Introduction
According to Wikipedia, "Crimping is joining 2 pieces of metal or other ductile material (usually a wire and a metal plate) by deforming one or both of them to hold the other. The bend or deformity is called the crimp."
Crimping is a good replacement to solder terminations. It provides a very good quality connection between a wire and a terminal at a comparatively low cost. Which method to use for applying crimp terminations depends on the application and volume. The methods range from handheld devices to fully automated systems. [1]
If we don't have a good understanding of the crimping process, and the factors that can affect it, the result may not be satisfactory. [2]
The three key elements in the crimping process are the terminal, the wire, and the tooling.
Terminal
For quite a number of applications, it is economically impractical for connector manufacturers to design terminals to accept a single wire size, a single wire stranding, and a single insulation diameter (UL type) as well as Mil Specification ( United States defense standard, often called a military standard). Most terminals accommodate many wire sizes, stranding, and a range of insulation diameters, and the terminals are designed to meet acceptable levels over this entire range. [3]
Wire
The wire insulation type and stranding can vary a lot within one wire size. Wire strands can be made of copper, can be tinned, over coated, or top coated. Wire insulation thickness, materials and diameters are different for different applications. [4]
Additional Information AWG - American Wire Gauge is a standardized wire gauge system used since 1857 predominantly in North America for the diameters of round, solid, nonferrous, electrically conducting wire. [5]
Wires are of two types: [6]
- Solid: Solid conductors consist of a single strand of metal. It is easy to terminate these than stranded conductors. These wires are also mechanically tough. They are inexpensive. However, they have a major disadvantage: Lack of flexibility.
- Stranded: Stranded conductors consist of multiple metal strands bunched together in any number of configurations. They overcome the drawback of solid conductors because they are much more flexible. The higher the strand count, the more is the flexibility of the wire. While this can increase the cost, it is quite necessary for any wire or cable that will need to withstand any kind of flexing, or any other movement.
A finely stranded wire improves crimped joint performance. A wire made up of a few larger sized strands will tend to act as a solid wire. There are some stranded wire crimp configurations which are unsatisfactory for solid wire. More deformation are essential to be imposed in order to form wire and barrel into a solid mass. Finer strands, on the other hand, will more readily fill the inside corners of the crimp shape and more evenly distribute the forces of the crimp. [4]
Procedure
Prepare the Wire
- Check the stranded wire to see if any strands have loosened and expanded to be larger than the wire and the insulation together. If this has occurred, twist the wires to the size they were before they were stripped.
- Check the insulation to ensure that there has been a nice clean cut. Wires with damaged insulation should not be used.
Setup and Operate a Hand Crimp Tool
- Ensure that the hand tool is designed to crimp the size wire and the proper terminal shown on the Hand Crimp Tool Specification sheet.
- Place the terminal in the tool.
- If using a locator, lift the locator and insert the terminal in the proper nest with the barrel up and against the locator bar. Release the locator blade to hold the terminal in position.
- Insert the wire.
- Squeeze the handle.
- Inspect for proper crimp location.
Importance of Proper Crimping
Proper attachment of terminal to the wire is critical. Mechanical as well as electrical connections are important - The result of a properly crimped joint is a reliable mechanical and electrical connection.
The mechanical connection is the crimping of the terminal to the conductor. It must be secure enough not to vibrate loose or to be pulled off through normal use.
The electrical characteristics are just as important. The major concern is the amount of electrical resistance caused by the mechanical joint which determines the crimped joint’s ability to conduct current.
One indication of the importance of proper crimping is evidenced in a study for the Space Shuttle Program that traced 28% of all defects to improperly assembled wiring and connectors.
Tips for Crimping
Step 1: Choosing the Wire
Depending on your application, you may or may not have a choice on the wire to use. Firstly do not use solid cored wire, and if you want a reliable job definitely avoid solid wire.
Step 2: Determine the wire size
This may be listed in a number of ways, the most common being AWG (American Wire Gauge)(e.g. 16 AWG), Cross sectional area in square mm (e.g. 1 sq mm) or strand and diameter count (e.g. 32/0.2).
If buying new wire, the size will be listed on the reel or packet.
Many wires are now printed into the insulation with this information repeated along the length. Insulation diameter is important for the most reliable crimps as it affects how the rear of the crimp grips the wire, however as long as you use standard wires, then this should not give you a significant issue.
Step 3: Choosing the Crimp Terminal
Now you know what wire size you have, you will also need to work out what you need to connect to. There are many, many variations of crimp, but there are a handful of very common ones.
The terminal must be of sufficient cross section size and conductive material that it is as good as an electrical conductor
The surfaces of the wire and terminal that are pressed into contact in the crimp must be clean and free of heavy, non-conductive films such as oxides, sulfides, and similar substances
Pre-Insulated Terminals
If using pre-insulated terminals have a heat sleeve to grip the wire insulation.
All terminals are sold with a defined wire size range- this should be listed on the packet, but if not and you are using pre-insulated parts you can tell by the colour of the sleeve.
The generally adopted standard is:
- Red Insulation: 0.5-1.5mm2 / 22-16 AWG
- Blue Insulation: 1.5-2.5mm2 / 16-14 AWG
- Yellow Insulation: 4.0-6.0mm2 / 12-10 AWG
There are other colours around, but you are unlikely to come across these unless you are doing industrial, aerospace or military work.
Step 4: The Crimping Process
See https://www.robotshop.com/blog/en/how-to-crimp-connectors-4225.
You can also watch a video tutorial here: https://www.youtube.com/watch?v=kjSGCSwNuAg
References
- http://www.molex.com/pdm_docs/ats/TM-640160065.pdf
- https://www.thomasnet.com/articles/machinery-tools-supplies/types-of-crimpers
- https://www.burndy.com/docs/default-source/PDF's/crimp-booklet_finalforprint_07162013.pdf?sfvrsn=0
- http://www-public.tnb.com/shared/inst/ta01977-tb2.pdf
- http://www.mouser.com/ds/2/276/640031200-588377.pdf
- https://www.youtube.com/watch?v=_ClY1pssIQs - Crimping Made Easy-Do watch
- https://www.youtube.com/watch?v=nEjbFngw6DY
If you are done reading this page, you can go back to Mechanical Subsystem.
- ↑ https://www.shearwater.com/wp-content/uploads/2012/08/qual_crimp.pdf
- ↑ https://www.mouser.com/ds/2/276/TM-638000029-588559.pdf
- ↑ https://www.rbracing-rsr.com/downloads/wiring_pdfs/crimp_molex.pdf
- ↑ 4.0 4.1 https://media.digikey.com/pdf/Data%20Sheets/Molex%20PDFs/Quality%20Crimp%20Handbook.pdf
- ↑ https://en.wikipedia.org/wiki/American_wire_gauge
- ↑ http://www.awcwire.com/conductor-stranding