High five

Five-axis machining is spreading throughout workshops, helping manufacturers extend the life of tools by reducing vibration and cut cycle times. Martin Oakham reports.

Digital drive and control technology and software developments are helping machine tool builders offer several machining functions in a single machine and control multiple axes simultaneously. As a result, manufacturers have hugely improved set-up times and floor space requirements.

Five-axis machining has left the exclusive realm of aerospace and is already commonplace in the mould and die, power generation and automotive sectors. Now it is spreading rapidly to more general workshops, where it is proving cost-effective.

Greater rigidity during five-axis machining extends the range of parts that can now be successfully machined. The ability to cut five sides of a cube enables components to be completed in one setting, which might otherwise have taken two or more operations.

Five-axis machining also allows the use of shorter, more rigid cutters, which helps reduce vibration, extends the life of cutting tools and reduces cycle times. These developments are further enhanced by high-speed spindle designs and improved polycrystalline diamond and cubic boron nitride tools from companies such as Sandvik, Kennametal, Sumitomo Electric Hardmetal, Mitsubishi Carbide and Iscar.

The subcontractors’ drive to consolidate and automate processes is adding further impetus to this technological revolution, making it viable for machine tool builders to experiment with linear drive technology, position feedback systems on machine monitoring systems, temperature compensation and automated loading/unloading stations.

Fifteen years ago, this technology only existed in university research labs and was considered out of reach by most machine builders, which had to work to a price to stay competitive.

The Mori Seiki’s NMV5000 DCG five-axis vertical machining centre was designed to increase rigidity and reduce vibration. It uses Mori Seiki’s DCG (Driven at the Centre of Gravity) technology, which incorporates two ball screws on both the Y and Z axis, aligned to drive the machine table through its centre of gravity.

Conventional machines only use one ball screw. This creates forces that are out of balance, thus vibration, as the machine finds its next position.

The low levels of vibration inherent with DCG enable the machine to cut faster than conventional machines, improving the accuracy and surface finish.

Rigidity is at the heart of the machine’s design. Its massive castings provide solidity while its box-in-box construction makes it compact. Mori Seiki carries out both static and dynamic analysis of its machine components to check and optimise performance under live cutting conditions.

Additionally, to secure the supply of high-quality castings, the company has taken a 33 per cent share in the Japanese Watanabe Steelworks. The company says with the growth in the Chinese economy, much of the casting manufacturers’ capacity will be taken up with domestic demand, making it difficult for users of Chinese castings to meet delivery and quality targets.

The NMV5000 features an octagonal ram supporting the direct drive spindle. The symmetry of the octagonal guides cancels out the effects of heat distortion associated with square guides, ensuring that the centre of the spindle is unaffected and benefits from improved rigidity.

Both the spindle and the rotary table use direct drive motors, thus eliminating backlash associated with more traditional geared systems.

In the event of a collision on the machine worm drive, parts can become damaged, introducing further inaccuracies and vibrations into the system. Combining these features enables the machine to cut a cone shape using all five axes simultaneously to achieve a roundness of 3.11nm, compared with 20-30nm on the previous model.

The Hardinge Group designs and manufactures CNC machining centres, grinding machines, lathes, collets, chucks and indexing fixtures, and has manufacturing operations in North America, Europe and Asia. It distributes machines to all the big industrialised countries.

In recent years it has acquired many other machine tool builders, including Kellenberger, Bridgeport, Hauser, Tripet and Tschudin.

The Hardinge XR 500 HSC (formerly Bridgeport’s HSC 500), is a high-speed vertical machining centre ideally suited to the machining of graphite and copper electrodes.

The XR 500 HSC machines have a rigid cast iron portal construction and are equipped with high-speed, heavy-duty HSK E32 40,000rpm spindles. The spindles have ceramic bearings, which generate less heat than conventional bearings.

These, and thermally-controlled refrigerated cooling jackets, help reduce thermal distortion and improve part accuracy and repeatability — even during long and unattended machining operations.

The machine’s linear guides, fast acceleration/deceleration (0.85g) and 15m/min feeds and quick-change tool changer help increase work throughput and reduce part cycle times.

The machines are also supplied with the Heidenhain iTNC 530 control, which provides short block processing times (0.5 milliseconds).

The machine’s productivity can be further enhanced by incorporating a range of optional automation features, including automated pallet changing systems.

Market-leading precision tool and die-making specialist Lasercomb Dies has recently invested in two HSC 500 high-speed machining centres from Hardinge-Bridgeport to machine brass embossing dies for applying Braille text onto pharmaceutical packaging.

The high-speed spindle is ideal for the small diameter tooling required. It maintains the surface speed necessary to cut the embossing dies cleanly and accurately, while meeting the tight lead time of two to three days demanded by the customer.

‘Of equal importance in our machine tool decision-making process was the after-sales and service back-up,’ said Alistair Baxter, sales director at Lasercomb Dies.

‘We operate in a demanding and pressurised manufacturing environment.

‘Machine downtime is not an option for us so we need to know not only that the machine tool is reliable, but that if repairs or parts are required they can be carried out and delivered immediately.