Cable Lug Crimp Cross-Section Analysis: Compression Geometry, Voids and Acceptance Evidence

A crimped cable lug can pass a visual check while hiding cut strands, an underfilled barrel, asymmetric compression, folded material, a seam opening, large voids or poor strand consolidation. It can also produce a misleading micrograph if the specimen was cut obliquely, smeared during grinding, over-etched, measured at the wrong axial position or photographed without scale.

Cross-section analysis is therefore two controlled processes: making the crimp and preparing/measuring a representative section. The RFQ must define both. A polished photograph with no drawing limits is descriptive, not acceptance evidence.

This guide concentrates on compression geometry and microsection evidence for cable lugs. It does not repeat the broad tool validation, pull testing and process setup in the cable-lug crimp tooling guide. It makes no unverified claim about a SINAWATTS lug, conductor, tool, cross-section laboratory, acceptance value, certification, stock, price, MOQ, lead time or test result.

Direct answer: what must a cross-section RFQ require?

Require a controlled cross-section plan with:

• exact cable manufacturer/part, conductor material, class/strand construction, nominal and tolerance cross-sectional area, plating and insulation;
• exact lug manufacturer/part, barrel material/plating, barrel dimensions, seam and conductor range;
• exact die/tool part numbers, press, compression sequence, orientation and setup parameters;
• crimp locations and the required section plane relative to barrel end, indent/hex flats, seam, inspection window and palm;
• sample quantity across setup, production lot, cavities/dies, operators or machines as applicable;
• cut, mount, grind, polish, clean and etch/stain method;
• image magnification, scale calibration, lighting, resolution and raw-file retention;
• measured geometry, strand condition, void definition and acceptance source for the exact cable-lug-tool combination;
• reviewer qualification, repeatability checks and borderline-result escalation;
• linkage to crimp height/compression dimension, pull/retention, resistance and temperature evidence; and
• first-article, periodic, changeover and requalification frequency.

Do not accept universal void percentage or compression ratio unless the lug/tool manufacturer or governing specification defines it for the exact termination. Different constructions can have different acceptable shapes.

Freeze the termination combination before reading an image

Cross-section criteria belong to a defined combination, not to “35 mm² cable” in general. Record strand count and individual strand diameter, because the same nominal area can pack differently. Highly flexible conductors can require a different barrel and die than coarser stranding. Tinned strands can present different image contrast and interface behavior than bare copper.

The lug barrel must be qualified for the conductor size, material and class. Record whether it is closed, brazed, seamless or has a formed seam; whether it uses a bell mouth; and whether inspection holes are present. Freeze barrel wall thickness and internal diameter tolerances.

The die geometry controls the final shape. Hexagonal, circumferential, indent and other compression systems use different acceptance characteristics. Record die index and tooling revision, number and order of compressions, spacing, rotational orientation, and distance from barrel end. A micrograph cannot rescue a lug crimped with an unapproved die.

Use the cable conductor strand-class guide to define the conductor input and the cable-lug stud-hole and barrel-geometry guide to freeze the terminal interface. Cross-section analysis begins only after those identities are controlled.

Choose section planes that answer a question

A single slice may not represent an entire compression. Select axial positions from the lug/tool specification. Useful planes can include the center of each compression, a location near the barrel entrance, a seam-sensitive location and an area between sequential compressions. Do not move the plane after seeing a defect unless the report preserves the original result and explains the additional section.

For each plane, define:

1. distance from a stable datum;
2. perpendicularity to the cable/lug axis or intended oblique angle;
3. orientation marker for top, seam, palm and die flats;
4. whether insulation support is included;
5. material removed during preparation; and
6. expected measurement features.

An oblique cut can make round strands look elongated, inflate apparent wall thickness and distort area measurements. A cut too near the bell mouth can show a transition instead of full compression. A cut between indents can miss the maximum deformation.

TE Connectivity’s official “Primer on Small Wire Crimping,” checked on 2026-09-28, states that cross sections provide a complete view into crimp quality and illustrates measurable features such as crimp height, width, support angle, support length, flank-end distance and flash for its open-barrel contact context. It also warns that standards can define different requirements for the same termination. Those named small-wire features should not be copied as acceptance limits for a large closed-barrel lug, but the source demonstrates why the exact application specification must define plane and measurements. TE small-wire crimping primer.

Prepare the specimen without manufacturing defects

Cutting generates heat, force and displaced material. Use a saw/blade, feed and coolant suited to copper, aluminum, plating and mounting media. Clamp the specimen without crushing it. Keep the cut far enough from the final plane to allow controlled grinding through disturbed material.

Mounting resin can support strands and edges during polishing, but vacuum impregnation or pressure can fill voids. If void area is measured, document how preparation media is distinguished from original empty space. Mark orientation before mounting.

Progress through abrasive steps that remove the prior scratch pattern without rounding edges or smearing soft copper across voids. Polish to reveal strand boundaries and barrel wall. Clean between grades to avoid coarse-particle contamination. Etching or electrolytic staining can improve contrast, but over-etching can exaggerate boundaries or remove plating. Freeze chemistry, time and neutralization.

Schleuniger’s official ElectrolyteStaining Unit 6 page describes a system for staining precut crimp sections for analysis and identifies it as one component of a modular micrograph process. The vendor says the process provides feedback on staining effectiveness. This product page supports the need for controlled preparation; it does not define pass/fail geometry for a lug. Schleuniger ElectrolyteStaining Unit 6.

Reject a section with heavy smear, torn strands, rounded barrel edges, deep scratches across measurement features or uncertain plane. Reprepare from another documented location; do not edit the image to hide artifacts.

Calibrate the image and preserve raw evidence

Include a traceable scale captured at the same optical configuration. Record microscope/camera ID, objective, calibration date, pixel size and software version. A scale bar pasted from a different magnification is unacceptable.

Preserve:

• original full-resolution image;
• annotated copy with measurements;
• uncompressed or lossless format where possible;
• orientation, plane and sample identity;
• brightness/contrast adjustments applied to the full image;
• reviewer and review date; and
• measurement export or audit trail.

Komax’s official CrimpLab 3 page says its software uses defined workflows that can be programmed, stored and reused. Its SmartVision page describes guided measurement and database/report export for several crimp forms. Those capabilities can support traceability and repeatability, but software automation does not choose the correct specification or fix a bad specimen. Komax CrimpLab 3 and Komax SmartVision.

Do not use aggressive image filtering, local cloning or edge enhancement that changes measurements. If automated segmentation is used for void percentage or strand boundaries, validate it against manual review and retain overlay evidence.

Measure geometry from the approved specification

Possible closed-barrel lug measurements include final width/height across defined flats, wall thickness at critical points, indent depth, symmetry, seam closure, conductor occupied area, strand deformation and distance between barrel features. The exact set depends on design and die.

Molex’s official product-engineering procedure for a named crimp family instructs users to measure crimp height at a defined central location and avoid anvil flash, and it calls for a minimum sample count during setup. This is product-specific, yet it illustrates two general controls: measurement point matters and setup approval needs multiple samples. Molex product engineering standard.

For large compression lugs, do not apply open-barrel “B-crimp” features unless the lug maker expressly uses them. Instead obtain the lug/tool system’s compression dimensions, die index and section examples. If the supplier proposes a calculated compression ratio, define areas and measurement method exactly:

• original conductor metal area versus nominal area;
• final enclosed cavity area;
• metal-only area excluding voids and plating;
• barrel contribution; and
• treatment of irregular boundary pixels.

Two suppliers can use the same phrase “compression ratio” for different equations. Put the equation and units on the report.

Evaluate strands, barrel wall, seam and flash

Review more than an average void percentage. Look for:

• all required strands present within the barrel;
• no cut, folded-back or escaped strands beyond permitted criteria;
• strand deformation consistent with the approved master;
• no severe strand fracture caused by over-compression;
• barrel wall intact without crack, tearing or excessive thinning;
• seam behavior within the exact design limit;
• no harmful flash or sharp extrusion;
• balanced compression without tool misalignment;
• plating condition where its preservation is required; and
• no foreign material inside the electrical interface.

Some visible gaps between round strands can be normal. A “zero void” demand can encourage destructive over-compression. Conversely, a low total void percentage can hide one large connected channel near the seam. Define both quantitative and location-based criteria if the specification requires them.

TE’s small-wire primer notes that some asymmetry is normal and directs users to the applicable limits rather than pursuing perfect symmetry. It identifies setup, feed, tooling quality and tooling condition as contributors. For a lug, trace an abnormal section back to cable insertion, die alignment, press closure and tool wear rather than accepting or rejecting by appearance alone.

Separate preparation artifact from real defect

A dark region may be a void, mounting resin, oxide, etching contrast or pulled-out strand. A bright line may be smear or a true interface. Train reviewers with controlled examples and, for borderline results, inspect adjacent planes or use another validated technique.

Use these questions:

1. Does the feature persist across polishing depth or adjacent section?
2. Is its edge consistent with original metal deformation or preparation tearing?
3. Did resin penetrate it before cutting?
4. Is it aligned with cutting direction?
5. Does it correlate with an external crimp or resistance anomaly?
6. Can a second reviewer reproduce the segmentation and measurement?

Never delete an unfavorable image because another plane looks better. The report should preserve all planned sections and additional investigative sections. State which plane controls acceptance.

Where plating thickness or intermetallic condition is important, ordinary optical preparation may be insufficient. Use the applicable microscopy/material method and qualified laboratory. Do not claim metallurgical findings from a low-resolution production micrograph.

Use a bounded hypothetical comparison

Assume a fictional closed-barrel lug specification defines final height 9.80–10.10 mm at the center of one hex compression, no barrel cracks, all strands contained and no connected void above a project-specific limit near the seam. Three sections measure 9.86, 9.97 and 10.18 mm.

The third is out of the stated height range even if its picture looks dense. The supplier should quarantine affected production, verify measurement plane/calibration, inspect press and die setup and take the investigation samples defined by the control plan. It should not edit the nominal value or substitute a pull result.

Now assume image software reports 4% total dark area on a fictional section, but manual review finds that half is mounting-resin pullout at the polished edge. Reprocessing may change the result. The lab must document segmentation rules and artifacts before comparing with any void limit. These fictional values are not universal acceptance criteria.

Correlate cross sections with other tests

Cross-section analysis is destructive and samples a small part of production. Pair it with process and performance controls:

• crimp dimension or press displacement;
• die/press setup and maintenance;
• crimp-force monitoring where applicable;
• conductor insertion and strip quality;
• pull-out/retention tests under the relevant method;
• four-wire assembly resistance;
• temperature rise under specified current;
• vibration/environmental conditioning; and
• production traceability.

Molex’s official Quality Crimp Handbook explains that under-crimping can fail to create adequate metal contact, while over-crimping can reduce conductor circular area and increase resistance. It describes pull force as a quick destructive indicator and lists strand damage, bell mouth, crimp height and tooling as contributors. The handbook is aimed at Molex crimp practice, not a universal lug specification, but it supports using complementary evidence rather than one photograph. Molex Quality Crimp Handbook.

A high pull force does not prove low electrical resistance, and a dense section does not prove fatigue life. Define each test’s purpose. Use correlation studies during qualification to set meaningful process controls.

Set sampling around process risk

Require sections at initial qualification, new tool or die, setup/changeover, cable/lug source change, press maintenance, unexplained process shift and scheduled production intervals. Sample all cavities or die positions that can produce different geometry. Include start-up and stable-run parts.

A risk-based plan should increase sampling after:

• die damage or replacement;
• press shut-height adjustment;
• conductor strand/OD or plating change;
• lug barrel revision;
• operator/process change;
• force-monitor alarm trend;
• resistance or pull-test drift; or
• customer/field failure.

Do not cut the only first article needed for fit or functional assembly. Plan sacrificial samples with the same material lots and process conditions. Mark samples before removal so identity is not lost.

For high-volume production, cross sections validate the process while nondestructive controls screen each cycle. No sample plan can justify ignoring a clear production alarm.

Handle long barrels and multiple compressions explicitly

Large battery lugs often use two or more compressions along a long barrel. One acceptable plane cannot prove that every compression was made in the correct position or sequence. The drawing should define the first compression datum, spacing between compressions, orientation if dies are rotated, and the no-crimp zones near the bell mouth, inspection window or palm transition.

Select sections that represent each distinct compression condition. If two identical hex compressions are required, the plan may still need evidence from both during qualification because cable insertion can be good at the entry and poor near the closed end, or vice versa. For indent tools, inspect the region of maximum indentation and any seam-opposite region specified by the manufacturer. Preserve an exterior photograph with compression marks before sectioning so an internal defect can be related to tool position.

Sequential crimp order can move conductor material or barrel length. Record whether work proceeds from palm toward cable or the reverse, and follow the lug/tool instruction. A supplier should not change order to improve one micrograph while leaving production drawings unchanged. Check that compression does not encroach on the lug palm or create a sharp cable-side transition.

For a barrel approved to accept more than one conductor, require a dedicated qualification for the exact conductor count, sizes and arrangement. Do not infer multi-conductor acceptance from total copper area. Strand distribution, insertion depth and void paths can differ substantially, and a section can miss a shorter conductor. Mark insertion lengths and, where needed, section longitudinally or use a complementary method to confirm every conductor reaches the required position.

Compare supplier reports

On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.

Control laboratory and reviewer capability

Use a written work instruction and proficiency samples. Two trained reviewers should reach consistent results within defined measurement repeatability. Conduct periodic measurement-system analysis for critical dimensions and segmentation where practical.

Protect sample and data chain of custody. File names should not be the only identity; embed sample number, order, lot and plane in the report. Back up raw images and prevent silent overwriting. Record any remeasurement, reason and approver.

If an external laboratory is used, define its scope and reporting method. Accreditation, if required by the project, must cover the relevant work; do not infer it from a logo. The supplier remains responsible for linking the tested specimen to production.

Control changes and failure investigation

Require requalification review after changes to conductor supplier, strand construction, plating, insulation strip, lug material/barrel, die, press, software, preparation method or acceptance specification. Tool wear is a gradual change and needs preventive maintenance plus trend evidence.

When a failure occurs, preserve the original assembly and planned section locations. Do not immediately cut through the hottest or cracked location without documenting the exterior. Gather resistance, X-ray or other nondestructive data first if useful. Section both failed and known-good controls under the same preparation.

Separate root cause from symptom. A connected seam void can result from wrong conductor, incomplete insertion, die mismatch, misalignment or insufficient compression. Correct the process cause and verify new sections plus performance tests. Do not close the action by accepting a new photograph alone.

Send a complete cross-section RFQ

Attach cable and lug specifications, tool/die schedule, crimp drawing, planned planes, preparation method, measurements, defect criteria, sample plan and complementary tests. Request native images and measurement exports with the report. Ask suppliers to identify any criterion they cannot support before award.

Use the battery cable first-article guide to integrate the microsection with finished-assembly release and the SINAWATTS knowledge center for resistance and environmental tests. When the controlled combination is defined, send the project-specific RFQ with exact section planes and evidence deliverables.

Buyer FAQ

Is one polished cross section enough to approve a crimp process?

Usually not. Sample count and planes must represent setup, tooling positions and production variation. Pair sections with crimp dimensions, pull/retention, resistance and relevant environmental evidence.

Is a low void percentage always a good crimp?

No. Over-compression can damage strands or barrel wall. Void location and connectivity matter, and the accepted range must come from the exact termination specification.

Can an open-barrel contact micrograph standard be used for a cable lug?

Only if the applicable lug specification explicitly adopts its features. Open-barrel B-crimp geometry and large closed-barrel compression geometry are different. Use the exact lug/tool criteria.

Why must section location be specified before cutting?

Geometry changes along the barrel. Choosing the plane after inspection can hide a defect or sample a transition rather than full compression. Use a datum and preserve every planned section.

How can preparation smear be distinguished from real metal?

Use validated cutting and polishing, inspect scratch direction and edges, compare adjacent depths/planes, and obtain a second review. Reprepare when the artifact prevents a defensible measurement.

Does pull-force passing prove the cross section is acceptable?

No. Pull force is a mechanical indicator. It may not reveal electrical resistance, barrel cracks, strand distribution or local voids. Each criterion remains independent unless the approved specification states otherwise.

Should every production crimp be sectioned?

No; sectioning is destructive. Use risk-based periodic and event-triggered samples, while controlling every cycle with appropriate process checks. Increase sampling after changes or alarms.

Can image software decide pass/fail automatically?

It can support repeatable measurement when the workflow and segmentation are validated. A qualified reviewer still needs to confirm plane, preparation quality, specification and artifacts, especially for borderline results.

What raw data should accompany the report?

Keep full-resolution calibrated images, orientation and plane, preparation record, measurement overlays/exports, sample identity, tool/cable/lug lots, reviewer, software version and any remeasurement history.

When must the microsection qualification be repeated?

Review changes to conductor construction, lug/barrel, plating, die/tool, press, setup, preparation method, software or acceptance criteria. Also repeat after tool damage, unexplained resistance/pull drift or relevant field failure.