This paper reports an investigation of the effects of process parameters on the quality characteristics of polymeric parts produced by micro injection moulding (μIM) with two different materials. Four injection moulding process parameters (injection velocity, holding pressure, melt temperature and mould temperature) were investigated using Polypropylene (PP) and Acrylonitrile Butadiene Styrene (ABS). Three key characteristics of the mouldings were evaluated with respect to process settings and the material employed: part mass, flow length and flash formation. The experimentation employs a test part with four micro fingers with different aspect ratios (from 21 up to 150) and was carried out according to the Design of Experiments (DOE) statistical technique. The results show that holding pressure and injection velocity are the most influential parameters on part mass with a direct effect for both materials. Both parameters have a similar effect on flow length for both PP and ABS at all aspect ratios and have higher effects as the feature thickness decreased below 300 μm. The study shows that for the investigated materials the injection speed and packing pressure were the most influential parameters for increasing the amount of flash formation, with relative effects consistent for both materials. Higher melt and mould temperatures settings were less influential parameters for increasing the flash amount when moulding with both materials. Of the two investigated materials, PP was the one exhibiting more flash formation as compared with ABS, when corresponding injection moulding parameters settings for both materials were considered.
Two inbred parental lines, their f lt and six inbred lines selected for high yield after three cycles of recurrent selection in this population were evaluated at three locations for two years. The Fj yielded 32.6% more than the midparent value and exceeded the higher parent by 13.3%. The F! also exceeded the midparent values for several components of yield, including lint percentage, weight per boll, number of bolls per plot, lint index, and seed index.The mean yield of the six selected lines exceeded that of the F! by 5.5%. Each of the six lines was higher in lint yield and lint percentage than the higher parent of the original cross, which indicated that transgressive segregation for these traits had occurred.Fifteen possible crosses among the six lines were compared with the above entries at three locations in the second year. These hybrids averaged 9.6% higher in yield than the mean of their parents. Significant heterosis was also detected for lint percentage, weight per boll, number of seed per boll, and lint index.Estimates of general combining ability from the set of diallel crosses were significant for all traits except lint percentage, which demonstrated the importance of additive genetic effects for those traits. The variance for specific combining ability was significant only for lint percentage.
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