Titanium alloy is a highly desirable material in aerospace and biomedical industries for its light weight and relative strength. However, machining titanium alloys warrant a specialized approach to conserve tool integrity and expedite the process while maintaining quality results. Approach the machining of titanium alloys with the optimal equipment and techniques.
The physical properties of titanium driving its desirability are the reason for its reputation as a challenge to mill. Titanium conducts heat poorly, therefore look for opportunities to mitigate heat build-up. Heat generated from cutting is concentrated along the edge, potentially degrading the tool face. Round inserts distribute the heat along a wider surface and make thinner chips. If tool path, mill cutter geometry and inserts aren’t selected carefully, this excess heat can cause chips to re-weld along the edge. Ideally, chips are migrating away from the edge, carrying stored heat with them. The number of flutes on the mill cutter aids chip distribution. Constant engagement between cutter and work piece is preferred.
Titanium’s low modulus of elasticity and tendency to deflect calls for a rigid system. Design the physical conditions of the milling set-up for stability. The right piece fixtures, spindle connections, tool diameter, short cutters and accurate tool point centering contribute to reduced vibrations that spare the work piece and parts of friction and heat. Selecting a high-pressure coolant, preferably non-chlorinated, is also vital in the machining of titanium alloys.
Shortened tool life is a concern when machining titanium alloys, as it has a high tendency to react with other materials. This calls for attention to the tool face material. Coated carbide, particularly titanium aluminum nitride (TiAlN) coated carbide is recommended to reduce wear from hardness and heat. If everything in the system is optimized, mill cutters will remain sharp longer, reducing cost. With all this in mind, the tool may be the least expensive variable, relative to time and material cost. Replacing the tool often enough to ensure it is cutting effectively requires regular visual inspection. And for all the planning one can do, nothing replaces short test runs to verify that cuts are light, the speed is optimized and heat is being dissipated.
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