The injection molding process is beneficial for those who want to quickly produce high quantity replicas of a plastic part. On a very simplistic level, it involves heating plastic granules until they have melted enough to be injected, using high pressure force, to fill a mold. Once the mold is filled and held in position for a long enough period, the plastic will cool and harden again into its new shape. The outcome is a part that forms the exact shape of the mold. Multiple parts can be quickly created in this way to produce perfect replicas.
The Initiation of the Injection Molding Process
The first stage of the injection molding process involves the moving and fixed platens clamping the mold together. At this point the plastic is heated and the injection process is initiated. There is a gate or opening through which the plastic is injected into the mold. The right gate size and type will play a part in how the part is molded and cosmetic appearance and warping can occur if the wrong type of gate is used for the part. It’s also important that the mold be filled carefully as stress can make a part warp, crack, distort, or fail. Stress can occur to the molecular structure of the plastic resin because of high pressure as well as being forced at high pressure around sharp corners. The perfect balance of heat and pressure is necessary during this part of the injection molding process.
The Cooling Stage
Once the plastic has filled all of the mold cavities it must be held in place and allowed to set. The plastic will become hard in its new shape during the cooling stage. At this point in the injection molding process the clamping around the mold can be released, allowing the mold to open. Molds contain internal ribs and outside walls that are tapered in the direction that the mold will open. The draft will assist the part in breaking free from the mold, as soon as it opens. In process of ejecting the plastic from the mold, various tools are used, including rods, plates or air blasting. This is the last step in creating a plastic part using the injection molding process.
Vital Factors to Consider
It’s essential to check that you are using the best plastic materials suited to the type of part you’re intending on creating. Temperatures, pressure levels, gate type, and drafting designs all contribute to how well the production fares. Problems that can occur include burn marks which occur when the injection speed is too high and there’s not enough venting, blisters from the heat being too high, color streaks from materials not blending well, sink marks from hold time or pressure being too low or cooling times too short, as well as a variety of other distortions or warping issues that can be solved with simple adjustments.
The plastic injection molding process, used for producing so many of the parts that create the items we use every day, is both simple and complex and it’s important to do all the research necessary to get the best possible outcome.