Flexible friends

Innovation is leading to a new generation of machine tools claimed to deliver higher performance and productivity at a price designed to ensure a competitive edge. Martin Oakham reports.

Automation once had a limited role in the machine tool building industry, but now manufacturers are relying on robots for much more than loading and unloading machines.

Companies are beginning to use automated assembly technologies for everything from mass production to made-to-order equipment.

Automated pallet changing systems, tool change systems and bar feeders are helping the production of batches ranging from tens to tens of thousands. Machine tool builders are also including testing, finishing, marking, assembly and other secondary operations within the basic machining unit for a wide range of production volumes.

At the same time, manufacturers are beginning to offer machines that are more versatile, compact, ergonomic and accurate — with better access and a much higher amount of visibility of the work area.

Mikron’s HPM 800U, for example, represents a new concept in 5-axis high performance machining (HPM). The 800U is equipped with rotary direct-drive technology as opposed to standard drives, which is an industry first for HPM machines. This, coupled with the machine’s Steptec direct-drive and in-line spindle technology and rigid polymer concrete construction — which lessens the effects of heat and vibration by a factor of 10 over cast iron — gives users greater flexibility and machining performance.

The machine can be supplied with either a single table, or a twin-pallet (two-station), or seven-position automatic pallet changer (APC) depending on customer requirements.

However, to cope with customers’ changing manufacturing needs the 800U can easily be re-configured from a single table to a twin-pallet or seven-station APC. This additional ‘automation’ has been planned for and designed-in from the outset, and is achieved by fitting and integrating the new APC system to the back of the 800U.

This means customers needing to increase their capability and capacity can do so without lengthy, problematic and costly retrofitting of APC systems that can compromise the machine tools’ performance.

It also means that machines can be integrated and linked together to create flexible manufacturing systems and cells, with robots and/or workpiece load and unload systems for continuous production.

A similar design flexibility exists with the 800U’s automatic tool changer (ATC). Equipped with either a 30, 60, 75, 120, 170 or 220-position ATC, customers can select the most appropriate size/scale to meet their machining requirements. The machine is also equipped with Mikron’s ‘intelligent’ technology software which helps to optimise the 5-axis machining process.

The latest 5-axis control technology is available with DMG’s compact 5-axis universal milling machine, the DMU40 monoBLOCK. This has high-speed motor spindles up to 42,000rpm, a footprint of only 4m2 and height of 2m — yet it still provides a work area of 450mm x 400mm x 480mm in X/Y/Z. The fast, dynamic NC swivel milling head functions as a B-axis (with negative angles to 30º), and has a fast NC rotary table which is 100 per cent visible and accessible with large viewing panel in the wide-opening revolving door.

The machine’s sturdy design makes it possible for longitudinal and lateral motions to be performed by the milling head, while only the vertical motions need to be traversed by the table. This, according to DMG, leads to increased speeds and accuracy, and ensures optimal traction in the Z-axis guideway.

The funnel design of the machine bed also guarantees the best return of chips and coolant. The monoBLOCK has liquid cooled motor spindle, digital drives with direct measuring systems, roller guideways and geometric temperature compensation.

A standard machine setup includes: 5-axis simultaneous milling DMG ERGOline control with 19in screen with choice of 3D control; Heidenhain iTNC530, or Deckel Maho MiIIPlus iT V600, 12,000rpm main drive to spindle options between 12,000 and 42,000rpm and a controlled NC swivel milling head (B-axis). The machine also includes an integrated scraper-belt swarf conveyor and 2501 coolant tank, pick-up tool change system (16 pockets) and collision monitoring on the Heidenhain iTNC530.

Mazak’s Horizontal Centre Nexus 8800-II (HCN 8800-II) features several design innovations. These include a roller gear cam mechanism for the C-axis, a novel design for the slideway covers, a new tool-change mechanism and a greatly increased tool capacity. In developing these features, Mazak has reduced the number of mechanical parts by up to 20 per cent, depending on the options taken.

The move to a roller gear cam mechanism from the traditional worm and wheel gear system for positioning the rotary table is a major step forward in technology — similar to switching from leadscrews to ballscrews. The roller gear cam eliminates backlash from the system, allowing precise, controlled movement in any direction.

Furthermore, the system is more rigid, which allows machining to take place without clamping, making contouring operations quicker, simpler and more productive.

To prevent an age-old problem of the slideway covers sticking, particularly at high traverse rates, Mazak has developed a novel ‘pantograph system’ that supports the covers and ensures that they move in a synchronised fashion. The company has also developed an electronic tool-change system to replace the more traditional hydraulic system. This gives a significant reduction in components and reduces the chip-to-chip tool-change time by a claimed nine per cent.

The maximum length and diameter of individual tools that can be stored in the carousel has also been increased. The standard diameter tool is 125mm assuming all tool pockets are filled. If adjacent pockets are empty this rises to 260mm and, if specific tool pockets are chosen a limited number of tools up to 320mm diameter can be used.

Tools of this size are useful in industries, such as oil, where length is often necessary, and automotive, for machining cylinder heads where multiple passes with a smaller diameter tool are not acceptable due to the witness mark that may be left. The maximum tool length on the HCN 8800-II is 800mm.

An active vibration control function allows profiles and contouring to be carried out quickly by monitoring the vibration frequencies that occur naturally when one axis stops and another starts. The active vibration control uses electronic dampers to compress these vibrations, which in turn allows the machine to change direction quickly, while improving surface finish on the component.

These innovations are leading to a new generation of machine tools that deliver higher performance and productivity at a price comparable to the machines they replace, thus ensuring a competitive edge.