Diode Laser Improves Canister Welding

Brent D. Johnson

A laser-assisted welding technique is helping manufacturers construct the next generation of weapons for the US military. By reducing the thermal distortion that traditional welding approaches induce in the workpiece, the process is reducing manufacturing times and welding wire consumption in the production of missile canisters.

A laser-assisted welding technique is enabling manufacturers to produce quad-pack missile canisters for the US Navy's MK 41 Vertical Launching System.

United Defense builds canisters for the US Navy's MK 41 Vertical Launching System, which fires weapons -- such as the Tomahawk cruise missile, Standard Missile, Vertical Launch Anti-Submarine Rocket and Evolved Sea Sparrow missile -- from the decks of ships at targets in the air, on sea or on land. The most recent version of the Vertical Launching System features four missiles per canister, rather than a single wea-pon. This configuration presented the manufacturer with some unique challenges.

The canisters are made of thin metal skins reinforced by multiple braces, and United Defense had affixed the parts using a pulsed metal/inert gas welding process in which the wire was continuously fed from a spool to the end of an electrode fitted with a gas nozzle. A mixture of argon and oxygen gas came in contact with the electrode, forming an arc plasma that melted the wire onto the joint to be welded. However, the distortion caused by the heating proved to be too much for canisters with one-quarter the cross section of the previous ones.

The company replaced the arc with a 4-kW laser diode system from Nuvonyx Inc. on a Panasonic Factory Automation robot. This reduced heat input by a factor of almost 10.

Because of the level of precision that the application required, a Sense-i Gauger sensor from Servo-Robot Inc. of St. Bruno, Quebec, Canada, was added. This system uses a low-power laser to measure part placement to calculate welding offsets. Because it is based on noncontact optical technology, it is much faster than traditional touch sensors. The robot can move to the reference points and compute the offset values within seconds.

United Defense has produced more than 100 units with the new approach. It has found that, although the weld rate is unchanged, the labor hours have fallen by 30 percent because less thermal distortion means less postweld processing. Moreover, weld wire consumption has been reduced. The standard process used approximately 10 lb of wire per canister; the laser process uses only 2 lb.