a simplified representation. During thread grinding, the traversing axes X, Z and the rotational axis 13 of the workpiece 3 (not shown separately) must be able to move together in an interpolating manner.

[0041] With regard to the grinding spindle stock 22, it is shown how the grinding element 4 is clamped between the two drive shafts 6.1 and 6.2 rotating about their respective longitudinal axes 9, namely by both axes exerting axial pressure against each other, so that the grinding element 4 is clamped between the two drive shafts 6.1 and 6.2, i.e. the drive shafts clamp the grinding element 4 by engagement of their drive shaft heads 7.1, 7.2.

[0042] The grinding spindle stock 22 is designed such that both drive shafts 6.1 and 6.2 clamp the grinding element 4 between them, depending on the desired internal contour 2, in such a way that the longitudinal axes of the drive shafts 6.1 and 6.2 are aligned. Additionally, the grinding spindle stock 22 allows the first drive shaft 6.1 and the second drive shaft 6.2 to be offset 8 from each other while parallel to their axes. The respective drive shaft ends 7.1 and 7.2 engage with the grinding element 4 in such a way that, depending on the offset 8 of the longitudinal axes 9 of the drive shafts 6.1 and 6.2, an inclination 10 of the grinding element 4 is achieved. This is necessary, for example, when an internal thread with a defined pitch is to be ground. Thus, in addition to the adjustability of the inclination 10 of the grinding element 4 by the respective offset 8 of the drive shafts 6.1 and 6.2, the grinding element 4 can be adjusted.2 in relation to each other, in particular the clamping of the grinding element 4 between the axial pressure exerted on each other drive shafts 6.1 and 6.2 for fixing the position of the grinding element 4 in the respective inclined position 10 is realized.

[0043] The offset 8 of the drive shafts 6.1, 6.2 is thus used to deliberately bring the grinding element 4 into a defined inclined position 10, so that, for example, the respective helix angle for a thread 16 can be pivoted and ground as an internal contour 2. This offset 8 of the two drive shafts 6.1, 6.2 is realized in the vertical direction to the axis of rotation 13 of the workpiece 3. In the illustration according to Fig. The offset 8 of the drive shafts 6.1, 6.2 is not shown in the top view because this offset occurs in the vertical direction. This adjustment of the offset 8 of the drive shafts 6.1, 6.2, or the axially parallel adjustment of the rotation axes of the drive shafts 6.1, 6.2 relative to each other, can be performed manually or, ideally, automatically using a CNC-controlled axis. As mentioned previously, this is possible using the adjustment axis Y.

[0044] If grinding wheels that do not require dressing are used, the pivot angle can be adjusted manually. However, grinding wheels that do require dressing are frequently used, which is then carried out by interpolating form dressing on a diamond wheel. In this case, the pivot angle is reset to 0° for dressing. This means that the offset 8 between the two drive shafts 6.1 and 6.2 required for grinding a pitched internal contour is set to 0°, so that both longitudinal axes of the drive shafts 6.1 and 6.2 are aligned.

[0045] The grinding spindle stock 22 is now designed such that, in principle, both drive shafts 6.1 and 6.2 can be driven. At least one of the two drive shafts is rotaryally driven by means of a high-frequency drive unit. In this case, the undriven drive shaft is merely a rotating support shaft, which nevertheless must be able to execute a stroke 19 in the axial direction. This stroke 19 is necessary so that the double-sided supported grinding element 4 can be inserted into the inner bore to be ground. This axial stroke movement is shown by the dashed line on the left. Fig. 1 is shown on the front side of the grinding spindle stock 22.

[0046] If, as is advantageous for higher performance, both drive shafts 6.1 and 6.2 are driven, they are designed to run synchronously. This "dual" drive significantly increases the grinding performance of the grinding machine.

[0047] In Fig. Figure 2 shows a basic representation of the front view of the grinding spindle stock 22, whereby for the sake of simplicity only the HF drives with the drive shafts 6.1 and 6.2 are shown, which fix the grinding element 4 designed as a slip ring 5 in an inclined position 10 between their respective drive shaft heads 7.1, 7.2, by the drive shaft heads 7.1, 7.2 being in clamping engagement with the slip ring 5. The axial offset of the two drive shafts 6.1 and 6.2 relative to each other results in the inclined position 10 of the slip ring 5. Depending on the design of the slip ring 5, which is not shown separately here, the drive shaft heads 7.1, 7.2 can either engage in reliefs 5.5 in the inner area of ​​the base body 5.1 of the slip ring 5, or convex projections 11 can be provided in the inner area of ​​the base body 5.1, which engage in correspondingly concave recesses in the respective drive shaft heads 7.1 and 7.2.To achieve the axially parallel offset 8 of the first drive shaft 6.1 and the second drive shaft 6.2, a Y-axis, preferably designed as a CNC axis, is provided. In order for the slip ring 5 to be fixed in the appropriate position inside a bore and clamped between the two drive shafts 6.1, 6.2 for grinding, a stroke movement 19 of at least one of the two drive shafts 6.1, 6.2, which are also CNC-controlled via rotary axes 100, must first be axially displaceable. The axial displacement is sufficient to allow the slip ring 5 to be inserted into the bore of the workpiece 3, followed by the insertion of the corresponding drive shaft 6.1 or 6.2 into the bore, and the slip ring 5 to be clamped in the desired inclined position 10 for grinding.This makes it clear that the highly flexible mounting of the slip ring 5 and the adjustment of its inclined position 10 can be achieved by the double-sided mounting of the slip ring 5 according to the invention. The axial stroke movement 19 of the drive shaft 6.1, 6.2, which is designed for this purpose, is effected by means of high-precision guides and a hydraulic or electric drive.

[0048] In Fig. Figure 3 shows a simplified representation in which the workpiece 3 is held on the workpiece spindle (not shown separately) and clamped centrally by means of a chuck 18. To achieve the necessary accuracy in forming the internal contour 2, a face stop 23 is also provided for the workpiece, so that a positionally aligned internal contour can always be produced repeatably by means of this fixed reference. The chuck 18 is designed so that the workpiece 3 is freely accessible from both sides, so that the grinding ring 5 and the two drive shafts 6.1 and 6.2 can be inserted into the workpiece 3 and clamped in place, allowing the desired internal contour 2, preferably a threaded contour, to be ground with the selected pitch.

[0049] Fig. For the sake of simplicity, Figure 4 shows only the areas of the two drive shaft heads 7.1 of the first drive shaft 6.1 and 7.2 of the second drive shaft 6.2. An axial offset 8 between the two drive shafts 6.1 and 6.2 is shown, whereby, according to the first embodiment, the drive shaft heads 7.1 and 7.2 engage in concave reliefs 5.5 in the concave base body 5.1 of the slip ring 5 such that a positive and frictional clamping connection for the slip ring 5 can be maintained between the drive shaft heads 7.1 and 7.2. This ensures a stable grinding position for the slip ring 5, as it is supported on both sides. Furthermore, the axial offset 8 between the two drive shafts 6.1 and 6.2 achieves the desired inclined position 10 of the slip ring 5.

[0050] Of the two drive shafts 6.1 and 6.2, at least one is rotaryally driven. At least one of the two drive shafts 6.1 and 6.2 is adjustable relative to the corresponding other drive shaft by an offset 8 to the longitudinal axis 9 of the other drive shaft by means of the adjustment drive Y. The magnitude of the offset 8 defines the inclination 10 of the slip ring 5 within the inner contour 2 to be ground (not shown). The offset 8 can be adjusted manually or automatically using the Y-CNC axis.

[0051] Out of Fig. Figure 4 shows that in the embodiment of the slip ring 5, relief cuts 5.5 are provided which, at their laterally present chamfers, engage the respective drive shaft heads 7.1 and 7.2 in a form-fit and friction-fit manner. When clamping and aligning the slip ring 5 into the desired inclined position 10, the surfaces of the drive shaft heads 7.1 and 7.2 slide on the corresponding chamfers or sliding areas of the relief cut 5.5, which is why correspondingly higher material requirements must be placed on at least the drive shaft heads 7.1 and 7.2. Either the area of ​​the drive shaft heads 7.1 and 7.2 or the entire drive shafts 6.1 and 6.2 can be made of tool steel, heavy metal, or CFRP material, or a combination of these or other different materials.

[0052] As previously described, at least one of the drive shafts 6.1 or 6.2 can be extended out of the bore with an axial stroke 19 so that the slip ring 5 can be inserted, temporarily fixed on a drive shaft 6.1 or 6.2, and after retraction of the drive shaft 6.1 or 6.2 with an axial stroke 19, the slip ring 5 can be engaged with the slip ring 5 in the desired inclined position 10 according to the offset 8 of both drive shafts to each other, so that a thread 16 with the desired pitch can be ground in this inclined position 10.

[0053] It is also important that the drive shafts 6.1 and 6.2 exhibit very high stiffness values, as considerable lengths may need to be ground for the inner contours, which can lead to some deflection, even though the double bearing of the slip ring 5 between the two drive shaft ends 7.1 and 7.2 contributes to good stability. The longer the drive shafts 6.1 and 6.2 are, the lower the system stiffness and thus their tendency to vibrate. Therefore, it is also necessary that the drive shafts 6.1 and 6.2 have the best possible concentricity in the area of ​​the drive shaft ends 7.1 and 7.2; for example, the concentricity should not exceed 2 µm. To ensure low wear in the area of ​​the drive shaft ends, this area must either be hardened, made entirely of wear-resistant carbide, or have a correspondingly hard and wear-resistant coating.

[0054] At the in Fig. In the embodiment of the slip ring 5 with concave reliefs shown in Figure 4, the drive shaft heads 7.1 and 7.2 are spherically shaped and engage in the chamfers provided on both sides of the slip ring 5. Thus, the slip ring 5 is held by the two drive shafts 6.1 and 6.2 under axial preload at the two precision-machined chamfers. If a drive shaft 6.1 or 6.2 is inserted into the bore in which the inner contour 2 is to be ground, the inserted slip ring 5 must be held in position in the area of ​​the drive shaft heads when the other drive shaft 6.2 or 6.1 is not engaged, so that slippage and falling off do not occur. Preferably, therefore, at least the second drive shaft 6.2, or alternatively the other, i.e., the first, drive shaft 6.1, can be hollow, so that the interior of the respective drive shaft 6.1 and / or 6.2...2. A vacuum can ensure that the slip ring 5 is, so to speak, attracted to this drive shaft and temporarily fixed in place. The final desired inclined position 10 of the slip ring 5, corresponding to the offset 8, is automatically set or pressed when the second drive shaft 6.2 is inserted and axial pressure is applied to the slip ring 5 and from there to the opposite drive shaft 6.1. The grinding position of the slip ring 5 is fixed by a sufficiently high axial clamping force exerted by the drive shaft 6.1, ensuring proper centering.

[0055] In Fig. Figure 5 shows a further embodiment in which the basic structure is adapted to the Fig. This corresponds to the explanation in section 4. As one way to prevent the slip ring 5 from slipping or sliding out after or during its insertion into the bore and engagement with the first drive shaft 6.1 already located in the bore, a flexible shaft 20 is provided in the hollow first drive shaft 6.1. This flexible shaft is equipped at its front end with a positive-locking retaining element 21, by means of which the slip ring 5 can be held in a defined pre-fixing position. This allows the first drive shaft 6.1 to be inserted into the bore after the slip ring 5 has been held on the second drive shaft 6.2, and the slip ring 5 to be finally fixed in the desired inclined position 10. The axial stroke 19 is performed by having the first drive shaft 6.1 already inserted into the bore, so that the slip ring 5 is then attached to the second drive shaft 6.1.2. The slip ring 5, pre-fixed by means of the flexible shaft 20, can be inserted into the bore together in such a way that, after reaching the drive shaft head 7.1 and applying axial pressure, the slip ring 5 can be fixed in the desired inclined position 10 for grinding. Both drive shafts 6.1 and 6.2 can be driven, as indicated by the axis of rotation 100, whereby in the case of the Fig. 5 axial offset 8 of the two drive shafts 6.1 and 6.2 to each other as also shown, the respective drive shafts 6.1 and 6.2 rotate about the respective longitudinal axis 9.

[0056] According to the in Fig. In the embodiment described in Figure 5, the flexible shaft 20 can transmit additional torque via the positive-locking retaining element 21 inside the slip ring 5, potentially increasing the grinding performance even further. Furthermore, by applying slight axial tension to the flexible shaft 20 in the second drive shaft 6.2, the slip ring 5 can be temporarily fixed in place when the first drive shaft 6.1 is not engaged. This prevents the slip ring 5 from slipping or falling out of its temporary fixation position.

[0057] If, after an interruption or completion of the grinding process, the slip ring 5 changes its pivot angle after being released, the slip ring 5 is pushed back into the correct position when the first drive shaft 6.1 is then engaged again. This centering then occurs automatically again due to the resulting force components when the axial pressure force is applied when engaging the first drive shaft 6.1 with its corresponding preload force.

[0058] In Fig. Figure 6 shows two embodiments of friction-fit (left figure) and form-fit and friction-fit (right figure) reception of the respective drive shaft heads 7.1 and 7.2 by the chamfers on the slip ring 5 for receiving the corresponding areas of the drive shaft heads 7.1 and 7.2. With a spherical design of the drive shaft heads 7.1 and 7.2 and a chamfer on the slip ring 5 as a circumferential conical surface, theoretically only a linear contact of the drive shaft head 7.1 or 7.2 occurs with the conical chamfer or receptacle for the drive shaft head on the slip ring 5. This is a friction-fit connection, for which the conical area should have a very good roundness tolerance of, for example, a maximum of 1 to 2 µm.

[0059] In the right part of the Fig. Figure 6 shows that the inner cone of the slip ring 5 for receiving the spherically shaped drive shaft head 7.2 or 7.1 is located opposite the left figure in Fig. 6 is concavely spherical, i.e., dome-shaped, so that the receiving surface of the slip ring 5 for the spherical drive shaft heads 7.1, 7.2 is form-congruent and thus has surface contact. With such a design, a positive and frictional connection is therefore given. The design according to the right-hand figure in Fig. Size 6 may have advantages in this regard, as the force distribution and thus the Hertzian surface pressure are lower. However, it must be noted that fitting such curved surfaces together within the required tolerances demands considerable manufacturing effort, which also entails higher costs.

[0060] In Fig. Figure 7 shows another embodiment of the slip ring 5. The slip ring 5 has a base body 5.1 and a grinding surface 5.2 on its outer surface. The slip ring 5 has an axis of rotation 5.6 around which the slip ring 5 rotates during grinding. The base body 5.1 is concave, forming concave reliefs 5.5 on both sides. The concave reliefs 5.5 cause the base body 5.1 to be relatively deeply indented in its central region and, in the outer area of ​​the slip ring 5, to have overhanging sections, analogous to the construction of an I-beam, on the outer circumference 5.3 of these overhanging sections, on the outer circumference 5.3 of which the grinding surface 5.2 is arranged. The overhanging area limits the clearance cuts 5.5 by means of the underside 5.4 to the grinding surface 5.2 on each side of the slip ring 5. The clearance cut 5.5 is now designed such that a correspondingly designed respective drive shaft head 7.1 and 7.2 is received by the chamfer in a form-fit and / or friction-fit manner. The respective drive shaft heads 7.1 and 7.2 thus engage in the relief 5.5 of the slip ring 5. This provides support for the slip ring 5 on both sides, and also allows it to be tilted accordingly by an axial offset of the first drive shaft 6.1 relative to the second drive shaft 6.2 after axial pressure is applied to the drive shafts. Since the offset 8 is continuously adjustable, the tilt 10 of the slip ring 5 can also be continuously adjusted. The tilt 10 of the slip ring 5 results in the formation of a defined pitch, for example, of a thread 16 inside the bore, when grinding the inner contours 2.

[0061] The abrasive coating 5.2 of the slip ring 5 can be CBN, an electroplated layer, a ceramic coating, or other bonds or combinations thereof, such as resin-bonded or metal-bonded abrasive coatings. In contrast to electroplated CBN slip rings 5, ceramic, resin-bonded, or metal-bonded CBN coatings on slip rings 5 ​​are dressable. Only after the grinding process is restarted is the slip ring 5 returned to the desired inclined position 10 by the offset 8 of the two drive shafts 6.1 and 6.2 relative to each other.

[0062] Because the slip ring 5 transmits the corresponding drive powers through the drive shaft heads 7.1 and 7.2 engaging in the clearances 5.5, high hardness and wear resistance must be achieved for the base body 5.1 of the slip ring 5.

[0063] Fig. Figure 8 shows a further embodiment of a slip ring 5, in which, contrary to the embodiment according to Fig. 7. No relief cuts 5.5 are formed on the base body 5.1, but rather the base body 5.1 has projections 11, so that the base body is convex. The slip ring 5 has an axis of rotation 5.6 and has a region on its outer circumference 5.3 where abrasive lining 5.2 is arranged. The regions of the abrasive lining 5.2 on the outer circumference 5.3 correspond to those of the in Fig. The slip ring 5 described in section 7 with relief cuts 5.5. The projections 11 are now designed to fit together with the concave drive shaft heads 7.1 and 7.2. Because the projections 11 fit into the concave areas of the drive shaft heads 7.1 and 7.2, the same function is achieved as described in the embodiment according to [reference to relevant figure]. Fig. 7 has already been described. If the concave areas of the drive shaft heads 7.1 and 7.2, which receive the slip ring 5 with its projections 11, receive the slip ring 5 between them, and their drive shafts 6.1 and 6.2 have an axially parallel offset 8 to each other, then when the drive shafts 6.1 and 6.2 are axially clamped to each other with the slip ring 5 between their drive shaft heads 7.1 and 7.2, an inclination 10 of the slip ring 5 results, which can be stepless if and insofar as the offset 8 of the longitudinal axes 9 of the drive shafts 6.1 and 6.2 is also stepless.

[0064] This function, described in the previous example, is applicable to this second embodiment according to Fig. 9 identical to the previously described embodiment according to, for example Fig. 4.

[0065] In Fig.Figure 9 shows that the inclination 10 is generated by the offset 8 of the longitudinal axes 9 of the drive shafts 6.1 and 6.2. The convex projections 11 of the base body 5.1 are received by concave areas of the drive shaft heads 7.1 and 7.2, respectively, so that a positive and / or frictional connection is established between the slip ring 5 and the drive shafts 6.1 and 6.2 or their drive shaft heads 7.1 and 7.2 when the drive shafts clamp the slip ring 5 with axial pressure between them and are fixed in an inclined position 10. It is understood that the offset 8 between the drive shafts 6.1 and 6.2 or their longitudinal axes 9 can be set to zero, in which case when clamping the slip ring 5 between the two drive shafts 6.1 and 6.2, no tilt 10 results, but rather that in such a case the axis of rotation of the slip ring 5 coincides with the axes of rotation of the first drive shaft 6.1 and the second drive shaft 6.2 coincide. This can be used, for example, when a defined surface is to be ground within a bore without having to grind a corresponding pitch of the threads or thread pitch, as is the case with thread grinding.

[0066] The present embodiments emphasize that when grinding internal contours, a grinding ring not directly clamped onto drive shafts by, for example, a screw connection, but clamped by axial pressure between the drive shaft heads of two drive shafts, can be used to grind a defined internal contour in a bore, whereby with an additional offset between the rotation axes of the drive shafts and a corresponding design of the drive shaft heads, the grinding ring can be set to an inclined position according to the selected offset, with the help of which a pitch of, for example, a thread can be ground as an internal contour in a bore. Reference symbol list 1 grinding machine 2 inner contours 3 workpieces 4 grinding elements 5 slip ring 5.1 Concave basic body 5.2 Abrasive pad 5.3 External circumference 5.4 Underside of the abrasive pad 5.5 Clearing 5.6 Rotation axis slip ring 6.1 First drive shaft 6.2 second drive shaft 7.1 Drive shaft head first drive shaft 7.2 Drive shaft head second drive shaft 8 Offset of longitudinal axes 9 longitudinal axes drive shafts 10 Inclination 11. Protrusion of convex base body 12 CNC axes 13 Rotation axis workpiece 14 Swivel angles 16 threads 17 Workpiece spindle stock 18 chucks 19 axial stroke 20 flexible shaft 21 retaining element 22 Grinding spindle stock 23 Plan posting 100 Rotation axis drive shafts

Claims

[1] Grinding machine (1) for grinding internal contours (2) of bores in workpieces (3) using a grinding element (4), characterized by , that the grinding element (4) is designed as a slip ring (5) which is mounted on both sides on a drive shaft (6.1, 6.2) and at least one of the drive shafts (6.1, 6.2) drives the grinding element (4) rotationally. [2] Grinding machine (1) according to claim 1, characterized by , that the grinding element (4) can be brought into a desired inclined position (10) by an offset (8) between the longitudinal axes (9) of the drive shafts (6.1, 6.2). [3] Grinding machine (1) according to claim 1 or 2, characterized by , that the slip ring (5) can be continuously tilted by continuously displacing at least one of the drive shafts (6.1, 6.2) from a position aligned with the other of the drive shafts (6.1, 6.2). [4] Grinding machine (1) according to claim 2 or 3, characterized by, that the drive shafts (6.1, 6.2) with their drive shaft heads (7.1, 7.2) are frictionally and / or positively connected to the slip ring (5) for grinding and the slip ring (5) can be fixed in the desired inclined position (10) under axial preload. [5] Grinding machine (1) according to one of claims 2 to 4, characterized by, that the slip ring (5) has a concave base body (5.1) and a grinding surface (5.2) attached to its outer circumference (5.3) and has a relief cut (5.5) on both sides between the radially inwardly directed undersides (5.4) to the grinding surface and the base body, in which a drive shaft (6.1, 6.2) engages with its drive shaft head (7.1, 7.2) which is designed as a convexity, wherein the drive shafts (6.1, 6.2) which support the slip ring (5) on both sides are axially displaceable relative to each other and when their drive shaft heads (7.1, 7.2) engage in the relief cuts (5.5) at the set offset (8) bring the slip ring (5) into the inclined position (10) with respect to its axis of rotation. [6] Grinding machine (1) according to one of claims 2 to 4, characterized by, that the slip ring (5) having an axis of rotation has a convex base body and a grinding surface area attached to its outer circumference, wherein the convex base body has projections (11) on both sides of the grinding surface area pointing in the direction of the axis of rotation of the slip ring (5), which each engage in concave drive shaft heads (7.1, 7.2), wherein the drive shafts (6.1, 6.2) supporting the slip ring (5) on both sides are axially displaceable relative to each other and, when the projections (11) of the slip ring (5) engage in the concave drive shaft heads (7.1, 7.2) at the set offset (8), bring the slip ring (5) into the inclined position (10) with respect to its axis of rotation. [7] Grinding machine (1) according to any one of claims 1 to 6, characterized by , that the offset (8) of the drive shafts (6.1, 6.2) to each other can be adjusted manually or automatically via a CNC axis (12). [8] Grinding machine (1) according to any one of claims 1 to 7, characterized by , that the offset (8) of the drive shafts (6.1, 6.2) to each other in a vertical direction to the axis of rotation of the workpiece (3) is adjustable. [9] Grinding machine (1) according to any one of claims 1 to 8, characterized by , that the dressing of the slip ring (5) takes place at a pivot angle of 0° or in a pivoted position. [10] Grinding machine (1) according to any one of claims 1 to 9, characterized by , that at least one of the drive shafts (6.1, 6.2) is axially movable to such an extent that it can be completely removed from the interior of the workpiece (3) and then the slip ring (5) can be inserted into the interior of the workpiece (3) up to the drive shaft head (7.1, 7.2) of the other drive shaft (6.1, 6.2). [11] Grinding machine (1) according to any one of claims 1 to 10, characterized by, that support steady rests are arranged on the freely accessible part of the drive shafts (6.1, 6.2) outside the interior of the workpiece (3). [12] Grinding machine (1) according to claim 11, characterized by , that when grinding threads (16) inside the workpiece (3) the thread entry, thread length and thread exit can be dimensionally corrected via an X-axis feed amount. [13] Grinding machine (1) according to any one of claims 1 to 12, characterized by , that the workpiece (3) is held in a workpiece spindle stock (17) by a chuck (18) which is freely accessible from both sides. [14] Grinding machine (1) according to any one of claims 1 to 13, characterized by, that at least one of the drive shafts (6.1, 6.2) is hollow and a vacuum can be applied over it, by means of which, after engagement of the drive shaft head (7.1, 7.2) with the slip ring (5), the slip ring is temporarily fixed to the drive shaft head (7.1, 7.2) until the desired inclination (10) of the slip ring (5) can be fixed by means of axial preload through the other of the drive shafts (6.1, 6.2). [15] Grinding machine (1) according to any one of claims 1 to 14, characterized by , that the other of the drive shafts (6.1, 6.2) is hollow and that coolant can be supplied to the grinding engagement area of ​​the grinding ring (5) via its inner bore during grinding. [16] Grinding machine (1) according to any one of claims 1 to 15, characterized by, that the slip ring (5) has a grinding surface (5.2) CBN electroplated, ceramic bonded, resin bonded or metal bonded and the base body (5.1) consists of partially hardened steel, heavy metal or hard metal. [17] Grinding machine (1) according to any one of claims 1 to 16, characterized by , that the internal contours (2) to be ground in the workpieces (3) are grooves, internal surfaces of bores and / or single or multi-start threads (16). [18] Method for grinding internal contours (2) of smaller diameter and greater length including threads (16) using an inclined grinding element (4), characterized by , that the grinding element (4) is a slip ring (5) which is held on both sides by a drive shaft (6.1, 6.2), at least one of the drive shafts (6.1, 6.2) drives the slip ring (5) rotationally and a first (6.1) of the drive shafts (6.1, 6.2) is inserted into the interior of the workpiece (3), the slip ring (5) is inserted into the interior of the workpiece (3) from the free side and is held in place by the first drive shaft (6.1). [19] Method according to claim 18, characterized by , that a second (6.2) of the drive shafts (6.1, 6.2) is inserted from the free side of the workpiece (3) into its inner surface, after the second drive shaft (6.2) is offset axially parallel to the first drive shaft (6.1), the second drive shaft (6.2) under axial pressure with its drive shaft head (7.2) fixes the grinding ring (5) in position so that the grinding ring (5) is held in a desired inclined position (10) and the internal grinding is carried out in this inclined position (10). [20] Method according to claim 18 or 19, characterized by, that the slip ring (5) between the drive shaft heads (7.1, 7.2) is held in the desired position uncoupled with them and the inner contour is rubbing. [21] Method according to any one of claims 18 to 20, characterized by , that the first and second drive shafts (6.1, 6.2) are supported on bezels in their freely accessible area. [22] Method according to claim 21, characterized by , that the slip ring (5) is dressed with bezel support and when it is aligned to 0° or in a pivoted position relative to its axis of rotation. [23] Method according to any one of claims 18 to 22, characterized by , that the offset (8) of the drive shafts (6.1, 6.2) is carried out automatically by means of a CNC axis (12). [24] Method according to any one of claims 18 to 22, characterized by , that the offset (8) of the drive shafts (6.1, 6.2) is carried out manually. [25] Method according to any one of claims 18 to 24, characterized by , that the slip ring (5) is temporarily fixed to the drive shaft head (7.1) by means of a vacuum applied in a through bore of the first drive shaft (6.1). [26] Method according to any one of claims 18 to 25, characterized by , that the second drive shaft (6.2) is penetrated in a through bore by a flexible shaft (20), which at its end engaging in the clearance (5.5) of the slip ring (5) intermediately fixes the slip ring (5) with a positive locking and / or friction locking retaining element (21). [27] Method according to any one of claims 18 to 25, characterized by , that cooling lubricant is supplied to the grinding ring (5) via its interior through a through-bore provided in the second drive shaft (6.2) and its grinding engagement area.

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