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Machine and Machinability

By David Shea

Many parts are machined to achieve close tolerances or controlled surface finishes.  Machining operations are expensive because they require precise capital equipment and trained labor. For some materials, the cost of metal cutting tooling can exceed the material cost. Therefore machining properties of materials must be considered in a competitive environment because they drive a substantial component of cost.

Historically, textbook and reference listings of machinability have been of limited value because they have focused on a single parameter such as tool wear OR chip formation under a fixed cutting condition.  Unfortunately, the real world cutting conditions may be different due to thruput, part stiffness or quality requirements.  There may also be bigger issues than chip formation.  As a result, the use of this myopic machinability data can be down right misleading, as all aspects of machinability have a strong impact on manufacturing cost.  In a highly competitive environment, the “cost shadow” of material decisions is not only long, but also hard to eliminate after SOP.

In this talk, the relationship between material properties and a variety of machining characteristics of materials was explored.  Topics covered included deformation conditions in machining as well as the effect of material strength, ductility, and microstructure on machining costs.  He also discussed the issues and difficulty in trying to extrapolate from the conditions of a controlled material test to machining conditions.  Particular attention was on aluminum alloys and the relative significance of chips and burrs versus tool wear for ductile alloys.