Remember building model cars planes as a kid? You had those neat chrome plated ‘metal’ parts, solid color structural parts that you ended up painting and then, you had those cool clear parts for the windshield, lenses, etc. All were injection molded and it was sort of described how they should go together.
Limitations prevented real world scenarios like that, because of the scale of the parts. Molding 1/24th scale replicas was simple. Too bad you couldn’t duplicate that process in real life….until now.
A story in PlasticsNews tells of the search for a lower cost replacement for the windshield for the F-16 fighter jets. The present method for fabricating the windscreens is laminating heated, drape-formed extruded plastic. With a cycle time of several weeks and a high drop-off rate of scrap, costs average $20.000-$40,000 per finished windshield. http://www.plasticsnews.com/headlines2.html?id=03040700401&q=envirotech+molded+products
Enter EnviroTech, a Salt Lake City-based molder specializing in what is referred to as ‘bulk injection molding‘. Bulk molding involves low pressure, high material volume molding, up to 500 lbs.+ per part. EnviroTech tackled this project as a part entry in the Society of Plastics Industry Structural Plastics Division (SPD) conference. “SPD gave two awards to EnviroTech Molded Products Inc. Designed for use on an F-16, the 78-pound canopy took home top honors with the Conference Award. The clear, bubble-free canopy also won for the Industrial & Military category in the 53-entry design contest…” according to PlasticsNews.
The material chosen was polycarbonate, and a custom mold yields optically-correct windshields for the heads-up displays incorporated into the F-16 avionics. EnviroTech molded about 160 of the F-16 windshields in 1993, and they passed Air Force impact tests. According to the article, “Compared with standard injection molding, cycle times are long, at about an hour. But much of that involves slowly removing the part and carefully cleaning the mold between each shot…” Work is progressing on a 200-lb. canopy for the F/A-22 Raptor.
So, don’t dismiss out of hand your need for an injection molded part larger than a few ounces or even a few pounds. The boundaries are being expanded daily to accommodate those larger than normal needs!