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Within a wire harness are a number of wire ends, or terminations. Previously, those ends needed to be soldered, which added time and cost to a product. Crimping technology was created as a way to still provide a quality connection between terminals, but at a lower cost. Different manufacturers utilize different methods, but across the board, the quality of the crimp rests heavily on properly setting and using the crimping tools.
Several applications can be used for wire crimping, depending on volume of production and the application of the final crimp, but they all come down to three factors, the wire, the terminal, and the tooling. Depending on the job at hand, crimping can be made with a press and die set, a stripper crimper, a basic hand tool, or with a fully automatic wire processing system.
What is the purpose of a crimp?
A crimp is an electrical connector. It allows the connection of two circuits using a device, rather than soldering. It could be a permanent joint between wires, or serve as a temporary link that can be removed. Crimps are often used in wire harness assemblies.
What is the crimping process?
During the crimping process, a metal crimp is placed on the end of the wire. A number of crimp types exist, depending on the application and wire used, but generally, it is a semi-circle, forming a metal cradle for the wire end. A tool is then placed over the metal crimp and squeezed, so that the metal cradle is crushed in two places. First, around the bare wires to make a solid connection, and second, around the wire jacket for a secure hold that can be easily connected to an electronic component. This second feature is why they are used when making a wire harness.
Choosing the proper size of crimp is important, so that all wire strands fit into the crimp. It is important to start with a clean cut at the end of the wires. Some tools strip the proper amount of the outer jacket off of the wire end as part of the crimp process. Others require the user to strip the wire ahead of time. If the jacket is hand-striped, care is taken to not mark or damage the wire. Some professional crimps include what is called a “bell mouth” in their design, which is a flared area located where the bare wires enter the terminal. It keeps the crimp from cutting into the wires.
Why is quality important?
When dealing with electric current, any device or process should be done with care. Crimping is no exception. The proper crimp will be perfectly tight, with no space between the conductor wire strands in the crimp. The crimp will not come off if pulled and it will be relatively resistant to normal fatigue. When a crimp is poorly done, the results can vary from ineffective to damaging. That failure can be costly, especially if it causes damage to the device or wire harness.
If a crimp is loose and “under crimped,” the connector will not make a tight bond between the strands of wire conductors. Normal moisture in the air can get in and around those wires and eventually corrode. After corrosion, there could be resistance in the flow of electricity. That resistance could cause heat, leading to mechanical failure or fire. A loose crimp could also pull away from the wires, causing the device to fail, and potentially exposing current to unintended elements. When a crimp is too tight, the metal is overly stressed and can fatigue easily, causing the crimp to fail or break.
When a good crimp is made, it is not simply a matter of one metal smashed into another to make a connection. The proper tool and process will actually make a “micro cold weld.” That means that when the metal of the crimp piece is being deformed around the wire from its original shape by the crimping tool, the wires are completely pressed together, so they adhere. A good tool will clean the wires in the crimping process, which makes the atoms of the wire act as one, rather than as individual wires. Any contamination around the wires will disturb the process and cause a poor crimp. A cold weld creates a high performing electrical connection that is durable to the elements and long lasting.
Professional crimps, such as those used in a wire harness, are measured with accuracy to small tolerances. With strict guidelines and highly calibrated tools, professional crimps, and the harnesses they are in, can be reliable and safe. Many manufacturers also utilize methods for quality control and process improvement.
If you are interested in learning about a wire harness, contact LoDan Electronics, Inc.