Bulge Formation In Laser Assistant Machining Of Polymer Microfluidic Chips

CO₂ laser has enhanced the manufacturing methods of the polymer microfluidic chip and it has been utilized in the fabrication of micro-channel and reservoir. Bulge formation is a prevalent phenomenon in the CO₂ laser processing PMMA and this is the most important obstacle in the more widely utilization of CO₂ laser in the fabrication of microfluidic chip. This paper investigates the mechanism of bulge formation in theoretical analysis, simulation and experimental validation and then provide solving plan according to the main influencing factors.The transformation mechanism of PMMA under the CO₂ IR laser is analyzed on the basis of the experiments. PMMA experienced three kinds of state change in the processing according to the analysis of heat transfer and material physical state change. During this process two kinds of forces appears in the substrate. The movement and distortion of different states of substrates under the gas pressure and thermal stress, which lead to the bulge, are investigated. And then, the influence of bulge on the chip fabrication is analyzed. According to the analysis, the process of movement, distortion and bulge formation is simulated with the ANSYS. An on-line observing system is established by microscope, CCD and image processing software, which is to observe the bulge formation process, and this provide the direct validation for the theoretical analysis and FEA simulation. Other phenomenon such as rim bubble and backward gas provide an indirect validation for the analysis and simulation.The influence of heat on the bulge is researched. The tropism of extruded PMMA and its influence on the bulge is analyzed and then validated by the observing experiments. The results show that the key mechanism of bulge formation is Heat Affected Zone and the relationship of HAZ with heat and material property is investigated. Using proper laser parameters and gas cooling can be useful for the HAZ decrease according to the expression. The gas cooling system is then established and the effect is apparent.The craft of eroding, together with the principle and critical parameters, is brought forward. The feasibility of the craft is validated by standard detection. The results show that the bulge can be eliminated by the combination of proper laser parameters, gas cooling and eroding craft.