Vision Systems Accelerate Ford Wheel Production

Welds checked, valve hole positions located in automotive line upgrade

 

Two vision systems made by Cognex have solved major quality assurance 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 meet Ford's stringent QA levels for automatic wheel inspection, and have simultaneously accelerated production by 20%, eliminating 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 then undergo a forming process to create the right profile, and proceed down to a stamping station where valve holes are punched in a specific position relative to the weld. This positional relationship is important for the central disks (spiders) that are later welded to complete the wheel assembly.

 

The line has a production target of 10,000 wheels per day.   However, two factors were preventing this goal from being met – 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, valve hole position was determined by spinning the rim under a camera, looking for the weld using an optical system, and then spinning the rim another 30 percent.  This meant that the wheel had to spin for up to one complete revolution just to find the weld. 

 

Weld inspections are done immediately after the hole position is located, as the weld position is fixed at that point. Previously, weld tests were performed electro-magnetically by searching for the eddy current variations caused by a bad weld. However, setting-up this equipment was difficult and its positional accuracy needed to be very precise, leading to missed faults and an additional inspection process.  An objective of the upgrade was to eliminate this factor, and to speed up the line and synchronize the valve hole punch machine with the plant's 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.  Hay contacted Cimac, Ford's on-site integrator at Dagenham, for help with selecting and implementing two new vision systems. 

 

Cimac chose to implement an In-Sight™ vision sensor from Cognex for the weld location system.  In-Sight is a compact, general-purpose vision sensor featuring a full library of vision software tools, a vision spreadsheet interface for application set up, and built-in network communications.   

 

The sensor is mounted above the line, looking down onto each wheel, with lighting arranged to illuminate the inside of the rim.  The In-Sight sensor uses the PatFind® part location tool to locate the rim, and then uses its FindCurve tool to locate the center of the wheel. The vision sensor then locates the weld, determines its angle, and transfers the positional data to the PLC, which rotates the wheel to the correct alignment.

 

Once the weld position is fixed, the wheel moves to a second inspection point.  There, a Cognex MVS-8000™ PC-based vision system inspects the weld by looking for light, which may come 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.  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 a 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 vision system and we have been able to greatly improve the rigidity of the mechanics, thus increasing lifetimes and decreasing life cycle costs."

 

This article is provided by Cognex Corporation, www.cognex.com.