Engineering plastics vs. metals – where are the advantages?

In many industrial applications, the question arises: Plastic instead of metal – when does switching materials make technical and economic sense? Engineering plastics can replace steel, aluminium or other metals in suitable components and offer advantages in weight, corrosion resistance, friction, electrical insulation and design freedom.

Whether replacing metal with plastic is possible, however, always depends on the specific requirements. Load, temperature, dimensional accuracy, chemical contact, wear and component geometry must be considered together. In the following comparison you will see where engineering plastics play to their strengths and when metal remains the better choice.

Lightweight construction and weight reduction

One of the most obvious advantages of plastics over metals lies in their weight. Engineering plastics such as POM, PA or PEEK are significantly lighter than aluminium or steel. This property plays a central role above all in vehicle and aircraft construction, but also in mobile devices. By reducing weight, not only can energy efficiency and performance be improved, but transport costs can also be lowered.

Advantages of plastics in lightweight construction:

• Low weight with comparable strength
• Simpler handling and assembly
• Energy savings through lower mass inertia

Chemical resistance and freedom from corrosion

Compared with metals, many engineering plastics offer high resistance to chemicals, solvents and moisture. This proves to be a decisive advantage particularly in medical technology, the food industry or chemical plant construction. While metals often have to be coated at great expense or alloyed to be rust-free, many plastics are inherently corrosion-free.

Typical areas of application for plastics due to chemical resistance:

• Laboratory technology and medical devices
• Pipes for aggressive media
• Tanks and pumps in the chemical industry

Processing and design freedom

Plastics can be formed into complex geometries more easily than metals. Injection moulding processes allow the production of highly complex components in large series without elaborate post-processing. In addition, the use of fillers, additives and reinforcing fibres allows specific properties such as strength, stiffness or sliding properties to be influenced in a targeted manner.

Material comparison: plastic vs. metal

Property	Engineering plastics	Metals
Weight	Very light	Medium to high
Corrosion resistance	High (depending on type)	Often low, prone to rust
Electrical insulation	Very good	Conductive
Temperature resistance	Up to approx. 250 °C (PEEK)	Very high
Mechanical load capacity	Medium to high	Very high
Design freedom	Very high (injection moulding)	Limited (milling, casting)
Recycling potential	Limited to possible	Very good

When is plastic instead of metal worthwhile?

A replacement of metal by plastic is particularly interesting when maximum strength or stiffness alone is not required. It is often worthwhile to examine an engineering plastic when several of the following requirements come together:

• Component weight is to be reduced
• Corrosion is to be avoided without additional coating
• Good sliding or wear properties are required
• Lubrication or maintenance effort is to be reduced
• Electrical insulation is required
• The component comes into contact with moisture or chemicals
• Noise and vibrations are to be reduced
• Complex component functions are to be combined in the design

Plastic is not a blanket replacement for metal. Particularly with very high stiffness, strong continuous loads, high temperatures or structurally critical loads, metal may remain more suitable. With thermoplastic materials, thermal expansion and creep behaviour must also be taken into account during design.

Which plastic can replace metal?

Which engineering plastic comes into question depends on the existing metal component and its function. A direct material substitution without adapting the design is not always sensible.

Engineering plastic	Typical strength in metal replacement	Examples of components
POM	Dimensional accuracy, good machinability as well as sliding and wear properties	Guides, gears, rollers, bushes
PA	Toughness and wear resistance	Bearings, rollers, guides and machine parts
PEEK	High thermal, chemical and mechanical load capacity	Demanding precision and functional parts

For higher requirements, high-performance plastics in particular may be of interest. For selection, continuous and peak temperature, mechanical load, media contact, tolerances and service life should be taken into account, among other things.

Costs and economic efficiency

Whether plastic is more economical than metal cannot be judged on the material price alone. What is relevant are the total costs of the component over production and use.

Depending on the design, plastic components can offer economic advantages because corrosion protection or additional surface treatments are eliminated, the component weight is reduced or several functions can be combined in one component. For sliding components, suitable plastics can also help to reduce lubrication and maintenance effort.

For machined parts, the machinability of the respective material also plays a role. Martan Plastics manufactures individual components using various plastic machining processes.

The economic assessment should therefore always consider component geometry, quantity, manufacturing process, service life and maintenance effort together.

Plastic or metal: the application dictates the material

Plastic instead of metal is worthwhile above all when low weight, freedom from corrosion, electrical insulation, good sliding properties or reduced maintenance are important requirements. Engineering plastics can therefore represent a high-performance alternative to steel or aluminium in many machine and plant components.

Metal, on the other hand, remains sensible when exceptionally high stiffness, load capacity or temperature resistance is required.

For a successful material switch, therefore, the existing metal should not simply be replaced by a plastic with similar characteristic values. Component geometry, load, temperature, media contact, tolerances and manufacturing must be considered together. Martan Plastics supports you in selecting suitable materials and in the plastic-appropriate design and manufacture of your components.

Frequently asked questions about plastic instead of metal

When can plastic replace metal?

Plastic can replace metal when the mechanical, thermal and chemical requirements lie within the property profile of the chosen plastic. Switching materials is particularly interesting for components where low weight, freedom from corrosion, sliding properties or electrical insulation are important.

What advantages does plastic have over metal?

The most common advantages include lower weight, corrosion resistance, electrical insulation, good sliding and damping properties as well as diverse possibilities in material selection and component design.

Which plastic is suitable as a replacement for aluminium?

For suitable applications, for example POM, PA or high-performance plastics such as PEEK may come into question. The selection depends on load, temperature, dimensional accuracy, media contact and component geometry. A blanket assignment of aluminium to a particular plastic is therefore not sensible.

When is metal better than plastic?

Metal is often the better choice when very high stiffness, high continuous mechanical load capacity, extreme temperature resistance or electrical conductivity is required. With plastics too, thermal expansion and time-dependent deformation under continuous load must be taken into account.