How to "Undress" Without Hurting the wire harness "Skin"?

The Wire Harness Art of Stripping — How to "Undress" Without Hurting the wire "Skin"?

In the wire and cable processing industry, stripping is the "throat" of all operations. If this step is not done right, subsequent processes like crimping, soldering, and assembly become impossible.

If we compare stripping to "undressing," then the conductor is the delicate "skin." Many times, a difference of just 0.01 mm in cutting depth can turn a perfect wire into a damaged reject — with nicked strands, broken wires, necking, and more.

So, how do you strip insulation cleanly without damaging the copper underneath? This is not just about adjusting machine parameters — it is an art of micro-manipulation involving mechanics, geometry, and materials.

1. Why Does the "Skin" Always Get Hurt? The Physics Behind Stripping

Many people think the stripping blade cuts through the insulation like a knife through a vegetable.

Wrong!

The actual automated stripping process happens in two stages:

• ✅Cut-in stage: The blade moves vertically downward (or closes symmetrically) into the insulation, typically cutting 60%–80% of the insulation thickness.

• ✅Pull-off stage: The blade stops pressing and moves laterally (the stripping stroke). The remaining uncut insulation becomes thinner under tension and finally tears naturally at the blade edge.

The truth about "hurting the conductor": Most damage is not caused by excessive pulling force, but by the blade cutting too deep.
When the cut-in depth exceeds the insulation thickness limit, or when the gap between the blade and copper is insufficient during pull-off, any tiny vibration or eccentricity will cause the blade to "engrave" the copper surface — leaving permanent marks that seriously affect conductivity and mechanical strength.

2. Say No to "Brute-Force Stripping": Fine-Tuning the Three Core Parameters

To avoid damaging the conductor, you must master these three "golden parameters" on fully automatic stripping machines.

2.1 Cut-in Depth — Finding the "Critical Point"

This is the most critical parameter and must be calculated based on the actual insulation thickness.

Correct understanding:
✅Insulation thickness = (Wire outer diameter – Conductor outer diameter) / 2
✅The cut-in depth (per side) must be less than the insulation thickness, leaving a safety margin.

Recommended formula:

Cut-in depth = Insulation thickness – (0.02 to 0.08 mm)

Practical empirical values (for standard electronic wires):

• Fine wires (AWG28 ~ AWG24): Cut 0.02–0.04 mm shallower than insulation thickness

• Thick wires (AWG18 ~ AWG12): Cut 0.05–0.10 mm shallower than insulation thickness

Practical tip — "Start shallow, then go deeper":
During setup, start with a conservative depth that will certainly not damage the conductor (e.g., 0.1 mm shallower than insulation thickness). If the insulation does not pull off cleanly or leaves long "tails" (burrs), increase the cut-in depth in steps of 0.01 mm until you achieve a clean strip.

2.2 Retract / Back-off Value — The "Lifesaver" of Stripping

This is the most powerful technique to prevent scraping of the copper, yet many operators are unaware of it.

Principle:
After the blade cuts to the preset depth, before it starts the lateral pull-off, the blade retracts (opens) slightly by a very small distance.

Why it matters:
This tiny "retraction" creates a safety gap (typically 0.01–0.05 mm) between the blade edge and the copper wire. During the pull-off stroke, the blade actually "pushes" the insulation forward instead of "scraping" against the copper. Stripping without a retract value is brute-force stripping.

Recommendations:

• Hard insulation (e.g., Teflon, PVC): Use a smaller retract value (0.01–0.02 mm)

• Soft insulation (e.g., silicone, TPE): Use a larger retract value (0.03–0.05 mm) to prevent material sticking

2.3 Stripping Speed — Firm yet Gentle

Speed has a significant effect on cut quality and conductor stress.

Note: Too fast may increase vibration and cause depth fluctuation; too slow may lead to "tough" tearing. Fine-tune based on the actual wire.

3. Troubleshooting Clinic: What About Residue, Scratches, and Broken Strands?

Q1: After stripping, the wire surface feels "sticky" or has broken insulation residue?

Deep analysis:
This is usually caused by adhesion between the insulation and copper from the extrusion process, or because the insulation material has a low melting point (e.g., PVC, TPE) and cutting heat causes melting/sticking.

Solutions:
① Use "partial strip" function: Do not strip the entire length at once — strip a short section first to reduce friction and heat buildup.
② Use coated blades: Choose PTFE (Teflon) coated or diamond-like carbon (DLC) coated blades to reduce adhesion.
③ Reduce stripping speed to minimize frictional heat.

Q2: The copper strands are not broken, but have obvious shiny marks or whitening?

Deep analysis:
This is a classic symptom of insufficient retract value. The blade is scraping across the copper surface like a planer, causing cold welding or scoring.

Solutions:
Increase the retract value (let the blade open 0.01–0.03 mm more). Also check the blade edge for tiny nicks.

Q3: When stripping fine multi-strand copper (e.g., 7/0.127 mm), one or two strands always break?

Deep analysis:
Two common causes: ① The wire is eccentric (conductor not centered in the insulation); ② The multi-strand bundle is loose, and the blade edge gets caught between strands.

Solutions:
① Change blade type: Replace the standard V-blade with a radius blade (U-blade), which better conforms to the round conductor and distributes force more evenly.
② Reduce cut-in depth slightly, and compensate for eccentricity by using partial stripping or staged stripping.
③ For ultra-fine multi-strand wires, prefer rotary stripping (rather than straight-cut) or laser stripping.

Q4: After stripping, the insulation end shrinks back, exposing too much conductor?

Deep analysis:
Common with TPE or silicone wires. The pulling tension causes elastic stretching of the insulation, which retracts after cutting.

Solutions:

• Use heated stripping (temperature-controlled blades) to cut the insulation more easily in a slightly warm state, reducing retraction.

• Adjust the "pre-stretch" or "dwell time" parameters to allow the material to relax.

4. The Intuition of a Master Craftsman: From "Parameter Tweaking" to "Reading the Condition"

In real production, no single set of parameters works forever for all wires. Changes in ambient temperature (insulation becomes stiffer in winter, softer in summer), blade wear, and batch-to-batch wire variations all affect the result.

The professional's self-discipline:

• Periodic checks: Inspect stripping results every 1–2 hours. Do not rely on the naked eye alone — use a 10× to 20× magnifier or stereo microscope to check for nicks, shiny marks, or micro-cracks on the conductor surface.

• Document parameters: Create a "process card" for each wire type, recording cut-in depth, retract value, speed, and blade type — reducing repeated trial-and-error.

• Monitor blade life: Standard high-speed steel (HSS) blades need replacement or sharpening after 5,000–10,000 cycles; carbide blades last longer, but their edges still require regular inspection.

Remember: The best stripping process is one where the insulation falls away like ripe fruit peel, leaving the copper underneath as bright and pristine as ever.

Master this art of "undressing without hurting the skin," and you will be one step closer to top-tier wire harness processing technology.