Material Selection for Case Construction

What does a case need to do?

A case is the enclosure around a product’s components. In an electronic system, it helps protect the components from damage and provides a usable outer shape. It may also support controls, displays and connections. Material selection therefore starts with the product’s purpose, not simply its appearance.

For example, a handheld electronic controller needs a case that is comfortable to carry and can withstand everyday knocks. A display cover may need a rigid sheet material, while a case with many shaped features needs a material and process capable of producing those features accurately. These requirements can lead to different choices even though all three products contain electronic components.

The designer must balance physical properties, working properties, sustainability and manufacturing processes. A material that meets only one of these considerations may still be unsuitable overall.

Connect properties to the product’s requirements

Physical properties describe characteristics such as density and thermal or electrical behaviour. Density affects how much a case weighs for a given volume: this matters more for a portable product than for one that remains on a desk. Thermal and electrical behaviour must also suit the system inside the enclosure.

Working properties describe how a material behaves under forces or during manufacture. For case selection, a particularly useful property is toughness: resistance to breaking under impact. A tough enclosure is useful where a product may be dropped because it helps protect the components inside. Rigidity is important where the case must retain its shape rather than flex excessively.

Think about the conditions of use as well. A material must withstand the temperatures it will experience without losing the shape or performance needed by the case. There is little value in choosing a material that is inexpensive and easy to shape if it cannot cope with the product’s operating conditions.

Properties need to be linked to a consequence. ‘The material is tough’ identifies a characteristic; ‘its toughness helps the case survive knocks during portable use’ explains why it is suitable.

Compare suitable polymers

Polymers are widely used for electronic cases because suitable types can combine useful working properties with the ability to be moulded into complex shapes.

ABS — acrylonitrile butadiene styrene — is used for consumer electronic casings. Its durability and toughness make it a candidate for a case exposed to regular handling, and it can be moulded into complex shapes. This makes it worth considering where the enclosure needs shaped details as well as protection.

Polycarbonate is another polymer used in electronic casings. It is tough and impact-resistant, so it is a strong candidate where resistance to knocks is a priority. However, it can be more expensive than lower-cost polymers. Its extra performance must justify the cost for the intended product.

Acrylic is a rigid polymer available in sheet form and used for display cases and protective covers. Sheets can be cut and formed, making acrylic worth considering for a bespoke enclosure or prototype. Its suitability still depends on the forces and conditions the finished case will experience; rigidity alone does not establish impact resistance.

Polypropylene is a relatively inexpensive polymer used in high-volume products. It may be attractive where cost is important, but the designer must still check that its properties meet the case’s requirements. Low price cannot compensate for inadequate protection or performance.

These are alternatives to compare, not a fixed ranking. The intended use determines which advantages matter most.

Choose the material and manufacturing process together

The same case design can be economical at one production quantity and uneconomical at another. Material selection must therefore take account of both the required shape and the scale of production.

For a one-off case or prototype, polymer sheet can be cut and formed into the required parts. Acrylic or polycarbonate sheet may be suitable starting materials. This approach allows a bespoke shape to be developed without committing immediately to production tooling.

For large quantities of complex cases, injection moulding is a suitable option. Molten polymer is injected under pressure into a mould, then cooled. The process can produce intricate shapes with a high-quality finish, and the tooling has a long working life. However, the mould is a significant initial investment, so the quantity being made matters when judging overall cost.

Vacuum forming offers another route for suitable case shapes. A thermoplastic sheet is heated until soft, then air is removed beneath it so that it is drawn over a mould. Compared with injection moulding, moulds are generally cheaper and new designs can be accommodated more easily. This can make the process attractive when a design may change, although the required shape and detail must suit sheet forming.

A useful decision is therefore not just ‘choose a polymer’, but ‘choose this polymer in this stock form, made by this process’. The material, case geometry and manufacturing method must work together.

Assess sustainability over the whole life

Many polymers are made from oil or natural gas, which are finite resources. Extraction, processing and manufacture use energy and can produce emissions. Selecting recycled polymer can reduce the demand for new raw material, but it must still provide the performance required by the case.

A life-cycle analysis considers environmental impacts at each stage:

• extraction and processing of raw materials, including energy inputs;
• manufacture and assembly;
• transport to the customer;
• use of the product;
• disposal or recycling.

For a case, durability is part of this assessment. An enclosure that lasts and protects its components can help avoid premature replacement of the whole product. Conversely, repeated replacement creates further demand for materials, manufacturing and transport.

End-of-life design matters too. Choosing a recyclable material is more useful if the case can be separated from the electronic components and collected for recycling. Thermoplastics can be reheated and reshaped, whereas thermosetting polymers cannot be remelted in the same way. Recycling possibilities therefore differ between materials.

Do not assume that a plant-based or biodegradable polymer is automatically the best enclosure material. It must still meet the product’s performance requirements, and its environmental value depends on its complete life cycle and how it is dealt with after use.

Reach a justified material choice

Suppose a manufacturer is developing a handheld electronic controller in large quantities. ABS would be a reasonable candidate because its toughness and durability suit regular handling, while injection moulding can produce a complex case consistently. Polycarbonate would be an alternative if impact resistance were especially important, but its higher material cost would need justification.

The final decision should weigh protection, shape, cost, production quantity and environmental impact together. For a one-off prototype, cut and formed sheet might be more appropriate than investing in an injection mould. For the production version, a durable moulded case using suitable recycled material could offer a better balance. A justified choice explains why the selected combination fits the particular product better than the alternatives.