Double-sided microchannel patterning and through-hole production using injection molding of polypropylene

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 44-45).An experimental study was conducted on injection molded polypropylene parts with microchannels and through-holes. The quality of the microchannels and through-holes was observed with optical microscope and SEM images. A part-to-part variation analysis was conducted for ten parts by averaging the channel height, channel width, and hole diameter measurements obtained with an optical profilometer. The results were compared to a research study previously conducted on hot embossed and through-hole punched parts. The walls of the injection molded microchannels were observed to be smoother than the hot embossed microchannels, but ridges were detected on the outmost channels of the injection molded parts which resulted in measurement errors. The through-holes of the injection molded parts formed completely, without burrs or flash, in contrast to the through-hole punched parts where the quality of the hole varied by the substrate material. The average variance ratio of the channel height and width of the injection molded parts was 0.83% and 0.21% respectively, when the sites containing ridges (sites 1 and 4 of the top side) were not included in the calculation. The average channel height variance ratios were approximately the same for injection molding and hot embossing, while injection molding had less than half the variance ratio for the channel width. The hole diameter variance ratios of the injection molded parts averaged 0.094%, making it better than the other dimensions. No consistent expansion or shrinkage rate was observed in the injection molded parts, but the hot embossed sites primarily experienced shrinkage.by Nancy Diaz.S.B