037 roof trim
Technical Report
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Coating of plastics and metal

Safe and economical processing of thin, fragile roof trim strips

Extravagant design elements such as the roof trim strips for the Peugeot 308 RCZ sports coupé make high demands on the suppliers. In this case a safe method had to be found for automatic grinding and polishing of a thin-walled, fragile component as part of a normal three-shift operation.

The French automotive manufacturer Peugeot (PSA Group) has developed a new 308 RCZ sports coupé that is intended to emphasise the image of Peugeot as an innovative producer of series vehicles. The inclusion of the sports car segment extends the product portfolio of the French company. The 308 RCZ series also serves as a technology carrier, in which new concepts and methods can be applied, which can also be used in modified form for vehicles produced in larger numbers. The 308 RCZ sports coupé is an excellent example for the international product integration in automotive constructions because many components and modules are produced by well-known automotive suppliers and delivered to the assembly lines ready for installation.

Design as a production-orientated challenge

At first glance, the roof joint cover strip and trim, which in the Peugeot 308 RCZ ranges from the A- to the C-column, is a simple technical component. It is currently being produced by the English supply company Sapa Components (Pressweld) Ltd. in Gloucester (Great Britain). This roof trim strip has a very clear-cut appearance and soon proved to be a technically complex, difficult component to produce. One of the reasons for this is that the strip would be very visible later and that the surface finish would thus have to be absolutely perfect. When forming the curved roof trim strip from an extruded section, care had to be taken to obtain the smoothest possible surface structure without grooves and scratches. As an experienced development partner and supplier in the automobile sector, Sapa was in its element here, especially as the company can provide good in-house production depth. Like the roof trim strip, most components are made from extruded sections, which subsequently pass through pressing, forming, bending, cutting and sawing processes to give them the desired shape. Depending on the application, this is followed by grinding, polishing and bright anodising before assemblies are created by joining additional plastic elements using a combination of riveting and adhering.

Robot controlled grinding and polishing

Grinding and polishing a roof trim strip does not sound very exciting at first. In the case of the roof trim strip for the Peugeot 308 RCZ, however, this component has a complex "banana" shape, is very long and is therefore very fragile before it has been fitted. Sapa was thus looking for a supplier who could provide the necessary systems technology to cope with this demanding application. It was decided to approach LEA Manufacturing, the British branch of SHL. After various grinding and polishing tests on original components, SHL submitted a concept for a robot grinding system and a robot polishing system which Sapa found convincing.

The robot grinding system is an integrated processing centre, consisting of a 6-axis industrial robot of the IRB6640-235/2,55 type made by ABB using IRC5 controls. The grinding work is carried out by three free-running and contact-disk grinders of the FKS250/450 ROB ALU series by SHL. The controls were developed by SHL, with a bus system for controlling and programming, which also has an interface for communication with the robot control system. In addition, a lubricant cooling system ensures that the grinding process at all three grinding stations is continuously cooled. The fragile components can be accurately and carefully picked up by the robots with the aid of a basic exchange gripper device. A vacuum generator supplies the combined mechanical and vacuum component tension grippers with the necessary vacuum. The left and right roof trim strips each have their own clamping tools. The combined mechanical and vacuum tension grippers are particularly important, as they must fix and clamp the long and rather fragile components with great accuracy, so that they can be brought into contact with the grinding stations at continuous pressure and accurately positioned there. Any slipping during grinding or even a slightly different pick-up process could result in rejects. The required surface quality can only be achieved with the corresponding repeat accuracy. A largely similar second station is used for polishing, but in this case two SHL polishing machines of the P550 ROB type are being used. The raw components are kept in loading and unloading stations, just like the ground or polished components, thus ensuring continuous operation in three shifts around the clock.