What OEMs Should Know About Engineering Grade Plastics Before Moving an Injection Mold

OEMs relocate tooling for a multitude of reasons, and when that transfer includes a material conversion, the technical stakes are even greater. Many approach Thogus with an injection mold that has spent years running commodity resins, but their next generation of parts require the thermal and mechanical performance benefits of engineering grade plastics.

This shift changes how the tool behaves and can cause warpage, flash, or premature wear in previously reliable steel. Since 1950, family-owned Thogus has applied deep material expertise to help OEMs understand these effects and complete transfers without compromising part quality or production.

Read on to explore our full insights and reach out to us for more information about our engineering support solutions and metal to plastic conversions.

Why Material Change Is the Riskiest Part of the Move

Commodity resins have broad processing windows, but engineering-grade plastics require tighter control and melt temperatures that often exceed 550 degrees Fahrenheit. These demands can affect the tool’s thermal performance, wear resistance, and ability to produce consistent parts. For that reason, a material conversion should be treated as a redesign rather than a simple relocation.

Shrinkage Will Change Part Geometry

Injection mold cavities are cut to compensate for a specific shrink rate. Unfilled polypropylene may shrink 1.5 to 2.0 percent, while 30 percent glass filled nylon can shrink as little as 0.3 percent in the flow direction. Since glass fibers orient along the flow path, shrinkage across the flow is typically two or three times greater. This anisotropy leads to warpage and out-of-tolerance dimensions. Plan for steel modifications. Thogus engineers typically recommend a steel-safe approach, keeping critical features oversized until sampling confirms shrinkage.

Tool Steel Must Resist Abrasive Fillers

Glass and mineral fillers can accelerate abrasive wear, particularly at gates and shutoffs. Pre-hardened P20, typically around 30 HRC, may not provide enough wear resistance for high-volume production with reinforced engineering grade plastics. Depending on the resin, production volume, and tool design, hardened H13 or S7, wear-resistant inserts, or nitrided surfaces may provide better long-term performance.

The Biggest Gap? Thermal Control

Running PPS or PBT in a cold mold may produce parts that pass initial inspection but later experience dimensional drift. Achieving the proper mold temperature may require pressurized water or oil units with high-temperature seals and baffles. Insulator plates can also stabilize cavity temperatures by reducing heat loss to the platens.

New Venting Requirements

Low viscosity nylons flash through gaps that polypropylene would never enter. A 0.0015-inch vent that worked well for a polyolefin may need to be reduced by about 0.0005 inches. At the same time, fast fill speeds can compress trapped gas until it ignites. This is a defect known as dieseling, and it’s a key reason why vent depth and placement deserve reevaluation.

Gate and Runners May Require a Design Update

Gate design influences fiber orientation, weld line strength, and residual stress. While a small gate may have been suitable for ABS, it can subject polycarbonate and degrade it. Semi-crystalline engineering grade plastics introduce the opposite problem as undersized gates can freeze before the cavity is filled. Hot runner components must also align with the new melt temperature and be fitted with wear-resistant tips.

Material Drying Is a Must

Engineering grade plastics are usually hygroscopic, meaning when wet material is molded, hydrolysis breaks the polymer chains, thus reducing mechanical strength. Parts may look perfect but fail during final testing. Desiccant dryers reaching a dew point of -40 degrees Fahrenheit, paired with moisture verification at the press, keep resin within tolerance.

Plan for Complete Process Requalification

Old process sheets provide little value after the switch to an engineering grade resin. When you transfer a tool to Thogus, our team applies scientific molding principles to establish a new process. We use viscosity curves, gate freeze studies, and cavity balance data to create a robust process window. Regulated programs may also call for PPAP or IQ/QQ/PQ documentation, so it is important to plan those deliverables at the outset.

Partner with a Molder with Engineering Grade Plastics Expertise

Thogus’s expertise is in molding high-performance parts using engineering grade plastic materials. Our equipment and engineering processes are tailored to the demands of these resin place on tooling, which allows us to identify potential transfer risks before they enter production.

If you’re looking to move an injection mold and use a new material for your program, get in touch with our team of professionals for guidance backed by decades of experience and advanced capabilities.