Seeing the bigger picture

Advances in portable optical dimensional measurement technology are opening up new opportunities in freeform measurement. Jaguar Land Rover (JLR), with help from the National Physical Laboratory's FreeForm Centre (www.npl.co.uk/ freeform), is looking at how new freeform measurement technologies and standards can help streamline its processes. Items that are freeform are unconventional in shape or design, usually being asymmetrical and irregular, but with a flowing outline. Freeform objects depart from standard geometrics or cannot be described by a simple mathematical model. Examples include car door panels, bonnets, windscreens and manifolds that feed gas and air into the engines. Traditionally, such forms have proved difficult to measure, often requiring inspection with tactile coordinate measurement machines (CMMs) away from the production line, which can take hours. Inspecting every part at each stage of the production is, therefore, impractical. Image: gathering loads of data, but what to do with it JLR is finding that point measurement is not a practical way to fully understand the complex interfaces between panels within car bodyshells, which are critical to its build. They are increasingly using laser scanners during the product development process to gain insight into the root cause of issues before vehicles go in to production. While its rigorous final inspection process guarantees the quality of any product which leaves the factory, like all manufacturers JLR stands to save time and money by identifying errors as early as possible. In order to do this, it is increasingly moving to scanning and freeform measurement techniques. Such technologies are quicker and provide more data, meaning that, potentially, every item can be checked. This type of analysis also provides a colour contour map, detailing the complete topography of the part, which is far more meaningful to non-metrologists than the lists of figures associated with tactile systems. This makes it much easier to understand and identify the route cause of an error and rectify it much earlier in the production process. JLR is now working with NPL to exploit recent advances in freeform measurement. It has taken advantage of the equipment and advice available at the FreeForm Measurement Centre to select the most appropriate technologies for the job, while a scientist from NPL's National FreeForm Centre has been seconded to JLR to help with this project. This has allowed the company to make more effective use of its existing laser scanners, and it is now looking to implement additional equipment to provide freeform measurement around the factory, as well as to invest in equipment that will provide new capabilities, such as measuring on a much larger scale. PRACTICAL APPLICATION ARRIVES While the optical equipment that JLR is using has been around for a while, its practical applications in this field are only now becoming possible, thanks to reductions in the size of equipment and increased resolution of the cameras. However, such advantages are partly limited by poor metrology infrastructure, lack of measurement traceability, absence of specialised test facilities and a limited knowledge base. This is why Dr Michael McCarthy at NPL established the FreeForm Centre, which is working with industry to help overcome such problems. Image: White light scanning is a method of capturing surface data NPL's FreeForm Centre has over £1 million of new state of the art freeform kit housed in the centre, including a high specification Mitutoyo CMM (01264 353123) with revolutionary laser scanning probe, fixed laser scanners, several white light fringe projectors, portable articulated arms with laser scanners and tactile probes. The centre is actively involved in helping UK manufacturers establish an adequate infrastructure by using this equipment to provide facilities, testing, consultancy and traceability routes. For companies like JLR, such infrastructure is critical for it to fully benefit from the advantages that the new equipment promises to deliver. One of the key issues that the company needs to overcome relates to the capabilities of the equipment in different circumstances. A laser system that performs well on a grey primer can be reflected far less favourably on a shiny surface, such as the lightweight aluminium used in many car body panels. NPL is working with Jaguar Land Rover to better understand how such surfaces reflect the lasers in optical measurement machines and develop programmes to compensate for this to allow for the useful collection and processing of data. Other problems arise from the data itself. New systems may capture useful data, but software needs to be developed by measurement experts to ensure it is interpreted correctly. Perhaps most important is the need for freeform verification standards for this equipment. NPL is working with industry, academics, and other measurement institutes and ISO-standards to produce verification artefacts for freeform measurement for use by industry. They are developing such artefacts for a wide range of systems, including CMMs with tactile and non-contact probes, laser scanners, articulated arms and fringe projection systems. RAPIDLY GROWING KNOWLEDGE NPL's work in this area is also allowing it to establish a rapidly growing knowledge base on freeform measurement, and helping to develop further standards and software, as well as best practice. This is allowing accurate verification of freeform measurement technology, and supporting the development of new systems and software to ensure meaningful results are obtained from inspection. While JLR has been using scanning systems for some time, NPL's growing expertise is allowing the company to deepen its understanding of freeform measurement, introduce new equipment, reduce measurement uncertainties and implement more efficient processes. This, it hopes, will allow quicker root cause analysis and corrections to be put in place, with the ultimate aim of bringing higher quality vehicles to the market quicker and more cost effectively. Box item NPL and the National FreeForm Centre The National FreeForm Centre at NPL (www.npl.co.uk/freeform) supports UK end users, manufacturers and academics in freeform measurement by providing evaluation and verification processes for 3D coordinate measuring with tactile and non-contact probes, laser scanners, articulated arms, fringe projection systems and point cloud processing software. Examples of the gains potentially achievable with suitable advances in freeform manufacture include higher efficiency aero engines, drag reduction for automotive bodies and increased life span for prosthetics. The National Physical Laboratory (NPL) in Teddington, Middlesex, is one of the UK's leading science facilities and research centres. It is a world-leading centre of excellence in developing and applying the most accurate standards, science and technology available. NPL occupies a unique position as the UK's National Measurement Institute, and sits at the intersection between scientific discovery and real world application. Its expertise and original research have underpinned quality of life, innovation and competitiveness for UK citizens and business for more than a century. First published in Machinery, January 2011