Mold Design Fundamentals P3

When the plastic melt fills the mold, it displaces the air. The displaced air must be removed quickly, or it may cause burn spot (due to the fast compression of trapped air pocket by the low-thermal-conductivity polymer melt), or it may restrict the flow of the melt into the mold cavity, resulting in incomplete filling (short-shot problem). Consider the injection-molding of a air bag housing. Notice that the part consists of a thin central region and a thick rim around it. A single gate is adopted in the original design. Most of the melt flow along the part side since...