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Quality Monitoring in Laser Welding Gains Importance

Source: Industrial Laser Solution

Increased output from laser welding systems drives this need

Laser welding has become more popular in automotive body-in-white and component production because it is highly productive—a single laser welding robot can replace up to five conventional spot welding robots. High-power disk or fiber lasers, combined with a scanner welding head and an industrial robot for on-the-fly laser welding, can produce more than one hundred welds per minute.

This causes a challenge: if the production is so high, how can one ensure that stable, good-quality welds are produced? Often, crash safety-relevant parts are produced in the automotive industry, making weld quality even more important. AWL-Techniek, as a specialized machine builder, supports its customers in tackling this challenge(FIGURE 1).

This article will discuss the three aspects of a stable production machine: the machine itself, the limits of quality control by a human inspector, and automatic quality inspection.

THE LASER WELDING MACHINE

Quality starts in the welding machine. The laser welding fixture must be able to clamp the parts in a stable manner even if the tolerances are rough, as is often the case in stamped metal parts.

The fixture must also be able to prevent errors by the operator. A good laser welding fixture detects if all single parts are loaded correctly before the laser welding process can be started. Poka yoke systems (a Japanese development of any mechanism in a lean manufacturing process that helps an equipment operator avoid [yokeru] mistakes [poka]), product detection sensors, and a well-designed tolerance chain are needed. Attention must be paid to clean air supply and fume exhaust, and the fixture must be easy to clean and to service (FIGURE 2).

FIGURE 2. Fixtures for car seats optimized for high-quality laser welding are shown. (Courtesy: AWL-Techniek)

FIGURE 2. Fixtures for car seats optimized for high-quality laser welding are shown. (Courtesy: AWL-Techniek)

AWL-Techniek has developed specific robot software to make industrial robots more accurate. Using this software enables production of edge welds without a seam tracking system. This software is an essential tool for curved welds where high accuracy is needed—for example, in circular edge welds. These examples show that designing and building laser welding fixtures and laser welding machines is a complicated task that requires great skills and experience.

HUMAN VISUAL VS. AUTOMATIC INSPECTION

For the weld quality control system, some people argue that an operator can easily do a visual quality check while he or she is handling the parts. That’s not necessarily true—research from the aviation industry shows that for a quality control task, inspectors miss small defects easily and after only one hour on the job, they miss almost 70% of defects (FIGURES 3 and 4).

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