Method and apparatus for continuous production of tubular bodies by means of laser longitudinal seam welding

An apparatus for making seamed tubular bodies from a slit tube steel strip defining a pair of strip edge faces utilizing a laser beam characterized by;

• a strip edge preparation means (71) for preparing said strip edge faces to a mean roughness depth of less than one half a beam diameter adjacent the focus diameter of said laser beam in the weld point,
• guide elements (27, 28, 56 and 57) for bringing said strip edge faces (4 and 5) together to define a gap having a width less than the focus diameter of said laser beam,
• first measuring means (42) for measuring the offset of said strip edges and the width of the weld gap between said weld point and said guide elements (27 and 28) and outputting electrical signals representing said measured offset and said measured weld gap,
• position sensors (39 and 40) for converting the instantaneous positions for said guide elements in the vertical direction parallel to the edges offset to electrical signals representing said positions,
• first processing means (41) responsive to the electrical signals output by said first measuring means (42) and by said position sensors (39 and 40) for outputting control signals to said guide elements,
• a laser weld head (61),
• a three-coordinate control means (60) for said weld head for positioning the focus point of the laser beam such that said strip edges are spaced at equal distances from the axis of said laser beam,
• a first contactless measuring system (20) for determining deviation of the weld gap and outputting electrical signals representing said deviation,
• a second contactless measuring system (58) for measuring the spacing of the tube surface at the strip edges relative to the focus point of the laser beam and outputting electrical signals representing said spacing,
• second processing means (59) responsive to said electrical signals output from said first and said second contactless measuring systems (20 and 58) for controlling three-coordinate control means (60),
• heating means (52) for heating said strip edges in the vicinity of said weld point,
• temperature measuring means (55) for measuring the temperature of the seam weld after upsetting and outputting electrical signals representing said temperature,
• third processing means (54) responsive to said electrical signals output from said temperature measuring means (55) for controlling said heating means (52),
• feedable upset means (64 and 65) for upsetting the seam region to form an upset bead,
• pickup means (67 and 68) for measuring said upset bead subsequent to upsetting and outputting electrical signals representing a geometrical quantity of said bead, and
• fourth processing means (66) responsive to said electrical signals output from said pickup means (67 and 68) for controlling the feed rate of said upset means.