The Applied Research of Cryogenic Metalworking

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In applying the cryogenic metalworking to sheet metalworking, wire drawing and sheet rolling, the surrounding apparatus and technology; namely the cooling and carrying conditions of metal, the material and construction of die set, the post-treatment of worked products, etc; are investigated here.1. Sheet metalworkingThe hydraulic press machine having the capacity of 10 ton is used for the experiment. After cooling pure aluminium and corrosion-resistance aluminium alloy sheets of 0.5mm in thickness at the temperature of liquid nitrogen (LN), cryogenic bulging is carried out in the interval of 50 mm using transfer die set. By analysing the change of temperature before and after metalworking, theoretically and experimentally, it is clarified that the most appropriate structure of die set is the combination of die cooling by LN and blowing-up of LN. SUS 304 is useful for die material.2. Wire drawingPure copper and some kinds of copper alloys are used for wire drawing experiment. Frictional coefficient in cryogenic wire drawing is 1/2-1/3 of that in room temperature drawing, as a result of ice lubrication. Cryogenically drawn wires bring the strengthening of about 10 kgf. <mm^(-2)> in comparing with the strength of room-temperature drawn wires. This can be explained by the increase of dislocation and the formation of fine cell structure. For precipitation type alloys, this is useful for decreasing the precipitation temperature.3. Sheet rollingPure aluminium, corrosion-resistance aluminium alloy sheets are used for rolling experiment in using small 2 high mill. The change of frictional coefficient is calculated by measuring rolling load and forward slip. Cryogenically rolled sheets bring the strengthening of about 10% in comparing with the strength of room-temperature rolled sheets. This can be explained by the increase of dislocation and the formation of fine cell structure.