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A feature on a part that will not allow a mold that contains it to slide away along the parting direction. An undercut can be either a protrusion or a depression (hole or pocket) and is described as being either external or internal. An undercut requires an additional mold piece, such as a side-core or an internal core lifter, to form its shape.

Uniform cross section

A part whose cross section does not change along any one axis, disregarding any draft angle.

Unit power

The amount of power required to remove one cubic inch of material from the workpiece during a machining operation, measured in horsepower per cubic inches per minute. Unit power, also known as specific cutting energy, is a material property but is also affected by the type of machining operation and the material and sharpness of the cutting tool. Values for unit power are typically in the range of 0.1-2.5 hp/in^3/min (most steels have a value of 1.0-1.5 hp/in^3/min).

Unscrewing device

An additional mold piece that is used to form threaded features (internal or external). External threads on a feature perpendicular to the parting direction can be formed by the two mold halves. However, other external threads and all internal threads require an unscrewing device. The device is inserted into the mold to allow the threaded feature to form and is then unscrewed to be removed.

Unscrewing device - External threads on Y axis
External threads on Y axis
Unscrewing device - Mold can form threads
Mold can form threads
Unscrewing device - External threads on Z axis
External threads on Z axis
Unscrewing device - Mold cannot separate
Mold cannot separate
Unscrewing device - Internal threads
Internal threads
Unscrewing device - Mold cannot separate
Mold cannot separate


The amount of time that machines are running during the manufacture of parts, also called the run time. The uptime is often expressed as a percentage of the total production time, which includes the down time.

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