MIM Process Options
MIM Feedstock Options
Feedstock then is a mixture of the powder and binder as homogeneous paste that can be molded. The tool cavity is designed around the feedstock, and includes consideration of the binder melting temperature, particle size of the powder, feedstock viscosity, and feedstock strength.
Best molding is attained when the hot feedstock viscosity is near 100 Pa∙s (1000 poise). As a benchmark, this is thicker than most paints (which are small particles such as titania dispersed in acrylic emulsion binder) and more like toothpaste (which also consists of small oxides particles in a binder formed from cellulose or gum dissolved in water), but not like cold ice cream. A typical feedstock is formed into pellets that are properly formulated to directly feed into the injection molding machine.
Shown below is a picture of typical feedstock pellets.
It is possible to purchase premixed feedstock for common alloys, but it is also possible to formulate custom mixtures to adjust mold-ability, alloying, or other features. The situation is comparable to buying premixed cookie dough versus making cookies from scratch. There are merits to both approaches. More than a dozen feedstock suppliers exist, each with a range of materials. SMP primarily utilizes the BASF Catamold feedstock, due to their highly engineered compounding processes and very consistent certified batch to batch properties.