Cluster hobbing is a hobbing process technology utilizing at least two different hobs for the hobbing operation on one workpiece. One application may be rough and finish hobbing of the same gear. In this instance, especially for finish hobbing of planetary gears and gear sun, the substrate material of the rough cut hob is PM-HSS, and the substrate material for the finish cut hob is cemented carbide or cermet. The economic benefit of this application is the optimal use of substrate material performance for higher chip thicknesses at the rough cut, and the highest level of accuracy in finish cut under reduced feed rates and chip thicknesses.
A second application may be hobbing of two different gears on one workpiece, like an input shaft of a manual transmission or from a double clutch transmission (DCT). See Figure 1.
On this application two different hobs with respect to module, number of gashes or outside diameter are used for generating two different gears. This is the preferred method when two gears must be oriented in relation to each other on the same part. Another consideration is the production volume of the part. At annual volumes of fewer than 180,000 workpieces, the cluster hobbing process is suitable for use on one hobbing machine. The disadvantage of reduced hob shifting capacity is more than offset by the savings in machine and set-up costs. At increased annual production volumes of perhaps 210,000 and higher, cluster hobbing becomes less economically viable. The two gear hobbing operations may be divided between two separate machines.
