Switching From Metal to Plastic

The manufacturing sector is constantly evolving and seeing new trends and practises develop. Among the most exciting of these is the relatively recent idea of designers replacing metal parts with injection-moulded plastic ones.

If you haven’t encountered this trend yet, this idea may seem a little unusual. Metal parts have long represented the gold standard in many applications from the very moment that humanity learned how to work the material in the first place.

Nevertheless, a great many advances in both technology and materials have slowly began to challenge this assumption. In many high-tech sectors, such as the automotive and aerospace industries, there has been a profound shift towards the use of advanced, highly-engineered plastics in areas that would once have been the exclusive domain of metals.

The exact reasoning behind this can vary from piece-to-piece, but there are several factors that usually come into play:

• Weight
• Strength
• Reliability
• Sustainability
• Finish
• Cost

Weight

One of the most important reasons often found behind the move towards plastic is that of weight. In the vast majority of situations, it is a simple fact that metal parts are going to be heavier than plastic ones. And when those parts are going in a high-performance car, or even an aeroplane, every single gram that you can save in design can translate into improved performance.

However, weight does not only factor into billion-dollar, high-performance projects. Even in relatively mundane products, a reduction in weight can have a real impact when it comes to factors such as ease-of-use and shipping costs. Even cutting an amount as apparently minor as ten percent can result in noticeable changes in the amount you pay to get your product to customers or distributors.

Strength

While it is true that metals are usually stronger than plastics, in some situations a move towards plastic components can actually result in boosted strength and performance. Engineering-grade plastics can often come out on top of metals in terms of tensile strength – the maximum load that a material can support when being stretched before it fractures - when compared to commonly used metals.

This advantage becomes especially clear when looking at the ratio between strength and weight – a factor that is of prime importance in a great many applications.

Reliability

In addition to this, the strength of plastic parts can be more reliable and last longer than their metal counterparts. This is thanks to the use of additive agents in the plastic that help slow down the process of oxidisation and degradation, which in turn, increases product shelf-life.

Many plastics also have a greater chemical resistance than metals, and don’t get corroded so easily. This can often mean that products and parts don’t need to be treated quite so extensively before they go into use, or, alternatively, that it’s possible to sell products that last longer or don’t simply need as much maintenance.

Sustainability

Even with improved reliability, every product does eventually reach the end of its lifespan. Even here, however, plastics can offer an advantage, as they are much easier to recycle. Melting down and re-smelting metals takes a lot more time and energy than recycling thermoplastics.

Finish

While it is rarely of much impact on internal parts, the different finishes of plastics can offer a great many advantages over the uniformly metallic appearance of metals. Injection moulded plastics can be produced with virtually any colour or texture that can be imagined.

This not only allows designers to put their creativity on display, it can also allow a simple way to apply a company logo to a part. There’s no need to paint it on or apply a decal, you can make the logo an integral part of the design.

The smooth finish of plastics can also impact several other secondary operations. Plastic parts don’t need the intensive de-burring of metal, and assembling the finished product is much simpler when you remove the need for welding.

Cost

As well as reducing shipping and assembly costs, the process of making plastic parts is usually much cheaper than creating metal ones. Injection moulding plastics has a much lower cycle time than it does for producing metals, making them generally easier and cheaper to produce.

Of course, it’s worth remembering that plastics will never be able to replace metals in every situation, but it’s certainly worth considering. If in doubt, you can always contact the experts if you are looking to switch out some metal parts with plastics.

As always, if you have questions or concerns, feel free to contact one of Protolabs’ applications engineers at +44 (0) 1952 683047 or [email protected] to discuss options.