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Conventional Wire Crimping Process

Electrical connectors play a vital role in the control system. The numbers, types, and complexity of electrical network systems in a commercial vehicle are continuously increasing, and the number of electrical contact points increases as well. Within this circumstance, the demand for lifespan and reliability of electrical components are increasing. The electrical connections are often a weak point in the electrical systems (Williams et al., 2015).

Crimping of terminal is one of the fastest and most reliable interconnection methods.

However, if the terminals are not crimped properly onto the wire strands, it severely affects the integrity of the electrical connectivity and mechanical strength. Compression using conventional crimping tool deteriorates the material due to relaxation or partial release. Nevertheless, a specific care should be considered. Faulty crimps can lead to considerable damages and in the worst case can cause a fire (Soulinaris et al., 2014).

Some important and most widely used applications of terminal-wire interconnections are shown in Figure 2.1 (a) overhead power transmission, (b) underground power transmission, (c) connectors connected to bus bars for high voltage application, (d) industries circuit connection for high power transmission, (e) battery connection of in aerospace application, (f) crimped connections in a cockpit of jet plane, (g) electrical power transmission of an automobile, (h) battery connections and, (i) power transmission system in buildings.

A proper terminal-wire crimping mechanism which can properly execute a crimp connection to make electrical reliable and mechanically strong connections in a single operation is still a significant challenge in the electrical industry. Crimping tool is a critical part for a quality crimp. Crimping takes advantage of the properties of metals to achieve electrically and mechanically sound connections. Metals used in crimp connectors, like copper, brass, aluminium, or bronze, are both ductile and malleable.

Figure 2.1 Different application of connector terminals

A metals ductility is the degree to which it can deform under tension, while malleability is a measure of how metal deforms under compression. Crimping involves applying significant compressive forces onto the crimp connector terminal and the wire, so the malleability of each element is an important factor in crimp quality. But ductility plays a role too as both connector and wire undergo significant stretching during the crimping process. As more pressure applies to the connection, metal in the wire strands begins to stretch and flow which loosens and increases contact resistance (Prin et al., 2002).

There are many terminal-wire crimping tools patents (Hashimoto and Kaneko, 2005;

Katou, 2017; Mc Caughey, 1973; Theiler, 1980). But in every patent, there is one standard part that is a “crimping die”, which deforms or squeezes the terminal onto the wire strands to take the shape of the crimping dies when force is applied by using a lever or electrical motorised. Traditional crimping tools not only leaves the marks of the dies over the terminal surface but excessive pressure sometimes leads to the crack formation leading to mechanical fracture.

A properly executed crimp connection is electrically safe, reliable and mechanically robust. Some critical challenges which are faced by cable industries are:

 Improper deformation of wire strands resulting in voids.

 Excessive pressure leads to crack over the terminal.

 The improper pressure of the crimping tool leads to flash and burrs.

 An excessive pressure is leading to fractures over the terminal.

 Non-uniform deformation of the terminal.

 Uneven deformation of wires and a high percentage of voids which affects the pull force results and electrical performance.

As shown in Figure 2.2, executed crimp cross-section showing defects consisting of wire strands and terminal. The most important problem faced by wire crimping industry is the spring back of terminal on tool relaxation which generates a gap between wire strands and terminal contact interface. This increases resistivity and high amount of losses in wiring system (Weddeling et al., 2015).

Figure 2.2 Cross-section of terminal crimped over the copper wire strands

As such electrical connector terminals work at different operating circumstances such as vibration, temperature gradient and different electrical environments that cause fretting corrosion/wear and relaxation of the contact forces. The most common failure mechanisms are surface film formation due to unsealed terminals, relaxation of the contact force due to high temperatures and wear or fretting corrosion due to mechanical or thermal micromotions. Vibrations are often the parameters which limit the lifespan of electrical contacts, but how large the damages become depends among other things on the electrical environments; current, voltage and inductance (Shim et al., 2016).

Therefore, it is essential to develop a new technique for wire crimping which can provide required mechanical strength with minor resistance at the contact interface to minimise the power losses and failure rates. So, that it can benefit the industries to produce reliable,

efficient and long lasting crimp joint. In comparison to conventional crimping tools which are most widely used in industries, EM crimping shows many advantageous like uniform pressure distribution, contactless process, low mold cost, lesser spring back of the material, minimum wrinkling, improved formability, no lubrication, few seconds for process completion, no tool deterioration, improved hardening due to shock pressure waves and good repeatability (Golovashchenko, 2007; Psyk et al., 2011).