Vision systems accelerate Ford's wheels
Vision systems accelerate Ford's wheelsKeywords: Machine vision, Automotive
Two vision systems made by Cognex have solved major QA and production challenges at Ford's Dagenham, UK plant, where wheels for the Ford Focus and Ford Fiesta cars are made. The vision systems are helping wheel inspections meet Ford's stringent QA levels automatically and have simultaneously speeded up production by 20 per cent, unblocking a bottleneck at the plant.
Wheel rims are made from continuous steel strip which, after pre-stressing and flattening, is cut to length, formed into a circle and then joined by flash welding. Rims next undergo "fairly dramatic forming processes" to create the right profile and are then passed on to have their valve holes punched in a particular position relative to the weld. This positional relationship is also important for the central disks (spiders) that are welded in later to complete the wheel assembly. The line has a production target of 10,000 wheels a day but two factors were preventing this being reached – the time taken to locate the valve hole position for punching and the need to prove the integrity of the flash weld.
Wheels are conveyed horizontally through the valve hole punch machine. Previously, the position for the valve hole was determined by spinning the rim under a camera, looking for the weld using an optical system and then spinning the rim another 30 per cent. In theory this meant that the wheel had to be spun for up to one complete revolution just to find the weld, though in practice the average figure was 210 degrees.
Weld inspections are done immediately after the hole position is located because by then the weld position is fixed. Previously, weld tests were performed electromagnetically by searching for the eddy current variations caused by a bad weld. But setting up this equipment was difficult and its positional accuracy needed to be very precise, which meant some faults were being missed and an additional inspection process was necessary. An objective of the upgrade was to eliminate this factor. Another was to speed up the line and synchronise the valve hole punch machine with the Kieserling rim machine.
Ford Motor Company Engineer, Robin Hay joined the Ford Wheel Plant at Dagenham in August 2000 and one of his first tasks was to find new solutions to these challenges. Ford at Genk had already used vision systems for checking welds, so one of the first things Robin Hay did was to phone Cognex who agreed that both requirements were possible using latest vision technology. He then placed the responsibility for purchase with Cimac, Ford's on-site integrator,which has engineers permanently working at Dagenham. Development work on the systems by Cimac and Cognex together confirmed that the requirements could be met, so orders were placed. The systems were built off-site and commissioned by Cimac during the next shutdown. A Cimac programmer attended a Cognex training course and all the programming and commissioning was undertaken by Cimac themselves, with good off-line support from Cognex when needed.
The weld location system uses an In-Sight vision system. A camera is located above the line, looking down onto each wheel, with lighting arranged to illuminate the inside of the rim which is less likely to be marked by the forming machine. The In-Sight software uses the PatFind tool to locate the rim,then FindCurve to locate the centre of the wheel. FindMultiLine then locates the weld and GetAngle pinpoints its angle. After determining if this is a positive or negative angle the data is sent to the PLC, which rotates the wheel to the correct alignment.
The method allows accurate positioning within an average 90 degrees rotation. Even using the same motor as before and allowing for ramp-up and ramp-down times, this has had a major impact on production rates, reducing the time taken by 20 per cent and enabling the line to reach its targets. "It even gives us time for playing now," says Robin Hay.
Once the weld position is fixed, the wheel moves to a second inspection point, where the weld is checked by inspecting for light escaping through any faults in the weld. "With the weld lined up accurately, it's easy to do,"says Chris Greenleaf, Cimac Project Engineer. "We use two cameras outside the rim to give us full coverage of the weld and we shine a powerful light through from the inside. The PC-based vision system uses the Cognex 8000 PC Frame Grabber card to capture an image and the PC software checks for pixels of light. This process is superior to the previous method and, even though we lift the wheel into the test position, the process still takes place inside the hole alignment time and does not add to production times."
"Both inspection systems work fully automatically," says Chris Greenleaf. "Ford set us the target of five seconds overall process time to ensure that the line can be kept in step with the Kieserling. This indirectly creates manpower savings because there is no need for a buffer line now. Reliability has far exceeded the older system and we have been able to greatly improve the rigidity of the mechanics, thus increasing lifetimes and decreasing life cycle costs."
More information is available from the Cognex online Web site at: http://www.cognex.com
Technical contact: Katrina Dixon, Cognex UK, Units 7-9, First Quarter,Blenheim Road, Epsom KT19 9QN, UK. Tel: 0800 0180018, Fax: +44 (0)1372 726276;E-mail: kdixon@cognex.com
