2.1 Wire Preparation: Single Conductor Processing

Cutting,Wire stripping,preparation and crimping formis the high-speed automated foundation of reliablethe entire harness manufacturing process. Errors introduced here — variable lengths, nicked conductor strands, or damaged insulation — are often impossible to detect after termination and result in latent reliability failures. This stage transforms raw material into precision components, requiring strict machine capability controls and visual standards that exceed simple dimensional checks.

2.1.1 Length Control and Machine Capability

Modern Cut-and-Strip machines are high-precision CNC tools. However, wire harnesselasticity, manufacturing.spool Thesetension, stepsand determinedrive notroller onlyslippage introduce variation. Relying on a single "First Article" measurement is insufficient; statistical control is mandatory.

Capabilities and Tolerances

• Machine Capability (C_pk): The cutting process must demonstrate a C_pk ≥ 1.33. This ensures that 99.99% of wires fall within the physicaltolerance fitwindow without constant operator adjustment.
• Standard Tolerances: Unless specified otherwise, industry baseline length tolerances are:
  • Wire length < 1000 mm: ± 2 mm
  • Wire length > 1000 mm: ± 5 mm or 0.5% of conductorstotal andlength.
• Strip terminalsLength butTolerance: alsoThe the long-term electrical and mechanical integritylength of the assembly.exposed Precisionconductor atis thiscritical stagefor reducesthe downstreamcrimp variability, prevents costly rework,"brush" and ensures"bellmouth." connectorsTypical engagetolerance with the same assured consistency across every build. The right tooling, disciplined process control, and well-defined acceptance criteria transform these basic operations into a repeatable source of quality.

  2.1.1 The aim (in one line)

  Every lead comes off the benchis the± same0.5 length, the same strip, the same crimpmm—so connectors seat with a click and never come back.

  
  

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  2.1.2 Tooling overview (pick the right hammer)

  Cut/Strip

  • Automatic cut/stripers (bench or inline): fastest, programmable lengths/strips; great for batches.
  • Bench strippers (mechanical/rotary): versatile; rotary is kinder to fine strand.
  • Thermal strippers: for PTFE/FEP and brittle jackets—no nicking, slower cycle.
  • Coax prep tools: multi-step dies that expose braid/dielectric/center length in one squeeze.
    .

  Crimp

  Process
  • Press + applicatorMandate: (open-barrelProduction “B-crimp” with insulation support): production standard, controlled crimp height.
  • Hand ratchet crimpers (with locators): for low-mix/repair;runs must be the manufacturer’s tool/die.
  • Hex/square crimpers: ferrules, closed-barrel terminals, and shields.
  • Coax crimp sets: separate nests for ferrule, shield, center pin—follow the family’s spec.
    

  Golden rules

  • Use the terminal maker’s applicator/die whenever possible.
  • Ratchet tools only; no pliers.
  • Tie tools to cal/verification in your gage program (18.2).
    

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  2.1.3 Cutting: length that actually fits

  • Measure along centerline, bare-end to bare-end (state in drawing, 19.2).
  • Post tolerances: e.g., ±5 mm ≤500 mm; then ±1% beyond.
  • Keep blades sharp; dull blades crush insulation → strip problems later.
  • Batch discipline: lot tag each bundle with wire ID, length, strip plan, and WO.

  Quick check: pull 5 random pieces onto a go/no-go stick for that length; record if any miss.

  
  

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  2.1.4 Stripping: clean copper, no casualties

  • Strip length peruse wire table; typical crimp ends want no tinning (stranded wire + crimp likes bare copper).
  • Do not nick strands. Rotary or thermal for fine strand/teflon; mechanical for PVC/XLPE if sharp and set right.
  • Leave a tiny conductor brush (0.2–0.5 mm) beyond the conductor crimp after crimping.
  • Keep insulation debris out of contacts; bench vacuum helps.
  • For twisted pairs: maintain twist up to the terminal unless the spec says otherwise.

  Strip defects & causes

  • Nicked/missing strands → jaws set too tight / dull blades → re-set or change blades.
  • Short/long strip → wrong program / measuring from wrong datum → fix strip stop and re-train.
  • Flagging insulation → dull blades / pull-off speed too high → service tool and slow pull.
    

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  2.1.5 Crimp setup (make the die do the thinking)

  • Set wire range exactly (e.g., 20–22 AWG); don’t “make” 18 AWG fit.
  • Adjust crimp heightstraighteners to the terminal spec; lock jam nuts/knobs.
  • Set insulation support wings so they capture insulation, not copper.
  • Useremove the locator"memory" so(curvature) seam sits wherefrom the makerspool. intendsKinked (nowire rotatedleads barrels).
  • First-articleto routine:inconsistent 10 samples → measure crimp height, pull force,lengths and feed jams.visuals.
    Keep

    2.1.2 themStripping asQuality: goldensThe forDefect Atlas

    Stripping is the lot.
    

  mechanical

  
  

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  2.1.6 What “good” looks like (visual cues you can teach in a minute)

  • Conductor crimp: tight barrel, symmetrical “B”, strands fully captured, small front bellmouth, light rear bellmouth.
  • Conductor brush: 0.2–0.5 mmremoval of copper just visible.
  • Insulation support: wings wrap insulation (nowithout piercing into copper), seated flush to barrel.
  • No flares/flags: no stray strands, no split seam.
  • Terminal position: locator marks correct; cavity latch/TPA engages freely.

  Post a postcard-sized photo sheet: GOOD / MARGINAL / REJECT.

  
  

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  2.1.7 Acceptance: crimp height & pull-force

  Crimp height (CH)

  • Measure with a flat-anvil micrometer acrossdamaging the centerunderlying conductor. The choice of the conductor crimp, perpendicular to the seam.
  • Compare to terminal manufacturer’s specblade (preferred).V-Blade Ifvs. absent, set your own NOM from first-articleDie-Blade) and guard-bandblade ±0.03–0.05sharpness mmdictates quality.

    Critical Stripping Defects (light wires tighter, heavy looser).

  • Record CH mean/Cpk by lot if you run volume; adjust press if drift shows.
    

  Pull-force (destructive test)

  • Use the maker’s minimums when available. If not, a starter plant baseline (replace once you have vendor data):
    
  IPC/WHMA-A-620)

  AWGDefect Type	MinMechanism	Acceptance pullCriteria (N)Class 3)
  Nicked Strands	28–30The blade cuts too deep, scoring or notching the copper strands.	10–15Reduce Current/Fatigue Risk. Allowable nicks are strictly limited. Class 3 typically permits zero severed strands and minimal nicking (≤ 5% of strand diameter).
  Cut/Missing Strands	26Complete severance of one or more conductor strands.	20Defect. Reduces the cross-sectional area and current carrying capacity.
  Insulation Slug	24A piece of waste insulation remains attached to the conductor.	30Defect. Prevents proper insertion into the crimp barrel or solder cup.
  Birdcaging	22Strands flare out or separate, creating a "cage" shape.	40Defect. Prevents insertion; strands may be bent back outside the terminal, causing shorts.
  Insulation Damage	20Blade marks, crushing, or burning on the remaining insulation.	60Defect
  18 if the damage reduces insulation thickness by > 20% or exposes the conductor.	80
  16	100

  Method:Setup Note: pullV-Blades inlineare atuniversal but risk nicking strands if the wire is not perfectly centered. ~25–50 mm/minDie-Blades until(sized failure.exactly to the conductor) are mandatory for high-reliability aerospace/medical stripping to guarantee concentricity.

  2.1.3 End Preparation: Twisting and Pre-Tinning

  Once stripped, the conductor strands act as individual loose wires. End preparation consolidates them for the next step.

  A) Twisting

  Twisting restores the lay of the strands that may have been disturbed during stripping.

  • Mandate: Twist must be in the Acceptsame direction whenas copperthe original manufacturer's lay.
  • Tightness: The twist must be tight enough to prevent splaying (stray strands) during insertion into a crimp barrel or PCB hole, but not so tight that it increases the effective diameter beyond the terminal's capacity.

  B) Pre-Tinning (For Solder Terminations Only)

  Pre-tinning involves dipping the twisted end into a solder pot to fuse the strands failinto beforea solid unit.

  • Application: Mandatory for wires intended for solder cups or PCB through-holes.
  • Prohibited for Crimping: Never pre-tin a wire that is intended for a crimp termination. Solder is a soft metal that "creeps" (cold flows) under compression, causing the crimp barrelto slipsloosen (forover open-barrel types)time and the peak ≥ minimum. Log result.

    Note: These are starting points. Always supersede with contact-specific pull values from the manufacturer’s data sheet.

    
    

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    2.1.8 Special cases (so you don’t learn the hard way)

    • Ferrules (square/hex): size ferrule to conductor cross-section, not AWG label; no tinning under ferrules; use square for spring terminals, hex for power lugs.fail.
    • CoaxWicking Control:: threeThe crimps—centercritical pin,quality metric is limiting braid/ferrulesolder wicking, optional strain boot; lengths are critical (usecapillary action) up the family’swire stripunder template).the insulation.
      • The Defect: If solder wicks too far up, it creates a rigid "stress riser" point where the wire loses flexibility. Vibration will cause the wire to snap exactly at the end of the wicking.
      • High-flex wire (Class 6)Limit:: rotaryWicking ormust thermalstop strip; ensure insulation support iswithin gentle3 mm (no≈ cutting0.125 inch) of the jacket).insulation end, or as defined by the spec. The wire must remain flexible immediately behind the termination.
      • Tin-plated wire: okay; don’t add solder to improve pull—solder wicks and embrittles.
        

    
    

    Final

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    Checklist:

    2.1.9Wire ProcessPreparation control (lightweight but real)

    • Lot start: 10-piece first article (CH + pull + visuals).
    • Hourly (or every reel change): 3-piece CH check + 1 visual.
    • Per 1000 crimps (or at changeover): 3 pulls.
    • Track CH on an I–MR chart (15.5); react to rules, not wiggles.
    • Tie tooling to PM & calibration: die wear and ratchet timing drift show up as CH/pull slips (18.1/18.2).

    
    

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    2.1.10 Common defects → quickest reliable fixControls

    DefectMandate	Why it happensCriteria	FirstVerification fixAction
    UndercrimpCpk Validation	Cut and strip machines must demonstrate Cpk ≥ 1.33 (low pull, fat CH).	HeightPeriodic toocapability highstudies /using wrongautomated wirelength size	Lowermeasurement CH per spec; confirm wire rangetools.
    OvercrimpStrand Integrity	Zero cut strands (cutallowed strands,for barrelClass cracks)3. Nicks limited to <5% of strand diameter.	HeightVisual tooinspection low	Raise(10x CH;magnification) scrapof diethe iffirst seam5 damage
    Strandspieces outsideat barrel	Short strip / poor insertion	Increase strip length; teach locator usesetup.
    Insulation in conductor crimpQuality	Over-stripStrip /cut wiremust pushedbe inclean tooand farsquare; no ragged edges or slugs remaining.	ReduceVisual strip;check. setEnsure wirestrip stoplength /matches locatorthe terminal's required "brush" length.
    NoTinning insulation supportRule	Do not tinWings mis-setwires /intended jacketfor too smallcrimping.	Re-formProcess wings;audit ensureensures correcttinning wireis ODonly rangeapplied to soldered terminations.
    NickedWicking strandsLimit	Aggressive/mechSolder stripwicking onunder fineinsulation wiremust be minimized (typically < 3 mm).	SwitchTactile check: The wire must remain flexible right up to rotary/thermal;the replacetermination bladespoint.
    TerminalBirdcage won’t latch/TPA failsPrevention	DeformedStripped contactends /must wrongremain cavitytwisted and coherent.	CheckVisual locator;check verifyto cavityensure numbering;no changesplayed astrands bentthat contactcould cause shorts.

    
    

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    2.1.11 Pocket checklists

    Before you start

    • Wire ID, length, strip dims from wire table
    • Correct terminal PN and tool/die (with locator)
    • Strip method chosen (rotary/thermal for fine/PTFE)
      Press set to initial CH; insulation support formed

    First article (10 pcs)

    • CH within spec (record mean/range)
    • Pull ≥ min; failure in copper, not slip
    • Visuals: bellmouth/brush/insulation support OK
    • Keep samples as goldens; release lot

    During run

    • Hourly CH check (3 pcs); trend quiet
    • Swap blades/dies if nicking or CH drift
    • Housekeeping: no copper whiskers in nests

    Close/trace

    • Record terminal lot, wire lot, tool/die ID, CH/pull results
    • Tag any rework; isolate suspect batches
      

    
    

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    Clear datums, calibrated tools, and disciplined checks ensure every lead matches specification and every crimp meets strength requirements. By standardizing these fundamentals, harness shops eliminate recurring defects, stabilize process flow, and build assemblies that lock in place with confidence.