Essential Strategies for Plastic Injection Mold Design

Upon completing the product design and transitioning into the plastic mold design phase, the following are key points to consider, covering critical issues such as draft angle, P/L surface parting line, ejection marks, gate marks, and product undercuts:

Draft Angle Design: Ensuring that the product allows for an appropriate mold removal direction is crucial as it directly affects the smooth demolding of plastic products. Mold designers will design based on the product’s demolding direction. The deeper the product, the greater the draft angle required to prevent scratches, increased ejection marks, or even difficulties in demolding.

P/L Surface Parting Line Treatment: The parting line at the closure of the plastic injection mold significantly impacts the appearance and may leave marks. By designing the parting line at a step difference or the edge of a corner, the unaesthetic appearance can be reduced. Moreover, using mold surface treatment techniques such as sandblasting, engraving, or electrical discharge machining can effectively reduce the visibility of the parting line.

Optimization of Ejection Marks: Ejector pins are used to push the plastic product out of the mold and can leave circular or rectangular marks on the product. Although they cannot be completely eliminated, the use of a knockout plate mechanism in the design can prevent the appearance of ejection marks, thus improving the product’s surface quality.

Control of Gate Marks: The injection molding process inevitably has a gate point where a mark, possibly a line or a dot, may form. To avoid bumps or burrs, a recessed design is recommended to ensure it does not protrude above the plane. In areas with extremely high requirements, an in-mold cutting mechanism can be used to eliminate the gate mark.

Prevention of Product Undercuts: Undercut issues typically arise in the vertical direction of the product’s male mold. If they cannot be resolved through mechanism design, they can hinder mold development. Professional mold designers will carefully inspect and identify potential undercut issues during the disassembly of product drawings, communicating promptly with the client to ensure the feasibility of the mold design and the smooth production of the product.

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