Cutting & Folding Defects in Li-ion Pouch Cell Manufacturing
Cutting & Folding Defects in Li-ion Pouch Cell Manufacturing
After the pocket has been formed in the aluminum laminate, the film must be cut to size and folded so that it becomes a pouch with a space for the jelly roll and flat edges for sealing. Cutting separates the pouch blank from the film web and trims the pocket and top edges. Folding brings the two halves over each other, forming the fold line and the sides that will later be sealed.
In the line, this stage sits between laminate pocket forming and jelly roll insertion. It looks like simple mechanical work, but every dimension created here sets how much sealing area is available, how the tabs will exit, and how well the pouch fits the cell. If the geometry is wrong, the sealing stage will inherit the error.
Why this stage matters
A clean, accurate cut and a sharp, even fold give a pouch with predictable edges. When the cut edge carries a burr, the sharp edge can scratch the sealant layer of the neighbouring film. A crack along the edge can grow under heat and stress. Wrong top-cut height shifts the tab clearance, and an incomplete fold leaves one half of the pouch higher than the other, so the sealing bars close unevenly.
These faults are cheap to prevent and expensive to fix later. A well-maintained blade, a correct die clearance and correct fold alignment protect the seal and the barrier layer, and they reduce rework and scrap further down the line.
How the process works
- Feeding. The formed laminate comes in with its pockets at a set pitch. Sensors confirm each pocket position.
- Pocket cutting. A die and blade set cuts the pocket outline, or the blank around it, to the drawing size.
- Folding. A folding tool presses the film along the fold line, bringing the two halves together while the pocket stays open for the jelly roll.
- Top cutting. The top edge is trimmed to the required height, leaving the specified margin for the top seal and tab area.
- Waste removal. Trim scrap is removed by suction or conveyor, so that small pieces do not land on the pouch.
- Inspection. A camera checks the cut line, fold and corners. Gauges are used for sampled dimension checks.
Key process parameters
Typical settings depend on cell design, materials and equipment supplier, and the dimensional tolerances come from the cell maker's drawing and specification.
| Parameter | What it controls | How it is checked |
|---|---|---|
| Blade sharpness and wear | Edge quality, burr size | Blade inspection schedule, magnified edge check |
| Blade clearance | Clean shear instead of tearing | Feeler gauge at setup, trial cut inspection |
| Cutting position and pitch | Edge placement relative to the pocket | Camera measurement, calliper |
| Fold line position and straightness | Symmetry of the two halves | Camera, gauge |
| Folding pressure | Crease quality, stress on the film | Pressure setting, visual check of the fold |
| Top-cut height | Seal margin and tab clearance | Height gauge, camera |
| Tool alignment | Edge, corner and fold accuracy | Alignment checks at setup and after maintenance |
Typical defects, causes and corrective actions
| Defect | Common causes | Detection | Corrective action |
|---|---|---|---|
| Burr on edge | Dull or chipped blade, wrong clearance | Magnified edge check, visual under good light | Replace or sharpen blade, reset clearance |
| Uneven pocket cutting | Misaligned cutting tool, feed error | Camera, dimension check | Re-align tool, verify feed length and sensors |
| Pocket folding defect | Wrong folding pressure, tool misalignment | Visual, camera | Re-set pressure, align folding tool |
| Incomplete fold | Low pressure, tool alignment, process variation | Visual, gauge on fold height | Adjust pressure, correct alignment, review timing |
| Top cut height variation | Positioning drift, sensor error, worn guides | Height gauge, camera | Recalibrate positioning, replace worn guides |
| Edge crack | Excess stress, poor tooling, brittle or aged film | Magnified visual, bend check on samples | Correct tooling, check film lot and storage |
| Corner damage | Tooling shape, misalignment, high stress | Visual, camera | Re-grind or replace tool, correct alignment |
Quality checks and measurements
- Dimension checks of pouch length, width, pocket position and top-cut height against the drawing.
- Edge inspection under magnification for burrs, whitening or cracks.
- CCD inspection of fold line, cut line and corners on every unit.
- Blade and tool records, showing hours or counts since sharpening and any chipping.
- First-piece approval after startup, blade change or tool adjustment.
- Reject trend review, so repeated defects can be traced to a tool or a position.
Safety and handling notes
- Blades and dies are sharp and can cause serious cuts. Never reach into the cutting area while the machine can move, and apply lockout before changing blades.
- Use blade-handling tools and cut-resistant gloves during maintenance, and store used blades safely.
- Scrap film has sharp edges. Dispose of it in the proper bin, not loose on the floor.
- Dust and fine plastic particles from cutting should be removed by extraction, because they can later contaminate the seal area.
- Keep guards and light curtains in place. Do not bypass interlocks to clear a jam faster.
Interview questions
1. What is a burr and why is it a problem?
It is a raised, rough edge from cutting. It can scratch or pierce the sealant layer, and it can lead to leaks.
2. How does blade clearance affect the cut?
Correct clearance shears cleanly. Too much or too little gives tearing, burrs or an uneven edge.
3. Why does top-cut height matter?
It sets the margin for the top seal and the clearance around the tabs.
4. What does an incomplete fold lead to?
The two halves do not meet evenly, so the sealing bars apply uneven pressure and weak seals can result.
5. How would you find the source of repeated edge cracks?
Check tooling and stress points first, then the film lot and storage age, then the process settings.
6. What records help control cutting quality?
Blade life logs, first-piece reports, dimension data and reject trends.
FAQs
How often should cutting blades be replaced?
There is no universal figure. Plants set a schedule from blade-wear data and edge-quality trends, then adjust when defects begin to rise.
Can burrs be removed after cutting?
Generally no. The correct approach is to prevent them with maintained tooling, and to reject affected pouches.
Are cutting and folding done on the same machine?
In many lines they are stations of one machine, but the arrangement varies between equipment suppliers.
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