H & S Specialties Inc.
120 14th Ave NE
Glenwood, MN 56334
Phone 763-792-2184 Toll free 877-562-5070
Injection Molding Information.
Fax 763-785-9065 Toll Free Fax 877-280-2087
Injection molding, a manufacturing method of inserting a liquid plastic into a mold (the tooling used to produce custom parts).
As the plastic sets or hardens in the mold, it takes on the shape of the mold. A substance called a release agent is normally
used to make it easier to removed the plastic from the mold. The molds are held by injection molding machines or presses,
that keeps the mold from opening during production. Presses range from 5 tons to 6000 tons of holding pressure.
The materials used for producing the mold, will determine the life of the mold. Those that are made out of hardened steel
that is heat treated after being machined, are the longest lasting. Aluminum molds are less costly to make but cannot withstand
the production of millions of parts like the steel molds can. Beryllium copper is used in the parts of the mold that need fast
heat removal or needs the most heat generated. Molds are typically made by CNC or EDM machines.
Molds are designed with two sides to allow the part to be removed. The plastic material enters the mold, traveling through gates
into the cavities, around the cores, taking on the shape of the part. Any air inside the mold is forced through slight gaps into
vents. Either pins or ejector plates are used to remove the parts from the mold.
M.U.D. style molds are sometimes used to help reduce the cost of a mold. The outside of the mold is designed to hold several
interchangeable inserts, there by being able to make several different parts.
Overmolding is a process that lets previously molded parts be reinserted in a mold, with a new plastic layer formed
around it. Two-shot or multi-shop molds are used to overmold a part within one molding cycle. This requires a special
machine with two or more injection units.
Molds can be designed with more than one cavity for the same part allowing for faster production. A family mold is designed
to mold parts of the same family or set at the same time.
John Hyatt was the first person to use the injection molding process in 1868. He injected hot celluloid into a mold to make
billiard balls. John and Isiah Hyatt built the first injection molding machine in 1872 using a plunger. Revolutionizing
the plastics industry in 1946, James Hendry made the first screw injection molding machines. This type of machine is still
being used today (screws are used to mix, heat and inject the plastic into the mold).
We do not guarantee the accuracy of cost estimator linked here. David O. Kazmer's, P.E., Ph.D. Java Injection Molding Cost Estimator.