Plastic as a replacement for metal: when is it worthwhile?

Switching from metal to plastic can reduce weight, maintenance and costs. Here’s how to know when it’s the right move. The switch requires you to look at the application as a whole, not just the material price per kilo.

Why switch to plastic?

Plastic weighs less than metal. In applications where weight matters, such as transport and logistics and moving machine parts, the weight reduction can bring direct benefits. Lower weight means lower energy consumption and easier handling.

Plastic does not rust. In damp, chemical or marine environments, plastic can therefore offer a longer service life and require less maintenance than steel or aluminium. PE-1000, PVDF and PTFE are examples of materials that can withstand harsh environments.

Plastic can also reduce noise and vibrations. Gears and bearing housings made from POM run more quietly than equivalent metal components. This improves the working environment and can reduce the need for sound insulation.

Disadvantages to consider

Plastics have lower stiffness and strength than metal at high temperatures. If the component is to bear a heavy load at elevated temperatures, you must choose the right material, such as PEEK or glass-fibre-reinforced PA6.

Plastic also has a different coefficient of thermal expansion and can deform under prolonged stress, a phenomenon known as creep. Therefore, the design must be adapted to the material’s properties, rather than simply copied from a metal original.

Another limitation is that plastics do not conduct heat and electricity in the same way as metal. In some applications, this is an advantage; in others, a disadvantage. Heat-dissipating plastic grades are available, but they do not replace metal in all cooling applications.

Materials that often replace metal

POM-C and POM-H often replace brass and steel in mechanical engineering for bearing housings, gear wheels and sprockets. PA6 is used for wear parts and wheels. PC replaces glass in machine guards.

For harsh environments, PVDF, PTFE and PEEK are available. For food contact, there are food-grade grades of PE-HD, PA6 and POM. POM, PA6 or PE-HD are often used for electrically insulating components.

Before changing materials, you should carry out a comparison of service life and costs. Take into account material costs, machining, maintenance and downtime. In many cases, plastic can offer a lower total cost despite a higher material price per kilogram.

Examples of successful replacements

A common application is replacing steel wheels with nylon wheels in industrial trolleys. This reduces weight and improves the wheels’ resistance to corrosion. Another example is replacing brass bearing housings with POM, which reduces both weight and friction.

In conveyor belts, PE-1000 is used instead of steel to reduce friction and wear. In tanks and containers, PVDF or PTFE replaces metal when chemicals are involved.

Next steps

Are you considering switching from metal to plastic? Contact our materials advisers for a consultation, view the materials in our range or use VisualCutter to order blanks in the correct dimensions.

Calculate the total cost

When comparing plastic and metal, you should consider more than just the material cost. Factor in machining, assembly, maintenance, downtime and logistics. A plastic component may be more expensive to purchase but cheaper to maintain.

Also consider service life in the specific environment. A metal component that rusts may need to be replaced frequently, whilst a plastic component will last longer in the same environment.

Design adaptation

Changing materials often requires design modifications. Plastic cannot withstand the same stresses as metal and may require thicker walls or reinforcements. The design should make the most of plastic’s advantages, such as mouldability and low friction.

Work with both the designer and the materials supplier at an early stage. With the right design, plastic can replace metal without compromising on function.

How to switch from metal to plastic

A switch from metal to plastic begins with assessing the load, temperature, environment and assembly requirements. Compare the mechanical properties of the current metal part with possible plastic alternatives. Bear in mind that plastic may require a larger cross-section or reinforcement to withstand the same load.

The next step is to redesign the component for plastic. Metal designs are often optimised for the way metal behaves, whilst plastic components can benefit from rounded corners, uniform wall thickness and friction-reducing surfaces. Prototype manufacturing is a good way to test fit and function before mass production.

Also bear in mind the costs of tooling and production. Plastic can reduce weight, minimise corrosion damage and eliminate the need for lubrication. In many cases, the component can be manufactured directly from sheet material by turning or milling, without the need for expensive moulding tools.

Summary

Plastic can replace metal in many applications, offering lower weight, better corrosion resistance and reduced maintenance. The choice of material and design determines whether the switch will be successful.

Compare properties, redesign the component and produce a prototype. Please contact us if you would like to discuss whether your metal parts can be replaced with plastic.

Frequently asked questions

Can all metal components be replaced with plastic? No. Components exposed to very high temperatures or extreme mechanical loads may still require metal.

Is plastic always cheaper than metal? Not always. Plastic can offer a lower total cost through reduced weight and maintenance, but the material itself is not always cheaper.

Are new drawings required? Yes, a plastic component often needs to be redesigned to suit the properties of the plastic, rather than simply copying the metal original.