Densif cation

Sintering finishing

Fig. 8 Flow chart for the LPM process, showing the four major stages and highlighting the important parameters within each

A critical requirement for any molding operation is that the feedstock viscosity allow complete and uniform mold filling (Ref 18). The viscosity of suspensions depend on many variables such as temperature, shear rate, particle characteristics, and solids loading (Ref 19, 20). For example, thermoplastic polymers and waxes soften and flow easily above their melting point. Certain polymers and suspensions display a shear thinning behavior, wherein the viscosity decreases with increasing shear rate. Particle characteristics such as shape, size distribution (mean and width), packing characteristics, and surface chemistry have all been recognized to play a role on the suspension viscosity. A semiempirical equation (Ref 18) relating the suspension viscosity, '/, to some of these variables is:

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