PRODUCING PRECISION TITANIUM-ALLOY ARTIFICIAL HEART VALVE STAMPINGS

摘要

In the isothermal stamping of the titanium alloys, in addition to the regime in which the temperatures of the die and the blank are specified to be the same, which creates the well-known advantages of the process, there are also the regimes in which the temperatures of the die and of the blank that is placed in the die are different. This stamping process is termed quasi-isothermal.If the stamped blank has high narrow ribs on a relatively thin sheet, i.e., when it is desirable to maximally force the metal to flow into the slot while having minimal shrinkage on the sheet, and also in the case when it is not possible to heat the metal to the stamping temperature in the furnace because of significant grain growth (this is particularly important for the #alpha#-alloys) or for reduction of the thickness of the oxide layer on the surface when heating the blank, we use the process in which the temperature of the die exceeds the temperature of the blank. Being heated from the die, the surface layers of the blank acquire increased plasticity in comparison with the core, which, on the one hand, facilitates the flow of the blank into the slot without significant deformation of the material in the central zone of the blank, i.e., the shrinkage on the sheet of the blank on the side opposite the rib decreases. On the other hand, in this stamping process the grain in the metal that is heated from the die is not able to grow during the time of deformation, which has a favorable influence on the structure of the blank. In this case the oxidation of the surface of the blank that is being stamped decreases, thanks to which the die service life increases because of the absence of the scratches that are caused by the oxide scale.