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December 3, 1999
3 Min Read
Central Fine Tool (CFT—Ena-City, Gifu Prefecture, Japan) has developed what it calls an “assembly mold.” The mold is designed to allow single-step molding and assembly on a standard molding press with no additional capital investment. Assembly molds (see Figure 1) also increase design freedom by creating products with undercuts and pockets that have been impossible to do with conventional molding technology.
Assembly molds can significantly downsize automated assembly complexities, like the absolutely precise dimensional control of molded parts and the equally perfect positioning fixtures such automation requires. In fact, they could obviate the need for automated assembly lines altogether in many cases (see “Avoiding Assembly Costs by Letting the Mold Do It,” February 1998 IMM, pp. 81-83).
Prototype parts have already been run for skeptics to demonstrate the mold’s potential. In one case, the mold opens, a clear PC molded product is removed, and you see a finished gear assembly incorporating one sun gear, three orbital gears, one ring gear, and front and rear housings—seven parts precision molded and fully assembled right out of the mold (see Figure 2).
Other assembly molds have produced prototypes that could never be molded in one piece, including a part with a compound cam assembled into a pocket, and a crank mechanism that converts revolutions into linear motion. CFT sources say their assembly molds can run most ETPs. And they add that even more value can be added running insert molded components in assembly molds.
Index Table Assembly
A device CFT calls the index table is in the core of the mold (see Figure 3). The index table is equipped with a number of transport stations. On the mold’s periphery, there are cavities that form each component of the molded assembly.
The peripheral cavities are listed in this schematic as “A” through “F.” When the part in the A cavity is molded, the mold opens, and the molded part is held in a transport station. The table turns and the transport station indexes to the next cavity. Here, the mold closes and the next part is formed; the mold opens, and this part is transferred into the holder.
With each opening and closing of the mold, the transport station indexes unidirectionally one step. Parts are automatically assembled one-by-one in the transport station holders. When all the parts from cavities A to F are assembled, the finished assembly is ejected from the mold.
CFT’s prototypes were made of a single type of plastic, but when used with a multimolding machine, different materials or colors could be used. Assembly mold technology also could be used to make parts from PIM metal and ceramic feedstocks.
Thinking Must Change
Kazuhiko Miyake, the executive director involved in developing the technology at CFT, has a word of caution about real-world application of assembly molds. “The way of thinking must change in regard to quality assurance and, of course, design and production processes,” he says.
Who should be responsible for quality assurance of parts assembled in the mold, Miyake asks, the moldmaker or the molder? He also asks you to bear in mind that assembly mold technology is limited to unidirectional inmold assembly, and he cautions that large parts cannot be made because of die plate size limitations.
There also are production volume limitations. Given the same surface area, more individual components can be molded than assemblies can with the index table in the assembly mold. However, Miyake is quick to add that with the growing trends toward smaller lots and greater parts diversification, the limitation may not prove to be such a big drawback after all.
CFT is a moldmaker and molder that started out in 1982 with EDM equipment from Sodick. It later helped Sodick develop CAM software for its EDMs. Today it has five Sodick wire and sinker EDMs and 12 seats of Sodick CAD/CAM software. It also has a horizontal Sodick V-line and a 40 ton vertical Sodick V-line injection press it uses for some rather complex hoop molding work. Sodick represents CFT in the States.
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