Design for Manufacturing / Parting Line and Mold Construction
DfM In-Depth
Parting Line and Mold Construction: the choice that directly determines your mold price
The parting line and the number of sliders directly determine the mold price. The parting line is the separation between the two mold halves and always appears on the product as a fine seam. A shape that can be made with a simple two-part mold is cheaper and more reliable than one that requires sliders and lifters.
The parting line at the same time determines the release directions of all faces. Design and parting line are therefore in fact one decision, which we at QDP make early in the process together with the mold maker.
Designing out undercuts using the parting line
| Approach | Effect |
|---|---|
| Relocating or letting the parting line jump (stepped parting line) | Many undercuts disappear by themselves; this is above all the discussion between designer and mold maker |
| Breakthrough instead of undercut | A window in the wall allows a mold part to pass through; the two mold halves together form the hook without movement |
| Tilt feature outward | An internal groove becomes external, a cross rib extends in the release direction |
What a moving mold part costs you
If the undercut is functionally unavoidable, you consciously choose which moving mold part: a slider for external undercuts, a lifter (angle ejector) for internal hooks and clips, or a core puller for deep transverse cores. Every movement in the mold means a higher purchase price, longer construction time, extra marks on the product, and a greater chance of malfunction during series production. For low quantities, mold price is a major factor, while for high quantities, susceptibility to malfunction is more important.
Ejection is also part of this early choice: the product must be pushed off the core somewhere. Plan ejector pins on the non-visible side, on flat, sturdy zones such as rib crossings or boss edges.
You determine parting line and gating in the same step: view the complete DfM-pillar or go to gating and mold-flow.
What does this mean for your design?
Calculate your mold and unit price in 2 minutes, or ask our engineers for a DfM check.