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PRJ-2023-04Northline Rolling Stock — 2023
1,800 fatigue-rated bogie frames per year, with weld distortion engineered down 63% so machining removes stock instead of correcting shape.
Northline's frame supplier was meeting the drawing but not the schedule. Frames arrived at machining with up to 12 mm of distortion, which meant heavy stock allowances, long cycle times, and occasional structures that could not be recovered at all.
The program also had to satisfy EN 15085 CL1 welding coordination across a ramp from 400 to 1,800 frames per year without a quality excursion during the ramp.
Weld distortion was modeled before any fixture was cut. The model drove a revised sequence — balanced, symmetrical, and interrupted for intermediate measurement — that trades a slightly longer weld cycle for far less correction downstream.
Six dedicated robotic cells were commissioned with fixtures that hold the frame in its final constraint condition rather than in a convenient one.
Welding coordination was formalized under EN 15085 CL1, with welder continuity tracked in the same system that releases work orders, so an expired qualification physically stops the job.
Distortion fell 63%, and machining stock allowance dropped from 12 mm to 4 mm — a direct cycle time saving on every frame.
The ramp to 1,800 frames per year completed on schedule with no quality excursion, at 99.1% on-time delivery across the program.
Northline has since placed traction motor mounts and gearbox housings on the same line.
“The distortion model was the whole program. Everything downstream — cycle time, stock allowance, our own assembly line — followed from getting that right first.”
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