- 學位論文
氣體反壓在射出成型製程中對產品殘留應力及收縮影響研究
Study of the Effect of Residual Stresses and Shrinkage on Part by Gas Counter Pressure in Injection Molding
摘要
現今日常中充滿眾多種類的塑膠產品，射出成型製程在塑膠產業上有著大量生產與品質穩定等優勢，但熔膠在充填與冷卻過程中會產生殘留應力與收縮，導致翹曲變形與凹陷等缺陷，所以為減少產品在成型過程產生收縮變形，射出機螺桿在充填完畢後會進入保壓階段，將熔膠不斷推往模穴，補充產品收縮量而提升外觀品質與強度，但過高的保壓壓力會造成內部殘留應力增加。 本研究以氣體反壓應用在射出成型製程上，於模穴末端導入氣體，對熔膠波前施予壓力，與螺桿保壓共同擠壓熔膠，減少產品收縮缺陷；透過射出壓力、射出殘餘料量等機台反饋數據變化，探討反壓對於製程參數之影響；本研究利用較薄之平板形產品，以光彈效應、輝度計等測量方式，探討反壓氣體對產品殘留應力之影響，並以較厚之迴紋針形產品，探討氣體反壓對於厚件部份之收縮影響。實驗結果顯示，加入氣體反壓能增加熔膠射出量，提升產品重量與穩定性，同時反壓能有效改善截面收縮率，而在最靠近反壓口之收縮率變化更為明顯；反壓對平行與垂直於流動方向之收縮，可以改善32%、16%，另外經偏光應力與輝度(Luminance)觀察，發現適當的反壓壓力能有效改善產品內部殘留應力。
並列摘要
Today there are many types of daily products made by plastic. In plastic industry injection molding has many advantages such as mass production and stable quality, but the melt will have residual stress and shrinkage in the filling and cooling process, lead to the defects like warpage and depressions etc. To reduce the product shrinkage in the molding process, after filling the melt injection screw will start the packing stage by pushing the melt into the cavity. This way will enhance the quality and strength of product appearance. However excessive packing pressure will cause internal residual stress increases. In recent years it is found that Microcellular foam molding process with gas counter-pressure technology can inhibit the molten foaming size effectively with high-pressure gas filled in the mold cavity. This study discuss the effect of back pressure on process parameters by the injection pressure, the residual plastic quantity, and other data from the injection machines. This study applied counter pressure on the injection molding process. In the end of the cavity importing gas to provide the melt wavefront pressure, and the screw holding pressure co-extruded melt in result that reduce product shrinkage defects. This study uses the plate-shaped products to discuss the impact of gas counter pressure for residual stress by photo elastic effect and luminance meter measurement, etc. and the paper clip-shaped products to discuss the effects of gas counter pressure on shrinkage for thicker part. The results show that by adding gas counter pressure can increase the amount of melt injection and improve product weight and stability, while the counter pressure can effectively improve the cross-section shrinkage, especially at the area which is the closest to counter pressure. Counter pressure on parallel and perpendicular to the flow direction can improve the shrinkage of 32% and 16%. By polarizing stress and Luminance observation, it is found that a suitable counter pressure inside the product can effectively improve the residual stresses.