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Winning designs in structural plastics

June 1, 1997

5 Min Read
Winning designs in structural plastics

For those who wondered if gas assist was just another blip on the injection molding radar, the evidence on display at this year's Structural Plastics Conference suggests otherwise. Of the 80 products

in this year's design competition, 21 parts were molded wholly or partially with gas assist, tied with low-pressure structural foam, second only to solid-wall molding and up 10 from last year's total. This included everything from a large utility shed roof panel to an infant carrier to auto roof rails and minivan door handles.

Joe Bergen, president and CEO of Sajar Plastics (Middlefield, OH), says he thinks gas-assist molding has proven itself as a legitimate process, leading many molders to try the gas option. He also credits the decrease in litigation surrounding gas-assist technology and its licensees. "I think molders are more relaxed, more willing to try gas assist, less worried about who's suing whom," he says.

As in years past, the leading material of choice for parts in the competition was PPO/PPE, although it is not nearly as dominant as it was in past competitions. Rounding out the field were the usual suspects: polycarbonate, polyethylene, PC/ABS, ABS, urethane, and nylon.

This year's winners that were injection molded are pictured and described on these pages.

Conference Award

Instrument PanelInstrument panel. The instrument panel above, designed for Freightliner commercial trucks, is a unique blend of materials and processes - one that takes advantage of almost every molding process you can think of. It includes 16 plain injection molded parts, 10 counterpressure structural foam parts, two conventional structural foam parts, and six gas-assisted parts. Off-the-shelf parts include HVAC ducts, louvers, mounting hardware, and floor lights. The four main assemblies are bonded together with an acrylic adhesive. Consolidated Metco (Bryson City, NC) is the molder of the panel. Tom Simon, sales and marketing director at the Metco Plastics Div., says Freightliner's president saw and liked the "feel" of the dash on the model of the panel. To replicate that appearance, texture on the dash is molded in and then covered with a coat of soft-touch paint. Materials include ABS and PC/ABS for parts above the knee line. The panel also includes a bevy of extras, such as a retractable built-in trash can and scads of cup holders.

Building and Construction

SledgehammerSledgehammer. In what may be one of the most heavy duty applications of an injection molded part, Lifetime Tool (Madison Heights, MI) designed the integrally molded sledgehammers pictured on p. 46 to withstand heat, cold, and repetitive beatings. The material is Hivalloy, a filler-less engineering grade PP alloy from Montell. Dennis Siekierski, president of Lifetime Tool, says the 8-, 10-, or 12-lb heads are insert molded in a 700-ton press, giving the sledgehammer its one-piece design, an industry first. The plastic also attempts to overcome such OSHA hot buttons as cracking, splintering, and vibrating - all chronically associated with wood- or fiberglass-handled versions. And if it performs as well in the real world as it did in tests, the sledgehammer should prove a success. Siekierski says he tried more than 100 materials before settling on the Hivalloy. In third-party tests, the hammer passed 100 hits at 180F, Ð20F, and Ð40F, outperforming conventional designs.


Bristle squareBristle square. Gerber Garment Technology (Tolland, CT) makes a fabric cutter, the bed of which is composed of several of the 4-by-4-inch bristle squares pictured above. Each square needs to support the cut fabric, withstand vacuum pressure, and endure impact loading from a cutting cam device. Alliance Precision Plastics (Rochester, NY) made the complex mold and molds the part. Each square is molded from nylon and has 2450 bristles to support the cloth, and 1021 holes in the base through which the vacuum is pulled. Because the bristles are not indestructible, four feet on the bottom of each square snapfit to tracks built into the cutter, making replacement relatively simple and inexpensive.

Consumer Products

MugsMug. Coinjection molding and a proprietary phase change material provided by Phase Change Laboratories (San Diego) make the above mug a winner for designer, toolmaker, and molder Co-Mack Technology, based in Vista, CA. The inner and outer skin is molded from polypropylene, sandwiching the phase change material in between. Co-Mack reports that the phase change material holds temperature for more than an hour.


Pool PanelFlexible pool panel. After you win big bucks in the lottery and when you're ready to install your new swimming pool, be sure to check out the flexible pool panels from Horizon Plastics (Cobourg, ON) pictured at left. The living hinges in these structural foam molded panels allow pool designs to follow contours and shapes of almost any ilk. These 42-by-48-inch panels are molded from polypropylene, mainly to provide cold-weather impact for the living hinge. The hinges occur vertically every 4 inches to allow frequent twists and turns within one panel. Strips, drilled at different lengths, are attached horizontally to set the curve of each panel.


Intake ductIntake duct. To the untrained eye, this intake duct may seem pedestrian, but the beauty is in the detail. Designed by Fuji Heavy Industry and molded in Japan, this duct is molded not by lost core, but via gas assist using 40 percent glass-filled MXD6 nylon. The threads are insert molded, and postmold machining is used to open the ends of the duct. Fuji reports that it achieved a smooth finish, consistent wall thickness, and no hollow sections with a patent-pending gas-assist process.

Computers and Business Equipment

Business equipmentBusiness equipment. The label for this complex equipment is rather generic because manufacturer Lexmark International (Lexington, KY) was playing its cards close to its vest at the Structural Plastics Conference. That does not, however, detract from the significance of the design. The assembly consists of three parts, fastened to each other via molded-in mating features and thread-cutting screws.

This PPO/PPE structure uses 27 percent glass filler and 13 percent mineral filler. In the end, the frame assembly contains 65 machine interfaces and controls the positioning of all of the subsystems in the machine. Because there are only three primary parts, critical tolerances are minimized and machine-to-machine variation is reduced.

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