Apparatus for sealing an end portion of a tubular workpiece in a mold for internal high-pressure forming

Apparatus for sealing an end portion of a tubular workpiece placed in a mold for internal high-pressure shaping of the workpiece, said apparatus comprising a pressure application unit including a housing having a compartment, a piston constructed for displacement solely by admission of hydraulic fluid from the pressure source and accompanying increase in pressure within the compartment and having a piston face on a compartment-proximal end and interacting with a mandrel on a compartment-distal end, and a check valve, disposed in an axial passageway of the piston between the compartment and an interior space of the workpiece, for controlling a flow of hydraulic fluid under pressure from the pressure compartment to th interior space such that the piston is moveable in a first phase during pressure buildup in the compartment in a direction of the workpiece to urge an end face of the mandrel into a flat engagement against a confronting end face of the tubular workpiece, thereby sealing an interior of the tubular workpiece without projecting into the tubular workpiece, and hydraulic fluid is allowed to flow in a second phase into the interior space of the workpiece, as the pressure in the compartment exceeds a closing force of the check valve, to carry out a shaping operation of the workpiece while the mandrel is maintained in sealing contact against the end face of the tubular workpiece.

A mold for internal high-pressure forming of a tubular workpiece, comprising:

• a pair of dies defining a space for receiving a workplace;
• and
• a pressure application unit for sealing an end portion of the workpiece, when placed in the space between the dies, and applying an internal hydraulic pressure in an interior space of the workpiece, said pressure application unit including a housing having a compartment, a piston constructed for displacement solely by admission of hydraulic fluid from a pressure source and accompanying increase in pressure within the compartment and having a piston face on a compartment-proximal end and interacting with a mandrel on a compartment-distal end, and a check valve, disposed in an axial passageway of the piston between the compartment and an interior space of the workpiece, for controlling a flow of hydraulic fluid under pressure from the pressure compartment to the interior space such that the piston is moveable in a first phase, during pressure buildup in the compartment in a direction of the workpiece to urge an end face of the mandrel into a flat engagement against a confronting end face of the tubular workpiece, thereby sealing an interior of the tubular workpiece without projecting into the tubular workpiece, and hydraulic fluid is allowed to flow in a second phase into the interior space of the workpiece, as the pressure in the compartment exceeds a closing force of the check valve, to carry out a shaping operation of the workpiece while the mandrel is maintained in sealing contact against the end face of the tubular workpiece.