a. the cold-runner two-pi ate mold (this design is the simplest};
b. the cold-runner three-plate mold, in which the runner system is separated from the pan when die mold opens;
c. the hot-runner meld (also called the runnerless mold), in which the molten plastic is kept hot เท a heated runner plate.
In cold-runner molds, the solidified plastic in the channels that connect the mild cav¬ity to the end of the barrel must be removed, usually by trimming This scrap can be chopped and recycled. In hot-runner molds, which are more expensive, there are no gates, runners, or sprues attached to the molded pan. Cycle times are shorter, because only the injection- molded part must be cooled and ejected.
Metallic components, such as screws, pins, and strips, can also be placed in the mold cavity and become an integral pan of the injection-molded product (insert molding, big. IS.6). The most common examples of such combinations are electrical components.
Multicomponent injection molding (also called coinjection or sandwich molding) al¬lows the forming of parts with a combination of colors and shapes. An example is the mul¬ticolor molding of rear-light covers for automobiles made of different materials. Also, printed film can be placed in the mold cavity, so that pans need not be decorated or labeled after molding.
Overmolding. This is a term used for producing hinge joints and ball-and-socket joints in one operation and without any post-molding assembly. Two different plastics have thus far been used, to ensure that no bond will form between the molded halves of the joint, because otherwise motion would be impeded.
A new process, called Ice-cold molding, uses the same type of plastic to form both components of the joint; its use can be seen in a typical door hinge. The process is earned out in one cycle in a standard injection-molding machine. It Involves a two-cavity mold and uses cooling inserts positioned in the area of contact between the first and the second mold¬ed component of the joint. In this way. no bond forms between the two pieces.