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B piping sink hole at the end of billet under direct

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Unformatted text preview: let under direct extrusion. c) Surface cracking: High part temperature due to low extrusion speed and high strain rates. Process Variables in Direct Extrusion Figure 15.4 Process variables in direct extrusion. The die angle, reduction in cross-section, extrusion speed, billet temperature, and lubrication all affect the extrusion pressure. Extrusion Analysis Extrusion ratio, rx = Ao Af Assuming all sections are circular, ideal deformation, no friction, no redundant work: = ln rx p = Y f ln rx Ram pressure p = Y f (a + b ln rx ) Taking into account friction, where a =0.8 and b =1.2 to 1.5. Extrusion Analysis For direct extrusion, additional pressure, pf, required by the extruder to overcome the wall friction is related as p f Do2 follows: 4 = pcDo L For the worst case that the friction shear stress at the wall equals to the shear yield strength of the work pc = Ys metal: p f = Yf 2L Do The additional pressure: The total ram pressure: The power required: 2L p = Yf x + Do P = Fv Extrusion Dies For the case of non-circular extruded section, a shape factor has to be introduced: C K x = 0.98 + 0.02 x C c 2.25 where Kx = shape factor Cx = perimeter of...
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