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Making Consistent and Reliable Crimped Terminations is Easy – With the Right Tool

By: Bill Schweber 2023-07-27

From soldering to crimping

That’s when I remembered an alternative. I had a basic manual crimping tool in my toolbox, which offered another solution (Figure 2). You may be familiar with this one. It looks like a large pair of pliers with a designated area at the tip of the jaws for crimp barrels of three sizes, along with other wire-stripping and screw-shearing functions.

Figure 2: My crimper was part of a multifunctional tool that could also strip wires and shear small screws. (Image source: Harbor Freight Tools)

What is crimping? Crimping is a joining method that connects two components using a defined pressing procedure. The method forms a secure connection between the conductor and contact and has replaced the soldering process in many cases. Crimping can be used with many types of connectors, including wire-end ferrules, which are then inserted into mating receptacles or connector bodies (Figure 3). This crimped wire-end ferrule is available in many sizes and has a plastic collar (offered in many colors) as an additional insertion aid due to the conical shape in the inner diameter of the collar. It also prevents the angular edges of the conductor insulation from getting caught in the insertion funnel of the contact point.

Figure 3: This crimped wire-end ferrule is available in many sizes and has a plastic collar as an additional insertion aid due to the conical shape in the inner diameter of the collar. (Image source: Weidmüller Interface GmbH & Co.)

Even if you are an admirer of a well-done solder joint (as I am), there are many reasons to use crimping. A good crimp is mechanically rugged, electrically consistent, and forms a gas-tight contact between the wire and termination, which prevents the ingress of moisture and subsequent corrosion. It is quick and easy to set up, interrupt temporarily, or stop entirely; there are no hazardous fumes or materials, and there’s no heat to distort insulation or even cause ignition and fire.

So I bought a box of spade lugs with insulated barrels, practiced crimping on about ten of them to make sure I could do it right, and then did the actual installation (Figure 4). It went fairly smoothly, and the system was up and running after resolving some minor wire-routing problems. Despite the haphazard appearance of the loop entry feeds (beyond my control), the actual relay and interconnection wiring, with its crimped spade lugs and barrier strips, is clean, organized, crisp, and reliable.

Figure 4: Despite the haphazard appearance of the loop entry feeds, the actual relay and interconnection wiring, with its crimped spade lugs and barrier strips, is clean, organized, crisp, and reliable. (Image source: Bill Schweber)

However, while crimping the spade lugs, I found that it was tricky to make consistent crimps, as my tool was manual and uncalibrated and relied upon the user (myself, in this instance) to place the spade lug correctly in the jaws and apply the correct amount of pressure. It was easy for me to be off target in the final crimp position and to also apply more pressure than necessary. For example, some spade lug barrels were crimped too little, some too much, and some had insulation partially under the crimp zone.

What I now wish I had was a crimping tool like the Weidmüller PZ 6 ROTO ADJ (Figure 5). It reliably and consistently crimps wire-end ferrules over a wide range of wire cross-sectional areas from 0.14 square millimeters (mm²) to 6 mm² (roughly 26 AWG to 10 AWG). It works with wire-end ferrules, with and without plastic collars. Its ratchet guarantees precise crimping and a release option in the event of incorrect operation.

Figure 5: The Weidmüller PZ 6 ROTO ADJ is an adjustable crimping tool that provides consistent results, is comfortable to use, and handles a range of wire sizes and types. (Image source: Weidmüller Interface GmbH & Co.)

Among its other features are the adjustable handle width for optimum ergonomics and fatigue-free work, a weight of just 425 grams (15 ounces), and a rotatable crimp die for adapting it to a wide range of installation situations.

Getting technical

Due to its versatility, convenience, and potential performance, the physics and mechanics of crimping have been extensively studied. For example, Weidmüller’s 17-page white paper “Crimping: A permanent connection” begins with a discussion of wire types, stranding, and gauges; contact types; ferrules; and tools.

It examines the relative pros and cons of different press shapes such as trapezoid, square, and hexagon. It looks at preparing the wire, showing the problems, which can occur if the wire is not cut properly (Figure 6) or the insulation is not stripped properly (Figure 7).

Figure 6: Shown are the three ways a wire can be improperly cut, as well as the appearance of one done correctly. (Image source: Weidmüller Interface GmbH & Co.)

Figure 7: Shown are three examples of insulation stripping errors as well as a properly stripped wire. (Image source: Weidmüller Interface GmbH & Co.)

The white paper also calls out the many DIN and IEC standards related to crimping, such as conductor (wire) classes, stripping errors, tool lifetimes (in cycles), die connector compartment sizes versus wire size, and crimp actuating force.

Then there’s testing

One of the challenges with crimped connections is that there is no easy way to non-destructively test them. This is the same dilemma designers face when using many other components, such as standard, thermally activated fuses: you can’t test them, so they have to be perfect by design and manufacturing. As crimping is widely used in countless mission-critical applications, this testing limitation poses a quality assurance challenge.

Recognizing this, NASA has developed a patented ultrasonic-based, nondestructive evaluation method that operates in real-time at the crimp installation location. In this approach, the quality of the contact between the connector and the wire is determined by sending an acoustic wave through the crimp assembly (Figure 8). As the applied pressure increases and the crimp terminal deforms around the wire, the ultrasonic signature passing through the crimp is altered.

Figure 8: This portable instrument developed by NASA can non-destructively identify both good crimps and the many types of bad crimps in real-time. (Image source: NASA)

The system analyzes the changes in the signal signature, including the amplitude and frequency content, as an indication of the quality of both the electrical and mechanical connection between the wire and terminal (Figure 9).

Figure 9: The NASA system uses ultrasound-derived signatures to identify crimp quality and problems. (Image source: NASA)

Crimp-related issues such as under-crimping, missing wire strands, incomplete wire insertion, partial insulation removal, and incorrect wire gauge have been tested using this system. The results demonstrate that the instrument consistently distinguishes between good and poor crimps for these issues, among others.

Conclusion

In the end, I redid a few of my crimps, which did not meet my admittedly subjective standards, and the three-zone, smart-thermostat control system has worked without any issues for three winters. Using the uncalibrated crimp tool, with its user-dependent variations in squeeze pressure, made me realize yet again, that having the right tool is a very important part of delivering consistent, properly made results. If I ever have to do a similar job, I’ll beg, borrow, or buy the needed tool.