Influence of the tool profile on the wear behaviour in gear hobbing

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Abstract

Being the dominating green manufacturing technique to create external gears gear hobbing is of major industrial importance. The technology is characterized by a simultaneous superposition of kinematics and tool profile. Even though these tool profiles are standardized, in industries they are regularly being altered to fit the gear designer's demands regarding strength and contact ratio. Cutting gears with these modified and partly extreme tool profiles some geometries show critical wear behaviour. Despite existing experience-based knowledge, no systematic knowledge base is available. Therefore, this paper summarizes geometrical influences of the tool profile on the wear mechanisms. A variety of different tool profiles and gear geometries were tested within the fly cutting analogy test. The effects were also studied by means of FEM-simulation and interpenetration simulation. Finally, the wear phenomena were matched with load parameters.

Section snippets

Problem description

Modern high-performance gearboxes require gears with specially designed tooth geometry to meet the demands of their application. Beside other factors, the main demands are a sufficient flank bearing and tooth root strength and minimized noise emission during running. To adjust the tooth strength, an alteration of the pressure angle or the addition of profile and flank modifications is possible. Aiming for low noise emission, a large contact ratio between the gear and the corresponding counter

Frame of investigation

Investigations regarding the wear influence of the gearing (tool profile and workpiece geometry) were only partially performed in the past [4], [5]. The systematic identification of changing wear mechanisms and tool loads following the alteration of the tool profile is of major interest. Geometrical parameters whose wear influence was investigated and their corresponding values are displayed in Fig. 1.

Besides tool profile modifications, the helix angle of the workpiece was investigated as well.

Test results

In this main chapter of the paper, the different effects following the alteration of the standard tool profile are being discussed for the most distinctive elements of the profile.

New geometrical load parameters

Analysing the crater wear behaviour of different tool profiles and accessing coherences, it was not possible to explain all the test results with conventional load parameters such as cutting length, chip thickness, number of tooth engagements or clearance angle. On the other hand FEM-simulations and cutting test results suggest that the chip formation itself and the flow of the material have a large impact on the tool load.

Therefore it was necessary to follow a new theoretical approach to

Conclusion

Within hobbing an alteration of the tool profile or the helical angle of the gear lead to a change in tool lives and occurring wear phenomena due to changing process loads, see Table 2.

Depending on the geometrical parameter these changes were significant or insignificant.

By means of interpenetration and FEM-simulation different wear mechanisms and individual changes in the wear behaviour were accounted for.

Using the new geometrical load parameters it is possible to assess tool profiles without

Acknowledgement

The research project was supported and supervised by the German Machine Tool Builders’ Association (VDW).

References (11)

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