A cutting-edge technology to increase the friction coefficient in bolted joints in a simple way

Lightweight vehicles are one of the most efficient solutions to reduce the fuel consumption and the emission of polluting gases, which leads the automotive industry to the constant need to manufacture ever lighter vehicles. Due to these current requirements, there is a general move toward compact and lightweight powertrain system designs. Although more compact, these systems must be able to transmit the same or even higher forces and torques. Dealing with these contradictory requirements adding to the constant request to minimize production and assembly costs is a huge challenge to engineers. One approach is to enhance the coefficient of static friction in friction joints. When friction joints are designed, physical parameters such as overall size and surface pressure usually can only be varied in a tight window. Load transmission capability in friction joints is thus limited by the friction coefficient of the mating materials. An efficient solution for these limitations is to apply a nickel diamond coating either to the actual parts of the joints or to friction shims for installation in the joint. In this context are the 3M™ friction shims, steel foils with a coating of electroless nickel embedded with diamond particles. When the shim is placed between two components in a bolted connection, the diamonds cut into the metal mating surface and create a micro-scale interlock that significantly increases friction between the two parts. This friction shims are thin enough to fit within close engineering tolerances, creating possibilities for lightweight compact design while increasing potential load and peak torque in bolt connections, making them a cutting-edge connection technology capable of transmitting effectively and reliably up to four times higher torques than conventional systems without requiring modifications to the joint design. The objective of the paper is to demonstrate the theory involved in this technology as well as practical evidence through tests performed using friction shims as an alternative to increase the coefficient of static friction in bolted joints.