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impact test

Test to determine the behavior of materials when subjected to high rates of loading, usually in bending, tension or torsion. The quantity measured is the energy absorbed in breaking the specimen by a single blow, as in Charpy and Izod tests.

in-process gaging (in-process inspection)

Quality-control approach that monitors work in progress, rather than inspecting parts after the run has been completed. May be done manually on a spot-check basis but often involves automatic sensors that provide 100 percent inspection.

inches per minute (ipm)

Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.

inches per tooth (ipt)

Linear distance traveled by the cutter during the engagement of one tooth. Although the milling cutter is a multi-edge tool, it is the capacity of each individual cutting edge that sets the limit of the tool, defined as: ipt = ipm/number of effective teeth 5 rpm or ipt = ipr/number of effective teeth. Sometimes referred to as the chip load.

inclination angle

Angle that the cutter edge makes with a plane that is perpendicular to the direction of tool travel. Determines the direction the chip curls.

included angle

Measurement of the total angle within the interior of a workpiece or the angle between any two intersecting lines or surfaces.

indexable insert

Replaceable tool that clamps into a tool body, drill, mill or other cutter body designed to accommodate inserts. Most inserts are made of cemented carbide. Often they are coated with a hard material. Other insert materials are ceramic, cermet, polycrystalline cubic boron nitride and polycrystalline diamond. The insert is used until dull, then indexed, or turned, to expose a fresh cutting edge. When the entire insert is dull, it is usually discarded. Some inserts can be resharpened.

indexing machine

Assembly machine designed to assemble parts sequentially. Each station consists of tooling for subsequent operations. Parts are moved through their assembly sequence by an intermittent rotary motion.

indicator drop measurement

Method of determining if the primary and secondary reliefs on an endmill or other cutter have been properly ground. See clearance; relief.

induction hardening

Surface-hardening process in which only the surface layer of a suitable ferrous workpiece is heated by electromagnetic induction to above the upper critical temperature and immediately quenched.

industrial robot

Robot designed for industrial use. Primarily used as a material-handling device but also used for changing tools, assembling parts, and manipulating special tools and measuring devices. Depending on design, an industrial robot can be programmed to perform a task by means of a controller, or it can be “walked” through the required movements by utilizing a digitizing system that translates movements into commands that the robot can be “taught.” See robot; teaching pendant.

inner diameter (ID)

Dimension that defines the inside diameter of a cavity or hole. See OD, outer diameter.

inscribed circle (IC)

Imaginary circle that touches all sides of an insert. Used to establish size. Measurements are in fractions of an inch and describe the diameter of the circle.


Process of physically checking a part or product to ensure that it meets specific, predetermined dimensions. Because errors can be caused by out-of-tolerance measuring instruments as well as out-of-spec parts, it is important to periodically check the measuring tools for accuracy. See calibration.

interchangeable parts

Parts and components produced to specified tolerances, permitting them to be substituted for one another. Essential to mass production, permitting the high-volume output that results in economies of scale. Less critical to operating costs in computer-integrated manufacturing operations but facilitates maintenance and repair. See CIM, computer-integrated manufacturing; modular design, construction.


Process of generating a sufficient number of positioning commands for the servomotors driving the machine tool so the path of the tool closely approximates the ideal path. See CNC, computer numerical control; NC, numerical control.

interrupted cut

Cutting tool repeatedly enters and exits the work. Subjects tool to shock loading, making tool toughness, impact strength and flexibility vital. Closely associated with milling operations. See shock loading.

investment casting

1. Casting metal into a mold produced by surrounding (investing) an expandable pattern with a refractory slurry that sets at room temperature, after which the wax, plastic or frozen-mercury pattern is removed through the use of heat. Also called precision casting or lost-wax process. 2. Part made by the investment-casting process.

ion nitriding

Surface-hardening process in which nitrogen ions are accelerated under an electric potential in a closed chamber and become embedded in the surface of the parts being treated, where they interact with minor constituents of the treated metal to form nitrogen compounds.

Izod test

Impact test in which a V-notched specimen, fixed at one end, is subjected to a sudden blow delivered by the weight at the end of a pendulum arm. The energy required to break off the free end is a measure of the impact strength or toughness of the material. See Charpy test.