This is the last project log. It will be a small compendium where i describe what i have learned in past half of a year.
I have made replaced the xaar printhead with hp45. I had struggled a lot with it as it has smaller drop sizes. This means that it is harder to wet the base material properly. This is why I have decided to use Xaar128 on the final design. It is also a lot easier to use.
I have worked with a lot of materials. Besides the wetting properties and structural properties I was also working on sintering properties. I have found out that for sintering you want to slowly (100°C/h) heat up to the temperature a bit lower than the melting point of the material. Have it at this temperature for at least an hour (this increases shrinking and final density). Then cool it down at the same rate.
I made the printing materials from:
- Ceramics powder
- Magnet dust (SrFe12O19)
- Bronze blend
- Titanium powder
I found out that methyl cellulose works very well as a binder and it can be easily used with any of above materials. Only problem I have encountered with it is when I was sintering at temperatures lower than 1000°C. It didn't burn away properly and it has left carbon everywhere. I was mixing it at about 10% of mass of material dust (1g of methylcellulose/10g of final mixture). It depends on the density of material so for titanium i had to use a bit more (15-20%).
When using metals keep in mind that they can oxidise when particles are small enough (especially with aluminum, this is also a reason why I didn't work with it). They can be easily printed with but problems do appear when sintering. You need an inert gas when sintering, this is a must. Even with argon few samples of titanium oxidised.
Alloy blends are not viable option as they wil not mix. This will leave you with samples that look beautiful but are completely useless.
If you want metal parts from this kind of printer you will need to infiltrate them using some other metal (bronze).
First things first, the magnets were ferrous, this means that they are a lot weaker then neodimium. I have used SrFe12O19. It prints really well even though it tends to clump up. There is one problem, it is very dirty (if this stuff touches any surface it is going to get stained by a very dark shade of brown). There is also a nice thing about using it where one does not need to sinter it as it can be infiltrated (filled with epoxy or glue). They need to be magnetized at the end.
Ceramics and hydroxyapatite
Theese two behave very simmilarly. You need to sinter them at T>1300°C. If they are not sintered well they will be very crumbly. Otherwise they are a really good starting point as they do not oxidise. The only downfall is they have a high sintering temperature.