13 June 2012
Worth their weight in gold - large machine tool developments
Steed Webzell reviews the heavy hitters of the machine tool world, discovering no lack of innovation when it comes to tackling big components
(Video shows Doosan Puma VTS1620 - see later)
Typically, wherever bulky raw materials appear on the work schedule, large amounts of capacity and power provide the solution, although sometimes it takes a little more, as Yamazaki Mazak UK (01905 755755) can demonstrate with its new Orbitec 20. Here, Mazak has created a novel approach to machining eccentric large turned features in an irregular shape that are not conducive to normal turning operations. Such components can be difficult to rotate, challenging to hold, heavy, out of balance and can change geometric shape dynamically during turning operations.
Specifically developed for oil and gas sector components, such as eccentric shafts and valve bodies, which can only be produced by turning, for reasons of geometric shape or function by design, the Orbitec 20 moves the cutting tool, while the turned part remains in a fixed position.
The key component of the Orbitec 20 is the virtual X-axis created by the facing head, which uses a 'circle within a circle' design that is naturally balanced. This allows the machine to undertake operations that are both difficult and expensive with traditional turning methods.
There are several examples of innovation with the Orbitec 20: the spindle headstock design with a facing head eccentric mechanism has an integral balancing system that allows it to run at higher rpm. Together with a secondary mechanism, this ensures that the turning tool centre line is maintained. In addition, the headstock design provides the capacity to turn diameters of 508 mm on large, awkward and complex parts, fitting into a cylinder up to 1,050 mm in diameter and 1,300 mm in height.
Of course, manufacturers of large, heavy components are increasingly demanding the capability to complete them in a single set-up to achieve short lead times, improve accuracy and reduce work-in-progress. Aimed at these users is the new Okuma VTM-1200YB from UK agent NCMT (0208 398 4277).
This 30-tonne, double-column machine has been designed as a cross between a heavy duty vertical turning and boring facility, and a fully-featured, 5-axis machining centre. Structurally, it is configured as a bed-type machining centre, but, instead of a conventional table, it has a 30 kW,
500 rpm/6,000 Nm torque turning spindle with 360,000-increment C-axis positioning.
The table has a pair of large cross-section X-axis slideways, carrying a substantial column with vertical Z-axis slides. These, in turn, locate a saddle with
Y-axis cross-slides to support a 37 kW/10,000 rpm/505 Nm milling spindle (B-axis) with HSK-A 100 taper. By locking it using a Curvic coupling, turning operations on components up to 1,200 mm diameter by 1,080 mm long can be carried out, without risk of damaging the bearings.
B-axis positioning (150°) allows standard tooling to be used in situations where specials might otherwise have to be considered. In addition, it is possible to improve milling efficiency when using ball-nose cutters by using the tool at an angle to avoid zero surface speed cutting at the tip. Similarly, angled holes can be produced without the need for special fixtures, using a 3D co-ordinate conversion facility within the control software.
Retaining the vertical theme, Mills CNC (01926 736736) has launched two new large capacity Doosan ram-type vertical turning lathes. The machines, the VTS 1620 and VTS 1620M, are the biggest VTLs available from Mills, and have 2,000 mm maximum turning diameter and 1,600 mm maximum turning height capacity. Both machines feature a large square cross-section ram (250 by 308 mm) that has a 960 mm maximum vertical travel and which is integrated with the travelling cross-beam.
Image: The VTS 1620 and VTS 1620M are the biggest VTLs available from Mills CNC
The vertical position of the cross-rail moves in 200 mm increments and is hydraulically clamped to the vertical rails to ensure that the ram is in the most rigid and optimum position for machining. The machine table is 1,600 mm diameter and can have either 4-jaw manual clamping or a combination table that offers 4-jaw manual independent, plus 3-jaw hydraulic clamping. The table has maximum 250 rpm and a weight capacity of 10,000 kg.
Moving to horizontally configured turning machines, a large turn-mill centre has been introduced by DMG UK (01582 570661) for machining components up to 3,000 mm in length and 700 mm in diameter. The CTX gamma 3000 TC
is equipped with a ±120° B-axis for flexible turning operations and milling in up to five axes simultaneously. Two steady rests may be used to support even longer workpieces.
Image: The CTX gamma 3000 TC tackles parts up to 3,000 mm in length and 700 mm in diameter
The machine has the option of a 12-station turret as a second toolholder, which can have live VDI40 tools in all stations rated at 9.4 kW/4,000 rpm/30?Nm. The additional turret opens up the possibility of multi-axis machining at one spindle or parallel machining at both main and counter-spindles. The structural design of the CTX gamma 3000 TC is based on a robust travelling column, mounted horizontally on the Z-axis, while linear guideways are widely spaced for stiffness and stability during machining.
Turning operations also play a huge role in the new StarTurn range of travelling gantry, 6-axis mill-turn machining centres from Asquith Butler (01484 726620). These machines, capable of achieving micron tolerances, are based on Asquith Butler's established StarCut range of 5-axis prismatic machining centres, but are augmented by the addition of a turning table that can be supplied in 3, 4 or 5 m diameters, according to preference. Existing Asquith Butler machining centres in the field may also be retrofitted with the new table.
The machine's linear axis travels range from 3 to 30 m in X, 3 to 6 m in Y, and 1 to 3 m in Z. Rapid traverse is 20 m/min, while 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 5-sided machining to fully interpolative 5-axis profiling.
Capable of equally high precision when vertical turning as when milling and boring, the StarTurn is aimed at the nuclear industry, particularly for the manufacture of large, high integrity pumps, valves and pressure vessel components.
Image: The StarTurn range is particularly suited to large nuclear industry components
Another new machine tool 'heavyweight' on the market is an energy-efficient, 200-tonne, travelling-column SHW machining centre called PowerForce 8. Available in the UK from Geo Kingsbury Machine Tools (023 9258 0371), X-axis travel is modular in 1 m increments from 10 to 50 m, while the vertical Y-axis can be 7,100 or 8,100 mm and the cross Z-axis travel is 2,000 mm. According to requirements, customers may opt for a fixed bed or rotary table variants. Despite its large size, the machine offers 2 m/s² acceleration up to 40 m/min rapids. Positioning accuracy is ±0.01 mm over 2 m.
While machine shops of modest resources sometimes shy away from heavy machining contracts, wary of the sizeable capital investment often associated with the required machinery, having just one such machine could pay dividends – in a big way. Furthermore, prices for heavy duty machine tools in relative terms have fallen in recent years, in proportion with the steadily increasing numbers of market entrants.
Box item 1
Big deal for Mollart
Mollart Engineering (0208 391 2282) has won a major aerospace partnership contract for producing key operations on a family of turbine shafts that could progressively build-up to be worth £4 million a year within three to four years for the Chessington, Surrey, site.
Operations director Mike Pragnell explains how the contract was secured: "It was our ability to combine three essential elements of our business – namely deep-hole drilling, our associated tooling development expertise for special bore production, as well as our large capacity turning and boring capability."
An initial trial was performed in September 2011 that involved machining the first of the alloy steel, free-issue forged components some 2,200 mm in overall length and weighing up to 800 kg in the raw (supplied in the rough turned and heat treated condition). Following the successful machining operations, it took some three months to carry out evaluation, which included a strict quality audit of the Mollart business. This was followed with sample part production before Christmas, leading to the issue of the first production batches involving two parts per week earlier this year.
The parts are machined on Mollart's Weiler E90 CNC lathes (Kyal Machine Tools – 01780 765965) with 6 m bed length. Currently, overall production time is running at 40 hours per shaft.
Box item 2
Newburgh opts for Hartford
Rotherham-based subcontractor Newburgh Engineering has installed a Hartford PBM-115AG precision horizontal boring and milling centre from TW Ward CNC Machinery (0114 276 5411) as the centrepiece of a new manufacturing cell to machine 1.7 m long cast iron workpieces.
Image: Newburgh opted for a Hartford PBM-115AG precision horizontal boring and milling centre
The parts required for the new contract are currently produced at the rate of 60 per week and Newburgh initially set up a cell based on two reconditioned Giddings & Lewis horizontal borers. The process of using re-engineered machines has traditionally served the company well, but, in this case, frequent machine downtime/breakdowns "were causing a certain level of frustration", according to David Greenan, operations director.
"We decided to replace these units and went to the market to find the best solution for performing the face milling and hole boring operations required on the faces of these components," he says. "Machine reliability and robustness – and, of course, value for money – were the key selection criteria."
The robustness of the Hartford five-axis (W+B) PBM-115AG is based on construction principles deploying a single heavy duty cast iron bed and a single, ribbed alloy frame casting for the spindle head that allows the Z-axis drive and spindle head to be mounted on the same centreline. The machine has heavy duty, hardened and ground solid slideways.
The PBM-115AG with 40-station ATC has a table/pallet working area of 1.6 by 1.4 m with travel in X, Y and Z axes of 2, 1.6 and 1.5 m respectively, plus a W-axis (spindle) travel of 500 mm.
First published in Machinery, June 2012
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Asquith Butler Ltd
DMG (UK) Ltd
Geo Kingsbury Machine Tools Ltd
Mills CNC Ltd
Mollart Engineering Ltd