GB2231520A

GB2231520A - Finish machining of cylindrical gears

Info

Publication number: GB2231520A
Application number: GB9010962A
Authority: GB
Inventors: Ingo Faulstich
Original assignee: Hermann Pfauter GmbH and Co
Current assignee: Hermann Pfauter GmbH and Co
Priority date: 1989-05-17
Filing date: 1990-05-16
Publication date: 1990-11-21
Anticipated expiration: 2010-05-16
Also published as: FR2647041B1; DD297926A5; IT1239982B; CH681866A5; IT9020291A0; GB9010962D0; DE3915976C2; DE3915976A1; GB2231520B; JPH0398714A; FR2647041A1; IT9020291A1

Description

2 2:3 3- -15 2 0 Process for the finish machining of the flanks (tooth

surfaces) of cylinder gears by hob peeling alid a-device for inplem.ting such a process 5. The invention relates to a process for the finish machining of the flanks of cylinder gears by means of hob peeling according to the preamble of claim 1 and a device for implementing such a process according to the preamble of claim 2.

10. Hob peeling is a continuous process for the production of cylinder gears by metal cutting. The tool resembles a gear shaper using the generating process; its axis of rotation, however, is inclined relative to the axis of the work piece. In the course of machining. the tool and the work piece perform a primary rotation. The speeds here are in inverse ratio 15. to the number of teeth on the two elements. Superimposed on the primary rotation, the tool perform a screw motion relative to the work piece. This screw motion consists of a displacement of the tool in the direction of the work piece axis and an additional rotation of the work piece proportional to this displacement. The additional rotation is 20. calculated in such way that, in the case of the machining of a work piece without a tooth trace modification, the additional rotation amounts to 2W, if the axial carriage path is the same as the lead of the gear toothing to be produced. The following therefore holds:

25.

AY Az 2 5 H 30. or 4 z H. AT P. A? 2 Ti 2- and AY 1. LZ p 5. where A z by H p axial carriage displacement additional rotation lead of the work piece reduced lead 10. In practice, it is frequently desirable to form the flanks of cylindrical gear toothing not exactly as involuted helicoids, but rather to modify the profile and tooth trace. For example, the gear teeth are intended to be cut with crowning in depth and width. The description of these modifications is usually done with the aid of profile or tooth

15. trace diagrams.

Flank modifications can be produced by hob peeling. The following holds in a first approximation: profile modifications are produced by a modification of the tool profile and tooth modifications by a 20. modification of the machine motion.

Upon closer inspection, however, it can be seen that the modification of the machine motion also affects the profile of the work piece.

25. This influence leads, for example, to the creation of distorted flanks with the hob peeling of crowned gears. This distortion means that in different transverse sections there are profiles with different profile angle variations and that on different cylinders there are tooth traces with different tooth trace angle variations.

30.

Fig.1 should assist in explaining how this distortion comes about.

Fig. 1 shows the right flank of a left-handed helical cylinder gear.

Where: b face width coordinate in direction of work piece, related to the centre of the face width 5.

FP tooth trace variation (or modification) I front face of gear 10. 11 rear face of gear The term "front face" is used to describe the given flank as the right or left flank. The tooth trace deviation is measured on the graduated cylinder, in Fig. 1 on the line F1P,', and the profile variation in the 15. transverse section in the centre of the face width. i.e. on line PiP, '. Variations of the flank from the relevant unmodified involuted helicoid should be represented at rightangles to the plane of projection.

In order to facilitate an understanding, let it be assumed in the first 20. instance that all traces on a flank take the same course and all points on a trace are at the same distance from the unmodified involuted helicoid, i.e. they lie above or below the plane of projection by the same amount. When the flank (tooth surface) geometry is described with the aid of a conputer, the sinplifications set out above are of course 25. not necessary.

Let a course of the tooth trace wvariationw be prescribed in accordance with the representation on the right-hand side of Fig. 1. On the graduated cylinder, the high point of the flank lies in the centre of 30. the tooth face; in the root area of the gear teeth it lies at S,, in the tip area at S,'. Virtually the same course of the tooth trace variation exists on each cylinder between the root cylinder and the tip cylinder. only the high point is displaced in the Z direction in accordance with the z-cornponent of trace SiSi'. Since the length of the FA-diagram is 35. always equal to the tooth width, it will always be the case that a somewhat different region of the of the prescribed course will be measured on different graduated cylinders. Relative to the course on the prescribed graduated cylinder, therefore, the curve needs to be lengthened on side I to describe the Fp-course in the tip area of the 5. gear teeth and on side II to describe the course in the root area of the gear teeth.

The profile variation in a certain transverse section is the distance of the given point under consideration from the unmodified involuted 10. helical surface. According to the statements made above, the profile variation in the centre of the tooth width at the points P, (root circle) and P,' (tip circle). for example, is obtained as the distance of the traces running through these points from the unmodified involuted helical surface. Accordingly, P, has the same distance as point H6 from

15. the unmodified involuted helical surface, namely the distance H' H" 6 6; correspondingly, P,' has the distance H2 H2. If this idea is carried through to further points between P, and P,', the following can be seen: the course of the profile variation F&C in the centre of the tooth width is the same as the course of the tooth trace variation FA between H6' 20. through H,' to H2'.

25.

Measured magnitude or cylinder I Gear centre II Measurement plane Measurement between points P2 - P2' P1 - P1, P3 - P3' Course of deviation H3' - H4' - H5' H6' - H,' - H2' H9' - H8' - H7' F&C Root cylinder F3 - F3' H3' - H9, 30. F prescr. grad. cyl. F, - F,' H4' - H8' tip cylinder F2 F2' HS' - H7' If the results are plotted graphically, the respresentation according to Fig. 2 is obtained. In this representation, the variation present at the given point is designated by q, i.e.

5.

qi Ill' 11] = 0 q2 HO Hw 2 2 1 v cb H 3 H 3 10.

Furthermore, designates the tooth trace variations on the root cylinder 15. FFa designates the tooth trace variations on the tip cylinder Apart from the points on the trace S, S,', all the points of the modified flank stand back compared with an unmodified involuted helical 20. surface; the magnitudes q2 qq therefore have negative signs.

If the tooth trace angle variation is designated by fHAf on the root cylinder and by fila on the tip cylinder,, the following are obtained 25. fHAf qq - q3 fH&Ca q7 - qS 30. The set of the tooth traces is 14 fHA fHpa - fHpf From the profile angle variations fHcI qS - % 5. in plane I and FHKII q7 - q9 -in plane II, the set of the profile is obtained at 10.

A fHeC fHWII - fHMI It should also be noted that in the exanple considered here, A fHAand 15. AfIt: have positive signs. This can easily be traced from the magnitudes represented in Figs. 1 and 2.

The above statements concern the right flanks of a left-handed helical tooth systeiri. The considerations can easily be transferred to the other

20. cases, and thus to the left flanks of a left-handed helical tooth system and to both flanks of a right-handed helical tooth system or spur toothing. To do this, it is only necessary to have the course of the tool trace on the given work piece flank.

25. The trace can be calculated in the context of the tool dimensioning or in the simulation of the manufacturing process. In the other cases too, i.e. especially with spur toothing, it runs obliquely over the work piece flank. Fig. 3 shows the principal course of the traces for the above-mentioned cases.

30.

Spur toothing can be machined by hob peeling only with a helically toothed tool. The sign of the "lead" of the traces depends here upon the sign of the tooth helix angle. There are, therefore, the two sketched courses in the case of straight-toothed tools.

Whereas, in the case of the right flank of the left-handed helical tooth system, the points of the trace in the tip area of the work piece teeth, compared with the root area, lie closer to the plane II, these points on the left flank of the left-handed helical tooth system lie closer to 5. plane I. Using the method of calculation explained above, it is found that the set of the tooth traces and the set of the profile of the left flank of the left-handed helical tooth system have a negative sign. It has already been mentioned that the corresponding magnitudes of the right flanks have a positive sign. in the other cases too, the following 10. applies: the set of profile and tooth trace possess on the right flank the opposite sign to the set of these magnitudes on the left flank.

The distortion of the flanks of cylinder gears finished with hob peeling, describable by the set of profile and tooth traces, is often 15. undesirable. This gives rise to the task of further developing the process of the generic type and the device of the generic type in such a way that the distortion of the flanks is avoided or reduced to a negligibly small value.

20. According to the invention, this task is solved using the process of the generic type with the characteristic features of claim 1, and the device of the generic type with the characteristic features of claim 2.

According to the invention, it is proposed to dispense with any 25. eccentricity of the tool (e = 0) and to change the swivel angleMuring the displacement of the axial carriage, i.e. to change it dynamically. A profile angle variation arises here in the centre of the tooth width on the two work piece flanks. These must be taken into account when the tool is designed. At the same time, a small degree of longitudinal 30. crowning occurs with the dynamic change in the swivel angle T_. If this causes a tolerance to be exceeded on the tool, it must be taken into account in establishing the machine motion for producing the desired crowning (through a [zl and/or p [z]).

With the solution proposed here, there is the additional advantage that in many cases a purely cylindrical tool can be used, i.e. a tool without a design clearance angle.

5. It is also possible to cnsate for a distortion of the flanks by changing the eccentricity of the tool during the displacement of the axial carriage, i.e. by a dynamic change in the eccentricity e. Relatively large changes in eccentricity are required for this. This leads to different root circles arising on the work piece in different 10. transverse sections. This should be counteracted by an adjustment of the axial distance during the axial carriage displacemenit.

At the same time, a large tooth trace variation arises with the dynamic change in the eccentricity e. This should be conpensated by a dynamic 15. adjustment of the reduced lead p.

The tool should be designed in such a way that no profile angle variation occurs in the centre of the tooth width.

20. The simulation of the production process set out above for the dynamic adaptation of the adjustment data should be repeated iteratively until the work piece tolerances are met.

The hob peeling machine intended for the execution of the process 25. described is represented in Figs. 4 and 5. It has a base 1 upon which an axial carriage 2 is displaceable in the Z direction. It carries a radial carriage 3 which is displaceable relative to the axial carriage 2 in the X direction. on the radial carriage 3 there is a peeling head 4 mounted pivoting about an axis 5, said peeling head being displaceable with the 30. radial carriage in the X direction. A work piece spindle unit 6 is attached rigidly to the base 1. The peeling head 4 and and the work piece spindle unit 6 each have a spindle 7 and 8 to receive respectively a tool 9 and a work piece 10.

11 During the machining of the work piece 10, the tool 9 and the work piece 10 perform a primary rotation in the known manner. In this respectr they rotate in inverse ratio to their given number of teeth. in the course of machining, a narrow band of the final work piece toothing is produced 5. during a work piece rotation. A screw motion is required in order to form the teeth on the work piece 10 over the whole width. This is brought about by the fact that the axial carriage 2 is displaced in the Z direction and at the same tire the work piece 10 perform an additional rotation. The axes of tool 9 and work piece 10 are swivelled 10. at an angle,to one another during the machining in the known manner.

Claims

Claims

1. A process for the finish machining of the flanks (tooth surfaces) of spur or helical, internally or externally toothed cylindrical gears by means of hob peeling, whereby the right and left flanks are produced in separate machining operations and whereby. in order to produce tooth trace modifications such as crowning and/or flank end relief, the device, depending on the axial carriage displacement, executes a change in the centre difference and/or a change in the additional rotation of the work piece relative to the tool, characterised in that, during the axial carriage displacement, one or simultaneously several of the 10. adjustment magnitudes - centre difference (a), eccentricity (e) of the tool (9), pivoting angle (ú) and reduced lead (p) - used to describe the additional rotation is changed automatically in such a way that the distortion of the work piece flank arising with the creation of the tooth trace modification is compensated for and a tool (9) is used for 15. the machining, the cutting geometry of said tool on the right and left flanks being adapted to the adjustment magnitudes effective during the removal of the shaving by the given cutting edge.

2. A device for the implementation of the process according to claim 1, 20. with a base on which a spindle for a tool having teeth and a work piece spindle are arranged, characterised in that the axis of rotation of the tool (9) is adjustable relative to the work piece axis during machining.

3. A device according to claim 2, characterised in that the eccentricity 25. (e) of tool (9) is adjustable during machining.

4. A process substantially as hereinbefore described with reference to the acccnying drawings.

30. 5. A device substantially as hereinbefore described with reference to and as illustrated in Figs. 4 and 5.

Published1990 at The Paten Of:lce.StatEHwise.66 71 High Holborn. London WC1R4TP Further copies maybe obtained from The Patent Office. Sales Branch. St Mary Cray, Orpington, Kent BR5 3RE. Printed by Multiplex tecljuques ltd, St Mary Cray, Kent, Con. 1187 1