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Generalized approach to the choice of lubricant for hot isothermal forging of aluminium alloys

Petrov P.

Computer Methods in Materials Science

2007

Vol. 7, No. 1

106-111

Isothermal forging is a technological process of hot bulk forging which is related to definite temperatures of dies and workpiece heating. Usually, isothermal forging is performed with the help of low-velocity forging equipment like hydraulic presses. So that the maximum value of die velocity is not more than 5 mm/s. To avoid die chilling the dies are heated up to approximately the same temperature as the workpiece. In this range, conventional die materials for hot bulk forging cannot undergo the significant loss of strength or hardness. So, special tool materials should be applied for dies production. The development of any technological process of bulk forging and namely isothermal one requires the solution of the following tasks: 1) choose the forging method or forming process (forging with/without flash); 2) design a forging part in accordance with a machined part; 3) determine the necessary amount of forging operations; 4) determine the size and shape of workpiece; 5) design forging dies; 6) choose the suitable press-forging equipment and lubrication; 7) try out experimentally the developed technology and if necessary make some modifications. In most cases, the application of forging in isothermal conditions means the production of a near net shape forging. Design of near net shape forging part according to a machined one can be carried out with the help of some recommendations which are based on practical experience of forging. One of the technological parameters which has a strong influence the quality of a near net shape forging is the type of lubricant. The choice of a lubricant for isothermal forging is major task, especially in case of aluminium alloys deformation. The isothermal forging of Al-alloys belongs to the forging processes in which the slight increase in contact friction affects on the material flow, the quality of the forgings and gives rise to increase in deformation load. The efficiency of any lubricant can be estimated by at least three criteria: 1) the lubricant should have good tribological properties; 2) the lubricant should have good heat-shielding properties; 3) the lubricant should produce little or no smoke. So that, some laboratory tests should be carried out. The present paper is a generalization of the results which were obtained for the last three years. It implies the investigations of interfacial friction in hot isothermal deformation of such non-ferrous material as Al-Mn, Al-Mg, Al-Cu-Mg and Al-Cu-Mg-Fe-Ni aluminium alloys. Two completely different types of lubricant were used for the research on. Wide range of temperatures was observed. Moreover, the hydraulic press and screw press were used for the deformation of the samples of aluminium alloys under study. The tribological properties of lubricants were determined with the help of ring upsetting technique. The sets of calibration curves were drawn. Each set of calibration curves corresponds to the definite type of aluminium alloy as well as definite conditions of deformation. Some practical recommendations were given.

Uogólnienie wyników uzyskanych na przestrzeni czterech nich lat (Petrov et al., 2003, 2004, 2005, 2006) z zakresu i wpływu tarcia międzyfazowego podczas odkształcenia na gorąco jest tematem niniejszej publikacji. W pracy analizowano materiały nieżelazne na bazie aluminium: Al-Mn (AA3003), Al-Mg (A95456), Al-Cu-Mg (AA2024) i Al-Cu-Mg-Fe-Ni (A92618). Analizę prowadzono dla szerokiego zakresu temperatur i dwóch różnych smarów z wykorzystaniem prasy hydraulicznej. Własności trybologiczne wykorzystanych smarów określono bazując na wynikach spęczania pierścieni. W pracy wykreślono krzywe wzorcowe odpowiadające konkretnym warunkom odkształcenia i danemu stopowi Al. Zamieszczono również uwagi praktyczne.