3.1 Continuity, Hipot & Resistance

Crimping is the most critical process in wire harness assembly. It is not merely folding metal around a wire; it is a precision metallurgical process that creates a permanent, electrically conductive joint. A proper crimp transforms the wire strands and terminal into a solid metal mass, achieving reliability often superior to soldering. However, because the connection is hidden inside the metal barrel, verifying its quality requires strict adherence to geometry and tooling setups.

3.1.1 The Physics of Crimping: Cold Welding

The goal of crimping is to create a gas-tight seal between the terminal and the conductor. This is achieved through controlled physical compression, not heat.

Plastic Deformation: As the crimp dies close, the terminal barrel wraps around the copper strands. The pressure is high enough to exceed the yield strength of both the copper and the terminal material (plastic deformation), but not their ultimate tensile strength (breakage).
Cold Welding: Under this immense pressure, the oxide layers on the individual wire strands and the terminal interior are scrubbed away. The clean metal surfaces are forced into intimate contact, causing atoms to share electrons across the boundary. This fusion is a "cold weld."
The Gas-Tight Seal: A successful crimp compacts the strands so tightly that no air (oxygen) or corrosive gases can enter the interstitial spaces (voids). Without oxygen, the connection cannot oxidize, ensuring low contact resistance for the life of the product.
The Honeycomb Effect: In a cross-section (micrograph), a good crimp looks like a solid honeycomb. The individual round strands are deformed into polygons, eliminating air gaps.

3.1.2 The Crimp Zone: Anatomy of a Terminal

A reliable crimp is defined by specific geometric features. Each zone serves a mechanical or electrical function.

A) The Conductor Crimp (The Electrical Core)

This is the area where the cold weld occurs.

The Crimp: The metal wings are folded down and curled inward into a "B" shape (F-Crimp), compressing the strands.
Target: All strands must be captured; compression must be sufficient to eliminate voids (typically 15-20% reduction in cross-sectional area).

B) The Bellmouth (The Strain Relief)

The bellmouth is the flared edge at the entry (and sometimes exit) of the conductor barrel.

Function: It acts as a funnel to guide the wire in and, more importantly, prevents the sharp edge of the crimp tool from cutting the wire strands during flexing.
Mandate: A visible bellmouth is mandatory at the wire entry side.

C) The Brush (The Extension)

The "brush" refers to the wire strands protruding past the conductor crimp barrel.

Function: It confirms that the wire passes all the way through the crimp zone, ensuring full electrical contact along the entire barrel length.
Limit: The brush must be visible but not so long that it interferes with the mating connector or locking mechanism.

D) The Insulation Crimp (The Mechanical Support)

This rear section grips the wire's insulation.

Function: It provides strain relief, absorbing vibration and bending forces so they are not transferred to the electrical crimp.
Target: The insulation crimp should firmly grip the wire without piercing the insulation to the point of touching the conductor.

3.1.3 Applicator Setup: Matching Feed and Geometry

The Applicator is the tooling assembly inside the press that feeds terminals and houses the crimp dies. Setting it up correctly is the first line of defense against defects.

A) Die Geometry and Wire Gauge

The crimp dies are machined for a specific range of wire gauges. Using a die designed for 18 AWG on a 22 AWG wire results in under-compression (loose wire). Using it on a 16 AWG wire results in over-compression (crushed strands/cracked terminal).

Verification: The operator must verify the Terminal Part Number matches the Wire Gauge and the Applicator ID listed on the work instruction.

B) Terminal Feed Alignment

The applicator feeds the terminals onto the anvil.

Feed Timing: If the feed is too slow, the terminal is crushed by the crimper. If too fast, the "cut-off tab" (the metal scrap) is too long.
Centering: The terminal must sit perfectly centered on the anvil. If it is misaligned, the crimp wings will curl unevenly, creating a "banana" or twisted crimp.

C) Crimp Height Setting

The applicator allows for micro-adjustment of the crimp height (shut height).

The Dial: Most applicators have a rotary dial to adjust the crimp height in 0.02 mm increments. This is the primary knob used to dial in the Crimp Height Measurement (CHM) to meet the gas-tight specification.

Final Checklist: Crimp Fundamentals

Mandate	Criteria	Verification Action
Bellmouth Check	A Bellmouth must be visible at the wire entry side.	Visual inspection (10x mag). Absence indicates a risk of cut strands.
Brush Visibility	Wire strands (brush) must protrude past the crimp barrel.	Visual inspection confirms full wire insertion.
Gas-Tight Seal	Crimp geometry must effectively turn strands into a solid mass.	Micro-section analysis during setup validation shows "honeycomb" compression and no large voids.
Insulation Support	Insulation crimp must grip the jacket firmly.	Bend Test: Insulation should not pull out or rotate when the wire is flexed.
Tooling Match	Die set must match the specific wire gauge and terminal.	Validation of the setup sheet against the physical tooling tags.