Forever in a Tight Spot
Many electrical connections in automotive components must last forever after the initial bonding – or at least as long as the life of the car. For plug and clamp connections, this is no easy task, considering all the strong vibrations they are subjected to. Through experiment and simulation, Bosch researchers are mastering the challenge.
Snap. The cap is on; the electrical contacts have been made; the component is now fully functional. At Bosch, electrically conductive connections are established between joined parts simply by pressing one into the other or clamping them, without any welding or soldering. Among researchers, this is known as “cold joining technology,” and it is a new frontier in automobiles, where the conditions that must be withstood are very wide-ranging. The advantages are obvious: The press-in or clamping operations take place on simple machines, which cuts down investment and process costs. When a pin is inserted into an eye or a flat contact into a stamping grid, the components have an automatic joining function. In addition, cold joining can be parallelized to a high degree, and there is no heat stress on the components, as the name of the technique suggests. When a pin is inserted, for example, it is pressed against the inside of the eye. These contact pressures must last “for a lifetime.” In addition, the connecting process mustn’t under any circumstances result in chips that could cause the electronic circuits to malfunction. In experiments and simulations, Bosch researchers are studying which pin and eye profiles are ideal for optimal retention force and how the stresses are distributed in the component.
They’re also changing materials and material parameters, such as hardness and ductility, and studying their variations in finite-element simulations. In insulation displacement connections, for instance, a wire is pressed into a clamp and locked there permanently. If the wire is coated, the coating is simply sheared off and contact is established. But it has to be durable too. That’s why Bosch researchers are searching for the optimal retention force. Simulations have shown that a tighter clamp doesn’t necessarily increase the retention force on the wire. For a given profile geometry of the wire and clamp, there is also a certain insertion depth with the highest retention force. Now that researchers better understand the physics of how the electrical contact depends on the clamping forces and surrounding conditions, these processes are increasingly being used for production components. Insulation displacement contacts are well-suited for connecting enameled coil wires in the entire field of solenoid valve technology, for example. Only the very thinnest of wires, those that measure less than 100 micrometers in diameter, are still exclusively welded together. But researchers are convinced that even this limit will soon be surpassed.
They’re also changing materials and material parameters, such as hardness and ductility, and studying their variations in finite-element simulations. In insulation displacement connections, for instance, a wire is pressed into a clamp and locked there permanently. If the wire is coated, the coating is simply sheared off and contact is established. But it has to be durable too. That’s why Bosch researchers are searching for the optimal retention force. Simulations have shown that a tighter clamp doesn’t necessarily increase the retention force on the wire. For a given profile geometry of the wire and clamp, there is also a certain insertion depth with the highest retention force. Now that researchers better understand the physics of how the electrical contact depends on the clamping forces and surrounding conditions, these processes are increasingly being used for production components. Insulation displacement contacts are well-suited for connecting enameled coil wires in the entire field of solenoid valve technology, for example. Only the very thinnest of wires, those that measure less than 100 micrometers in diameter, are still exclusively welded together. But researchers are convinced that even this limit will soon be surpassed.
Pin-and-socket process (above): A rectangular-profile pin is pressed into a pre-punched hole in the metal piece. Insulation displacement connections (below): Contact is created with enameled wires at ideal insertion depth.
