CNC machining is commonly associated with metal parts built for strength, durability, and long service life. However, metal is not the right material for every component. Machined plastics can provide useful alternatives when a part needs to reduce weight, resist corrosion, limit friction, provide electrical insulation, or meet other application-specific requirements.
Replacing metal with plastic is not simply a material swap. The replacement has to perform the required job while offering a practical reason to move away from metal in the first place.
In this article:
- How plastic and metal parts compare
- Why manufacturers replace metal parts with plastic
- When plastic can replace an obsolete metal part
- Which metal parts can be replaced with plastic
- Answers to FAQs about replacing metal parts with plastic
Not sure if metal or plastic makes more sense for your part? Contact Roberson Machine Company or call 573-646-3996 to discuss the application and your machining options.
How Are Plastic and Metal Parts Different?
Plastic and metal can sometimes perform the same job, but they bring different properties to the application. The better choice depends on which of those properties matter most for the finished part.
| Consideration | Plastic vs. Metal |
|---|---|
| Weight | Plastic is generally lighter, which can reduce component and assembly weight when metal-level strength is unnecessary. |
| Strength and Stiffness | Metal generally handles heavier loads and provides greater rigidity. Engineered plastics can work where loads remain within the material’s limits. |
| Corrosion and Chemicals | Many plastics resist moisture and chemicals without additional corrosion protection. Metal applications may instead depend on material selection, finishes, or designs suited for corrosive and washdown environments. |
| Friction and Wear | Certain plastics provide low-friction wear surfaces and may reduce or eliminate lubrication in moving components. |
| Heat and Dimensional Stability | Metal generally tolerates higher temperatures and changes dimensions less with temperature. Plastic performance varies considerably by resin and grade. |
Why Replace a Metal Part With Plastic?
A plastic part does not need to outperform metal in every category to be the better choice. For manufacturers and buyers, the practical question is whether changing materials solves a production, cost, or sourcing problem without sacrificing the performance the application requires.
Lower Total Part Cost
The price of the raw material is only one part of what a finished component costs. Depending on the design and material, switching to plastic may reduce expenses associated with:
- Material and machining costs
- Labor and setup time
- Handling and shipping
Fewer Production Steps
Changing materials may eliminate steps required to produce the finished part. If a plastic component is machined to its final condition without additional finishing, coating, heat treatment, or other secondary operations, the production process becomes shorter and involves fewer handoffs and opportunities for delay.
More Material Options
Replacing metal with plastic expands the range of materials available for consideration. That flexibility is useful when sourcing becomes part of the production problem.
- Material shortages: A suitable plastic may provide an alternative when a specified metal or alloy is difficult to obtain.
- Long lead times: Material substitution may keep production moving when the original material cannot be sourced within the required schedule.
Can Plastic Replace an Obsolete Metal Part?
Part obsolescence can turn a simple repair into a sourcing problem. An original metal component may no longer be manufactured, available from the original equipment manufacturer (OEM), or practical to obtain in the quantity needed.
What the Replacement Must Match
- Critical dimensions and mating features
- Required load and movement
- Wear surfaces and contact points
- Operating temperature and environment
A machined plastic replacement may meet these requirements without reproducing the original material. Engineered plastics provide the strength, wear resistance, and environmental performance needed for many applications.
The replacement can then be machined to the dimensions and features required to return an obsolete component to service.
What Metal Parts Can Be Replaced With Plastic?
Bushings, Sleeves, and Other Round Parts
Plastic may replace metal in bushings, sleeves, spacers, rings, pulleys, rollers, and other components produced through precision CNC machining. Roberson has used machined plastic for components such as ink rollers.
Housings, Covers, and Fixtures
Housings, covers, brackets, plates, mounts, manifolds, and fixtures may also be candidates for plastic when metal-level strength or rigidity is unnecessary. Examples include acrylic instrument parts machined for medical equipment.
Complex and Multi-Sided Parts
Plastic replacement is not limited to simple shapes. Examples of more complex machined plastic parts include:
- Contoured housings and enclosures
- Valve and sensor components
- Tooling and fixture components
- Parts with features on multiple sides
When should a part stay metal? High structural loads, sustained high temperatures, or demanding rigidity requirements may make metal the more appropriate choice.
FAQs About Plastic vs. Metal Parts
Is plastic cheaper than metal for machined parts?
Not always. Material price is only one part of the finished cost, and some engineering plastics can be more expensive than common metals.
Plastic may still reduce total part cost when the application requires fewer production steps, secondary operations, coatings, or other treatments.
Is CNC plastic machining the same as 3D printing?
No. CNC machining is a subtractive process that cuts a finished part from solid plastic stock. 3D printing is an additive process that builds a part layer by layer.
Machining can be a better fit when a plastic component requires tight tolerances, specific stock materials, machined surface finishes, or properties provided by solid plastic stock.
How long does CNC plastic machining take?
The production time for a machined plastic part depends on the material, geometry, tolerances, and quantity. A simple component may take considerably less time to produce than a complex, tight-tolerance part.
When requesting a quote, useful information includes:
- Part drawings or CAD files
- Material requirements
- Required quantity
- Tolerances and critical features
- Requested delivery date
Are machined plastic parts strong enough to replace metal?
They can be. The selected plastic must provide the strength, stiffness, wear resistance, and other properties required by the application. Parts exposed to high structural loads or demanding service conditions may still require metal.
Which plastics are commonly used to replace metal parts?
Different engineering plastics are used as metal alternatives depending on the equipment and application. Examples include:
- Acetal: Conveyor components, precision gears, valve parts, and mechanical assemblies
- Nylon: Industrial rollers, gears, bearings, and heavy-duty wear components
- UHMW: Conveyor guides, chute liners, wear strips, and material-handling equipment
- PTFE: Seals, valve components, chemical-processing equipment, and electrical components
- PEEK: Aerospace components, medical equipment, semiconductor equipment, and high-temperature industrial parts
Machine Plastic Parts Built for the Application
Roberson Machine Company machines plastic components for new designs, replacement parts, and applications where plastic may be a practical alternative to metal.
Before moving a part from metal to plastic, consider:
- What the component needs to do within the larger assembly
- Which dimensions, loads, and operating conditions the replacement must accommodate
- What the material change could mean for production, sourcing, and finished part cost
Planning a new or replacement plastic component? Contact Roberson Machine Company or call 573-646-3996 to discuss your CNC plastic machining project.
