Helical milling: An enabling technology for hard machining precision holes in AISI D2 tool steel

Inevitable catastrophic fracture that follows accelerated wear of the cutting edges severely deters hard drilling of AISI D2 tool steel. An analysis of stresses induced in the cutting edge attributes such rapid failure to the geometry inherent to drills. The present work hence investigates helical milling of this material, which employs a rotating endmill that traverses a helical trajectory to generate a hole. This innovative method is found to facilitate hole-making in this steel in its hardened state with an order of magnitude enhancement in tool life, under conditions of progressive tool wear. Helical milling is shown to be capable of machining H7 quality holes with a surface finish of 0.3μmRa such that the need for reaming is eliminated. The process represents an enabling technology with the additional advantage of being able to accomplish dry cutting, which yields significant environmental and cost benefits.