Injection molding machine
An Injection molding machine, also known as an injection press, is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, an injection unit and a clamping unit.
Injection molding
machines can fasten the molds in either a horizontal or vertical
position. The majority of machines are horizontally oriented, but vertical
machines are used in some niche applications such as insert molding,
allowing the machine to take advantage of gravity. Some vertical machines
also don't require the mold to be fastened. There are many ways to fasten
the tools to the platens, the most common being manual clamps (both halves
are bolted to the platens); however hydraulic clamps (chocks are used to
hold the tool in place) and magnetic clamps are also used. The magnetic and
hydraulic clamps are used where fast tool changes are required.
The person designing the mold chooses whether the mold uses a cold runner
system or a hot runner system to carry the plastic from the injection unit
to the cavities. A cold runner is a simple channel carved into the mold. The
plastic that fills the cold runner cools as the part cools and is then
ejected with the part as a sprue. A hot runner system is more complicated,
often using cartridge heaters to keep the plastic in the runners hot as the
part cools. After the part
is ejected, the plastic remaining in a hot runner is injected into the next
part.
Types of injection molding machines
Machines are classified primarily by the type of driving systems they use: hydraulic, mechanical, electric, or hybrid.
Hydraulic
Hydraulic presses have
historically been the only option available to molders until Nissei Plastic
Industrial Co., LTD introduced the first all-electric injection molding
machine in 1983.
Hydraulic machines, although not nearly as precise, are the predominant type
in most of the world, with the exception of Japan.
Mechanical
Mechanical type machines use the toggle system for building up tonnage on the clamp side of the machine. Tonnage is required on all machines so that the clamp side of the machine does not open (i.e. tool half mounted on the platen) due to the injection pressure. If the tool half opens up it will create flash in the plastic product. Reliability of mechanical type of machines is more as tonnage built during each cycle is the same as compared to hydraulic machines.
Electric
The electric press, also known as Electric Machine Technology (EMT), reduces operation costs by cutting energy consumption and also addresses some of the environmental concerns surrounding the hydraulic press. Electric presses have been shown to be quieter, faster, and have a higher accuracy, however the machines are more expensive.
Hybrid
Hybrid injection molding machines
claim to take advantage of the best features of both hydraulic and electric
systems, but in actuality use almost the same amount of electricity to
operate as a standard hydraulic,
A robotic arm is often used to remove the molded components; either by side
or top entry, but it is more common for parts to drop out of the mold,
through a chute and into a container.
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