Thursday’s BIW cell passed path verification. Coupons from mid-shift showed incomplete penetration and root porosity. Focus had drifted 0.6 mm after a lens clean, joint gap opened on a stamped flange lot, and power was left at the recipe that assumed tight fit-up. The robot repeated strokes perfectly into a collapsing keyhole.
Robotic laser welding owns path and timing. This brief owns the keyhole as a process window: power density, focal position, travel speed, and gap must keep a stable vapor cavity. When any one walks, the cavity collapses and freezes defects that NDE finds later—or the customer finds first.
What keeps a keyhole honest
Focus and optics. Contaminated cover glass and wrong standoff move the waist out of the joint. Clean optics without re-verifying focus is how “after PM” scrap starts.
Gap and fit-up. Keyhole mode forgives less than conduction mode. Stamp springback and clamp wear are MoC events for laser recipes, not assembly footnotes.
Power vs. speed. Raising speed to hit takt without power or focus compensation shortens the cavity; incomplete fusion follows the robot serial, not the steel heat.
Shield and plume. Unstable assist gas or a dirty nozzle lets porosity seed at the root while the bead looks cosmetic on top.
Review pack for the cell
- Same-shift macro or CT on a witness coupon when optics, tip, or material lot changes.
- Gap capability from the stamp/clamp station tied to the laser recipe ID.
- Focus check log after every optics service—signed, timed, machine ID.
Do not chase robot speed for porosity while focus and gap are out of window. Do not release a “path OK” cell that skipped coupon after a lens change.
The robot owns the stroke. The keyhole owns whether that stroke is a weld or a tunnel of voids waiting for fatigue.