Multimolding applications, whether for appearance or functional reasons, or both, are multiplying, especially in North America. Production technology choices are almost equally varied, including some lower-cost options.
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.
Why so much noise now? At the most basic level, blame it on the cumulative growth in awareness, particularly among product designers. Designers today see the possibilities multimolding offers for product differentiation and are widening the gamut of applications. Complementing this increased design awareness has been a parallel development of multimolding technologies.
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.
Form, Function, Fit
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. 
Vertical machines are as adaptable to multimolding as horizontal models, and as easily incorporated into automated cells like this one from Battenfeld for hand-tool maker Belzer.
One can also add MM technology through the side door. Krauss-Maffei recently joined the ranks of companies supplying bolt-on injection units. Easily retrofitted to an existing machine, a bolt-on can ease the cost of technology adaptation. And since a bolt-on can be moved from one machine to another, a molder has a flexible tool to increase overall market offerings. Micromolding, another growth area, is also going multimaterial. Hunold says a Krauss-Maffei system is now making a two-component sensor bearing with a total weight of roughly a gram. The LSR second component is 20% of that and the part is running on short cycles in a four-cavity mold.
Many new applications, says Hunold, are driven more by functionality than appearance, and many are strikingly innovative. A new two-component seal for automobile frames has a nylon structural component and a proprietary foaming compound as the second material. But the foaming does not take place in the mold. It occurs when the seal, already in the frame, meets the heat of the frame’s dipping bath. The compound foams to fill all voids, thus creating a custom seal without manual or robotic intervention.
The Processing Choices
As we run through the choices for multimolding hardware, keep in mind that we are talking about multishot molding—that is, two or more separate shots. We are thereby omitting such technologies as sandwich molding, where one material is injected behind another through the same nozzle. Derived from the same technology base and also growing in popularity for its ability to create a high-quality surface around a lower-cost core material, it is a close cousin of MM. 
We have listed the alternatives as mold-centric (“In and around the mold,”) or machine-centric (“Machine configurations galore,”), but it should be noted that most MM production systems combine process-specific mold and machine technologies. Also, nearly all use robotics (often quite sophisticated). Some systems are hybrids, and some are just plain hard to classify.
For example, take multiple machine systems using two or more single-material IMs. Component A is molded in one IM and transported by robot or manually to a second machine for component B. Pros: can use existing standard IMs and molds. Cons: transport time, intermediate storage, shrinkage of component A, floor space, cost of two IMs and molds vs. one MM system. One large molder running a robot between two machines told us that the change in material A improved the bonding with material B.
Because of the increased interest and activity in multimolding, material choices are expanding. Most machine companies supplying MM systems have a materials compatibility chart (see “Simplifying Multicomponent Design,” March 2004 IMM). However, material suppliers and compounders are steadily working on ways to marry materials that were formerly considered incompatible (see “Plasma Plays Matchmaker,”).
The best idea may be to determine your performance parameters and an optimum material combination; then call the suppliers to see what they recommend. Don’t rule out seemingly unworkable combinations without researching them first.
Plasma plays matchmaker
Supported by the German state of Bavaria, New Materials Fürth (NMF) is a technology transfer company doing contract research with the University of Erlangen-Nürnberg. Its aim is to supplement the resources of medium-sized processing companies. Among its various projects, NMF is currently researching inline plasma treatment to improve adhesion of multimolded component materials, including pairs normally considered incompatible.
The project uses a system that consists of a plasma source on an articulated-arm robot and a 125-ton Krauss-Maffei two-component CZ Series injection machine. Following the first shot, an articulated robot positions the plasma source to treat the parts. The beam can be precisely directed to break up adhesion-inhibiting surface layers and create a reactive or active surface that supports a good bond between materials that normally show poor to no compatibility.
Initial results are positive. A number of previously unworkable material combinations have proven viable. Further research and applications development are ongoing.
Web-exclusive sidebar: An investment in multimolding
Saviplast (Vicenza, Italy) decided to make multimolding a key part of its strategy to deal with a stagnant market, and invested in new production cells and a skills-upgrading program to make it work. Primarily a custom molder making technical parts for European electronics, industrial, furniture, and sporting goods markets, 30% to 40% of Saviplast’s production serves its own line of pump and electric motor components. Many of its products are housings, some for underwater use. Making the gaskets for these products within the mold, rather than separately, substantially increases productivity and quality. 
Seeing multimolding as a key strategy to overcome a down market, Saviplast invested in a pair of two-material production cells from Mir to integrate gaskets with its broad line of pump and motor housings. A three-component cell was added later and a fourth cell is being installed currently.
To accommodate the variety of these components, three fully automated production cells from Mir SpA based on 140-, 180-, and 280-ton multicomponent injection machines from its RMPE Series have joined Saviplast’s existing 27 injection systems. The 140- and 180-ton systems are two-component machines, with the second injection unit mounted vertically. Saviplast decided to forego a rotary machine platen since the gasket overmolding to be done in these cells is well suited for sliding core molds. 
The multimolding strategy has proven effective. A fourth Mir production cell is being installed at Saviplast’s primary factory to make an innovative component for underwater pumps.
Mir USA Corp.
Leomister, MA
(978) 537-4792
www.mirpresse.it (end)
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