In what could open the door to a sparkling new market for gas-assisted injection molding, Mid-Central Plastics Inc. has started making snowmobile bumpers of long-fiber-reinforced thermoplastics for Arctic Cat Inc.
The front bumpers, which went into production in April, represent an uncommon marriage of long-fiber materials to gas-assisted molding. In the past, reinforced fibers were considered by many industry experts to lack the impact strength needed for a gas-assisted structural part.
That especially was true for parts operating at low winter temperatures, said application development engineer Eric Lee of Polymer Composites Inc., the Winona, Minn., compounder providing the bumper material.
``It's not just that Arctic Cat has started using thermoplastic bumpers,'' Lee said. ``What makes the application so interesting is that it opens up an entirely new market for long-fiber materials in anything that requires the strength of metal or aluminum.''
Arctic Cat, based in Thief River Falls, Minn., is installing the thermoplastic panels on about half its snowmobiles currently in production, said spokeswoman Heather Hauschild. The line includes its redesigned, high-visibility ZR-Series snowcraft, which is used both for competitive racing and recreation, and its economy-minded Jag and Puma models and ZL series.
Two years ago, the leading snowmobile maker began looking for a lighter-weight material for its ZR line, to coincide with its sleek new look. A goal was to create a snowmobile better-suited for racing by increasing the vehicles' power-to-weight ratio, Hauschild said. Formerly, the model's bumpers had been welded from extruded aluminum.
``We aggressively went with some new designs,'' Hauschild said. ``We consider the [ZR Series] the next generation of snowmobiles.''
After some initial failures, Mid-Central was contacted to come up with a more-suitable alternative. The processor, based in West Des Moines, Iowa, tested Polymer Composites' Celstran material, a blend of 60 percent polypropylene and 40 percent glass-reinforced fibers. The fibers are 11 millimeters long — about half an inch.
Mid-Central had used gasassisted technology on other products, including stacked office chairs made of polypropylene. As far as the molder knew, long fibers had never been tried with the gas-assist process, said Mitch Carlson, director of sales and marketing.
In addition, the use of short fibers with the process had produced structural pieces with thin spots caused by inconsistent mold distribution, said Lee with Polymer Composites. The compounder, a business unit of Hoechst Technical Polymers of Summit, N.J., convinced the molder to try the long fibers.
Test results were positive. The hollow bumpers reduced weight by 37 percent compared with aluminum while providing similar uniform strength, Carlson said. In addition, the molding process was much faster than aluminum extrusion — which requires forming, drilling and painting — and led to a 73 percent cost savings, he added.
Hauschild said the plastic bumpers helped decrease the snowmobile's weight 200 pounds, down to 500 pounds.
``That will help us win the power-to-weight race with our competitors,'' said Hauschild of Arctic Cat, which recorded sales of $468 million in 1996, an increase of 16 percent from the previous year.
The molder produces the bumpers on a Cincinnati Milacron press with a clamping force of 500 tons, Carlson said. The process also uses a Cinpres conversion unit to process the gas. Unit volumes for the bumpers were not disclosed.
The company operates 25 injection presses with clamping forces of 85-1,500 tons at its 125,000-square-foot West Des Moines plant.
``I've never heard of anyone using gas-assist with long-fiber materials, especially with hollow-core structural parts,'' Carlson said.
``But there was no smoke and mirrors involved in our process. We used similar equipment as other [molders] and no special nozzles or trade secrets.''
Arctic Cat is considering the use of gas-assist compounds for other structural parts, said David Branscomb, plastics component engineer.
``We use a tremendous amount of plastics, and it will continue to grow,'' he said. ``We set history rolling with plastics for structural materials.''
Mid-Central recorded $22 million in North American injection molding sales during 1996, according to Plastics News' ranking of top injection molders.