Automated Inspection and Optimisation of MAG Welded Seams
Daimler AG becomes the first vehicle manufacturer to utilise a system for the automated inspection and optimisation of welded seams. The overall concept, developed by Daimler, was implemented for the first time for rear axle carrier assembly on the new C-Class. Since installing VITRONIC's weld seam inspection technology at Mittingen in February 2007, more than 8 million welded seams alone have been successfully inspected and, if required, optimised.
The goal of Daimler AG was to replace the existing manual welded seam inspection and reconditioning, with an automated inspection and optimisation system working in a line cycle. Based on a comparison of different sensor systems, the inspection system VIROwsi by VITRONIC was certified for use after extensive field tests, and customised according to Daimler AG's user-specific needs. The inspection systems were calibrated during the launch of rear axle carrier production for the new C-Class. The process capability of VIROwsi automated inspection and optimisation has been persistently proven.
Installation of the Assembly Lines
The rear axle carriers are manufactured on lines in several assembly stages, with each line operating exactly the same production methods. Components with a different number of seams are welded together in a welding booth, with the welded assembly being inspected automatically during the next stage of production. If necessary, the components are optimised and inspected again.
Operation of Optical Welded Seam Inspection
The inspection takes place automatically in the inspection and optimisation areas. The VIROwsi inspection system is based on a laser triangulation method. A semiconductor laser, housed in a compact sensor, projects a line on the welded seam while a high-speed camera, also housed in the sensor, captures the line as an elevation profile. A three dimensional image of the welded seam surface is created gradually through the relative motion of the sensor and the object.
All relevant deviation from the ideal welded joint is identified with 100 per cent accuracy. Therefore, a broad range of defect types, which are available for further processing after the inspection procedure, were defined for the start of production.
Detailed Defect Information for Optimisation
An extensive proprietary software toolbox for inspection and optimisation, which processes the defect's type and location information for the automatic optimisation, was developed by the PWT/VUF department. Additionally, this toolbox also carries out the visualisation and archiving of all inspection results. The burner for re-welding is also mounted next to the inspection sensor on the inspection/optimisation robot. If a defect is detected by the inspection system, the software decides if and how the optimisation process will be performed.
Documentation of Test Results
To complete the full documentation of each welded joint, the software also archives all inspection results. Each test result is stored in a designed database. The database contains all relevant information like the component number and the quality of each component (good/bad) in order to guarantee complete traceability. The production process can be optimised and visualised consequently.
For rapid system/welded seam optimisation, all testing results can be represented in different ways. For example, the defect's location is shown in colour directly on the component for the machine operator. Additionally, tables/statistics with detailed information about several thicknesses are available in the system.
The automated and optical welded seam inspection process has been used for simpler inspection tasks in industrial production for years. As the first vehicle manufacturer, Daimler AG goes one step further and puts into practice an automated optimising line cycle process.
Daimler AG is also committed to this concept for future axle models. Additionally, the propagation of its use to other components is being looked into.