Cutting tools - Cutting cylindrical wheels

The hobbing tool is always characterized by two main functions:

• the cutting function to remove material; on this point, the reader is referred to the theory of cutting common to all tools in the article Materials for cutting tools. in this treatise;

• the function of producing gear teeth either by direct reproduction or by generation. In the latter case, the laws of cutting motion are intimately linked to the often complex kinematic processes. This is the subject of this article. However, the reader is referred to the article Gear cutting and grinding: processes. devoted in particular to machines.

It's on the basis of a set of specifications, or at least a definition plan, that the gearmaker will learn about the product to be produced. The overall cost, the quality level, the quantity to be produced per unit of time, the reliability of the materials used, etc., will complete this data. As we will see in the following paragraphs, the chosen solution will be preceded by research to optimize the product itself and the means used to produce it.

Cutting costs are generally high. Nevertheless, they have been significantly reduced thanks to productivity gains achieved over the last few decades. To give an order of magnitude, for mass production, the share of cutting tools used for trimming represents around a quarter of all cutting tool expenditure (including sharpening) allocated to the powertrain (engine and gearbox). On the same basis, for a hobbing operation, the breakdown of the cost per operation is roughly as follows:

• from 35 to 50%, machine depreciation ;

• 20 to 25%, cutting tool costs with sharpening ;

• 15 to 40%, labor costs ;

• 8 to 10%, miscellaneous costs including utilities, energy, rent, maintenance, etc.

This text only deals with the cutting function of hobbing tools. The gearing characteristics discussed in this text are only relevant to this function. Readers interested in the theoretical aspects of gears and the study of processes are strongly advised to refer to the articles Gears: practical elements of definition, design and calculation [B 636] and Gear cutting and grinding: processes. in the present treatise, as well as to the general works