Single-minded

Rapidly-developing technology means machine tools are now able to offer several functions in a single unit which improves set-up times and cost efficiency. Martin Oakham explains


Technology is developing and changing so rapidly that manufacturing processes, machines and tooling that were productive even two years ago have more than likely been overtaken.

Further driving this revolution is the push by subcontractors to consolidate and automate processes to reduce set-up times and floor space, thus making it viable for machine tool builders to use innovations such as linear drives, temperature compensation, position feedback systems and high-speed direct drive spindles.

Prior to this, machine development was restricted by customers not being prepared to pay premium prices for these improvements. Today, largely due to digital control technology and software developments, machine tool builders are able to offer several functions in a single machine and control multiple axes simultaneously relatively easily, thus hugely improving set-up times and floor space requirements.

And as if this were not enough, demand for machining capacity across Europe is driving the take up of five-sided and simultaneous five-axis machining as the aerospace and power generation sectors in particular strive to meet projected delivery targets.

According to machine builder Deckel Maho Gildemeister (DMG), production lead times have to be reduced and the number of operations performed on a component cut dramatically to meet demands, thus presenting suppliers with a challenge. DMG believes the solution lies in combining 15-20 operations into one or two separate cycles, and supporting this by building machines with higher powered spindles, controls and software linked to CAD/CAM systems.

Richard Watkins, DMG UK’s milling specialist, said: ‘if users want to eliminate multiple set-ups and datuming, they need a five-face approach capability with full simultaneous five-axis processing to maintain geometric relationships between features.’ They must also eliminate any chances of damage or distortion due to re-clamping, while being able to take heavier cuts — often out of solid and difficult-to-machine exotic alloys.

At the top end of its range, DMG has addressed user needs from the universal DMU P-Series with the benefits of travelling column set-up and the advantages of gantry design. Here, linear-driven axis traverse speeds of 80m/min and acceleration up to 10m/sec2 significantly reduce positioning times. Heavier duty cycles and lighter, high-speed operations can be accommodated with the available 35kW and up to 42,000 revs/min spindles.

Japanese machine tool builder Okuma has developed a way of turning tapered bores and outside diameters using its horizontal machining centres. The technique, called turn-cutting, is in contrast to the established process of revolving a component on the rotary table of a 4 or 5-axis machining centre and feeding in a static turning tool mounted in the spindle to machine the outer diameters (ODs).

The bore would be impossible to turn with any reasonable accuracy because a long right-angle head would be needed. Instead, the turn-cut function in the Okuma OSP-P200M control allows a single-point turning tool in the spindle of one of its horizontal machining centres to turn a static component, even on a 3-axis machine.

The process uses linear feed rates up to 60m/min to circular-interpolate the X and Y axes rapidly while feeding forward in the Z-axis.

The control continuously orientates the tool by rotating it at precisely the same speed as the circular X/Y path. The tool therefore cuts at the correct rake angle at every point throughout 360º to ensure efficient and precise metal removal.

The benefit of turning on a machining centre is that components can be finished in a single clamping, avoiding a subsequent set-up on a lathe and the consequent handling costs, increased floor-to-floor time and tolerance build-up. If parts are heavy and/or have eccentric bores or ODs, rotating them for conventional turning becomes difficult, and it requires expensive lathes that can lead to further inaccuracies.

All aspects for ultra-high tolerance, high-speed, five-axis machining are incorporated in the latest Toyoda Mitsui Seiki Vertex 550-5X universal VMC from 600 Centre of Shepshed near Loughborough. The machine combines a high-speed 25,000 revs/min spindle with 48m/min feed rate in X, Y and Z axes, has high accuracy linear scale positioning, A1 contour control, ultra-fast data server function and tilted plane machining command software.

The slideways are located above the machining area, minimising thermal distortion and avoiding ingress from swarf and coolant. Additionally, the weight of all moving elements is reduced, maximising the machine’s dynamic characteristics. And with the cutting zone below the area of bearing support, positioning error is minimised. Heidenhain linear scales are standard, ensuring a positional accuracy of +0.001mm.

Specialist subcontractor, Hemlock Engineering of Stapleford, Nottingham, has recently invested over £1m in new equipment based upon the latest five-axis machining centre technology. The company is offering two new Mikron XSM 600U 5-axis Vertical Machining Centres (VMCs), that offer customers more competitive prices, improved quality and reduced lead-time.

The move to adopt five-axis machining led Hemlock’s managing director Paul Cobb and his team to conduct a market study to find the best high-speed vertical machining centre that would incorporate pallet loading for extended running. It also sought out new software for true continuous five-axis machining.

‘With the five-axis capability we have installed we can set totally new standards in production machining by attacking five faces of a component in one high-speed machining set-up,’ said Hemlock’s Nick Marks. ‘This enables better control of critical feature relationships and also reduces piece part price due to the reduction or elimination of labour cost; with machines this sophisticated we can also provide dramatic improvements in surface finish.’

With better general understanding of high-performance/multi-axis machining, companies can learn to use new equipment to its fullest potential for better results that are comparable with showroom demonstrations.

Today’s machines should be considered as part of a package encompassing mechanical characteristics, control and servo drive performance, tooling, tool holders, fixtures, part processing and even machining strategies.

Customers looking for a better finish or repeatability may find that this change in strategy and tooling makes a world of difference.