INTRODUCTION TO CRMP TECHNOLOGY

INTRODUCTION TO CRIMP TECHNOLOGY
Developed to replace the need to solder terminations, crimping technology provides a high quality connection
between a terminal and a wire at a relatively low applied cost. The methods for applying crimp terminations depend on the application, volume, and range from hand-held devices to fully automated systems.
The application methods include a basic hand tool, a press and die set, a stripper crimper, or a fully automatic wire processing system. However, no matter what method is used, the setup of each tool is critical for achieving a quality crimp.
Today, many OEM companies are using Statistical Process Control (SPC) to continuously improve their crimp
terminations. Crimp termination is a complex process and to ensure consistent quality it is necessary to understand the variability and inter-relational interactions that the technology involves.
Without a thorough understanding of the crimping process, and all the factors that can affect it, the result may not meet expectations. The three key elements in the crimping process are the terminal, the wire, and the tooling.

Terminal
For most applications, it is not economically practical for connector manufacturers to design a terminal to accept one wire size, one wire stranding, and one insulation diameter (UL type) as well as Mil Specification. 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.

Wire
The wire stranding and insulation type can vary widely within one wire size. For example, there is more than 18% more material in an 18 AWG by 19-strand wire than an 18 AWG by 16-strand wire. The insulation diameter of an 18 AWG wire can range from 1.78mm (070") to over 4.57mm (180"). Wire strands can be copper, tinned, over
coated, or top coated. Wire insulation materials, thickness, and durometers vary from application to application.

Tooling
What type of tooling does the application require? Does the application require hand stripping of the wire or does the volume dictate an automatic wire-stripping machine? Does the application and volume require hand tools,press and die, or fully automatic wire process machines? Crimping with a manual hand tool, semi-automatic press and die, or fully automatic wire processor, all involve different levels of variability. The terminal, wire, and type of application tooling all affect the quality of the completed terminations.

Quality Crimps
Quality is something that must be measured by some set of criteria. Four major agencies give test criteria for solderless terminals. They are:
■ U.L. (Underwriters Laboratories)
■ CSA (Canadian Standard Association)
■ NEMA (National Electronic Manufacturers Association)
■ Federal Government Spec - Mil-T-7928

In all of the above standards specific reference is made to the following areas:
■ Copper or brass quality specifications
■ Tin-plating specs type and thickness
■ Smoothness of edges and lack of burrs
■ Firmness of fit between metal and insulation

Then there is a whole series of tests to be performed on the crimp area after the crimp is made:
■ Tensile test
■ Dielectric withstand
■ Salt spray
■ Vibration
■ Heat rise

The most widely used field test for testing the quality of the crimp is the pull test, or tensile test.
The two most widely used measurements are the U.L.and Military Tensile values. See Section 8. Note that the Military is higher than the U.L.

Visual Inspection of OPEN BARREL Crimps

■ Insulation Not Damaged
1. Crimp the insulation just enough (may have a slight indentation to hold the wire in place). If the insulation has been pierced or crushed, the wires inside may have been damaged also.
2. Be sure that the conductor insulation has not been pierced or crushed by the crimp.

■ Insulation Support Crimp

1. Be sure that the insulation barrel tabs are not bent.
2. Form the tabs properly.
3. If one of the tabs is bent, the insulation crimp will not be strong enough to provide the needed stress relief.

■ Wire Visible
1. Be sure that both the wire and the insulation are visible in the window.

2. If only the insulation is visible, you may have crimp insulation in the conductor barrel. (Reject)
3. If only the bare wire is visible, you cannot assume that the insulation has been properly crimped.

4. If there is no insulation support crimp, be sure that wire visible behind the conductor crimp does not extend the diameter of the insulation. If the visible wire exceeds the diameter of the insulation, the terminal could cause a short.