Traditionally, injection molding has been a production process featuring high initial (tooling) costs and low production costs. It has not been until the recent introduction of aerospace inspired metal alloys combined with sophisticated electronic control of machine functions that truly inexpensive injection molds, capable of serious production have been possible. Up until the late 1980s, soft injection molds, usually made of aluminum, were used for prototyping, seldom being capable of producing more than 1000 parts. Modern alloys, along with molding machines designed to apply molding pressures more evenly and gently, have resulted in the ability to design low cost injection molds capable of running as many as a million parts. These economical injection molds can cost from 1/2 to 1/4 as much as traditional hard steel molds. At the same time that improvements were being made in machine and mold technology, the tools and procedures for rapid changeover from one mold and material to another mold and material were being developed, resulting in low cost injection molding for short runs.
Below are several examples, with prices, of injection molded items. There is a range of sizes and materials demonstrated, as well as different orders of complexity.
This innovative test tube rack is molded from polypropylene. It accepts 4 sizes of test tubes, and each hole is numbered for keeping track of individual portions. In use, the rack is inverted and filled with water. A tight rubber bottom (not shown) is then fitted over the bottom and the rack is placed in a freezer. The frozen water keeps the test tubes chilled during use. Soft $6800 mold cost, parts $2.49 in 1000 lot.
Traditional clay tennis courts require a closely regulated moisture content. A watering/drainage grid controls the water, and this container has an inlet for pressurized water, a drain collection outlet and a feed outlet. A valve regulator float on the internal post controls the water level. The internal hole is tapped as a second operation. This large, very complex part replaced an equivalent part assembled out of a number of PVC fittings. Soft $16,500 mold cost, parts $6.28 including second operation.
These colorful “windshield spikes” are decorative items for motorcycle windshields. The imbedded bolts are stainless steel, and are inserted into the mold during the molding cycle. This is a six cavity mold, making six spikes per cycle. Soft $3500.00 mold, parts $0.25 including stainless steel bolt.
Filter ring, for a high pressure filter, molded from glass filled Celcon (acetal copolymer). Approx. 8 ” in diameter, it must withstand the pressures of a large pump. The soft mold cost $2900, the parts $1.80 in small quantity.
These two 8 inch styrene parts snap together to make a watering bowl for a flower pot. These parts come from a hard mold, capable of making hundreds of thousands of parts. The two molds priced at $19,000, parts are $1.71/set in volumes of several thousand. This is molded in a number of different transparent colors.