Patent Grant
8944891
The invention relates to a centerless cylindrical grinding machine for grinding workpieces in rod form with a cylindrical outer contour using the throughfeed grinding process having certain features. The invention also relates to a method for the centerless cylindrical grinding of workpieces in rod form having certain features. A cylindrical grinding machine and a method of this type are known from DE 101 00 871 C1. In the cylindrical grinding machine according to the prior art, two individual cylindrical grinding machines are combined as separate assemblies on a common base plate to form one unit. The rod-shaped or tubular workpiece runs continuously through the two separate grinding units for grinding one after another. Here, in every grinding unit, a comparatively wide cylindrical grinding wheel lies opposite an assembly of regulating wheels which are comparatively thin and are arranged at a spacing from one another on a common spindle. Together with the customary support blade, the grinding and regulating wheels are situated in a common axial region; the two assemblies are also independent of one another in every regard. For example, the grinding geometry, that is to say the spatial assignment of grinding wheel, regulating wheel and support blade in relation to the workpiece, can be different in each of the two units.
In the known cylindrical grinding machine, two grinding gaps are therefore formed which are situated at an axial spacing from one another and through which the rod-shaped or tubular workpiece runs. The two units of the known cylindrical grinding machine can serve different tasks; for example, the rough grinding can take place in the first unit, whereas the finishing is performed in the second unit. However, the finishing can also already be started in the first unit, with the result that more machining time is available overall for the process of finishing. As a result, the tool wear can be reduced considerably during rough grinding with a relatively low erosion rate. In both units of the known grinding machine, the workpiece is arranged in the grinding gap in such a way that it is situated “below the middle”. The following is therefore meant in an exact definition: the workpiece is fixed in the radial direction in the widening grinding gap in accordance with a reference plane which is placed through the rotational and drive axes of regulating wheel and grinding wheel; here, the workpiece longitudinal axis is situated such that it is moved away from said reference plane within a part region of the grinding gap between said reference plane and the supporting face of the work rest blade. This arrangement has the advantage that the workpiece is clamped in a certain way in the grinding gap between the regulating and grinding wheel on one side and the supporting face of the work rest blade on the other side. It therefore also cannot be ejected out of the grinding gap when machining is carried out with relatively great grinding forces. The cylindrical grinding can therefore be carried out “below the middle” with a high material removal rate, and the axial advancing of the workpiece in the grinding section and in the grinding gap can be high.
The arrangement “below the middle” is therefore preferred in many applications in centerless cylindrical grinding. The limits of the arrangement are shown, however, when rod-shaped or tubular workpieces are to be ground which have a small diameter. The workpiece then has to bear against the grinding and regulating wheel in a region of the grinding gap, in which the outer contours of the wheels already merge into an approximately parallel profile. The workpiece therefore lies very far to the top in the grinding gap, with the result that it can migrate upward out of the grinding gap in the worst case. It at least becomes more and more difficult to ensure a secure and steady position of the workpiece during grinding by way of the usual support blade. If the grinding gap becomes narrower and narrower, finally the region is approached, in which the grinding wheels would abut one another; centerless cylindrical grinding of workpieces with a small diameter is then no longer possible in the conventional way.
German patent specification 801 500 has disclosed a special device which is to be actuated by hand and by way of which two lateral grinding points are to be machined on a workpiece at the same time by centerless cylindrical grinding. To this end, two grinding wheels are arranged in a floating manner on a common shaft and are driven rotationally; their axial spacing from one another is variable. In order to grind the lateral grinding points, one movably arranged grinding wheel is moved in axially from the outside toward the second stationary grinding wheel. During the grinding of the lateral grinding points, the two grinding wheels remain at an axial spacing from one another. A regulating wheel for driving the workpiece is arranged opposite on the other side of the workpiece. The regulating wheel and the grinding wheel are offset with respect to one another because, in its axial position, the regulating wheel is situated where the gap between the two grinding wheels exists on the opposite side of the workpiece. In each case only one single workpiece is to be ground by way of the known apparatus, which workpiece has to be introduced into the apparatus and removed from it again for this purpose. The workpiece has approximately the shape of a spindle, as is present in the hubs of bicycles.
In a centerless cylindrical grinding machine which is known from DE 478 720 A, long, thin round rods are to be ground and transported using the throughfeed grinding process by three separate groups of wheels. Each of the three groups comprises a common spindle which is driven rotationally and on which the wheels of said group are situated at a mutual axial spacing. The three groups extend along the round rod to be ground and enclose the latter between them. Here, the first group consists of grinding wheels; the associated spindle extends parallel to the axis of the round rod. The spindle of the second group is inclined slightly with respect to the axis of the round rod; the wheels which are arranged on said spindle are guide wheels with a conical edge which is fitted with felt. The guide wheels bring about the transport of the round rod in the axial direction. The grinding wheels and guide wheels lie opposite one another at a radial spacing in the customary way, to be precise such that exactly one guide wheel lies opposite each grinding wheel.
The third group of wheels in the cylindrical grinding machine according to DE 478 720 A is arranged below the round rod which is running through, on a common spindle in such a way that said wheels engage from below into the axial intermediate spaces between the grinding wheels and the guide wheels and support the round rod. The known machine has no support blade. Rather, the wheels of the third group act in a similar manner to a support blade; in addition, they bring about the rotary drive of the round rod. The known machine according to DE 478 720 A should make the utilization of different-grained grinding wheels possible and at the same time ensure vigorous spinning of the workpieces with powerful axial advancing.
In contrast, the invention is based on the object of improving the cylindrical grinding machine and the cylindrical grinding method of the type stated at the outset, in such a way that even rod-shaved or tubular workpieces of small external diameter are held in a reliably stable and steady manner in the grinding gap which is formed by the grinding wheels, the regulating wheels and the support blade, with the result that a satisfactory grinding result is achieved even during grinding with a high material removal volume.
This object is achieved in the cylindrical grinding machine and the cylindrical grinding method of the invention.
In the centerless cylindrical grinding machine according to the invention, it is therefore provided that the regulating and grinding wheels are arranged offset in the axial direction with respect to one another, the regulating wheels projecting into the axial intermediate spaces between the grinding wheels and, conversely, the grinding wheels also projecting into the axial intermediate spaces between the regulating wheels. The regulating and grinding wheels can therefore no longer come into contact with one another, and the grinding gap does not already begin in the abovementioned reference plane, but rather at a distance from the latter in a region, in which the spacing between the outer contours of grinding and regulating wheel is enlarged increasingly. The workpiece therefore bears against the grinding and regulating wheel on two tangential contact lines which extend in its longitudinal direction, said contact lines being at a relatively great spacing from one another. A person skilled in the art calls this a “great below-middle extent”. As a result, the position of the workpiece in the grinding gap remains reliably steady and stable even when work is carried out with a high material removal volume.
It is possible by way of the cylindrical grinding machine according to the invention to allow the grinding wheel to run at the contact point with the workpiece in the same direction as the surface of the latter or in the opposite direction thereto. Independently of this, the rotational direction of the grinding wheel can also be selected in such a way that, at the point of its contact with the workpiece, the grinding wheel circumference moves toward the reference plane, that is to say into the grinding gap. This has the advantage that, during grinding, the workpiece is pressed more powerfully against the regulating wheels and therefore the work rest blade is relieved. The wear of the work rest blade is therefore reduced.
One advantageous development of the cylindrical grinding machine according to the invention consists in the fact that the basic pattern of the multiple set comprises in each case one row of two or more wheels, of which one row with regulating wheels is arranged on one side of the workpiece and the other row with grinding wheels is arranged so as to lie opposite on the other side of the workpiece. In comparison with the known cylindrical grinding machine which was mentioned at the outset and is expressly fixed to two grinding units which are independent of one another, this therefore results in a comparatively simple basic construction, in which three and more regulating and grinding wheels can also be driven jointly one behind another in the axial direction.
Here, in every section of the grinding gap, the grinding and regulating wheels are then driven in a constant rotational direction; here, the rotational speed of the regulating wheels firstly and of the grinding wheels secondly can be set independently, as can the two-sided setting of the wheels against the workpiece, it goes without saying that it is also possible via the machine controller to adapt the rotational speeds and the setting movement of the two wheel groups to one another in a controlled manner.
In addition to these considerations, it can be provided, according to further advantageous embodiment, that the regulating wheels and the grinding wheels have diameters which increase in a stepped manner in the axial throughfeed direction of the workpiece and, in this case, the work rest blade is also adapted with its supporting face to the diameter of the workpiece, which diameter decreases in its longitudinal direction, in this embodiment, during running grinding operation, no further setting movement of the regulating and grinding wheels is performed. Rather, the radial setting during the grinding via the wheels has been made superfluous by virtue of the fact that the rod-shaped workpiece runs through wheel groups with an increasing diameter, the grinding gap becoming narrower and narrower. A change in the setting required only when the grinding wheels have to be changed or when a change to workpieces with a different diameter to previously takes place.
In the cylindrical grinding machine according to the invention, the regulating and grinding wheels are no longer immediately opposite one another in the transverse direction. The offset arrangement of the wheels means that there is the risk of deflection, if small, for the workpiece. In the worst case, the grinding result could be impaired as a result. Therefore, according to a further advantageous embodiment, it is provided preventatively that the lateral overlap regions of the regulating and grinding wheels are separated from one another by axial gaps, the width of which is only so great that the regulating and grinding wheels do not mutually impair their function or even make contact, even during continuous production operation. The correct dimensioning of the gap width is the result of simple operational tests; a guide value for practice can be, for example, the range between 0.5 and 2 mm.
A further advantageous measure for avoiding bending loads in the workpiece consists in the fact that the axial width of the grinding wheels is smaller than the axial width of the regulating wheels.
It is essential for the operation of the cylindrical grinding machine according to the invention that the grinding wheels have a long service life. Only then can grinding be carried out with a high material removal volume, without subsequent correcting of the setting being required during grinding operation. CBN grinding wheels, the CBN grinding lining of which can be coated galvanically and can be ceramically bonded or metal-bonded, are therefore preferred for the cylindrical grinding machine according to the invention.
The high load capacity of the workpieces in the cylindrical grinding machine which is designed according to the invention also means that regulating wheels made from steel can be used. They should advantageously be provided on their outer circumference with a thread profile which, in a similar manner to a conveying worm, exerts an axial thrust on the workpiece in the direction of the throughfeed direction, in which the workpiece runs through the grinding gap. Here, the outer circumference of the regulating wheel or the thread profile should advantageously be configured as a friction lining which is composed of a different material than steel, preferably of a galvanically bonded CBN layer.
Further advantageous refinements relate to the guidance of the rod-shaped workpiece in the grinding section and to the drive of the workpiece in its longitudinal and movement direction, that is to say the throughfeed direction in the grinding section.
For instance, an inlet support wheel with an elastic circumferential covering can be arranged at the inlet E of the multiple set in the row of the regulating wheels, in front of the latter, which inlet support wheel, together with the regulating wheels, is fastened on the regulating wheel spindle and is driven rotationally by the latter. Said inlet support wheel can compensate for a lateral deviation of the workpiece if the latter enters the grinding section with its front end as an out-of-round raw rod. Even the out-of-round workpiece is then introduced reliably into the grinding gap.
In a similar way, an outlet support wheel made from steel can be mounted freely rotatably on the grinding wheel spindle at the outlet A of the multiple set in the row of the grinding wheels, behind the latter. It is the object of the outlet support wheel to compensate for the forces which act on the rod-shaped workpiece at the outlet A of the grinding section. The aim here is also to prevent bending forces and a deflection of the workpiece at its end. A grinding wheel as final wheel would exert too high a lateral force on the workpiece and deflect the latter laterally. It would be similar with a driven regulating wheel as final wheel. The arrangement of an outlet support wheel made from steel is expedient, in particular, when galvanically coated CBN grinding wheels are used. In the case of the latter, their diameter changes only to a very small extent during their use; the effect of the outlet support wheel remains virtually unchanged as a result.
A further advantageous refinement of the outlet support wheel is that it is provided with a thin damping lining on the steel basic body, which lining firstly has a damping action on the finally ground workpiece during the exit from the grinding gap. The running smoothness of the workpiece out of the grinding gap can therefore be improved further (and therefore also the surfaces, measuring and dimensional accuracy on the workpiece). As a further advantage, the thin damping lining can also absorb small diameter changes of the grinding wheel.
The action of the inlet support wheel can be assisted further by virtue of the fact that a device for precentering the rod-shaped workpiece which is running through is arranged in front of the multiple set. Said device can comprise a supporting prism and a pressure roller which is assigned to the latter, the workpiece running through between the supporting prism and the pressure roller. The device for precentering therefore facilitates the first entry of the workpiece into the grinding section.
Finally, it can also be provided in an advantageous way that a device is provided at the start of the workpiece movement path, which device imparts a forward thrust to the workpiece in its longitudinal and movement direction. The forward thrust action of said additional device then takes place together with the effect of the thread profile on the outer circumference of the regulating wheels. The effect of both devices has to be adapted to one another in an expedient way.
The method according to the invention advantageously achieves a situation where continuous radial feeding of the grinding and/or regulating wheels against the workpiece during grinding operation is no longer required. Rather, the grinding and regulating wheels remain unchanged in their radial position with respect to the workpiece; instead, the workpiece runs continuously through the grinding gaps, formed one behind another, of regulating and grinding wheels, the spacing of which from one another becomes smaller and smaller in a stepped manner from the inlet E toward the outlet A of the grinding section, in accordance with the grinding progress. This reduction is brought about by the fact that the diameters of the regulating and grinding wheels become greater in a stepped manner toward the outlet of the grinding section.
The method according to the invention advantageously achieves a situation where continuous radial feeding of the grinding and/or regulating wheels against the workpiece during grinding operation is no longer required. Rather, the grinding and regulating wheels remain unchanged in their radial position with respect to the workpiece; instead, the workpiece runs continuously through the grinding gaps, formed one behind another, of regulating and grinding wheels, the spacing of which from one another becomes smaller and smaller in a stepped manner from the inlet E toward the outlet A of the grinding section, in accordance with the grinding progress. This reduction is brought about by the fact that the diameters of the regulating and grinding wheels become greater in a stepped manner toward the outlet of the grinding section. The radial setting movement of the regulating and grinding wheels during running grinding operation is therefore replaced by the movement of the rod-shaped workpiece in its longitudinal direction.
One advantageous development of the method according to the invention consists in the fact that the movement direction of the grinding wheel circumference, at the point of its contact with the workpiece, extends in the direction of the reference plane. In this procedure, the grinding wheel exerts an action of force on the workpiece which is pressed against the regulating wheel as a result. As a result, the loading of the work rest blade by the workpiece is reduced, as is therefore also the wear of the work rest blade.
Finally, it is also noted that the expression of the “rod-shaped workpieces” is also to include tubes. The rods or tubes which come into consideration here are intended to have a length of, for example, 6 meters. They are intended to be ground in the cylindrical grinding machine which is configured according to the invention, from the raw rod as far as a completely finished ground rod with a small diameter tolerance. Here, a high material removal rate can be achieved in a secured process with as low a workpiece rotational speed as possible. In the view from above, the longitudinal and rotational axes of the regulating wheels, the grinding wheels and the workpiece extend parallel to one another; the same also applies to the longitudinal extent of the work rest blade. In a view from the side, the longitudinal axis of the work rest blade can also extend in a slightly inclined manner with respect to the longitudinal axis of the workpiece, in accordance with the decrease in diameter of the workpiece.
In the following text, the invention will be explained in yet further detail using one exemplary embodiment which is shown in the figures. In the drawings:
a shows the function of the apparatus according to
a and 5b explain details of a regulating wheel, and
According to
The arrangement, shown in
In the arrangement which is shown in
However,
Enhanced machining options result from the design which is shown in
All the regulating wheels 3 are set jointly in rotation via the regulating wheel spindle 16; all the grinding wheels 5 are likewise set jointly in rotation via the common grinding wheel spindle 17.
The workpiece 1 which is shown using dashed lines in
The advantages of the amended arrangement can be seen immediately from
In order to clarify this situation,
a otherwise also shows a further essential detail. As is apparent there from the rotational direction 12 of the grinding wheel 5, the circumference of the grinding wheel 5 moves into the grinding gap at its contact point with the workpiece 2, that is to say toward the reference plane 14. The grinding wheel 5 therefore exerts an action of force on the workpiece 1, which action of force leads to additional pressure of the workpiece on the regulating wheel 3. As a result, the force is reduced, with which the workpiece presses onto the supporting face 8 of the work rest blade 7. As a result, this leads to the wear of the work rest blade being reduced.
The mutually offset arrangement in the axial direction of the regulating and grinding wheels 3, 5 means for the workpiece 1 that there is the risk of a deflection, even if said deflection is small, which might impair the grinding result in the worst case. This is counteracted firstly by the fact that the diameters of the regulating wheel and grinding wheel spindles 16, 17 are dimensioned to be comparatively great. Secondly, the axial width b3 of the regulating wheels 3 is configured to be greater than the axial width b5 of the grinding wheels 5, in order that the high setting force of the grinding wheels 5 which acts in the radial direction during the grinding can be absorbed reliably by the regulating wheels 3.
In the attempt to keep bending forces away from the workpiece 1, the width s18 of the axial gap 18 also has to be kept as small as possible, which axial gap 18 exists in the lateral overlap regions 19 between the regulating wheels 3 and the grinding wheels 5. A generally valid regulation cannot be drawn up for this; however, it can be determined reliably by way of tests without relatively great outlay how small the gap width s18 can be, without the regulating and grinding wheels 3, 5 themselves impairing their function mutually in continuous production operation or even making contact with one another. A guide value for practice can be, for example, the range between 0.5 and 2 mm.
A device which imparts an advancing movement to the rod-shaped workpiece 1 in its longitudinal and throughfeed direction 2 and 22 can be set upstream of the grinding section which is shown in
The support blade 7 has to be adapted to this decrease in the workpiece diameter. To this end, said support blade 7 can be set obliquely over the entire length of the grinding section or can consist of individual adapted sections which in each case project a bit further into the grinding channel 15 step by step in the throughfeed direction 22. The decrease in the workpiece diameter is shown on a greatly exaggerated scale in
The grinding wheels 5 are galvanically coated, ceramically bonded or metal-bonded CBN grinding wheels which are preferred on account of their high material removal performance and their stability. The regulating wheels 3 have a basic body made from steel and are provided on their outer circumference with a friction lining which can consist of a galvanically bound CBN layer. Here, the friction lining is expediently configured as a thread profile 25, cf.
A further device 29 is arranged at the inlet E of the grinding section, which further device 29 consists of a supporting prism 30 and a pressure roller 31, between which the rod-shaped workplace 1 runs through, cf.
When the rod-shaped workpiece 1 has passed the device 29 for precentering, it next passes into the action region of an inlet support wheel 26. The latter is mounted fixedly on the regulating wheel spindle 16 so as to rotate with it, is set upstream of the regulating wheels 3 and is driven rotationally together with the latter. The inlet support wheel 26 is provided with an elastic circumferential covering 27 and can compensate for the lateral deviation of an out-of-round workpiece 1 when the latter enters the grinding section with its front end as a raw rod. In this way, the out-of-round workplace 1 is also introduced reliably into the grinding gap 15.
An outlet support wheel 28 is provided at the outlet A of the grinding section on the side of the grinding wheels 5. Said outlet support wheel 28 is mounted freely rotatably on the grinding wheel spindle 17, and is therefore not driven together with the grinding wheels 5. The outlet support wheel 28 can be composed of steel and is given its rotary drive by contact with the workpiece 1; it does not have a thread profile on its circumference. The task of the outlet support wheel 28 consists in compensating for the forces which act on the rod-shaped workpiece 1 at the outlet A of the grinding section. A grinding wheel 5 as final wheel would exert too high a lateral force on the workpiece 1 and deflect the latter laterally. It would be similar with a driven regulating wheel 3 as final wheel. The arrangement of an outlet support wheel 28 made from steel is particularly expedient in the case of the use of CBN grinding wheels; this is because, in the case of the latter, the diameter reduces only to a very small extent during their useful life; the action of the outlet support wheel 28 then remains virtually unchanged.
A regulating wheel support (not shown) brings about the radial setting of the regulating wheel spindle 16 with all of its regulating wheels 3 and the inlet support wheel 26 against the workplace; a grinding wheel support (not shown) likewise serves for the radial setting of the grinding wheel spindle 17 with all its grinding wheels 5. During grinding operation, the position of the regulating and grinding wheels 3, 5 radially with respect to the workpiece 1 does not have to be changed, or only has to be changed insignificantly, because the diameter of the CBN grinding wheels 5 remains virtually unchanged during their useful life. Renewed setting becomes necessary only during the change of the grinding wheels 5 or if a change takes place to workpieces having a different diameter. Continuous adjustment of grinding and regulating wheel 3, 5 in accordance with the decreasing workpiece diameter is not necessary in any case in the throughfeed grinding process, because the rod-shaped workpiece 1 instead migrates through a grinding gap 15 which gets narrower in a stepped manner.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 010 758 | Mar 2010 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/053396 | 3/7/2011 | WO | 00 | 10/12/2012 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2011/110529 | 9/15/2011 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2043972 | Merryweather | Jun 1936 | A |
| 2436252 | Duncan | Feb 1948 | A |
| 2939253 | Richard et al. | Jun 1960 | A |
| 3079741 | Render | Mar 1963 | A |
| 4194323 | Blocker, Jr. | Mar 1980 | A |
| 4841682 | Waelti | Jun 1989 | A |
| Number | Date | Country |
|---|---|---|
| 478720 | Jul 1929 | DE |
| 801500 | Jan 1951 | DE |
| 101 00 871 | Jun 2002 | DE |
| 431471 | Jul 1935 | GB |
| Number | Date | Country | |
|---|---|---|---|
| 20130165022 A1 | Jun 2013 | US |
