Loxham Precision’s µ6 machine product is a departure from incremental developments of the traditionally conservative machine tool sector. It is a 6 axes nanometre resolution ultra-precision machine offering diamond turning and micro-milling processes at leading accuracy levels. The µ6 machine is of low mass with super low energy consumption design that provides an unprecedented automated ultra-precision machining capability. Perhaps most striking of all is its overall size: that of a domestic white goods product. As Loxham’s Director Paul Shore says “it is a new era machine tool".
Research pedigree and thinking
The µ6 machine design emerged from the UK’s Engineering and Physical Sciences Research Council (EPSRC) funded Centre for Innovative Manufacturing in Ultra Precision which was operated by Cranfield University Precision Engineering Institute and the University Of Cambridge Institute Of Manufacturing from 2011-2016. Though the research questions that led to the µ6 were very simple: Why do machine tools that make small scale parts need to be so large and energy consuming? And how could ultra-precision and micromachining systems be designed to be more easily automated? From these simple research questions the new era µ6 machine was conceived. The µ6 design concept has now been taken to the market by Cranfield spin out: Loxham Precision Limited.
µ6 design
When compared to a standard turning and milling machine tools the Loxham µ6 product looks as if it must have been conceived from a different set of precision machine design principles, and yet nothing could be further from the truth. The µ6 machine is very much based around the precision machine design principles advocated by leading machine tool design experts such as Pat McKeown, OBE, Jim Bryan and Manfred Weck.
The key difference is that during the µ6 machine concept design optimisation higher rankings were placed on reduced moving masses and energy consumption. These prioritised design rankings together with desire for higher sub-system integration and eased automation yielded the small µ6 design.
The compact design of µ6 means that its heat generating sub-systems are fully integrated within the machine itself. For example the mounting frame of the machine structure houses all the electronics, drives and controls. These items by necessity are directly temperature cooled as is the aluminium structure of the machine.
The small dimensions of the main linear motions are achieved by integrating the water cooled rotary axes within the linear motion carriages. This integration results in small Abbe offsets of encoders and very low moving masses which requires limited power from the linear axes motors.
High stiffness of all the motions is achieved by employing specially devised air bearings throughout. The load capacity of employing air bearings is not a limitation as the scale of material removal in precision machining is limited as is the load from the moving masses.
To ease automation the µ6 design has a vertical arrangement that sees components loaded from the top. Specially devised robot handling systems have been created to enable workpieces to be loaded, cleaned, centred and measured prior to machining starting. Rotation of machines A axis by 180 degrees brings the precision positioned component into the enclosed machining zone. An optical tool setting system is also mounted on the A axis. This optical tool set station automatically measures the shape and position of both turning and milling cutters.
Below the upper three (X, A and C) axes which handle the workpiece are three additional axes, two linear and one rotary (Y, Z and B). The B axis carries both turning tool holders and a high speed milling / drilling spindle. A range of tools can be loaded automatically into the milling / drilling spindle. Tools are held within a small 20 position rotary tool carousel. Tool loading is performed by an air actuated micro-robot such that tools can be exchanged rapidly.
The resulting µ6 machine tool has the scale of a domestic white goods product, its low weight of 500kg makes it easy to move. Its low mass, low friction design yields a super low electrical power rating. The machine is rated and fused at 6 Amps on single phase electrical supply with typical operating power consumption in the 600W region.
To ensure heat loss from the integrated electrical systems that are located within the machine base do not degrade the high precision motions, and to avoid thermal distortion of the machine structure, intelligent water cooling is applied. Key advancement in this area is the direct water cooling to the motion amplifiers and the symmetric closed BOX shape machine structure.
µ6 is a fully safety inter-locked machine complying with all Machinery Directives and made available with automation from robot load/unload systems. A post process metrology option is also offered that ensures 100% automatic inspection can be achieved. The machine CNC can be safely operated via a tablet. Performance and machine condition monitoring is available via Wi-Fi link up to Loxham’s own local area network.
µ6 machining accuracy capability and capacity
µ6 is small, highly economical to run, easy to house and transport, it is nonetheless a fully capable micro-milling and diamond turning production system. µ6 offers true ultra-precision machining qualities.
Typically, conventional diamond turning machines accuracy performance is proven by cutting spherical surfaces to high accuracy levels in terms of their surface roughness and form accuracy. The µ6 machine is capable of producing roughness levels below 5 nm Ra and on high quality materials a good deal better than that. Form accuracy achievement from the µ6 is equally impressive at 25 – 30 nm RMS (~1 µinch).
µ6 is a fully functional 6 axes CNC machine tool capable of turn – mill processes combining turning milling and drilling. By using its novel multi axes machining modes with automated tool changing, optical tool setting and post process metrology high complexity geometric components can be produced at unprecedented levels of accuracy.
Although µ6 is small its volumetric workpiece capacity is an impressive 125 mm diameter by 100mm, considered not too bad for a machine of 600mm by 600mm by 1200mm.
µ6 automation and built-in intelligence
Automated the µ6 machine has been achieved using a gantry load/unload machine that employ linear motors and force feedback. This robotic loading system, is complemented by some built-in intelligence into the µ6 control system. This built in intelligence enables the machine to identify the exact position the component has been placed on the workpiece holding fixture, and if necessary it is able to gently reposition the component to a location accuracy of 0.001mm.
µ6 applications and outlook
µ6 offers manufacturers of optics, sensors, integrated devices, print heads, medical devices, etc. a comprehensive precision fabrication capability within a single small scale machine tool. The cost of ownership is significantly lower than conventional machines and Loxham Precision believes its eased automation will in the future bring about new application areas including those of finishing additively fabrication components of complex shape requiring limited material removal levels.
Just now the µ6 machine has been sold into some UK research centres. The Optoelectronics Research Centre at the University of Southampton has recently invested in a µ6 machine tool as part of their work within the UK’s Quantum Technology and Sensors programme.
For further details please contact Loxham Precision via: info@loxhamprecision.com