Replacing Aluminium with Plastic: When Is It Worth It?

Replacing Aluminium with Plastic – Key Takeaways

• Plastic can offer significant weight advantages compared to aluminium.
• Substitution is particularly worthwhile for housings, covers, load carriers, trays and technical packaging solutions.
• The decisive factors are component geometry, mechanical load, temperature, production volume, operating environment and desired additional functions.
• Thermoformed plastic parts can enable corrosion protection, electrical insulation and functional integration without additional coating or assembly.
• Aluminium often remains the better choice for very high temperatures, safety-relevant load-bearing structures or extreme point loads.
• A technical DfM assessment is useful because aluminium components usually cannot be transferred to plastic without design changes.

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When Is It Worth Switching from Aluminium to Plastic?

Switching from aluminium to plastic is particularly worthwhile when the component is not just “manufactured differently”, but can also be functionally improved. Typical reasons include:

• lower weight
• easier assembly
• electrical insulation
• corrosion resistance
• or lower total costs in series production.

Substitution is especially relevant for components that have previously been made from aluminium but do not have to meet permanently extreme mechanical or thermal requirements. Examples include:

• technical housings
• battery and electronics covers
• claddings
• trays and workpiece carriers
• transport packaging
• inlays and load carriers
• protective covers
• covers for machines or devices

For these applications, thermoformed plastic parts can be an economical and technical alternative, especially when the component is required in medium to higher quantities.

What Advantages Does Plastic Have over Aluminium?

Plastic differs fundamentally from aluminium in several material properties. Depending on the application, these differences can become a decisive advantage.

Weight Reduction

Plastic is significantly lighter than aluminium. Depending on the material, wall thickness and component geometry, weight advantages can be achieved without compromising the function of the component. This can reduce transport costs, simplify handling and improve energy efficiency in mobile applications.

Especially for trays, housings or covers, every gram saved has an impact across the entire series.

Corrosion Resistance

Plastic does not corrode in the traditional sense. In humid, salty or chemically demanding environments, this can be a major advantage. Aluminium is generally corrosion-resistant, but depending on the medium and operating environment, it may require additional surface treatments such as anodising, coating or painting.

For components that regularly come into contact with moisture, cleaning agents or chemical substances, plastic can reduce the effort required for surface treatment and maintenance.

Electrical Insulation

Plastic is naturally electrically insulating. This is particularly important for battery housings, electronic components or workpiece carriers for sensitive parts. Aluminium is conductive and, in such cases, often requires additional insulation measures, coatings or inserts. Plastic can reduce process steps while improving the function of the component.

Functional Integration

With thermoformed plastic parts, certain functions can be integrated directly into the geometry. These include, for example:

• holders
• contours
• positioning aids
• sealing surfaces
• stacking geometries
• grip recesses
• guide elements
• labelling or marking areas

This can reduce the number of additional components, while assembly effort and post-processing can also be reduced depending on the application. Complex clips, hinges or snap-fit connections depend more strongly on the specific process and geometry and should be technically evaluated.

Use of Recycled Materials

Another advantage can be the use of recycled plastics. High-quality recycled materials made from ABS, PP or PET can be used in many technical applications, provided the mechanical, thermal and optical requirements are met.

An application-specific evaluation is important here. Recycled material is not automatically suitable for every component. However, if the requirements are met, the use of recycled plastic can reduce costs and improve the sustainability balance.

When Is Aluminium the Better Choice?

Plastic is not the better solution for every application. Aluminium remains a sensible choice when particularly high mechanical, thermal or safety-relevant requirements apply.

Aluminium is often better suited when:

• permanently high operating temperatures occur
• maximum stiffness is required in very limited installation space
• load-bearing or safety-relevant structures are involved
• extreme point loads act without any tolerance for deformation
• very tight tolerances are required
• only individual parts or very small batches are needed without tool investment
• electrical conductivity is explicitly required

For continuous temperatures above the range of many standard plastics, it must be carefully checked whether a suitable engineering plastic is available. High-temperature plastics can expand the application range, but they are usually significantly more expensive and not economical for every thermoforming project.

What Does Material Substitution from Aluminium to Plastic Mean?

Material substitution does not simply mean producing an aluminium part from a different material. In many cases, the component is rethought entirely. Aluminium parts are often produced by milling, punching, bending, welding or assembling several individual parts. Plastic parts, on the other hand, can be manufactured by thermoforming, injection moulding, 3D printing or machining plastic, depending on the application.

In plastic thermoforming, a thermoplastic sheet or film is heated and formed over a tool. This produces components with adapted wall thicknesses, radii, draft angles and process-compatible geometry. Switching to plastic is therefore always also a change in design logic.

The goal is not to copy aluminium exactly. The goal is to create a plastic component that fulfils the same function and ideally offers additional benefits.

What Does It Cost to Switch from Aluminium to Plastic?

The costs of a material change depend heavily on component geometry, production volume, material, tooling effort and post-processing. A general statement would therefore not be reliable. However, typical cost drivers can be compared.

Comparison of Aluminium and Thermformed Plastic

Thermoforming is particularly interesting when a component is required in series production and the tooling costs can be amortised across multiple parts. For very small quantities, aluminium may remain more economical because there are no or only low tooling costs.

For medium and higher production volumes, plastic can offer advantages because material costs, component weight, assembly effort and post-processing can be reduced. The decisive factor is always the total cost analysis, not just the unit price.

Which Costs Should Be Evaluated?

For a reliable assessment, the following points should be considered:

• tooling costs
• material costs
• unit costs
• post-processing
• assembly effort
• weight and transport costs
• coating or surface treatment
• inspection effort
• adjustment costs in the event of changes
• service life and reusability

Only the combination of these factors shows whether plastic is more economically viable than aluminium.

Which Plastics Are Suitable Alternatives to Aluminium?

Material selection depends on the requirements of the component. The most relevant factors are mechanical load, temperature, chemical resistance, fire protection, electrical properties, appearance and recyclability.

Commonly Used Plastics at a Glance:

• ABS: housings, covers, load carriers, electrical insulation
• PP: transport packaging, chemically resistant components, lightweight construction
• PC: protective covers, viewing windows, impact-resistant components
• PET: food contact, transparency, recyclability

What Should You Consider When Replacing Metal with Plastic?

A common mistake in substitution is trying to manufacture an existing aluminium component from plastic without changing the design. This often leads to problems with stability, demoulding, wall thickness or assembly. Plastic behaves differently from aluminium. The following points must therefore be evaluated from a design perspective:

• wall thicknesses
• radii
• draft angles
• material distribution
• stiffness
• fastening points
• temperature behaviour
• tolerances
• post-processing
• stackability or assembly capability

Design for Manufacturing is therefore an important step. It evaluates whether geometry, material and manufacturing process are compatible. This allows technical risks to be identified early and unnecessary revision loops to be avoided.

Practical Example: Plastic Battery Housing Instead of Aluminium

Energy storage manufacturer NAEXT replaced heavy aluminium battery housings with thermoformed plastic solutions made from recycled ABS. The material change resulted in weight reduction, better electrical insulation and lower total costs. The cover and lower section were produced in a combination tool, which reduced tooling costs and shortened delivery time.

You can find the full case study here: NAEXT Battery Housing – From Aluminium to Plastic

Decision Guide: When Is It Worth Switching from Aluminium to Plastic?

The following overview provides an initial assessment of whether plastic can be a suitable alternative to aluminium.

This table does not replace a technical evaluation, but it provides initial guidance. Especially for functional components, early assessment based on CAD data or technical drawings is worthwhile.

Conclusion: Replacing Aluminium with Plastic Is a Technical and Economic Decision

Switching from aluminium to plastic can be worthwhile when weight, electrical insulation, corrosion behaviour, functional integration or costs play an important role. Thermoformed plastic parts in particular offer interesting possibilities for housings, covers, trays, inlays and technical packaging solutions.

At the same time, plastic is not automatically the better choice. For very high temperatures, safety-relevant load-bearing structures, extreme point loads or very small quantities, aluminium may still be the more suitable option.

The decisive factor is a technical assessment of the specific component. Material, geometry, manufacturing process and production volume must be aligned. If these factors are evaluated early, an aluminium component can become a plastic solution that is economical, functional and suitable for production.

Have your project technically reviewed. formary evaluates whether a thermoformed plastic part is a suitable alternative to your aluminium component.

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