Polyurethane Injection Molding

PU injection molding offers exceptional durability and flexibility, making it ideal for a wide range of applications.

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Erye Offer Polyurethane Injection Molding Service Specific to Your Needs!

Urethane injection molding is a process we use to make tough, flexible, and long-lasting polyurethane parts. It works well for both simple shapes and more complicated designs. The basic idea is to heat up the polyurethane, inject it into a mold under pressure, and let it cool down into the final shape. PU has solid mechanical properties—it’s flexible, handles impact well, and resists wear—so it’s a good fit for a lot of different jobs.

Here’s what we can help with on the urethane injection molding side:

We’ll help fine-tune the design to work better for molding
Build precise molds and tooling in-house
Handle anything from small batches to high-volume runs
Do post-processing like assembly, surface finishing, and packing
Adjust the material mix to meet specific performance needs

PU Injection Molded Part Design Guide

Quick reference tips to help you design polyurethane injection-molded parts with consistent quality and easy manufacturing.

Item	Description
Wall Thickness	PU flows well but cures slowly. Keep walls uniform (3–8 mm typical). Use smooth transitions to prevent voids or uneven curing.
Draft Angles	PU is tackier than thermoplastics. Provide at least 3° draft (5° if textured) to avoid sticking in the mold.
Corners & Radii	PU benefits from generous radii (≥2 mm small features, ≥5 mm structural) to reduce stress and bubbles. Avoid sharp edges.
Gates & Vents	Because PU foams easily, add vents at the end of fill (0.02–0.05 mm deep). Gate into thicker sections for smoother flow.
Shrinkage & Tolerance	Allow 0.5–1.2 % shrinkage. Critical dimensions should be oversized and finished by secondary machining if needed.
Inserts / Overmolding	PU bonds naturally to metal and some plastics. Roughen or undercut inserts, preheat them to 40–60 °C to improve adhesion.
Undercuts	Avoid where possible. If needed, design flexible PU sections or use special mold actions to release.

Features of PU Injection Molding

Advantages

Wide Range of Hardness

Polyurethane can be made really soft or really hard. It covers everything from soft rubbery parts (Shore A 20) to tough pieces (up to Shore D 90).

Easily Bond to Other Materials

PU adheres to metals and plastics easily during molding. Helpful for overmolded parts that need a strong connection

Handles Heavy Loads Well

PU holds its shape under pressure, so it works great for things that take a beating.

Stretches Without Tearing

PU can stretch quite a bit before it tears. Some grades hold up really well even under repeated stress.

Good for Outdoor Use

PU can handle sun and weather pretty well with additives. It lasts much longer outdoors than standard plastics—usually 2 to 3 times longer.

Limitations

Moisture Sensitivity During Processing

PU resins absorb moisture quickly; requires careful storage and drying to avoid bubbles and defects.

Require Complex Molding Equipment

Often requires specialized mixing/injection machines (high-pressure or low-pressure systems) rather than standard thermoplastic injection units.

Limited High-Temperature Resistance

Most PU grades soften or degrade above ~80–120 °C (176–248 °F), which restricts use in hotter environments.

Higher Raw Material Cost

Usually more expensive than commodity plastics like PP or PE.