A £1.8 million DMU 340 G linear machine tool is coming to the University of Sheffield’s Advanced Manufacturing Research Centre (AMRC), UK, at the end of the year. It is said to be the first of its size to be fitted with an ultrasonic-capable spindle for use in five-axis machining applications.
The specification for the machine – which has a 59 m2 footprint – has been developed with the input of Dr Kevin Kerrigan, the lead for the Composites Machining Group at the AMRC Composites Centre, helping manufacturer DMG Mori create a product it is able to market to the world.
The DMU 340 G is capable of providing significant improvements in composite machining, ranging from high-end luxury vehicle monocells to next-generation lightweight aeroengine fan blades. It is also capable of titanium drilling and finishing operations and working with materials such as glass fibre reinforced aluminium (a glass fibre in a resin laminate interspersed with sheets of aluminium), and an array of high-temperature composite materials.
The machine’s features include linear motors for high accuracy and rapid motion, novel dust extraction technology, high pressure cutting fluid delivery systems, on machine inspection technology, and Industry 4.0 capabilities such as wireless in-process monitoring and control technologies, enhanced connectivity and plug-in technologies to interface with the AMRC’s data analytics suite.
Project proposals are already in the pipeline and the machine will have applications for companies like McLaren, Roll-Royce, Boeing, BAE Systems and Airbus. It also opens up opportunities in the renewables, medical and construction sectors.
“This machine is the first of the DMU 340 G product range to have the ultrasonic assisted machining kit,” says Kerrigan. “It cements the AMRC’s reputation for world-leading research for capabilities in composite machining.”
The advantage of the machine’s ultrasonic capabilities is that the high frequency movements – 40,000 micro-movements per second – bring a higher degree of control of chip formation and heat within the system. The result is less damage, less waste and a better finish, which is why the technology is suited to machining hard, abrasive, brittle materials like carbon fibre composites, alloys and CMCs.
“The ultrasonic-assisted machining process is basically the same as a standard rotatory cutting tool operation, but with an added highly tuneable, micro-scale, axial motion of the cutting tool providing a secondary motion during cutting,” Kerrigan explains. “It is the additional movement that has the ability to control the amount of energy supplied into the cutting interface, affecting the amount of thermal energy and fracture energy associated with the process. The incoming machine also has linear drives which create better acceleration and change of acceleration, i.e. jerk, to push the machine really fast during five-axis tool paths, which helps when producing complex shapes at high rate whilst retaining part geometric accuracy. With this linear drive system the machine can get up to feed rates of 90 m/min. Current feed rates, between 1 and 4 m/min, are mostly driven by the fact that the forces generated during cutting, even with rpms of over 20,000 rpm, would snap the tools if feed rates got any faster. That is a massive difference and a huge benefit to productivity.”
A customisable controller allows the machine to integrate process-monitoring techniques, providing data that can measure performance but also help to improve tool life.
“The usefulness of this is really on the process monitoring side of things,” states Kerrigan. “The 840D controller is considered state-of-the-art for enabling the extraction of process information, enabling machine health monitoring, shop floor connectivity and closed-loop adaptive control. It can also link to additional live retrofit process measurements that are linked to things like tool wear, damage defects on a part. That’s useful information that gives us greater insight into the machining operations being undertaken on complex materials.”
A fundamental part of the Composites Centre’s work into machining research is measuring cutting forces and temperature as these provide a wealth of information about the health of the process, such as whether a process is dynamically stable, if there is any chatter or forced vibration, the rate of tool wear and whether a machine is being driven beyond its capabilities or experiencing mechanical/bearing wear.
“For carbon fibre-based composite materials, because it’s a highly abrasive process – even with diamond as the cutting tool which is commonplace in industry – you have to replace your tool very regularly to the point where 50-60% of the whole process cost comes from cutting tools,” Kerrigan notes. “The proposed data that will be extracted from this machine can be used by artificial intelligence platforms, such as IBM Watson, to learn how to stretch the life of a tool without interrupting the process.”
The ‘composite capable’ machine is able to operate in both dry and wet machining configurations without harm to machine moving parts, electronics or operator, and has high productivity through rapid traverse rates. It also has particle controlled door opening, an infrared measuring probe and the tool changer introduces DMG’s novel modular carousel design.
The DMU 340 G linear is due to arrive at the AMRC in late December and is likely going to be sited in the original AMRC 1 building.
Image provided by DMG Mori
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