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A glance at a 3D blow molded duct (top) versus a conventional extrusion blow molded version pinpoints two key benefits—minimal flash generation and absence of vulnerable parting lines. (Photo: SIG Kautex)
SIG Kautex claims its patented phased-transition method for sequentially blow molding hard-soft ducts improves the integrity and performance of the joints (Photo: MPC).
Although this continent has been slow to follow Europe’s example, market forces in North America are finally shifting in favor of three-dimensional blow molding. That’s the view of officials at SIG Kautex, currently North America’s sole provider of 3D blow molding technology. These sources say the 3D approach is ideal for molding long, convoluted automotive ducts and pipes.
“New under-hood opportunities for metal and rubber replacement lie on the horizon,” declares Kautex president Wolfgang Meyer, who cites air ducts for turbo-charged diesel (TCD) engines, along with specialty coolant ducting and fuel filler-pipes. 3D blow molding already has made inroads in Europe in those uses as well as in oil filler tubes and seamless door handles (in the Porsche Boxster, for example). Meyer also sees potential for 3D blow molding in off-road vehicle parts, furniture (arm rests and chair legs), and large-appliance plumbing.
SIG officials expect that European successes in 3D technology soon will spill over to the U.S., where until now 3D technology has seen limited use. To spur a takeoff, SIG recently adopted a strategy of going directly to automotive parts makers to educate them about 3D blow molding’s benefits. As part of that effort, SIG recently forged an alliance with Rousch Industries, an engineering support company and automotive specialist near Detroit. SIG also launched collaborative programs with DuPont, Daikin America, and others to develop materials for the 3D process. DuPont has a 15-ton SB lab unit in Europe to aid its development efforts.
Under-hood ducts beckon
SIG introduced 3D equipment a decade ago and has installed some 80 machines—90% of them in Europe. About 70% of those in the field are SB series suction blow molding (SBM) units that use directed air to guide parisons into a segmented mold cavity before blowing. The rest, used for parts with more extreme shapes and radii, are KBS machines that robotically manipulate a parison to place it in the cavity. KBS machines come with either vertical or horizontal clamps.
Jack Tinsley, SIG’s 3D applications director, says the process is adept at making complex parts that eliminate failure-prone parting lines, minimize flash, and enhance wall-thickness uniformity in hollow parts. 3D blow molding also fosters parts integration, which opens avenues for cost cutting through eliminating assembly steps. The technology lends itself to sequential (hard-soft) and multi-layer structures.
Yet 3D blow molding until now has failed to gain traction in the U.S. Among the reasons, say industry sources, are high machine costs—SBM units with twin-head tools now cost $800,000 to $1 million—plus extended cycle times and higher reject rates than in standard extrusion blow molding.
Despite these hurdles, there have been a few early adopters, such as MPC in Walworth, Wis., which operates three SIG Kautex SBM machines. Rousch has installed an SB-8 (8-ton clamp) unit for development purposes. A handful of others use 3D equipment supplied by Japan’s Excel and Placo, but both companies are currently inactive in the U.S. market.
Emerging applications are changing the U.S. outlook for 3D blow molding, says Joe Krupp, SIG’s v.p. of sales for the process. Around 45% of European-built cars now use TCD engines, not the aspirator types used in virtually all U.S. cars. Krupp says Europe’s proclivity for TCD engines is related to their superior driving performance and fuel economy. He expects the U.S. to join the trend in the next few years, and cites Ford’s decision to develop a TCD diesel option for its Focus in 2007. Krupp also notes expanding use of TCD engines in U.S.-built light trucks as another entry point for 3D ducting in the region.
If TCD engines catch on even modestly here, 3D blow molding would benefit mightily. Turbo-chargers compress air and boost air temperature, so longer, more convoluted flow paths for hot- and cold-side ducting are typically required. TCD engines typically require four to five ducts versus the current two to three: Crankcase breathers, air-charger inlets, air-charger returns, and other ducts are targets for 3D blow molding.
“Applications in which parts integration is realized by 3D processing show the biggest payoffs,” adds Randal White, senior technical specialist for 3D molding at DuPont. He cites one TCD duct converted from a seven-piece nylon design to one piece molded of Hytrel TPE with 3D technology. That change reduced part weight 50% and cost 15%. DuPont offers blow moldable grades of nylon 6 and 66 and Zytel HTN high-temperature nylon suitable for TCD ducts.
A second promising application for 3D blow molding is specialty coolant ducting, traditionally made of rubber and metal assemblies. DuPont seeks to replace those with 3D blow molded nylon 66 to reduce weight and part count. Initial uses are set to appear shortly in Europe.
Another emerging frontier for 3D blow molding is air ducts, fuel pipes, and fuel breather and fume tubes for large-engine vehicles. “We find that half our applications for 3D technology are parts for forklifts, tractors, and other construction vehicles,” says Chris Corbett, SBM product engineer at MPC. The company uses its 3D machines for around 40 active part programs. Only one, a U-shaped air duct for a commercial truck with very sharp radii, uses the robotic manipulation capability on one MPC machine.
MPC is active in TCD engine and coolant ducting. For example, Corbett cites a hard-soft Hytrel/PBT duct using DuPont materials that is part of a system included in an accessory kit for a super-charged version of the Mazda Protégé.
SIG’s alliance with Rousch Industries is intended to help bolster 3D blow molding’s credibility with automotive customers. Rousch’s SB-8 unit is being used to make prototype and low-volume production parts. Rousch designs and builds 3D tools in fast turnaround times.
Barrier filler pipes next
A challenging market for 3D blow molding is fuel filler pipes, typically multi-part systems of metal and rubber. One shift favorable to 3D parts is a drive to reposition the fuel tank in what some designers view as the safer mid-section of the car, which would require long, complex filler pipes. Moreover, regulations are being developed to require warranties as long as 15 years on auto emission-control equipment. These would favor use of 3D multi-layer barrier structures in fuel filler pipes as replacements for rust-prone metal. DuPont is proposing a three-layer 3D blow molded solution using its Zenite liquid crystal polymer (LCP) as the inside barrier layer.
Daikin America is pushing a two-layer 3D blow molded structure for fuel filler pipes using its new Neoflon EFEP fluoropolymer. The resin is said to have excellent hydrocarbon barrier and an unusually low melting point. It also coextrudes readily with various resins without requiring an adhesive.
Prospects for 3D blow molding are also improved by refinements in sequential hard-soft-hard molding. For example, SBM units today can achieve right-angle turns within as little as 25% of the part diameter, versus 200% just a few years ago. Also, SIG machines operate both extruders continuously while varying their relative speeds to create a gradual, phased transition between the hard and soft sections. This is said to improve delamination resistance and increase freedom to tailor physical properties of the part.
In addition, DuPont has de-veloped pairs of complementary hard and soft grades of its TPE, nylon, and LCP families for use in sequential ducting.