Laser Welding Eliminates Distortion
THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS
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This stainless steel railway vehicle was fabricated in Japan by Kawasaki Heavy Industries, using a trial
laser welding technique. By 2005, the company will replace most of the spot welding used in the mass
production of these vehicles.
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Continuous, automated process reduces the exposure of stainless steel to excessive heat.
By Keiji Toyabe
Nickel Magazine, November 2004 -- Kawasaki Heavy Industries (KHI) plans to introduce a robotic laser welding system at a plant in Hyogo, Japan, that assembles stainless steel railway vehicles. The projected cost is 700 million yen.
KHI has completed the trial manufacture of a stainless steel railroad vehicle using laser welding technology. By mid-2005, the laser welding mass production system will replace traditional spot welding.
One of the problems associated with spot welding is the welding mark that is left on the welded surface. Laser welding eliminates this mark, thereby improving the appearance and strength of the stainless steel being welded. The result is a vehicle of higher quality.
The overuse of spot welding in the assembly of stainless steel vehicles can result in distortions, mainly because of excessive heat. Many welding marks, of a diameter of about 1 centimetre, are left on the surface. Also, seal materials are needed to prevent water penetration through the roof of a vehicle. Laser welding solves these problems because it is a continuous process.
Typically the surface flatness of railway cars is specified at ±3 millimetres. Laser welding enables surface flatness to be maintained at about ±1 millimetre, and so unevenness on the surface is virtually undetectable.
Laser welding can also improve productivity. Whereas spot welding can progress at about 1 metre per one minute, laser welding can proceed at a rate of about 5 metres per minute.
The technology is called "partial joint penetration laser welding," and KHI has developed control systems for laser power output and movement speed. To facilitate stable and continuous welding, the company has also developed a special head for lap joint welding.
KHI carried out strength analysis and load testing of the trial railroad vehicle. These tests confirmed improvements in both strength and flexural rigidity.
The manufacturing system KHI plans to build will employ laser welding for all components of the railway vehicles except floor parts.
Keiji Toyabe is the Tokyo-based Manager of Nickel Institute Japan.
PHOTO: Kawasaki Heavy Industries
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Kawasaki Heavy Industries |
