An electrical crimp is a type of solderless electrical connection which uses physical pressure to join the contacts.
Crimp connectors are typically used to terminate stranded wire.
History
The technique of soldering wires has remained common for at least a century, however crimp terminals came into use in the middle of the 20th century. In 1953, AMP Incorporated (now TE Connectivity) introduced crimp barrel terminals, and in 1957 Cannon Brothers experimented with machined contacts integrating crimp barrels. During the 1960s, several standards for crimp connectors were published, including MS3191-1, MS3191-4 and MIL-T-22520. In 2010, the predominant standard for crimp connectors changed to MIL-DTL-22520.
Characteristics
The benefits of crimping over soldering and wire wrapping include:
A well-engineered and well-executed crimp is designed to be gas-tight, which prevents oxygen and moisture from reaching the metals (which are often different metals) and causing corrosion Because no alloy is used (as in solder) the joint is mechanically stronger Crimped connections can be used for cables of both small and large cross-sections, whereas only small cross-section wires can be used with wire wrapping Crimping is normally performed by first inserting the terminal into the crimp tool. The terminal must be placed into the appropriately sized crimp barrel. The wire is then inserted into the terminal with the end of the wire flush with the exit of the terminal to maximize cross-sectional contact. Finally, the handles of the crimp tool are used to compress and reshape the terminal until it is cold-welded onto the wire.
The resulting connection may appear loose at the edges of the terminal, but this is desirable so as to not have sharp edges that could cut the outer strands of the wire. If executed properly, the middle of the crimp will be swaged or cold-formed.
More specialized crimp connectors are also used, for example as signal connectors on coaxial cables in applications at high radio frequencies (VHF, UHF) . These often require specialised crimping tools to form the proper crimp.
Crimped contacts are permanent (i.e. the connectors and wire ends cannot be reused).
Theory
Crimp-on connectors are attached by inserting the stripped end of a stranded wire into a portion of the connector, which is then mechanically deformed by compressing (crimping) it tightly around the wire. The crimping is usually accomplished with special crimping tool such as crimping pliers. A key idea behind crimped connectors is that the finished connection should be gas-tight.
Effective crimp connections deform the metal of the connector past its yield point so that the compressed wire causes tension in the surrounding connector, and these forces counter each other to create a high degree of static friction which holds the cable in place. Due to the elastic nature of the metal in crimped connections, they are highly resistant to vibration and thermal shock.
Two main classes of wire crimps exist:
Closed barrel crimps have a cylindrical opening for a wire, and the crimping tool deforms the originally circular cross section of the terminal into some other shape. This method of crimping is less resilient to vibration. Open barrel crimps have "ears" of metal that are shaped like a V or U, and the crimp terminal bends and folds them over the wire prior to swaging the wire to the terminal. Open-barrel terminals are claimed to be easier to automate because of avoiding the need to funnel stranded wire into the narrow opening of a barrel terminal.
In addition to their shape, crimped connectors can also be characterized by their insulation (insulated or non-insulated), and whether they crimp onto the conductor(s) of a wire (wire crimp) or its insulation (insulation crimp).
Shapes
C crimp
D crimp
F crimp (a.k.a. B crimp) O crimp W crimp Overlap/OVL crimp Oval (confined) crimp Four-Mandrel crimp Mandrel (crescent) crimp Mandrel crimp-narrow (indented) Hexagonal crimp Mandrel (indent) crimp Square crimp Trapezoidal crimp Trapezoidal indent crimp Trapezoidal crimp front Tyco crimp Western crimp
Applications
Crimped connections are common alternatives to soldered connections. There are complex considerations for determining which method is appropriatecrimp connections are sometimes preferred for these reasons: