semisolid metal forming
DESCRIPTION
Semi-solid metal casting (SSM) is a near net shape variant of die casting.[1] The process is used with non-ferrous metals, such as aluminium, copper,[2] and magnesium. The process combines the advantages of casting and forging. The process is named after the fluid property thixotropy, which is the phenomenon that allows this process to work. Simply, thixotropic fluids shear when the material flows, but thicken when standing.[3] The potential for this type of process was first recognized in the early 1970s.[3] There are four different processes: thixocasting, rheocasting, thixomolding, and SIMA.SSM is done at a temperature that puts the metal between its liquidus and solidus temperature. Ideally, the metal should be 30 to 65% solid. The metal must have a low viscosity to be usable, and to reach this low viscosity the material needs a globular primary surrounded by the liquid phase.[2] The temperature range possible depends on the material and for aluminum alloys is 5–10 °C, but for narrow melting range copper alloys can be only several tenths of a degree.[4]Semi-solid casting is typically used for high-end castings. For aluminum alloys typical parts include engine suspension mounts, air manifold sensor harness, engine blocks and oil pump filter housing.[5]TRANSCRIPT
SEMISOLID METAL FORMING (THIXOCASTING)
SEMISOLID METAL FORMING(THIXOCASTING)BYMD RAKIB SHAIKHDEPT. OF MECHANICAL ENGG.INTRODUCTION Semisolid Metal Forming ( Thixocasting ) also called Semisolid Metalworking originated from work by researches at MIT in 1971.
The semisolid slurry with a spheroidal microstructure suspended in liquid had a very low value of flow resistance and that it would be possible to use this in developing new forming process.
CHARAETERISTICSSemisolid process is the process shaping materials during semisolid state (called slurry)Operation temperature is at a temperature that between its liquidus and solidus temperature(red area)Ideally, the slurry should be approximately 30-65% of solid.
LSL+SSTRUCTURAL EVALUTION DURING COOLING
DEFINATION The metal or alloy has a nondendritic, roughly spherical, and fine grain structure when it enters the die or mold then the alloy exhibits thixotropic behavior(velocity decreases when its slowly solidifying) for this it is called thixoforming or thixocasting .This technology is also used in making cast metal-matrix composites.FLOE DIAGRAMPROCESSES OF THIXOCASTING
ADVANTAGESAs the metal is just above the solidification temperature when injected to a die, resulting in reductions in solidification and cycle times.Productivity is high respect to other die casting.Shrinkage porosity is reduced because of lower superheat involved. Both thin and thick part can be made.DISADVANTAGESMaterial and overall cost is higher than normal die casting.Precise control of operating condition is required.Liquid segregation may occur as a result of non-uniform heating.
APPLICATIONSPressure tight parts such as master brake cylinders,fuel tank, air conditioner compressor housing etc.High strength parts such as engine mounts, tie rods etc.Wear resistant parts such as compressor piston, brake drums, gear shift levers etc.
FUTURE DEVELOPMENTProcess development.Mechanism of formation of non-dendritic structure.Alloy development.Simulation studies of process.Viable process for steel and Cast Iron.
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