From: Brian B. Mathewson (email@example.com)
Date: Thu May 30 2002 - 17:32:01 EEST
A few types of machinable ceramics like Macor are readily available from McMaster-Carr (www.mcmaster.com) and other distributors.
Glass-mica ceramics like Macor machine well and can hold excellent tolerances when machined properly. Chipping can occur if you're not careful, and I recommend using sharp carbide tools. However, note that the strength of machinable ceramics is a fraction of what you can expect from a typical sintered alumina ceramic.
Bisque-fired ceramics also machine easily, but are initially more fragile than Macor. Once fired to 1500 degC or so they become as strong as regular alumina, but be sure to take shrinkage due to densification into account when machining. It may be difficult to keep thin bisque-fired parts from breaking during handling.
Hard, strong ceramics like alumina aren't machined in the conventional sense, but are ground with diamond wheels or tools. This is fine for simple shapes like tubes and plates with simple features, but becomes very expensive for more complex shapes.
Green machining usually allows more finely detailed features than the options above, since an organic binder reinforces ceramic powder during machining. After removing the binder the part is sintered with a uniform shrinkage, which can be 15% to 20% depending on the material, with tolerances usually around 0.5%. Green ceramic materials are not usually available directly in a convenient form, so you'd have to have a ceramic component manufacturer about this.
For your thin plates, the best accuracy is provided by ultrasonic or laser machining of sintered ceramic substrates, because no shrinkage (as in green machining) will occur. I'd still be concerned about the narrow threads of materials between the holes, but it could be done. The Macor should hold up while machining such a thin part, but the overall strength is significantly lower. The geometry is not a problem for green machining, and because it's so much easier to machine green parts than fired ones, it could be less costly but still provide the accuracy you need with all the strength of alumina.
Brian B. Mathewson
----- Original Message -----
To: RP Mailing List
Sent: 29 May, 2002 17:03
Subject: Machining Ceramics?
Here is what I am looking for...
Do any of you work with machinable ceramics?
If so which type is preferred to hold the best tolerance?
I am looking to put in 40-50 0.150mm holes spaced at 0.165mm, thickness to drill through is 0.5-.75mm.
I will be working up some drawings for this in the next day or two, any input you could give me now would aid in this design.
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