Judging by the noise level surrounding it these days, you would think multimolding (MM)—molding two or more polymers, components, or colors into one part—was just invented. But MM was an active technology in the 1960s; back then, the applications were almost all different colors of the same material. Telephone dials with numbers that never wore off were the best-known example. Since then, multimolding has been growing—but slowly compared to what is happening today.
THEN: The combination of a Weber tool in an Arburg machine was making two-color phone dials in 1963. At far right, another Arburg-Weber combination shows how things have changed.
Considering how much multimolding technology is now available surrounding materials, molds, machines, robotics, and full production cells, the only problem may be too much choice. This article takes a very basic look at the options. We say “very” for two reasons: On the supply side, new multimolding technology and ingenious system design are appearing at every trade fair; on the demand side, many designers and manufacturers have already climbed the MM learning curve, and many more are coming along.
The applications tide is still rising, especially in North America, both in terms of numbers and variety. The products we have seen the most of until now—combining colors, hard structure with soft-grip surface—are the tip of a big iceberg.
NOW: A cooperative development between moldmaker Weber and machine maker Arburg, this mold for telephone housings offers another cycle-shortening solution for multimolding. In the photo, the finished two-material housings are being robotically removed while the mold is closed and simultaneous shots are being made and held. In this mold there are three banks of four cavities arranged in a triangular layout, and the mold rotates 120° using a rotary machine platen. The first and second stations mold the two materials sequentially. Concurrently, the third station is exposed by a cutout on the nonrotating mold half for part removal. Another time saver: The mold opens only enough to turn one half; no time is added for the robot to enter and exit.
Marketers increasingly are seeing how color and texture can make them winners. It can even make them stand out in so-called commodity market segments. As an example, take toothbrushes. Multicolor/multimaterial designs have totally overhauled that market. The attraction of color and the functionality provided by the grip material have created the product differentiation that marketers crave. Hard structure with a tactile grip similarly has changed the markets for hand and power tools. Being different can be worth a lot of money. When asked about MM applications today, Helmut Eckhardt, technical director of Battenfeld Injection Molding Technology, said that he sees much of the new MM activity coming from the following:
Functional soft/rigid combinations—for example, an integrated seal or gasket that eliminates separate molding and assembly.
Other combinations that eliminate post-molding operations.
The combination of different polymers, grades, or fillers to customize properties in the final part or assembly.
The combination of multimolding with other processes, e.g., gas or water assist, backmolding, IML, and so on.
Krauss-Maffei product manager Dietrich Hunold is also busy with multimolding applications. Despite last year's generally flat to negative machinery market, MM business grew about 30% at Krauss-Maffei. Europe, which took to multimolding early, holds a lead in application numbers, but North America is very active right now. Hunold says that, given the continuing tight market, it definitely helps that molders are realizing there are ways to enter the field at reduced cost.
Operationally, he says molders see how a multicomponent system can do single-material jobs until the MM volume grows. Also, many molders clamp two traditional molds into their MM systems in what Hunold describes as a variation of the family mold idea. It works very well when the molded components will be assembled after molding.
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