Reliable impregnation and plating process for intricate locking disc manufactured using powder metallurgy
A locking disc manufactured using powder metallurgy is part of a passive pedestrian protection system designed to minimise the consequences of accidents such as injuries. In the event of a head-on or similar collision with a pedestrian, the locking disc actuates a release mechanism that causes the bonnet of the vehicle to spring open just below the windscreen. The bonnet thus cushions the impact and reduces the risk of the pedestrian's head, for example, colliding with hard parts of the engine. The intricately designed disc fulfils an important unlocking function, which is why the long-term functional reliability of the component is absolutely essential. Here, corrosion resistance plays a key role, particularly in the exposed engine compartment area. The locking disc and the cams that interlock and connect in the event of a collision are made using powder metallurgy, as such intricate parts can hardly be manufactured using cutting or milling techniques.
However, despite their structural advantages, components made using powder metallurgy (sintered materials) have the disadvantage that they cannot simply be electroplated, making it difficult to improve their resistance to corrosion. Due to their porous structure, sintered components tend to absorb the aqueous liquids required during the plating process and gradually release them in the course of time. The resulting defect is known as "bleed-out" and causes salts to be deposited on zinc or zinc alloy electroplated surfaces. These salts frequently attack the plating, leading to localised corrosion on the sintered part. Although sintered components are usually impregnated prior to electroplating, the conventional processes adopted from the casting industry did not prove to be particularly successful for this purpose.
Solution with added value
With Sinter Surface Solutions, the Holzapfel Group has developed a complete solution for impregnation and plating that reliably prevents the defect known as bleed-out. For Sinter Surface Solutions, the impregnation process was specifically optimised by adapting both the process itself and the resins used, in order to meet requirements compatible with the plating process. The key innovation is the adaptability of the hardening process, which ensures that the pores are reliably impregnated to cover the entire surface of the component. This solution with improved impregnation, optimised hardening and special-purpose plating was also used for the locking disc.
The automotive industry, e.g. for transmission parts (rings, hubs and clutch bodies), for components in the engine compartment (gearwheels, bearing covers, sprockets) and in the steering system (pistons, guides)