Re: What's on your workbench?
Not really on the bench because it is too big...
IT WORKS!
OK, the vacuum pump is attached to the vacuum degassing chamber which is then attached to the former chamber. The repressurisation valves allow suction to be isolated between the chambers. So what would happen is, the rig is set up as shown (paper removed of course), then suction is applied to get a seal. That 10mm (yes 10mm) perspex bowed in today. It was almost scary.
So once the plastic is under about 10"HG, the valve between the two chambers is closed off leaving the plastic bowed. The heater is then placed on top.
as soon as the plastic softens, it will be pulled down. By the time the plastic is hot, the degassing chamber would have been taken to a full 30"Hg ready to apply sudden surge of suction to the heated plastic. It will have no choice but to be pulled into the tool.
Next up is the heater assembly and then the rubber matting for thero-forming.
Exciting stuff.
There are two way to do this -
1. Traditional male tool vacuum forming where the plastic covers the entire rig (as shown). Normally there is a very tight time window for the plastic to be heated, pulled down and for all the air to be sucked out in order to make the process work. As a result, even pro vacuum form systems are prone to fail if the plastic is too thick, not hot enough or a seal can't be made.
2. Thermo forming where I use a silicone sheet as a membrane to complete the seal. This method requires the parts to be heated externally (I am in the process of modding the heater to work as an oven as well as top loading heat source) and are then placed in the tool whilst still hot. The membrane seals of the form and pulls the hot plastic into the shape of the tool to make the part. The real magic here is that the plastic is only thermally shaped, not stretched, so it does not lose any thickness. Also the parts are pre-cut to size and sometimes even shape meaning it more economic as it uses less plastic to do the same job.
I've been playing with vacuum forming for a few years now and I have done some good pulls and had a heap of fails.
So I have designed this rig to take the time/heat/seal fail factors out. The key reason I am using female tooling is that the seal can be made whilst the plastic is still cold.
This removes the need to rush to make a seal before the plastic begins to cool. This is why so many DIY vacuum forms fail.
Once the seal is made, the plastic can be heated from above. Traditionally, heated plastic forms a bulge towards the heater. If it touches, game over. In my case, this can not ever happen. Because a seal with suction has already been made when cold, as soon as the plastic is hot enough to be formed, suction pulls the plastic down away from the heater and into the tool.
I am using both a surge tank and vacuum pump, not a vacuum cleaner. I will therefore have greater than 6x the suction of a vacuum cleaner to evacuate the air and form the plastic. Unlike traditional vacuum forming, the heater in my system remains on during the process ensuring the plastic can not cool down whilst it is being formed.
