3.2 Crimp Quality Assurance

A finished crimp hides its internal quality. To the naked eye, a loose crimp and a perfect gas-tight crimp often look identical. Therefore, quality assurance cannot rely on visual inspection alone. It requires a tiered validation strategy: Crimp Height (process control), Pull Testing (mechanical strength), and Micro-Sectioning (internal metallurgy). Validating the process at the start of every shift and batch is the only way to guarantee the reliability of the thousands of connections produced in between.

3.2.1 Crimp Height Measurement (CHM)

Crimp Height is the primary non-destructive variable that correlates directly to the gas-tight nature of the connection. It is the measure of vertical compression.

The Measurement Mandate

• The Tool: Measurements must be taken with a specialized blade-micrometer or "crimp mic" (point-to-flat). Standard flat-jaw calipers cannot be used because they bridge the curvature of the crimp bottom, giving a false high reading.
• The Target: The height is defined by the terminal manufacturer's specification for the specific wire gauge (e.g., 1.15 mm ± 0.05 mm).
• Process Control: Crimp height is a Critical-to-Quality (CTQ) characteristic. Automated presses usually include Crimp Force Monitors (CFM) that detect height variations by measuring the force required to close the die.

Action: Measure 5 pieces at setup. If the mean height is not centered within the tolerance window, adjust the applicator dial. Do not run production at the edge of the specification limits.

3.2.2 Pull Testing: Destructive Verification

The Pull Test verifies mechanical tensile strength. It ensures the wire will not separate from the terminal under tension or vibration.

Test Protocols

• Frequency: Mandatory at Setup, Material Change (new wire spool), Tool Change, and at defined intervals (e.g., start/end of shift).
• Method: The wire is pulled axially from the terminal at a constant speed (typically 25 to 50 mm/minute). Jerking or snapping the wire gives invalid results.
• Failure Modes:
  • Pull Out: The wire slips out of the crimp. This indicates under-compression (crimp height too high).
  • Break: The wire snaps outside the crimp area. This is the preferred failure mode, indicating the crimp is stronger than the wire itself.
  • Tear: The terminal tears or breaks. Acceptable if the force exceeds the minimum.

Minimum Force Requirements (Reference: UL 486A / IPC-620)

• 22 AWG: 36 N (8 lbs)
• 20 AWG: 58 N (13 lbs)
• 18 AWG: 89 N (20 lbs)
• 16 AWG: 133 N (30 lbs)

Warning: A crimp can pass the pull test but fail electrical resistance checks (e.g., if the crimp is slightly loose but holds mechanically). Therefore, Pull Testing must always be paired with Crimp Height Measurement.

3.2.3 Micro-Section Analysis: The Ultimate Validation

Micro-sectioning involves cutting the crimp in half, polishing the face, and inspecting the interior under a microscope. It is the only way to "see" the cold weld.

Analysis Criteria

1. Void Percentage: Large voids indicate insufficient compression. The target is a "honeycomb" structure with minimal gaps.
2. Symmetry: The two crimp wings should curl symmetrically and touch (or nearly touch) at the bottom.
3. Wing Closure: The wings should support each other but not pierce the bottom of the terminal barrel.
4. Strand Count: Verifies that no strands were missed during insertion.

Mandate: Micro-sections are required for Class 3 setup validation and whenever a new wire/terminal combination is introduced.

3.2.4 Defect Atlas: Visual Cues

Visual inspection is the final gate. Inspectors must check for machine setup errors that distort the terminal.

Defect Name	Appearance	Root Cause	Risk
Banana (Bending)	Terminal is bent up or down relative to the wire axis.	Damage to the carrier strip; excessive Crimp Force; incorrect anvil alignment.	Mating alignment failure; connector damage.
Flag / Twist	Terminal is twisted or bent sideways.	Misalignment in the applicator feed track.	Terminal will not fit into the connector housing.
Cut Strands	Individual wire strands are severed at the bellmouth.	No bellmouth present (sharp edge); Crimp Height too low (over-compression).	High resistance; potential arc/fire; mechanical failure.
Insulation Entrapment	Wire insulation is pinched inside the conductor crimp area.	Strip length too short; wire inserted too far.	High Electrical Resistance; intermittent connection (insulator blocks the metal-to-metal contact).
Insulation Support Failure	Insulation crimp pierces the jacket or does not grip it at all.	Wrong insulation diameter setting; wrong terminal size.	Wire breaks due to fatigue (no strain relief).

Final Checklist: Crimp Quality Controls

Mandate	Criteria	Verification Action
Height Verification	Crimp height must measure within the manufacturer's spec (e.g., ± 0.05 mm).	Measured with Blade Micrometer at setup and every batch change.
Mechanical Strength	Pull Test force must exceed UL/IPC minimums for the wire gauge.	Destructive test performed at Setup and logged. Preferred failure mode is "Wire Break."
Internal Integrity	Micro-section shows honeycomb compression and symmetric wing closure.	Performed during New Product Introduction (NPI) or Class 3 validations.
Visual Geometry	No Banana, Twist, or missing Bellmouth defects.	100% visual check by the operator immediately after crimping.
Entrapment Check	Zero insulation allowed inside the conductor crimp barrel.	Visual inspection of the "window" between the insulation and conductor crimps.