Lately, a common question keeps coming up in conversations with our clients: steel and aluminum are getting more expensive—can plastics replace some metal parts?
The context is clear: tariffs are rising, energy prices are up, transportation costs are increasing… all of which push raw material prices higher. For companies that rely on metal parts, procurement costs are under pressure. In this environment, “plasticification” is increasingly being considered.
In this article, we’ll explore together: which parts are suitable for switching from metal to plastic, how cost-effective it is, and what potential risks might exist.
Why Consider Plastics Instead of Steel or Aluminum?
Simply put: cost pressure.
- Steel is cheap per kilogram, but the processing steps are complex, and with large volumes, production can get bottlenecked in CNC or stamping lines.
- Aluminum is light but already expensive, and processing efficiency is limited.
- Plastics (especially engineering plastics) may have a higher raw material cost, but once injection molding is used, the amortized cost per part can drop significantly.
To put it plainly:
Small batches → metals might be more cost-effective.
Large batches → plastics often win.
Case 1: Automotive Parts
A U.S. automotive supplier recently shared that their intake manifold, originally made of aluminum, saw a 15% unit cost increase due to tariffs. They tried using PA66 with glass fiber via injection molding. Although the initial mold cost was high, at scale, the unit cost ended up being lower than aluminum.
Even better, the plastic parts were lighter, slightly reducing vehicle fuel consumption—a win-win situation.
Case 2: Electronics Enclosures
A consumer electronics client insisted on aluminum for laptop shells because of the “premium feel.” But CNC machining aluminum was slow, and material waste was high.
Switching to a PC/ABS blend with coating treatment resulted in an almost identical look and feel, while cutting unit cost by roughly 20%.
Case 3: General Mechanical Components
Gears and pulleys are often made of steel. Some factories experimented with POM or PA6 replacements:
- Noise levels dropped (plastic has lower friction)
- No need for additional anti-rust treatment
- Cost became competitive in mass production
The drawback: load-bearing capacity is limited. Not all steel gears can be replaced.
Bottom Line: When Plastic Works
Not all parts are suitable for replacement. Limitations include:
- High temperature (>150°C) → most plastics fail
- Heavy load structural components → plastics may deform or fatigue
- Extremely high wear resistance → metals remain superior
Generally, parts that can be replaced are:
- Complex shapes with limited load
- Weight-sensitive components
- Parts exposed to corrosion
Does It Actually Save Money?
Here’s a practical reference:
| Material | Raw Material Cost ($/kg) | Processing Method | Amortized Unit Cost in Mass Production |
|---|---|---|---|
| Steel | 0.8–1.2 | CNC/Stamping | Cheaper for small batches, more expensive at scale |
| Aluminum | 2.0–2.5 | CNC/Extrusion | Moderate |
| PA66+GF | 3.0–3.5 | Injection Molding | Mass production significantly lowers cost |
| POM | 2.5–3.0 | Injection Molding | Suitable for small parts replacing steel |
Notice that the raw material for plastics isn’t necessarily cheap, sometimes even higher than steel. The key difference is: metal machining wastes material and is less efficient, whereas plastics can be molded quickly. At scale, plastics can undercut metals on unit cost.
Final Thoughts
If you’re evaluating a part for plastic substitution, it’s best to do a cost-performance comparison and consider supply chain risks.
At RJC Mold, we’ve helped numerous clients evaluate such decisions. If you’re exploring this path, we’re happy to discuss feasibility for your specific parts.
Continue Reading:
5 Design Pitfalls to Avoid When Switching Metal Parts to Plastic
Which Plastics Are Best for Replacing Metal Parts?
CNC Machining vs. Injection Molding for Plastic Parts: How to Choose