Injection Mold

The wonderful thing about plastic injection molding is the low cost of the parts being produced when you need a large volume of parts. The downside is the cost of injection molding tooling. The toolings, or the molds, range in price anywhere from $2000 for a simple one, to over a hundred thousand dollars for a big and complex injection mold. The way the injection molders figured out how much to charge per part was to weigh the part complete with runner to determine how much plastic resin is used for each part. The size of the part determines what size injection molding machine must be used, and how big the mold is etc.

Injection molding is a common method of producing intricate plastic components in high volume. Injection molds are made from hardened tool steel, although aluminum may be used for some low volume applications of injection molding. Injection molds can vary from simple open-shut injection molds, single cavity injection molds to complex multi-cavity injection molds with moving cores, stepped shut-offs, unscrewing devices. Due to the tonnage used in this high pressure process, proper materials, supports, parting line locks etc. must used to ensure the life of the mold. Cavities may be polished or textured to achieve a desired finish on the injection molded part.

The Plastic injection molding machine has two parts: the injection unit which melts the plastic and injects the plastic into the mold, and the clamping unit which holds the mold. The injection molding unit clamps the mold in a closed position during injection, opens the mold after cooling, and ejects the finished part. Injection molding's efficiency varies by the number of parts you plan to produce. For a small quantity, such as 10 parts, it may be less expensive to simply machine the desired part utilizing a milling machine. On the other hand, if you desire several thousand parts, injection molding is ideal. When you submit your order for an injection molding part, the websites will assign staff to help evaluate the most appropriate mold material which will vary by part tolerance and number of units anticipated.

The 2-shot injection molding process creates the first plastic component, and the material molded round it, using a single mold and a 2-shot injection molding machine. 2-shot machines have two-barrels (one for each material) and they have the ability to rotate the mold. The machine injects the first shot material into cavities on one side of the mold, rotates the mold 180 degrees, and then injects the second shot material onto the first shot. The first and second shots occur at the same time. When the mold opens, it ejects the completed parts from the second shot cavities and it rotates the mold to position the first shot for the second shot. This is accomplished in a machine running in an automatic injection cycle. Because the 2-shot injection molding process is fast and highly repeatable, the shrinkage of the first shot is very consistent and two materials can be molded together with virtually no flash. 2-shot molding is the process of choice when molded-in graphics or other fine details are required. The elimination of the shrinkage variable allows 2-shot molding to produce details impossible to achieve with over-mold injection molding.