Experimental investigations and analytical modeling of multi-pass CO2 laser processing on PMMA

In this research work, microchannels have been fabricated utilizing multi-pass CO2 laser processing on Poly-methyl meth-acrylate (PMMA) substrates. CO2 laser engraving machines are cost effective and less time consuming compared to other tools and methods of fabricating microchannels on PMMA. However, the basic problem of low surface finish of the microchannel walls still restricts thus fabricated product from many potential applications. In this work, experimental and theoretical investigations of multi-pass CO2 laser processing on PMMA have been conducted. A number of experiments were performed to establish the relationship between laser power and scanning speed with microchannel parameters like width, depth, heat affected zone, surface roughness and surface profiles. Experiments were conducted at four different power settings with 50 mm/s of constant scanning speed and seven numbers of passes in each setting. Changes in thermo-physical properties of PMMA were observed for as-received PMMA sample and PMMA sample residing in heat affected zone (HAZ) for first pass and secondary passes respectively. Effect of different numbers of passes on microchannel width, depth, HAZ and surface roughness were explored for different power setting. Microchannel profiles resulting from different numbers of passes have been compared. Energy dispersive X-ray analysis was performed to determine elemental composition after each pass. Many advantages of multi-pass processing over single-pass processing were recorded including high aspect ratio, low heat affected zone, smoother microchannel walls and reduced tapering of microchannels. An energy balance based simple analytical model was developed and validated with experimental results for predicting microchannel profiles on PMMA substrate in multi-pass processing. Multi-pass processing was found to be time and cost effective method for producing smooth microchannels on PMMA.