Injection Molding Safety

Thermoplastic injection molding is the most widely used of all plastic processing methods. The injection molding machine reduces pelletized raw material and colorants into a hot liquid. This "melt" is forced into a cooled mold under tremendous pressure. After the material solidifies, the mold is unclamped and a finished part is ejected. Injection molding offers the lowest piece prices available, but tooling prices are generally the highest. Thermoset injection molding is similar to thermoplastic injection molding except that uncured thermoset resins are mixed, injected, and held in the mold until cured. As with thermoplastic molding, the price per piece can be low, but the tooling prices are generally very high.

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 injection molds, single cavity injection molds to complex multi-cavity injection molds with moving molding 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.

About 2 years ago I purchased a tool set. It came with a wonderful set of tools, but a really low end, thin and hollow plastic injection molding case that belies the namesake and tradition. Needless to say, the case finally gave up the ghost this past week. I began shopping for a replacement tool box for the old set that has since grown to over 200 pieces. Wanting some level of organization that is needed on the trail while off roading, the plastic tool box intrigued me due to its thick plastic construction and it's similarity to a larger tool chest with extendable drawers. Its size and depth allowed me to place it in the same spot as where I held the old plastic injection molding case in my truck.

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 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 safety 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.

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.