By Jan H. Schut
The past three to six years have seen an astonishing burst of creativity in new multi-process, or hybrid, injection molding for large durable parts, especially automotive. Ignore the fact that some of these new machine concepts aren’t even half injection molding anymore. Big global automotive and electronics companies are buying into the idea and pushing developments in Europe and the Far East (not so far in North America). The concept started with large multi-shot parts made on rotating molds, which saved dramatically in cycle time and material cost. Then other processes were added to injection molding to make unusual high volume composites with even more dramatic potential weight and cost savings.
Multi-process molding combines thermoplastic injection with a wide range of other plastic processes in one machine and one mold, typically a rotary mold. Developmental “multi-process” molding machines, for example, combine injection molding with compression, foam, reaction injection molding (RIM), PUR foaming, glass-reinforced compounding, continuous fiber reinforcement, and vacuum forming. These processes have been serially combined for low volume composite parts like sports equipment for years, but combining them into one high-output machine is new.
A series of parts for Hyundai-Kia Automotive Group in Seoul, Korea (www.kia.com), shows how multi-process is evolving. When Hyundai made a soft-touch central console for a 2011 CUV using two-shot injection molding with a rotary mold, cycle time dropped from two hours to two minutes, and the part cost 20% less than the previous painted one. The two-shot technology, called “Dolphin,” was developed by automotive tool maker Georg Kaufmann Formenbau AG in Busslingen, Switzerland (www.gktool.ch), together with Engel Austria GmbH in Schwertberg, Austria (www.engelglobal.com).
Dolphin, which was launched in 2006, was also used for an interior desk part for a 2011 Mercedes Actros long-haul truck. The technology used two injection presses, sequential pressure, and rotary molds to form three layers with two materials: first a shot of rigid PC/ABS for the core, then a shot of solid, grained TPE for the skin with thickness adjusted by cooling time, then the same shot of TPE for microcellular foam in between, using MuCell technology from Trexel Inc., Wilmington, MA (www.trexel.com). The Mercedes truck part, which won an SPE Automotive Division prize in 2012, reduced process steps from eight to two and cost 25% less than the previous part.
Molder ABC Group Inc., Toronto, Ont. (www.abcgroupinc.com) and Delta Tooling Co., Auburn Hills, MI (www.deltatechgroup.com), also developed a patented alternative injection molding technology (U.S. Pat. # 8048347) for Ford Motor Co. Ford calls it SPT (structural plastic technology); Delta calls it STPO (structural thermoplastic polyolefin). By either name, the process molded a structural foam TPO rocker panel for a 2013 Ford Edge Sport model. First TPO with endothermic blowing agent was injected into the mold with nitrogen gas assist to fill thin-walled sections of the part first with solid TPO and get a paintable Class A surface. Then fill pressure was reduced, allowing foam to expand in thicker areas of the part forming a rigid cellular structure. Both Dolphin and SPT injection molding technologies form solid and foamed structures from the same shot in the same tool—they’re multi-step, but not multi-process.
Kaufmann’s next step was the patented Varysoft process (U.S. Pat. # 8512616), developed with Hyundai and introduced at an open house in 2010. Varysoft molded a demo instrument panel with three shots and three presses instead of two: first glass-filled ABS/PC substrate, then soft TPO skin, then TPE foam in between.
The next Varysoft technology, in development for Hyundai, goes further still. Instead of three shots, it uses three processes in a two-level rotary stack mold. Demonstrated by Engel at K 2013 in Germany, it makes the soft-touch surface with TPO film heated with an IR heater on top of the machine, then vacuum formed for surface texture on the upper level of the rotary mold. In a separate cavity the glass-filled ABS/PC substrate is injection/compression molded using MuCell microcellular foam. (MuCell typically shortens cooling time, uses about a third less clamp force, and saves about 10% in material.) The TPO skin and ABS/PC substrate are then brought together. The tool rotates 180 degrees, and the contoured space between skin and substrate is filled with PUR foam, injected with PUR foaming equipment from Hennecke GmbH, St. Augustin, Germany (www.hennecke.com). The demo part thus combines vacuum forming, thermoplastic injection/compression molding, and PUR foaming.
SOMEONE HAS TO BE FIRST
A seat pan for a 2013 Opel Astra sedan is believed to be the first multi-process part actually in commercial series production. It’s made with an unusual continuous fiber composite technology from Reinert Kunststofftechnik GmbH in Bissingen an der Teck, Germany (www.reinert-kunststofftechnik.de). The technology combines two processes in one complex linear mold with sliders, built by Maier Formenbau GmbH, also in Bissingen (www.maier-formenbau.de). First, a precut continuous glass fiber insert, pre-impregnated with nylon, is heated with an IR heater inside the mold. When the prepreg is hot and soft, something like a wet towel, it’s formed between the mold halves. Then it’s over-molded with short-glass-filled PA6 to fill out the part geometry. The same tool shapes the hot prepreg and overmolds it, achieving a weld-like bond between the two materials. The PA6 composite replaces a heavier conventional glass-filled plastic part (PA6 with 50% glass fiber and 2.5 mm thick) with 45% weight saving. Reinert also uses the technology to combine PP-impregnated fiber prepregs with glass-filled PP.
Composite molding machines also use rapid mold heating and cooling, such as “water/water” molds with heating and cooling lines and induction heated molds from RocTool S.A., Le Bourget du Lac, France (www.roctool.com), to produce glossy Class A finishes over fiber reinforcement and foam. At K 2013, Engel showed a combination of RocTool induction heated molds and woven carbon-fiber reinforcement to mold a demo case for an electronic tablet.
The demonstration took pre-pressed carbon-fiber sheets, inserted them into a cavity and over-molded them with high-gloss methyl methacrylate ABS for a glossy piano finish over woven fiber. Ju Teng International Holdings Ltd., Hong Kong (www.juteng.com.hk), recently opened a composite molding plant in China, planned for 100 presses using RocTool induction heated molds to produce cases for electronic tablets and cell phones that combine fiber with thin walls (down to 0.5 mm) and high surface requirements.
RocTool’s induction heated molds are also used to achieve Class A piano black surfaces such as multi-shot molding of an air vent control part for the dashboard of a BMW 320, made by Fischer Automotive Systems GmbH in Horb am Neckar, Germany (www.fischer-automotive-systems.de). The unpainted part combines matt and high gloss surfaces. RocTool induction molds are used with MuCell microcellular foam for the cover of an automotive entertainment system molded by Groupe Plastivaloire, Langeais, France (www.groupe-plastivaloire.com), for Johnson Controls GmbH in Germany (www.johnsoncontrols.com).