LASER BUTT-WELDING DEVICE AND METHOD
BACKGROUND OF THE INVENTION
The present invention generally relates to a method 5 and device for butt-welding metal strips together by employing a laser beam for cutting and welding.
In the past, there have been various attempts to provide an acceptable method for butt-welding metal strips. One such attempt, known as flash butt-welding, 10 involves joining contiguous ends of a leading (take-up) coil or sheet metal roll and a trailing coil by resistance welding Another butt-welding technique has been to weld the ends of the leading coil and the trailing coil using pipe welding electrodes. The plasma welding 15 method is also known, as is the use of clinches whereby the coil ends are joined together by stamping.
All of these methods incur the development of weld reinforcement. This can result in a leading coil that is not round when wound up. In addition, the roller pass 20 can be damaged. Further, with thin strip material, the weld reinforcement presses into the coil. The plasma welding method suffers from an additional disadvantage due to the higher heat transfer in the weld pursuant to the wider heat influence zones, which results in the 25 hardening of the weld zones with poor forming qualities. This disadvantage is shared by the microplasma welding method, which is used for welding very thin strips together.
A further method and device for butt-welding steel 30 strip disclosed in European Patent EP-OS 0 151 848. In this technique, the strips are cut mechanically and then welded together by a laser beam. The expense incurred with this device is relatively high.
It is therefore desirable to provide an efficient 35 method and device for butt-welding metal strips which avoids the development of weld reinforcement and associated disadvantages and which results in a strong weld. It is further desirable to provide a device which requires only a single laser and which allows for con tin- 40 uous operation of the leading coil.
SUMMARY OF THE INVENTION
The present invention provides a device and method for butt-welding a first metal strip from a trailing coil to 45 a second metal strip of a leading coil. The device of the present invention comprises a first clamping bridge operatively aligned with the first strip for clamping the first strip at a first cutting position, a second clamping bridge operatively aligned with the second strip for 50 clamping the second strip at a second cutting position, apparatus for moving the first and second strips into butt-welding relationship at a welding position, a laser for generating a laser beam, apparatus for positioning the laser for cutting the first and second strips at the first 55 and second cutting positions, respectively, and for welding the first and second strips at the welding position, and apparatus for moving the laser along a cutting and welding path.
The method of the present invention utilizes such a 60 device to carry out the following steps. First, the first strip of material is clamped by the first clamping bridge. While this strip is clamped, the laser is moved into position above the portion of the strip protruding from the first clamping bridge and the end of the strip is severed 65 by the laser beam as the laser moves along a horizontal path perpendicular to the direction of transport of the strip. Next, the same procedure is carried out for the
second strip, using the second clamping bridge and the same laser, with the laser being repositioned over the end portion of the second strip. This results in a clean straight strip edge for welding. After both strips have been thus prepared for welding, the edges of the first and second strips are moved into butt-welding relationship and the first and second strips are welded together with the laser, the laser again moving perpendicular to the transport direction of the strips.
The first and second clamping bridges may each comprise an upper and lower clamping jaw which can be set in a clamping position and in an open position by a motor or other drive means, the first and second strips being wider than the respective clamping jaws and the first clamping bridge being mounted on a horizontal sledge whereby it can be selectively moved in the transport direction of the strips by a motor.
The laser positioning apparatus may comprise a transverse sledge for supporting the laser, the transverse sledge being mounted on a traverse whereby it can travel perpendicular to the transporting direction of the strips, and longitudinal sledges located at each end of the traverse on a supporting frame, whereby the longitudinal sledges can travel synchronously, by means of a motor, parallel to the direction of transport of the strip.
The device of the present invention may further comprise first and second supporting units which can be selectively raised for supporting the strips when clamped between the clamping jaws, the supporting units being oriented perpendicular to a lower surface of the strips and located between the first and second clamping bridges. In a preferred embodiment, the supporting units each comprise two gibs which define a hollow space through which gas can be supplied and drawn off, the hollow space narrowing to a gap at a given distance below the lower surface of the strips in the welding area. The gibs are connected to a transverse pipe operatively connected to a drive means for raising and lowering the supporting units. The end portion of the strips which protrudes from the clamping jaws is positioned above the gibs, with the upper clamping jaws of the first and second clamping bridges defining a gap between them for passage of the laser beam during welding.
Where the first strip differs in thickness from the second strip, the welding step further comprises positioning the laser so that a beam from the laser will strike at an acute angle to the upper surface of the strips This requires an apparatus for adjusting the vertical height of the laser as well as an apparatus for rotating the laser relative to the upper strip surface to achieve the proper angle of impingement for the laser beam.
Where a portion of the second strip is continuously moving, e.g. where the second strip is being continually wound onto a leading coil, the device of the present invention further comprises a buffer facility for storing a portion of the continuously moving second strip, whereby a portion of the second strip at the point of the clamping is stationary during the cutting of the second strip and the welding. An example of an application having a continuously moving second strip would be a coating process performed downstream of the welding In a preferred embodiment, the buffer facility comprises two groups of rollers, each group comprising at least one roller, and wherein the storing step comprises increasing a distance between the groups prior to the cutting of the second strip and the welding to store a