Having already received extensive product and technical support from WNT (UK) in the development of its high specification off road cycles, including the world’s first 3D printed bike, Empire Cycles has once again turned to the Sheffield-Based tooling specialist as it prepares to launch its latest model, the VX8.
The VX8, which stands for Vertical Cross 8-inch travel, is a dedicated downhill racer that will make use of some components from the earlier MX6 (Mountain Cross), but also features several key components that have been designed specifically for the VX8. These include the all-new, billet machined, headstock, which connects the front forks/steering to the rest of the frame. The headstock is billet machined to reduce weight and improve performance, but the resulting complex shape brought with it manufacturing issues. A key selling point of the Empire range is that it is designed, machined, and built in the UK at Empire’s Bolton facility. As a result, it is vital to keep control of labour costs and initial prototypes of the headstocks were taking one hour and 50 minutes each to machine, which was not cost-effective.
“Ideally, a part of this complexity would be machined on a five-axis machining centre in a single operation, but Empire only has a three axis machining centre capability available. While this was OK for the initial prototypes, the near two hour cycle time and inefficient part handling would not be commercially viable once production got underway,” says Tony Gale, WNT’s Project Sales Engineer. With investment in five-axis machine capacity not being an option, WNT was called in to review the project and provide a viable process within the confines of existing three-axis machine capacity and the added challenge of getting the cycle time for each headstock down to one hour.
The initial stage was to bring the components into WNT’s technical centre in Sheffield, where Project Sales Engineer Tony Gale and Application Sales Engineer Billy Poore could work on a more efficient process. And one that could be easily transferred back to Empire Cycles when complete. It was an opportunity for the pair to think ‘outside the box’ and be creative with WNT’s range of workholding systems and tooling. After due consideration the solution was to break the process into four operations, with two components being finished machined at the end of each cycle. All of the workholding would be mounted on WNT Zero Point bases. Operation one saw the aluminium billets held in a pair of WNT ZSG Centric vices so that location points for the Zero Point setting plug for the second operation could be machined. Once complete the parts are transferred to a WNT Zero Point base for the second operation. This is where the outer profile and pockets are rough and finished machined using WNT’s new Type W solid carbide cutters. Following this machining sequence the parts are rotated 90 degrees and fixtured to drill and finish the main bore of the component, with the final operation mirroring the rough and finish profiling of the second side of the part.
The innovative 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, while the end geometry of these cutters is designed with plunging operations in mind. This allowed the roughing operations, using a Torus-style cutter, on this project to be carried out at spindle speeds of 11,000 revs/min at a feedrate of 2500 mm/min. The finishing passes used a ballnose variant of the Type W cutter at a spindle speed of speed 10,000 revs/min and feed of 2000 mm/min. This cutting data and process meant that two finished parts were created from a solid billet in just one hour ten minutes, or 35 minutes per headstock, a cycle time reduction of 68 per cent compared to the original process and almost 50 per cent of the allocated target cycle time set by Empire for the project to be commercially acceptable.
“This was a fascinating challenge for us to take on as not everyone can afford, or has the need, to invest in five-axis machining centres, but by not having them they may have to turn away some types of work. By using existing products from the WNT range and some creative thinking we have provided an alternative 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, who want to make use of our in-house expertise as the big advantage for them is that we can develop these new machining strategies/processes on their behalf away from their machines, meaning they lose no valuable production time. The whole process is, in effect, risk free for them,” says Tony Pennington, Managing Director, WNT (UK).
Editor’s Note: The Empire VX8 mountain bike along with the workholding system and tools used to achieve the required cycle time will be available to view on WNT’s stand (5641) at MACH 2016.