Go with the flow

Metal spinning, as a method of manufacturing, has origins dating back thousands of years. However, it wasn’t until the industrial revolution that motorised equipment was introduced, changing this traditional hand working method to a powerful and advanced manufacturing technique, which devolved into a number of associated processes. One of which is flow forming.

CNC-based flow forming is a manufacturing technology popular in countries, such as China, America and throughout Europe; it can be used in a number of sectors including nuclear, oil and gas and medical instruments amongst others – but notably not so much in the UK – particularly in relation to aerospace.

Flow forming sees the incremental reduction of the wall thickness of a cylindrical preform, stretching and extruding it out through the application of forming rollers which flow the material along a mandrel. It’s a highly controlled process that allows for the creation of long cylinder components with varying wall thicknesses and complex geometries.

Typically, these components would be manufactured through more traditional methods, such as machining from large forgings, but this brings with it a significant amount of material wastage, machining time and ultimately cost.

Presently within aerospace manufacturing, flow forming is used to manufacture components, such as control rods, hydraulic cylinders and hollow tubular sections. But, at the AFRC, after researching this technology since 2014 and working on numerous demonstrator projects, we have proven that it can be used for critical, high value, components such as engine shafts and landing gear components, of which the majority are manufactured from solid forged billets.

A number of benefits

There are a number of benefits to flow forming, some more obvious than others that can be seen with the naked eye, other benefits are more inherent and require sophisticated material analysis to identify and therefore appreciate. These are the benefits that are lesser known within industry.

The most obvious benefit with flow forming is the amount of material saved. It is widely reported throughout the sector that the buy-to-fly ratio, the amount of material originally bought in versus the amount of material that actually flies in the plane, can be as little as 20%. With flow forming this increases to as much as 60-70%.

At the Farnborough Airshow, as part of the High Value Manufacturing Catapult stand, we will be exhibiting a large, fully-flow formed representative engine shaft, over two metres long, which we’ve been working on as part of a large Innovate UK funded project. Alongside it will be the pre-form, just a third of its length, and we’ll show the amount of material saved by this process compared to the standard machining process.

There are also less visible, inherent benefits that come from cold flow forming - a higher strength on the surface of the material, but also the grain structure in the material gets refined, creating greater strength. The property benefits in the process are particularly applicable to aerospace, where high-grade nickel alloys are being used, and flow forming is a good way of achieving property enhancement through the actual process itself.

It’s a win-win, with both a better quality product and a lot of money saved in waste reduction. It’s also a lot quicker - machining a 2m shaft can take hours or even days to achieve the final product, whereas using flow forming a near net shape part can be formed in as little as 45 minutes.

Flow forming presents the aerospace industry with a vast opportunity to change how engines and other structures are made. It brings with it huge cost savings, significant property enhancement, and benefits in efficiency and environmental impact. Aerospace manufacturers are aware of legislation on lightweighting and noise reduction and are under pressure to drastically reduce costs whilst improving efficiency, flow forming can assist with all of this.

Adoption of flow forming

Over the last four years at the AFRC, we’ve been working on a series of programmes to demonstrate not just the geometries that can be achieved with flow forming, but also the strength of the end product through materials testing and residual stress measurement, proving this technological process can be applied to the more critical parts of the engine that are currently machined from solid.

We’ve worked with a number of companies on flow forming R&D projects which has led to major OEMs seriously considering adopting the use of flow forming, but for companies that haven’t yet been exposed to it they are still uncertain of the structural integrity of the output. We will work with these companies to expel those uncertainties.

A lot of the work we do at the AFRC is about de-risking innovation. If a potential partner declares an interest, our typical approach is to review the component geometry and look into whether it’s a candidate for flow forming or another novel manufacturing process.

We then design a programme of forming trials on our industry scale kit, incrementally showing the benefits, which ultimately lead to the production of a full-scale demonstrator part backed by the country’s most advanced materials science expertise.

If a project is successful, we can work with the company involved to investigate what it needs by way of kit and specify and guide on what is required. We have flow forming equipment manufacturers as our members and can recommend what is needed for any given requirement.

And the equipment needn’t be too expensive. Our own machines have all the ‘bells and whistles’ because they need to be able to handle any type of customer project, but an individual production facility may require a much less complex flow forming machine costing around £600-700k as opposed to £1-2 million and it’s key that companies recognise this.

Our aim is simple, we want to help manufacturers and boost the UK manufacturing supply chain, flow forming presents significant opportunities in both areas, especially given that there is a clear gap in the market.

www.strath.ac.uk/research/advancedformingresearchcentre