Operating at Renault's factory at Sandouville in France, a Cognex vision inspection system checks for laser weld imperfections that can send an assembled vehicle to the scrap yard. Here is an example of what can be obtained by using industrial vision to do quality checks before adding value to parts on a production lineThe Cognex In-Sight vision system, installed in Renault's press shop at Sandouville in France, checks the right and left sides of the body shell of Laguna cars. Just one installation checks four different parts. Each side of the body shell is made up of two parts, which are laser welded. It is around the weld that defects can appear and need to be detected. While the various pressing operations - which give the part its shape - are being carried out, clear or partial breaks can be produced. As the parts are stored manually at the end of the line, those parts showing such faults are easy to spot and remove. It is not so easy to spot when the faults are small holes, some of which can measure less than 0.3mm in diameter, which form along the bead of the weld. If the presence of these holes is not detected at the end of the line, and if the part is not removed, breaks can be produced during shaping, causing numerous problems for the downstream assembly line.Weld checks were previously a manual operation involving the placing of a light source on one side of the part and checking for any light passing through on the other side, revealing breaks or holes. While effective to a point, this method failed to highlight holes of a very small diameter.Automated systems manager at Renault, Patrice Dumont decided to evaluate industrial vision systems for this inspection task. Several suppliers were called upon, and Cognex proved the most reactive. A system based on the company's In-Sight vision sensor range was prototyped and trials revealed 100% detection of faults. Two roughly similar inspection benches were subsequently commissioned, one for the Laguna body shell sides and the other for the side frames of several vehicle models.The first of these is located at the end of the Laguna lower body shell pressing line. Four Cognex In-Sight 1000 cameras, each placed in a protective casing, are positioned at the top, over the inspection platform, on a cross support beam. A control system and display screen is positioned at one end of the platform, while a marking system for defective parts is fitted at the other end. A backlighting system based on LEDs is also installed.The body shell sides, which measure 3.4x1.6m and weigh nearly 30kg, are placed on a support structure by robot. The target areas, measuring approximately 10x5cm, are covered by two of the cameras, each inclined at 45o, as the part forms a U-shape over the welded area. The cameras are able to detect very low light levels, including any back light passing through holes of only 0.1mm diameter. If the part is declared sound, this is displayed on the screen. If it is defective, this is also displayed, a red light comes on at the end of the line and the part is ink-jet marked. We had to teach the system what faults were to be identified , recalls M Dumont. That was done progressively, while we familiarised ourselves with the system. Once the system had memorised the type of fault, the recognition rate was 99.99%. Our main concern was the ambient lighting. Because of the existing lighting in the workshop, the layout of the area and the orientation, reflections appearing on the parts occasionally showed up non-existent faults. Placing curtains at the end of the line resolved this problem .The welding checks are now carried out reliably on the whole production at Sandouville (body shell sides and side frames). With the fault recognition rate obtained, the defective parts are very quickly identified and removed. Previously, entire body shells had to be sent to the scrap yard, so the savings made in this area alone fully justified the investment.