An improved punch assembly (10) for a punch press comprises a main piston (13) driving a punching tool (11) and an auxiliary piston (17) which can be selectively enabled to cooperate with the main piston (13) in a high force, slow speed mode or disabled to allow the main piston (13) to operate alone in a low force high speed mode. The punch assembly (10) also comprises a pressure transducer (41) and position transducer (25) whose respective outputs are connected to a microprocessor controller for the punch assembly. Operation of the punch press is microprocessor controlled to reduce noise and punch cycle time. A stripper assembly (42-48) is also provided and operates in conjunction with the punching tool (11) under microprocessor control to facilitate tool stripping. The stripper assembly (42-48) can also be used for automatic measuring of work sheet thickness.