There are many miscellaneous applications of plastics for injection molds. Some of the more important are covered in the following sections. Integral Molds Integral molds are those molds which actually become a part of the final assembly. Although somewhat different from the accepted concept of “plastics mold tooling,” some mention should be made of them. The mold maker technique is primarily being used in the electronics industry to encapsulate electronic assemblies. One of the most widely used techniques involves the use of the relatively new epoxy molding compounds. These are of particular benefit be cause of the extensive use of epoxy resins for potting and encapsulating. Thus, the encapsulating material is made of the same material as the mold. The epoxy compound is molded by high-production compression or transfer-molding techniques in the shape of a component case suitable to enclose the assembly. The electrical assembly is inserted in the case, and potting or encapsulating resin is poured to fill the case and enclose the assembly. Such operations can be carried out on a rapid assembly-line basis. After cure of the encapsulating material the assembly is complete. Obvious benefits result from elimination of mold preparation, and stripping of the potted assembly from the mold. Also, the integral mold provides a strong case around the complete assembly.
Nylon mandrels made from stock shapes are used to help bend aluminum extrusions by Lite Vent Industries, Inc. They are used both as mandrels to fit inside the extrusions and maintain original cross section during machine-bending, and as protective shoes to fit over pre-finished aluminum extrusions which must be hand-bent in the field. The mandrels are used to bend three tubes at a time in a machine. Aluminum tubes are slipped over the mandrels (supplied by National Polymer Corp. ) and clamped to the machine table. An air cylinder draws the forming roller and the mandrels around the bending plate. Mandrels slide smoothly, without galling, along the rough interior of the tubing. Nylon provides sufficient flexibility to conform to the bend, yet high enough compressive strength to keep the aluminum extrusion from crushing or buckling at the point of bend. Several types of mandrels are used. Cut grooves or slots, spaced about Y2 in. apart along the length of the nylon rod increase flexibility. Longitudinal grooves are cut in mandrels for clearance of internal flash in welded tubing. For hand bending, nylon shoes are placed over the straight end of an aluminum extrusion. As the forming roller is pulled across the face of the bending plate, the shoe pivots on the plate. The shoe does not mar the finished face of the extrusion.