Secrets of metal replacement

Albis answers questions on substituting metals with plastic.

Q) What are the main challenges when substituting metal components with plastic?
A) There are a number of factors that any designer, engineer or material specifier needs to keep in mind. These include:
- Thermal and mechanical performance as well as the chemical resistance of plastics compared to metals.
- Component design issues such as wall thickness, fixing and joining of different types of materials all need to be optimised.
- it is rarely a straight swap!

Q) What are the main advantages of plastic materials over die-cast metals for mass produced parts?
A) There are numerous benefits that plastics offer including being lightweight. They also offer greater design freedom, and can be used to integrate features in a one-stage production process such as seals or clips, reducing secondary operation processes and costs. Production is very high precision and repeatable, with lower scrap and waste, including having lower energy consumption in production as well as the final product’s lifecycle.

Q) What are the most common pitfalls when switching?
A)
There are a couple of pitfalls that many can suffer from, but two big things to look for are:
- Adequate component wall thicknesses – 20mm wall sections are not uncommon to see!
- Use ribbing, particularly on long, unsupported walls or surfaces to add strength and support to the part.

Q) Which industry sectors are at the forefront of metal replacement and what are the main drivers?
A)
Without doubt, the automotive industry has led the way in the replacement of metal components with plastic in all areas of the car. In turn this has led to vastly improved fuel efficiency, lower emissions and to the explosion in high tech and stylish interior design possibilities.
The aircraft industry has also made great strides, predominantly with carbon fibre reinforced composites for larger sections of the fuselage, but also within the cabin area using extruded and injection moulded parts made from thermoplastics to meet stringent aircraft specifications regarding smoke density and toxicity.
In the wider engineering and industrial sectors, plastics have found many applications where at one time metal was the only viable option, including gears and pumps.

Q) What are the decisive factors for successful substitution?
A)
Material selection: matching the in-service technical requirements of the application to the plastic which best fits these requirements, whilst ensuring the most cost-effective manufacturing process and final part quality, lie at the heart of successful metal replacement projects.
Good design: using state-of-the-art simulation tools ensures strength and stiffness requirements are achieved.
Tool design: optimum tool design, including tool steel selection, runner and gate systems, cooling channels, venting and ejection systems to best fit the properties and processing characteristics of the selected thermoplastic have a significant influence on the manufacturability, repeatability and reliability of components made from plastic.

Q) Which thermoplastics should be used to replace metal?
A)
Where high strength and stiffness are the drivers, then Polyamide 6 or 6.6 (PA 6 or PA 6.6), reinforced with glass or carbon fibres (or sometimes a combination) achieve the very high tensile modulus values required. In some cases, specially reinforced Polypropylene (PP) compounds, such as ALBIS’ ALTECH NXT can be used, achieving even greater weight savings and shorter injection moulding cycle times.
For high temperature applications (> 220 C), Polyphenylene Sulphide (PPS) is used to replace metal die casts. PPS also demonstrates exceptional chemical resistance and is inherently flame retardant to UL 94 V-0 at 0.75mm.
Where thermal management in confined spaces is critical, e.g. for heat sinks and other components in lighting applications, thermally conductive plastics based on PA or PPS offer many advantages over die cast metal components.
For applications where extreme continuous use temperature (above up to 240 C) and chemical resistance are required, such as in aerospace components, then PEEK is an excellent option.


01565 755777
www.albis.com

Author
Albis (UK) Ltd

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No mention of bushing Igus have a vast range of plain polymer bearings. light weight and long lasting.

Comment Peter R Wills, 08/09/2015
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