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British machine tool manufacturer, Asquith Butler, is ‘turning to a new dimension’ with the introduction of its Starturn range of travelling gantry, 6-axis mill/turn machining centres, according to managing director, Paul Hinchliffe.
He and co-owner, group chairman Craig Wilkins have in the past decade returned the Yorkshire-based company to its former status as one of the world's leading manufacturers of high precision, large capacity machining centres.
The new machine, capable of achieving micron tolerances, is based on Asquith Butler's established STARCUT range of 5-axis prismatic machining centres. It is augmented at the company's Brighouse factory by the addition of a large capacity turning table which can be supplied in 3m, 4m or 5m diameters according to customer preference. Existing Asquith Butler machining centres in the field may also be retrofitted with the new table.
Advantages of 5-axis prismatic machining combined with turning in the same set-up include significantly more versatility when establishing production processes, enabling higher productivity, reduced labour costs and the elimination of tolerance build-up through repeated refixturing.
The machine's linear axis travels range from 3m to 30m in X, 3m to 6m in Y, and 1m to 3m in Z. Cutting feed rate is up to the rapid traverse of 20m/minute, maximising metal removal and ensuring short idle times. Rotary axes are the 360° C-axis on the ram and a 220° A-axis head – both indexable in 1° increments or servo-operated, enabling everything from five sided machining to fully interpolative 5-axis profiling.
Capable of equally high precision when vertical turning as when milling and boring, the Straturn is aimed at the nuclear industry internationally, particularly for the manufacture of large, high integrity pumps, valves and pressure vessel components. Asquith Butler has been working closely with a number of leading manufacturers and technical institutions in this sector as demand increases due to the requirements of the nuclear new build programme.
The machine is also well suited to machining components for the oil, gas and renewable sectors, which employ similarly large components that often require a significant amount of rotational machining. Applications are also expected to be found in the marine and defence industries.
Automatic exchange of multiple milling heads, 50kW of spindle power and speeds from 3,000rpm to 12,000rpm allow rough, semi-finish and finish milling, according to the type of head chosen. In turning mode, the 100kW of power available allows good all round turning performance with high precision finishing.
The rotating ram allows up to eight Capto C6 or C8 turning toolholders to be mounted on a turret-type attachment to suit the machining application, avoiding manual intervention for tool change. Positioning and clamping is achieved using a Hirth coupling and four pull studs, allowing high metal removal rates. If more turning tools are needed to complete a cutting cycle, the requirement is met by automatic exchange of the turning head or individual tools. Turning tool attachments to accommodate long bars for internal boring are also available.
The chain-type magazine for automatic exchange of prismatic machining cutters and turning tools has 60, 80, 100 or 120 pocket options. Coolant delivery to the cutting area is via external flood as well as advanced, high pressure, internal through the spindle systems.
Positional feedback to the Fanuc, Siemens or Heidenhain control is via linear scales and high resolution rotary encoders to ensure utmost precision.
Volumetric and thermal error mapping and compensation of Asquith Butler machines is available using a system developed by the company in association with the University of Huddersfield's Centre for Precision Technology (CPT).
Development of the Starcut machine range has enabled Asquith Butler to achieve excellent machine accuracy to meet its customers' demanding requirements. Specific installations of 9m x 4m x 1.25m Starcut machines have achieved flatness and straightness accuracies of 12µm over 9m and ballbar circularity under 15µm in the main working plane.
Behind the machine's long-term, micron level accuracy and repeatability, despite its large size, are high levels of stiffness and vibration damping designed into the structure using the latest finite element analysis techniques. Further features ensuring close tolerance machining include optimised bed and gantry structures and generously proportioned guideways.