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Laser & Waterjet Profiling
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With a current order book topping £110 million, Joy Mining faces ever growing pressures from global competition in exporting over 80% of its £160 million turnover to China, USA, Poland, Australia and South Africa. As Solutions discovers, the expertise of its production engineers plays a significant role in the utilisation of often complex machining cycles.
Based on a 50 acre site in Worcester, the company produces components for armoured face conveyors, large gear cases, sprocket ring gears, framed components for powered roof assemblies and hydraulic rams, as well as performing assembly tasks on a range of large valves. This array of components, often produced from difficult materials, is destined for use by the mining sector around the world.
Joy Mining was originally established in the 1930s as the Mining Engineering company (MECO) which led to a series of takeovers including Dowty (1970), a management buyout (1980) and an acquisition in 1996 by US mining specialist, Joy Mining Machinery, now a division of Joy Global. Joy Mining is a truly global force and has risen to have the world’s largest service and support infrastructure for underground mining machinery used in the extraction of coal and other bedded materials.
The Worcester operation employs 250 people where almost £3.5 million was invested in 2011 (and £1 million in 2010) on project-based equipment. The projected spend in 2012 is expected to top £1.3 million.
As production engineering manager Robert Wilks affirms: “Because much of our work is small batch and very diversified, the extensive skills of our setters and operators are key to not only running the machines but also for tooling up, programming and for taking complete responsibility for all manufacturing tasks.”
Indeed, this directive came into play when the company was looking to replace a hard worked, ageing Butler Elgamill CNC universal bed mill used to machine castings and flame cut large plates. Aside from everything else, Joy Mining was adamant the replacement machine had to allow the company to gain maximum advantage from the strength of its skill base.
The selection and installation in September 2011 of the Soraluce SP 8000 travelling column bed type universal milling/machining centre from Sheffield-based Ward CNC is a prime example of the benefits that can be gained from such a strategy, because not only has the machine halved cycle times and reduced tool costs on the castings and plates but its ability to produce other components, such as large gearbox housings, has also been capitalised on.
As part of the specification, the machine’s Heidenhain iTNC530 control with its well proven operator conversational interface provides the two setter/operators that man the Soraluce around the clock with the ideal solution to prepare and program the next scheduled component while the machine works through the existing product cycle.
“As cycle times vary between one hour to two days (four shifts), we have ample time to work together and incorporate our machining experience in planning the next task while overseeing the cycle that’s being run,” explains day shift operator, Ean Stamp. “This may not be to achieve the fastest cycle time but it ensures the part fully conforms to requirements.”
The 5-axis Soraluce SP 8000 has a 45kW, high torque 1,045Nm drive to its double-jointed automatic universal indexing head, which has one joint vertical to the spindle centre line giving a full 360° rotation and the other at 45° providing a total of 20,736 (144 x 144 on each joint) specific positions. As part of the justification, Ward CNC had to ensure the machine met the specific requirements of Joy Mining’s management team against five other competitor machine suppliers.
In addition, other key elements in the selection, justification and purchase of the machine included its ability to operate in a self-contained cell type environment as well as the pedigree of the builder and the supplier’s proven service record.
While both Soraluce and Ward CNC qualified with an acceptable pedigree of manufacturer and supplier, the SP 8000’s build quality was carefully scrutinised to achieve a 10 to 20 year production life span. Here, its inbuilt rigidity and robustness for heavy machining was qualified by the Worcester machine shop, which had already gained good experience with an existing Soraluce bed mill supplied and supported by Ward CNC.
That said, it was the machining trials carried out at Soraluce’s headquarters in Spain that finally drew the signatures to the machine order. As part of the buying process, Soraluce had to satisfy the machining demands of samples of Hardox high strength and impact abrasion resistant steel plate (425 to 475BHN), a material widely used in coal face conveyoring.
Since installation, the machine has demonstrated overall savings of some 50% on milling and particularly drilling cycles plus has provided a significant reduction in tool costs as a result of its inherent rigidity. Says Mr Wilks: “We very rarely have to change inserts, which is helping our tool inventory and costs.”
Following installation, the Soraluce has recorded spindle uptime of over 80% (75% is the company target) and has even machined fabricated assemblies some 5m long by 3m wide and high, which overlap the side of the 8m by 1.35m table. Also, large drive sprocket transmission cases having 20 to 50µm hole tolerances and between centre hole geometries of 0.05 to 0.1mm have been produced, which include the production of main bores in transmission castings.
Significant is the fact that the full power of the machine can be exploited in the BT50 ‘Big Plus’ patented spindle system which provides a dual BT50 taper and flange face interface for the tooling back ends. The tool is also clamped in the spindle with a force of some 15,000Nm which has enabled Seco’s latest Performax indexable insert drills to be used for the first time as a test bed for the tooling supplier in producing bracket holes between 10mm and 70mm diameter and bores up to 90mm diameter from solid utilising the 20 bar through the tool coolant pressure.
The 32-tonne Soraluce has an X-axis travel of 6,500mm driven by two Heidenhain servo motors and gearboxes through a double rack and pinion. The vertical Y-axis is 1,600mm and the Z-cross-axis is 1,200mm. The special ram assembly is 480mm by 500mm which also houses the Heidenhain water cooled direct drive spindle motor delivering between 20 and 4,000rpm.
Included in the specification are adaptive feed control, DXF download and dynamic collision monitoring, plus Renishaw non-contact laser probing. Heidenhain linear scales ensure accuracy is maintained in X-, Y- and Z-axes within ±0.005mm. A 30 tool magazine will accept tools up to 125mm diameter by 400mm long (tool diameter can be extended to 250mm with adjacent packets being left empty). Maximum tool weight is 20kg.
Of particular interest to Joy Mining’s engineers was the machine’s universal head design, which is able to deliver a massive 10,420Nm of torque and maintain an indexing accuracy through both Hirth coupling joints within ±1 second.
As part of the ability to utilise the skill of the setter/operators, the Soraluce SP 8000 was called upon to support an overflow condition for producing four different split gear cases some 1,500mm long by 750mm wide by 400mm high. Each of the cast iron housings that have to transmit 11,000bhp have three main bores of 700mm diameter. As part of the cycle the split fine faces had to be milled, 12 bolt holes drilled to 33mm diameter and 40mm deep in one casting half and 400mm deep in the other. Holes were drilled and tapped M24 and thread milled M36.
In the second operation, the castings were relocated on the joint face and certain features milled, holes drilled and spot-faced, two inch BSP gas threads tapped and a series of M24 holes drilled and tapped.