Gm Global Technolgoy Operations, Inc.

William C Jenuwine

Umit Bilge

Gregory L Nagel

Dixon Cleveland

James R Havens

Basil A Decina, Jr

Christopher E Jurczyszyn

A method of laser welding steel sheets that have a thin corrosion protective coating of zinc. The steel sheets are positioned vertically. A pulsed laser beam, which is positioned normal to the sheets is applied to the sheets to melt the material of the sheets and create a weld. During welding, the laser beam is pulsed ON and OFF and the sheets and pulsed laser beam are moved vertically relative to each other such that laser heating of the material creates a cavity. Liquid or molten material flows vertically downwardly by gravity to elongate the cavity and thereby facilitate the escape of zinc vapors from the cavity.

Laser welding method

A method of laser welding steel sheets that have a thin corrosion protective coating of zinc. The steel sheets are positioned vertically. A laser beam, which is positioned normal to the sheets is applied to the sheets to melt the material of the sheets and create a weld. During welding, the sheets and laser beam are moved vertically relative to each other such that laser heating of the material creates a cavity. Liquid or molten material flows vertically downwardly by gravity to elongate the cavity and thereby facilitate the escape of zinc vapors from the cavity.

During a weld period the weld parameters are monitored and data representing the weld resistance curve and the power curve are acquired and stored for analysis by a suitably programmed computer. The derivative of R, R is calculated and stored and the function is divided by power P to obtain R/P. The resistance curve is searched to obtain the maximum value R.sub.m which occurs during the heating phase and the function R/P is searched prior to the time of R.sub.m to find the maximum of that curve representing the highest rate of resistance increase. Then the R/P curve is searched subsequent to its maximum to determine when the function reaches a specified percentage of the maximum. That value occurs at the knee of the resistance curve and approximates the onset of melting in the weld. A prediction of whether a weld is a nugget or a sticker is made by calculating the ratio of weld energy after the onset of melting to the total weld energy, the ratio of the resistance drop after the resistance peak to the peak resistance, and then a weighted sum of the energy ratio and resistance drop ratio. An edge weld geometry is detected by calculating from the resistance and power curves the weld energy during the period of expulsion, if any, divided by the cumulative energy between the onset of melting and the end of expulsion, a measure of expulsion intensity based on the maximum degree of resistance inflection, and then a weighted sum of the energy value and the inflection value.

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Marine City, MI, United States of America

William C Jenuwine