CMS router achieves 1 thou tolerances machining military radomes
Keywords: Aerospace industry, Machining, Military
Complas Ltd, a major specialist contractor for the aerospace industry based in Witney, Oxfordshire, is reported to be achieving tolerances as fine as one thousandth of an inch (.025mm) while machining carbon fibre composites and quartz for military radomes on a RYE CMS PF102 5-axis CNC router. Manufacturing manager Clive Brooks explained that the electrical and physical specifications of the radomes used to protect vital antennae on military aircraft require both that they use materials with low dielectric constants, which are extremely expensive, and that they achieve extremely precise machining (Plate 3).
Plate 3 Complas Ltd, a major specialist contractor for the aerospace industry based in Witney, Oxfordshire, is achieving tolerances as fine as one thousandth of an inch (.025mm) while machining carbon fibre composites and quartz for military radomes on a RYE CMS PF102 5- axis CNC router (pictured). Manufacturing Manager Clive Brooks explained that the electrical and physical specifications of the radomes used to protect vital antennae on military aircraft require both that they use materials with low dielectric constants, which are extremely expensive, and that they achieve extremely precise machining
"Our radomes have to fit precisely and withstand the thermal stresses of an aircraft climbing rapidly to high altitude, plus the physical stresses of being attached to a wing or an airframe which is subject to complex forces" he said."They have to do that without losing their electrical performance –antennae have to see out of a radome as clearly as we see out of a float glass window. Any distortion will make signals received or transmitted by the aircraft unreliable".
He made the point that the special fibre materials used for radomes cost between two and three times as much as the carbon fibre composites used for building Formula 1 cars.
He went on to explain that, until late 1999, the company had used sub-contractors with CNC equipment to do their machining, but due to scrap this had been getting expensive.
"Sub-contracting was costing us up to £2,500 for each component –and, because each component costs as much as £16,000 to make before it gets to the machining stage, any slight imprecision in the machining meant a reject which was hugely expensive" he said. "As we grew, the reject rates from sub- contractors were getting far too high, and that was simply because of a lack of precision. Something had to be done".
When, in 1999, the company won an order for a particular high precision component which was to be made in large volume, it was both a challenge and an opportunity. With this order on the books, it made substantial sense for the company to buy its own CMC machine.
"But, from the start, it was clear that we did not need a low-cost, high volume production CNC router" went on Clive Brooks. "Our people are extremely skilled engineers. What we needed was a precision CNC machine capable of utilising their skills and talent to the full to deliver a high- precision resuit".
The project team from Complas looked at a number of alternative CNC machines available on the market. Most manufacturers they talked to could either not deliver the tolerances needed, or could not supply the size they were looking for. But when they saw the RYE CMS model PF CNC router, the project team was confident that they had found a potential solution.
"The machine just looked the part," said Clive Brooks. "After detailed studies we placed an order which was conditional on the factory in Italy being able to demonstrate that the machine could achieve the required fine tolerances". So all the tools necessary for the job were shipped to Italy, where the CMS team carried out all the CAD and CAM work independently to prove that the PF 102 router could do the job to the standard required. A Complas engineer travelled to Italy to observe the process and assess and report on the machine's capability.
With that test completed to Complas' complete satisfaction, the order was confirmed and the CNC router was installed in November 1999.
"It was up and running and producing components from day one," said Clive Brooks. "But our engineers have progressively developed our own CAD/CAM front end to achieve the best possible precision and improve on the standards CMS achieved in Italy. We completed that only at the beginning of 2001. Before that we were writing code manually. Now, where RYECMS managed to machine a radome to 5 thou tolerances, we have got it down to 1 thou".
The key benefits to the company said to have been in increased productivity,greater flexibility and the virtual elimination of costly rejects. "Where, using sub-contractors, it was taking us a week and a half to get components machined for electrical testing, we can now do three in a week" said Clive Brooks. "That increases customer confidence and improves our bottom line".
An essential element in the quest to maintain 1 thou tolerances has been the rotation of tools. Clive Brooks explained that, with polycrystalline diamond tools costing upwards of £300 each and £60 to sharpen,sub-contractors are inevitably tempted to make the tools last longer than they are capable of delivering precision.
"Even a polycrystalline diamond tool can lose 1 thou in a few hours when cutting quartz" he said. "We check our tool settings every day and rotate the tools frequently. There's no other way if you want precision".
Compas asserts that its RYE CMS PF102 CNC router is delivering the performance and reliability that it requires. Clive Brooks is confident that they have got the decision right.
"If I needed another machine. I'd go to RYE CMS" he said. Cost would not even come into the calculation".
RYE CMS Limited. Tel: +44 (0)1494 441211; Fax: +44 (0)1494 440345; E-mail: sales@rye-cms.com; Website: http://www.rye-cms.com
