Grinding – a developing process

Early grinding, which largely involved rubbing one hard surface against another by hand (such as the pestle and mortar), dates back further than most imagine. For instance, the manual grinding of grain, together with the baking of bread, go back at least 8,000 years, while rotary mills, turned by slaves or animals, are known from at least the 2nd century BC. Today, of course, there's a degree or two more automation available to modern manufacturing companies. The surprise, perhaps, is that, despite nearly two centuries of development since the industrial revolution, grinding shows none of the signs associated with being a so-called mature technology. One company able to demonstrate the fruits of investing in the latest grinding machines is Peterborough-based Marlor Tooling, which has just installed its eighth tool and cutter grinder from Walter Machines UK (01926 485047) – namely a Helitronic Micro. "The Micro is targeted at the fast machining of tools from 0.5 to 12.7 mm diameter (for regrinding, 2.5 to 12.7 mm) and, while it extends our capability in the smaller diameter range, it will also process much of our current tooling at the higher end of that diameter capacity," says Marlor's managing director, Kevin Taylor. "This means it will reduce cycle and overall lead times on existing work, besides enabling us to also offer tool manufacture and regrinding in the micro range," he adds. High resolution measuring systems and linear drives on all of the Helitronic Micro's six axes combine with the machine's ability to 'adapt to its environment', in terms of thermal compensation. Furthermore, it has a 1,000 rpm A-axis workhead and a 10,000 rpm spindle featuring three grinding spindle heads that can accommodate up to 12 grinding wheels. In addition, the optional robot loader will accommodate up to 1,500 tools, depending on diameter – "we'll never buy another tool grinder without a loader", offers Mr Taylor. Image: Marlor Tooling has installed numerous Walter grinding machines Another tooling manufacturer with a planned investment programme is Sheffield-based Lomas Engineering, which has recently taken an RX7 tool and cutter grinder from ANCA UK (024 7644 7000). "Although a previous enthusiastic user of ANCA grinders, mindful of the technical advancements in the field we considered the merits of the available options," explains managing director, Ian Lomas. "However, having seen the RX7 put through its paces, we had no hesitation in placing the order. "Now in full production, with the help of a robot feed, we operate the RX7 around the clock in 'lights-out' mode," he adds. "Given the machine's high yield and the quality of its output, we are expecting rapid payback on our latest acquisition." The ANCA RX7 offers a double-ended spindle allowing up to eight grinding wheels for a single job, while an optional wheel changer makes six wheel packs available for increased versatility. When it comes to manufacturing technologies, new markets are one of the main drivers of ongoing development. For grinding, one such new market can be confirmed by Abwood Machine Tools (01322 225271), wheel specialist Meister Abrasives UK (01327 703813), and an application involving photovoltaic solar panels. Abwood has been supplying grinding machines involved in the production of multi-crystalline wafers for the photovoltaic industry since the 1990s, firstly in manual format, then with full automation to support round-the-clock manufacturing. These Abwood TS2 twin-spindle models grind two opposing faces at the same time before the workpiece is rotated 90° to grind the other two faces. SURFACE FINISH CHALLENGE For many years, surface finish tolerances were around 0.4 Ra. However, an industry push for thinner wafers demanded less sub-surface damage on the ground blocks and, therefore, improved surface finishes. Superior surface finish is also an industry goal for multi-crystalline wafer manufacturers to allow infrared 3D inspection to look through the block before it is cut into wafers. Here, a mirror-like surface finish of around 0.05 Ra is required. With this in mind, Abwood's general machine design going forward is to deploy two roughing and two finishing wheels on the same machine, using four spindles. To avoid a resulting very long machine, Abwood came up with a clever solution to keep the machine compact. "Rather than have two pairs of spindles, we designed the new machines with the finishing wheel inside the roughing wheel," explains Abwood's engineering director, Rob Nicholas. "A 300 mm diameter Meister Abrasives vitrified diamond roughing cup wheel has a 275 mm diameter Meister Abrasives vitrified diamond finishing cup wheel sat inside it. Through the spindle is a splined servo driven shaft, so the cup wheels have independent linear movement in and out to adjust the depth of cut and compensate for any wheel wear." A D20 vitrified diamond finishing wheel from Meister Abrasives achieves the required surface finish. This wheel can take off up to 0.08 mm per pass at a feed rate of 400 to 50 mm/min, whereas a resin wheel would be running at 150 to 200 mm/min. Using this dual wheel operation with resin wheels, the company can push up to 200 mm/min for a combined roughing and finish grinding process. However, with Meister Abrasives' wheels, it is able to achieve up to 400 mm/min. Another niche, but growing, market for grinding and finishing applications is optical systems. In order to drive down costs, lens and mirror manufacture is moving away from direct machining of glass blanks towards glass press moulding. Aware of this trend, CNC polishing machine manufacturer Zeeko (01530 815832) has developed an automated process for improving the surface quality of such moulds. A Zeeko 7-axis CNC intelligent robot polisher, using either bonnet or fluid-jet polishing, has been shown to be able to correctively polish moulds automatically and consistently to very high accuracy, in terms of form error peak-to-valley (P-V) and surface texture (Ra). The result is a significant improvement in the quality of the optics, which can be of any shape: concave, flat, convex, aspheric or free-form. Box item Grinding technology developments in brief To win new business, manufacturers today must be quicker, better, more accurate than their competitors. To this end, grinding machine suppliers engage in relentless development programmes as they vie for market share. [] At grinding machine specialist Colin Gladwell Machine Tools (01872 864777), there's a plethora of recently released models available, including three new machines from Amada: the Meister G3 is a multi-tool grinder for everyday use, capable of grinding steel, carbide, ceramics and other materials in manual mode or full CNC; the Winstar, with CCD camera technology, for extreme dimensional and flatness accuracy; and Techster, which, due to its bridge-type structure, is highly sturdy and productive. From the same stable comes the revised version of the Shigiya GSU CNC universal grinder, which offers 10 wheelhead configurations, as well as the all-new Shigiya GAV/GPV small vertical cylindrical grinder. The GAV (angular approach) and GPV (straight approach) accommodate workpiece sizes up to 30 mm diameter and 150 mm long. Image: The all-new Shigiya GAV/GPV [] Retaining the vertical theme, the new VG series of universal vertical grinding machines from Danobat Group (+34 943 748044) has been designed for the precision grinding of medium/heavy components, such as aircraft engine stators, transmission gears and bearings. [] Other new products include: the SB-1000 grinding wheel balancer controller from Schmitt Europe (02476 651 774); Norton Quantum ceramic grain wheels from Saint-Gobain Abrasives (01785 222000); and Akasel diamond grinding discs for surface preparation prior to metallographic analysis from Aptex (01564 206393). First published in Machinery, November 2011>/b>