Module assembly looks like conventional assembly with heavier parts. It is not. The product is electrically live at the end of the line, the scrap cost is measured in thousands of dollars per unit, and a single metal particle can create a field failure two years later.
Carrier design comes first
The carrier does three jobs: it locates the module for robotic handling, it insulates the module from the conveyor frame, and it contains any leakage if a cell vents.
Use an insulating carrier body in a glass-filled engineering plastic or a coated aluminium carrier with insulating inserts. Metal carriers are common and acceptable only if the module is fully isolated and the insulation is tested after every carrier repair.
Design the carrier for cleaning. Coolant, electrolyte and dust collect in pockets, and a carrier that cannot be washed will contaminate every module that passes through it.
Busbar handling
Busbars are thin, flexible and easily bent. A bent busbar will not align with the cell terminal, and forcing it damages the weld surface.
Transport busbars in a rigid tray that supports them along the full length, and present them at the station in the orientation they will be installed. Every manual pick-and-place of a busbar is a chance to bend it; automate the transfer where volume justifies it.
Laser welding of busbars needs a gap tolerance of under 0.2 mm between the busbar and the terminal. That tolerance is set by the carrier and the fixture, not by the robot. If the carrier locating repeatability is 0.5 mm, the weld quality will vary with it.
Cleanliness zones
Divide the line into zones by particle sensitivity: cell handling, stack assembly, welding, and final assembly. Each zone needs a defined cleanliness class, a pressure cascade so air flows from clean to less clean, and a pass-through that does not defeat the cascade.
A simple conveyor passing through a wall opening defeats the pressure cascade unless the opening is guarded with an air curtain or a tunnel. This is routinely missed in factory layouts, and it is expensive to fix after the walls are built.
Insulation and hipot testing
The insulation resistance test and the hipot test are performed at the end of the module line, and the conveyor must deliver the module in a known, repeatable state. Three requirements follow:
- The carrier must isolate the module from earth during the test, otherwise the measurement includes the conveyor frame.
- The test station needs a physical guard and an interlock; hipot voltages are lethal and the station is accessed every cycle.
- The test result must be tied to the module serial number before the module leaves the station, not after.
Test time is typically 5 to 20 seconds per module, which is usually longer than the takt. Either duplicate the test station or test in parallel on two carriers.
Safety around live modules
From the moment cells are stacked, treat the module as live. That means insulated tools, no loose metal on the conveyor, and a carrier that cannot short the terminals if it tips. Specify the conveyor with non-conductive guide rails in the live section, and mark the boundary on the floor.
Arc flash risk is low at module voltage, but short-circuit current is high. A dropped wrench across terminals produces a burn hazard and a ruined module within a fraction of a second.
Throughput reality
A module line is usually balanced around the welder and the test station, not around the conveyor. Check those two cycle times first; the conveyor can always be duplicated, but a second laser welder is a different budget conversation.
