TransForum Vol. 4, No. 3

ARGONNE'S WELD MONITORING TECHNOLOGY FINDING NEW ROLES

Heat treating: the latest automotive application for versatile sensing system

The infrared (IR) sensing system developed by Argonne and industrial partners for real-time quality monitoring of laser welding processes may be adapted for similar use in heat- treating applications. A leading U.S. automotive manufacturer is evaluating the technology for its ability to monitor a heat-treating process for automotive parts.

Argonne's IR sensing technology was originally commercialized by Spawr Industries (Lake Havasu City, Arizona). A Spawr customer, DaimlerChrysler, was the first to extensively implement the Argonne technology, employing more than two dozen of the units to monitor laser welding operations in its transmission plant in Kokomo, Indiana. Argonne's system replaced the plant's ultrasonic immersion tank weld-testing equipment and reduced scrap from bad welds by more than 10%.

The same technology is also being used by Spawr customers in laser welding applications for airbag production and for assembling tailored blanks, which are used to produce automotive body panels. The economical, easy-to-operate system uses a passive sensor with integrated optics to measure IR emissions from the molten metal of a weld as it forms. The sensor detects the weld's infrared signature and instantly compares it to the expected profile. The system can automatically signal the welding unit to correct its operation if a weld signature does not fall within user-defined parameters.

In the new application that is currently being tested, the sensor monitors the quality of laser transformation surface hardening (LTSH) — a heat-treating method that is growing in popularity. Laser heat treating alters the microstructure of metals through controlled surface heating and cooling. The process offers the advantage of being able to treat precise areas of components without involving the entire part. The mass of the material being treated is generally adequate for rapid heat removal or "quenching." LTSH's self-quenching operation eliminates the need for oil or water quenching and results in little thermal distortion, so refinishing parts after heat treatment is unnecessary. The Argonne sensor system provides real-time monitoring of LTSH quality (i.e., surface hardness and case depth) and therefore does not add to cycle times, unlike conventional chemical, mechanical, visual, and eddy- current methods.

In tests for heat-treating applications, the IR monitor was integrated into the delivery optics of an Nd:YAG laser, and oversized, off-axis optics were used to collect the IR signature from the weld. Argonne engineer Keng Leong explains that "a direct relationship was found between the strength of the voltage produced and the hardness and case depth on the treated surfaces. This relationship means the Argonne system can provide accurate, real-time monitoring of an LTSH process to ensure quality and help reduce the scrap rates of treated parts."

Argonne researchers are currently exploring other applications for the IR sensor and are talking with potential partners, including a Tier One automotive supplier, about collaborative research projects.

Argonne's infrared sensor system monitored the operation as an Nd: YAG laser test system (bottom) produced horizontal and vertical heat-treated tracks on a cast iron component (top).