Computer-monitored hydraulic bulging of tubes

Abstract

A hydraulic bulging machine with independent pressure and axial-force control has been designed and constructed. This machine consists of a horizontal press frame with two opposed hydraulic units at the ends of two sliding units carrying the die halves. Two sets of three hydraulic cylinders open and close the die halves containing the tube to be bulged. Once the die halves are closed, two differential pistons operating in two pressure vessels attached to the end plates move in and seal the tube. Then hydraulic pressure is applied to the tube through the central bore of one of the differential pistons. Thereafter, by actuating another hydraulic circuit, the pistons apply an axial compressive force on the tube. During the bulging process, the hydraulic pressure inside the tube and the axial force on the tube can be varied independently. When the bulging is complete, the tube is de-pressurized, the pistons withdrawn, the die halves opened and the bulged tube removed. Initially, a PLC was used to control the internal hydraulic pressure, the axial load, compression of the tube and the operating sequence of the process, but experiments conducted with this control system in place indicated that closer control of the process parameters was needed. Recently, a personal computer together with a data logger was used to monitor the axial force and the hydraulic pressure. Results of the bulging experiments conducted with this set-up are reported in this paper.