Factory focus: Manufacturing Technology Centre
Florine Hiersemenzel discusses how the Manufacturing Technology Centre, UK, is furthering the use of focus variation outside of the laboratory.
Using a focus variation (FV) technique, the metrology team at the Manufacturing Technology Centre (MTC), Coventry, part of the High Value Manufacturing Catapult, is advancing the use of optical surface texture measurement technology normally used in research applications. The work represents an important step towards establishing the process as an integral part of the inspection and measurement cycles built into volume manufacture. The FV technique is of particular interest, being robust towards vibrations compared with other optical surface texture measurement techniques, as well as having the capability to measure high aspect ratio (angled) surfaces, lending further potential for use in industry.
The first company to commercialise this technology was Alicona, which is now joined by other entities, including Zeta Instruments and Nikon. FV instruments have been adopted in many institutes and industries around the world and are establishing a presence in volume manufacturing. Applications of FV systems can be found in the medical industry, forensics, microelectronics, aerospace, automotive, materials science and print.
Surface texture measurement is the youngest of the sciences in the metrology toolbox. Material surfaces were assessed by comparison methods and roughness scales up until the mid-20th Century. The comparison scales method relied on subjectivity and experience and, due to the need for higher reliability, the industry turned to electronic surface measuring devices. Computerised profilometers were developed, which remain the most trusted surface measurement instruments.
Between 1960 and 2000, optical techniques for machine vision were developed and later applied to surface texture measurement. The initial need to develop optical techniques was for the development of advanced robotics. The intention was to facilitate manufacturing processes by improving the visual control of a robot.
As a result, a number of techniques arose during this time, such as shape from contour and shading. Shape from focus (SFF) was also among techniques put forward during this time by Professor Shree K Nayar from Carnegie Mellon University, USA. Although not initially designed for surface texture application, SFF formed the basis for the FV technique. The SFF method was based on a standard camera and applied to prismatic objects, and followed processes including depth of focus. Advances in the supporting optics, linear encoders and computational power have resulted in FV becoming a highly accurate surface measurement technique.
MTC metrology engineers use the Infinite Focus G4 machine made by Alicona for several research projects. It is used to assess differently machined surfaces to find the best machining parameters. It is also used in the assessment of rust layers to support a project looking at material degradation after submersion in water. Engineers are also using FV to study materials made with different heat treatment techniques, and to assess the thickness of materials made with different rapid manufacturing methods.
The technique uses a white LED-illuminated optical system, which has a moveable Z-drive. To measure a rough surface, this equipment creates a stack of images at regular intervals. Each image has a small depth of focus, which is only a fraction of the surface height variation. The instrument then uses the contrast information to calculate where in the stack of images the focused areas are. The remaining areas of the images are discarded and a 3D representation of the surface’s topography with its colour information is left over.
Further advances will mean that FV systems can be integrated reliably into high-speed inspection cycles on an industrial scale. If that can be achieved then the advantages will be felt in a wide range of applications, including rapid manufacturing.
Manufacturing Technology Centre
The MTC was established in 2011 to prove innovative manufacturing processes and technologies in an agile environment in partnership with industry, academia and other institutions. The MTC houses some of the most advanced manufacturing equipment in the world, creating an environment for the development and demonstration of new technologies on an industrial scale. This provides an opportunity for manufacturers to develop new and innovative processes and technologies. The MTC is an open access centre, providing a flexible approach to working with companies of all sizes, from SMEs
to large OEMs.
Initial staff of 44, now over 400
16 industrial members initally worked with the Centre including Rolls-Royce and Airbus. There are now over 80
Construction of the 12,000m2 centre took 14 months
£40m was awarded by Advantage West Midlands and the East Midlands Development Agency to fund the centre in 2011