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Crimping – a permanent connection

Suitable precision tools ensure reliable connections

 
Crimping requires not only a tradesman's skill, but also a suitable crimping tool and the appropriate contacts. The requirements for crimping connections are specified in international standards and guidelines, e.g. DIN EN 60352-2. An essential quality factor is the tensile strength achieved in the connection, as well as the avoidance of typical crimping errors. However, caution is required: every conductor does not fit every contact and no single tool is suitable for all tasks.
Crimping is no mean feat. The extremely wide range of tools alone indicates the multi-faceted usage: there are crimping tools for wire-end ferrules and crimping tools for other contacts, including for cable-lug sleeves and cable-lug connectors with pre-rolled crimping claws, for PVC, PC and polyamide insulated connectors, for uninsulated cable lugs and connectors, for fibre-optic cables, for coaxial connectors such as BNC, TNC and N plugs and for SUB-D contacts. Pressing tools or special crimping tools are used when handling special cables.

Crimping – high quality according to standards

Crimping generally binds two components permanently. According to the function triad - cutting, stripping insulation and crimping - a conductor end can be crimped with the matching contacts or wire-end ferrules once it has been stripped.

The quality of a crimp connection calls for more than just manual skills; indeed, professional tools and high-quality materials are also crucial factors

Previously, conductors and contacts were securely connected via soldering. Today, crimping has extensively replaced soldering as the leading method: crimping creates a homogenous, non-detachable connection element. A high quality tool helps here. The result is an electrically and mechanically secure and reliable connection. There are numerous mechanical crimping tools available on the market. They make handling easier and more secure, offer an integrated ratchet with release mechanisms and guarantee optimum processing quality.

Various international standards and guidelines must be taken into account for crimping connections: 1) DIN EN 60352-2: solderless connections – Part 2: Crimp connections – general requirements, test procedure and advice on use, 2) DIN EN 2242: Testing Tools for Crimping Electrical Wires, 3) MIL-DTL-22520 (replaced by SAE-AS-22520): Crimping tools, Wire Termination, General Specification, 4) ECSS-Q-ST-70-26C (formerly: ECSS-Q-70-26A ESA PSS-01-726): Crimping of high-reliability Electrical Connections as well as WHMA/IPC-A-620: Requirements & Acceptance for Cable & Wire Harness Assemblies.
It is impossible for there to be just one tool that can be reliably used for every combination of conductor and crimping material, given the large number of different cables and wires. Moreover, it is not the cheapest or most expensive tool which determines the quality of the connection, but the most-appropriate tool. Nevertheless, manufacturers with many years' experience and who know the material are able to use just one tool for a number of different applications, or integrate different functions into equipment. During selection, you should note that even if the conductor and the crimping material – in themselves – conform to the respective applied standards, this does not mean that the standard requirements will be achieved for the crimped products. This is because the individual manufacturing tolerances of conductors and crimping materials do not allow for every conductor to be processed with every contact. Therefore, the combination of conductors, crimping materials and crimping tools must always match up, which is made complicated by the large volume of products on the market. Consequently, the material must be defined and the crimping result tested. You must always ensure that the test and subsequent use of the tool take place in the same conditions. Consequently, the recommendation in DIN EN 60352-2 is to source tools and contacts from a manufacturer. Consistent high quality can only be ensured in this way. Otherwise, it is the user who is responsible for the quality. Therefore, users should ensure that the manufacturer complies to verifiable international standards and currently applicable guidelines.
Crimping wire-end ferrules – the devil is in the detail
We recomend manufacturing an optimal crimp with different cross-sections as a sample. The following information can be used to visually evaluate a crimp connection regardless of whether manual tools or crimping machines are used: the conductor insulation must be pushed into the plastic collars. The sleeve tube must be completely filled by the conductor. The conductor should protrude around 0 to 0.5 mm from the sleeve tube, depending on the cross-section.

Thanks to its rotatable crimp insert, Weidmüller's PZ 6 Roto L crimping tool can be used as space conditions permit. As an optional feature, cables and wire-end ferrules can be integrated in the tool from the front or side

A series of errors can occur when crimping wire-end ferrules: cracks can form along the longitudinal edges and stamp marks, the wire-end ferrules can split open, unsymmetrical crimping shape, severe burring along the longitudinal edges, ferrules not filled by the conductor, single wire ends can be pushed back / protrude from the collar, single conductors squeezed, plastic collars damaged by crimping stamps, conductor insulation not pushed into the plastic collar, wire-end ferrules bent longitudinally after crimping.

Note on testing: after the initial connection in any terminal belonging to the conductor cross-section (with tightening torque according to IEC 60947 - 1), the sleeve may not split open.

Wire-end ferrules are not only used because of the professional, optical appearance, but mainly because of the long-term quality of an electrical connection.

Manufacturers such as Weidmüller offer a wide range of wire-end ferrules: wire-end ferrules with plastic collars in standard colour codes or those according to DIN 46228, further wire-end ferrules in reel packaging with plastic collars - also in rolls, twin-shaped wire-end ferrules with plastic collars and finally, wire-end ferrules without plastic collars.

Wire-end ferrules with plastic collars: gas-tight, electrically and mechanically flawless connections

Using the appropriate crimping tools, such as the Weidmüller PZ series and the corresponding wire-end ferrules with plastic collars, guarantees that flawless gas-tight, electrical and mechanical connections are created.  Crimps with Weidmüller crimping tools and wire-end ferrules according to DIN 46228, T 4, correspond to DIN IEC 60512-6 requirements. They are gas-proof and precisely formulated - the user can verifiably assume a "gas-proof press connection".

As no gas-proof tests are required or anticipated as standard for wire-end ferrules and the term 'gas-proof is also not clearly defined (test atmosphere/criteria), a test for corrosion resistance according to DIN 50018-KWF 2.0 S (test in a condensation alternating climate with sulphur dioxide contained in the atmosphere) has been defined for Weidmüller wire-end ferrules. The evaluation of the "gas-proof press connection" is carried out using a voltage drop measurement according to IEC 60947-7-1, before and after the corrosion test (limit value 3.2 mV or change <=50 %) using a screwed or screwless feed-through modular terminal. If the voltage drop moves within the limit values, a 'gas-proof press connection' can be assumed.

Why use wire-end ferrules with or without plastic collars? Firstly, wire-end ferrules with plastic collars provide significant advantages during assembly. This makes it easier to insert the crimped conductor into the clamping space. Furthermore, there is a secure contact, even when the conductor is repeatedly clamped and unclamped, making it suitable for revisional operation. In addition to this, pre-assembled conductors protect against splaying wires in uninsulated conductors. Wire-end ferrules with plastic collars also offer protection against bending, and the conductor cross-section is easier to identify thanks to the collar colour of the wire-end ferrule. Last but not least, the collar protects against contact being accidentally made between live parts. Secondly, wire-end ferrules with plastic collars offer the increased contact security of a flexible conductor with the use of a modular terminal. From a long-term perspective, a wire-end ferrule has nearly the same volume resistance as a solid conductor without a wire-end ferrule.

Conductors with wire-end ferrules continue to prove to be advantageous as they behave electrically, almost like a single-stranded conductor.  A long-term test carried out by Weidmüller shows that the voltage drops in single-stranded conductors remain significantly below the permitted value according to VDE 0611, even after years of use – despite partly aggressive climates.

International application options

Not all crimping connections with wire-end ferrules are suitable for international use. The North American regions and Canada in particular have specific requirements – they are not permitted to be used without the appropriate certificate.

However, European and Asian markets also each require their own certification. Weidmüller produces the UL certification and the already available CSA-US, DIN/VDE and VG certifications for its crimped, insulated wire-end ferrules.

 

The connection is certified as a whole, not as individual parts. UL - Underwriters Laboratories thereby certified the system, i.e. the wire-end ferrules together with the manual tools or crimping machines used. This certification means that Weidmüller can increase the high product quality for its customers and opens up new markets in the NAFTA regions (North America, Canada, Mexico). Wire-end ferrules with plastic collars are certified in individual packaging with the cross-section ranges 0.25 mm² to 50 mm² (AWG 26/1) - with the exception of 35 mm² (AWG 2) – together with the appropriate manual tools and crimping machines. UL certification does not just open up export-oriented companies in the North American and Canadian regions, the certified, solderless connections with crimped wire-end ferrules also now offer significant competitive and quality advantages in European and Asian markets. The UL certification is only valid if the wire-end ferrules can be processed with Weidmüller manual tools or crimping machines from the tool list.

There can be a wide range of consequences, should crimping connections fail. A thermally damaged contact can be put down to the incorrect base material or coating being used.

The UL certification for crimped, insulated wire-end ferrules means that Weidmüller has opened up a high number of possible applications for use around the world. Wire-end ferrules, manual tools and crimping machines, as an overall system, are approved

Corrosion can also strain crimping contacts. In order to ensure a reliable, durable crimping connection, users should define their area of application and requirements profile in advance. They should also pay attention to the contact description and the process standard / manufacturing documents (i.e. tool data sheet) during selection. It is well known that the quality of a crimping connection depends on personnel, contacts, cable / conductor as well as the stripping and crimping tools. Weidmüller does not just offer users assistance with high-quality tools and materials, but also provides comprehensive support. In addition to its new PZ 6 Roto L crimping tool, Weidmüller also provides KT8 quality tools, for example, to make cutting copper and aluminium cables easier, stripping tools for every type of cable and conductor, as well as a comprehensive selection of wire-end ferrules and cable and conductor connections. Weidmüller supplements detailed, technical data material with multimedia information, such as a wide range of videos about crimping and the handling of tools, and thus provides the equipment required for creating long-term, durable connections.