Apparatus for differential pressure forming an article in a sheet of thermoplastic material having a pair of opposed differential pressure molds at a forming and trimming station moveable between open positions and closed positions engaging opposite sides of the sheet of thermoplastic material for differentially pressure forming an article in the sheet. Mechanism is provided for severing the article from the sheet and includes a pair of opposed trim dies mounted on the molds for movement therewith between spaced apart positions and sheet engaging positions when the molds are moved between open and closed positions. After the part is formed, wedge mechanism is moved transversely of the relative path of travel of the dies for incrementally indexing one of the dies toward the other of the dies to sever the article at the forming and trimming stations.