Headroom: Understanding Crimp Sensitivity

Last month we introduced Crimp Force Monitoring: Optimizing Crimp Performance. The CFM Cycle as described is a real situation that a number of companies find themselves in. Optimizing the crimp process can help to exit the CFM cycle.

A terminal crimp as simple as it appears, involves several inputs. Wire, terminal, crimp tooling, the crimp press and operator (bench) or automated machine are all factors which can directly affect crimp quality and ultimately the performance and longevity of the product the wiring is installed in.

Headroom analysis is a valuable indicator of Crimp Sensitivity. Headroom isolates the wire and terminal and the match between the two.

Headroom Defined.

Headroom is the difference in peak force between crimping the wire with and without the wire. Headroom is typically expressed as a percentage. For example headroom of 85% means the wire represents 15% of the total peak force of the wire and terminal. The higher the headroom percentage, the more sensitive the crimp is for detecting small defects such as strands missing in the crimp. Conversely, the lower the percentage of headroom, the less sensitive the crimp process is.

What Can affect Headroom?

The terminal crimp size in relationship to the wire size is the main factor in overall headroom. If the majority of force is used to form the terminal only, then there is very little margin to add the force of the wire.

It is important to note that a wire of the same gauge but different strand count/strand thickness measure similar area. So headroom percentages are similar. But the strand count and individual strand thickness can affect the amount of strands a Crimp Monitor  (CFM) can detect that are missing from the crimp. Here a few examples of headroom with different wire sizes and strand counts.

Crimp with Wire

Crimp without Wire

7 Strand Wire: Average Peak Force (wire and terminal) is 6.78 (kn). Average Peak Force (Terminal Only) is 3.82 (kn). Headroom is: 6.78 – 3.82/6.78 = 43.7%.

  • Each Strand represents 6.24% of the wire portion of the crimp. Using a +,- 3% CFM tolerance, this means the CFM can detect one or more strands missing.

19 Strand Wire: Average Peak Force (wire and terminal) is 10.9 (kn). Average Peak Force (Terminal Only) is 7.36 (kn). Headroom is: 10.9 – 7.36/10.9 = 32.5%.

  • Each Strand represents 1.71% of the wire portion of the crimp. Using a +,- 3% CFM tolerance, this means the CFM can detect two or more strands missing.

26 Strand Wire: Average Peak Force (wire and terminal) is 4.52 (kn). Average Peak Force (Terminal Only) is 2.70 (kn). Headroom is: 4.52 – 2.7/4.52 = 40.3%.

  • Each Strand represents 1.55% of the wire portion of the crimp. Using a +,- 3% CFM tolerance, this means the CFM can detect three or more strands missing. And randomly detect two strands.

These are three examples of headroom calculations. Each application will be different depending on the terminal crimp profile and wire.

It should be noted that the ability of a CFM to detect small variations is greatly affected by the capability of each input in the crimp process. What may appear to be a “false reading” on a CFM is actually variation observed by the CFM compared to the reference samples. For example, Press Shut Height or Crimp Force can cause variation when all other inputs are in control. So in some cases, it may not be possible to reduce the CFM tolerance to a lower percentage due to variation in one or more process inputs.

The terminal design can affect headroom. The overall crimp profile is affected by the end use of the terminal. In some cases the terminal may require a thicker base material and that can translate into more material mass being crimped. Making headroom less sensitive.

Headroom is one tool used to Optimize Crimp Performance. The CFM-Lite CFM for Bench Presses is from C&S Technologies. This is a powerful tool for not only monitoring the crimp process but helping to troubleshoot crimp applications. Headroom analysis is a part of the CFM-Lite platform.

C&S CFM-Lite

Crimp Performance Optimization is part of Crimp Quality Solutions, end to end support for the terminal crimp process. For more information on how we can support your crimp process or the CFM-Lite, Connect Your Way to WPS.





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