How To Assembly Cylindrical Battery Pack?

The market for cylindrically-cell lithium battery packs continues to expand—from electric vehicles to energy storage systems, industrial equipment to portable power applications. 

• Cylindrical Battery Module & Pack Automation Line 

• EV Cylindrical Battery Module & Pack Assembly Line 

• EV Cylindrical Battery Module & Pack Assembly Lines 

This combined view covers the key components, equipment, process steps and considerations for a cylindrical battery pack assembly line.

Components & Equipment Overview

Before embarking on the assembly process, you should understand the standard work-stations and major equipment items typically used in cylindrical battery pack production:

• Cell testing and grading machines: for capacity, internal resistance and voltage screening of incoming cylindrical cells. 

• Insulation paper (barley-paper) pasting machines: to apply insulation around the positive terminal of cylindrical cells, improving safety and consistency. 

• Auto sorters / cell sort machines: detect and group cells by internal resistance/voltage to ensure pack consistency. 

• CCD testers / polar-detection machines: verify correct orientation (positive/negative) of individual cells before welding processes.

• Spot welding machines (for nickel strips or busbars): assemble cells into series/parallel groups. 

• BMS (Battery Management System) testers: validate protective electronics embedded in the pack. 

• Comprehensive testers / aging machines: conduct lifecycle, discharge/charge cycles, internal resistance, short-circuit testing etc. 

• Packaging / shrink-wrap / code-printing machines: for final external packaging, batch coding, shrink-film wrapping. 

Process Flow: Cylindrical Battery Pack Assembly

Here’s a proposed sequence of major process steps in the assembly of cylindrical battery packs, adapted from the Acey article and contextualised for line-automation.

1. Cell Sorting & Grading
   Incoming cylindrical cells (e.g., 18650, 21700, 26650, etc.) are tested for capacity, voltage, internal resistance. Cells outside thresholds are removed. This ensures consistency and helps avoid weak-links later in the pack. 

2. Insulation Paper Pasting
   Each cylindrical cell is wrapped or fitted with insulation paper (barley-paper) at the positive end to prevent short-circuits, dust ingress, and improve robustness under vibration and temperature. 

3. Cell Sorting by Resistance/Voltage
   After pre-insulation, cells are sorted into graded bins by internal resistance and OCV using auto sorters with barcode/tracking functionality. This step improves uniformity in the later series/parallel pack assembly. 

4. Polarity Detection (CCD Test)
   Before welding, a CCD vision system inspects each cell (or row of cells) to verify correct positive/negative orientation, avoiding assembly errors that could lead to shorts or defects. 

5. Spot Welding / Pack Formation
   Cells are welded together via nickel strips or busbar systems into configured series/parallel matrices. The spot-weld machine may support high current (e.g., 5 kA / 8 kA / 10 kA for 18650/21700 types) depending on pack size. 

6. BMS Integration & Testing
   The Battery Management System is installed in the pack. A BMS tester verifies protection functions—overcharge, overdischarge, overcurrent, standby consumption, etc. 

7. Comprehensive Testing & Aging
   The finished pack undergoes a series of tests—open circuit voltage, internal resistance, discharge, short-circuit protection, cycle life (aging machine) etc. Data is recorded for traceability. 

8. Shrink Packaging & Coding
   The pack is placed into outer casing or shrink-film, batch codes and production date printed using inkjet systems, and finally logged into the MES / tracking system. 

Key Considerations & Best Practices

• Cell consistency is critical: variation in internal resistance or capacity will reduce overall pack performance or longevity.

• Insulation and safety: especially for cylindrical packs, vibration, thermal expansion and unexpected short-paths are risks; early insulation steps reduce downstream issues.

• Orientation accuracy: mis-polarity insertion or weld errors can lead to catastrophic failure—CCD detection and automated fixturing minimise human error.

• Automation & throughput: implementing high automation (movable robots, conveyors, data tracking) improves yield, reduces labour and supports large-scale production. 

• Data traceability: From cell input to final pack, each unit should be tracked via barcode, test log, and database so that any failure back-trace is possible. 

• Flexibility for formats: Though cylindrical, sizes vary (18650, 21700 etc), so machines with modular moulds or adaptable fixtures help. 

Conclusion

Building a robust cylindrical battery pack assembly line demands more than just spot-welders and testers. It is a coordinated sequence of sorting, insulation, welding, BMS integration, testing, packaging and data management. By leveraging a full-line perspective

For companies specialising in cylindrical battery formats (18650/21700 and beyond), investing in automated sorting, CCD inspection, high-current weld systems and aging testers, along with full data architecture, is the roadmap to successful pack manufacturing.