MACHINING ZIRCONIUM AND HAFNIUM
Three basic machining parameters should be used for all operations involving zirconium and hafnium alloys:
A flood coolant system using a water soluble oil lubricant.
Zirconium and hafnium exhibit a marked tendency to gall and work harden. Therefore, higher-than-normal clearance angles
on tools are needed to penetrate the previously work-hardened surface and cut a clean, coarse chip. Good results can be obtained with
both cemented-carbide and high speed tools. However, the cemented carbide usually provides a better finish and higher productivity.
Zirconium and hafnium alloys machine to an excellent finish, and the operation requires relatively light horsepower compared with
that for alloy steel. Fine chips should not be allowed to accumulate on or near the machining equipment because they can be easily
ignited. The chips should be continually removed and stored, preferably under water in remote and isolated areas that are far removed
from the production site.
Both vertical face and horizontal slab milling give good results. Wherever possible, zirconium and hafnium alloys should be
climb milled to penetrate the work at the maximum approach angle and depth of cut while emerging through the work-hardened area.
The faces and edges of milling cutters should be kept very sharp. A set of herringbone cutters will permit positive axial rake angles to
be effective at both sides of a recess. Optimum surface finish and tool life are obtained when the tool is ground with a positive 12o to
15o radial rake along with cutting corner. A high spiral flute should also be used. The work should be flooded or sprayed with a
coolant to completely wash away all chips from the tool. The penetration can range from 0.005 to 0.010 inch per tooth at 150 to 250
SFPM. The work absorbs about 10 percent of the cutting energy with sharp cutters. Zirconium and hafnium alloys require only about
75 percent of the horsepower required for SAE 1020 CR steel.