Injection molding feedstock

Question 1

What is injection molding?

Answer 1

~ similar to injection molding of plastics

~ powder injection molding (PIM), powder dispersed in an organic fluid is injected into a die

~ the organic is extracted, leaving a near-net-shape ceramic powder compact which is then sintered

Question 2

What does feedstock consist of?

Answer 2

~ binder and ceramic particles

Question 3

What are the components of binder?

Answer 3

~ backbone, solvent/plasticizer, and lubricant

Question 4

What are some examples of backbone waxes? Backbone polymers?

Answer 4

~ waxes: parrafin, beeswax, carnauba

~ polymers: low molecular weight thermoplastic polymers like polyethylene or polypropylene

Question 5

What makes the two wax/polymer additives partially miscible?

Answer 5

~ differing molecular weights

~ often present in equal proportions so each remain interconnected throughout the binder

Question 6

What does lubricant do?

Answer 6

~ improves powder wetting to the binder and mutual particle sliding

Question 7

What happens if u have too much binder? Too little?

Answer 7

~ too much: particle-particle contact inadequate for shape retention during binder extraction

~ too little: air voids in the mix, high viscosity

Question 8

What happens when the critical solids loading is reached?

Answer 8

~ above which the mix viscosity increaseds rapidly

Question 9

What is the optimum mix?

Answer 9

~ slightly binder rich of critical solids loading, 50-60% solids

Question 10

How is mixing done?

Answer 10

~ performed at high shear under vacuum to remove bubbles, at a temp at which the binder is fluid

~ mixing torque decreases once the binder/lubricant wets the particles

~ mix and recycled mix is extruded into cylindrical pellet feedstock