OCT for Time- and Material-Effective Laser Welding

The automotive industry is the technological trendsetter among manufacturing industries. Fully automated, fast remote laser welding of various components in unattended operation without time-consuming set-up is not an exception. Laser welding units must operate autonomously, especially in case of high-volume production. In  spite  of  the  high  welding  speed, the  laser  beam  must  precisely  hit  the joint.  OCT is a position control system ensuring that the laser beam is always directed at the desired welding position at a wide range of angle of incidence and along the various geometries of the weld path, regardless of the environmental factors and fixturing elements. OCT is advantageous for industrial laser processing since it always follows the laser beam in any welding direction, offering outstanding flexibility without time-consuming reorientation. It helps to solve following seam tracking problems during laser welding in automotive production:

  • OCT eliminates inaccuracies in the alignment of the scanner optics or in the guiding robot movements that may result in a shift of the laser beam from the predefined path;
  • OCT facilitates exact positioning of  laser  beam  at  the  nonlinear weld path with distortions  like  notches  or  abrupt  changes  of  welding 
  • OCT enables rigorous high-speed laser joining of metallic automotive workpieces containing hardly accessible non-linear seams.

 

OCT-equipped laser processing heads offer a number of benefits that are essential for the increase of the productivity and for the reduction of the production costs of automotive industry. Among them are consistency, precision,  real-time  performance,  indispensable  flexibility,  high  acquisition rate,  and  insensitivity  to  the  welding environment.

Legislative and customer requirements force automotive industry to improve fuel economy as a means to lower greenhouse gas emissions. Lighter vehicles with combustion engine require less fuel for propulsion. Traditional vehicle manufacturers are aiming to decrease the weight of vehicles through the use of new materials, especially lightweight aluminum alloys and thinner flanges. The integration of OCT as the seam tracking system enables to shorten the flanges and to use simplified clamping systems, offering precise fully automated and high dynamic detection and adjustment of the seam joint position over the total scan area.

OCT provides “on the fly” tracking and high accuracy detection of the joints with extraordinary high or small aspect ratio. Application of OCT is advantageous in particular for geometries inaccessible for traditional camera based techniques. For example, during welding of a car door: By a 90° change of the welding direction, the reorientation of the laser beam with a conventional welding head takes 1 – 1.5 s. With OCT and scanner it can be done in milliseconds.

The advantage of seam tracking with an OCT system is that it is not restricted by the predefined line or edge.

Successful real-time seam tracking by means of OCT on a automotive door panel with a non-linear edge like a notch. 

 

Resulted continuous weld.

 

OCT is an advantageous technique to be used in series production of body-in-white aluminum welding instead of conventional tactile optical systems. The ultrafast coaxial  seam tracking  with  OCT offers  the  possibility  to  use  high  welding  speeds  to stabilize  the  process,  in  particular  to avoid hot cracking in aluminum alloys. During fast welding, the cooling rate is faster, causing an increase of the tensile strength of the weld and the reduction of the incidence of hot cracking.

 

Real-time seam tracking during welding tests of a steel automotive door panel under remote configuration using the OCT seam tracking facility.

 

Stitch welds made on a steel car door: (a) selected good quality welds demonstrating precise seam tracking by means of OCT during production of numerous welds; (b) a few exceptions caused by accumulated weld smoke because of bad accessibility of the welds and short fore run of OCT.

 

The coaxial alignment of the OCT empowers system users to perform the measurements at a wide work angle range. In case of the steel workpieces, OCT is clearly detecting the surface topography under angles of incidence even higher than 50° while looking through the welding optics.

 

Being mounted on the remote scanner  optics,  Lessmüller  Lasertechnik OCT was applied for seam tracking during welding of the automotive structural conponents: T-joint under 12° work angle, and lap joint under 50° angle. Automatically detected joint position is marked with a vertical cyan line.

 

Even in case of a programmable welding the exact processing beam positioning is important since tolerances and operating gap changes are influencing the weld quality. OCT not only controls joint position, but also gap size, and angle of incidence prior to welding, in order to compensate for them online.  OCT-equipped LSO welding optics enables gap bridging by detecting and adjusting automatically exact welding position (lateral and axial), so that gaps of up to 0.8 mm can be bridged. This permits welding with enhanced speed, without use of the complicated oscillating optics.

 

With help of OCT, the angular errors were compensated and the laser beam power and position (offset) were corrected for gap bridging during welding of parts of body-in-white construction without additional time- and cost-unfavorable laser beam oscillation. A good bonding was achieved. The quality and microstructure of the weld seam met industrial quality requirements. 

 

Due to the large working distance and high precision of the OCT tool, the detection of the joints  with  extraordinary high aspect ratio (flange joint) or small aspect ratio (powertrain gear V-joint) can be achieved.

Another exemplary application of OCT is seam tracking during the powertrain welding. Vertical cyan line indicates automatically detected joint position.

Successful experience with OCT operation in automotive line production makes it favorable as a sensing technology for today’s laser processing trends.  Its application contributes into the technological progress in automotive industry, driven towards fulfilling governmental regulations and customer expectations.

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