Wednesday, July 7, 2010

Printing with spray-dried powder

I just finished an initial test with the spray-dried powder. It’s amazing how much particle shape (a.k.a. particle morhology) affects how particles move. I'm starting to realize that mesh size is only part of the answer. Morphology is just as important, if not more so. These spherical particles move almost like a liquid. They don’t agglomerate (even in these current humid summer conditions).

CDF P-MF #2 on the left; spray dried material on the right. Note the lack of agglomeration with the spray-dried material.

The powder spreads very consistently with no streaking. It also packed very nicely, with no apparent need to compress the feed chamber (it has nowhere to compress to!).

There is nothing dramatic to note here. Both feed and build sides performed perfectly.

Detail of feed and build sides using spray-dried powder.

One thing I did notice… I occasionally found hairs in the powder on the feed side. I think these are due to the brush I am using, as its hairs sometimes find their way through the mesh.

Despite this being only ceramic materials, with no sugar or Maltodextrin, I decided to run a part. There were no issues here either. Unlike in previous cases where powder was not spreading properly, the surface filled predictably after each pass, so the binder was only ever applied to fresh powder.

A couple of images during the print. The image on the right is taken during a layer spread and shows that the spreading is occuring consistently between each layer.

A couple images after the print. There is almost no shrinkage (just a small hairline crack on the surface shown on the right). This compares favorably with the previous tests and suggests that the material is well packed with less potential for shrinkage.

I tried removing the object after printing but the part crumbled under its own weight (so that's why you need a binder!). Adding sugar/Maltodextrin in future tests should give the part post-printed strength. It may also increase shrinkage. For now I’m just excited to have figured out the basic physical requirements for a printable medium!

Next on the agenda: gain access to the spray drier so I can start batching some spray-dried powder from scratch.


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