Fundamentals of metalworking pptx

Fundamentals of Fundamentals of metalworking metalworking Suranaree University of Technology Jan-Mar 2007 Subjects of interest • Introduction/objectives • Classification of metal processes • Mechanics of metalworking • Flow curves • Effects of temperature on metalworking - Hot working - Cold working • Effects of metallurgical structure on forming processes • Effects of speed of deformation on forming processes • Effects of friction and lubricant Chapter 1 Tapany Udomphol Objectives Objectives Suranaree University of Technology Jan-Mar 2007 • This chapter provides classification of metal forming processes based on types of forces applied onto metals. • Mechanics of metal forming will be outlined to understand stress criterion for plastic deformation. • Differences between hot and cold working will be highlighted and advantages-disadvantages of hot and cold working will be given. • Effects of deformation speed and friction on metal working process will be included. Tapany Udomphol Classification of metal forming Classification of metal forming processes processes Suranaree University of Technology Jan-Mar 2007 (based on the type of force applied on to the work piece as it is formed into shape). • Direct-compression-type processes • Indirect-compression processes • Tension type processes • Bending processes • Shearing processes Tapany Udomphol • Direct-compression type processes : the applied force is normal to the direction of the metal flow in compression, i.e., forging and rolling processes. • Indirect-compression type processes : the primary forces are frequently tensile, with indirect compressive forces developed by the reaction of the work piece. The metal flow is therefore under the combined stress state, i.e., extrusion, wiredrawing, tube drawing. Suranaree University of Technology Jan-Mar 2007 Tapany Udomphol • Tension type processes : the applied force is tensile, i.e., stretching forming. • Bending processes : the applied force involves the application of bending moments to the sheet. • Shearing processes : the applied force involves the application of shearing forces of sufficient magnitude to rupture the metal in the plane of shear. Suranaree University of Technology Jan-Mar 2007 Tapany Udomphol Suranaree University of Technology Jan-Mar 2007 Metal forming Compressive forming Combined tensile and compressive forming Tensile forming Forming by bending Forming by shearing •Rolling •Open die forming •Closed die forming •Indenting •Pushing through a die •Pulling through a die •Deep drawing •Flange forming •Spinning •Upset bulging •Stretching •Expanding •Recessing •Bending with linear tool motion •Bending with rotary tool motion •Joggling •Twisting •Blanking •Coining Classification of metal forming by subgroups Tapany Udomphol Suranaree University of Technology Jan-Mar 2007 Mechanics of metal working Mechanics of metal working • Metal working occurs due to plastic deformation which is associated with analysis of complex stress distribution.  require simplification. Only (large) plastic strain is considered while elastic strain is very small and can be neglected. Strain hardening is often neglected. Metal is considered to be isotropic and homogeneous. Normally plastic deformation is not uniform and also have frictions, but we need to simplify the stress analysis in order to determine the force required to produce a given amount of deformation to obtain a product in a required geometry. Tapany Udomphol Suranaree University of Technology Jan-Mar 2007 • Required theory of plasticity, and for plastic deformation  a constant-volume relationship is required. 0 321 = + + ε ε ε …Eq. 1 In metalworking, compressive stress and strain are predominated. If a block of initial height h o is compressed to h 1 , the axial compressive strain will be: ∫ >−=== 1 1 1 1 ,lnln h h o o o o hh h h h h h dh ε …Eq. 2 For true strain For conventional strain 1 11 −= − = oo o h h h hh e …Eq. 3 Note: the calculated strain is negative  compressive strains. Deformation h o h 1 σ σσ σ σ σσ σ Tapany Udomphol Suranaree University of Technology Jan-Mar 2007 • However the convention is reversed in metalworking problems so that compressive stresses and strains are defined as positive. Note: e c is used as strain in deformation process. oo o c o c h h h hh e h h 11 1 1,ln −= − == ε …Eq. 4 And the fractional reduction (reduction of area) in metal working deformation is given by o o A AA r 1 − = From the constant-volume relation rA A L L r A A or A A r LALA o o oo oo − === −=−= = 1 1 lnlnln 11 1 1 11 11 ε …Eq. 5 …Eq. 6 A o A 1 L o L 1 σ σσ σ σ σσ σ Tapany Udomphol Suranaree University of Technology Jan-Mar 2007 Example: Determine the engineering strain, true strain, and reduction for (a) a bar which is doubled in length and (b) a bar which is halved in length. (a) For a bar which is double in length, L 2 = 2L 1 5.0 2 111 693.0 2 lnln 0.1 2 1 1 2 1 1 2 1 21 1 1 1 2 1 11 1 12 =−=−=−= − = === = − = − = L L L L A A A AA r L L L L L LL L LL e ε (b) For a bar which is halved in length, L 2 = L 1 /2 0.1 2/ 1 693.02ln 2 1 ln 2/ ln 5.0 2/ 5.0 2/ 1 1 1 1 1 11 1 11 −=−= −=−=== = − =−= − = L L r L L L LL eor L LL e c ε Tapany Udomphol [...]... lower density of dislocations or rearrangement of dislocation structure (as a consequence of strain hardening during deformation process) • Recovery process includes annihilation of dislocation, polygonization of dislocation, dislocation climb • Certain amount of stored energy is released during annealing without an obvious change in optical microstructure Polygonization www.esrf.fr Recovery of 38% cold-rolled... the recoverable elastic strain Suranaree University of Technology Tapany Udomphol Jan-Mar 2007 Flow curve Flow curve True stress True stress, σ σy 0 10 20 30 40 50 True strain, ε Reduction of area by drawing, % Flow curve constructed from stressstrain curves after different amounts of reduction Temperature Suranaree University of Technology εf Method of using average flow stress to compensate for strain... Jan-Mar 2007 Effects of grain size and strain on recrystallisation temperature Schematic of recrystallisation diagram Suranaree University of Technology Tapany Udomphol Jan-Mar 2007 Effects of grain size on properties Properties Ductility Strength Grain size • Small grains make dislocations more difficult to move • More slip plane, therefore, greater ductility Suranaree University of Technology Tapany... More slip plane, therefore, greater ductility Suranaree University of Technology Tapany Udomphol Jan-Mar 2007 Effects of strain rate and temperature Flow stress of aluminium as a function of strain at different temperature Temp Flow stress Suranaree University of Technology Flow curves of Cu Zn28 Strain rate Tapany Udomphol Flow stress Jan-Mar 2007 Secondary recrystallisation and grain growth • At higher... conditions Distortion of FEM grid in forging of a compressor disk Suranaree University of Technology Tapany Udomphol Jan-Mar 2007 Flow curves • Flow curve indicates whether metal is readily deformed at given conditions, i.e., strain rate, temperature • Flow curve is strongly dependent on strain rate and temperature Flow curves of some metals at room temperature Suranaree University of Technology Tapany... showing different sizes of subgrains Suranaree University of Technology Tapany Udomphol Jan-Mar 2007 Effect of recovery annealing on stress-strain diagram • Recovery process depends strongly on temperature • Increasing temperature (T ≥ 0.5Tm) during step tensile tests fig (b) reduces the yield stress, due to the rearrangement and reactions of dislocations during recovery Effect of recovery annealing... Jan-Mar 2007 Recrystallisation during hot working Deformed in direction of work Nuclei form at grain boundaries at points of max stress Nuclei grow into new grains • The minimum temperature at which reformation of the crystals occurs is called Recrystallisation Temperature • Above the recrystallisation temperature the kinetic energy of atoms increases and therefore they are able to attach themselves to... annealing twins surrounded by deformed matrix with high density of dislocations - Primary recrystallisation occurs at the beginning of the new grain formation process - Recrystallisation temperature does not depend on the metal alone, but on a whole number of variables temperature, strain and minimum dislocation density available (amount of deformation) - Small impurities in pure metals can considerably... yield point, the metal starts to flow under the influence of stress state This is in the plastic regime where stress is not directly proportional to strain • The manner of flow or deformation is dependent on the stress state Suranaree University of Technology Tapany Udomphol Jan-Mar 2007 FEM analysis • Finite element method (FEM) is used in metalworking plasticity where stresses are complex • FEM is... University of Technology Tapany Udomphol Jan-Mar 2007 Recrystallised grain size, mm Recrystallised grain size and prior plastic strain 10 Aluminium sheet 5 Critical deformation 5 10 15 20 25 Plastic deformation, % The greater the driving force (greater prior plastic deformation), the greater the number of nuclei that will form and the finer will be the final grain size Suranaree University of Technology . Fundamentals of Fundamentals of metalworking metalworking Suranaree University of Technology Jan-Mar 2007 Subjects of interest • Introduction/objectives • Classification of metal processes •. Mechanics of metalworking • Flow curves • Effects of temperature on metalworking - Hot working - Cold working • Effects of metallurgical structure on forming processes • Effects of speed of deformation. application of bending moments to the sheet. • Shearing processes : the applied force involves the application of shearing forces of sufficient magnitude to rupture the metal in the plane of shear. Suranaree