Turning technology treats

6 mins read

Andrew Allcock reviews recent turning technology applications, taking in the machining of hip replacement joints, fire extinguisher components, hydraulic connectors and scale models

Smith & Nephew Orthopaedics has recently invested in its 10th Doosan mill-turn centre from Mills CNC (01926 736736). The machine, an MX 2000ST (chuck size 8/10", 540 mm turning diameter, 1,020 mm turning length), was installed at the company's Advanced Bearing Systems' facility, in Leamington Spa, in autumn 2009 and is being used to manufacture complex, high precision orthopaedic ball (femoral) and socket (acetabular) components, used in BHR (Birmingham Hip Resurfacing) surgical procedures. BHR hip resurfacing, pioneered by UK orthopaedic surgeons Dr McMinn and Dr Treacy in 1997, uses low wear, metal-on-metal bearing resurfacing technology and is a procedure where the articular surfaces of the femur and acetabulum are replaced, leaving the femoral head substantially preserved. Image: Mills MX mill-turn technology is helping Smith & Nephew Orthopaedics manufacture medical parts BHR is a less radical and invasive bone sparing solution, unlike THR (Total Hip Replacement), to treating arthritis, disease and hip injuries in younger or more active patients. Well over 100,000 operations in over 42 countries have been successfully performed using the BHR approach. BHR was originally pioneered by Midland Medical Technology (MMT), with the company acquired by Smith & Nephew in 2004. Smith & Nephew subsequently embarked on an efficiency drive to improve its manufacturing performance. To ensure the consistent high quality and high precision of its BHR components (femoral heads and acetabular cups), and to improve productivity, eliminate waste, reduce manufacturing cycle times and lead times, and ramp up production, etc, lean manufacturing and continuous improvement strategies were implemented at its Advanced Bearing Systems facility. "When we set up our manufacturing operation here in Leamington, building on our earlier experiences, and began cellularising all elements of production – we needed access to advanced CNC machine tool technologies," explains Paul Footman, manufacturing and production manager. "Essentially, we were looking for machine tools that could achieve and maintain consistently high levels of precision." BHR components are made from cobalt chrome castings, an extremely hard and durable material, and part accuracy, repeatability and surface finish requirements are demanding - roundness tolerances are generally less than 2 micron; surface finish requirements are in the region of Ra 0.015 µm). Mr Footman continues: "We also wanted to significantly reduce cycle times, to meet demand, reduce lead times and increase productivity, and to standardise our method of production. "We invited three machine tool manufacturers to enter into a trial to produce sample batches. Mills CNC, with its Doosan MX 2000ST machine, was one of the companies invited." Smith & Nephew's trial was not just limited to identifying the optimum machine tool; the company was also looking for a full turnkey manufacturing solution, involving tooling, fixturing, coolant,etc The performance of the MX machine, combined with Mills CNC's technical and applications expertise and support, resulted in Smith & Nephew continuing its investment in MX 2000ST machines in 2005. And now, some five years on, a further eight MX machines have been purchased, all of which are covered by Mills '360' Service Contracts. Wakefield-based Aqua-Mist Fire Protection needed extra capacity, as business turned up for its innovative range of low pressure water-mist fire prevention technology. The company's award-winning LP2000 water mist system dissipates small water droplets to absorb heat and which expand by over 1,600 times as they are converted to steam, displacing oxygen and extinguishing fires, with significantly reduced water damage. Each water mist head produced at the company's manufacturing site incorporates a brass spinner and nozzle (above) and the company was subcontracting out the production of its two nozzle types and two spinner types, as the quantity of anything up to 3,000 of each component was beyond its capacity. As Aqua-Mist production director Geoff Nash explains: "We had concerns over the capacity capability of our subcontractor, so we decided to look at bringing the parts in-house. This would enable us to control production, costs and overall quality of the parts. We reviewed four or five suppliers of turning centres and asked them to meet our specified criteria. Leader CNC gave us the first and most comprehensive response, while alternate manufacturers just gave us a generic response that wasn't tailored to our needs. We conducted extensive reviews, but the Unamuno turning centre from Leader CNC (02476 353874) was a clear winner." Leader CNC installed a Unamuno turning machine at Aqua Mist to help it make parts like these OVERLAPPING OPERATIONS Aqua-Mist acquired its Unamuno Optima 36 turning centre with Samsys Multi-3000 barfeed in November 2009. The Optima 36 (36 mm bar diameter) offers simultaneous multi-tool and multi-axis machining by using its sub-spindle, gang slide and upper slide system. With up to 22 tool positions and six linear axis and two rotary axes, the 3-axis upper slide has eight fixed tools, or a combination of three driven and four fixed, while the 2-axis gang slide offers 14 tool positions. This combination allows for three overlapped, simultaneous operations on the main and sub-spindle. For Aqua-Mist, this means that its nozzles can now be produced in 45 seconds. The spinners that require milling by three different tools are manufactured in 1 minute 30 seconds. The subcontract cost of almost £1 per part (£5,000+ per month) has been reduced to under £0.50 per part, credited to Optima's ability to run lights-out. "The barfeed for the Optima can be loaded with over 40, 13 mm diameter bars that are 1.5 m long," says CNC line manager Andy Taylor. "This can feed the machine overnight, while the 36 mm capacity Optima has a part catching arm that places the parts into a bin, without any damage. Despite running around the clock, the rigidity of the Optima ensures that our tolerances will not deviate beyond 0.01 mm through the course of a shift. With a barfeed, part catcher, swarf conveyor and an air blast and spring loaded collet for ejecting parts, we can machine lights-out with confidence and, what's more, with a Windows-based operating system, the machine is extremely easy to use." "The Optima initially had a three-year payback period, but we are now confident the machine will pay for itself within 12 months," offers Mr Nash. "If our business doubles its production, as expected in the future, the cost savings will be even greater and the payback period reduced even further." Meanwhile, C&M Precision of Maldon, Essex completed a contract of 10,000 hydraulic connectors within 10 days of installing a 14-axis Citizen M32-V CNC sliding-head turning centre (01621 852569), which involved passing some two tonnes of 1¼ in steel through the machine. Citizen M32 machines are familiar to C&M setters, making the running of the latest machine easy Explains managing director John Cable: "The M32 was installed within four days in the machine shop, which involved quite a lot of work by the Citizen Machinery team, due to the high specification we had ordered. It was then set up for the job and, from pressing the start button, it ran continuously day and night, including being totally unmanned through the first and every other night. It never missed a beat." But Mr Cable and his team of setters are not strangers to the Citizen top-of-the-range M-Series. His company had already installed two M32-V machines over the past two years, following earlier purchases of smaller capacity Citizen M16 and M12s. The decision to add the third M32 was, he says: "Simple! We had a rising order book for up to 32 mm components involving complicated milling operations that we could complete in single machining cycles and for which the machine is ideal." He maintains that his setters are familiar with Citizen's M-series machines, and that these are always specified with options to ensure the maximum productivity and machine utilisation. "This means we are able to be very competitive, maintain delivery promises and achieve the level of quality that is very consistent, due to the repeatability of the machine." Nine-employee C&M Precision's M32-V was ordered with IEMCA bar feed, a special LNS Turbo swarf conveyor able to accept both stringy and chipped swarf, Absolent filtration, fully programmable robotic unload coupled to a parts conveyor, plus the Coolblaster 2,000 psi high pressure coolant system. "If you plan to run unmanned, you need confidence the machine will repeat its cycle. You do not want to come in the next day and find the night's production wasted," underlines Mr Cable. MODEL MANUFACTURER Most children enjoy making models of one sort or another, but, for Ben Lyons, managing director, Model Products, the model making has never stopped. In fact, it has provided the basis for a thriving business employing eight people and specialising in making complex engineering models. And today, the models are made strictly for business purposes. One striking example is a model of the Boeing X-48B aeroplane that served as the centrepiece for Cranfield Aerospace's stand at the 2008 Farnborough Airshow and has since appeared at several other events – including an 'Innovation in Action' event hosted by Cranfield University and attended by the Duke of Edinburgh. Having served an apprenticeship as a model maker at what was then the Royal Aircraft Establishment Bedford, Ben Lyons eventually joined the British Hydromechanics Research Association (now the BHR Group). On finding the model making department short of work he took to the road in search of new customers. However, when the volume of new work overtook the internal orders of the newly privatised BHR Group, which had decided against expanding in that direction, he took the plunge and started his own model making business. The business soon expanded and evolved to cover all types of research and development work. "Many of our models are working prototypes and require complex, often quite large, metal components to be machined," Mr Lyons explains. "So, before long, we needed larger capacity machines than the traditional model maker's lathe and mill. We also opted for CNC machine tools, because of the complicated shapes specified for many of these components". The first machine to be installed following relocation to larger premises in Wootton, Bedfordshire, was a ProtoTRAK CNC/manual bed mill supplied by XYZ Machine Tools (01823 674200). This was soon joined by a second ProtoTRAK-equipped mill and then by an XYZ ProTURN CNC/manual lathe and an 11 kW (15 hp)/8000 rpm XYZ Mini Mill 560 compact vertical machining centre equipped with Siemens ShopMill conversational CNC. Model making made easy with XYZ machines All four XYZ machine tools are ideally suited to prototype and low volume production, enabling the multi-discipline team at Model Products to take a customer's ideas in any format, from sketches to full CAD drawings, and quickly and easily program parts ready for machining. First published in Machinery, June 2010