The plant built three seat variants for two vehicle models: a manual seat, a power seat and a heated power seat. The line had to run all three at a 45-second takt, with a changeover that did not stop the line.
The constraint
The three variants shared a frame but differed in the trim, the wiring harness, the switch pack and the test program. The power seat had a motor and a memory module, which added 9 seconds of work. The heated seat added a harness and a test step. A line balanced for the manual seat would have been over takt on the power seat.
The plant had 14 stations available and could not add floor space. The line had to fit in the existing 22-metre bay.
The line design
We used a speed chain line with a 700 mm pitch and 14 stations, double-sided in the middle section. The carrier was common; the nest was variant-specific. The nest located the seat by the frame and had a cut-out for the motor on the power variant.
The changeover was designed as a subplate system: the nest was mounted on a subplate that located on two pins and locked with a cam lever. The operator could change the nest in about 40 seconds, which is less than one cycle, so the line did not stop.
| Variant | Work content | Stations | Test time |
|---|---|---|---|
| Manual seat | 38 s | 12 | 20 s |
| Power seat | 44 s | 14 | 32 s |
| Heated power seat | 45 s | 14 | 38 s |
Sequencing and buffers
The line controller sequenced the variants to alternate the high-content and low-content seats. A buffer of three carriers before the power-seat stations absorbed the difference. The sequence was displayed at each station, and the material was delivered in the same sequence.
The material for the power seat was presented in a sequenced kit that travelled with the carrier. The kit had a scan label that the operator confirmed before fitting the motor. If the kit did not match the seat, the line rejected the carrier.
Torque and traceability
Each station with a critical fastener had a torque tool connected to the line controller. The controller read the seat ID from the carrier and stored the torque result against it. If a torque was out of limit, the carrier was routed to a rework lane at the end of the line.
The rework lane had its own torque tool and a read station, so the reworked seat had a complete record. The customer's auditor could trace a seat from the frame build to the final test in under a minute.
What was difficult
The power seat motor added weight to one end of the seat, which changed the centre of gravity. The carrier tilted slightly at the transfer, and the trim station had to be adjusted. We added a counterweight to the carrier and a guide rail at the transfer.
The second issue was the test time. The heated seat test took 38 seconds, which was close to the takt. We added a second test fixture in parallel, which gave 19 seconds effective. The test station became the constraint until the second fixture was installed.
Lessons
Design the nest change before the line layout. The subplate system was the reason the line could run mixed models without stopping. Do not leave the test station until last; it is often the real bottleneck in a mixed-model line.
Frequently asked questions
How long does the nest change take?
About 38 seconds with the subplate system, which is less than one 45-second cycle.
Can the line run a fourth variant?
Yes, if the work content fits within 45 seconds and the nest can be designed. The line has spare stations at the end for a future variant.
How is the sequence controlled?
The line controller receives the build sequence from the customer's MES and displays it at each station. The material kits are sequenced to match.
If you are planning a mixed-model seat or component line, send the variant matrix and takt to our engineers through the contact page.
