Machining brittle materials

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. 

Sieving procedures are standardized in BS 1796 [14], Dry sieving by machine is used for coarse separation but other procedures are necessary as the powder becomes finer and more cohesive. Conventional dry sieving is not recommended for brittle material since attrition takes place and an endpoint is difficult to define. If the rate of passage of particles does not decrease with sieving time, it may be due to particle attrition, deagglomeration or a damaged sieve [72]. 

Powder blasting, or abrasive jet machining, is a technique in which a particle jet (typically A1203 particles of 3-30 lm) is directed towards a target for mechanical material removal. It is a fast (typically, 500 pm depth in 20 minutes), inexpensive, and accurate directional etch technique for brittle materials like glass, silicon, and ceramics. For complex and small structures a mask can be used. 

An experimental uniaxial stress-strain relationship, determined in tension, would provide the necessary design information for ceramics and hard materials Young s modulus, Poisson s ratio and the tensile fracture strength. However, tensUe data for brittle materials are often unreliable, due to parasitic bending stresses associated with dimensional inaccuracy in machining tensile dog-bone specimens and misalignment of the specimen grips. 

Ductile-mode micro-cutting is aimed at suppressing fracture in micro- or nanoscale machining of brittle materials like silicon wafers. Ductile-mode cutting can be achieved if the... 

Superabrasives, Fig. 6 Comparison of abrasives at machining of ductile material (top) or brittle material (bottom), (Helletsberger et al. 2011), with copyright permission from publisher... 

The initial study on the ductile-mode machining of brittle materials was done by Yoshikawa and Taniguchi who have developed the general description for the behavior of briffle materials in the plastic flow zone, by generalizing the microplasticity" of Mcmahon, and the elastic/plastic theory of Hill and Hertz. 

In machining of brittle materials, it is generally known that ductile behavior is achieved when the specific material removal unit is small enough. The critical depth of cut d is specified as... 

Blackley, W.S. and Scattergood, R.O., Ductile-regime machining mode for diamond turning of brittle materials, Prec Engg, 13, 2 (1991) 95. 

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