Puma gets more bite

The significance of the launch of a new range of Puma, single turret CNC turning centres by South Korean machine tool maker Doosan, through Mills CNC here in the UK, might easily be missed, without further analysis. These machines, like just about all others, after all, look like a box; while the combination of single turret, driven tools, C-axis, Y-axis, sub-spindle and tailstock in a lathe does not seemingly push the boundaries of current technology. But this new generation of Puma, the fifth, in fact, is a highly significant launch for Doosan, the world's fifth largest metalcutting machine tool maker, by turnover – number two or three by numbers produced - and it is why, says Mills CNC's technical director, Andrew Jack, it has taken fully three years to bring the new range to market. Image: Andrew Jack talks about the new range to an interested party at the recent MACH exhibition, where the new range was unveiled "I have never seen so much time and resource put into the development of a new machine range," he underlines. And he should know, for, uniquely among Doosan's global distributors, Mills is a member of the company's global development team for new products, having been so for some six years, attending meetings in Korea two to three times a year. It is the only non-Korean member of the team, in fact. So, while 5-axis machining centres might be the leading edge technology that gets the headlines, with Doosan having recently launched such a machine, the Doosan Puma is a "bread and butter" line for the Korean company, and is similarly so for Mills CNC. ESTABLISHED; SOLD IN VOLUME Puma CNC lathes, first introduced in 1980, have sold almost 50,000 units worldwide, with the last generation launched in 2005. In the UK, Mills CNC has an installed base of many thousands, too. "The Puma range is already very successful and has a reputation for both power and longevity," highlights Mills CNC managing director Nick Frampton, adding that the relationship between Doosan and Mills CNC is one of 27 years' standing – the longest of all dealers in the world (initially via Daewoo machine tools, which was bought by Doosan – see Machinery website, here). Improving on an already well accepted range, while also not adding much, if anything, to the purchase price is, then, clearly something not to be undertaken lightly. Especially when a complete range of 36 machines is introduced in one go, as it was (see box item for machine specifications). With a 'bread and butter' range like this, launching 36 machines is no mean feat. It must be right The new range got its first UK outing at the biennial manufacturing technology show, MACH, in June of this year. So how exactly has Doosan improved on an already successful line of CNC turning centres? Well, from the outset, the machine range specifications were set by benchmarking three key competitors' equivalent machines, with capacity or power benefits built in over and above these. But within this, the headline benefit for the machines is an improvement in workpiece accuracy. Under strict testing in the factory, Doosan has confirmed that the new range of lathes holds workpiece accuracy to closer limits over an 8 hour period (1 shift) under sensible temperature conditions. This is more important than headline accuracy figures stated in every machine tool builder's documentation, as it represents what can be achieved under real manufacturing conditions. Mr Jack adds that other factors can influence workpiece accuracy, such as ambient temperature variation. For ultimate accuracy, coolant chillers and linear scales can add more benefit. In addition to this accuracy, increased machine rigidity sees surface finishes, particularly those that are milled, of a very high standard, without the tell-tale cutter witness marks often seen (curved striations). Such a demonstration was performed at MACH, in fact. Achieving these key benefits, however, has meant attention to detail in a number of areas, just about all of which are hidden from view. First of all, at an overall level, the machine structure has benefited from the application of Finite Element Analysis to determine static and dynamic stiffness, leading to a more stable, better damped structure. Previous generations would not have benefited from this latest FEA technology, highlights Mr Jack. Another key feature is that the range is modular, seeing the use of common parts across all models. The latter has helped keep costs down, allowing for the improvement in technology at very similar prices to the outgoing models. For example, the same turret is employed across the whole range. Mills CNC managing director Nick Frampton says the company has put in the most aggressive forward order requirement of any of Doosan's dealers. ATTENTION TO DETAIL Moving on to more detailed elements, and the machine base casting footprint has been increased by up to 158 per cent, although the machine footprint overall is not much different; a new, more stable base levelling block design is also present; box guideways, a distinctive feature of the heavy duty Puma range, have been made 50 per cent thicker; saddle width along the Z-axis has been increased; distance between Z-axis slideways on which the saddle sits has been increased; mounting area for the headstock is 90 per cent greater; mounting area for sub-spindle has also been increased by 50 per cent. As before, but critical, are build quality, particularly the hand-scraping of the Turcite coating of the saddle surfaces that slide on the Z-axis boxways, together with accurate pretensioning of ballscrews, Mill's CNC's technical director points out. In addition to these mechanical improvements, the effect of heat-generating elements has also been considered. So, heat generated by the hydraulic power pack is directed away from the machine; hot air is driven upwards out of the control cabinet with a heat wall between it and the machine; heat from the main spindle's hydraulic cylinder is similarly driven up and out of the machine; Z-axis guideway covers stop coolant affecting them (chilled coolant is an option); air/oil lubrication for the driven tooling gear train reduces heat generation, while heat from the motor is directed away from the turret; oil/air lubrication to ballscrews similarly reduces heat generation; X and Y servos have their own cooling fans, driving heat away from the ballscrew; angular contact bearings in the spindle, rather than roller, again reduce heat generation. Finally, all sub-spindle models supplied in the UK will have 15kW /134Nm motors, which allows heavy duty turning on second operation work. This is higher rating than many 8" chuck single spindle CNC lathes currently on the market. Mills CNC has got significant forward stock on order and all of its machines will come as standard with: automatic Renishaw tool setter; parts catcher (2100/2600); 10 bar coolant; tow-along, live centre tailstock (all tailstock models); parts conveyor; pneumatic parts ejector (sub-spindle models); coolant through sub-spindle; external air blast (sub-spindle models). Box item 1 – machine specification details Box item 2 – machine performance data Box item 3 – Doosan company overview Box item 1 Fifth generation Pumas The new range of 36 machines replaces the existing Puma 1600, 2000, 2500, 240, 280 and 300 ranges, a total of 40 machines - the new range eliminates model overlap that previously existed. It includes three models – 2100, 2600 and 3100, that's 8, 10 and 12 (15) inch capacity. The 2100 (8 in/65 mm bar) has two bed lengths – 520 and 760 mm – and there are six models for each bed length – 2100 (plain turning), 2100M (with driven tool), 2100S (with sub-spindle), 2100MS (with sub-spindle and driven tools), 2100Y (with driven tools and Y-axis) , 2100SY (with driven tools, Y-axis and sub-spindle). This represents an extension of the technical options available over previous generations. The 2600 (10 in/76 mm bar) again has two bed lengths, 750 and 1,250 mm, and the same six models in each. The 3100, a true 12 in chucker (102 mm bar), has four bed lengths – 750, 1,250, 2,000 and 3,000 mm – and three models in each length: there are no sub-spindle variations for this large capacity machine. It can also sport a 15 in chuck. The phrase 'true 12 inch' model means that there is no collision potential in the case of chuck and turret-held tools. The test is whether an adjacent tool would hit the chuck when facing to centre, Mr Jack explains. The machine also supports a 15 inch chuck, but there may be issues around interference that need to be taken account, in this case. Main spindle power for the 2100 for belt-driven spindles can be: 18.5/15 kW (30 min/cont), 183/148 Nm (30 min/cont), 4,500 rpm (standard package); 15/11 kW (30 min/cont), 254/186 Nm (30 min/cont), 4,500 rpm; and 18.5/15 kW (30 min/cont), 307/249 Nm (30 min/cont), 4,500 rpm. Optional built-in spindle motors can have a number of different windings and, hence, characteristics: max 22 kW (S3), torque up to 358 Nm, 5,000 rpm; and max 22 kW (S2), torque up to 477 Nm (S3), 5,000 rpm. For the 2600 series, the figures for belt-driven spindles are: 22/18.5 kW (30 min/cont), 240/201 Nm (30 min/cont), 3,500 rpm (standard package); 18.5/15 kW (30 min/cont), 523/424 Nm (30 min/cont), 3,500 rpm; and 22/18.5 kW (30 min/cont), 622/523 Nm (30 min/cont), 3,500 rpm for belt-driven spindles. The optional built-in spindle motors again have low or high windings: max 22 kW (30 min), torque up to 599 Nm, 4,000 rpm; and max 26 kW (30 min), torque up to 700 Nm, 4,000 rpm. For the 3100, belt-drive only is available, but multiple windings are offered: 22 (15 min), up to 1,123 Nm torque, 2,800 rpm (standard package); and 30 kW (30 mins), up to 1,203 Nm torque, 3,000 rpm for belt-driven spindles. Sub-spindle performance for the 2100 and 2600 models is: 7.5/5.5 kW (30 min/cont), 85/62 Nm (30 min/cont), 4,500 rpm (standard package); and 15/11 kW (30 min/cont), up to 134 Nm torque, depending on winding (low or high), 6,000 rpm. Main and sub-spindle can be belt-driven or integral motor type, the latter is recommended for Y-axis machines and where contour milling is undertaken, otherwise Mills CNC is forward ordering lower cost belt-drive for stock. The Tailstock can be either tow-along or servo-drive, with Mills CNC choosing to go for tow-along with live centre as standard for its stock machines. "The only benefit of servo-type is speed, but they can be a bit more temperamental, while the tow-along is more rigid, being hydraulically clamped to the slideway – we have never lost an order because we didn't have servo-type," says Mr Jack, making a similar claim for belt-driven spindles on 2 and 3 axis models, in fact. The common tool turret features 12 positions, but with the ability to half index such that, with special tool holders, two tools can be fitted at a single station. And, in the case of endworking tools, on machines with Y-axis, there is the possibility to have three tools located at a single station. Driven tool holders are of BMT65P size (ER32 collet size), versus a 55 size previously, and it is now possible to use them either facing forwards or backwards. Previously there was a restriction, due to the through-toolholder coolant supply. As standard, three Eppinger driven toolholders are supplied. Driven tool power is 5.5 kW (15 min rating, respectively), with 47 Nm torque, respectively, top speed is 5,000 rpm. Doosan machines employ Fanuc CNC systems, but there are special Doosan elements included. A particularly novel feature is the automatic compensation for inertia when interpolating C-axis with others to generate surfaces. This takes account of the different characteristics associated with parts of different weight. Tool load monitoring is a function, allowing thresholds for tools to be set during an initial cycle. There's also a CNC feature that allows for the logging of different operators' performances, while maintenance support information has also been enhanced. A utility to help users recover from turret malfunctions is another offering, while an on-screen calculator is yet another capability. In keeping with green thinking, the machine light turns off if the operator panel is not touched for a prescribed length of time. Similarly, the machine goes into sleep mode if it is idle and the operator panel has not been touched for a set length of time. Maintenance has also been given attention, with, for example, sub-spindle alignment made easy through easily accessible adjustment screws; access to the sub-spindle itself is made easy through the ability to slide the guard housing the control cabinet to the left, giving full access to that area. In addition, the coolant tank can be removed from the front of the machine, without the requirement to remove the chip conveyor. Box item 2 Performance data Roundness – using a Puma 2600SY with belt-driven spindle, a carbon steel workpiece (SM45C) 60 mm diameter by 50 mm long was machined at 3,500 rpm at a cutting depth of 0.025 mm and feederate of 0.025 mm/rev, using a 0.4 mm radius tool of TNMG style. The achieved figure is 0.5 micron. This compares to 3.2 micron for the current generation. Surface roughness was 0.11 micron Ra, 0.83 micron Rz and 0.92 micron Rmax. End milling – versus the previous BMP55P driven tool unit, which had a metal removal capability of 90 cm3/min on the previous generation Puma, the BMP65P (on a 2600Y) can machine at a rate of 105 cm3/min in SM45C. Tool diameter is 20 mm versus 18 mm previously. Face milling – chip removal rate in SM45C is 53.9 cm3/min versus 35.9 cm3/min previously. Tool diameter is 63 mm in both cases, but depth of cut is 50 per cent greater – 4.5 instead of 3 mm. Threading – again using a 2600Y model, tapping performance is now M24 by 2.5 versus M20 x 2.5 mm in SM45C. Tests also demonstrate the metal removal performance of the new machines. Figures are given for the Puma 2100M and 2600Y when cutting SM45C. For turning, metal removal is 528 cm3/min and 616 cm3/min, respectively (standard motor); for a 63 mm diameter U-drill, the figures are 472 and 630; and for grooving, the figures are 169 and 241. Box item 3 Doosan machine tools The main Doosan machine tools plant is headquartered at Changwon, near Busan on the south east coast of South Korea. Busan faces towards Japan's Kyushu island, particularly Fukuoka. Kyushu is Japan's southernmost of its four main islands. Busan is around 200 miles distance from South Korea's capital, Seoul, which is in the very north of the country. The new turning centre range is manufactured at the main Changwon plant. Also produced at the Changwon site are all horizontal machining centres, all large lathes, all high specification machines, such as the 5-axis machining centre and its B-axis lathes. Other machines are made in satellite factories, with one dedicated to vertical lathes; another to horizontal borers; another makes the Lynx range of lathes; and another for standard vertical machining centres. All quality is controlled by quality control personnel from Changwon, however. The company has, at its Changwon plant and satellites, a capacity to make 1,200 machines/month and had a turnover of $1.1 billion prior to the recession, shipping 1,000 machines/month, having experienced 300 per cent growth over a six-year period. Within a recently opened new R&D facility, the company has over 320 engineers. Its biggest markets are currently China and South Korea itself, which takes over 300 machines/month. In addition, Doosan has a high market share in the USA and Europe. The company, which sells only through distributors throughout the world, has just had a record month for order intake, with orders for 1,700 machines placed in May. There is also a Chinese plant, making machines solely for the local market. Currently it is making 1,000 units/month, with this ramping up to 2,000. Here in the UK, Mills CNC is Doosan's longest serving distributor and is regularly recognised for its performance, having won technology awards for the last three years. During 2009, Mills were the best performing dealer in Europe, a title normally held by Italy, which operates in a much larger machine tool market. Mills CNC's performance is 25 per cent up on this time last year, in terms of units shipped from Doosan, says managing director Nick Frampton, adding that the company is shipping 25-30 machines/month. Ex-stock delivery is key in winning business, he confirms. Indeed, for the new machines, at the beginning of the year the company put in what Mr Frampton describes as one of "the most aggressive stock programmes of any Doosan dealer". Indeed, although final machine build and test time is typically four weeks, from order to ship is four months and then there's a month on the water, so forward ordering is imperative. First published in Machinery, August 2010