A portable inspection instrument needed a fabricated aluminum enclosure with consistent display and connector interfaces. The enclosure also had to fit the internal plastic components after anodizing. Meeting the unfinished sheet-metal dimensions was therefore only part of the acceptance task.
The project focused on the relationship between machining, surface treatment and final assembly. The resulting controls covered finished dimensions, color consistency and usable threaded holes rather than appearance alone.
The customer’s challenge
Anodizing changed the interface dimensions by a reported 0.005–0.02 mm per face, with enough variation to make some display windows and connector openings too tight or too loose. Different production lots also showed visible color differences, and some threaded holes became obstructed after treatment.
These issues appeared at assembly, where the finished enclosure met plastic parts and the display. An acceptable pre-finish opening did not necessarily provide an acceptable final clearance.
Material and fabrication route
The enclosure used 2.0 mm 6061 aluminum, with a 2.5 mm front panel. Its approximate overall size was 280 × 200 × 60 mm.
Process route: Laser cutting → bending → welding → surface blending → chemical cleaning → anodizing → screen printing → dimensional reinspection → assembly.
The recorded anodic film thickness was 10–15 μm. Dimensional inspection followed treatment, placing the acceptance check after the operation that had been changing the mating interfaces.
Manufacturing changes
The team introduced a dimensional compensation allowance before anodizing. Critical mating holes received secondary precision machining after treatment, bringing the final interface under dimensional control at the point where the part would actually be assembled.
Aluminum from the same material batch was processed together for anodizing to reduce appearance variation. Protective plugs were fitted to threaded holes before treatment, and the finished threads were checked with go/no-go gauges.
Before-and-after dimensional records linked the treatment step to the final inspection. This made the change in a feature visible rather than leaving the assembly team to discover it through difficult fitting.
Engineering analysis
The key distinction was between coating thickness and the dimensional change recorded at a mating surface. The project tracked both; the film-thickness value was not used as a direct replacement for the measured change in an opening.
Compensation and post-finish machining solved different parts of the problem. Compensation anticipated treatment effects, while secondary machining defined selected critical interfaces after those effects had occurred. The locations requiring that sequence must be agreed on a project drawing.
Thread protection and material-batch consistency complemented the dimensional controls. They addressed assembly usability and appearance without changing the customer’s display or internal plastic interfaces.
Inspection and project results
| Project measurement or production detail | Recorded value |
|---|---|
| Anodic film thickness | 10–15 μm |
| Dimensional change after anodizing | ≤0.02 mm per face |
| Finished mating-interface tolerance | ±0.03 mm |
| Color difference | ΔE ≤1.0 |
| Approximate enclosure size | 280 × 200 × 60 mm |
| Project production quantity | 120 parts per week |
The finished interfaces maintained uniform assembly clearances. All threaded holes passed the recorded go/no-go checks, and the enclosures passed assembly on the first attempt in the reported project work.
The dimensional and appearance results belong to this enclosure and finishing route. A new alloy, geometry, finish specification or mating part requires a separate review.
Planning a similar OEM component
For custom instrument enclosures, include:
- Final, post-treatment dimensions for the display and connector interfaces.
- The specified alloy, sheet thickness and surface treatment.
- Thread-protection areas and any approved post-finish machining.
- An appearance reference and the required dimensional inspection records.
Use the sheet metal DFM guide to organize the fabrication inputs before agreeing how the enclosure will be accepted after finishing.
