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A mandrel-free hot-spinning was developed as a near-net-shape titanium alloy plate forming technique. In this work, a Ti-6Al-4V alloy conical product with a wall angle of 34 degrees and 170mm height was formed from a large size Ti-6Al-4V plate (890∼920mm dia. × 30mm thick). The product was characterized metallurgically and mechanical properties were measured, and the shape of formed products was investigated. It was found that the mandrel-free hot-spinning is able to form a large size titanium alloy plate. Material properties including tensile strength and microstructure of the formed products satisfied the material specifications. Fatigue stress of the formed product was higher than that of the typical Ti-6Al-4V material. For a further improvement, a forming method using pre-formed material was proposed and which was successfully conducted with two types of preforms and found to be effective in the forming process.

A comprehensive study on the evaluation of mill designs was carried out for three types of multiroll mill for wire rolling by using both prototype mills and numerical experiments. The laboratory experiments were carried out in order to examine both the deformation and loading characteristics of two-, three-and four-roll mills using a set of rolls of the same diameter. As a result, the data allow a direct comparison of the rolling characteristics among the three types of mill, which is not found in previous work. The analytical results showed a good matching with the experimental results, and evaluation was then carried out on the three mills. It has been found that the four-roll mill ensures the highest reduction and the two-roll mill the lowest reduction under the restriction that certain dimensional precision of the rolled wire be maintained. This tendency becomes greater as wire diameter decreases and in practice it is recommended that a four-roll mill equipped with smalldiameter rolls be used when rolling small-diameter wire. As regarding the loading characteristics, similar conclusions apply. Finally, domains were determined where four-roll mills show their marked superiority.

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