DELANO, MINN. — Custom rotational molding, with tight deadlines and product development capability, stands a world apart from bang-it-out commodity sectors such as tanks, say officials at Minnesota molders Solar Plastics Inc., Pawnee Rotational Molding Co. and Aggressive Industries Inc.
Solar Plastics President Chuck Carlsen said lots of companies call themselves custom molders, but only a few can do complex, engineered parts.
``You can find these guys who are making a square box and saying, `This is custom molding.' That doesn't cut it,'' Carlsen said.
Rod Miller worked for eight years at Solar before he moved to Pawnee as general manager. He said lots of firms claim to be custom rotomolders, but only about 25 percent fall into the ``upper echelon'' of high-quality firms.
Some people outside the industry still consider rotomolding an antiquated process, but custom molders boast that they are pushing the technology forward into computer-aided design and automation. Mirroring the trend in custom injection molding, rotomolders also are doing more assembly, in some cases shipping finished products out the door.
Carlsen said all four of Solar Plastics' factories are electronically linked. Customers send part drawings electronically. Solar engineers develop parts using CAD systems and finite element analysis that predicts performance.
Consultant Glenn Beall, who designs rotomolded parts, said rotomolding is perfect for short custom jobs.
``They can change those molds very rapidly. There's very little downtime. Rotomolders change the mold, they do not have to change the material. So they can actually run 10 parts, then take the mold off and put another one on,'' Beall said.
That means that small one- or two-machine shops can do custom molding. But small firms often are not well-managed, Carlsen said. ``The little guy doesn't know what his costs are,'' he said.
Carlsen said Solar has focused on complex parts to avoid being low-balled by the ``little guy.''
``That's how you differentiate yourself from somebody that's making a square box. We just figure these are markets we're not going to be in,'' he said in an interview at Solar's Delano factory.
The company built the modern factory three years ago.
``We try to put everything in here in terms of secondary operations,'' said Don King, Solar's vice president of operations.
Computer numerically controlled routers — machines that automatically trim off flash and drill holes — have swept through the thermoforming industry. Now rotomolders are buying them. Each of Solar Plastics Inc.'s four factories sport a Motionmaster CNC router. Minneapolis-based Solar has ordered a second router for its Davenport, Iowa, plant. The price for each one: $600,000.
Pawnee also has a CNC router at its plant in Maple Plain, Minn. Minneapolis molder Aggressive Industries also has ordered one.
Beall said it's not always easy to switch from hand finishing to running multiaxis routers. ``It takes companies awhile to build up enough work to keep the machine busy all the time. It also takes awhile to learn how to run all the jobs on that new machine. Sometimes it's easier to continue doing the job by hand,'' he said.
But the payback is big, said Beall of Glenn Beall Plastics Ltd. in Libertyville, Ill. ``The benefits were so overwhelming that now you see two or three of those machines in a thermoforming plant.''
Aggressive Industries has borrowed technology from another plastics sector.
Sales manager Corey Claussen said the firm adapted injection molding management software.
``We bought it primarily because of the scheduling function,'' he said. ``It's helped us considerably.''
Rotomolders also are doing more rapid prototyping work, thanks to new CNC-machined molds. Beall said rotomolding is ideal for making prototypes, then using the same mold for full-scale production.