3. Extrusion Extrusion

1 ME477 Fall 2004 Kwon113. Extrusion A compressive forming process in which the work metal is forced to go through a die opening in a shape of desirable cross-section. Direct vs. Indirect Hot, warm and cold Solid, Hollow and Semi-hallow parts Continuous vs. Discrete Advantage Variety of shapes but a uniform cross-section no waste of material2workbilletExtrusionv, FcontainerDieRamDirect Extrusion (Forward Extrusion )v, FIndirect Extrusion (Backward or Reverse)3 Extrusion Analysis I Reduction ( Extrusion ) ratio Assuming no friction, true strain Pressure required: With friction, where a (~ ) and b ( ) increase with dies angle Indirect Extrusion : Direct Extrusion : Ram Force, F=pAo Power P=FvfoxAAr=xrln= xfrYpln=xxrbaln+= xfYp = +=oxfDLYp2 4 Extrusion Analysis IIIn direct Extrusion , these is additional pressure, Pf,to overcome the friction at the container DirectIndirectRam PressureRam stroke5 Extrusion Dies and Press Shape factorCx=perimeter of the extruded cross-sectionCc=Perimeter of a circle with the same area Formula Impact & Hydrostatic +=cxxCCK +==DLYKpYKpxfxxfx2 For IndirectFor Direct6 Die Angle & Orifice Shape Optimum angle depends on work material, billet temperature, and lubrication Low die angle - surface area is large, leading to increased friction at die-billet interface.

2 Which results in larger ram force Large die angle - More turbulence in metal flow during reduction, which increases ram force required Shape of die orifice affects ram pressure Simplest shape = circular die orifice As cross-section becomes more complex, higher pressure and greater force are required ME477 Fall 2004 Kwon27 Problem billet that is 75mm long with diameter=35mm is directly extruded to a diameter of 20mm. The Extrusion die has a die angle of 75 . For the work metal, K=600 MPa and n= In the Johnson s equation, a= and b= Determine (a) Extrusion ratio, (b) true strain, (c) Extrusion strain and (d) ram pressure at L=70, 40 and 10mm.(a) rx=Ao/Af=(352)/(202)= (b) =lnrx= (c) x=a+blnrx= + ( )= (d) Yf=600( ) L=70mm, Did Extrusion took place?

3 75 35mm10mmh=(R1-R)/tan 75 = (R2H-R12(H-h))= (75-70)/4= ; p= ( +2(70)/35)= ; p= ( +2(40)/35)= ; p= ( +2(10)/35)= Wire and Bar Drawing The cross section of a bar, rod or wire is pulled while deforming through a die Reduction:Draft:foDDd =ofoAAAr =EntryApproachBack ReliefBearing Surface(land)Approach Angle: (6-20o)(30o)Lc9 Drawing Analysis Mechanics of DrawingrAAfo ==11lnln ideallyfofAAYlntan1 +=realistically =+=+=fofffAAYAAF lntan1 +==Draw ForcewherefofAAYln= 10 Maximum Reduction per pass For an ideal plastic material1111lnln11lnlnlnmax= = = = === ===eereAAfo11 Problem stock of initial diameter =90mm is drawn with a draft=15mm. The drawDie has an entrance angle=18 , and the coefficient of fraction at the work-die interface = The metal behave as a perfectly plastic material with yield stress =105 MPa.

4 Determine: (a) area of reduction, (b) draw stress, (c) draw force required for the operation and (d) power to perform the operation of exit velocity= (a) r=(Ao-Af)/Ao=(902-(90-15)2)/902= (b) =ln(Ao/Af)= = + (D/Lc) = where D= (90+75)= andLc= (90-75)/sin18= d=Yf(1+ /tan ) (lnAo/Af)= (c) F=Af d= ( )=271,475N(d) P=271,475(1m/min)= practice Usually cold working & round cross-sections Difference between bar drawing and wire drawing is stock size Bar drawing- large diameter bar and rod stock Wire drawing- small diameter stock - wire sizes down to mm ( in.) are possible Preparation of the Work Annealing to increase ductility of stock Cleaning- to prevent damage to work surface and draw die Pointing to reduce diameter of starting end to allow insertion through draw die