One of the things on my ToDo list for some time has been to build vacuum therm-forming machine, so I could produce the vacuum formed 1/8" ABS ABS plastic housings for the ATC in-house, rather than having to drive 40 miles to Silicon Valley and rent a commercial machine. I have finally done that, and here's what it looks like:

First, the framework. The frame is built using a small portion of the several hundred feet of 8020 extrusions and aluminum diamond plate that was given to me by a friend several months back.



The plywood/aluminum vacuum table is at the bottom, supported by the lower square 8020 frame. A second identical frame is at the top, to support the heating elements. Inside the two uprights, you can see the linear guide rails and linear ball-bearing carriages that will allow the frame (now shown) that will support the plastic sheet, and allow it to be moved up, by pneumatic cylinders, to a few inches below the heaters.

The down-facing heater assembly is made of four 24"x5", 1000W carbon-fiber electric heater elements. Each heater is driven by its own PWM for temperature control. The control knobs for these PWMs are on the black control panel at the top of the machine. The wiring is, obviously, temporary, and very much NOT UL-approved.





The vacuum is created by a pair of "vacuum ejectors" which us an air venturi to create a -25 in-Hg vacuum using compressed air. I used an old, failed pressure storage tank from our water well as the vacuum reservoir. The reservoir is connected to the machine through about 7 feet of flexible hose normally used for plumbing a Jacuzzi.



Here is the entire machine. You can see the first formed parts in black near the bottom. This was the very first "pull" done with the macine. The four silver-ish knobs clamp the two halves of the frame that hold the plastic sheet. The whole frame assembly, with the pentagonal black plastic side pieces moves up and down via the pneumatic cylinders.



Operation is simple:

1) Connect air supply to vacuum ejector, to get reservoir evacuated. Full evacuation takes about 15 minutes.
2) Turn on the heaters, and adjust PWMs to obtain an even heat distribution, and heat the entire plastic sheet to just under 350F.
3) Clamp the ABS sheet into the frames, tightening the clamping knobs securely to ensure the sheet does not pull out when stretched over the forms.
4) Once the heaters are up to temperature (just a few minutes), open the air valve to pressurize the pneumatic cylinders, to raise the plastic up under the heaters
5) After two minutes, the plastic should be up to temperature, and sagging 6-10" in the center.
6) Remove the air from the pneumatic cylinders, allowing the clamping frames and now soft plastic to fall back down over the table, and forms.
7) Open the vacuum reservoir to the underside of the plastic, and it is instantly pulled down tightly over the forms.
8) After about 5 seconds, disconnect the vacuum supply.
9) After about 1 minute, the clamping frame can be opened, and the now solid, formed plastic can be removed, and the process completed.

These first parts are, obviously, less than perfect, as the temperature was too low in some places, too high in others, and the vacuum not low enough (due to leaks since corrected), which is part of the reason there are so many "webs". But, once I get all the settings dialed in, the next one should be perfect.



Regards,
Ray L.