Table 6.

Comparison of various techniques using which MMC can be manufactured.

Sr. No.	Criteria	Solid State Processing		Liquid State Processing
		Friction Stir Processing	Powder Metallurgy	Centrifugal Casting	Stir Casting	Squeeze Casting	In-Situ Technique
1	Capability of manufacturing composites	Surface composites	Bulk Composites Functionally Graded Composites (FGM) Composites having step-wise structure	Functionally Graded Composites	Bulk Composites	Bulk Composites Functionally Graded Composites	Bulk Composites
2	Shape of resulting composites	Plates	Depends upon the die and punch, possible to manufacture complex shape	Hollow shape	Depends upon the mould, possible to manufacture complex shape	Depends upon the die and punch, possible to manufacture complex shape	Depends upon the mould, possible to manufacture complex shape
3	Requirement of major equipment	Vertical milling machine & fixture for holding workpiece Friction Stir Welding Setup	Melt atomization or Ball miller (for powder preparation) Rotating Drum or double cone screw mixer blade mixture (for mixing powders) Hydraulic Press (for compacting) Furnace (for sintering)	Furnace (for preheating particles and melting matrix) Rotating Mould (for generating centrifugal force)	Furnace (for preheating particles and melting matrix) Mechanical Stirrer (for mixing molten mixture) Mould (for getting required shapes)	Furnace (for preheating particles and melting matrix) Hydraulic Press (for compacting) Die and Punch (for manufacturing complex shapes)	Furnace (for preheating particles and melting matrix) Mould (for getting required shapes)
4	Types of defects that manufactured composites may have	Cracks, pores, voids and tunnel, fragment, lack of penetration, kissing bond, hooking, flash, and other surface defects	Ejection cracks, density variations, micro-laminations, and poor sintering	Gas porosity, shrinkage defects, mould material defects, pouring metal defects, cracking/tearing around circumferences and metallurgical defects	Gas porosity, shrinkage defects, mould material defects, pouring metal defects, cracking/tearing around circumferences and metallurgical defects	Gas porosity, shrinkage defects, mould material defects, pouring metal defects, cracking/tearing around circumferences and metallurgical defects	Gas porosity, shrinkage defects, mould material defects, pouring metal defects, cracking/tearing around circumferences and metallurgical defects
5	Level of defects	Microscopic and sometimes Macroscopic	Microscopic and sometimes Macroscopic	Both Microscopic and Macroscopic	Both Microscopic and Macroscopic	Both Microscopic and Macroscopic	Both Microscopic and Macroscopic
6	Frequency of defects in manufactured composites	Moderate	Low	High	High	Moderate	High
7	Controlling content of reinforcement particles	Difficult to control weight or volume percent of reinforcement	Easier to control weight percent of reinforcement particles	Easier to control both weight and volume percent of reinforcement particles	Easier to control both weight and volume percent of reinforcement particles	Difficult to control weight or volume percent of reinforcement	Difficult to control weight or volume percent of reinforcement
8	Distribution of reinforcement particles	Homogenous distribution	Homogenous, Step wise distribution, Varying distribution along the thickness	Varying distribution along the thickness	Homogenous distribution	Heterogeneous or Homogenous distribution	Heterogeneous or Homogenous distribution
9	Equipment and production cost	Moderate	High	Low	Low	Moderate	Low
10	Highlighting Feature	Green manufacturing technique for altering the microstructure	Ability to combine materials in powder form that are otherwise immiscible	Composites can be made in almost any length, thickness and diameter	Simplicity, flexibility and applicability to large quantity production with cost advantage	Minimize both solidification shrinkage and gas compression	Cheapest method, suitable for large scale production
11	Limitation	Low production rate, lesser flexible, cannot process non-forgeable materials	Intricate designs cannot be made, economical only for mass production	Requires skilled labour, difficult to control internal diameter of composites, limited strength of cast composites	Thermal mismatch, poor wettability, possibility of interfacial reaction, requires post processing techniques to resolve agglomeration and casting defects	Low flexible, high cycle time, difficult to maintain homogeneity and higher possibility of reaction between matrix and reinforcement	Composites with higher content of reinforcement particles cannot be manufactured