Laser welding of coated steels assisted by the formation of at least one preliminary weld deposit

A method of remote laser welding a workpiece stack-up that includes at least two overlapping steel workpieces, the method comprising:

• providing a workpiece stack-up that includes overlapping steel workpieces, the workpiece stack-up comprising at least a first steel workpiece and a second steel workpiece, the first steel workpiece providing a top surface of the workpiece stack-up and the second steel workpiece providing a bottom surface of the workpiece stack-up, wherein a faying interface is established between each pair of adjacent overlapping steel workpieces within the workpiece stack-up, and wherein at least one of the steel workpieces in the workpiece stack-up includes a surface coating of zinc or a zinc-iron alloy;
• operating a scanning optic laser head to form at least one preliminary weld deposit that extends from the top surface of the workpiece stack-up either partially or fully through the workpiece stack-up, each of the at least one preliminary weld deposits being formed by directing a solid-state preliminary welding laser beam at an initial spot location on the top surface of the workpiece stack-up to create a preliminary molten steel weld pool that penetrates into the workpiece stack-up from the top surface towards the bottom surface, followed by ceasing transmission of the preliminary welding laser beam at the initial spot location to cause the preliminary molten steel weld pool to solidify;
• operating the scanning optic laser head to direct a principal welding laser beam at the top surface of the workpiece stack-up after formation of the at least one preliminary weld deposit, the principal welding laser beam impinging the top surface within an annular weld area defined by an inner diameter boundary and an outer diameter boundary on the plane of the top surface to create a principal molten steel weld pool that penetrates into the workpiece stack-up from the top surface towards the bottom surface, the annular weld area surrounding a center area on the plane of the top surface that spans the at least one preliminary weld deposit formed in the workpiece stack-up;
• and
• coordinating the movement of tiltable scanning mirrors within the scanning optic laser head to advance the principal welding laser beam relative to the plane of the top surface of the workpiece stack-up and along a beam travel pattern that lies within the annular weld area and surrounds the center area that spans the at least one preliminary weld deposit, and wherein the principal welding laser beam is advanced along the beam travel pattern at a travel speed that ranges from 2 m/min to 120 m/min.