（28） Fusion joint Apparent In mold filling,Injection Molding Process Defect Handling Manual

Apparent In mold filling, a weld is a line where the front ends of each fluid meet. Especially where the mold has a highly polished surface, the weld seam on the product looks like a scratch or a groove, especially on products with deep or transparent colors. The position of the fusion joint is always in the direction of the material flow.
Physical causes
The place where the weld joint is formed is the place where the thin streams of molten material diverge and are connected together. The most typical is the molten flow around the core or products using multiple gates. At the point where the thin streams meet again, the surface will form fusion joints and flow lines. The larger the core around the melt or the longer the flow path between the gates, the more obvious the weld seam will be. Small fusion joints do not affect the strength of the product.
However, where the process is long or the temperature and pressure are insufficient, insufficient mold filling can cause significant grooves. The main reason is that the fluid front end is not uniformly fused to produce weak light spots. Spots may occur where pigments are added to the polymer due to significant differences in orientation. The number and location of gates determines the number and location of fusion joints. The smaller the angle at which the fluid fronts meet, the more obvious the weld seam.
In most cases, process commissioning cannot completely avoid fusion seams or material flow lines. What can be done is to reduce their brightness or move them to inconspicuous or completely invisible places
The causes and improvement measures related to processing parameters are shown in the following table:
1. Injection speed too low Increase injection speed
2. Melt temperature is too low to increase barrel temperature
3. Too low mold surface temperature increases mold temperature
4. If the pressure maintaining is too low, increase the pressure maintaining, and switch the pressure maintaining as soon as possible
5. Improper gate position Reposition the gate and move it to an invisible location
6. The size of the vent hole at the material flow path without an exhaust hole should conform to the characteristics of the material