I'll try to shortly explain how I made the "molded" thorax (upper body plate).
It's a very easy method and you'll need very few tools. I used some different hammer's, a heat gun and high pressure air for fast cooling (not necessary but useful). A picture of the tools:
At first I used a bandsaw to saw out the lower and upper body plates:
I'm sorry for not having any pictures when I did the actual process.
Next step in the process was to make a solid frame for holding the body plate in a fixed position (especially the coxa positions). I used 5mm aluminium to make the frame. Then I placed the frame onto two wood stick I had laying around:
Then I mounted the upper body plate with the bottom side upwards onto the frame. After that I started to heat up the body plate (ABS plastic) with the heating gun. You've to heat it alot until a critical point when the plastic starts to get very soft. At this point you can easily shape it using different tools like a hammer etc. I used the pressured air for fast coolant.
This picture show my first attempt that didn't go so very well because I was stupid enough to drill the holes for the head section before I started the "molding" process.
Anyway, I think this gives you a little picture of how I did it.