The short answer: if your metal part is a structural housing, bracket, cover, or fitting that doesn't carry extreme loads or sit above 250°C, you can usually replace it with an engineering plastic — and cut weight, cost, and machining time at once.
Why metal-to-plastic is worth a look
Metal parts are machined, cast, or forged — every one of them. That means every unit costs roughly the same to make. Plastic parts are molded: you pay for the mold once, then every unit after that is cheap and identical.
Here is what you typically gain:
- Weight — plastics are 5 to 7 times lighter than steel, about 2 times lighter than aluminium
- Cost at volume — once past the mold, per-part cost drops sharply
- Corrosion — no plating or coating needed for most fluids and outdoor exposure
- Part consolidation — three machined parts can become one molded part, cutting assembly time
- Repeatability — injection molding holds tight tolerances part after part
What converts well (and what doesn't)
Good candidates: housings, brackets, covers and guards; valve components such as seats, seals, stems and bodies; gears, bushings and wear pads; handles, knobs and mounts; any part where you are paying for multiple machining operations.
Poor candidates — keep these in metal: parts under high structural load or impact; parts that must survive above about 250°C continuously; parts needing very tight flatness over long spans; electrical or thermal conductors.
The honest rule: metal wins on extreme load and extreme heat. Plastic wins everywhere else.
Choosing the right plastic
This is where most conversions go wrong — people pick a generic plastic and it fails.
| Material | Best for | When to choose it |
|---|---|---|
| PEEK | Wear, chemicals, heat to 250°C | The metal-replacement default — strongest, costliest |
| PSU | Medical, fluid handling, sterilisation | Transparency plus hydrolysis resistance |
| PPS | Chemical resistance, dimensional stability | Precision parts in harsh chemicals |
| PA66 plus glass | Structural, cost-sensitive | High strength at a lower price |
| POM | Gears, wear, tight tolerances | Low friction, self-lubricating feel |
The cost truth (and where the mold comes in)
A machined aluminium bracket costs money every single time you make one. A molded equivalent costs more up front — the mold — but the per-part cost after that is a fraction.
That is why we keep our mold lead time short (30 days) and our MOQ low: you don't have to commit to tens of thousands of pieces to justify the tooling. You can start with a small batch, validate the part in the field, and scale up only when it is proven.
How we do it in-house
- Review your part — we check load, heat, tolerances and fluids, and tell you honestly whether conversion makes sense
- Pick the material — we recommend the right resin and validate it with you
- Re-engineer the design — plastic needs different wall thicknesses, ribs and draft angles than metal; we redesign for molding, not just copy the metal shape
- Prototype and test — we build a prototype on our in-house CNC so you can validate before committing to tooling
- Mold and produce — in-house mold making and injection molding, small batch or mass production
The bottom line
Metal-to-plastic conversion isn't about cheaping out — it is about using the right material for the job. If your part runs under about 250°C and doesn't take extreme load, an engineering plastic like PEEK, PSU or PPS will usually be lighter, cheaper at volume, and corrosion-free.
Send us your drawing or 3D file, and we will tell you in plain terms whether it is worth converting — and quote both the mold and the parts within 24 hours.
Continuous-use temperature figures reflect publicly available technical data from material suppliers (SABIC, BASF, Solvay).