Injection Mold Design Guide ((hot))
Require stainless steel (420 SS) or hard chrome plating. Abrasive materials (GF-PA): Require D2 or A2 tool steel with TiN coating.
| Ejector type | Use case | |--------------|----------| | Round ejector pins (2–10 mm dia) | General – standard | | Sleeve ejectors | Around core pins (hubs, bosses) | | Stripper plate | Large flat parts, thin-wall | | Air poppets | Deep ribs, fragile features |
Maintain a consistent wall thickness throughout the part. If changes are necessary, make them gradual (50% max change over a short distance). Guidelines: Ideal thickness is generally 1.5mm - 3mm. B. Draft Angles injection mold design guide
Rib thickness should be 40% - 60% of the nominal wall thickness to avoid sink marks on the opposite surface.
| Defect | Root Cause in Mold Design | The Fix | | :--- | :--- | :--- | | | Rib too thick; Wall too thick. | Reduce rib to 50% of wall; core out backside of boss. | | Weld Lines | Gate too far from obstacle; No vent. | Move gate; Add an overflow well; Add vent 0.5mm from weld point. | | Flash | Clamp force too low; Venting too deep . | Increase tonnage; Reduce vent depth to 0.0005". | | Burn Marks | Trapped air compressing & igniting. | Add vents to the last place the plastic fills. | | Warpage | Uneven cooling; Non-uniform walls. | Balance cooling lines; Add ribs to stiffen against internal stress. | | Short Shot | Gate too small; Runner too long. | Increase gate cross-section; Use a hot runner. | Require stainless steel (420 SS) or hard chrome plating
This is the most violated rule in plastic design. Thick sections cool slower than thin sections, causing sink marks and voids.
Not all molds are built equally. The SPI (Society of the Plastics Industry) classifies molds by lifespan. If changes are necessary, make them gradual (50%
Draft is the taper applied to vertical walls to allow the part to release from the mold.
General-purpose tool steel that can be polished or heat-treated, offering better corrosion resistance than P20. H13 is ideal for high-volume production and abrasive resins like glass-filled nylon.