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MOULDS MACHINING METHODS
Plastics moulds define the shape forming complete three dimensional plastic parts.
They are required for all plastic process like Blow, Injection, Rotational,
Compression and are very important component in the plastic processing. A die, on
the other hand, is used to form two of the three dimensions of a plastic part. The third
dimension, usually thickness or length, is controlled by other process variables. The
plastics processes that use dies are extrusion, pultrusion and thermoforming. Many
plastics processes do not differentiate between the terms mould and die. Moulds,
however, are the most predominant form of plastics tooling.
Types of Mould: The basic types of mould, regardless of whether they are
compression, injection, transfer, or even blow moulds, are usually classified by
the type and number of cavities they have: (a) Single-cavity or (b) Multiple-cavity.
Moulds are built through two main methods: standard machining and electrical
discharge machining (EDM) or spark erosion.
Standard Machining: in its conventional form, uses lathe machines, drilling,
turning, boring, milling, broaching, sawing, shaping, planing, reaming, and tapping,
grinding and honing for building moulds. With technological development, computer
numerical control (CNC) machining became the predominant means of making
more complex moulds with more accurate mould details in less time than traditional
methods.
Electrical Discharge Machining (EDM): or spark erosion process has become
widely used in mould making. EDM is a simple process in which a shaped electrode,
usually made of copper or graphite, is very slowly lowered onto the mould surface

(over a period of many hours), which is immersed in paraffin oil (kerosene).Material
is removed from the work piece by a series of rapidly recurring current discharges
between two electrodes, separated by a dielectric liquid and subject to an electric
voltage.
Computer Numerical Control (CNC) Machine: In modern CNC systems, end-to-
end component design is highly automated using computer-aided design (CAD)
and computer-aided manufacturing (CAM) programs. The programs produce a
computer file that is interpreted to extract the commands needed to operate a
particular machine via a postprocessor, and then loaded into the CNC machines for
production. Since any particular component might require the use of a number of
different tools-drills, saws, etc., modern machines often combine multiple tools into
a single "cell" In other cases, an external controller and human or robotic operators
that move the component from machine to machine. In either case, the complex
series of steps needed to produce any part is highly automated and produces a part
that closely matches the original CAD design.
Computer Aided Design (CAD) allows engineers to create detailed designs of
parts with maximum efficiency and minimal cost. The days of the drawing boards are
essentially over with the release of affordable and easily used 2D and 3D CAD
packages. The aim of CAD is to apply computers to both the modelling and
communication of designs. This includes automating such tasks as the production
of drawings or diagrams and the generation of lists of parts in a design are now
closely integrated with the techniques for modelling the form and structure of the
design.

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