What Could The Mold Of Tomorrow Be Like?What Could The Mold Of Tomorrow Be Like?
January 31, 2003
If one can look into the future, perhaps out to 2030, I’m sure both the world and injection molds will be different than today. What will an injection mold look like? I’m uncertain if anyone knows the answer, but some features just might turn out to be similar to ideas that I have brainstormed in the past.
Molds might be built by laser-hobbing the cavities, using patterns developed by CAD solid models. Stainless-steel cavity materials, with thermal conductivity ratings on the order of 200 Btu, and hardnesses from 65 to 70 Rockwell, would not require benching and/or polishing. The mold database could be generated over lunch, and the cavities would be cast in the afternoon.
Cores could be cut by high-speed laser-machining at 10 m/s, from high-thermal-conductivity copper alloys in the 60 to 65 HRc range. Laser-drilling and laser-tapping could create ejector-pin holes and mounting holes and do engraving. Side actions and/or movements could be made by either method, depending if the detail is standing or recessed, and they could be effortlessly guided by air bearings.
Cooling channels for high-pressure conductive gasses would surround the plastic-forming cavity and core detail. The gasses could both heat the molding surfaces, on plastic injection, and cool the surfaces by pressurization and forcing the gas to turn to a liquid, for part ejection.
Other inert gasses could be introduced into the runnerless system to form an insulation layer between the mold steel and plastic. The insulation layer would eliminate the need for maintaining plastic temperature, which in turn would eliminate the need for heating elements and a manifold.
The same gasses could contain the colorant for the plastic, eliminating the need for painting of items such as automotive body panels and interior trim. The same gasses could be used to assist in forcing the plastic away from the cavity walls, breaking the vacuum on cavity surfaces, and allow the cooling cycle to be even shorter.
The core side (ejector half) could also use the gasses to break the part from the male surfaces just after the mold starts to separate. Using pressure on full surfaces, as opposed to localized ejector points, yields less overall pressure and reduced forces, allowing the cycle time to be trimmed further.
Using flexible, self-healing, memory-return mold materials, gates could be 10 times greater than the wall thickness. The steel’s memory would close the gate at the end of ejection. Pack and hold times could be eliminated as the gasses could continue to apply pressure to the plastic during the cooling portion of the cycle. The reduction in fill times, elimination of shear heat, and subsequent removal of shear thinning and stress all yield a higher-quality part.
Using thermal sensors, applied with a specialized plating process, feedback from the advancing melt front could be interpreted by a microprocessor, allowing for varying injection speeds and profiles. Additional information could provide feedback for localized heating or cooling of the molding surfaces, providing more even temperatures.
Leader pins and bushings, acting as both guiding and interlocking mechanisms, would insure precise alignment and rapid, smooth mold opening and closing. The same mechanisms could provide locking, eliminating the heavy clamp mechanisms on the molding machine.
The best part of the mold of the future is that lead times will be measured in hours, cycle times in tenths of seconds, and the accuracy of mold steel in nanometers. Multiple-cavity molds would basically cost the same as single-cavity molds, with only additional costs for materials.
So, will my vision become reality? Time will tell, but many things change with time. After all, when I first got into mold engineering, we calculated shrink with a slide rule — there weren’t calculators then. I’ll probably be working on that high-pressure gas concept, too.
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