SKD kit assembly line analysis - sharing observations from a recent process audit that might be useful
"We recently completed a process audit of an SKD kits and parts assembly operation that had been experiencing yield inconsistencies that did not correspond clearly to any single station failure. Sharing the findings because the root cause pattern might be familiar to others who have worked in similar environments.
The yield inconsistency was occurring across multiple assembly stations without any single station showing obvious performance deviation. Individual station cycle times were within specification. Individual station quality checks were passing. The assembled units were failing final inspection at a rate that the individual station data did not predict.
The investigation revealed that the issue was in the sequence and handling between stations rather than at any station itself. SKD component positioning tolerance at one station was creating variation that fell within that station's acceptance criteria but was cumulative with positioning variation at the subsequent station, producing assemblies where both stations had passed their local checks but the combination produced a final assembly outside specification.
Tolerance stack analysis applied retrospectively to the process confirmed what we found empirically. The individual station tolerances were appropriate in isolation but had been specified without adequate consideration of how they interacted across the assembly sequence.
The corrective action involved tightening positional tolerance at the upstream station and adding a cumulative check between the two stations that caught combinations likely to result in final assembly failure before they reached final inspection.
One of the engineers on the audit team made an observation about SKD operations globally that I found interesting from a supply chain perspective. He noted that reading procurement discussions in online shopping sites industrial components categories had shown him how differently SKD operations in different regions defined kit completeness, which had implications for process design that were worth understanding before specifying assembly sequences.
Has anyone else found tolerance stack issues presenting as distributed yield problems rather than locatable station failures?