Method and apparatus for the heat treatment of welds

A method for the inductive heat treatment of weld seams in a welding machine with a laser welding head for connecting steel strip,

• a heating process of the weld seam and the adjacent weld seam areas upstream and downstream of the actual weld being carried out by line inductors,
• the weld-seam area being heated by an adjustable multipart line inductor whose parts can define zones of different power densities, the inductor having a multiple division of its conductor loop lengths and/or with a different plating of the conductor loops and/or with a plurality of spacing steps from the steel strip,
• wherein
• division of the entire heating power density to be applied for the heating in first and second heating stages is carried out such that a steeper temperature increase takes place in the first heating stage than in the second heating stage.

An apparatus for inductive heat treatment of weld seams in a welding machine with a laser welding head for connecting steel strips, the apparatus comprising:

• an adjustable multipart line inductor that can be used for preheating and postheating with different power density over its length, the division of the power density being produced by
• several conductor loops and stepwise change of the partial conductor lengths or
• a different plating of the conductor loop over its length, wherein a different power density can also be achieved within one conductor loop or
• different stepwise relative spacings between the line inductor and the steel strip, through which likewise a different power density is produced within a conductor loop.

A method of welding together edges of two metal strips, the method comprising the steps of:

• relatively displacing a laser welding head and the metal strips in a predetermined direction such that the head passes the edges of the strips while welding the edges together with the head;
• heating the edges upstream of the head with an upstream line inductor at a high power density so as to rapidly heat the edges upstream of the head;
• and
• heating the edges downstream of the head with a downstream line inductor at a lower power density so as to heat the edges less rapidly than with the upstream line inductor.