I would like to know if the following is possible:
Can you thermoform a part WITHOUT a vacuum pump by only using a top and bottom plate to form the desired shape (similiar to an injection moulding tool but without the injecting/ejection).
The material I would like to form is 4 mm thick ABS and the draw depth is approximately 50 mm. The finished part size is fairly large (1200 x 800 mm). The sheet would still be heated using normal vacuum forming methods.
That's a definite maybe. If the shape is agreeable, and you have enough material stretch from the heating and gravity, then it could work. But, more likely, is that it won't stretch the exact way you want and be a little ugly. With enough heat and pressure, will still work, but without those it could be wrinkled or even lumpy in spots.
I can only assume the no vaccum is because you don't want holes in the mold? You might use a bottom mold and a silicone blanket to make a vacuum press like people do for veneers. A little fabric top and bottom to allow air pockets to evacuate would be advisable too.
Thanks very much for your input. The reason I asked about top and bottom plates is that we have hydraulic presses in our facility and don't have access to vacuum forming machinery. But I value what you have said and will probably look at developing a vacuum former if the need arises.