Wire End Quality Assurance - Crimp Force Monitoring

In modern, high volume wire harness production, automatic wire strippers are used to strip insulation from the wire prior to the crimping process where a terminal is fixed to the stripped wire. 

Crimp-on terminals are attached to wires to allow the wires to be easily connected to electrical component terminals and quick-connect terminals.  Crimp-on terminals are attached by inserting the stripped end of a stranded wire into the tubular portion of the terminal, which is then compressed tightly around the wire in a crimping die on either a bench press or automatic crimping machine.

Wire processing involves high speed precision cutting and stripping, and often the placement of a weather seal onto the wire before the terminal is applied.  Failing to ensure absolute quality through every step of this high speed process can result in significant penalties, containment, reduced profits, or loss of business. Providing this type of critical quality assurance at ‘parts per second’ speed for ‘pennies per part’ prices poses a significant challenge.

To accomplish this, leading wire harness manufacturers employ 2 primary quality assurance methods to assure the quality expected by their customers.  The first is the crimp force monitor, which can be considered a ‘process variation monitor’.  The other is an in-process strip and seal inspection device, such as the LPA56B WireScan™.  These are complimenting technologies – process variation monitoring, combined with wire strip and seal inspection that will ensure effective and reliable detection of wire processing defects for even small gauge wire processing applications.        

Crimp force monitors have proven to be essential for in-process monitoring of the crimp quality for wire processing, and are now mandated by most wire harness manufacturers globally.

Crimp force monitors, or more appropriately called crimp process variation monitors, detect process variations that can be directly correlated to crimp defects, tool wear, incorrect alignment or adjustment, etc. that might result in defective parts, accumulation of unnecessary scrap, and rework.   To date, there have been few technological innovations in the wire processing industry that have proven to be as effective as crimp process monitors. 

 How it Works

The CFM series of crimp force monitors from OES utilize a piezo-strain sensor bolted to the frame of the crimping press to capture a “signature” of the relative force of the crimp stroke over the time of the cycle.  On stable equipment, this signature is highly repeatable, so that any variance in the process will be reflected in a change in the signature, as in this example of a strand out of the core.

The patented analysis of each production curve against a learned reference curve of a known “good” crimp, allows the monitor to provide a Pass for cycles within tolerance or a Fail output for cycles outside of tolerance allowing the part to be segregated for quality assurance.

Detectable Defects: Missing wire strands, strands out of the core, no strip, high/low insulation, missing terminals and twisted terminals, changes to crimp height, and scrap in the tooling.

Key Features and Options of the CFM4000™:
• One to three channel Crimp Force Monitor utilizing the most current microprocessor technology.

• Unique automatic setup features with user-friendly alpha-numeric and graphic displays to minimize setup time.

• Three display screens available in RUN mode, showing:
   1. Graphic display of process relative to compared Control Limits.
   2. Engineering data results on each crimp (target, actual, tolerances, deviation).
   3. Graphic display of Force Curve following every crimp.
 
• Option to store multiple force signatures for special applications.

• CPK computation and automatic optimization of the control limits based on process capability.

• Two levels of failure detection and ability to interface with advanced wire processing equipment batch separators, choppers, etc.

• A counter that maintains a running total of passes and failure types for each press.

• Communication port configurable for a wide range of requirements (computer for crimp studies using OES “CFMView” Software, external    printer, network link, etc.)

• Built in self-diagnostics.

• WIFI option for remote monitoring, configuration and setup.