s crimped on to
coaxial cable. The bottom middle cable is missing its crimping collar. 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. Stripped wire is inserted through the correctly sized opening of the connector, and a crimper is used to tightly squeeze the opening against the wire. Depending on the type of connector used, it may be attached to a metal plate by a separate screw or bolt or it could be simply screwed on using the connector itself to make the attachment like an
F connector.
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. 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 • W crimp • Overlap/OVL crimp • Mandrel (indent) crimp • Square crimp • Wire pin Crimping is also a common technique to join wires to a multipin connector, such as in
Molex connectors or
modular connectors. Circular connectors using crimp contacts can be classified as
rear release or
front release, referring to the side of the connector where the pins are anchored: •
Front release contacts are released from the front (contact side) of the connector, and removed from the rear. The removal tool engages with the front portion of the contact and pushes it through to the back of the connector. •
Rear release contacts are released and removed from the rear (wire side) of the connector. The removal tool releases the contacts from the rear and pulls the contact out of the retainer. Crimp connections are used typically to attach RF connectors, such as
BNC connectors, to coaxial cables quickly, as an alternative to
soldered connections. Typically the male connector is crimp-fitted to a cable, and the female attached, often using soldered connections, to a panel on equipment. A special power or manual tool is used to fit the connector.
Wire strippers which strip outer jacket, shield braid, and inner insulation to the correct lengths in one operation are used to prepare the cable for crimping.
Quality A crimped connection will only be reliable if a number of criteria are met: • All strands have been deformed enough to cold-flow into the terminal body • The compression force is not too light, nor too strong • The connector body is not overly deformed • Wires must be in solid working condition, cannot have scrapes, nicks, severing or other damages • Insulation should not show any signs of pinching, pulling, fraying, discoloration, or charring • Large voids are not left inside the crimp (caused by not enough wire inside the connector) • The wire should have as many strands as possible, so that a few damaged or uninserted wires will not adversely affect the crimp density, and thus degrade the electrical and mechanical properties of the connection. Micrographs of the crimped connections can be prepared to illustrate good and bad crimps for training and quality assurance purposes. The assembled connection is cut in cross-section, polished and washed in nitric acid to dissolve any copper dust that may be filling voids leading to a false indication of a good crimp.
Terminal insulation colors == Other uses ==