email: [email protected], bemail: [email protected], cemail: [email protected]
Keywords: Brittle Material Machining, Micro-High Speed Machining, Surface Roughness,
Optimization, Genetic Algorithms, Response Surface Methodology.
Abstract. Soda lime glass is a very important material in diverse manufacturing industries,
including automotive, electronics, and aerospace. In these applications, the glass surface needs to be
defect free and without impurities. However, the machining of glass is difficult due to its inherent
brittleness which leads to brittle fracture and easy Cr-ack propagation. This research investigates the
high speed micro-end milling of soda lime glass in order to attain ductile regime machining. It has
been found by other researchers that ductile mode machining can avoid brittle fracture and sub
surface Cr-acks. Also, in this study, a special air delivery nozzle is used to blow away the resultant
chips and keep the machined surface clean. To accomplish this, Design Expert software and a
commercial NC end mill were used to design and perform the machining runs, respectively. The
surface roughness of the resultant surfaces was later analyzed with a surface profilometer.
Microphotographs of the machined surfaces were also taken in order to see how effective the air
blowing method is. The results of surface roughness measurements were then used to develop a
quadratic empirical model for surface finish prediction. Finally, desirability function and genetic
algorithms were used to predict the best combination of cutting parameters needed to obtain the
lowest surface roughness. The predictions were later tested by experiments. The results demonstrate
that this type of machining is viable and the roughness obtained is very low at 0.049 µm.
Soda lime glass, a brittle material, plays an important role in modern industries, especially in
aerospace, automotive, optical electronics, and semiconductor sectors . This is due to its unique
properties like chemical inertness, resistance to corrosion, high strength and stiffness at elevated
temperatures, transparency to light and infrared etc. However, for these high-tech applications, the
glass surface needs to be almost free of defects or impurities . Such high surface finish and
precise dimensions can be obtained through the selection of appropriate machining parameters so
that ductile regime machining can be obtained .
Ductile mode machining is a special class of ultra-precision machining which is used to machine
brittle materials. In this type of machining, material is removed predominantly by the chip formation
process and leads to Cr-ack-free machined surfaces with surface roughness as small as a few
nanometers . Several approaches have been investigated in order to achieve ductile regime
machining, including: low depths of cut (in micro-meter range), negative tool rake angle, and high
static pressures. This research uses high speed micro-machining to attain ductile mode machining of
soda lime glass. Micro-machining takes advantage of low depths of cuts, usually between 1 and
999µm. On the other hand, high speed machining (HSM), more specifically end milling, exploits
the glass transition temperature in order to cut without brittle fracture .
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