Defects and their control

Question 1

What’s the effect of low solids loading?

Answer 1

~ causes particles to migrate together during thermolysis

~ porosity b/w these agglomerates can cause cracks to form before and/or after sintering

Question 2

What’s the effect of too rapid thermal binder extraction?

Answer 2

~ can lead to bloating on the part via released gases

~ initial binder extraction must be VERY slow (ex: 2C/hour)

~ when pore channels are opened, heating (extraction rate) can be more rapid

~ Tg experiments are worthwhile to establish sensitive temperatures

~ around 60 hours are required to remove 40% of the binder

Question 3

What are the effects of voids?

Answer 3

~ decrease solids loading

Question 4

What are the effects of short shots?

Answer 4

~ increase feedstock temp to prevent premature freezing of the gate

Question 5

What is flashing?

Answer 5

~ excessive pressure forces mix into the seam between the mold halves

Question 6

What do binders with short molecular lengths do?

Answer 6

~ avoid polymer orientation during injection, which would otherwise facilitate non-uniform contraction during solidification, leading to cracking and warping

Question 7

How can you make small corrections to final part dimensions?

Answer 7

~ by variations in solids loading

Question 8

What are the dimensional restrictions?

Answer 8

~ difficult and time-consuming for binder extraction of large parts

~ largest dimension: ~10cm
~ total component volume: 100cm^3