Plastic injection parts are used for automobiles, electronic products, machinery, cellular phones and consumer products. Injection-molded parts can have a complicated shape, do not need pose-processing and have an advantage of mass production. Molding defects occur in plastic parts according to changes in material properties, complicated molding shapes, and process parameters. The injection molding defect, molded sink mark, affects the dimensions and warpage of the product. The molded sink mark is caused by crystallization, elastic recovery of a injection part, crystalline and amorphous polymer, or molding operation conditions (packing pressure, packing time, resin temperature, and mold temperature). The sink mark produces warpage of plastic part.
A method to improve the warpage of the plastic part is removal of residual stress of the plastic product. by making non-uniform cooling occurring in the injection molding process into uniform cooling. In this thesis, the rapid heating and cooling device was developed using a peltier module for uniform cooling.
A heat sink was designed to remove the heat generated for the purpose of increasing the efficiency of the peltier module. The efficiency was compared between the heat sink of Pine fins and that of Pin fins in an tunnel structure at each natural and forced convections. It was verified with computer-aided engineering (CAE) technology and experiments. As a result, the heat sink of Pine fins has a low temperature distribution toward the fin center both in the forced and the natural convection. The forced convection had better efficiency than the natural one regardless of the configuration.
A rapid cooling and heating device (RCHD) was manufactured and compared with the traditional water cooling device (TWCD) method in warpage leading to analysis results. The materials used were crystalline polypropylene and amorphous acrylonitrile-butadiene-styrene polymer. Variations in warpage were compared according to the molding process parameters such as packing pressure, packing time, resin temperature, and mold temperature. Molecular arrangement of injection-molding parts was examined with chemical etching against cooling time and mold temperature.
It can be shown that the RCHD method has a lower warpage than the TWCD method and consequently a more uniform cooling for amorphous acrylonitrile-butadiene-styrene polymer. Injection molded parts of amorphous acrylonitrile-butadiene-styrene polymer were examined after chemical etching. The injection-molding parts by the RCHD method have less distribution of white areas than those by the TWCD method and consequently it can be found that the RCHD method produces a uniform cooling.
The distribution state of the acrylonitrile-butadiene-styrene polymer was confirmed Through the Scanning electron microscope. In the TWCD method the distribution state of the polymer be densely distributed, and RCHD method be distributed wider than TWCD method. this is that injection molded parts be seen that cooling was made uniformly. As the temperature of the mold is gradually progress, The particles of the polymer is increased, this is that internal stress was reduced.
Through of experimental method(DOE), Optimum molding condition of the injection molding are a mold temperature of 75℃, holding time 2.5sec, cooling time 20sec, and the holding pressure for 20kg/cm2 in the ABS resin. and mold temperature of 35℃, holding time 2.5sec, cooling time 20sec, and the holding pressure for 20kg/cm2 in the PP resin.