CH710569A2 - A method for machining a workpiece with a multiple speed grinding worm. - Google Patents

Abstract

The invention relates to a method for machining a workpiece, preferably of cylindrical gears with involute toothing (20) with a multi-start grinding worm, wherein in the case that the number of workpiece teeth and the tool gear number is integer, the workpiece is ground in a first step with the multi-speed grinding worm. In a second step, the pitch (p) of the workpiece is measured and, in a third step, the pitch result is assigned to the respective flight. In a further step, the dressing tool is delivered according to the division measurement result in order to re-finish the grinding tool in a fifth step. The steps are carried out until the graduation result meets the tolerance requirements.

Description

The invention relates to a method for machining a workpiece, preferably of cylindrical gears with involute toothing, with a multi-speed grinding worm and a dressing method for dressing the grinding worm and the associated method for correcting the dresser depending on measured pitch errors on the workpiece.

When grinding gears with a multi-speed grinding worm in the rolling process, the geometry of the grinding worm is essentially determined by the teeth to be ground. The grinding performance is significantly influenced by the diameter of the grinding worm and its number of turns. Thanks to high-precision and stiff NC drives, multi-turn grinding worms can be used effectively and with narrower tooth numbers within narrow tolerances. However, the mechanical load of the tool and the dynamics of the meshing increase, so that ultimately increasing the number of gears brings a performance increase, but partly at the expense of workpiece quality and tool life is.

Another point to consider when selecting the grinding worm relates to the determination of the number of threads in terms of divisibility workpiece tooth number to tool speed. If possible, an up-to-date ratio should be avoided here, as otherwise the gear pitch error of the grinding worm will influence the pitch accuracy of the workpiece when the number of teeth increases.

On the other hand, the choice of a non-rising number of teeth ratio is also not entirely unproblematic, since pitch error in the tool represent as feed marks in the flank line. Although these markings are only a few micrometers in size during grinding, even with very narrow tolerance specifications, they can cause the teeth to no longer be ground to tolerance.

Due to the ever increasing demands on the quality of the workpieces in the production of gears an ever greater effort must be driven to achieve the required quality. In addition, if possible, the number of tool types for a large number of workpieces to be produced should be reduced. This would be desirable for the user, a method in which no longer necessarily on an optimized ratio of the number of teeth must be paid to each workpiece without the required workpiece quality must suffer.

In DE 10 2012 005 228 A, a method for grinding a gear by means of a multi-speed machining tool is described, in which an increased quality of the machining is possible, especially at an unfavorable ratio ratio. In order to achieve a high pitch accuracy, the workpieces are ground in a two-stage process. First, the workpiece is ground in a first part grinding process with a multi-start tool, wherein the machining tool is delivered to a first gap to be machined of the workpiece. In a second partial grinding process, the same workpiece is ground again, this time the tool being delivered to a second gap other than the first gap.

Overall, so at least two Teilschleifprozesse necessary to complete the workpiece. A particularly positive grinding result is achieved in particular when the second partial grinding process takes place only with little or even no delivery. A disadvantage of this method is that thereby the grinding process is extended by a further process step. This is of particular importance in mass production.

DE 4 339 041 A describes a dressing tool for zweigängige cylindrical grinding worms. This dressing tool is constructed in several parts and can be adjusted by adjusting individual dressing wheels or dressing wheel halves by the distance between the dressing surfaces can be adjusted to each other via screws and ground spacers. The disadvantage of this is the complex assembly / disassembly and the precision of the setting on the machine.

It is required in practice to make corrections to the order of less than 1/1000 mm. However, this is not or only very complicated to implement with the solution described above.

The object of the present invention is to provide a grinding process with multi-stage grinding tools and the associated dressing tool, with the required surface quality on the flanks of a processed teeth can be produced in a simple manner.

According to the invention this object is achieved by a grinding and dressing method with the features of claim 1 or claim 3. Advantageous embodiments and further developments of the invention are described in the subclaims.

The inventive method according to claim 1 has the following steps: Machining the workpiece with the multi-stroke machining tool. Measurement of pitch individual deviation fp separately for the right and left flanks of the toothing. Correction of the movement of the dressing tool relative to the grinding worm in the axial direction of the tool as a function of the determined Teilungseinzelabweichung per tool gear and possibly in dependence on the tool width position. Alternatively, with multi-stage dressing tools, the dressing tool can also be readjusted or reworked according to the measurement result. With the corrected dressing method or the corrected dressing tool, the grinding worm is then dressed again and then another workpiece is ground. Once again, the pitch individual deviation fp is measured separately for the right and left flanks and, if necessary, the dresser position is corrected in relation to the grinding tool or the dresser. The steps are repeated until the desired pitch deviations fp correspond to the tolerance specifications for the workpieces. Subsequently, series production is started with the original workpieces.

According to a preferred embodiment, a toothed wheels, in which there is a non-integer ratio between the number of workpiece teeth and the number of tool speeds, made as an upstream step, a replacement toothing with integer ratio. If the original toothing has, for example, 17 teeth, a replacement toothing with 18 teeth is produced, which can then be machined with a 6-screw screw, for example. In the following, the replacement toothing will be processed instead of the original workpiece.

According to the invention it no longer depends on whether an integer number of teeth ratio is due to the optimized dresser or dressing process.

According to the independent claim 3, there is an alternative method according to the invention with non-integer ratio between the original number of workpiece teeth and the number of turns of the tool to minimize the pitch error on the workpiece. Here, an additional second cut with low delivery (for example, 0.005 mm) and very high axial feed is performed. As a result, each gear of the grinding worm cuts a groove in the tooth flank. In between, there must always be an area where the previously perfectly ground flanks remain, which serves as the reference value for determining the pitch deviation for the individual gears. In the deeper grooves created by the individual gears, it is now possible to see whether one or more tool threads are particularly prominent and can then correct this gear / these gears accordingly. Following this second cut, step 4 continues with the above procedure.

The procedures initially sound quite expensive. But taking into account that this usually has to be done only once for a new multi-speed dressing tool or when starting production for a new series of transmissions, the effort put into perspective, if you get significantly better workpieces in mass production. If necessary, random checks can also be carried out during the series. If the result of the random sample then deviates from the specifications, the corrections based on the findings from the initial installation or Erstjustage be carried out with little effort.

The correction of the dresser is made depending on whether it is a dresser for a single flight or a multi-speed dresser.

Serves the dresser to dress only one gear, an offset value can be determined by the controller when approaching the position for the next gear. This value may also vary depending on the worm position and on the particular gear.

However, if it is a multi-start dresser, the dressing tool can be corrected either by an additional dressing wheel, which is clamped in the machine. Alternatively or if the correction amounts are too large, the dressing tool must be reworked outside the machine.

An expedient embodiment of the inventive concept provides that the gear cutting machine for the application of the method has a suitable control function that supports the user accordingly. This can be done, for example, by automatically determining and outputting corrections for the dressing tool from the graduation measurement made by the machine control. If the graduation measurement and correction of the dresser takes place within the machine, the modifications can be performed user-guided by the controller.

Therefore, the pitch measurement is possible also within the gear cutting machine, since then the assignment of the machined workpiece gap to the grinding worm gear is relatively easy as long as the workpiece is still clamped and thus the Wälzkopplung is not canceled. Alternatively, the gear cutting machine can also stop the workpiece and the tool in a defined position, so that the machine operator can mark the workpiece accordingly and thus the assignment of the pitch measurement to the tool path is also given for the case that the workpiece is measured on an external measuring machine. Again, the machine control can provide appropriate support.

Another strategy to assign the measurement results on the workpiece to the pitch error of the grinding worm or the dresser is to initially selectively modify a gear by a larger amount. This then occurs clearly in the grinding result, especially when the method is used in which the workpiece was ground again in the second cut with increased feed. Thus, the other courses are then assigned and can be corrected after the measuring bit on the gear together with the more modified gear.

With the inventive method, a high pitch accuracy is achieved in order to improve the smoothness of the gear pair thus processed and thus to produce low-noise transmission.

Further features, advantages and features of the invention are explained in more detail below with reference to several embodiments illustrated in the drawings. Show it: <Tb> FIG. 1 <SEP> a grinding worm with a dresser in the form of a profile roll, <Tb> FIG. 2 <SEP> a grinding worm with a solid profile dresser, <Tb> FIG. 3 <SEP> an end cut through a workpiece profile, <Tb> FIG. 4 <SEP> a measurement log of a pitch individual deviation fp for a flank ground with a multi-start tool with pitch error, wherein the ratio between the number of workpiece teeth and the number of gears of the tool does not rise, <Tb> FIG. 5 <SEP> a measurement log of a pitch individual deviation fp for a flank, Grinded with a multi-start tool with pitch error, where the ratio between the number of workpieces and the number of turns of the tool is an integer, <Tb> FIG. 6 <SEP> a measurement log of a pitch single deviation fp for a slope grinded with a multi-speed tool with pitch error, wherein the ratio between the number of workpiece teeth and number of threads of the tool is an integer and the dresser has been corrected by the inventive method and <Tb> FIG. FIG. 7 shows a partial view of a toothing which has been processed by the method according to the invention in order to determine the pitch error on the dresser and the associated correction amount.

Fig. 1 shows a known profile roller set 13 for dressing a grinding worm 10 (shown here a 2-speed grinding worm). The dresser consists of a Flankenabrichter 12 (Doppelkegelabrichter) and a Kopfabrichtrolle 11, with each of either the left and right flanks of a flight and the associated Kopvorundungsradius is dressed. In a second pass, the opposite flank and the other head radius are dressed.

This is done with multi-speed tools initially for a worm gear over the entire screw width. Subsequently, the Abrichtwerkszeug is offset by a gear, brought back into engagement to also trim the second flight. The number of dressing passes is proportional to the number of passes of the tool. The advantage of this dresser concept lies in its flexibility. By pivoting the dresser about an axis transverse to the tool axis, corrections, for example, pressure angle corrections on the grinding tool can be generated. This dresser concept is also available as a two-flute dressers where the right and left flanks of a flight are simultaneously trued and thus the dressing cycles can be carried out faster. In this embodiment, part of the Kopfabrichtrolle is also omitted. In this case, the head of the grinding worm is modified via fixed dresser.

A further reduction of the time for the dressing cycle can be achieved in a known manner with the solid profile roller 14 shown in FIG. 2 for dressing a grinding worm 10. Solid profile rollers are often used for dressing multi-speed grinding worms for generating grinding of small-modulus gears. The profile of the dressing roller corresponds exactly to the grinding worm profile. Thus, with a few dressing passes, depending on the width of the dresser in relation to the worm width, a grinding worm can be completely finished.

The time for dressing a grinding worm is indeed significantly reduced. However, this is at the expense of the dressing flexibility, since only the dresser profile can be transferred to the grinding worm exactly. If changes to the grinding worm profile are required, the dresser must be reworked. However, this is a proven procedure for mass production of gear wheels.

With reference to FIG. 3, the problem underlying the invention can be explained. Fig. 3 shows schematically an end section of a toothing 20. The illustrated pitch ptim frontal section is defined as the length of the pitch circle arc between two consecutive right or left flanks. Measured in practice, the distances of rectified flanks in the middle of the profile. The deviations are to be converted linearly to the pitch circle. From the pitch divisions pt, certain characteristics such as e.g. the division-individual deviation fpbrechnchnet. This designates the difference between the actual dimension and the nominal dimension of a single end division of the right or left flanks. On a gear with z teeth there are z pitch individual deviations of the right and left flanks. The deviation fp results as the differences between the individual measured values and the average of all z measured values. Between tooth 1 and 2 here too large distance is recorded. This means that the left flank of the tooth 2 is farther from the left flank of tooth 1 than the mean value. The tooth gap 2 is thus too large. Between the teeth 3 and 4, an example is shown with too little distance. The smaller the fluctuation of these distance values fails, the smoother the gearing can run with its mating wheel.

The following FIGS. 4 and 5 show evaluation diagrams 30, 31 for division individual deviations 33 for a flank at different teeth, which were processed with different tools. This shows how a multi-start tool with pitch error between the tool passes, with different ratios between the number of turns of the tool and the number of teeth of the workpiece zW in the pitch individual deviation represents. Shown is the pitch individual deviation with respect to the mean value 32 of the tooth pitches on the workpiece.

Fig. 4 shows a measurement result 30 of a pitch-individual deviation for a 6-speed tool with which a workpiece with 17 teeth was made. In this case, the number of teeth ratio does not occur and a pitch error on the tool has only a minor effect on the pitch measurement, since a constant change of the tool paths between the individual workpiece teeth takes place during machining.

If this is compared to FIG. 5, in which a workpiece with 18 teeth was machined with the identical tool, the gears can be identified on the basis of the pitch errors in the measurement log 31. Particularly outstanding is the error in the tool aisle has edited the fourth tooth gap. Here, the pitch individual deviation is too small compared to the mean value of all measured value. The next Teilungseinzelabweichung over the tooth gap 5 is too large. This suggests that here the distance between the tool threads which have worked the tooth gap 3 and 4 is too small. By assigning the recording, which workpiece tooth was ground with which tool path, and the value measured here, the tool can be corrected during dressing.

Depending on the type of dressing tool used, either the control must offset the position of the dressing wheel when dressing this screw to the measured value as an offset in the axial direction of the tool. Alternatively, with a multi-speed dressing tool, this gear must be corrected.

This can be done either on the gear cutting machine by using a second machining tool, the dresser is reworked or by the tool on an external machine is touched up.

Likewise, it may be necessary to correct both the dresser position and the dresser, since it is possible, for example, with a 3-speed dresser in addition to a 3-speed grinding worm, also one with 6, 9 or even more gears train. In this case, a combination of corrections may be required.

Fig. 6 shows the measurement result 34 for a workpiece according to FIG. 5, which was processed with a grinding tool, which was previously processed with a nachkorrigierten dresser. In this case, only the worm gear has been corrected, which works the fourth tooth gap, to make the effect of the invention clear. If the achieved pitch accuracy is not sufficient, the inventive method can also be performed for the other screw flights.

The method described here for a grinding worm can of course be transferred to other, roller-coupled working, machining / hard finishing processes in which a specific workpiece tooth can be assigned exactly to a defined tool tooth / gear during machining and in which it is a certain accuracy arrives. This method would be conceivable, for example, during skiving, skiving, but also during gear honing or gear cutting.

Fig. 7 shows a schematic partial view 40 on a toothing the one edge (left flank = LF) was processed with the inventive method with a 3-speed tool to determine the pitch error on the dresser and the associated amount of correction. For this purpose, the workpiece was first processed in a first step with the processing parameters optimized for this toothing. In a second process step, a further grinding passage with a low infeed but significantly increased feed of the tool in the axial direction of the toothing was ground. By doing so, the individual gears 41, 42, 43 of the grinding tool and their deviation can be identified and determined. If additionally a gear 43 was purposefully modified in preparation for the multi-start grinding worm, then this can be clearly identified on the grinding result. Between the markings on the flank of the ground toothing surfaces 44, which were due to the high axial feed of the tool, were not processed in this grinding cycle, stopped. The depth of the feed marks (shown here in excess) relative to the non-machined surfaces 44 and the difference between the individual gears together with the knowledge of what value the tool has been radially delivered, the information by what amount and in which direction the gears Grinding worm must be corrected. From this the necessary corrections can be calculated on the dresser.

Claims (10)

1. A method for machining a workpiece with a multi-start grinding worm, wherein the workpiece in the event that an integer ratio between the number of teeth of the workpiece and the number of turns of the tool is ground in a first step with the multi-stage grinding worm, in a second Step is measured this workpiece in terms of its division, in a third step, the Teilungsmessergebnis associated with the respective screw, in a fourth step, the associated dressing tool is the Teilungsmessergebnis supplied and / or modified and in which the grinding tool is dressed in a fifth step again, wherein the correction cycle is carried out iteratively until the division measurement result meets the tolerance requirements. 2. The method according to claim 1, characterized in that at a non-integer ratio between the number of teeth of the workpiece and the number of turns of the tool in a preceding step, a replacement workpiece with a modified number of teeth is made, wherein the number of teeth is chosen so that the teeth ratio now integer is. 3. A method for machining a workpiece with a multi-start grinding worm, characterized in that preferably at a non-integer ratio between the number of teeth of the workpiece and the number of turns of the tool after the first processing step with this tool, a further processing step is performed with the tool at the low feed and very large axial feed the workpiece is machined, wherein the axial feed is chosen so large that each passage of the grinding worm cuts a groove in the tooth flank, wherein between the grooves an area remains, which was generated by the first processing step, whereby it is possible to check on the basis of the groove depth in the tooth flank in relation to the flank surface after the first cut, whether the individual courses of the grinding worm are cut equally deep, and whereby it is possible, from a possibly resulting difference of the e to calculate a correction value for the correction of the dresser. 4. The method according to any one of claims 1-3, characterized in that the single-step dressing tool receives an offset position in the direction of the tool axis, which is determined by the machine control from the Teilungsmessgebnis when dressing another, different from the previously dressed screw flight worm gear, this can be different over the tool width position. 5. The method according to any one of claims 1-4, characterized in that the dressing tool, in particular a multi-stage dressing tool, is corrected on the gear cutting machine by post-processing its surface according to the Teilungsmessgebnissen. 6. The method according to any one of claims 1-3, characterized in that the dressing tool, in particular a multi-stage dressing tool is corrected on a separate machine tool by post-processing its surface according to the Teilungsmessgebnissen. 7. The method according to any one of the preceding claims, characterized in that instead of a dressing tool directly a machining tool is corrected by post-processing its surface according to the Teilungsmessgebnissen. 8. Control program for the automated implementation of the method according to one of the preceding claims, characterized in that the control program performs the assignment of the division measurement results on the workpiece to the grinding worm gear. 9. Control program for automated implementation of the method according to one of the preceding claims, characterized in that the control program specifies correction values for pitch correction on the dresser. 10. gear cutting machine for carrying out the method according to one of claims 1 to 7 with a device for pitch measurement of machined workpieces, a hard finishing tool and a dressing tool.