Instrumentation and Computer Interface Design for Forward Extrusion Tool

Abstract

This paper describes the instrumentation and computer interface design for an extrusion tool to monitor certain process parameters during forward cold extrusion. A load sensing component, i.e. load cell was designed and manufac- tured to measure the extrusion forces. The load cell consisted of an individual component within a die set mounted in a 200-tonne hydraulic press, designed to study forward extrusion of aluminum alloys. The extrusion load measurement is based upon a number of strain gauges bonded to the central section of the component. The extrusion force was transmitted through a pressure plate to the load sensing component. A linear variable differential transformer (LVDT) was used to provide an output on the punch linear travel during the extrusion process. Both the load cell and the LVDT were cali- brated and a complete programme of cold extrusion of aluminum was carried out to validate the setup. The extrusion process was monitored using personal computer (PC) running LabVIEW software. Much of the research in metal forming operations has fo- cused on experimental studies of die wear and life. By minimising the load and energy used in the extrusion proc- ess, die life is maximised and die wear is maintained at a minimum (1). Various researchers have attempted to esti- mate the energy consumed in the extrusion processes by means of modelling approaches (2 & 3). Other researchers have combined theoretical and experimental studies of fric- tion in metal forming (4 & 5). In metal forming experimenta- tion, determination of the forming loads is critical to the suc- cess of the process. The force required for forming has con- sequences in the design of tooling and fixtures, and also for the machinery used (6). Various methods of measuring the forming loads during processing have been proposed (7-9). In cold extrusion, which is used for the manufacture of spe- cial sections and hollow articles, the material is generally made to flow in the cold condition by the application of high pressure. The high pressures force the material through a cavity enclosed between a punch and a die. Cold extrusion can be used with any material that possesses adequate cold workability - e.g., tin, zinc, copper and its alloys, aluminium and its alloys. Indeed it is for these metals that the process is more widely adopted. Low-carbon soft annealed steel can also be cold extruded. If the product cannot be fully shaped in a single operation, the extrusion process may be per- formed in several stages (10). The relationship between ex- trusion velocity with both temperature distribution within the extruded part and extrusion load has been investigated by a number of researchers (11-15). The extrusion load was shown to increase with extrusion velocity. The magnitude of the increase is larger at higher reduction ratios.