Part tracking and traceability hits the mark

Traceability is a key requirement for automotive manufacturers and suppliers these days. The most effective method of ensuring this is to use some sort of component identification and a database that keeps track of which parts have been fitted to which vehicle, which supplier supplied them and which batch they came from. Direct part marking is one method of doing this. Although the responsibility for ensuring traceability often rests with quality assurance, design engineers can help by working on ways of fool-proofing the system . This means controlling and managing the identification and classification of parts and assemblies, from the initial drawing stage to design sign-off. The problem is one of awareness. Many design engineers are simply not aware of the need for traceability or are content to carry on using traditional forms of marking such as stamping. Stamped numbers can get misaligned, shattered or damaged and are often reliant on the machine operator to change the code. TRW Automotive has recently designed and manufactured electrically-assisted power-steering (EPAS) for Fiat’s new Stilo car. Traditionally, power-assisted steering is achieved by using a continuously-operating hydraulic pump, but the electrical version is more energy-efficient, only drawing power when it’s needed. At the heart of the EPAS system is a gearbox made from an aluminium alloy pressure die-casting. TRW receives the fully-machined and inspected casting from JR French’s factory in Wales, which has dedicated production cells that cast, clip (to remove the runner and feeder), shot blast, machine and wash the parts. Each die casting is then placed in an automated verification machine. This machine uses snug-fitting gauges to check that all of the features have been machined correctly and special sensors inspect the tapped holes. If everything is as it should be, a 2D Data Matrix machine-readable code is applied using a rapid indent laser marking machine, supplied by Worcestershire????-based firm Technifor. The code is generated automatically using a Technifor universal controller. Finally, the part is released from the verification machine so that the operator can pack it ready for despatch to TRW. When the parts are received at TRW, the first operation is to read the Data Matrix code using an MXi handheld reader from Robotic Vision Systems (RSVI), linked to a PC with RSVI’s verification software to interpret the code. This assures TRW that the part has been passed by JL French’s verification machine and the part, which has a unique code, can then be tracked through the entire assembly line using strategically-placed cameras. JL French has an identical handheld reader to monitor the quality of the codes. Because the marking is so consistent it is only necessary to check the codes once per shift on the same components that are removed for dimensional inspection on the co-ordinate measuring machine. No adjustment of the process has yet been required and, so far, 150,000 castings have been produced and marked in this way. “It is phenomenal how much information can be stored in such a small code, though it is essential to have a reader available to check what’s being generated – the codes are not human-readable,” explains JL French’s project manager Chris Niblock. “Using rapid indent marking has been a true ‘fit and forget’ system. Once everything was working we’ve not had to touch it since.” Technifor’s complete system costs around £25k, £7k to £8k of this is for the laser marking machine and around £3k for the reader. Although the idea of marking a 2D machine-readable code and capturing this with a vision camera may seem light years away for most manufacturing companies, many industries including automotive, aerospace, high-tech electronics, medical and pharmaceutical, are beginning to demand such levels of traceability. And for many manufacturers, the responsibility for ensuring this starts at the design stage. How does Data Matrix coding work? TRW engineers specified that a 2D code conforming to RVSI’s Data Matrix symbology should be used because of the Reed-Solomon error correction and data redundancy that ensures fast and accurate code reading, even if part (up to 30%) of the code is obscured or damaged. It was decided to use rapid indent marking because of the permanence, consistency and quality of the mark, and the code readability is even good on bright aluminium castings. A 16x16 dot code is used, which is theoretically capable of carrying 24 numeric digits or 16 alpha-numeric characters. In this particular application, the code measures 9.4mm by 9.4mm. The contents of the code are a part number (eight digits and a letter), a unique part identifier (up to six digits), a supplier reference number, a shift code and a date code. All of this is generated automatically by the Technifor UC 200 controller.