Productivity push for grinding

Northern Tool and Gear Company (NTG – 01241 872626), one of the UK's largest family-owned precision gear subcontractors, has invested more than £2 million in new equipment over the last few years to improve its capability as a 'one-stop' gear manufacturer. As part of its recent investment, the 60-year-old company selected a Jones & Shipman Ultragrind 1000 CNC cylindrical grinding machine (0116 201 3050). The investment was made by the Arbroath, Scotland-based firm to replace an existing J&S Series 10 cylindrical grinder that had given the company 13 years of productive service. Process improvement was a key factor in this investment, as managing director Gordon Strachan's company was about to renegotiate a three-year automotive contract for a new generation of seven components as part of a transfer gearbox assembly. The existing gearbox had been taken from prototype development with the customer in to serial production by NTG and, to demonstrate the success of the project: "Over 3,500 sets have been supplied, plus spares – and not one had been rejected," he said. "With the new machine, we have a 300 mm diameter capability by 1,000 mm between centres and can multi-feature grind components weighing up to 200 kg. So far, we have seen around a 15% improvement in cycle time, setting is also reduced considerably, due to the benefit gained from the touchscreen on the control and the Jones & Shipman software." And he adds that, due to the inherent built-in accuracy and rigidity of the machine: "We now easily maintain one to two microns, without need of the optional in-process diameter gauge unit, which further reduces set-up time." The Ultragrind is fitted with the latest Fanuc 320 is touch-screen control, with Windows XP embedded, which, Mr Strachan maintains, is ideal when resetting jobs, as the average batch size is around 15 parts. "We often grind just one or two components and the largest run is probably 150 parts, which means resetting has a big influence on productivity." Image: NTG chose this Jones & Shipman Ultragrind 1000 CNC cylindrical grinding machine to support the winning of an automotive contract UNIVERSAL WHEEL Due to the wide range of work, with 90% of production through the machine based on hardened and tempered EN36, NTG developed a universal specification of 500 mm by 100 mm wheel, and uses single-point dressing, which is "so easy and straightforward to program on this machine", again shortening changeovers. An important factor when ordering the machine was the simplicity of the control with its full graphical image support that could be tailored at the front end by J&S to suit the application and the operator. While initial training took just three days for both the night shift and day shift setter/operators, as they became more proficient they requested minor changes to suit their applications, which J&S was able easily to accommodate. The control provides three modes of fully interactive programming – graphical, text view and ISO for the grinding and wheel dressing cycles. The operator can select macros and enter key data around graphical images for diameters, speeds and feeds, simply by touching the screen. In addition, ISO is fully supported, as is G and M code programming, which the operator can use at any time. The graphical interface and G and M code pages update each other seamlessly, so there is true flexibility for each operator and each shift. The Ultragrind has a modular wheelhead design that enables up to four external or internal wheel spindles, or any combination of the two to suit the application. A B-axis, programmable to 0.0001°, rotates and positions these wheels and allows three separate datums to be created for each wheel to provide full flexibility. NTG opted for a plain 90° approach external-only wheelhead. However, Mr Strachan arranged for J&S to include a further contour generation macro, in addition to the existing ISO contour grinding facility, now a standard machine feature. NTG has ground a whole series of components, including multi-diameter parts up to 200 mm diameter by 800 mm long and weighing up to 160 kg to tolerances of 0.015/0.020 mm. Other parts have been ground with up to 12 diameters and adjacent faces in a single cycle. The range of different transfer gearbox components has involved the production of up to five diameters, four traverse ground and one involving a plunge grind cycle. Cycle times are up to seven minutes each. At Mayes & Warwick, Burntwood, Staffordshire, which has earned a world-wide reputation for its range of thread and form rolling dies, a Studer S33 has replaced an older Matrix machine. In addition to other in-house grinding applications, the main work of the new machine would be grinding very precise annular grooves on to in-house manufactured crushing rolls, which are a critical element in maintaining the accuracy of the company's products. The crushing rolls are used to 'crush' precise thread forms onto the company's grinding wheels; the treated wheels are subsequently used to grind thread forms onto the company's thread and form rolling dies. Mayes & Warwick produces a range of flat thread rolling dies in a variety of thread profiles for rolling all types of screws, bolts and fasteners. Also manufactured are rolling dies for lock bolts and rivets. All products are made to a level of accuracy that ensures each die is interchangeable and can be set in a stack off the machine, optimising both tool life and machine running time. Dies can be manufactured for screws and fasteners featuring all standard thread forms, from 1.1 to 32 mm diameter (0.043"to 1.1/4"), with pitches from 0.32 mm (>80TPI). Special form rolling dies can also be designed and manufactured for specialist applications, while products can be developed in conjunction with customers. Managing director Peter Lawrence explains the purchase of the Studer: "Having formulated a list of technical criteria for our proposed new high precision CNC grinder, we investigated the alternatives. Disappointed with the inability of several potential machine tool suppliers to satisfy our wish-list, we contacted Micronz (01352 75 88 40), the UK agent for Studer Grinders. "Micronz, and subsequently Studer, immediately understood our requirements and were able to recommend the S33 as the answer to our needs. An in-depth, successful demonstration, replicating some of our most challenging grinding tasks, together with the reputation enjoyed by Studer for the quality of their machines, convinced me to make the purchase. "Now in full production, our S33 is providing the levels of high quality output promised by Studer. In fact, as we are learning new ways to exploit our new Studer grinder, the machine is becoming ever more productive." Image: Mayes & Warwick produces a range of flat thread rolling dies in a variety of thread profiles for rolling all types of screws, bolts and fasteners, and Studer technology helps the company do so Box item New honing rings last longer A new range of gear honing rings (picture, above), using specially fused abrasives said to last virtually twice as long as similar consumables on the market, has been introduced by Tyrolit (01788 824500). Called MIRA, not only do the rings last longer, but cycle times are also reduced, as infeed rates can be increased. Both factors combine to raise honing productivity by up to 30%, without the need for capital investment in new machine tools. In the manual transmission of a luxury car, up to 70% of the gear wheels undergo honing on the flanks. Finish-honing of large volumes of gears in their hardened state is therefore called for and it is this trend that prompted Tyrolit to develop the new abrasive specifications for its MIRA rings. Three categories of Tyrolit's patented MIRA honing rings are available. Resin-bonded rings use aluminium oxides embedded in an epoxy matrix. Compound rings use a novel construction involving vitrified conglomerates embedded in a resin matrix, resulting in outstanding grain retention and stock removal, combined with the good damping characteristics of epoxy. The third product group comprises vitrified rings for high performance gear honing, capable of stock removal rates up to 0.1 mm per flank. Image: A new range of gear honing rings are said to last virtually twice as long as similar consumables on the market First published in Machinery, April 2011