Reliable identification in engine block manufacturing

At the Chemnitz, Germany, engine plant of Volkswagen Sachsen, two production lines have been equipped with Balluff RFID identification systems (BIS C) to provide reliable, automated identification and a convenient solution to ongoing process data updating for the production part.

There are many reasons for part identification. Beyond simple verification of origin, in connection with documented production and quality parameters, identification of parts has long been a component of any logistics or automation solution in manufacturing and assembly. In the area of automation, parts identification is no longer used simply for purposes of traceability — it has become the basic element in process control or product assurance by enabling continuous process data correlation and production status transparency.

Both elements, namely process-secure readability and ongoing writeability, were the deciding criteria at the Chemnitz engine plant for changing from data matrix coding to RFID technology in the production lines for cylinder heads and engine blocks.

The Balluff identification systems in use at Volkswagen are ‘industrial strength’ RFID solutions. They were developed for use in production and assembly lines with adverse conditions such as heat, lubricants, contamination or eddy currents and frequency disturbances caused by metallic materials. Key components in the Balluff BIS identification systems are the rugged, miniaturised data carriers. The circuitry, consisting essentially of a coil, control logic and an EEPROM or FRAM memory device, is fully housed to protect against the harsh ambient conditions. With EEPROM memories as used here, the number of write cycles is limited, but the number of read cycles is unlimited. A Balluff identification system includes one or more read/write heads with a corresponding number of processors. To exchange data, the inductive data carrier receives an energy signal from a read/write head and uses this to create its supply voltage. It can then send its data as a pulse width modulated signal to the read/write head. Pulse width modulation is extremely insensitive to external noise and ensures repeatable, error-free communication. The processors serve as buffer memories to manage the data transfer between data carrier and host systems.

For engine block production, the data carriers (RFID tags) are placed in plastic sleeves that serve as extensions and then attached to the parts using special M8 screws. The production line for cylinder heads is equipped with two data carrier loops. In the first area for mechanical machining, the work piece carriers are first fitted with RFID tags. Here the data carriers are inserted into special screws without the plastic extension, remaining firmly attached to the work piece carriers. The latter are used in the production loop, and with each new unmachined part, data recording begins over again onto rewritable data carriers. In the last production section the cylinder heads are passed from process to process without work piece holders. Here, appropriate mounting surfaces are available, so that the screws holding the data carriers can be attached directly to the cylinder heads — which is also a fully automated process, as is removal at the end of the line. In both lines the respective read/write heads are mostly located at the process stations — at the linked machining centres as well as on the testing fixtures and the incoming and discharge stations. One exception is a measuring machine which is manually operated and therefore equipped with Balluff portable scanners. These are like the fixed read/write heads, but housed in a hand grip. They are connected to the respective processor using spiral cable. The lines are also equipped with additional portable read/write devices. These units, developed by BHS-TEC, contain a read/write head, an integrated processor, a display and a keypad. They are used for checking purposes on the lines and make it possible for workers to read data from work pieces in situ. Each line also includes a Balluff Handy Programmer that is used to manually write data for service purposes.

The information stored on data carriers generally includes a sequential number assigned by the Balluff system and a unique identifier for each part in YYMMDHHMMSS format, as well as an additional ID number which represents a Volkswagen number. For cylinder head machining, an adapter plate number is added for the work piece carrier used. As the process continues, work piece status (OK/NOK) as well as information for the work sequence associated with the respective machines is assigned. Each individual process step is supplemented with the time of machining and, if appropriate, the associated spindle on the respective machining centre for purposes of traceability. The result is a total of 500 bytes of data, which are read out at the end of the line and sent to an archiving computer. There they can be recalled at any time and uniquely associated with the part.

Both lines together include over 90 read/write heads with 60 processors incorporated into Profibus networks. Over 2000 data carriers circulate in the plant, and are continually being updated on the work piece carriers of the cylinder head line and on the work pieces themselves. Inductive data communication results in reliable identification in a fully automated process, while transport of the process data throughout the lines makes data handling significantly easier.

Balluff-Leuze Pty Ltd
www.balluff.com.au