Library Articles  Injection molding generally uses molds made in
two parts. The first part is the cavity, which gives a concave
part its external shape. The second part is the core, which
gives a part its internal shape. The cost of the mold depends on
the geometry of the part being made; as the part become complex,
the mold increase in complexity and hence more expensive. During
the injection molding process, an injection molding machine
melts and inject thermoplastic into the mold under high
pressure. The molten plastic then takes on the shape of the
mold, cools and solidifies. The formed part is then ejected from
the mold. An ejection system is needed to push the part off the
mold because the part shrinks onto the core as it cools. This is
accomplished with ejection pins and they are usually located in
the core of the mold.  Injection Molding  Extrusion is suitable
to manufacture long part with uniform cross section such as
tubes and rods. Thermoplastic pellets are placed into a hopper
to feed the extrusio