Crimping & Crimp Quality - Issue 2
20 years ago, the opinion amongst experts was that crimping would be replaced by some new connection technology. However, it seems that in wire processing, "those condemned to die, live longer," as crimp processing remains unchallenged despite numerous new types of connection technologies, and the end is not in sight.
Crimping, also known as terminating, can be understood as the gastight connection of a wire and a terminal. There are an almost infinite number of different crimp terminals available on the market, but they all have one thing in common: they are joined to a wire through a mechanical deformation process (“crimping”).
Banded or Loose?
Terminals are either sold as banded (connected together on a carrier strip) or as loose piece terminals. Banded terminals are simpler to handle as they can be easily fed from a terminal reel and processed on semi- or fully automatic machines.
single-banded, carrier strips front
single-banded, carrier strips in the middle
double-banded, carrier strips front and back
With loose terminals, there are no carrier strips. Loose-piece terminals must be brought into the correct position either manually or by a vibratory feeder. Due to their more demanding handling, loose-piece terminals are not used as often as banded terminals.
Open or Closed?
Both banded as well as loose-piece terminals can be open- or closed-barrel type terminals. This term "open" or "closed" relates to the design of the terminal. With closed barrel terminals, such as insulated wire end ferrules or insulated quick-disconnects, the terminal is shaped like a fully closed cylinder. The stripped wire must be inserted into the circular crimp barrel from the open end of the terminal. Open barrel terminals are shaped like the letter "U," allowing the wire to be moved downwards from the top into the crimp barrel. As open-barrel terminals are easier to automate, they are used most often in mass production.
Side- or Rear-Feed?
With open-barrel, banded terminals, a deciding factor in the selection of an appropriate processing medium is whether the terminals are connected on the carrier strip end-to-end or side-by-side. The arrangement on the carrier strip determines the type of feed into the crimping press as well as the transport direction of the crimping tool (from left, right or rear). Manufacturers of crimping machines and tools, such as Schleuniger, offer different variants of their equipment to be able to process virtually all terminal types.
Single or Double?
Other than open or closed, and side or rear feed, banded crimp terminals can also be single-banded or double-banded, depending on the number of carrier strips between the terminals. The position of the carrier strip between the terminals, as well as the number of carrier strips, determines the design of the crimping tools. The majority of crimp applicator manufacturers have focused on the most common terminal types. However, the Schleuniger crimping specialists follow a different strategy: from standard terminals to complex terminal types, Schleuniger offers machines and tooling to process every terminal. For instance, the Uni-A crimp applicator, for cable cross-sections up to 6 mm², is available as a side- and rear-feed applicator, with mechanical or pneumatic feed, for single- and double-banded terminals of different types.
In addition, the Uni-A and Schleuniger crimping presses, such as the UniCrimp 200 (with standard Split Cycle Function), can also process closed barrel terminals (e.g. insulated wire end ferrules) or Mylar banded terminals. In addition to the Uni-A and FlexoCrimper (up to 6 mm²) universal crimp applicators, the Schleuniger range of applicators also includes the HeavyCrimper applicator up to 35 mm² as well as special crimping tools for loose terminals up to 50 mm².
Wire and Insulation Crimp?
As a rule, with banded terminals, two connection procedures take place simultaneously – the wire crimp and the insulation crimp.
Insulation and wire crimp
The continual development of connection technology has led to many new crimp connections types, such as the 3-zone crimp for coaxial cable. The wire crimp forms the mechanical-electrical connection between the stripped inner wire (e.g. stranded conductor) and the terminal. It must be gas-tight. The insulation crimp should absorb influencing forces such as vibration or tension so that they do not affect the wire crimp. The insulation crimp forms a purely mechanical connection between the terminal and the insulation of the cable. Therefore, it is important that the insulation is not damaged during the insulation crimp process.
B-Crimp, O-Crimp or U-Crimp?
The final shape of the terminal after the crimping process has led to the relatively common terms “B-crimp”, “O-crimp” and “U-crimp.”
Different types of insulation connections
Other types of crimps, which are used less frequently, include the 4-point crimp, the hex-crimp and the trapez-crimp. After the stripped wire is inserted into the terminal, the terminal and wire are compressed through terminal-specific parts (known as tooling) of the crimp applicator during the crimping procedure. The characteristic shape, which has led to the name, can be seen in the cross-section of the crimped terminal and wire, in both the insulation crimp and the wire crimp.
Wire Crimp
The most common wire crimp used for stranded wires is the B-crimp. When the ears of the terminal are formed during the crimping process, the individual wire strands move symmetrically within the terminal inner space due to the symmetry of the crimped terminal shape. A gas-tight connection is easier to achieve for stranded conductors with a B-crimp than with an O-crimp. In contrast, crimping of solid wires cannot be gas-tight with a B-crimp since there are no individual strands that can move during the crimping process. Therefore, the wire crimp for solid wires is generally carried out as an O-crimp.
Different types of wire crimp connections
Insulation Crimp
As the insulation crimp serves exclusively to absorb influencing forces on the wire crimp, the challenge is to form a connection to the insulation without damaging it. In this case, a B-crimp allows very high connection stability but damages the insulation to a certain degree. The danger of damage is greater than with an O-crimp or U crimp, where the crimping ears only surround, rather than penetrate, the insulation.
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