Companies make countless decisions every day. There are micro decisions affecting short-term operations and macro decisions affecting the company’s big picture over the long term. Whether micro or macro, good business decisions are made using factual information. They should be based on objective analysis and free of subjective influence.

That advice is no less valid when assessing the performance of your terminal crimping process. You need objective evidence to determine if your equipment and operators are producing quality terminations. “Objective evidence” can apply to a wide range of situations and will serve a basis for effective decisions. “Objective evidence” is defined as: “Information based on facts that can be proved through analysis, observation and other such means of research.” Objective evidence will ensure that the actions taken from decisions will cause positive results.

How can you gather objective evidence about the performance of your wire termination process? Here are some questions to start with:

Material verification. Surprisingly, introducing the wrong materials into the production stream is a common cause of defects and rework. Hopefully, such a mistake is caught before the finished product leaves your facility. It’s a major issue if it’s caught by the customer. Is your system set up to eliminate the possibility of employee error when picking materials for production?

Applicator setup. Has the applicator been prepared for production? Was the applicator inspected after the last production run? Is the tooling capable of producing crimps that meet quality specifications? Has the applicator been installed correctly?

Press setup. Is the press set to the proper shut height? Variation in press force and shut-height can effect crimp quality. Dynamic measurement of these variables provides an accurate method of analysis for press capability.

Crimp measurements. Are you following the “recipe” for each terminal and wire combination? The recipe, or defined measurements, for crimp validation include wire crimp height, crimp width, pull force and visual factors. Pull force data alone is not enough to verify crimp quality. A crimp that passes the pull force test can still have unacceptably high electrical resistance. Crimp height is the primary method terminal suppliers specify to measure crimp quality.

Remember, it’s not enough to ask good questions. Acting on the answers to those questions is critical for managing a system of people, processing equipment and process monitoring tools.


Never Assume

Ensuring that your preproduction validation process continues into production will effectively reduce the chances of nonconforming assemblies leaving your production facility. However, assuming that everything is working merely because you implemented a new monitoring process can lead to unacceptable outcomes, including rework, customer returns and product recalls. Such outcomes can be costly, in both monetary and non-monetary ways.

By itself, a crimp-force monitor (CFM) will not solve your crimping problems nor will it guarantee nonconforming crimps. It can only go by the tolerance thresholds you input. Set the tolerances too wide, and you’ll run the risk of producing nonconforming crimps. Set them too narrow, and you could scrap otherwise good parts.

Several factors can affect a CFM’s ability to keep an eye on your crimping process. The terminal-to-wire match is one factor; head room can influence the sensitivity of a CFM. Equipment condition is another.

To determine if the thresholds for crimp defect detection are acceptable, test the CFM with sample errors, such as missing strands. If it can’t detect a known error, you know you have work to do.

It’s also a good idea to take visual and physical measurements. Take a batch of processed wires and fan them out. Check wire position in the crimp to ensure insulation is not in the wire crimp, the bell mouth and brush positions are correct. Measure wire crimp height and pull force and confirm they meet the manufacturer’s specs.


Removing Operator Bias

Let’s face it. After a long period of time, operators and setup people can form their own bias towards quality. Left unchecked, this bias can be a problem in improving process quality. It can even be a process variation itself.

Lock down the validation and monitoring process. Connect your bench and automated crimp machines into a network. Process parameters do not change over time and should be stored in a central database. Create a process where validation of process parameters is required before machines are released for production. Then monitor the process to ensure ongoing conformity to the validated process

The stakes are never higher than they are today. Exposure to liability from nonconforming products can be reduced by following a repeatable process. 


Putting Pull Force Testing Into Perspective

Pull force testing—measuring the tensile strength of a wire-to-terminal crimp—has been a quality measurement since the advent of pressing a wire to a terminal for electrical assembly.

Test methods have varied from weights and fish scales, to portable manual testers, to benchtop, motorized digital instruments. I have even heard stories of an acceptable pull force test being performed by pulling on a terminal with one’s teeth. A dentist’s nightmare!

Given today’s demands for higher reliability and failure rates approaching zero, how does the pull test process fit in with other testing methods? Are you even performing pull tests properly?

The pull force test is a destructive test to determine the mechanical strength of a terminal crimp. A good mechanical crimp assures the crimp can withstand the normal handling and installation process.

Typical process parameters for pull force testing include:

  • Disengaging the insulation support, so the pull force reading is based on the wire crimp alone.
  • Pulling at a constant rate of 50 to 250 millimeters per minute.
  • Ensuring the wire is taut prior to applying pull force.

Pull testing does not measure electrical performance. It measures the strength of the mechanical connection. However, low electrical resistance results from a crimp with a wire under compression.

Terminal suppliers validate crimps by optimizing the crimp barrel size to match the wire. The crimp tool profile is also a critical factor. Using the proper crimp tool profile, the wire and terminal are compressed together. Pull force and electrical resistance readings are made, and the recommended conductor crimp height is established.

Engineers must follow those guidelines to ensure an optimum crimp. Conductor crimp height should be your primary measurement, and a mechanical pull test should be your secondary standard.

Pull force and electrical resistance measurements rarely follow in tandem. Typically, pull strength peaks before electrical resistance. Therefore, it is possible to meet a minimal pull test without optimizing electrical resistance. There will always be a compromise between electrical resistance and tensile strength.

Pay attention to how the wire separated from the terminal. This is an indication of the wire compression. Strands completely broken at the wire crimp indicate overcompression. Conversely, strands that completely pull out of the wire crimp still in a round shape indicate severe undercompression. Crimps with good compression should primarily break outside of the wire crimp.

Depending on mechanical strength as your primary crimp quality measurement leaves you open for premature crimp failure. But, as part of an overall regimen of crimp measurements, pull force testing can be a valuable part of your quality assurance process.