Billet upsetting

The ability to scale up the abc deformation approach to form SMC structure in a large-scale Ti-64 billets was demonstrated via prototype production. The billets (150 mm in diameter and 200 mm in length) solution treated at 1010°C for 0.5 hr followed water cooling were subjected to near-isothermal multi-step forging comprising of specific combination of multiple upset/drawing operations [3] at the thermo-mechanical conditions provided formation of submicron-sized microstructure. 

The billet is upsetting and pressure rises to its peak value. 

A considerably improved design of this type of press is shown in Fig. 89. It is equipped with separate return devices for crosshead and piercer crosshead and an advancing device for the main plunger. This renders possible to advance the ram with the mandrel retracted, whereas up to that time the piercer crosshead with the mandrel was advanced first thus entraining the crosshead. This improvement allows for the billet to be upset in the container prior to piercing and for more accurate wall thicknesses in the tubing, because the mandrel can no longer deflect in the upward direction (see p. 146). 

Prior to piercing, the billet must therefore be upset so that it fills the container space completely in order to do that the face of the dummy-... 

In order to obtain accurate wall thicknesses and clean surfaces when making tubes from difficultly extrudable alloys, it is appropriate to use short billets whose surfaces are machined and which have been provided with a central hole. Extrusion is performed with floating mandrel to ensure a smooth inside of the tube furthermore the mandrel is changed after each extrusion cycle. Upsetting is not necessary, as the billet lies concentrically in the container bore after the mandrel has been inserted. In this case extrusion is carried out on the without shell method. 

The smooth fractures are as a rule caused by mechanical overstressing, if, for example, the billet is not properly upset in the container or if the billet is unevenly heated, in which case considerable bending forces bear upon the mandrel (see Fig. 120). Under such circumstances it may happen that a mandrel withstands 100 to 200 extrusions only, w hile its life - under more favorable conditions - might be ten times as long. This shows the immense importance of a uniform heating of the billet and of... 

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