Jlel12
Plastic
- Joined
- Dec 28, 2009
- Location
- Boston, MA, USA
Hi all,
I'm working on a project where I'm spending a lot of time machining bisque-fired alumina. For reference, bisque-fired alumina is aluminum oxide (Al2O3) powder plus some additives which has been pressed into a form and partially sintered. The partial sintering produces small, relatively weak bond areas between adjacent alumina particles, which break easily. This enables this material to be machined using conventional milling/turning tools instead of requiring grinding. It has the consistency of very hard chalk. I get my material from McMaster (PN 8484K61, for example), and they get it from a company called Superior Technical Ceramics. It can be purchased from other companies, including Aremco and Cotronics.
I'm posting today because I'd like to find out if anybody here has definitive recommendations for feeds and speeds for machining this material. I've been working with it for quite some time, and have feeds/speeds that work...kinda. However, I go through tooling at an alarming rate, and I'd like to improve this.
Here's what I have so far:
Anyway - if anybody here has specific experience working with this material, and can help me out with optimizing machining parameters, I'd very much appreciate them. Thanks!
I'm working on a project where I'm spending a lot of time machining bisque-fired alumina. For reference, bisque-fired alumina is aluminum oxide (Al2O3) powder plus some additives which has been pressed into a form and partially sintered. The partial sintering produces small, relatively weak bond areas between adjacent alumina particles, which break easily. This enables this material to be machined using conventional milling/turning tools instead of requiring grinding. It has the consistency of very hard chalk. I get my material from McMaster (PN 8484K61, for example), and they get it from a company called Superior Technical Ceramics. It can be purchased from other companies, including Aremco and Cotronics.
I'm posting today because I'd like to find out if anybody here has definitive recommendations for feeds and speeds for machining this material. I've been working with it for quite some time, and have feeds/speeds that work...kinda. However, I go through tooling at an alarming rate, and I'd like to improve this.
Here's what I have so far:
- Tooling: I know to use diamond-coated carbide tooling with bisque ceramic, since it's super abrasive. Recently, I was advised to use CVD coated tooling, since it's apparently a thicker coating that leaves a larger edge radius, meaning it will hold up for longer.
- Feeds & Speeds: The resources I've been able to find on machining bisque alumina are 1) Aremco's machinable ceramics recommendations (largely useless - I'm pretty sure it's just Corning's recommendations for Macor repackaged), and 2) an extensive guide from a company called sp3(very instructive - but targeted at green ceramic instead of bisque).
- Other advice: I have asked STC for recommendations. They are unwilling to give me any pointers, beyond saying that "...[their] speeds and feeds are somewhat lower (~30%) compared to [their] standard settings (for green ceramic)." This has been anecdotally confirmed to me elsewhere, with the explanation that it's better to be "digging" material out with the endmill, rather than "grinding" it away.
- Finally, some other things I've learned while working on this:
- Fixturing is critical to avoiding breaking parts. For loosely-toleranced operations, I'll put strips of electrical tape on my vise jaws, to give a little bit of cushion between the jaws & the parts.
- Starting with flat stock is also very important. Bisque alumina has low tensile strength, so if you put a blank that's even slightly warped in a vise, it will likely snap it.
- Sharp tooling is just as - if not more - important than fixturing. I go through a lot of tooling
- All of the normal machinable ceramic rules about material chipping out (avoiding drilling all the way through a part; adopting unusual milling strategies to avoid ever cutting through an edge from the inside) are relevant. I've recently had some luck with using double-angle drill bits designed for composites to drill through holes without substantial chipout (more work required to confirm)
Anyway - if anybody here has specific experience working with this material, and can help me out with optimizing machining parameters, I'd very much appreciate them. Thanks!