Injection Mold Design Guide Jun 2026

Automatically shear off during ejection, minimizing manual post-processing labor.

Used when a part requires gating in the center or at multiple points away from the perimeter. A three-plate mold features two parting lines, allowing the runner system to automatically separate from the part during mold opening. 4. The Feed System: Runners, Gates, and Sprunes

The boundary where the two halves of the mold (cavity and core) meet. Selecting a proper parting line is crucial to minimize flashing and ensure clean part release.

The feed system delivers molten plastic from the machine nozzle into the mold cavities. It must minimize pressure drop, material waste, and shear stress. Sprue Design

: The industry standard for medium-volume production (up to 500,000 cycles). It offers a great balance of durability, machinability, and cost. injection mold design guide

Draft is the taper applied to the sides of a part to facilitate its removal from the mold.

Mold cycle times scale with the square of the wall thickness. Keep walls as thin as structurally possible. Transition Gradually

As plastic fills the mold, air trapped inside must escape. Cut shallow vent channels (0.01mm to 0.03mm deep, depending on the resin viscosity) along the parting line and near the end of the fill paths. Insufficient venting causes air entrapment, which compresses the gas and burns the plastic material. 6. Managing Side-Actions and Undercuts

A standard injection mold consists of two primary halves that form the cavity. Injection Molding - Design Your Product for Manufacturing The feed system delivers molten plastic from the

Thicker sections cool slower and shrink inward, creating surface dents.

Before cutting steel, designers use CAD and CAE (Computer-Aided Engineering) tools to simulate the molding process.

Beyond geometry, the guide acts as a masterclass in thermal dynamics via the . While most observers focus on the injection phase, over 70% of the molding cycle is dedicated to cooling the part solid enough to be ejected. A design guide does not simply suggest adding water lines; it dictates their placement. Conformal cooling channels—which follow the shape of the part using 3D-printed mold inserts—represent the cutting edge. The guide instructs designers to place cooling lines closer to hot spots (like thick ribs or bosses) and maintain turbulent flow for efficient heat transfer. Efficient cooling design translates directly to cycle time reduction; shaving two seconds off a cooling cycle for a part produced one million times results in over 500 hours of saved machine time. Thus, the mold design guide is an economic tool, turning minutes into margin. turning minutes into margin.

Use a transition zone (a 3:1 chamfer or radius) if thickness variations are unavoidable. Draft Angles

The guide told the story of a foolish apprentice who made a mold for a nylon gear without accounting for the 2% shrinkage. The gears came out like wavy potato chips. The master toolmaker didn’t yell. He simply handed the apprentice a caliper and said, “Measure the river before you build the dam.”

Use ribs to increase structural stiffness instead of thickening the walls. Rib thickness should be 50% to 60% of the main wall thickness to prevent sink marks on the cosmetic flip side. Bosses used for fasteners should follow the same thickness rules and include internal gussets for reinforcement.

: Avoid sharp internal corners. Rounded edges improve material flow and reduce stress concentrations that can lead to structural failure.

The mold opens and mechanical pins push the finished part out. 2. Fundamental Part Design Rules