Thermoforming apparatus

DETAILED DESCRIPTION According to the invention, there is provided apparatus for manufacturing articles by thermoforming in which a preheated sheet of thermoplastics is intermittently fed to present successive preheated portions of the sheet in a work station having a forming tool for forming articles in each successive sheet portion and a stamping tool for co-operating with the forming tool to stamp the formed articles from the sheet portion, in which method and apparatus the forming tool has a plurality of forming dies movable successively and cyclically into the work station for forming articles in respective successive sheet portions, and the stamping tool engages a resilient counter-surface of each forming die to stamp from each sheet portion the articles formed therein by the corresponding die.
Due to the stamping means acting against resilient counter-surfaces on the dies, this surface being preferably slightly wider than the working surfaces of the stamping tool, the sheet material is reliably stamped even if the positioning of the die concerned in the work station varies somewhat from case to case.
Such deviation in positioning are impossible to avoid with movable forming dies.
The apparatus according to the invention thus offers a decisive advantage.
The use of a resilient counter-surface gives, for instance, the advantage that a slight inclination of the stamping tool at the moment of stamping can be taken up.
With the use of known stamping methods using, for instance, stamping strips against a solid surface, a deviation of only a few 100ths of a millimeter may result in incomplete stamping and cause a stop in production in the continuous process.
The apparatus according to the invention also gives the necessary precision in the stamping moment with respect to the position of the stamping tool.
The use of heated stamping tools in the form of stamping strips involves difficulty in obtaining a sufficiently flat surface because of the varying longitudinal expansion caused by heat since it is practically impossible to maintain a constant temperature over the stamping tool