Glossary Terms

Softening a metal by heating it to and holding it at a controlled temperature, then cooling it at a controlled rate. Also performed to produce simultaneously desired changes in other properties or in the microstructure. The purposes of such changes include improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties and increase in stability of dimensions.

Angle between the insert’s side-cutting edge and the line perpendicular to the milling cutter’s axis of rotation. Approach angle, which is also known as cutting edge angle, is used with metric units of measurement. See lead angle.

A file for automatically programmed tools that consists of the input language, an APT processor, an APT postprocessor and a computer of sufficient size to run the APT program. The APT system was initially developed for 3-, 4- and 5-axis milling machines, but because of further development, is capable of a range of applications, including point-to-point and turning work.

Shaft used for rotary support in machining applications. In grinding, the spindle for mounting the wheel; in milling and other cutting operations, the shaft for mounting the cutter.

The mathematical expression denoting one of several parameters that describe surface texture (same as average roughness Ra). Average roughness is the arithmetic average height deviation of the measured surface profile from the profile centerline. See surface texture.

Joining together two or more parts to complete a structure.

Hot deformation of metastable austenite within controlled ranges of temperature and time that avoids formation of nonmartensitic transformation products.

Heat-treatment for ferrous alloys in which a part is quenched from the austenitizing temperature at a rate fast enough to avoid formation of ferrite or pearlite, and then held at the to achieve the desired characteristics.

Solid solution of one or more elements in face-centered cubic iron. Unless otherwise designated (such as nickel austenite), the solute is generally assumed to be carbon. Austenite can dissolve up to 2 percent carbon. Austenite is relatively soft, ductile and nonmagnetic.

Heating an alloy above its transformation temperature and then quenching it in a salt bath or other medium that extracts the heat at a sufficiently high rate to prevent formation of undesirable high-temperature-transformation qualities on its surface or in its microstructure. See austenite; martensite; martensiting.

Machine for turning bar stock. Similar to an automatic chucking machine, except that stock size is limited to through-the-spindle capacity and workpiece is held by push, draw or stationary collets rather than by chucks. See automatic chucking machine; turning machine.

Machine with multiple chucks and toolholding spindles that permits processing of several parts simultaneously or multiple machining steps in one pass through the machine. See automatic bar machine.