Round and round - CNC turning case studies

5 min read

Oil and gas part production on DMG/Mori Seiki machines; Citizen sliding-head slashes cycle times; Doosan VTLs support forged wheel turning; product development supported by XYZ technology

BEL Valves has been using DMG/Mori Seiki machines at its Newcastle upon Tyne factory for years. It now has two SL2500s, three NL2500s, three NL3000s, one SL603, two NVX5100s, three NZX2000s, one Taiyo Koki vertical grinder, DuraTurns at its Indian plant, and is about to take delivery of an NZX4000 (0844 800 7650). BEL is a manufacturer of gate, ball, check, HIPPS, needle, double isolation and globe valves in subsea and surface oil and gas applications, where pressures can be 20,000 psi. Jonathan Lamb, group production director, BEL Valves, explains: "The oil and gas industry works with preferred suppliers and we have been testing our valves in subsea applications since 1992. To produce a reliable solution, we use finite element analysis techniques to help us to design for the very high pressures involved. "Preventing fugitive emissions, where corrosive and toxic gases leak from a valve, is also a high priority. Achieving exceptional surface finishes on our components is a major factor in achieving this. Overall, the cost of the valve itself is small, in relation to the project cost of an oil and gas installation. However, it is a vital part of the system, as the time and effort required for its installation are high. If it fails, the disruption to oil and gas production can be immense. To give some idea of the scale of these projects, the valve can be paid for within the first few hours of production." And he adds: "We selected DMG/Mori Seiki on its build quality." The slideways on the NL are 30% wider than a conventional machine and the torsional rigidity is 100% better than the previous model, and spindle rigidity is 50% greater. "We cut tough materials, such as stainless and exotic alloys, at low speeds. In particular, we have very demanding, 12 mm deep, grooving operations and, without a doubt, the damping capability of the DMG/Mori Seiki produces a better result. The 6 mm trepanning blade can cause less rigid machines to resonate, causing the tip to shatter and wrecking the turret. Additionally, the high output motor on the DMG/Mori Seiki has plenty of torque at low speed, enabling us to use its power to the full." As to the cost of such robust technology, he puts that to bed. "The extra hourly rate can be as little as £1. This is insignificant, when compared to the potential penalties we could face for late delivery, should the machine break down, so it makes economic sense to buy the best available equipment." High availability is also a prerequisite. "The service we get from DMG/Mori Seiki is very good and much better than most machine tool companies. Service support is excellent, as we get someone onsite next day or the same day. The engineers are highly competent in reaching the correct fault diagnosis. It could be our fault or DMG/Mori Seiki's fault, but fixing it quickly is the most important thing. Niggling recurring problems or a machine being broken down for a week would be completely unacceptable to us. I am glad to say that we have never had a lengthy break-down on our DMG/Mori Seiki." At Shepherd Engineering, the installation of the latest Citizen A32-VII CNC sliding-head turn-mill centre (01923 691500) has enabled the subcontract machinist to slash well-proven sliding head cycle times by an average of 20%. And this level of improvement is being seen even on a four-year-old, top-of-the-range Citizen M32. As a result, the company has been able to secure new contracts for 2013 worth £250,000 from one customer, and has been able to break into the demanding F1 and aerospace sectors. According to production director Craig Sargent, the 7-axis, 23 tool capacity Citizen A32 has great rigidity, due to its centre-rib bed construction, and, while it has less versatility and tool-carrying capability than the M32, running at the same speeds and feeds to preserve tool life and process predictability, what makes the difference on certain types of work is the machine's ability to effectively overlap axis sequences, the use of 45 m/min rapid traverse rates, its drive system acceleration rates and the control's increased data processing speed. HIGH PERFORMANCE ALLOYS Moving to world-leading, vertically-integrated manufacturer of high performance alloy wheels Rimstock Plc, and among the Doosan machine tool technology recently installed has been a three Doosan VT 750 vertical turning lathes. Supplied by Mills CNC (01926 736736), together with three Doosan vertical machining centres, they are the first Doosan machines installed by the company, with the six new machine tools in operation, virtually around the clock. The Doosan investments were related to a 2010 strategic decision to expand and diversify its operations. As an integral part of this, Rimstock strengthened its forged aluminium alloy wheel manufacturing capacity and capabilities. Matt Neal, Rimstock's marketing director, explains: "Modern car designers and manufacturers are constantly looking to minimise wheel weight (and therefore the un-sprung weight of vehicles) of performance cars, whilst maintaining strength and durability. "Reducing weight has a dramatic impact on car dynamics and performance. With forged aluminium, weight savings approaching 30% can be achieved (over traditional cast alloy wheels), and the wheel produced is stronger and stiffer, and improves acceleration, handling and braking performance." And he explains Rimstock's decision to invest in its first Doosan vertical lathe: "We could have attempted to ramp-up production by investing in horizontal lathes, but could see that vertical lathes, using gravity loading, were better suited to the machining of large, awkward shaped parts made from tough materials like forged aluminium alloys. We were also convinced that vertical turning would deliver long-term savings [reductions in set-up and cycle times, and dramatic increases in tool life], and improved performance [higher accuracies and repeatabilities, improved surface finishes etc]. And this has proved to be the case." Mills CNC won the business, based on a number of reasons, but including the performance and pedigree of the VT 750 machine and of Doosan's vertical turning technologies in general, the price and availability of the machine, and the support and after-sales service provided by Mills CNC. Summing up, Mr Neal says of the six Doosan machines: "The machines are reliable performers and haven't missed a beat." Various designs of direct and indirect high and low pressure systems machine tool fire extinguishing systems are manufactured by Ipswich, Suffolk-based Firetrace. And the company's latest investment — a 20 hp/5000 rpm/min Compact Turn 52 LTY turning centre, supplied by XYZ Machine Tools (01823 674200)— is itself protected by a Firetrace system. This, says Dave Melton, who with wife Chris began the business in 1976, is no reflection on the quality, performance, reliability or safety of the new CNC machine. "It is simply a sensible precaution to take, because, in the worst possible scenario, it is far better to deal promptly and effectively with a small fire than to suffer the consequences of a much larger one." DEVELOPMENT SUPPORT The recently installed XYZ turning centre, with 12-station VDI turret, driven tools Y-axis, swing of 400 mm, plus turned diameter and length capacities of 220 mm and 490 mm respectively, provides the flexibility needed to cope with diverse production demands, including essential development and prototype work. The Y-axis can travel 35 mm above and below centreline (70 mm total travel) and is ideal for components that would otherwise require separate milling and turning operations. Standard equipment includes a Renishaw automatic tool setting arm, hydraulic tailstock and parts catcher. Programming the Siemens 820D ShopTurn conversational control does not require G code knowledge, with canned cycles making shopfloor programming fast and simple. Once written, completed programs can be checked using graphical simulation, with the finished component displayed on-screen as a 2D or 3D image. Set-up and programming is the responsibility of David Forsdike, component production manager, who says: "Previous experience of the ease with which an XYZ Mini Mill VMC can be programmed made for a smooth transition to the new turning centre. In fact, the inherent flexibility of the CT 52 made it my first choice for the type of work we do here." First published in Machinery, March 2013