BOSTON—Judging by the winners of a recent plastics design competition, gas-assisted injection molding and reaction injection molding seem to be the methods of choice for cutting-edge molding.
Try telling that to Peter Bemis.
Bemis, executive vice president of Bemis Manufacturing Co. in Sheboygan Falls, Wis., is betting on coinjection molding.
Bemis and its Kelch Corp. subsidiary in Cedarburg, Wis., plan to add five more coinjection machines by midsummer, an increase from eight now. And Bemis is considering buying a 6,600-ton coinjection press, which it says would be the world's largest. Bemis declined to release details of that large machine.
In a speech at the Society of the Plastics Industry Inc.'s Structural Plastics Division's recent meeting in Boston, Bemis said: ``A lot of people at this conference are into gas-assisted molding. We've chosen as a company to take a strategy very strongly committed to coinjection molding.''
The process puts recycled material in a core of a molded piece, a prospect that Bemis says is ``one of the things that excites me about coinjection.''
Other industries have been more progressive in using recycled content, and the plastics industry should follow suit, he said. Bemis Co. also picked up two design awards at the SPI event, one for a coinjected John Deere tractor hood.
In a telephone interview, Jeffrey Davis, Kelch's market development manager for new technologies, said the two firms' 13 coinjection machines will range from 500-2,200 tons. He did not say how much the machines will cost, but an official with coinjection press maker Milacron Inc. said the machines cost 20-40 percent more than standard injection molding equipment.
Besides cost, the other significant drawback to coinjection is that it's a relatively untried technology, even though it has been around for years, said Joe McRoskey, president of Co-Mack Technology Inc., in Vista, Calif.
``Coinjection is not perceived to be a conventional and well-known and time-tried process,'' he said. Companies do not want to feel like guinea pigs, McRoskey said.
But automotive original equipment manufacturers are using more coinjection, which is pushing its acceptance, McRoskey said at the SPD event in Boston. Co-Mack is adding two more coinjection machines this year, giving it six total.
Coinjection is more common in Europe, while other types of multicomponent molding have taken off in the United States, said Jim Moore, vice president of sales for plastics technology for Milacron Inc. in Batavia, Ohio.
``The issue is how do you get that same kind of acceptance in coinjection,'' Moore said. ``Computer guys, auto guys, big housings — they kind of have to lead it.''
Coinjection encapsulates one material inside another in a way that completely hides the inner material from view, while other processes like two-shot molding put materials around each other but not always encapsulated.
An engineer at an OEM that is looking seriously at coinjection said the main driver is that coinjection can make parts cheaper.
The official, who asked that he and his company not be identified, said a 10-pound part made from a $2 engineering resin, filled with a 30 percent core made of a 50 cent-a-pound material, would save $4.50 per part.
While the company is in the process of converting several of its molds to coinjection and sees tremendous potential, it still wants to move slowly, the official said. It is concerned about how available coinjection molding equipment is and it wants to test several different core materials for its parts to get leverage against cost fluctuation for any one resin, he said.
Kelch's Davis said there are several other benefits emerging from Bemis' research on coinjection, including the ability to deaden sound and the as-yet-unexplained development that some material combinations appear to be much stronger together.
Bemis made a deck for a lawn mower out of polycarbonate/polybutylene terephthalate and found that adding a core of ABS regrind gave the part twice the maximum load of a PC/PBT monolayer part, Davis said. Using a polypropylene core does not give that benefit.
Davis cautioned against overselling that benefit.
``We're not quite sure why,'' he said. ``That's what's so exciting about this technology. It's like we're trying to split the atom.''