Bit for drilling cast iron

Reference Number: N 03-03

Inventors: Johnson, Jonathon S.

Owner: NISTAC

USPTO Link: 5065647

Invention Summary

The problems associated with the prior art have been overcome by constructing a diametrical blade implant of a two-phase material: a main phase of cemented carbide and insert phases of cubic boron nitride placed at high stress corners of such blade, the inserts being diffusion bonded to the carbide and being limited strictly to the radial cutting zone of the bit without penetrating the centering zone.

In particular, the method aspect of this invention comprises adapting a fluted drill bit for more effective drilling of cast iron workpieces, comprising the steps of: (a) providing, across the pointed end of the fluted drill bit, a diametrically extending slot; (b) forming a blade effective to snugly fit within the contours of said slot, said blade being comprised of cemented carbide powder within which is molecularly bonded a pair of inserts constituted of cubic boron nitride, said inserts being located at opposite outside corners of said blade and extending radially inwardly no greater than the cutting zone of said pointed end of the fluted drill bit; and (c) after seating said blade within said slot, fixedly securing the carbide surfaces of said blade to the walls of said slot. The interface between the steel of said bit and the cubic boron nitride of said blade is desirably limited to less than 2% of the total secured (brazed) area of the blade.

Preferably, the drill bit is comprised of high speed tool steel, such as ASTM M-2, and the blade is a dual phase material having a primary matrix phase of cemented carbide, such as ASTM C-2, and an insert phase of cubic boron nitride powder, the matrix and insert phases being commonly hot pressed at a temperature of 2500.degree. C. and a pressure of about one million psi to achieve diffusion bonding.

Advantageously, the pointed end of the tool bit has a conical end face with frontal cutting edges and lateral cutting edges along the tool's shank separated by flutes forming helical cutting edges, the frontal cutting edges and lateral cutting edges intersecting at opposite sides of said tool bit to form corners at which the cubic boron nitride inserts are located.