From standard CNC lathes to full B-axis manipulation and five axes of motion, Steed Webzell reports on a turning market hungry for more
As the most fundamental and primary machining operation, the drive for greater productivity and quality in turning operations continues to fuel new machine tool development, as vendors vie for market share. However, everyone wants value for money and this is particularly evident at the entry-level end of the turning machine market.
It's a point that hasn't gone unnoticed by Dugard (01273 732286), which says its new ECO 65 CNC lathe with driven tools and tailstock is the first in a new line of high quality, yet value-for-money CNC lathes. Despite its attractive price tag, this 65 mm bar capacity machine offers a list of features that include a parts catcher, barfeed, 215 mm 3-jaw hydraulic power chuck, manual toolsetting probe, 4,000 rpm spindle speed, 12-station VDI 30 turret, 30 m/min rapids, ±0.005 mm accuracy over 300 mm,, and a swing over bed of 500 mm.
PROVEN TRACK RECORD
The Dugard Eagle range of turning machines has a proven track record, bolstered recently by Canterbury-based subcontractor Inca Geometric, which cross-referenced its selection of a Dugard Eagle 400 against build quality, capability, support and value for money. Says Inca Geometric's works manager, Tony Clifford: "There was very little we could criticise in the Dugard Eagle 400 when compared to other machines available and that includes some machines that were considerably more expensive."
OEMs are equally thirsty for new CNC lathe technology, as Glasgow-based Waukesha Bearings can testify, following its recent investment in two new Doosan Puma 2600 lathes from Mills CNC (01926 736736). The lathes, which form the mainstay of a dedicated production cell, are being used to manufacture the company's Inpro/Seal custom-engineered system and bearing protection products. "These products were originally being manufactured by our facility in the US, but the decision to increase market share in European markets meant that we needed to set up a similar production facility here in the UK," says John Murray, Waukesha Bearing's engineering manager.
Image: Doosan lathes - the mainstay of a new production cell
Another new CNC lathe range to hit the market is the Vturn A-series from Victor (01706 648485). The design of the machines is based on a rigid, one-piece Meehanite casting that distributes stress throughout its structure. Furthermore, the Z-axis ballscrews are mounted on the lathe's slant bed, rather than the flat machine base: this configuration minimises the distance from the ballscrews to the tools to ensure greater cutting stiffness.
Image: The Vturn A-series' design is based on a rigid, one-piece Meehanite casting
Among the companies able to vouch for the rigidity of Victor Vturn machines is Huddersfield-based subcontractor Ardor Engineering. The company owns seven such models, which includes the recent arrival of two medium/large capacity Victor Vturn 36/85 CNC lathes. With a maximum spindle power of 26 kW available, Ardor says that the cost- effective '36' is capable of large depths of cut while still producing high quality surface finish.
Sometimes, the addition of a little extra functionality to a CNC lathe can enhance its appeal to a specific audience, and this is certainly the intention of the new NZL2500 with 4-axis control from Mori Seiki (0844 800 7647), which is designed specifically to achieve high productivity for shafts and flanges.
On the new machine, higher rigidity is achieved by using three independent guideways, so that turret 1, turret 2 and the tailstock can all move independently of one another. Allowing turret 2 to move in the Z-axis, without being restricted by the tailstock makes the latter very rigid, while the slideways used on all the axes give the NZL2500 50% more stiffness than a conventional machine, says Mori Seiki. It also has options for milling (MC type) and Y-axis machining (Y type) capabilities, which were not available on the ZL Series, enabling the completion of far more complex machining tasks.
Occasionally the capability of a new turning centre is able to replace two or more conventional machines, as Newcastle-based sub-contractor Northern Precision Engineering discovered following its recent investment in a Quick Turn Nexus 250-II MY turning centre from Yamazaki Mazak (01905 755755). The new Mazak machine replaced a large CNC lathe and a large horizontal machining centre.
Image: Two machines replaced by one at Northern Precision Engineering
TWO INTO ONE GOES
"We've essentially put two machines into one, with no loss in capacity and a significant increase in our manufacturing flexibility," says Dave Graham, the company's business development director. "Mazak's Mazatrol Matrix conversational programming is the key – it's a completely different mindset, but, once the operator has got it, the improvements in programming time offer a massive productivity bonus."
Greater productivity for complex parts is, of course, the premier reason why many of the latest turning machines offer advanced configurations. Among the most popular models for complex turning operations are sliding head lathes. For instance, the new Gamma range from Tornos (01530 513100) is available with either five or six linear axes, and two C axes. The Gamma 20/5 allows the customer to load 35 tools with up to 15 rotating, while the Gamma 20/6 permits the installation of 39 tools with 15 driven.
Image: The new Tornos Gamma
Able to vouch for the Tornos 20/6 is Tunbridge Wells-based Muffet Gears, which is using the machine for the production of parts for its own range of worm gearboxes. The machine was selected for two reasons: the ability of the 20 mm diameter capacity Tornos to conduct thread whirling in one operation; and the ability to switch to a guide bush-less system during set-up, which enables machining in the headstock and reduces material waste to circa 35 mm per bar.
Putting some perspective on the potential cost reductions; the company was previously machining bronze pins in a time of 20 minutes, with four operations on two machines at a cost of £9 per pin. The parts are now produced on the Gamma in 1 minute 5 seconds, at a cost of £0.80p per pin.
SMALL, ONE-HIT APPROACH
Another company making great gains through the application of sliding head technology is Basildon-based Specialized Engineering Components (SEC), which is turn-milling four diesel engine parts in one hit to close tolerances using its recently installed SR-20J from Star Micronics (01332 864455). Three of the parts were previously produced in three operations each – blank turning on a cam multi followed by manual milling and then drilling/reaming. The fourth part needed two separate operations. All are now produced from bar in one visit to the company's Star sliding-head lathe. "We produce 6,000 of each diesel engine component on the Star and ship them every month, whereas before we had to spread delivery over two months," says Steve Clifford, director at SEC. "Cashflow is better now, as we can invoice quicker and secure payment earlier."
Image: Star offers one-hit machining at SEC
In the adjacent county, Hertford-based Plastics Turned Parts (PTP) has provided much needed extra capacity with the recent installation of a Citizen (01923 691500) L20-IX. The machine has demonstrated reductions in machining times to the order of 5 seconds on a typical already well-proven 30 second cycle time. This is largely explained through Citizen's development of Streamline Machining Technology, which has also helped in achieving quicker and easier setting through the windows-based CNC program editing, especially on the more complex work.
As the result of the company's latest installation, PTP has been able to take on new business and relieve work load issues on its existing Citizen L16, K16 and B20 machines.
Fixed-head turning centres can be enhanced to embrace complex turning, through the addition of extra spindles and turrets. A case in point is the latest six-axis Miyano BNA-42 DHY, which features a totally new configuration. This compact, fixed-head turning centre combines a main 42 mm bar capacity with a secondary spindle, an eight-station, all-driven, Y-axis turret capable of providing up to 16 tool positions and a totally independent six-station sub-turret. The supplier, Citizen Machinery, says that, compared to a single turret turning centre, achievable cycle times when running 'one-hit' operations should be around 20% faster.
BEST OF BOTH WORLDS
Increasingly, subcontract machine shops appear to be adopting both fixed-head and sliding-head machines to provide customers with optimised solutions, and this is certainly the case at Hertford-based Qualiturn Products. Until October 2010, Qualiturn had 16 CNC sliding-head and two Miyano BNJ fixed-head turn-mill centres, which gave a maximum capacity of 42 mm bar size. Reacting to a shift in the market from customers requesting similar or even more complex components, but of a larger size, Qualiturn seized the opportunity and added another Miyano ABX-51SY fixed- head turning centre with a 51 mm bar capacity and a further 32 mm sliding- head machine to the plant list. Also taking over the next door unit, the company decided to split its operation into separate dedicated sliding-head and fixed-head production shops.
To add even greater functionality to turning operations, users must turn to B-axis machines, such as the new DMG CTX beta 1250 TC4A, which features an upper B-axis mill-turn spindle, and a conventional lower turret with live tool stations and direct drive.
Image: The DMG CTX beta 1250 TC4A features an upper B-axis mill-turn spindle and a conventional lower turret with live tool stations and direct drive
Compared with the single turret B-axis variant of this lathe, the new model, with additional bottom turret, is able to carry out more complex work at the main spindle. Either or both turrets can operate at the counter-spindle, if that option is chosen, or else simultaneous work at both spindles can be undertaken. The B-axis, with its 12,000 rpm motor spindle, swivels by ±100°. DMG estimate that productivity potential has been increased by up to 50% on the new lathe.
Versatile option suits Turnell and Odell
To cater for prototype development and batch production, precision machining company Turnell and Odell allocates much of its work to its new CNC/manual turning machine supplied by XYZ Machine Tools (01823 674200). Turning jobs range from small pins weighing a few grams to shafts up to 3 m long and 1.5 tons in weight – all machined on the XYZ Proturn SLX 555 gap bed lathe. CNC programs can be written offline, but the ease with which the Prototrak control can be programmed means that Turnell and Odell finds it quicker to program one-offs and low-volume work at the machine. The Prototrak SLX control offers constant surface speed, tool-tip radius compensation and the innovative 'traking' feature.
Traking allows the operator to execute a program by turning the apron-mounted hand-wheels. This boosts operator confidence, as the machine will move through the program at that speed, thereby contributing to collision-free machining.
Image: Shafts up to 3 m long and 1.5 tons in weight are tackled by the XYZ Proturn SLX 555 at Turnell and Odell
First published in Machinery, June 2011