Cutting inefficiency

Halesowen-based repetition turned parts specialist BMI Engineering has gained significant productivity, quality and efficiency benefits following the introduction of tooling supplied by Horn Cutting Tools (01425 481800). In some cases, it has been possible to rationalise the number of set-ups required to finish machined components, while in others significant reductions in cycle time have been accompanied by increased tool life and improved as-machined finish, reducing the need for manual deburring. An initial foray with Horn saw the subcontractor successfully employ Horn's System 312 triple edge insert for a particular grooving challenge, with this success leading to the two working together on other issues. BMI's machine shop supervisor, Robert Bingham, explains: "The capabilities available with Horn's range of grooving, threading and part-off tooling have made us more competitive. Our local Horn applications engineer has helped us to develop a number of modified machining cycles that save us time and material, in some cases making us competitive with suppliers operating in low-wage economies like India." Image: A selection of parts at BMI that have benefited from Horn technology A case in point has been the production of washers on a multi-spindle machine. The narrow profile of the Horn 224C part-off insert saves 1 mm of material, compared with alternative tooling - providing 'free' material for every third washer, while the sharpness of the cutting edge minimises the burr on the centre hole. SWARF PROBLEM TACKLED Elsewhere in the factory, use of a Supermini 105 threading tool has solved a swarf problem that was leading to regular breakage of M10 taps and resultant down time, but the most recent Horn application at BMI involves groove milling. For some time, the company has been producing a stud-type component, called a pivot pin. This requires a 3 mm wide keyway-type slot, having a fully radiused profile to locate in a mating component. Initial attempts to produce the feature in cycle, using a slot mill on a C-axis equipped CNC lathe, had not been successful. BMI had therefore resorted to producing the feature as a second operation using a manually operated horizontal spindle milling machine equipped with a slotting cutter. Mr Bingham recalls: "This wasn't a satisfactory method, as the cycle time was a lengthy 45 seconds and the component was manually fed, so finish was inconsistent. In addition, tool life was poor and the worn tooling would generate burrs, so we had quality issues. As we produce around 27,000 of these components per annum, an improved solution was desirable." The company had recently acquired a new CNC milling machine, which had time available, and Horn was consulted to provide a solution. This took the form of a fully radiused Type 313 groove milling insert ,while the existing fixture was modified to provide access for the Horn tooling, as the revised method requires that the cut be made at the 9 o'clock position rather than 12 o'clock. At cutting data of 220 m/min and a feed rate of 850 mm/min, the load to unload cycle time has reduced to 15 seconds, and both finish and tool life have improved significantly. Elsewhere, following extensive finish reaming trials at Hinckley-based Triumph Motorcycles to improve its critical inlet and exhaust valve guide production for the top-selling 12-valve, three-cylinder, 126 bhp, Daytona 675 Triple engine, the solution provided by LMT UK (01676 523440) has demonstrated tool life improvements of 43 per cent over the nearest tooling competitor. The engine has a valve guide diameter of less than 5 mm, which is too small for PCD, so the bore has to be held through carbide reaming to a tolerance of 0.015 mm on both inlet and exhaust valves, and uses highly abrasive sintered guideways. To machine the guides and corresponding seat, a combination tool having a short pilot reamer pre-sizes the bore and an insert generates the three angles that comprise the valve seat progressively. The pilot reamer enables the bore of the guide to be pre-sized leaving 0.03 mm of stock for final reaming, while the turning insert cuts the top leading and bottom trailing angles of the exhaust seat. FINAL AND CRITICAL A finishing reamer is then used to finally size the valve guide bore to a depth of 35 mm, while maintaining a tolerance of 0.015 mm. Using the same toolholder, the critical 90° sealing angle section of the valve seat, set between the leading and trailing angles, is finish machined, so that it is totally concentric with the bore of the valve guide. Due to the abrasive nature of the valve guide insert material, the in-cut time and tool life of the previous generation of carbide reamers became uneconomic. Frequent experiments with adjustments to the feeds and speeds had no impression, nor gave any sign of improvement. Meriden-based LMT UK then produced a series of test reamers for the final sizing element of valve guide production. In developing the trial cutters, another member of the group, LMT Bohlerit, created a sintered slug of material, incorporating radial coolant feed holes in preference to the normal method of production that uses the EDM process. The tool designer also created a front centre hole with a cone to ensure a high accuracy and consistency of grind when finishing the tool, especially at the leading edges of each blade. Image: LMT, via its Bohlerit operation, has developed special Reamers for Triumph Motorcycles The finishing reamer was run at 50 m/min, using a feed rate of 500 mm/min for the first portion of the 35 mm deep valve guide. The speed was then increased to 100 m/min and 2 m/min feed rate, followed by the slowing of the spindle to 10 m/min and the feed reduced to 54 mm/min feed. For the final 0.3 mm of tool stroke, the speed was again halved to 5 m/min and the feed rate set at 34 mm/min allowing the valve seat to be finished turned with a final dwell of 0.5 sec. LMT UK was then requested to perform trials on the pre-size pilot reamer. The pilot reaming process is likewise subject to a series of changes to speeds and feeds, with the initial pre-sizing carried out at 75 m/min and a faster 1 m/min feed rate, due to the improvements in rigidity from the more 'stubby' tool length. The spindle is then slowed to 9 m/min and 74 mm/min feed, and slowed again to 5 m/min with 30 mm/min feed, prior to dwelling for 0.5 sec at the bottom of the guide bore. This pause allows both the top and bottom angles of the valve seat to be finished by the turning insert. INVEST TO EXPAND Subcontractor Clitheroe Light Engineering has invested in modern machine tools in support of expanding its business. Founded when Kevin Wilkinson (father of the current directors), two sisters and one brother, along with his colleague Norman Burgess, some 37 years ago, the company has since created a niche for itself in the general subcontract sector by early adoption of technology. It bought its first CNC lathe in 1979 and, more recently, it has installed a Fastems 72-pallet loading system with three Mori Seiki NH5000, and one Daewoo Ace400 HMC horizontal machining centres attached to it - a total investment of more than £2.9 million over a five year period. Indeed, it is claimed that this is the only system of its magnitude in a private company in the UK. CLE has a three-year plan for further expansion, which will see an extension to the existing manufacturing site and, if required, the building of additional manufacturing space on land already owned by the company. The Fastems system will be completed with the addition of a fifth Mori Seiki horizontal machining centre and recruitment will also become a focus. To help this future expansion, CLE has worked closely with its suppliers, in particular WNT (UK), which provides the majority of its cutting tool needs. Support from WNT (UK) comes in two guises: that of Nigel Walls, its local technical sales engineer, and the installation of its TooloMat tool vending system. "Our ability to be able to throw problems at Nigel and be able to rely on his problem solving expertise and WNT's flexibility in their willingness to try different methods and cutting tool solutions is invaluable to a company like ours," says operations director Helen Meloy. "As we continue to expand our business, this will become a greater asset and, with an increase in business, we will have a need for a greater number and more variety of cutting tools. The vending system eliminates many of the concerns that we might have over stock, cashflow and logistics." Any stock contained in the two vending machines on-site at CLE is not reflected on the company's balance sheet, while they also provide the reassurance that tools will be available to meet the company's 24/7 manufacturing routine. "We saw an immediate improvement in administration of tool stocks when we had the machines installed," confirms Ms Meloy. "Prior to their arrival, we had three or four people responsible for tool buying; operators had secret stocks of tools by their machines. Now, thanks to the weekly reporting provided by WNT (UK), we have much more control over costs. We can cross check on who has used what and on which jobs, this gives us a much better insight into the true cost of manufacturing particular components and we can be more accurate when quoting for similar work." Another advantage is that the risk of obsolescence in its tooling stocks is avoided. As new tools are developed, they replace the previous tool, at no cost to CLE. First Published in Machinery, May 2010