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Publication Date: 10/1/2011
Archive >  October 2011 Issue >  Special Features: PCB and Production > 

Applicators: Getting to the Heart of the Crimping Process
Electrical mating portion of a terminal. Because of deformation of the contact points (left photo), the mating blade terminal did not have the proper contact force with the socket terminal. Right photo shows proper mating.

It's a cool Saturday morning and you're also looking pretty cool wearing your new sunglasses to protect you from the gorgeous sunshine while you wait for the green light before hitting the freeway. Suddenly, you hear a motor revving up next to you; it only takes a quick glance to the right to see you are being challenged to show your racing talents in a spontaneous drag race. Your caffeine-filled heart starts revving up too and you get your first shift ready; Green, GO! You floor the gas pedal, then hear that great squealing sound and start accelerating and then notice a strong hesitation in the motor. That was it for your 5 seconds of glory; you see the rear license plate of your opponent's car getting smaller and smaller.

You take your car to the shop and after a few days of painful troubleshooting you get the diagnosis: intermittent electrical connection to fuel injector #1. That is a darn good shop since this problem is very difficult to troubleshoot indeed. It would take Sherlock Holmes to determine the root cause for this failure, but pretending he would apply the good ol' "5-Why" Technique, it would go like this:

Why did I lose the race? Because the motor was hesitating.

Why was the motor hesitating? Because the injector was not working properly

Why was the injector not working properly? Because there was a bad connection between the electric terminal and the injector.

Why was there a bad connection to the injector? Because the terminal was damaged.

Why was the terminal damaged? Because the applicator that crimped the terminal was not adjusted correctly due to lack of maintenance.

Of course we could ask more "Why's" to determine the ultimate root cause but let's just stop right here.

Location, Location, Location
While this small incident was harmless, imagine what happens if you have a bad connection in an airbag sensor during a crash, or in an ABS sensor during emergency braking or in a headlight at night on a sharp curve. And while intermittent electrical connections are quite common, most of them can be prevented during the production process.

As a result of the deformation of the contact points, the mating blade terminal did not have the proper contact force with the socket terminal. In this example, not even today's quality systems or crimp force monitors would have been able to detect this failure during production process. This problem should have been addressed through a proper PFMEA (Process Failure Mode and Effect Analysis) and a control plan focusing in proper inspection and preventive actions through correct terminal applicator maintenance and setup. In this case, the terminal hold-down feature of the applicator was out of adjustment, hence applying more force to the terminal than required, but not enough to be caught by the Crimp Force Monitor or by visual inspection. The crimped portion of the crimp was within specification.

An applicator is best described as "The Heart of the crimping process". The terminal crimping applicator is what determines the shape of the mechanical connection between a wire and a terminal.

Maintaining the Crimping Process
The life cycle of a crimped connection for a certain application starts with the selection of the correct wire and terminal combination during the design phase of the wire harness. Once the application is defined, determining the correct applicator, performing the pertinent tests and releasing the tool for production are next. Once the quality procedures and controls are implemented, the last step is establishing a proper maintenance procedure. This final step will ensure that the applicator produces reliable crimp connections that will last for the entire life of the products in which they are used.

Regardless of the company's size, it is crucial to have clear and standard applicator maintenance procedures, the correct tools and equipment and properly trained technicians to carry out the work. Usually the strictest requirements can be found in military and automotive applications.

Proper Standards
As required by current Quality Systems, the first thing one needs to consider when establishing the proper maintenance procedures are the customer-specific requirements. Often, these requirements are not very detailed and only go as far as stating the crimping tools must be kept in good operating condition and that proper maintenance must be performed. However, since the wiring harness manufacturer is responsible for the crimping process, it is very important that if customer requirements are not clear or detailed enough, that proper maintenance and controls be developed internally.
Crimping machine (left), cross section of crimping operation (center) and final crimped connections (right).

As a starting point, it's a good idea to use the industry's best practices and adapt them to your individual needs.

Applicator Maintenance Procedures can be grouped into several types. To develop internal maintenance procedures, it's important to determine which type you would like to implement. In general, they can be divided into basic routine, detailed routine, and requalification routine.

Basic routine: inspection, cleaning and lubrication. This is aimed at basic cleaning and removal of debris, visual inspection for tool wear and ensuring smooth operation of the applicator by basic lubrication and fine adjustment. It's important to keep basic maintenance records showing who performed the maintenance and when. Usual time to complete this is 3-10 minutes.

Detailed routine: disassembly, cleaning, inspection, repair, exchange of tooling, lubrication and creation of crimped samples. This is aimed at detailed disassembly to inspect all components and ensure smooth and proper operation. This includes predictive replacement of crimp tooling (Punches and Anvils). Crimp quality evaluation and fine adjustments are made by creating actual samples using a crimping press. Now's the time to create detailed quality records with crimp dimensions, micrograph sections, etc. This is usually plotted in a SPC Chart to ensure stable process crimping. Usual time to complete this segment is 10-30 minutes.

Requalification Routine, Statistical. In addition to all procedures included in the Detailed Routine above, this procedure includes a complete evaluation for statistical re-release of all the wire-terminal combinations used in a particular applicator. Statistical machine/process capability is performed and fully documented.

There are general variables to be analyzed — conductor crimp height , width and pull force. General attributes that have to be evaluated are visual characteristics and micrograph cross sectional analysis.

This is when the decision is made to replace a worn applicator. The requalification usually takes from 30 to 90 minutes, depending on the quantity of wire-terminal combinations released for a particular applicator.

Once the procedures and general maintenance requirements are established, then the frequency at which these are performed must be determined.

Much like the maintenance plan for a vehicle, the frequency of applicator maintenance can be based on a predetermined time or quantity of crimping cycles.

How Often?
There are several factors that influence maintenance frequency determination, and often it is decided based on a combination of time and cycles. These factors include:

  • Type of production: high-mix/low-volume is usually based on time or low-mix/high-volume usually based on cycles.
  • ERP system, networked software or technological tools available. If these are available and data is analyzed constantly, usually cycle-based maintenance is easier to implement.
  • Production shift model.
  • Quantity of active applicators owned.
  • Quantity of cycles per applicator over a given period.
  • Criticality of the application (Airbag connection vs. Audio connection).
  • Previous failures or quality issues.
  • Geographical location and environmental factors such as temperature, dust, humidity.

The maintenance frequency must not be determined by the availability of technicians, tools or work space. On the contrary, the resources must be planned and determined based on the quality requirements and the time needed to complete the maintenance plans.

To be on the safe side, some basic starting points for these values can be:

  • Basic routine — every 7,000 crimps — probably once a day or once per shift.
  • Detailed routine — every 35,000 crimps — probably once every week.
  • Requalification routine — every 1,500,000 crimps — probably once a year.

For critical applications, these frequencies can be increased. Once the frequency of the routines has been established, then the proper controls and resources must be developed and allocated to ensure that it all works.

Thus implementing thorough analysis, research and comprehensive maintenance standards for crimping operations will reap great benefits such as increased uptime and efficiency for equipment, decreased scrap rates and increased quality that will benefit any bottom line, and keep your customers winning all those races.

Contact: Schleuniger, 87 Colin Dr., Manchester, NH 03103 603-668-8117 fax: 603-668-8119 E-mail: Web:

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