WireProcess Specialties

A customer asked this question during a crimp training session I was performing: What Frequency should you perform Cross Section Analysis on a specific wire and terminal combination?

I will provide a response to this question shortly.  But you need to understand the uses of Cross Section Analysis. And how it applies go the crimping process in general and specifically how it applies to your company.

For those who are new to this technology, a crimp cross section is an image of the inside of a terminated wire. This image shows the result of how the five elements of the terminal crimp process come together.  Valuable information can be pulled from this image. For a more detailed explanation, please read our post Terminal Cross Sectioning: Taking a Peek Inside.

I consider Cross Section Analysis as the Swiss Army Knife of Crimp Quality.  A Cross Section can serve many purposes. First as a base line master image of your crimp process in the initial production phase. This is a report that can be retained for future analysis or provided to a customer for their quality audit purposes.

Second, knowing the basic crimp configuration will provide an indication of how the crimp will perform. If the wire and terminal combination are specified and the crimp height is established by the terminal supplier then what you see in the cross section image is generally how the crimp will look through the crimp process. If the crimp wings are touching (or close to touching) the internal crimp walls or floor, this can cause crimp monitor alarms. Or if crimp wings are forming but not capturing stranding (uneven distribution), this is a sign the crimp could perform poorly in electrical testing or in use in the device it is installed into.

Crimp Wings Touching the floor of the crimp.

Under Compressed Crimp

Next, in process validation. Comparing the current image to the master image previously captured. Checking to see if crimp tool wear or other inconsistencies have caused the crimp profile to change.

Finally as a process improvement tool. When crimp elements come together, the process capability is the sum of these elements. Improving any of the elements (press, applicator, wire, terminal, operator/automation system) can improve the overall process. And that results in a better terminated wire.

So coming back to the frequency of cross section analysis, an initial image is important as a base line review of the crimp profile. Where there are crimp problems (crimp monitor “false alarms, customer complaints etc..) a crimp cross section helps to determine in process issues. This would be done on an as needed basis. In process image capture to compare the current image with the master image would depend on the overall volume of that crimp. Also consider any changes in the elements of the crimp process. For example crimp tool changes or wear or an introduction of a new wire supplier. Even as simple as an applicator removal and re installation at a later date can be a factor in variation.

There are no established guidelines on the frequency of cross section analysis other than what a customer may establish. But the use of cross section analysis as a validation, in process inspection and process improvement tool will only increase in the future. And why not? The information from this analysis can lead to a better quality electrical connection and a lower risk of failed electrical circuits from faulty electrical connections.

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The process of crimping a wire to a terminal is a time tested electrical connection method. But gone are the days of a crimp being processed using low grade wire strippers and crimp tools. A wire lead requires tools and processes which are highly accurate and repeatable. A quality improvement process identifies the processing inputs that are used in an assembly.  A baseline quality level is created and the company works to improve the overall process over time.

The quality of a crimp is the sum total of the process capability of five elements in the crimp process: Wire, Terminal, Crimp Press, Crimp Tooling and Operator.

To improve the overall quality, each individual element must be studied and improved. This article will outline some of the aspects of each element which can cause a less than desirable capability which in turn can affect the overall crimp quality. Also we will cover some of the typical tools used to assess and monitor the whole crimp process. This article deals with the crimp process for terminals on a reel but can equally apply to loose piece terminals.

The Five Elements of the Terminal Crimp Process

Wire.

The wire is one of the material elements of a terminal crimp. Typically process variation from the wire comes from a few external sources but mainly downstream processing steps leading up to the operator presenting the wire to the terminal for crimping.

Overall wire quality is an external source of process varitiation.

• Does the supplier have the necessary quality systems in place to reduce process variation? This includes:
  • individual wire strands
  • overall wire inside diameter
  • insulation material (consistency and overall outside diameter)

Changing wire suppliers or improving material quality can reduce variation.

Downstream processes can impact process variation.

• Wire stripping and handling:
  • Manual wire stripping or incorrectly adjusted wire processing machines. Correct strip length or piece by piece variation.
  • Blade Condition: cut strands
  • Wire ends frayed from handling. Semi-stripped wire reduces damage to the stripped end of a wire.

Terminal.

The other material element of the terminal crimp is the terminal itself. Like wire, supplier selection and supplier process controls are critical. External factors (supplier side) affecting process variation from the terminal and packaging include:

• crimp (wire and insulation) barrels. Straight or misaligned
• terminals feeding straight on the terminal strip.
  • can affect loading position in crimp applicator
• packaging (reel and carton) protecting the terminals from damage from handling and de-reeling.

The selection of the proper wire range to match the terminal crimp sections is very critical. Terminal manufacturers design the geometry of a crimp to match the wire size. This includes the wire and insulation crimp sections. Mismatched terminal to the wire (gauge and insulation OD) is a major cause of process variiation.

Crimp Tooling.

The crimp tooling includes the crimp punch and anvils as well as the feeding mechanism (the applicator). Some of the major factors in process variation are:

• worn crimp tooling
• feed track not adjusted properly, causing terminals not to feed straight.
• wire stop too far forward or backward. Or excess play in the wire stop itself. Causing variation in target position of the wire to the terminal. Failures are typically high insulation (insulation crimped in the wire crimp), low insulation (insulation not fully captured in the insulation crimp). Or inconsistent piece to piece variation.

Crimp Press.

The crimp press is the one processing tool which typically receives the least attention. Even if all of the above (wire, terminal and crimp tooling) are in control, press wear can cause excess variation. Wear on the crank or casting of the press can cause the press shut height and crimp forces to vary. This can create piece to piece variation. In excessive cases of wear, crimp height and pull test can go out of specification which can cause failure of the electrical connection.

Operator.

The operator is the final element of the five. The operator can cause variation due to improper loading of the wire to the applicator and not monitoring the inbound de-reeling of the terminals from the reel, through the applicator to the crimp tool. The operator can check the terminated parts and without controls in place has the power to accept rejected parts. Or not fully inspecting the batch of wires that have been processed. In the case of an automated machine where the wire placement is handled by a robotic arm, the wire placement is generally more consistent (assuming the machine is maintained and the servo motors or pneumatic actuation are providing repeatable wire position). Monitoring the terminal de-reeling and inspecting the crimped wires is still an operator based process.

Operator training and process monitoring can improve process variation.

 Process Improvement Tools

Crimp Height Micrometers

A specially tooled micrometer with a pointed spindle and flat anvil. The spindle is positioned on the underside of the terminal to avoid false readings from the anvil crimp tool impression on the terminal. A pre-process and in-process inspection tool. A model with output capability can provide data for capability studies and for data archive.

Pull Tester

A destructive test. Checking the secure-ness of the crimp. It should be noted that most pull test specifications are for the wire crimp only. The insulation crimp must be peeled back prior to performing the pull test. A pull tester is normally a pre-process inspection tool. Output as described above is a good feature.

Crimp Cross Section

Cutting the crimp in half and viewing inside is becoming a required quality validation process in a growing number of industries. A cross section analysis provides valuable information on strand distribution within the crimp and overall compression analysis. Designed as a pre-production analysis tool as well as validating the crimp after changes to the process (any of the five elements).

Crimp Force Monitor

Statistically speaking, 100% visual inspection is only 80% effective, leaving a high risk of 20% of production not fully inspected. A crimp monitor measures each termination in real time and compares the results with initial samples of terminations inspected and validated for production. All five elements described above are monitored as a whole. Crimp monitors take the decision making process away from the operator and provide a base line for the crimp process as a whole. As a process improvement tool, single improvements to the process will show as an improvement in the variation of the crimp curve. Providing an opportunity to reduce the process tolerances to detect smaller variations. The crimp monitor is a standard in process monitoring tool for most industries. Even without a customer mandate, a crimp monitor is a good tool for in process inspection and process improvement.

Press Analyzer

Calibrating a press to the required shut height only assures capability to the single calibration cycle. Ensuring the press meets a statistically controlled capability is an extension of the calibration process and assures the press can provide the repeatability required. Typically companies calibrate and run capability studies once per year, semi annually or quarterly depending on the volume being processed. Analyzing a press’ shut height and reference forces also allows maintenance personnel to prioritize maintenance schedules.

Summary

Improving the overall quality of a terminal crimp requires an evaluation of all five process inputs. Assuming what previously was acceptable is still acceptable or what is seen on the surface is acceptable under the surface is not a good quality strategy. Implications can be as basic as a circuit failure or as broad as product failure causing damage to property or injuries to the end user. There are real life examples of these conditions occurring which have caused damage to people, property and your company’s reputation. The risks in today’s business conditions are real but can be greatly reduced by adopting and maintaining a comprehensive quality validation, monitoring and improvement strategy.

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