Common Crimping Defects: Causes, Identification, and Solutions

Crimping defects are the leading cause of wire harness field failures. A single defective crimp in a vehicle harness can cause intermittent electrical faults, overheating, or complete circuit failure — problems that are expensive to diagnose and costly to repair under warranty.

According to industry data, incorrect crimp height alone accounts for 28% of all IPC-A-620 non-conformances. The remaining defects — strand damage, insulation issues, and barrel problems — make up most of the rest.

This guide covers the major crimping defects, what causes each one, how to identify them, and practical solutions.

1. Over-Crimping (Crimp Height Too Low)

What it looks like: The terminal barrel is compressed excessively. The barrel may appear flattened or show visible bulging at the edges. In cross-section, strands are severely deformed with near-zero void space.

What causes it:

• Crimp height set too low on the applicator
• Wrong crimper die for the terminal/wire combination
• Press stroke adjusted too deep
• Die wear causing gradual drift toward tighter crimps

Consequences:

• Conductor strands are damaged or severed, reducing effective cross-section
• Reduced fatigue life — the connection fails sooner under vibration
• Barrel may crack from excessive force
• Wire breaks at the barrel edge during flexing

Solution:

• Measure crimp height with a micrometer and adjust to specification
• Verify the correct die/anvil combination is installed
• Inspect dies for wear and replace if worn
• Implement SPC charting to catch gradual crimp height drift

2. Under-Crimping (Crimp Height Too High)

What it looks like: The barrel appears loosely compressed. The wire may move slightly within the barrel. In cross-section, strands remain mostly round with large voids between them.

What causes it:

• Crimp height set too high on the applicator
• Wrong wire gauge (wire too small for the terminal)
• Insufficient press tonnage
• Worn or incorrect anvil

Consequences:

• Poor metal-to-metal contact between strands and barrel
• High electrical resistance leading to heat generation
• Low pull-out force — terminal separates easily
• Intermittent electrical connections under vibration

Solution:

• Reduce crimp height to specification
• Verify the correct wire gauge is being used
• Check press tonnage is adequate
• Replace worn anvil

3. Insulation in Conductor Barrel

What it looks like: Wire insulation extends into the conductor crimp zone, trapped between the barrel and the conductor strands.

What causes it:

• Wire strip length too short — insulation not removed far enough
• Wire not fully inserted into the terminal
• Insulation pushed forward during insertion
• Stripping blade not cutting cleanly

Consequences:

• Insulation prevents proper metal-to-metal contact between strands and barrel
• High electrical resistance at the crimp point
• Reduced pull-out force
• IPC-A-620 Class 3 rejects any insulation in the conductor barrel

Solution:

• Adjust strip length to specification (typically 3-8 mm depending on terminal)
• Verify wire is fully seated before crimping
• Inspect stripping blades for sharpness and alignment
• Add a wire stop or depth gauge to ensure consistent insertion

4. Missing or Cut Strands

What it looks like: Fewer conductor strands than expected are captured in the barrel. Some strands may be visible outside the barrel, or the pull force is lower than expected despite correct crimp height.

What causes it:

• Strands nicked or severed during wire stripping
• Wire not fully inserted — some strands missed the barrel opening
• Strands caught on the barrel edge during insertion
• Wrong wire specification (fewer strands than expected)

Consequences:

• Reduced current-carrying capacity
• Lower pull-out force
• Higher resistance and heat generation
• Potential fire hazard in high-current applications

Solution:

• Inspect stripping blades and adjust depth to avoid nicking strands
• Ensure the bellmouth is properly formed to guide strands into the barrel
• Train operators on proper wire insertion technique
• Perform cross-section analysis to verify strand count

5. Cracked Barrel

What it looks like: Visible fracture lines or splits in the terminal barrel material, often at the crimp impression edges or along the barrel seam.

What causes it:

• Excessive crimping force (over-crimped)
• Terminal material too hard or brittle
• Wrong die profile for the terminal type
• Die misalignment creating asymmetric stress
• Terminal material defect (plating delamination)

Consequences:

• Structural weakness — barrel may open under vibration
• Exposed conductor creates short-circuit risk
• Connection will degrade over time
• Always a reject condition per IPC-A-620

Solution:

• Reduce crimping force / increase crimp height
• Verify correct die/terminal match
• Check die alignment — both halves must be centered
• Contact terminal supplier if barrel material appears defective

6. No Bellmouth

What it looks like: The front and/or rear edges of the conductor barrel are sharp and straight rather than having a slight outward flare.

What causes it:

• Die design does not include bellmouth formation
• Worn dies that no longer form the flare
• Crimp height too low crushing the bellmouth flat

Consequences:

• Sharp barrel edges cut into conductor strands during vibration and flexing
• Strand fatigue failure over time — wires break at the barrel edge
• Reduced service life of the connection
• IPC-A-620 requires bellmouth for Class 2 and Class 3

Solution:

• Replace worn dies with new ones that include bellmouth chamfer
• Adjust crimp height — bellmouth disappears when over-crimped
• Verify die design matches the terminal specification

7. Incorrect Wire Brush Length

What it looks like: Either no conductor visible past the barrel front (brush too short or absent) or excessive conductor extending past the barrel (brush too long).

What causes it:

• Wire strip length incorrect
• Wire not inserted to the correct depth
• Terminal feed position misaligned

Consequences:

• No brush = wire may not be fully inserted, risking pull-out failure
• Excessive brush = strands may contact adjacent pins or terminals, causing short circuits
• Strands extending into the connector mating area prevent proper terminal insertion

Acceptable range: 0.5 to 1.0 mm of bare conductor visible past the barrel front.

Solution:

• Adjust wire strip length
• Use wire stops for consistent insertion depth
• Check terminal feed alignment in the applicator

8. Asymmetric Crimp

What it looks like: The crimp impression is not centered on the barrel. One side is compressed more than the other, visible in cross-section as an uneven “B” shape.

What causes it:

• Die misalignment in the applicator
• Terminal not properly seated in the anvil before crimping
• Worn die or anvil creating uneven compression
• Terminal strip feed positioning error

Consequences:

• Uneven strand compaction — one side has good contact, the other doesn’t
• Reduced overall crimp strength
• Inconsistent electrical performance

Solution:

• Realign the upper die to the anvil
• Inspect terminal feed mechanism for proper positioning
• Replace worn dies or anvil
• Verify terminal strip indexing accuracy

9. Insulation Crimp Problems

Insulation Not Gripped

The insulation crimp wings do not properly wrap around the wire insulation.

Cause: Insulation crimp height set too high, or wire diameter smaller than expected. Fix: Adjust insulation crimp height. Verify wire outer diameter matches specification.

Insulation Pierced

The insulation crimp wings cut through the wire jacket.

Cause: Insulation crimp height set too low, sharp wing edges, or brittle insulation material. Fix: Increase insulation crimp height. Inspect wing edges for burrs.

Prevention Through Proper Setup

Most crimping defects are preventable through systematic process control:

1. Use a reference crimp — establish a golden sample with verified crimp height, pull force, and cross-section micrograph before production begins
2. Measure crimp height at startup and periodically — see how to measure crimp height
3. Maintain your applicator — inspect dies, feed fingers, and blades regularly
4. Match wire to terminal — never force a wrong wire gauge into a terminal
5. Train operators — proper wire insertion and strip length are operator-dependent
6. Implement crimp force monitoring — catches defects in real-time on every crimp

Conclusion

Crimping defects are almost always traceable to equipment setup, die condition, or wire preparation — not to inherent process limitations. A well-maintained applicator with the correct dies, operating at the correct crimp height, produces defect-free crimps consistently.

Anjali Machine Tools manufactures precision crimping applicators with adjustable crimp load and quick-change crimper sets that make proper setup fast and repeatable. We also provide crimp cross-section analysis services to help you identify and resolve quality issues. Contact us for technical support.