The customer needed a medical equipment chassis that could serve as a dependable assembly datum, not simply a base with the correct outer dimensions. Several folded faces carried dense mounting-hole patterns. Errors between those faces appeared later as misalignment of the modules installed above them.
This project combined a revised fabrication sequence with a dedicated production gauge. The important change was to control the functional relationship between the mounting surfaces and holes before releasing each chassis to assembly.
The customer’s challenge
Multiple bends introduced cumulative variation across the chassis. The mounting-hole patterns exceeded their position allowance, and upper modules did not line up as intended. Inspection relied on coordinate measuring machine sampling, which did not provide a fast check on every outgoing part.
The customer therefore needed two linked improvements: a more stable hole-to-datum relationship and an inspection method that could keep pace with production. Increasing inspection effort alone would not remove the underlying forming variation.
Material and fabrication route
The chassis used 3.0 mm Q235 cold-rolled steel, with local mounting-datum sections increased to 4.0 mm.
Process route: Laser cutting → multi-step CNC bending → welding → stress relief → CNC machining of mounting datums and hole patterns → powder coating → gauge calibration → full inspection.
Finishing the functional features after forming and stress relief moved their final definition later in the route. This addressed the accumulated effects that had previously reached the assembly stage.
Manufacturing changes
The team revised the bend sequence and relief features and applied springback compensation. Instead of relying on the final positions of holes produced before forming, the mounting-hole patterns were CNC-machined together after bending.
A dedicated go/no-go fixture checked the mounting datums and associated hole patterns as one functional arrangement. Gauge calibration became part of the release sequence, and every chassis received the fixture check before leaving the line.
This combined approach mattered: machining addressed the feature relationship, while the fixture provided a repeatable production decision on each part. The gauge was not treated as a substitute for controlling the fabrication process.
Engineering analysis
A chassis can have individually acceptable features yet still create assembly problems when their relative positions vary. Here, the useful inspection boundary was the interface used by the upper modules: the supporting datum surfaces and the mounting-hole patterns referenced to them.
The dedicated fixture shortened the routine acceptance task compared with the earlier CMM-sampling workflow. Its recorded measurement accuracy and cycle time describe this project’s gauge; another chassis would require its own datum arrangement and acceptance criteria.
Inspection and project results
| Project measurement or production detail | Recorded value |
|---|---|
| Mounting-hole pattern position | ≤0.08 mm |
| Chassis flatness | ≤0.15 mm/m |
| Mounting-hole groups | At least 36 per chassis |
| Gauge measurement accuracy | ±0.02 mm |
| Full-inspection cycle | ≤30 seconds per part |
| Project production quantity | 80 parts per week |
The project recorded no nonconforming parts at line exit after the changes, and assembly first-pass performance improved.
These results apply to the recorded chassis, fabrication route and inspection fixture. They are not a blanket tolerance or production-rate commitment for other medical equipment.
Planning a similar OEM component
For a comparable medical equipment chassis, provide:
- Released drawings identifying the functional mounting datums.
- Hole-pattern requirements across all formed faces.
- The mating-module interfaces and assembly acceptance criteria.
- The required inspection method, sampling or full-inspection scope, and report format.
The quality-control capability should be agreed alongside the fabrication route, so the finished chassis and its inspection records address the same assembly requirements.
