EP2931471B1 - Method and cylindrical grinding machine for centerless cylindrical grinding - Google Patents

Description

The invention relates to a method for centerless cylindrical grinding of workpieces with rotationally symmetrical contour according to the preamble of claim 1 and also a centerless cylindrical grinding machine according to the preamble of claim 2 for performing the method of claim 1. The method according to the preamble of claim 1 and the device according to The preamble of claim 2 are both of the USRE 17311E known.

In the best known embodiment of cylindrical grinding machines for centerless cylindrical grinding, the rotationally symmetrical workpiece is located between a rotating regulating wheel and a rotating grinding wheel and is additionally supported on the so-called supporting ruler, cf. for example Dubbel, Paperback for Mechanical Engineering, 15th ed. 1983, page 1003 , Fig. 50g, h. The workpiece is driven by the regulating wheel for rotation and ground by the grinding wheel. Regulating wheel and grinding wheel are in the usual way in drive units (in the grinding wheel known as the wheelhead or grinding spindle unit) stored, the peripheral speed of the regulating wheel must be lower than that of the grinding wheel. Due to the difference in rotational speeds, the so-called slip, the grinding effect comes about. The terms "grinding wheel" and "regulating wheel" are in this application as working terms in terms of their function in centreless cylindrical grinding, but do not limit their training in the axial extent. For example, these discs may be cylindrical, stepped or tapered, and may include multiple sections of different contour. The regulating wheel and the grinding wheel can be composed in the axial direction of individual section parts, which lie directly next to each other or are separated by intermediate spaces.

It has long been known to those skilled in the field of machine tools that the grinding result, ie dimensional accuracy, roundness and surface quality, is no longer the highest in centerless cylindrical grinding of machine components in mass production in which high speeds of control and grinding wheels have to be ground Meets all requirements. The regulating wheel was recognized as one of the possible sources of error. These may, depending on the quality of their design and their storage in the associated drive unit itself have a runout, which has a detrimental effect on the grinding result. In addition, the regulating wheel also has to be dressed from time to time, which can lead to further inaccuracies.

Thus, according to the DD 55 918 A proposed, in the centreless cylindrical grinding of disc-shaped workpieces with very small dimensions no longer drive the regulating wheel to rotate. Also, the support ruler was omitted. Instead, a support means is provided, which is referred to as "workpiece holder" and consists of two rows of ball bearings, which are easily rotatably mounted on two parallel axes in bearing blocks. In a sense, the driven regulating wheel and the supporting ruler have been replaced by two rows of non-driven regulating wheels. The grinding wheel and the two rows of ball bearings form a grinding gap in which the workpieces are located and rest on two opposing ball bearings. When grinding, the workpieces are rotated by the frictional connection with the grinding wheel, whereby the support of the workpieces on the ball bearings causes a low friction against the grinding wheel. The workpieces receive the rotation required for the grinding operation solely as a result of frictional entrainment by the grinding wheel.

The execution according to the DD 55 918 A Although the advantage of being structurally a bit easier, because the motor drive of the regulating wheel is eliminated. However, a significant cause of the inaccurate grinding result is maintained or even enhanced because the support of the workpiece to two rows of bodies of revolution is an unavoidable source of error. The roundness of the bearing outer rings and the accuracy of their bearing on the balls and the bearing inner rings are too small and uneven in relation to the accuracy that requires the centerless cylindrical grinding according to the application.

Another proposal for centreless cylindrical grinding without regulating wheel is the DE 43 30 800 A1 refer to. This proposal is also based on the recognition that the regulating wheel which touches the workpiece, in principle, is not free from concentricity errors, because it is rotatably mounted. The remedy should be that a single fixed prism is provided as support means for the cylindrical workpieces, which serves as a workpiece holder, and that serves as a rotary drive for the workpiece, a revolving endless drive belt. Furthermore, a finger loaded by a spring is provided, which presses the workpiece into the recess of the prism. A disadvantage of the embodiment according to the DE 43 30 800 A1 in that the arrangement of a drive belt compared to the ball bearings according to the DD 55 918 A again an increased structural complexity with an additional drive device requires. Because of the required longitudinal extent of the drive belt also given by the prism grinding gap is less accessible. Furthermore, it can not be ruled out that the flexible drive belt running over rollers causes irregularities in the rotational movement of the workpiece and introduces rhythmic disturbances or vibrations into the grinding process, which worsen the grinding result.

In DE 341 606 A a workpiece guide is described on machines for grinding cylindrical or conical body by means of three cooperating guide rails for centerless cylindrical grinding. Two of the guide rails form a wedge space which opens outward from the grinding wheel and in which the workpiece to be ground is arranged. On the opening side of the wedge space a back rail is arranged, which is movable in the direction of the other two rails, ie in the direction of the grinding wheel, so that the workpiece is pressed under the action of a consistently acting pressure against the two guide rails in the direction against the grinding wheel.

In DE 11 79 826 A a device for centreless cylindrical grinding is described, which has a conventional arrangement of grinding wheel, regulating wheel and support rail. The support rail may be formed as a prism support, which is pivotable about a free pivot point, that is arranged to be movable. Both the grinding wheel and the regulating wheel are provided with a drive. In order to avoid waviness of the surface of the workpiece to be ground, the free tilting of the workpiece support is used to always distribute the support points for the workpiece so that a compensation of the wave movement caused by a forward movement of the workpiece by the simultaneous return due to the wave troughs on the Bearing surfaces takes place.

In US RE 17 311 E is a centerless grinding machine described, with which cylindrical workpieces can be ground. The grinding wheel as well as a U-shaped guide block for guiding the workpiece to be ground on support rails are arranged on a machine frame. Within this U-shaped guide block a centrally arranged counter ruler and a top ruler and a sub-ruler are arranged. The rulers have bearing surfaces, with the bearing surfaces of the upper and lower rulers forming an angle to each other in the interior of the U. The centrally arranged counter ruler is adjusted by means of screws to a defined position, so that while grinding the workpiece outer contour, the workpiece is pressed by the grinding forces on this counter ruler, but at least pushed out of the system by a ruler, so that there is a game. Play on the contact surfaces can cause discontinuities in the workpiece to always be copied back into the ground surface on the workpiece.

A loss of accuracy is the result. The counter ruler is fixed and therefore can not act as a brake body with adjustable braking force. The grinding wheel is detected on the machine stand, and the workpiece is delivered manually with its U-shaped recording of the grinding wheel.

The invention is based on the object to provide a method and an apparatus of the type mentioned above, with which the rotationally symmetric parts are ground with great dimensional and dimensional accuracy even at the high operating speeds of industrial mass production, the required cylindrical grinding machine still basically in the Structure, so it is very cost-effective and works reliably over long periods of time with constant accuracy.

The solution of this object is achieved in terms of the method with the totality of the features of claim 1 and with respect to the cylindrical grinding machine with the entirety of the features of claim 2.

The advantage of the method according to claim 1 in comparison to the DD 55 918 A is that in addition to the rotational movement of the driven for rotation grinding wheel no further rotation-based drive or support parts are required. The two non-rotating contact surfaces, which are formed flat in the associated cylindrical grinding machine, in each case provide a more accurate support than the ball bearings in the prior art. Compared to the DE 43 30 800 A1 there is the advantage that a separate drive means for the rotation of the workpiece is not required. According to the method of the invention, a single rotary drive for the grinding wheel is required, which at the same time also sets the workpiece in rotation. Harmful influences from the additional drive device in the form of a rotating drive belt can be avoided in any case.

In the method according to the invention, the ratio of the speeds of the grinding wheel and workpiece or their rotational speeds are continuously monitored and adjusted to a certain optimum ratio. The feed force of the grinding wheel and the braking force exerted by the support means are adjusted so that a certain ratio of the speeds of workpiece and grinding wheel results, which leads to optimum grinding results.

With regard to the centreless cylindrical grinding machine, the object underlying the application is achieved in that the support device has at least one first planar contact surface and a second planar abutment surface, both operatively immovable in the circumferential direction of travel of the workpiece, extending at a distance from each other along the workpiece and engaging around the workpiece with sliding contact. Level contact surfaces, which correspond to the known support ruler, are a proven means for supporting the rotating workpiece. The workpiece is held by these flat contact surfaces with the greatest possible accuracy in its predetermined, optimal for the grinding process. All concentricity errors resulting from a rotating support are thereby excluded. The support surfaces are optimally adjusted to the circumferential direction of the workpiece and its diameter, this setting is so far operationally immutable.

The cylindrical grinding machine has a device for speed measurement, by means of which the workpiece speed is continuously monitored. In an evaluation and control arrangement, the optimum balance between the grinding wheel rotational speed, the feed force of the grinding wheel and the braking force of the brake body can be constantly maintained. In this way, not only the support means of the cylindrical grinding machine according to the invention is set up for an optimal grinding result, but certain optimal operating conditions can be maintained even with great consistency in the desired manner.

However, different settings of the first planar contact surface and the second planar contact surface depending on the diameter of the workpiece and the desired grinding process are required. An appropriate adjustment can be made easily before the grinding process by adjusting or replacing the contact surfaces. During the grinding process itself, however, the first planar contact surface and the second planar contact surface generally remain immobile in their entirety, which is expressed in the advantageous development according to claim 3.

In certain grinding processes, such as, for example, during plunge grinding, however, the contact surfaces sometimes have to be adjusted during the grinding cycle because they then have to be continuously adapted to the decreasing diameter of the workpiece 1 at the grinding position. According to the further advantageous embodiment according to claim 4 then the first contact surface and the second contact surface can be designed to be movable in operation.

A further advantageous embodiment is defined in claim 5. This embodiment may be important for itself or in conjunction with the other advantageous developments. It refers to the fact that the first contact surface is located on a support plate located below the workpiece, which is formed in the manner of the usual support ruler. The second contact surface may be located on a separate support rail, which is arranged opposite the grinding wheel. Support plate and support rail allow a stable mounting of the two contact surfaces, so that the required grinding accuracy is reliably maintained for a long time remains. In this way, the applied on the grinding wheel feed force presses the workpiece in an optimal contact with the first and the second support surface.

With the two contact surfaces stable and consistent contact surfaces are created, which in conjunction with a constant force of the grinding wheel also a substantially constant Apply braking force to the rotation of the workpiece. But it is also possible to set this braking force exactly to a certain value, which is to be selected for a particular grinding process. For this purpose, a brake with a brake body is arranged in the cylindrical grinding machine according to the invention on the support means, which acts via an adjusting device with adjustable braking force on the workpiece.

The brake may preferably be designed such that the brake body forms a further support body with a third contact surface.

Preferably, this third contact surface is arranged so that it is opposite to the first contact surface and acts on the workpiece from above.

Another embodiment of the cylindrical grinding machine according to the invention is important in itself, but may also be significant in connection with the other developments shown so far. Thereafter, the first contact surface and the second contact surface are combined to form a common support body, which forms a prism opposite the grinding wheel and engages around the workpiece. Such a prism can be formed solid and very stable, in which case a safe, low-wear and reliable support of the workpiece is ensured in the desired position. Such a solid prism can also be mounted as a whole and possibly swung out of its working position into a maintenance position, if necessary. In this case, the cross section of the prism can have the shape of an angle or the shape of a trapezoid (claim 9). It is crucial in any case that oblique contact surfaces are formed, which surround the workpiece.

Fig. 1

ist eine Prinzipdarstellung der wichtigsten Einzelteile bei einer Rundschleifmaschine zum spitzenlosen Rundschleifen, mit der das Verfahren gemäß der Erfindung ausgeführt wird.

Fig. 2

zeigt eine Ausführungsform der Rundschleifmaschine gemäß der Erfindung, bei der die erste und die zweite Anlagefläche zu einem Prisma zusammengefasst sind.

Fig. 3

hat eine abgewandelte Ausführungsform des Prismas aus Fig. 2 zum Gegenstand.

Fig. 4

veranschaulicht eine Ausführungsform, bei der eine Bremsvorrichtung in ein Prisma integriert ist.

The invention will be explained in more detail with reference to embodiments which are illustrated in the drawings. The figures show the following:

Fig. 1

is a schematic diagram of the most important items in a cylindrical grinding machine for centerless cylindrical grinding, with which the method is carried out according to the invention.

Fig. 2

shows an embodiment of the cylindrical grinding machine according to the invention, in which the first and the second bearing surface are combined to form a prism.

Fig. 3

has a modified embodiment of the prism Fig. 2 to the subject.

Fig. 4

illustrates an embodiment in which a brake device is integrated in a prism.

In the Fig. 1 a section of a cylindrical grinding machine for centerless cylindrical grinding is shown in cross section. The cylindrical workpiece 1 has a longitudinal axis 2 and, during operation, contacts the rotating grinding wheel 3, the axis of rotation of which lies outside the drawing surface. In the selected cross-section according to the Fig. 1 the horizontal connecting line 4 runs parallel to the horizontal longitudinal axis 2 of the workpiece 1 and to the axis of rotation of the grinding wheel 3, not shown. This results in the contact point 5 at which the grinding wheel 3 and the workpiece 1 touch each other on their circumference. It will be recalled, however, that in certain grinding processes, the axis of rotation of the grinding wheel 3 may be inclined from the horizontal by a small angle of about 3 ° to 5 °, for example in the continuous grinding of cylindrical workpieces 1, thereby receiving their longitudinal feed , For the material of the grinding wheel 3 corundum and CBN come into question.

Below the grinding wheel 3 is a support plate 6, which is formed as a conventional support ruler. Its upwardly facing flat surface is the first contact surface 7 of the support device designed according to the invention. The first contact surface 7 is inclined as usual by an angle λ, starting from its side facing the grinding wheel 3 side downward. To adapt to the particular grinding process to be mastered, the first contact surface 7 can be adjusted in height. Possible settings are next to the in Fig. 1 settings shown below "center" also the settings "center" and "center". The middle is given by the connecting line 4. In addition, it is possible to grind with different inclination angles A. For this purpose, the first contact surface 7 is adjusted, or the entire support plate 6 is replaced. In most cases, it is sufficient to make the changed setting before commissioning the cylindrical grinding machine; during grinding, the setting of the first contact surface 7 then remains operationally unchanged; Overall, it is "operational immovable". In other Cases, the support plate 6 must be adjusted during grinding; This is sometimes the case, for example, during plunge grinding when the first contact surface 7 then has to be continuously adapted to the decreasing diameter of the workpiece 1. Then, the first contact surface 7 "operatively controlled movable" is formed.

The grinding wheel 3 with a certain angular offset opposite a support rail 8 is arranged, at which the second planar contact surface 9 is located. The angular offset corresponds approximately to the angle λ. In Fig. 1 the second planar contact surface 9 forms an angle γ with a common tangent 10, which is placed in the contact point 5 on the workpiece 1 and the grinding wheel 3. Other angular positions are also possible. For the rest, the same applies to the support rail 8 and the second contact surface 9 as for the support plate 6 with the first contact surface 7. Both contact surfaces 7 and 9 can thus be provided "operational immovable" or "operatively controlled movable", the setting both Contact surfaces together or individually - first contact surface 7 and second contact surface 9 each individually - is possible. The contact surfaces 7 and 9 may consist of polycrystalline diamond (PCD) or carbide; the tops of the support plate 7 and the support rail 8 are then coated accordingly.

Fig. 1 shows a schematic representation of a brake 11. In this case, a brake body 12 is acted upon by a braking force P by an adjusting device, not shown, via an intermediate suspension 13. The brake body 12 abuts with a third contact surface 14 on the peripheral surface of the workpiece 1. The braking force P is exerted on the intermediate suspension 13 in such a way that in the grinding operation, the workpiece 1 is braked to the correct extent. Namely, the grinding wheel 3 must on the one hand drive the workpiece 1 for rotation, but on the other hand exert a grinding action by the speed of the workpiece 1 is lower than the speed of the grinding wheel 3. For this purpose, the speed of the workpiece 1 is constantly monitored, for which numerous options available stand, z. As sensors or structure-borne sound sensor. In accordance with the measured speed, an evaluation and control arrangement constantly the optimum balance between the grinding wheel speed, the feed force of the grinding wheel 3 and the braking force P ago, thus finally the optimal speed of the workpiece 1 is achieved.

When operating the in Fig. 1 In a circular cross-section machine shown in a partial cross section, the workpiece 1 abuts on the first contact surface 7 and on the second contact surface 9. When the rotating grinding wheel 3 is supplied against the workpiece 1, it exerts a feed force F in the X direction on the workpiece 1. At the common point of contact 5 of workpiece 1 and grinding wheel 3, the grinding wheel 3 acts as a "friction wheel drive" and takes that Workpiece 1 rotating with. The direction of movement 15 on the surface of the grinding wheel 1 and the direction of movement 16 on the surface of the workpiece 1 run at the contact point 5 in the same direction. The workpiece 1 is pressed against the first contact surface 7 and the second contact surface 9 with a certain contact pressure. The workpiece 1 can still rotate relatively easily on the contact surfaces 7 and 9, but is slowed down a bit and thus has a reduced rotational speed. In addition, when the brake 11 is operated, the rotational speed of the workpiece 1 decreases very noticeably. At the common point of contact 5 of workpiece 1 and grinding wheel 3, there is a noticeable slip in the entrainment of the workpiece 1 by the grinding wheel 3. The workpiece 1 is thus taken by the grinding wheel 3 only to a reduced extent for rotation, this results in the grinding effect which now exerts the grinding wheel 3 on the workpiece 1. The correct relationship between the drive effect and the grinding action is set and maintained by measuring the workpiece speed and the already mentioned evaluation and control arrangement. With the brake 11, the braking effect on the workpiece 1 can be set much more accurately than if the braking takes place solely by the first contact surface 7 and the second contact surface 9.

In the execution after Fig. 1 The first contact surface 7 and the second contact surface 9 together already look similar to a workpiece holder in the form of a prism, which is familiar to the expert. In the FIGS. 2 to 4 Further embodiments are shown in which the prism is realized in the usual sense as a structural unit. Here are in the FIGS. 2 to 4 compared to Fig. 1 the proportions of the grinding wheel 3 and the workpiece 1 changed significantly, so that the representation is clearer and also the drawings can be smaller.

According to Fig. 2 a grinding spindle unit 17 is provided which drives the grinding wheel 3 about its axis of rotation 18 for rotation. The grinding wheel 3 contacts the workpiece 1 at the contact point 5. The workpiece 1 is surrounded by a prism 19, which is formed in one piece and with the cross section of an angle. If the grinding spindle unit 17 is delivered in the feed direction X with the feed force F in the direction of the workpiece 1, the rotary drive of the workpiece 1 results at the contact point 5 by the entrainment as a result of friction. The workpiece 1 is pressed against the first abutment surface 7 and the second abutment surface 9 of the prism 19 and can rotate in the prism 19 only slowed down. As a result, the already mentioned advantageous slip between the grinding wheel 3 and the workpiece 1 at the contact point 5 comes about.

The Fig. 3 shows another form of a prism 20, which here has a trapezoidal cross-section. The workpiece 1 rests only on the two arms of the trapezoid on which the first contact surface 7 and the second contact surface 9 are located. The remaining details are the same as in Fig. 2 , The embodiment with the one-piece prism 19 or 20 is simpler than the separate version of the support plate 6 and support rail 8, thereby resulting in less effort to greater stability and accuracy.

Again, the execution is different Fig. 4 , Here, in principle, the design of a prism 21 before according to the Fig. 2 , However, an upper arm 22 is pivoted about a pivot axis 23 to the body 24 of the prism 21. The upper arm 22 can be pressed by an adjusting device 25, which is part of the brake, with adjustable and controllable effect on the workpiece 1. The effect of the brake 11 has already been described above. On the upper arm 22, the third abutment surface 26 is again formed.

Claims (9)

1. Method for the centreless cylindrical grinding of workpieces of rotationally symmetrical contour, in the case of which the workpiece (1) is ground by means of a grinding wheel (3) and is supported, guided, and has its rotation braked, by a supporting device (6, 8, 11), wherein the circumferential surfaces of the grinding wheel and workpiece move in the same direction at the point of contact (5), and it is only the grinding wheel (3) which is driven in rotation and, alone, causes the workpiece (1) to be driven in rotation, characterized in that the grinding wheel (3) is positioned for a grinding action against the rotating workpiece (1) and a first abutment surface (7) and a second abutment surface (9) are arranged in the manner of a prism such that during the grinding operation, by means of a positioning force (F) applied by the grinding wheel (3), the workpiece (1) is pressed, with sliding contact, onto the abutment surfaces (7, 9) of the supporting device (6, 8, 11), said abutment surfaces being immovable during operation and retaining the workpiece (1) in an optimum position for the grinding operation, and the rotational speeds of the grinding wheel (3) and of the workpiece (1), the braking force (P) to which the workpiece (1) is subjected by the supporting device (6, 8, 11) and also the positioning force (F) of the grinding wheel (3) are monitored continuously and are coordinated with one another to give an optimum grinding result.
2. Centreless cylindrical grinding machine for implementing the method according to Claim 1, having a grinding headstock and a grinding wheel (3) which is mounted in said headstock, is driven in rotation by a drive device and, alone, drives a workpiece (1) in rotation, wherein it is only the grinding wheel (3) which is driven in rotation and the circumferential surfaces of the workpiece (1) and of the grinding wheel (3) move in the same direction at the point of contact (5) thereof, and having a supporting device (6, 8, 11), which supports the workpiece (1) and, in addition, has an inhibiting effect on the rotary movement of the workpiece such that, in controlled interaction with the positioning force (F) acting on the grinding wheel (3), the workpiece (1) is both driven in rotation and ground by the grinding wheel (3), wherein the supporting device (6, 8, 11) has at least a first planar abutment surface (7) and a second planar abutment surface (9), which are arranged in the manner of a prism and are each arranged in an immovable manner during operation in the circumferential running direction (16) of the workpiece (1), characterized in that the grinding wheel (3) can be positioned in its radial direction against the workpiece (1) of rotationally symmetrical contour by the grinding headstock and the bearing surfaces (7, 9) of the supporting device (6, 8, 11) extend at a distance from one another along the workpiece (1) and are arranged so as to engage around said workpiece, with sliding contact, such that the workpiece (1) is retained in a position which is optimum for the grinding operation, in that a brake (11) with a braking body (12), which acts on the workpiece (1) with an adjustable braking force (P) via an adjustment device, is arranged on the supporting device (6, 8, 11), and in that a device is provided for measuring rotational speeds, this device being designed to monitor the rotational speed of the workpiece continuously, and in that an evaluation and regulating arrangement is present, said arrangement being designed to maintain an optimum balance, on a constant basis, between the rotational speed of the grinding wheel, the positioning force (F) of the grinding wheel (3) and the braking force (P) of the braking body (12).
3. Cylindrical grinding machine according to Claim 2, characterized in that the first planar abutment surface (7) and the second planar abutment surface (9) are arranged overall in an immovable manner during operation.
4. Cylindrical grinding machine according to Claim 2, characterized in that the first abutment surface (7) and the second abutment surface (9) are designed for controlled movement during operation, in adaptation to the workpiece diameter as it decreases during grinding.
5. Cylindrical grinding machine according to one of Claims 2 to 4, characterized in that the first abutment surface (7) is located on a supporting plate (6), which is located beneath the workpiece (1) and is designed in the manner of the conventional supporting straightedge, while the second abutment surface (9) is located on a separate supporting rail (8), which is arranged opposite the grinding wheel (3).
6. Cylindrical grinding machine according to Claim 5, characterized in that the braking body (12) forms a further supporting body with a third abutment surface (14).
7. Cylindrical grinding machine according to Claim 6, characterized in that the third abutment surface (14) is located opposite the first abutment surface (7) and acts on the workpiece (1) from above.
8. Cylindrical grinding machine according to one of Claims 2 to 4, characterized in that the first abutment surface (7) and the second abutment surface (9) are located on a common supporting body, which forms a prism (19, 20, 21), which is located opposite the grinding wheel (3) and engages around the workpiece (1).
9. Cylindrical grinding machine according to Claim 8, characterized in that the cross section of the prism (19, 20, 21) is in the form of an angle or of a trapezium.

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