FASTER, BETTER, MORE: MULTIMOLDING TAKES OFF
20 October 2006 - DTI Globalwatch

Moldmaker Foboha’s version of the rotating stack mold is called the Cube system, shown here molding mobile phone housings.

Johnson Controls’ multicolor molding process can accommodate interior parts with a net-zero gap between the two colors.

Still not ready for the growing revolution in molded parts? A world of possibilities awaits today’s adopters of multimolding design, and don’t look now, but those competitors are gaining on you.

Customers want more. It’s the rallying cry across every market where IM designers and molders play a part. These requests aren’t simply about cost reduction anymore; today, they also center on boosting aesthetic appeal for product differentiation and better profit margins, or performing secondary operations such as labeling and assembly in the mold. In all three cases, cost, appeal, and manufacturing efficiency, solutions can be found in multimolding.

Defining ”multimolding” can be daunting, as it often means different things to different people. For the purposes of this article, however, we’re using multimolding as an umbrella term that describes multimaterial, multicomponent, and coinjection processes.

Designers will likely be more than familiar with the creative and ergonomic possibilities of rigid-soft and rigid-rigid material combinations, multiple colors, and decorative effects made possible by multimolding. What they may not realize, however, is that this is an area of design in which it’s essential to know the latest in processing developments to take full advantage of the benefits (see “Why Designers Should Take Note of Processing Advances,” and “Options in Multi,”).

Not New, But Growing
It only appears that multimolding is new. In fact, the process of combining two materials in the mold began in the early 1960s. According to Arburg’s Uwe Haupt, the process was shrouded in secrecy at the time, complete with a lot of “we can’t tell you” practitioners. “While European countries have embraced multimolding more readily, the U.S. is now positioned to take advantage of the technology,” Haupt says. “Even as a niche market, it offers a chance to keep more business in this country.”

Growth categories span the gamut of markets that rely on plastics. Recent application development, according to Rob Banning, president of Trimax LLC, is moving beyond the traditional rigid-soft (hard plastic-TPE) combinations toward plastic-metal, plastic-wood, and plastic-plastic duos and trios.

Products that are seeing more multimolding application include:
Automotive interiors.
Kitchen goods, housewares, and small appliances.
Recreational and sporting goods.
Medical devices.
Caps and closures.
Industrial products such as pump and valve components.
Office products.
Aquatic gear.

Not only are product and market categories taking off, but designers are also finding new ways to use multiple materials for function as well as form. Molding an integral seal, for instance, qualifies not only as a part reduction, but also as a functional improvement over a separate part. TPUs and TPEs are being called on to impart vibration damping to underhood automotive components. Hearing-protection devices benefit from better sound attenuation and fluid sealing with multimolded components. Sensory effects such as added aromas or tactility are more easily incorporated with a second material.

What about the material side? There are many published compatibility charts that show which materials adhere chemically to others, but advances are being made in the multimolding of formerly dissimilar polymers.

Chris Cooper, Gerry DiBattista, Jim Kruger, and Marty Boykin of Bayer MaterialScience recently conducted studies in chemical adhesion between dissimilar polymers. Their results led them to conclude that good adhesion in this category is achieved when the following guidelines are observed:

Materials need to be joined in a freshly molded state, not using insert molding techniques.
The second material should be able to partially melt the substrate, but with a lower or similar melt temperature to avoid washout, bleeding, and deformation.
Avoid the use of mold release unless materials have good compatibility.
In addition, they suggest adding a mechanical joint for better adhesion. In tensile testing of a PC-TPU combination, the design that performed best was a tongue and groove, according to their report.
Fabrics are Multi, Too

A somewhat recent addition to the multimolding repertoire, at least in the United States, was showcased at K 2004 by Demag Plastics Group, Wittmann, and moldmaker PGAM Advanced Technologies. The three companies together created a workcell that produces a rigid substrate with a bonded textile surface for automotive interior applications such as A, B, and C pillars. The prototype cell produces door interiors.

Unlike low-pressure compression systems that are currently used to produce these parts, the cell operates with an IM machine at low pressure. In addition, the system fully automates both textile insertion and molded part removal. It contains a Wittmann Model W643 top-entry servo robot with dual end-of-arm tooling, a Demag ET 350/1250-2300 385-ton molding machine, and a PGAM single-cavity mold. The workcell is currently on display at the PGAM Technical Center.

According to Chris Gassell, a PGAM engineer, the materials’ melt temperatures are what limit the injection pressures. “Right now, we’re molding at about 700 psi, but better gating combinations are helping us to increase pressures without bleed-through,” he says. “Moldfilling analysis gives us some indication of where knitlines are going to be, but doesn’t simulate the action of the textile. For that, we’ve had to create our own models.”

Typical substrate materials include PP, ABS, and PC/ABS. Textiles are typically polyester nonwovens.

While relatively new to North America, this type of processing is more entrenched in Europe, where development began some 17 years ago. It illustrates one of the many frontiers for multimolding.

Automotive Advances
Although the majority of multimaterial design standouts can be found in consumer products, automotive designers are embracing this technology with a vengeance. It offers them the opportunity to add value, reduce cost, eliminate secondary operations, and differentiate products for the OEM customer.

Johnson Controls, for example, debuted a process called CrafTec multicolor injection in January at the Detroit Auto Show. Its goal is to bring the cost of two-color interior automotive parts in line with that of one-color processing by using a proprietary tool design and control system.

Dave Phillips, executive director for business development at JCI, explains that automotive OEM customers have taken multiple colors out of entry-level vehicle interiors to save money. By developing a cost-competitive way to add multicolor back to these vehicles, JCI believes it can change the landscape for its customers. Currently, MCI developers are working with olefinic materials such as PP and TPO, and the results have been well received. In fact, five future vehicle programs planned by two major automakers will make use of interior panels molded by the MCI process.

Multiple market potential
Multimolding applications are cropping up in every market. Download a pdf of tool, packaging, automotive, personal care, and industrial applications. Click here to download the file.

Why designers should take note of processing advances
At this year’s Molding 2005 conference in New Orleans, LA, Foboha sales engineer Lisa Mauro presented the following comparison (download pdf below) between a conventional turntable mold and a stack mold with four stations. While the numbers are based on reality, the application, a two-color mobile phone housing with 6500 production hours annually, is hypothetical. Notice that with only a 25% reduction in cycle time, part production is increased by 267%. Designing this housing for production in the stack mold would take advantage of that productivity and could earn a customer’s devout loyalty, in addition to saving more than $1 million in investment cost. It pays to be aware of the downstream options before creating the CAD file.

http://www.globalwatchonline.com

More News:
  • For October 2006
  • From DTI Globalwatch
  • For Government Departments