Mill turn centre

Three years of research and development at Mori Seiki  have culminated in the launch of the company's new NT series of integrated mill turn centres, which are a combination of the company’s NH series horizontal machining centres and its NL series of lathes.

The new range incorporates Mori Seiki’s DCG technology, using two in house manufactured ballscrews on both the X and Z axes. The resulting vibration reduction makes 50m/minute rapid feed rates possible combined with accelerations of up to 0.8G and metal removal rates of 550cc/min.

The machine structure draws on the ‘box in box’ construction of the NH series, resulting in a particularly rigid and massive design. The Y axis uses an octagonal cross section, 400mm across flats, fitting into a V shaped slideway.

From dynamic analysis, Mori Seiki engineers found this shape provided the optimum stiffness for supporting the direct drive motors for the B axis and the spindle. This permits heavy cuts to be taken with the milling head.

"Existing mill turn centres use an inclined bed. The resulting forces are not transmitted efficiently through the machine structure. We went through several design iterations before positioning the headstock and lower turret above a flat bed structure and marrying it to the vertical box structure of the NH series," said Mori Seiki’s Akihiro Mochizuki.

In the new machine, "the castings are massive, the machine weighs 18 tonnes, and we have also created a big machining area - 750mm in X, 1120mm in Z and 420mm in Y."

The arrangement has also assisted chip clearance, as the vertical sides ensure they drop cleanly onto the chip conveyor in the base of the machine.

Mori Seiki has a patent pending on its ball screw cooling and its spindle lubrication. Coolant is circulated around the entire ball screw support bearing area and in the motor base, while a spiral oil jacket completely encloses the spindle controlling temperatures, lowering friction and eliminating dust ingress.

The thermal control technology on the NT also includes a cooling jacket around the built in motor on the turret - measures designed to shield the transmission of heat and dissipate it safely to improve the accuracy of the machine.

Automatic tool changing on the NT takes place outside the machining envelope.

"Very small amounts of debris can interfere with tool changing. Keeping the ATC separate from the machining area ensures a clean environment and allows us to achieve a chip to chip time of 3.4 seconds, compared with 14 seconds on the MT," said Mochizuki.

Complex integrated machine tools like the NT can be difficult to programme. Mori Seiki has considered this problem and supplies the machine with its new MAPPS III control system.

The machine tool movements are monitored in real time, automatically carrying out interference detection and preventing axis collisions inside the machine. Additionally, MAPPS III includes a range of high speed and optimised canned cycles to simplify programming. Postprocessors are also offered for some of the most popular CAM systems with the machine tool, so that users can start work immediately.

There are nine models and 66 variations in the NT range including headstock, second spindle and lower turret options.