Improvement in Geometrical Resolution of Plastic Laser Sintering by using Reduced Spot Sized Laser
Plastic laser sintering is one of the most promising processes for rapid manufacturing among various additive manufacturing (AM) technologies. Though the process tends to be applied to fabrication of larger parts in comparison to stereolithography, its ability of creating complex structure as an advantage of additive manufacturing technologies should be demonstrated in production of smaller parts and parts including fine and complex geometries as well. In this research, narrow CO2 laser beams with spot diameters of 130µm and 150µm were tested while the commercially available machines are equipped with those around 500µm. Relationship between resolution (available wall thickness) and spot diameter is proportional when the diameter is greater than 150µm, but effect of reducing the spot size further is not significant. The minimum wall thickness of 180µm was obtained, but this part was so fragile that skill in breakout treatment is critical. To discuss the mechanical strength of micro-plastic-laser-sintering, packing rate of obtained parts was introduced as an index of the strength. Build parameter that minimizes the wall thickness without decreasing the tensile strength below 30MPa was searched, and a set of parameters that provides minimal thickness of 0.6mm was obtained. Reducing laser spot size inevitably leads to shrinkage of scanning range of galvanometer mirrors. To overcome this problem, the whole laser scanning system was set on an X-Y positioner which are driven by stepper motors. The whole exposure area is divided into some regions each of which is smaller than range of galvanometer mirror system, and it is exposed by repeating fast scanning by galvanometer mirrors and slow sliding by the X-Y positioner. Problems occurring at the region boundary were investigated. As counter measures, overlapping of exposure areas and switching of region boundary are introduced and successfully eliminate the problem.