Transcript INJECTION MOLDING

UNDERSTANDING THE PROCESS





THE FIRST STEP is usually drying the plastic material. most plastics have to be
heated to a certain temperature for a specific amount of time to pull
moisture from the plastic prior to molding.
PLASTIC IS HEATED to a liquid form. that plastic is forced into a mold and
cures. it sounds simple, but is a complex process.
THERE ARE THREE MAIN UNITS which make up an injection molding machine
– the feed hopper, the heater barrel and the screw. the plastic in the hopper
is in most cases in granular form.
THE PLASTIC from the hopper enters the heated barrel and is moved along
with the screw. as it moves, it is heated and by the time it reaches the end of
the barrel it has been heated to a liquid state and is injected from the end of
the barrel through a heated nozzle into the tightly clamped mold filling all
the cavities and then allowed to cool. thermoset plastics require a heated and
temperature controlled mold to set the plastic.
ONCE THE PLASTIC has cooled or set for the necessary time the mold is
opened and the part is ejected from the mold. the mold closes and the
process starts over again.


INJECTION MOLDING enables complex shapes
to be manufactured, some of which might be
near impossible to produce economically by
any other means.
IN VOLUME it is a low cost process, arguably
with minimal environmental impact. There is
little scrap created in this process, and scrap
that is produced, can be re-ground and reused.


THE INVESTMENT IN TOOLING Making the
mold - typically requires high volume
production to recover the investment, though
this does depend on the particular part.
PRODUCING THE TOOLING Takes
development time and some parts do not
readily lend themselves to a practical mold
design.


A HIGH QUALITY MOLD Although of relatively
high cost, will be capable of turning out
hundreds of thousands of parts.
THE PLASTIC ITSELF is quite inexpensive and
despite the energy required to heat the
plastic and cycle the press (to remove each
part) the process can be economical for even
the most basic items.



Making a mold often requires complex design, multiple
machine operations and a high degree of skill. A mold
is usually in two main assemblies clamped together in
the molder press. CNC machines have enabled a high
degree of the automation of the of mold manufacturing
process.
ALUMINUM The most common molds are manufactured
from aluminum when pressures and types of plastics
allow. Aluminum is cheaper and easier to machine.
STEEL Steel is used when higher pressures are used for
more complex shapes or more abrasive plastics such as
glass filled products. Steel offers longer mold life than
aluminum.
OPEN ALUMINUM MOLD
CLOSED ALUMINUM MOLD
120 Ton Machine
 250 Ton Machine
 390 Ton Machine
 Shot sizes up to 29 oz.
 2 core pulls
 MOLD SIZE – Up to 29” x 29” tie bar spacing (max
physical mold size)
 Common materials processed – PVC, Ultem
Polypropylene, ABS, Polycarbonate, Styrene, Acetal,
Delrin, Nylon

BLACK POLYPROPYLENE CONTAINERS
POLYPROPYLENE
POLYCARBONATE
ACETAL, HDPE, POLYURATHANE
ABS