The tooling provider (0114 249 6249) had already supported Empire Cycles in the production of the world’s first 3D printed bike, but was called upon with this latest development to help better machine several key components designed specifically for the VX8. These include an all-new, machined-from-billet head tube that connects the front forks/steering to the rest of the frame.
A key selling point of the Empire range is that it is designed, machined and built in the UK at Empire’s Bolton, Lancs, facility. Keeping control of labour costs is therefore vital, but initial prototypes of the head tubes were taking 110 minutes each to machine – not cost-effective. The head tube is machined from billet to reduce weight and improve performance, but there were manufacturing challenges.
Says Tony Gale, WNT’s project sales engineer: “Ideally, a part of this complexity would be machined on a 5-axis machining centre in a single operation, but Empire only has 3-axis machining centre capability available. While this was okay for the initial prototypes, the near two-hour cycle time and inefficient part handling would not be commercially viable, once production got underway.” But investment in 5-axis machine capacity was not option, so WNT reviewed the project and provided a viable process, with the challenge set at reducing head tube machining to one hour.
Components were brought to WNT’s technical centre in Sheffield, where Gale and application sales engineer Billy Poore could develop a more efficient process that could easily be transferred back to Empire Cycles. The solution lay in a combined WNT tooling and workholding approach, with the process broken into four operations where two components are finished machined at the end of each cycle. All operations used the WNT zero point system, with four zero point bases fixed to the machine bed (right, top).
Operation one sees two aluminium billets held in a pair of WNT ZSG Centric vices located on a base plate, with zero point-compliant locations machined into the block. The second operation locates and holds the block using those features, with the outer profile and pockets on one side rough and finish machined using WNT’s new Type W solid carbide cutters. Parts are then rotated 90° and again located via the zero point features to allow drilling and finishing of the main bore of the component. The final operation mirrors the second operation, but this time employing external clamping that locates in a base plate, since there are no zero point-compliant features in the part itself now.
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 end geometry is designed with plunging operations in mind. A torus-style cutter is used for roughing at a spindle speed of 11,000 rpm and feed rate of 2,500 mm/min.
A Type W ballnose cutter is used for finishing at a spindle speed of 10,000 rpm and feed of 2,000 mm/min. Two finished parts were created from a solid billet in just one hour 10 minutes, or 35 minutes per head tube, a cycle time reduction of 68%, compared to the original process and almost 50% of the allocated target cycle time set by Empire for the project to be commercially viable.
This article was first published in the May 2016 Tooling & Workholding supplement of Machinery magazine.
