An experimental study of micromilling parameters to manufacture microchannels on a PMMA substrate

Rapidly prototyping a polymer microfluidic device is a growing interest in the application fields of the disease detection, drug synthesis, and the environmental monitoring because of the benefits of the miniaturized platforms. Micromilling is one of the micromachining methods and it has been commonly used to manufacture polymer microfluidic devices. The advantages of using micromilling for polymer microfluidic devices include faster fabrication process, lower cost, easier user interface, and being capable of fabricating complicated structures, which make micromilling a perfect candidate in rapid prototyping polymer microfluidic devices for research idea testing and validation. This aim of this study is to understand the influence of each micromilling parameter to the surface quality, followed by the factor analysis to determine the optimal cutting conditions. The parameters included spindle speed, feed rate, depth of cut, and the selection of coolant (compressed air/oil coolant), and the milled surface quality was measured by a stylus profilemeter. Polymethyl methacrylate (PMMA) is the mainstream substrate material in the microfluidics due to its excellent optical property and popularity and is used as the target substrate. The experiment results showed that using the compressed air as a coolant can deliver a better surface quality than the oil coolant, and the smallest roughness achieved was 0.13 μm with the spindle speed of 20,000 rpm, feed rate of 300 mm/min, and the depth of cut of 10 μm. Factor analysis revealed that the depth of cut has the largest impact while the spindle speed has the minimized impact to the surface quality of a micromilled PMMA substrate. To further confirm the optimal cutting conditions, another 12 reservoirs were micromilled with the optimal cutting conditions and the average roughness is 0.17 μm with a stand deviation of 0.08 μm.