导光板成型技术台湾.ppt

導光板成型技術探討 K.C. Lin The Injection Molding Machine Common Problems in Injection Molding short shot and incomplete filling over-packing flash and resin bleeding air trap bubbles and voids jetting welding line part burning and degradation hesitation effect brittleness of part crazing of part discoloration of part flow marks surface waviness surface lamination surface defects mica specks, silver streaks sticking in cavities, demolding problem sticking in sprue sink mark shrinkage and warpage stress-induced problem others Fountain Flow Describes the phenomena of how plastics flows in a mold Material that enters the cavity first forms the frozen layer near the gate Material that enters the cavity last is in the center of the cross section Has direct influence on molecular and fiber orientation at the part surface Injection Pressure Pressure required to push the plastic into the mold cavity Limited by machine capability Hydraulic pump limitations Usually around 20,000 - 26,000 psi Modern machines can go up to 43,000 psi Major influence on final part dimensions Factors Affecting Injection Pressure Melt-Front Area(MFA), Melt-Front Velocity(MFV) Uni-Directions and Controlled Flow Pattern Avoid Hesitation Effects Moldex3D模流分析判圖說明短射 (流動遲滯) 遲滯現象發生區域容易造成塑料提早凍結(freeze)，使該區域發生滯料或充填不飽的問題。 手機設計常有遲滯問題，此問題來自不均勻的厚度設計，造成模腔內部的塑料形成競爭狀態，厚度較薄的區域阻力較大往往造成成品短射，成型後也因為有較高的殘留應力而造成局部區域破裂！ Avoid Underflow Packing Profile Prof1 on bottom starts to even out pressures within cavity. Volumetric shrinkage more uniform but can be made better Packing Profile Profiles made the shrinkage on the part more uniform overall In Profile 3, the minimum shrinkage was caused by area of overpacking Long gate freeze time means increased decay time required to reduce the shrinkage near the gate. This however leads to overpacking further from the gate. Flow-Induced Residual Stress Thermal-Induced Residual Stress Experimental Design In order to find how the system responds