Truck Painting Using Robotics

Reprogramming a complex robotic paint process results in a faster and less expensive operation.

A major truck manufacturing company wanted a faster and less expensive paint process to accompany its new, more viscous clear coats. The robots on line performed a complex painting process. Adding commands would make the process even more complex. In order to simplify and accelerate the process, the manufacturer chose to reprogram its robots.

Changing only one component in a robotic production process can be a costly endeavor. However, changes such as these are not uncommon. New paints and materials are developed continuously, necessitating process adjustments. Still, changeover is rarely quick and inexpensive, and the expense grows with the size and number of robots.

The paint line at the truck manufacturing facility consisted of 30 Fanuc P155e Robots with controllers and Sames 60 degree bell applicators for the end-of-arm tooling. Sixteen truck body styles (eight bodies with two-tone options for each) are sprayed on the line.

To accommodate the heavier clear coat, the process required recalibration of approximately 200 paths per robot, each with up to 60 robot locations. In total, more than 12,000 target locations were reprogrammed.

For paint dispensing applications, reprogrammers had to consider fluid flow, the bells' turbine speed and shaping air, which controls the pattern of the paint when applied. Clogging was not an issue because it was a closed loop system in which the clear coat was in continuous motion. Mixing was not an issue either.

Reprogrammers estimated that the standard manual reprogramming process, which uses teach pendants, would require up to four months of reprogramming. This included four weeks of production downtime, an average of 20 scrap trucks, as well as thousands of gallons of paint. The challenge was to reprogram this manual process efficiently and inexpensively. Repro-grammers used Tecnomatix's ROBCAD Computer Aided Production Engineering (CAPE) software tools to create the painting program.

Reprogrammers uploaded an existing path program from one of the robot controllers, then calibrated the clear module and cell to work with it. After incorporating the specific truck CAD data supplied by the manufacturer, reprogrammers created and ran a program using ROBCAD/Paint and TDL Controller, a ROBCAD programming language. Variables were tweaked until ROBCAD simulated the identical film the truck maker wanted to achieve on the plant floor. These variables included fluid flow, fan pattern, target distance, robot speed, fluid viscosity, and the densities in wet and dry percentages. Once this process cell was calibrated, the path program was modified with new clear coat parameters. Following testing on the plant floor, reprogrammers uploaded the remaining paint programs from the robot and repeated the process. After the entire process was simulated and tested off-line, the new paint programs were downloaded to the 30 robots with only two weeks of production line downtime and minor manual tweaking.

In just six weeks the line was operational, with a 95 pct accuracy. Using ROBCAD/Paint, A.M.T. saved nearly $1 million, including 1,000 man-hours, 20 scrap trucks and thousands of gallons of clear.

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