Validating the virtual clamp with CMM correlation on automotive production lines

Mechanical clamping has major disadvantages when used in the in-line measurement of a welded automotive assembly. It is hard to adjust the welding process, the clamp prevents the flexibility of optical measurement and clamping equipment is expensive to buy and maintain. A method called "virtual clamp" has been developed to provide the results of clamped measurement without physically clamping the part. This eliminates the disadvantages of the mechanical clamp. The accuracy of the virtual clamp was validated on four real-world automotive production lines. Correlation between the mechanically clamped parts using a CMM and virtually clamped parts using an in-line measurement system showed the accuracy of the virtual clamp to be around 0.04 mm in half- and full-vehicle size welded assemblies. Although this is a considerable contribution to the overall measurement uncertainty budget, the virtual clamp appeared to reduce other uncertainties affecting the budget. Correlation actually improved when using the virtual clamp. The research has opened a way to validate the accuracy of a virtual clamp that does not require additional investments and uses existing technology. The market indicates that the next generation of manufacturing needs more flexibility from in-line measurement, and this research clearly shows that the virtual clamp can provide it.