When compared with shaving or grinding, carbide finish hobbing offers reduced cycle times and reduced manufacturing costs for many applications. Finish hobbing is possible for green and hard manufacturing. Improvements made in tungsten carbide hob technology over the past ten years or so have provided reduced cutting edge roundness and higher red hardness in comparison to PM-HSS hobs. However, the initial cost of the solid carbide hob as well as the subsequent regrinding costs are very high, thus limiting its application to special cases involving small pitch gears like:
· Planetary Pinions
· Sun Gears
· Reverse Gear
· Synchronizing Gear
· Steering Pinions
· Timing Gears
· Splines
Due to profile quality requirements, the clearance angle wear on the hob can be limited to less than 0.1 mm. Most applications require a two-cut process, in which the first cut utilizes conventional speeds and feeds, but the second cut requires increased cutting speeds in the range of 450 to 1000 surface meters per minute, at an infeed of less than 0.15 mm.
For high surface finish quality, the feed rate is limited to less than 1 mm per revolution and requires the use of coolant lubrication oil. This process ensures surface roughness of less than Rz = 6.4 µm. Gear quality DIN class 6 may be achieved.
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