The first mold is finished. Welded 4 Plates for each side together and reinforced it with an additional metal-profile. Two bore-holes on each side will hold  screws and springs for applying pressure on the plate. After having the mold on the table, it seemed very heavy. So I will change the metal-profiles a little bit and start a testrun afterward. 

The main challange with the low cost 4 Plate solution is bending of the material during the welding process.