Sparks fly for EDM

Brite Precision, a Reaction Engines company, has earmarked its recently installed Sodick AQ750LH wire eroder (Sodi-Tech EDM, 024 76 511677) for use on the Skylon project, an unpiloted, reusable spaceplane intended to provide inexpensive and reliable access to space (see box 1). The high-tech engineering required calls for particular skills and capability. Skylon's developer, Abingdon-based Reaction Engines, looked to acquire a company with the required machining and manufacturing skills to help produce some of the complex parts some two years ago. Newbury-based Brite Precision became Reaction Engines' manufacturing arm, thanks to its proven track record as an established subcontract supplier of parts for gas panels, cryostats, goniometers, mirror mounts and remote handling equipment, typically in batches of 50 to 60-off. The acquisition was followed by a programme of investment. Among the top priorities was a wire EDM, installation of which would eliminate the need to continue subcontracting this process. "Not only would this aid confidentiality around Skylon, it would also bring greater control to our manufacturing process and cut subcontract costs for wire EDM, which previously were around £40,000 per annum," explains the company's workshop supervisor, Bob Harris. "We went to the MACH machine tool exhibition at the Birmingham NEC in 2010 and, although we saw a lot of machines, the Sodick AQ750LH was clearly the most impressive and so we placed the order." The machine was acquired for a very specific Skylon job, one that requires a working Z-axis height of 600 mm. The EDM unit will tackle a long tubular heat exchanger component made from Inconel that has 800 smaller tubes inside, with these cut to length inside the bore. Mr Harris says that the on-site training provided by Sodi-Tech EDM was particularly impressive – Sodi-Tech personnel spent three days on site at Newbury, training two Brite Precision employees. "Since the takeover by Reaction Engines, I've been on quite a few training courses for various pieces of new machinery, but the Sodi-Tech course was one of the best," he says. "The programming is easy to follow – either online or offline – and the machine does everything it's told. We hold tolerances of 0.01 mm or less, but nothing seems to be a problem. Put it this way – the next time we expand we'll be getting another Sodick EDM." FURTHER ONA INVESTMENT At C&M Tools, an NX3 ONA die sinking machine has been installed to replace a previous generation ONA EDM machine (Warwick Machine Tools, 01676 534534). Based in Verwood, Dorset, the company has been a long-time ONA user, favouring the technology for supporting large mould tool work, particularly for mould tool modification and repair for large tools, mainly for German and Chinese mould toolmakers for the automotive industry. This is because the head moves, rather than the table, which means that large tools such as automotive grilles and bumpers, where the tank is not large enough, can be supported outside the tank, with the machine only working on the area that requires repair or modification. This large mould tool modification work constitutes 30% of the company's turnover. However, the latest machine was purchased to support smaller, high precision work. A recent contract for a very small automotive clip produced in an eight-impression mould tool prompted the investment. Explains director Nick Moth: "It is one of the reasons we purchased the new NX3 ONA machine, which replaced a previous generation ONA EDM machine. We secured the new customer and part of the work involved very fine sparking. Installed at the beginning of October 2011, the machine has not stopped since it was commissioned. The new machine uses graphite electrodes much more efficiently than the old machine." Indeed, on a project for another tool maker that required detailed sink work with supplied electrodes, the company started the work, expecting to struggle with the tight lead time. However, the ONA NX3 finished the job some 12 hours quicker than expected. And athough the new NX3 has a new controller, there are similarities to the existing and previous machines that reduced the learning curve. The operating software has a Windows 'look and feel' and a training simulator runs on a desk PC to help training away from the machine. Concludes Mr Moth: "We believe you only get what you pay for, and we must be able to confidently run as many machines as possible through the night and into the weekend to remain efficient. Even when unmanned, the ONA EDM machines are not backed off, they operate at full speed." Box item Skylon project The innovative, 82 m long Skylon vehicle (image, next page) consists of a slender fuselage (6.25 m diameter) containing propellant tankage and payload bay, with delta wings attached midway along the fuselage that carry the Sabre engines in axisymmetric nacelles on the wingtips. The Sabre engines have dual-mode capability: in rocket mode the engine operates as a closed cycle Lox/Lh2 high specific impulse rocket engine, while in air-breathing mode (from take-off to Mach 5) the liquid oxygen flow is replaced by atmospheric air, increasing the installed specific impulse up to six-fold. The airflow is drawn into the engine via a two-shock axisymmetric intake and is cooled to cryogenic temperatures prior to compression. The hydrogen fuel acts as a heatsink for the closed cycle helium loop before entering the combustion chamber. Skylon will take some 10 years to fully develop and will be capable of transporting 15 tonnes of cargo into space. It has been designed as a practical, utilitarian machine for use by competitive commercial operators. Though Skylon's primary function will be launching satellites, consideration has also been given to its passenger-carrying capabilities. Current development options allow for the transport of 20 'tourists' when orbital facilities exist to accommodate them. However, anyone interested in taking up the opportunity will likely have to part with around $500,000 for the privilege. Box item EDM developments in brief [] Sodick has launched a compact range of wire-cut EDM machines. The AQ400L and AQ600L have installation dimensions of 2,980 by 3,675 mm and 2,400 by 2,930, respectively – www.machinery.co.uk/39885 [] GF AgieCharmilles' new Integrated Vision Unit (IVU) provides optical measurement of EDM-machined details, which, says the company, a 3D probe cannot deliver – www.machinery.co.uk/40536 [] Makino's latest version of its SuperSpark die-sink EDM technology, SuperSpark IV, reduces roughing times in deep-rib applications by up to 30%, it is claimed. SuperSpark IV is available on all Makino sinker EDMs with MGH6 generator/control or later – www.machinery.co.uk/40540 [] Vollmer has unveiled three EDM saw blade sharpening machines. The Vollmer CB 200, described as a 'little brother' to its CB 400, can be used to sharpen the tooth faces and tooth tops of carbide-tipped bandsaw blades used for the processing of aluminium, plastic, steel or cast iron. Vollmer's fully automatic CM 300 and CMF 300 machines are for sharpening carbide-tipped circular saw blades up to 1,440 mm diameter – www.machinery.co.uk/40746 [] Eurospark is offering a remodelled series of Joemars Wire EDMs, which, it says, provides high accuracy within a reduced footprint – www.machinery.co.uk/42218 First published in Machinery, June 2012