Automated paint experiment pays off for Audi

Gary Mintchell, Senior Editor -- Control Engineering, 9/1/2000

There's nothing like a custom paint job to make a car stand out. With the help of new automation tools, paint technicians at Audi's plant in Neckarsulm, Germany, are trying different ideas to make the company's most head-turning automobile designs really shine. This pilot plant performs special paint effects on prototypes, show cars, and very limited production cars to test various pigment and application combinations. .

Though skilled manual work is indispensable in this field, automation is a critical component as well. This part of the process involves controlling variables in air supply. Variations in air quality and temperature in the paint shop and its baking ovens can affect application results. Temperature curves also differ from paint job to job. Supply and removal of water needed for cleansing and removing paint residue is a third variable.

While planning a new production paint shop for its A6, A8, and future A2 models, Audi and Dürr, an automotive paint system OEM, evaluated the latest automation technology on a small scale at the pilot plant. Audi subsequently deployed industrial PCs from Siemens Energy & Automation (Alpharetta, Ga.; Erlangen, Germany) on its assembly line for parameter input and fault analysis. With PC-based control software becoming more powerful, Dürr designed a PC-based system using Siemens' Simatic WinAC.

WinAC allows Audi's technicians to control their process using standard PC applications, and perform process visualization on one, open hardware platform. This soft logic is programmed with Step 7, the universal development environment.

The plant's new system controls conveyors bringing car bodies through the paint shop, and integrates variable frequency drives directly as distributed intelligent I/O points. Intelligent modules communicate via Profibus to coordinate motion sequences. The PC running WinAC monitors signals, such as manual/automatic functions, from an IP65-rated Simatic ET 200X distributed I/O station that incorporates motor starter protection and intelligence.

Distributed PC-based control enhances users' ability to configure, test, and commission individual components independently of each another, which saves valuable system commissioning time. Modular, open hardware and software adds flexibility to Dürr's systems, which reduces overhead costs in subsequent projects.

Audi's Eberhard Vogler, who is responsible for planning and execution of control technology in the new paint shop, says this added flexibility increases benefits to users. "We undergo constant change in the paint shop, whether it's new paint or car models," he adds. "This means we have to constantly modify the line without interrupting production. This automation solution offered by Dürr, with distributed intelligence and higher-level PC-based control, allows us to test and evaluate a change to the system off-line."

However, before Audi integrates a system in one of its production facilities, it must undergo reliability testing over 24 successive shifts. Availability of 99% must be attained during this test phase. Dürr and Siemens' PC-based control system proved to be just as reliable as a PLC in the pilot plant. Mr. Vogler adds that Audi's operating and maintenance personnel readily accepted the system.

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