Micrometer resolution of OCT system can be utilized to inspect surface porosity during industrial laser welding of the battery components in electric vehicles. In particular for safety reasons, a hermetic bonding with high strength and very low porosity must be created during welding to prevent the penetration of moisture and corrosion.

By using OCT data, the entire seam topography is reconstructed and stored for part tracking issues. Accurate quantitative evaluation of the weld area with OCT enables recorded defects such as open pores. This permits eliminating subsequent quality-control efforts to ensure sufficient weld quality, even during very short cycles.

The quality-control accuracy of the instrument has been demonstrated during post-process testing of small circular welds with pores.

 

OCT for weld quality assessment of 16 – 33 mm circular seams welded with a cycle time of 1.5 s. A single red line on the video is a pilot laser indicating the position of the processing laser and in-process OCT scan. Series of the red crosswise lines show the post-process OCT scans.

3D seam topography of the seam section, whith the pore.

Another application in the e-mobilty sector is welding of busbars in various material combinations and geometries. The weld has to be profound enough to guarantee a sufficient bonding cross section for a minimum resistance and maximum strength. On the other hand, the weld must not penetrate through the busbar into the highly sensitive battery cell. In our lab, we have done tests with aluminum material (2.0 mm Al onto 1.2 mm Al) and a penetration depth of around 2.6 mm. Both cross section and OCT measurement show the same depth values and geometries.

 

OCT measurement of keyhole depth and corresponding longitudinal section of the identical seam.

As the OCT measures the lowest point of the open key hole it cannot detect porosities or defects that occur after or behind the key hole. The correlation of OCT measurement and longitudinal section has been proven in various tests and investigations.

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