MET1401 Engineering Fabrication PDF

SIT Internal MET1401 Engineering Fabrication  SIT Internal Manufacturing Categories SHAPING JOINING Casting (Metals) Welding Sand Casting Investment Casting...

SIT Internal MET1401 Engineering Fabrication  SIT Internal Manufacturing Categories SHAPING JOINING Casting (Metals) Welding Sand Casting Investment Casting Mechanical Fastening Die Casting Molding Bonding (Adhesives) Compression Molding Injection Molding Machining Turning / Contour Turning Milling Abrasive Machining Grinding Forming Rolling “In forming processes, the Forging starting material are typically in Extrusion the shape of a plate, sheet, bar, Drawing rod, wire or tubing” 2 Sheet Metal Forming  SIT Internal Forming Rolling Forging Extrusion Sheet Metal Forming (or Bending) 3  SIT Internal Manufacturing Categories Traditional manufacturing processes may be divided into : Mass Conserving The mass of the starting material is approximately equal to the mass of the final part. e.g. casting, injection molding, and closed-die forging Mass Reducing The mass of the starting material is greater than the mass of the final part. e.g. machining Finishing Produce the final appearance and feel of a product by processes such as coating, painting, or polishing. 4  SIT Internal Variety of Manufacturing Processes  SIT Internal Variety of Manufacturing Processes  SIT Internal Forming Apply stresses to change shape of metal pieces via plastic deformation 7  SIT Internal Forming Apply stresses to change shape of metal pieces via plastic deformation - over and over again … Stress after 1st deformation Increasing yield strength each time 2nd 3rd Decreasing strain to fracture each time Permanent set Strain 8  SIT Internal Forming Rolling as a Forming process Metals consist of polycrystals or grains When deformed plastically at low temperatures, grains and grain boundaries are deformed permanently in particular directions (anisotropic) Material tends to have higher yield strength but lower ductility 9  SIT Internal Forming Desirable material properties for forming : low yield strength high ductility An increase in temperature brings about: A decrease in material strength An increase in ductility A decrease in rate of strain hardening These effects promote ease of deformation => lower forces and power 10  SIT Internal Forming – Cold Versus Hot Working Forming operations below recrystalisation temperature = cold working Forming operations above recrystalisation temperature = hot working Tm = melting temperature Recrystallisation temperature is ~ 0.4 Tm (in kelvin) 11  SIT Internal Forming – Cold Versus Hot Working Cold rolling Hot working Plastic deformation above recrystalisation temperature. Changes in the grain structure of cast or of large-grain wrought metals during hot rolling. Hot rolling is an effective way to reduce grain size in metals for improved strength and ductility. 12  SIT Internal Forming – Cold Versus Hot Working Recrystallization is a process by which deformed grains are replaced by a new set of defects-free grains that nucleate and grow until the original grains have been entirely consumed. Recrystallization is usually accompanied by a reduction in the strength and hardness of a material and a simultaneous increase in the ductility. Thus, the process may be introduced as a deliberate step in metals processing or may be an undesirable byproduct of another processing step. The most important industrial uses are the softening of metals previously hardened by cold work, which have lost their ductility, and the control of the grain structure in the final product. Recrystallization temperature is the temperature at which the highly cold-worked alloy completely recrystallizes in about 1 hour ~0.4 Tm 13  SIT Internal Forming – Cold Versus Hot Working Cold Forming Hot Forming Better surface finish Surface oxidation, poor surface finish Near net or net shape Lower dimensional accuracy Strain hardening leading to better strength, fatigue and wear No strain hardening properties but loss of ductility Directional properties can be imparted which may or may not be Properties are generally isotropic useful Residual stresses introduced No residual stresses 14  SIT Internal Manufacturing Categories SHAPING JOINING Casting (Metals) Welding Sand Casting Investment Casting Mechanical Fastening Die Casting Molding Bonding (Adhesives) Compression Molding Injection Molding Forming Rolling Machining Flat Rolling Turning / Contour Turning Forging Milling Open-Die Forging Abrasive Machining Closed-Die Forging Grinding Extrusion Direct Extrusion Forming Drawing Rolling Sheet Metal Forming Forging Bending Extrusion Drawing 15 Sheet Metal Forming