The link had to resist bending under arm loads while staying light. Lightweighting pockets were placed to keep material where the load path runs and remove it where it doesn't.
Case study · Robotics
7075 Robotic Arm Bracket — Lightweight Structural Link
A 7075-T6 structural arm bracket with lightweighting pockets, precise bearing bores, and hardcoat anodize, machined for stiffness-to-weight in a robotic joint.
- 7075-T6
- Lightweighting
- Hardcoat anodize
Project overview
Project overview
This project is a 7075-T6 structural bracket that forms a link in a robotic arm — two bearing bores tied together by a lightweighted web. The design brief was the classic robotics trade-off: maximum stiffness for minimum moving mass, with bearing bores accurate enough to keep joint slop out of the end-effector.
7075 is the right alloy for this because its high yield strength lets the web sections run thinner than 6061 would allow, but it also carries residual stress that releases during heavy material removal. The routing removes material symmetrically, pauses for stress relief, and only then finishes the bearing bores to an H7 fit and ±0.02 mm bore-to-bore position — with hardcoat growth budgeted into the fit rather than fought after the fact.
Hardcoat anodize gives the link a wear-resistant surface for repeated fastening and handling, with the bearing bores masked so the coating never intrudes on the fit. Sizes, web thicknesses, and volumes are placeholders — the material choice, lightweighting logic, and bore accuracy are representative of the robotics work we machine.
Technical specification
Part specification
Key manufacturing parameters for this project. Values marked as placeholders stand in for confidential production data.
| Parameter | Specification |
|---|---|
| Overall size | Placeholder — e.g. 220 × 90 × 30 mm |
| Bearing bore fit | H7 (fit class specified, not raw ±) |
| Bore-to-bore position | ±0.02 mm |
| Web thickness | Placeholder — 3 mm nominal in lightweighting webs |
| General tolerance | ±0.05 mm (ISO 2768-f unless noted) |
| Hardcoat thickness | 25–50 µm, budgeted on toleranced bores |
Engineering challenges
What made this part difficult
The manufacturability risks we planned around before cutting metal.
Bore-to-bore position and fit drive joint slop, so bores were finished to an H7 fit and held to ±0.02 mm position, with hardcoat growth compensated.
7075 carries residual stress that releases during heavy material removal. Balanced roughing and a relief step limited warp before finishing the bores.
Manufacturing process
How the part was made
The routing from raw stock to finished, inspected components.
- Step 1: Engineering review
Reviewed web thickness, bore fits, and hardcoat growth on toleranced features before quoting. - Step 2: Balanced roughing
Symmetric material removal from 7075-T6 billet to limit stress-driven distortion. - Step 3: Stress relief
A relief pause so residual stress settles before the accuracy features are cut. - Step 4: Finish machining bores
Bearing bores and datum faces finished to H7 fits and ±0.02 mm position. - Step 5: Masking and hardcoat
Bores masked, then hardcoat anodize with thickness budgeted into the fit. - Step 6: Final inspection
CMM verification of bore positions and fits before sign-off.
Inspection methods
How quality was verified
Dimensional and process controls used to sign off the part. See our full aluminum part inspection process.
Bore diameters, positions, and parallelism mapped on a CMM against the datum scheme.
Full FAI on the first part with a report available; placeholder for the program's AQL.
Toleranced bores re-checked after hardcoat to confirm growth landed inside the fit.
Surface finishing
Finishing and post-processing
Finishing decided alongside the machining plan. Compare options in the aluminum surface finishes hub.
25–50 µm wear-resistant layer for a structural link that sees repeated fastening and handling.
Bores masked so hardcoat growth stays out of the H7 fits; growth budgeted where coating is allowed.
Hardcoat can be left natural or dyed for identification depending on the program.
Typical application
Where this bracket is used
Structural links and brackets like this form the load-bearing skeleton of robotic arms and motion assemblies, where every gram of moving mass costs cycle time and every micron of bore slop shows up as end-effector error.
7075 earns its place here: roughly double the yield strength of 6061, so the web sections can be thinner for the same stiffness.
- Manufacturability review
Every project starts with an engineering review of tolerances, wall thickness, and finish before we quote. - Prototype to production
The same routing scales from a first article to recurring production batches. - Documentation
Material certificates and first article inspection reports are available on request.
Explore the engineering
Related capabilities, materials, and pages
This project connects to our wider aluminum machining program. Start with our engineering capabilities, then dive into the specific products, materials, industries, and finishes involved.
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