DFM Checklist for LSR Custom Mold Design

Liquid silicone rubber (LSR) molding delivers high-precision, biocompatible parts for medical, automotive, and consumer applications. For buyers evaluating mold suppliers, understanding design-for-manufacturability (DFM) criteria is essential to avoid costly tooling revisions, ensure consistent part quality, and meet tight tolerances. This checklist focuses on molded part geometry, venting, gating, and ejection considerations specific to LSR’s low viscosity and rapid cure characteristics, helping you communicate clear requirements to your tooling partner.

Part Geometry and Wall Thickness

LSR flows easily into thin sections, but uneven wall thickness can cause differential shrinkage, sink marks, or warpage. Maintain uniform wall thickness where possible, targeting 0.5 mm to 3 mm for most applications. Avoid abrupt transitions; use radii of at least 0.5 mm on internal corners and 1.0 mm on external corners to reduce stress concentrations. Features such as ribs, bosses, and snap-fits should follow LSR-specific guidelines: rib thickness no greater than 60 % of nominal wall, height limited to three times wall thickness, and draft angles of 0.5° to 1.5° per side for easy ejection. Undercuts require side-actions or collapsible cores; confirm that the mold design accommodates these without increasing cycle time excessively.

Venting and Overflow Design

Due to LSR’s low viscosity, air entrapment is a common defect if venting is inadequate. Place vents at the end of fill paths, typically 0.02 mm to 0.05 mm deep and 2 mm to 5 mm wide, ensuring they are shallow enough to prevent flash but deep enough to allow gas escape. Use overflow wells or traps to capture excess material and prevent flash on parting lines. For complex geometries, consider vacuum-assisted venting or micro-vent arrays. Validate vent locations through mold flow simulation, focusing on areas where flow fronts converge. Proper venting reduces internal voids, improves surface finish, and minimizes post-mold trimming.

Gating, Runner System, and Ejection

LSR molds commonly use cold runner systems with valve gates or tip gates to control fill and minimize waste. Gate diameter should be sized to balance shear heating and pressure drop; typical ranges are 0.5 mm to 1.2 mm depending on part size and wall thickness. Position gates to avoid weld lines on critical surfaces and to promote balanced filling. Runner layout must be symmetrical to prevent uneven cooling and shrinkage. Ejection requires careful design: LSR parts can stick due to low surface energy. Use ejector pins with adequate draft, consider stripper plates for thin-walled parts, and specify surface treatments (e.g., nickel plating) on mold cavities to reduce adhesion. Include clearance for ejector return and verify that ejection forces do not deform the part.

Applying these DFM principles early in the design phase reduces risk, shortens lead times, and ensures your custom LSR mold delivers repeatable, high-quality parts. For a detailed review of your part design or to request a quote on custom mold making, contact our engineering team.

DFM Checklist Summary

Maintain uniform wall thickness (0.5 mm–3 mm) and use radii ≥0.5 mm internal, ≥1.0 mm external.
Limit rib thickness to ≤60 % of wall, height ≤3×wall, and add draft 0.5°–1.5° per side.
Place vents at fill ends, depth 0.02–0.05 mm, width 2–5 mm; validate with mold‑flow simulation.
Use overflow wells or traps to capture excess material and prevent flash on parting lines.
Select gate diameter 0.5–1.2 mm, position gates to avoid weld lines and ensure balanced filling.
Design ejection with adequate draft, stripper plates for thin walls, and surface treatments (e.g., nickel plating) to reduce adhesion.
Confirm undercut features are accommodated by side‑actions or collapsible cores without excessive cycle‑time increase.
Verify runner layout symmetry to prevent uneven cooling, shrinkage, and weld lines.

Apply this checklist to your next LSR project and let our engineers perform a quick DFM review or provide a no‑obligation RFQ—contact us today to get started.