Every injection mold has to have a gate, or an
opening through which the molten plastic is injected into the cavity of
the mold. The type and size of gate plays a very significant role in
the process of injection molding and must not be overlooked.
In
the custom injection molding business, margins are extremely tight.
This requires the mold maker to make a very accurate determination of
the size and type of gate for the injection mold. The wrong gate can
spell disaster, or at least reworking the mold, which can quickly eat
up profits.
There must be a gazillion plastic parts in the world:
cell phones, computers, hula hoops, keyboards, TVs, toy machine guns,
goggles, etc, etc.
Gates vary in size and shape depending upon
the type of plastic being molded and the size and shape of the part as
well. Obviously, larger parts require larger gates, or even several
gates.
Common types of gates
• Tab gates.
• Tunnel gates (also known as submarine gates)
• Banana gates
• Smiley gates
• Hot-tip gates
There are other types of gates, especially in the hot-tip applications, but that is a subject unto itself.
The tab gate
is the simplest of all. It is the type of gate you see when you buy a
plastic product that requires breaking from the runner, or tree-like
piece of plastic attached to the part. It is usually a flat, tab-like
connector that enables the plastic to flow into the part.
A tunnel, or
submarine gate, is more complicated and requires a much higher degree
of skill to add to the mold. This type of gate is a cone that is added
below the surface of the part, thus the name: submarine gate. It also
has the appearance of a tunnel. This is used when there cannot be much
evidence of the gate left on the part. This is known as gate vestige.
It
is also used in high production molds where everything is automated and
the part must break free from the gate in order to be separated and
packaged.
The smiley gate is so-called because when you
look at it, it resembles a smile, sort of. This is more difficult to
machine and is used to add a gate right at the bottom of a plastic
part. It is like a tunnel gate, except the bottom portion is cut off,
or truncated. This enables the gate to be right at the bottom of the
plastic part. Smiley gates are also used in high production
applications where the part must break free from the gate for purposes
of automation.
The banana gate is quite a novelty, but
very useful. These gates are used when there can be no trace of the
gate on the plastic part. It is like a tunnel gate, but curved, like a
banana, so it can reach underneath the part and allow the plastic to be
injected into a hidden area of the part.
Conclusion
The size, type and placement of the gate used in plastic injection mold making
have a dramatic impact on the quality of the plastic part, as well as
how quickly it is produced. Gates play an important role in the
automation of custom injection molding.