I have been in the field of Custom Plastic Injection
Molding for about 21 years now as of the writing of this article. I am
currently working as a Process Engineer, which I have done for about 15
of my 20+ years in the field of injection molding and I have primarily
worked for molders that were involved in the automotive field.
Plastic
injection molding, by definition, is the process of injecting plastic
into a mold (or mould in European circles), cooling the plastic,
ejecting it from the mold, and packing the finished product for sale to
the customer. This sounds simple and in it's basic form it is, but the
process involved with making all this happen is actually quite
complicated. Plastic can be injected into the mold with low pressure,
but typically is done under high pressure upwards of 30,000 PSI cavity
pressure.
There are many diverse types of injection molding and
as many different types of plastic injection molding machines to go
with it. Some of the more common types of plastic molding are standard
mold injection, insert molding, plastic extrusion, blow molding,
multi-color or material molding, stack molding, and rotary molding just
to name a few. There are custom plastics as well, from common every day
plastic resins to the more exotic engineering grade resins used in most
automobiles today. There are even injection molding grade "metals"
being experimented with and used these days.
There are many types
of injection molding machines all made for specific purposes. There are
the standard horizontal injection molding machines which range in size
from a few tons all the way up to 9000 tons and more. You could drive
car between the platens of a press that large. Vertical injection
molding machines are often used for insert molding (although this can
also be done horizontally) and share a common cover with two ejection
halves of the mold. This allows for de-molding and loading of inserts
in one half, while the other half is producing the next shot of parts.
There are also two and three shot injection molding machines for
producing multi-color or multi-material parts such as lenses for tail
lights and gear shift knobs with hard plastic inner core and a soft
vinyl out covering. The newest machines are "all electric versions"
which stray from the standard hydraulic injection machines used now for
years. These injection molding machines are much more efficient and
repeatable then their hydraulic cousins are. Common injection molding
machine manufacturers are Toshiba, Husky, Cincinnati, DeMaag, Engel,
Nissei, UBE, Arburg and Boy, just to name a few.
The basic steps to producing a plastic injection molded part on a stand injection molding machine are:
Heating the plastic resin to the required range of the product being used.
Developing the shot size through use of a reciprocating screw which conveys the melted plastic to the front of the screw.
Injecting the plastic into the mold under pressure to fill the cavity of the mold.
Packing the plastic to create a full part inside the mold.
Cooling the plastic in the mold through the use of cooling channels most commonly with water.
Ejecting the cooled part from the mold.
Repeating the process over and over again.
There
is a whole lot more that goes into this and you can read many more
articles on the custom injection molding process in more precise detail
on my site at http://www.wm8c.com/custom_injection_molding.htm but this should provide you with a basic understanding of what's involved.
Todd
has written hundreds of articles for his site about injection molding
and many other topics ranging from his hobbies and life experiences.
Other sites he maintains inlcludes http://www.lowerurtaxes.com and http://www.careersforliving.com
Subscribe to this comment's feed