Having already received extensive product and technical support from WNT (UK) Ltd in the development of its high-specification off-road bicycles, including production of the world’s first bike with a 3-D printed frame, Empire Cycles again turned to the Sheffield-based tooling specialist when it prepared to launch its latest model.
The VX8, which stands for Vertical Cross 8in travel, is a dedicated downhill racer that will make use of some components from the earlier MX6 (Mountain Cross); it also features several key components that have been designed specifically for the VX8. These include the all-new head tube, which connects the front forks to the rest of the frame. This component is machined from a solid billet of material to reduce weight and improve performance, but its complex shape created manufacturing issues.
A key selling point of Empire’s range of bikes is that they are designed, machined and built in the UK at the company’s Bolton facility. However, the prototypes of the head tubes were taking 110min each to machine, which was not cost-effective. Tony Gale, WNT’s project sales engineer, says: “Ideally, some of the complex machining would be carried out on a five-axis machining centre in a single operation, but Empire only has a three-axis VMC. While this was OK for the initial prototypes, the near 2hr cycle time and inefficient part handling would not be commercially viable once production got underway.”
With investment in five-axis machining capacity not being an option, WNT (
www.wnt.com) was called in to review the project and provide a viable process that would enable a three-axis VMC to fully machine a head tubein just 60min. Back at WNT’s Sheffield base, Mr Gale and application sales engineer Billy Poore began working on a more-efficient process based on WNT’s range of work-
holding systems and tooling.
Successful solution
Their solution was to break the process into four operations, with two finished components being produced at the end of each cycle and all of the work-holding mounted on WNT Zero Point bases. For the first operation, the aluminium billets are held in a pair of WNT ZSG Centric vices so that location points for the Zero Point setting plug for the second operation can be machined. The second operation sees the outer profile and pockets rough- and finish-machined using WNT’s new Type W solid-carbide cutters.
The parts are then rotated 90deg and fixtured for the drilling and finishing of the component’s main bore. The fourth — and final — operation is to mirror the rough- and finish-profiling sequence on the second side of the part. The Type W cutters feature a round chord profile and special grind that generates ‘small swarf chips’ that can be easily evacuated from the cutting area with the aid of the standard through-tool coolant supply (the end geometry of these cutters is designed for plunging-type operations).
The roughing operations are carried out at spindle speeds of 11,000rev/min and a feed rate of 2,500mm/min. The finishing passes use a ball-nose variant of the Type W cutter at a spindle speed of 10,000rev/min and a feed rate of 2,000mm/min. This process and cutting data results in two finished parts being created from solid billets in just 70min. This 35min per head tube is almost 50% of the target cycle time set by Empire for the project to be commercially viable.
Tony Pennington, WNT (UK) managing director, said: “This was a fascinating challenge for us to take on, as not everyone can afford — or needs — to invest in five-axis machining centres, albeit not having them may result in some types of work being turned away.
“By using products from the WNT range and applying some creative thinking, we have provided a solution that will give Empire Cycles — and other customers — the opportunity to maximise their existing three-axis machine capacity. We have already invested significantly in our applications support team, and this is an area that will see further development.
“We are seeing significant interest from customers that want to make use of our in-house expertise. The big advantage for them is that we can develop new machining strategies and new machining processes on their behalf away from their machines, so they lose no valuable production time. The whole process is — in effect — risk-free for them.”