Mold design is not just drawing. The first decision that drives everything else is the parting line. On a two-plate mold, we normally place it at the largest cross-section of the part so the molded product stays on the moving half after opening. Get this wrong, and you will fight sticking, short shots, or automatic drops that fail. Once the parting line is locked, the feed system has to be balanced. Gate location must avoid weld-line sensitive areas, especially on cosmetic or structural parts. For ABS, a side gate with a diameter of 0.8–1.2 mm is common. Too long, and you lose injection pressure; too short, and you risk jetting or snake flow that shows up as surface defects. In practice, I check gate size against wall thickness and flow length before cutting steel.

Cooling is where cycle time and dimensional stability are won or lost. Water lines are typically placed 12–15 mm from the cavity surface, with spacing equal to 3–5 times the water-line diameter. This layout keeps the mold surface temperature variation within ±2°C, which matters for warpage and sink marks. On multi-cavity tools, I also verify that each circuit has similar flow resistance so one cavity does not run hot. Ejection follows the same logic: calculate the ejection force from the part’s shrinkage grip, usually 0.1–0.2 times the holding force. Ejector pins should be no smaller than 2 mm in diameter to avoid punching through the part. For deep ribs or thin walls, use ejector sleeves or blades instead of round pins.

These numbers are starting points, not universal rules. Material grade, wall thickness, texture, and tool steel all shift the window. A balanced design review before wire EDM and cavity milling saves more time than any post-mold fix. If you are sourcing molds or comparing quotes, it helps to speak the same process language. For more mold sourcing information, visit MoldWorld at www.moldw.com.