Medical Devices: 6061-T6 Structural Parts for a CT System
A medical imaging equipment maker needed structural members for a CT system: not visible parts, but the parts that decide whether a moving assembly runs true. Flatness and hole position were the whole job.
- Industry
- Medical devices
- Process
- Extrusion + CNC (6061-T6)
- Alloy
- 6061-T6
- Key spec
- Hole position ±0.01 mm
What the customer needed
The customer builds CT systems and needed structural aluminum members for an assembly that moves. The parts are not cosmetic; they position other components, so their flatness and hole position propagate through the whole assembly.
The quantified constraint was hole position at ±0.01 mm across faces, with flatness agreed per part because it depends on how the member is mounted. A rail that is out of flat loads the frame unevenly, and the symptom appears as binding in an axis far from the part that caused it.
Material choice was fixed at 6061-T6: stronger and more machinable than 6063, which matters when the part carries load and has a lot of material removed.
Constraints that decided the part
- Hole position ±0.01 mm across faces
- Flatness agreed per part, measured after relaxation
- Material fixed at 6061-T6
- Dimensional report before finishing
- No medical-device certification claimed or implied
How the part was made
The same route we would propose today, in the order it actually runs.
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Datum strategy agreed at DFM
We asked which face the assembly references and machined from that face. Where two faces both matter, we quantified the cost of extra setups instead of quietly choosing one.
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Extrusion in 6061-T6
Blanks extruded in 6061 and aged to T6, with enough allowance for the material that will be removed.
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Rough machining
Heavy removal first, then the part is allowed to relax before finishing cuts. Measuring straight after roughing is how a part passes inspection and fails in assembly.
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Finish machining
Bearing seats, mounting holes and faces cut to ±0.01 mm, with as few setups as the geometry allows.
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Inspection before finishing
Flatness and hole position measured and reported on the finished lot, before any surface treatment that would change the reading.
The numbers the part had to hold
These are the tolerances and process values that governed the job. They come from our capability, not from a customer specification we cannot publish.
| Parameter | Value | Why it mattered |
|---|---|---|
| Hole position | ±0.01 mm | Position of downstream components in the assembly |
| Flatness | Agreed per part | An out-of-flat rail loads the frame unevenly |
| Bore and OD | ±0.04 mm | Bearing seats and locating features |
| Alloy and temper | 6061-T6 | Strength and machinability for structural members |
| Stress relief | Between roughing and finishing | Stops the part moving after inspection |
| Inspection | Report with each lot | Documented before finishing |
The part of this job that nearly went wrong
This is the section worth reading. Every program has one problem that decides whether the parts come out right, and it is usually not the one on the drawing.
The part moved after it was inspected
A structural member in 6061-T6 with a lot of material removed carries residual stress. Machined to size in one sequence, it measures correctly and then relaxes over the following hours, taking the flatness with it.
The risk
A part that passes goods-in and fails at assembly, with the defect appearing days after the measurement that cleared it.
What we changed
Roughing, stress relief, then finishing. Flatness is measured after the part has relaxed rather than immediately off the machine, and the report states the stage at which each value was taken.
Hole position across two faces
Mounting holes on different faces have to stay in position relative to each other. Every additional setup adds a datum shift, and on a long member the shift accumulates along the part.
The risk
Bearing seats that do not line up, producing binding in a moving axis and a fault that is hard to trace back to a machined part.
What we changed
The datum was chosen from the assembly reference rather than from the most convenient face, and the setup count was minimised. Where a second setup was unavoidable, the fixture repeated the first datum instead of establishing a new one.
Parts that measured the same after they relaxed
The members are machined in 6061-T6 with hole position at ±0.01 mm and flatness agreed per part, measured after stress relief and reported before finishing.
The change that mattered was sequencing, not equipment. Roughing, relief and finishing cost a little more machine time and removed the class of failure where a part passes inspection and then moves.
On certification: we do not claim ISO 13485, FDA or MDR approval. We machine aluminum parts to drawing and inspect them; qualification of the finished device sits with the device manufacturer, and we would rather say that plainly than imply otherwise.
Common questions about this program
The questions this case generates from engineers and sourcing teams.
Are you certified for medical device manufacturing?
No. We do not hold or claim ISO 13485, FDA or MDR certification. We machine and inspect aluminum parts to drawing; regulatory qualification of the assembled device belongs to the device manufacturer.
Why 6061-T6 rather than 6063?
6061-T6 is stronger and machines more cleanly, which suits structural members with a lot of removed material. 6063 remains our choice for housings where the wall thickness and anodized appearance are the constraints.
How do you hold flatness on a long part?
The flatness value is agreed per part, the datum comes from the face the assembly references, and the measurement is taken after the part has relaxed. If the value you need is tighter than the geometry supports, we say so before the order rather than after.
Have a Structural Part Where Sequencing Is the Risk?
Send the drawing and tell us which face the assembly references. We will confirm the datum strategy, the flatness we can hold and what the inspection report will cover.
What to send
- 2D drawing or 3D model (STEP, IGES, DWG, DXF, PDF)
- Alloy and temper
- Surface finish and color
- Estimated annual quantity
Client names are withheld under confidentiality. Figures reflect our verified process capability.
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