Glass-ceramics machinable hardness

Ultrasonic machining, also known as ultrasonic impact grinding, uses ultra-sonically induced vibration delivered to a tool to create accurate cavities and channels of many shapes [146]. It can be used to form deep cavities as small as 250 pm in diameter (with an accuracy of 50 pm) in both hard and brittle materials such as glass, quartz, polymers, ceramics and metals. This technique may be useful for fabrication of large masters. 

The major difference is that the hard component cannot be produced in the same machine, it is inserted into the mould in which it is finally overmoulded with the silicone rubber part. Metals, ceramics, glass, etc., are not too sensitive to high temperatures, which allows the process to run at a higher productivity than in the previous case, see Section 11.3.2, where cycle times are longer due to lower moulding temperatures for the silicone part. 

It is difficult to manufacture ceramic substrates in the pure form. The melting point of most ceramics is very high, as shown in Table 4.1, and most are also very hard, limiting the ability to machine the ceramics. For these reasons, ceramic substrates are typically mixed with fluxing and binding glasses, which melt at a lower temperature and make the finished product easier to machine. 

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