A wire harness has a few basic qualities, critical to performance and longevity of the device it is installed into. Low electrical resistance through the harness reduces heat and improves overall electrical performance. But as important is the ease of installation and the effect installation may have on electrical performance.
As we consider the critical elements of wire harness assembly and in particular the wire to terminal crimp process, a number of variables can make or break the performance of the most important aspect of a wire harness. Bend Angle is one of those variables which is receiving more scrutiny as we work to improve overall wire harness quality.
So what is Bend Angle?
Bend Angle is the condition caused by the crimping of the terminal. The pressure on the terminal from the press (and crimp applicator) causes the terminal to extrude outward. Extrusion is a natural occurrence of material (wire and terminal) being formed under pressure. The terminal actually can lengthen slightly during the crimp process. But excessive pressure can also cause the terminal to bend upward, in the shape of a banana. The banana shape is a measured attribute which is called Bend Angle.
So why is Bend Angle critical to the wire harness? It is important for two primary reasons.
First in the fit and function of terminals loaded into a multi-wire connector. When terminals are not straight, there can be mis-alignment between the pin and receptacle. On it’s own, one matching terminal pair can be harder to mate when the terminals are fixed in a housing. Consider the compounding effect of inserting multiple (unmatched) mating pairs in a housing. This can cause installation issues for the customer who is installing the wire harness.
Second is the potential of high electrical resistance at the mating point between the two terminals. We work to reduce electrical resistance of the terminal crimp by the proper crimp and crimp tool design along with a wire range rated for the crimp. Even with close attention to the proper wire/terminal match and recommended crimp height, high resistance can occur at the mating point.
It should be noted that bend angle is not as a factor with terminals that are not encased in a connector. More ‘forgiveness” in installing terminals that are not forced to mate in a confined space.
Reducing Bend Angle.
As mentioned extrusion during the crimp process is normal and some bend angle can occur. But ultimately reducing bend angle is important. Let’s consider some of the factors that can cause bend angle.
- Crimp Height Too Low.
- Worn Crimp Tools.
- The Wrong Crimp Tools.
- The Wrong wire size for the terminal.
Not only can these issues cause bend angle, they can also affect the electrical performance of the crimp.
Measuring Bend Angle and Parallelism.
There are actually two possible measurements: Bend Angle and Parallelism.
Bend Angle is measured from the top surface of the conductor crimp to the terminal body. Bend Angle can be measured from the top and side as pictured.
Bend Angle Side View
Parallelism is a “go/no go” measurement. Parallelism ensures all points are within a tolerance window in relation to a datum point. In the case of a terminal, measuring parallelism of both the insulation and wire crimp is possible. The datum line is placed on the conductor body and a set of parallel lines are placed on the wire and insulation crimps. The wire and insulation crimp must be enclosed within the parallel lines.
Bend Angle and Parallelism dimensions are established by the terminal supplier. And by the customer when supplier dimensions are not available
Bend Angle is an emerging issue which is expected to be introduced into crimp standards such as USCAR-21. Regardless the existence of a mandated standard of not, the condition exists for multi pin/receptacle connectors. If high connector insertion or electrical resistance are an issue, perhaps evaluating bend angle is a variable that could be checked.
Need to measure Bend Angle? We are prepared to help. Whether in house capability or ad hoc requirements, we can supply your own solution or provide this as a service through Crimp Quality Solutions. Connect Your Way to WPS to find out more.