Research on Behavior of Crater Wear of Hob in Dry Hobbing

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It is well known that cutting oils are used in hobbing with high-speed steel (HSS) hob. Recently, however, bobbing without cutting oils (dry hobbing) with HSS hob has become a center of attraction, because of prevention of environmental pollution and safety for the operator, as well as reduction of costs for cutting oil and its waste disposal. The behavior of crater wear on the face using different kinds of HSS hob materials coated with TIN and (Al, Ti)N in dry hobbing was mainly investigated in this research. Experiments were carried out using a fly tool on the milling machine. A summary of the research results is shown below : (1) The crater wear obtained with in dry cutting is smaller than that with in wet cutting (using a fluid containing sulfurized fatty oil), which was suggested that the deposited metal may affected on the crater wear. (2)From cutting speeds of 47 m/min to 86 m/min, the crater wear of corresponding to SKH 55 and M 34 hob materials coated with (Al, Ti)N increases with an increase in cutting speed. At a cutting speed of 117 m/min, it decreased remarkably. (3)With all of the hob materials tested, the crater wear decreases with increasing in number of threads and hob feed, that is, the condition of 3-thread hob and hob feed of 3.0 mm/rev is useful for decreasing it. (4)When using the fully coated tools, it was suggested that the crater wear mechanism is due to the plastic deformation of the coating film, which causes its delamination, after appearing the substrate, the crater wear increases by the abrasive action with the cutting chips. (5)Among the hob materials tested, the corresponding to SKH55 + (Al, Ti)N coated tool is suitable for dry hobbing.