Abstract:
The present invention relates to a method and a device in which: - a workpiece is welded with the aid of a laser, - the light intensity above the weld pool is measured with the aid of an optical sensor, - the value measured by the optical sensor is compared with a defined reference value, and, - the energy supplied to the weld pool per unit length is adjusted as a function of the difference between the measured value and the determined reference value. According to the invention, the reference value is determined by allowing the energy supplied to the weld pool per unit length to increase from a relatively low starting level or to decrease from a relatively high starting level until a step change in the measured light intensity from a relatively high level to a relatively low level or vice versa is measured, after which the intensity measured by the optical sensor is used as a control signal for the quantity of energy which is to be supplied to the weld pool per unit length, the energy which is to be supplied to the weld pool per unit length being allowed to increase when the optical sensor measures a relatively high level of the light intensity and the energy to be supplied to the weld pool per unit length being allowed to decrease when the optical sensor measures a relatively low level of the light intensity.
Abstract:
Substrate such as a turbine blade provided with a coating, which consists of a material that forms a sealing oxide skin on heating. This material is a ferrous metal aluminium alloy or a ferrous metal chromium alloy, wherein the oxide skin comprises aluminium oxide or chromium oxide, hi order to optimise the adhesion between the skin and the coating, it is proposed that a metal from the platinum group such as platinum or palladium be added in an amount of 0.1 - 0.5 % (m/m). It has been found that better adhesion is obtained with this method and the detrimental effects of sodium, potassium or calcium are counteracted.