Method and grinding machine for grinding grooved workpieces

Abstract

A method is disclosed for grinding grooves on workpieces using a profiled grinding wheel, the profile of which is crushed. A reshaping crush process includes driven crush rollers, each being controlled on the basis of a rotational speed and current consumption. Thus, relative advancement between the grinding wheel and crush roller is controlled according to the speed and current consumption. A grinding machine is also disclosed for grinding a workpiece, wherein the workpiece is held by means of a workpiece spindle head. A crush device comprising a crush roller with a dedicated rotary drive is provided on the grinding machine. The grinding wheel is applied to the crush roller in order to dress the grinding wheel profile. The crush roller has a profile-crushing portion for profile-crushing the grinding wheel with a first dressing volume and a reshaping profile-crushing portion for profile-crushing the grinding wheel with a second dressing volume.

Claims

1. A method for grinding grooved workpieces with a profiling of a grinding wheel corresponding to the cross section of a groove, by means of which the groove is grinded in a workpiece clamped in the grinding machine, wherein the profiling of the grinding wheel is crush dressed, wherein a reshaping crushing process of the grinding wheel is performed by means of a crushing roller driven by the grinding wheel, wherein a control of the crushing process is performed depending on a measurement of rotational speed and current consumption of a drive of the grinding wheel and the crushing roller, and a relative advancement between the grinding wheel and the crushing roller during the crushing process is controlled on the basis of said measurement, characterized in that in the profiling-crushing process with a profiling-crushing portion of the crushing roller, a larger truing volume is removed from the grinding wheel by means of a reshaping-crushing portion disposed on the same crushing roller, than in a reshaping-crushing process.

2. The method of claim 1, characterized in that the profiling-crushing of the grinding wheel is performed by the crushing roller on the basis of measured rotational speed and current consumption of respective drives of the grinding wheel and the crushing roller by controlling the relative advancement between the grinding wheel and the crushing roller on the basis of said measurement, wherein the profiling-crushing is performed before starting a grinding process.

3. The method of claim 2, characterized in that for crushing, the grinding wheel is applied on the crushing roller and is engaged with the same, wherein during the profiling-crushing, the crushing roller freely rotates with the grinding wheel without having its own drive.

4. The method of claim 2, characterized in that a cooling medium is fed to the crushing roller and the grinding wheel during the crushing process, in respective engagement regions of the crushing roller and the grinding wheel.

5. The method of claim 2, characterized in that a maximum relative advancement between the grinding wheel and the crushing roller during crushing depends on grinding machine parameters and crushing parameters and is determined before crushing, and is inputted as a threshold value into a grinding machine control.

6. The method of claim 1, characterized in that during the profiling-crushing process, the grinding wheel is engaged with the crushing roller and the crushing roller freely rotates with the grinding wheel without having its own drive.

7. The method of claim 1, characterized in that a cooling medium is fed to the crushing roller and the grinding wheel during the crushing process, in respective engagement regions of the crushing roller and the grinding wheel.

8. The method of claim 1, characterized in that a maximum relative advancement between the grinding wheel and the crushing roller during a crushing process depends on grinding machine parameters and crushing parameters and is determined before crushing, and is inputted as a threshold value into a grinding machine control.

9. A grinding machine for grinding grooved workpieces, which is provided with a grinding spindle stock, which is movable, under CNC-control, on a cross slide over a machine support along the X-axis and Z-axis, which holds a grinding wheel and rotationally drives the same for grinding a groove, and a workpiece spindle stock with a C-axis, wherein the workpiece is held in a clamping by means of a workpiece spindle head, and a rigidly installed crush device comprising a crushing roller with a dedicated rotary drive is additionally provided, which may be controlled by a control device, wherein the grinding wheel and the crushing roller may be driven and their rotational speed may be adjusted during a reshaping-crushing process, characterized in that the grinding wheel is applied to the crushing roller in order to dress a profile of the grinding wheel and the crushing roller has a profiling-crushing portion for profiling-crushing the grinding wheel with a first dressing volume and a reshaping-crushing portion positioned on the same crushing roller, for reshaping-crushing the grinding wheel with a second dressing volume.

10. The grinding machine of claim 9, characterized in that the crushing device is positioned in a housing and is fixedly connected with the machine support.

11. The grinding machine of claim 10, characterized in that the crushing device has a CNC-controlled drive, which is connected, through a clutch, with the crushing roller, which is particularly made of high performance high speed cutting steel or hard metal, for its rotational drive.

12. The grinding machine of claim 10, characterized in that the crushing device has a body-sound sensor, by which, in case of the grinding wheel being engaged with the crushing roller, a signal may be sent to the control device, based on which the engagement contact between the crushing roller and the grinding wheel may be determined for its monitoring.

13. The grinding machine of claim 10, characterized in that the grinding wheel during the reshaping-crushing process, may be applied onto the crushing roller and may be moved in a transversal direction with respect to the reshaping-crushing portion.

14. The grinding machine of claim 10, characterized in that at the beginning and/or during the profiling-crushing, the drive of the crushing device may be provided with drive pulses in case of a speed drop.

15. The grinding machine of claim 10, characterized in that the crushing roller is in one or two parts.

16. The grinding machine of claim 10, characterized in that the control device is adapted so that a maximum relative advancement between the grinding wheel and the crushing roller during a crushing process is smaller than a predetermined threshold value, which depends on the machine parameters and process parameters, and which may be input into the control device before starting the crushing process.

17. The grinding machine of claim 9, characterized in that the crushing device has a CNC-controlled drive, which is connected with the crushing roller for its rotational drive through a clutch, which is particularly made of high performance high speed cutting steel or hard metal.

18. The grinding machine of claim 9, characterized in that the crushing device has a body-sound sensor, by which, in case of the grinding wheel being engaged with the crushing roller, a signal may be sent to the control device, based on which the engagement contact between the crushing roller and the grinding wheel may be determined for its monitoring.

19. The grinding machine of claim 9, characterized in that the grinding wheel during the reshaping-crushing process, may be applied onto the crushing roller and may be moved in a transversal direction with respect to the reshaping-crushing portion.

20. The grinding machine of claim 9, characterized in that at a beginning and/or during a profiling-crushing, the drive of the crushing device may be provided with drive pulses in case of a speed drop.

21. The grinding machine of claim 9, characterized in that the crushing roller is in one or two parts.

22. The grinding machine of claim 9, characterized in that the control device is adapted so that a maximum relative advancement between the grinding wheel and the crushing roller during a crushing process is smaller than a predetermined threshold value, which depends on the machine parameters and process parameters, and which may be input into the control device before starting the crushing process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, possible applications and details are described in the following with the use of examples in the attached figures. In particular:

(2) FIG. 1 shows a simplified representation in principle of a grinding machine with a crushing device in a view from above,

(3) FIG. 2 shows a crushing device and associated grinding spindle with a grinding wheel according to the invention,

(4) FIG. 3 shows a crushing roller with an associated grinding wheel for a profiling-crushing,

(5) FIG. 4 shows a detailed view of the crushing roller and associated grinding wheel at the immediate start of the profiling-crushing,

(6) FIG. 5a) shows the crushing process of profile on the grinding wheel on a first flank,

(7) FIG. 5b) shows the crushing process of profile on grinding wheel of a second flank of the crushing roller,

(8) FIG. 5c) shows the crushing process, essentially at the end of crushing of profile on the grinding wheel by the crushing roller and

(9) FIG. 6) shows geometric relationships of groove depth and of peripheral surface provided for the groove depth in the groove and in the profile of the grinding wheel.

DETAILED DESCRIPTION

(10) In FIG. 1, a representation in principle, from above, of the arrangement of main components of an inventive grinding wheel on the machine bed is shown. A workpiece spindle stock with a workpiece spindle with a C-axis has a workpiece 1 clamped. For an optional clamping of workpiece on points, in the extension of the longitudinal axis of the workpiece spindle a displaceable tailstock 4 with a point is provided. On a cross slide which is fixed to the machine bed a grinding spindle stock with a grinding spindle is positioned, on which a grinding wheel 5 is attached. The grinding wheel 5 has a profile, with which the corresponding grooves are ground in the workpiece 1. To this end, the grinding wheel may be moved along CNC-axes in the X, Y and Z direction, and may be applied to the workpiece 1. Moreover, a crushing device 7 is provided, which carries a crushing roller. The axis of rotation of the crushing roller and of the grinding wheel 5 are parallel to each other, in any case when the grinding wheel 5 is subject to crushing of its profile.

(11) In FIG. 2 in the form of a detail of the arrangement of the grinding machine of FIG. 1 only the grinding spindle 2 with the grinding wheel 5 and the associated crushing device 7 with its crushing roller 8 are shown. In order to grind the corresponding grooves in the workpiece not shown in FIG. 2, the grinding spindle 2 is tiltable with its grinding wheel 5 around a CNC-controlled A-tilting axis. The grinding spindle may also be moved by CNC-control in the Z and Y direction.

(12) The main structure of FIG. 2 of the crushing device 7 is characterized by a high rigidity, which is evidenced, for example, by the fact that the crushing device 7 is positioned inside a housing 9, in which the crushing spindle 16 holding the crushing roller 8 is rigidly supported on both sides of the crushing roller 8 by roll bearings 12. The drive motor 11 of the crushing device 7 is also CNC-controlled and is connected through a clutch 10 with the crushing spindle 16.

(13) FIG. 2 shows a crushing roller 8, which has two crushing grooves or crushing slots. Both crushing grooves may be used in succession for crushing the profile of the grinding wheel 5. This can be, on one side, a profiling-crushing with the first crushing groove and a reshaping-crushing with the second crushing groove. However, it is also possible, that both crushing grooves of the crushing roller 8 are only used for reshaping-crushing. In this case, the crushing groove shown in FIG. 2 above is initially used for reshaping-crushing until it can no longer provide the required precision of profiling on the grinding wheel 5. Then the crushing groove shown below in the drawing is used for a further reshaping-crushing of the grinding wheel. When both crushing grooves are used for reshaping-crushing, the operating life of the crushing roller during crushing may be doubled with respect to a crushing roller with only one crushing groove. It is also possible that a higher number of crushing grooves are used or provided in the inventive crushing roller. In any case, with the inventive crushing roller, above all, also the higher rigidity can be considered, and a higher process precision during crushing of profile of the grinding wheel may be achieved, as well as a higher precision of workpieces to be grinded, if the at least two crushing grooves are positioned on an integral and therefore rigid crushing roller 8.

(14) FIG. 3 shows only the main part of the crushing device 7, the crushing roller 8, which is positioned on the crushing spindle 16. The crushing roller 8 has a profiling-crushing portion 14 and a reshaping-crushing portion 15. Moreover, in principle, a body sound sensor 14 is provided on the crushing device 7, with which the engagement contact of the grinding wheel 5, which is positioned on the grinding spindle 2, and which is rotationally driven around its C-axis, and the crushing roller 8 may be detected or monitored.

(15) The grinding wheel 5 shown in FIG. 3 is still not profiled and has therefore to be initially profiled-crushed for the actual grinding process. The term profiling-crushing means, in this context, the generation of the actual profile on the grinding wheel 5. This is performed in a profiling-crushing groove 15 provided for profiling-crushing on the crushing roller 8. To this end, the grinding wheel, which, prior to profiling-crushing is provided with a cross section deviating from the profile form, is initially applied on a flank of the profiling-crushing portion 14 of the crushing groove and slightly crushed. In the second step, a slight crushing is then performed on the second flank of the profiling-crushing groove 14. Then, the grinding wheel is moved at the center of the groove of the crushing roller, and both flanks are simultaneously profiled-crushed. After profiling-crushing, the grinding wheel is reshaped-crushed, wherein the grinding wheel obtains its final profile form with a very high precision.

(16) The reshaping-crushing groove 15 also shown in FIG. 3 is on the contrary used only during the actual grinding process, when the profile of the grinding wheel 5 has to be reshaped-crushed, since its shape no longer corresponds to the nominal form and since its sharpness has to be re-sharpened.

(17) The body sound sensor 14 reacts at each contact of the profile 6 to be produced of the grinding wheel 5 against one of flanks of the crushing grooves 14, 15 and therefore monitors the engagement contact during crushing. The initially flat trued grinding wheel 5 is then crushed by the profiling-crushing groove 14 of FIG. 3 in order to form a pointed profile, which is provided for thread grinding. Through separation of the crushing portions into a profiling-crushing portion 14 and a reshaping-crushing portion 15, due to the otherwise strong wear, which is normally experienced by the crushing roller 8, its life is extended. The reshaping-crushing groove 15 provided for reshaping-crushing ensures the generation of a profile 6 on the grinding wheel 5 for a highly precise forming of grooves in workpieces.

(18) In the state shown in FIG. 4 of straight starting of crushing of trued grinding wheel 5, the latter is driven through its grinding spindle 2, whereby the not driven crushing roller 8 on the crushing spindle 16, due to engagement contact of the trued grinding wheel 5 in the profiling-crushing groove 14, the crushing roller is driven by the grinding wheel and moves with it. A separate drive for the crushing roller 8 does not occur, i.e. either the drive is deactivated, or the clutch 10 (FIG. 2) between drive and crushing roller is set to separated. FIG. 4 also shows the body sound sensor 13, which records or monitors the engagement contact of grinding wheel 5 in the profiling-crushing portion 14. The signal generated by the sensor 13 in case of contact of grinding wheel 5 with crushing roller 8, represents the monitoring, that the grinding wheel 5 has actually formed a contact with the crushing roller 8 and starts the crushing process.

(19) Since the grinding wheel 5 usually has a rounding error, the crushing roller 8 is not completely driven at first contact with the grinding wheel 5. Therefore, the speed of the crushing roller 8 may drop. If a predetermined lower speed threshold is reached, the drive motor 11 of crushing spindle 16 may be activated in a pulsed way. This activation takes place until the crushing roller 8 has again the speed of the grinding wheel 5. This means that the drive pulse is active until the crushing roller 8 has reached its nominal speed corresponding to the speed of the grinding wheel 5.

(20) FIGS. 5a), b) and c) show different phases during crushing of profile 6 of grinding wheel 5. In general, during crushing, this procedure is followed, i.e. during profiling-crushing and reshaping-crushing. FIGS. 5a) to 5c) show examples of the reshaping-crushing process. FIG. 5a) shoes how initially a first flank of profile 6 of grinding wheel 5 is applied on a first flank of the reshaping-crushing groove 15 in the crushing roller 8 and slightly crushed. For achieving contact between the grinding wheel 5 and crushing roller 8 the grinding wheel 5 may be displaced along its CNC-controlled Z and Y axes. Thus, it is ensured that during crushing optimal crushing parameters regarding relative advancement, crushing forces and further parameters are maintained or obtained. FIG. 5b) shows how the laterally displaces grinding wheel 5 is applied with its flank opposed to the first flank of profile 6 on the second flank formed on the reshaping-crushing groove 15 and is subject in that position to the run-in process and slight crushing. Similarly to FIG. 5a) for the run-in of first flank, the grinding wheel 5 is displaced for application along its CNC-controlled Z and Y axes, in order to maintain the required and admissible crushing parameters.

(21) When both flanks of the profile 6 of the grinding wheel 5 have been individually applied and slightly crushed in the reshaping-crushing groove 15, the grinding wheel is moved in the Y direction, i.e. in the transversal direction, so that the profile is centrally positioned with respect to the crushing groove 15. This is shown in FIG. 5c). The simultaneous crushing of both flanks represents the last step of crushing of profile 6 of grinding wheel 5. In the present case, this is shown in the example of the reshaping-crushing. In the same manner, and with the same sequence, this is accomplished for the profiling-crushing by means of the profiling-crushing groove 14 of crushing roller 8 also shown in FIG. 5c).

(22) FIG. 6 shows the geometric relationships between the crushing groove 15 of crushing roller 8 and profile 6 of grinding wheel 5 in relation to two different planes with respect to the depth of the crushing groove 15. The reshaping-crushing groove 15 is also shown. Due to the fact, that both the grinding spindle and the crushing spindle are provided with individual separately controlled speed controls, it is possible to exactly define the level at which the peripheral speed of the crushing roller 8 and of the grinding wheel 5 have to be equal. It is to be noted that the grinding wheel 5 and the crushing roller 8 have different diameters. A level is in this case the annular peripheral surface 17. It is only a theoretical level, indicated with reference to FIG. 6, in which this level is represented for a single radius. The corresponding radius extending up to the peripheral surface 17 inside the crushing roller 8 covers, so to speak, the annular, cylindrical peripheral surface 17. Considering the different diameter of the crushing roller 8 and of the grinding wheel 6, different speeds are obtained on the grinding wheel 5 of the crushing roller 8 so that with respect to a selected level, the speeds, i.e. the peripheral speeds are constant. The ratio of these peripheral speeds is therefore equal to 1:1. In case of in particular step-less displacement of this theoretical peripheral surface 17 during the crushing process, the quality of the profile 6 of the grinding wheel 5 may be further increased after the crushing process, whereby the result of grinding of workpiece may be improved.

LIST OF REFERENCES

(23) 1 workpiece 2 grinding spindle stock 3 workpiece spindle stock 4 tail stock 5 grinding wheel 6 profile of grinding wheel 7 crushing device 8 crushing roller 9 housing of crushing device 10 clutch of crushing device 11 drive of crushing device 12 roll bearing of crushing device 13 body sound sensor 14 profiling-crushing groove/profiling-crushing portion 15 reshaping-crushing groove/reshaping-crushing portion 16 spindle of crushing device 17 peripheral surface 18 machine control