Robot Arm Frame in AL6061/7075-T6, One-Piece Milled with Lightening Cavities, Coaxiality 0.015 mm

About This Part

An arm is the part a robot accelerates thousands of times a day, so weight that survives in a static bracket is inertia here. This frame is milled in one piece from 220 to 300 mm aluminum plate, with its interior excavated into a matrix of lightening cavities and reinforcing ribs. The walls that remain carry the bending and torsion loads; the volume that is gone no longer fights the motors. One-piece milling keeps all of the mounting faces and bores in one rigid body instead of a weldment that can move over time.

The interfaces are the accuracy. One end carries a circular flange with a PCD pattern of tapped and dowel holes at H7, +0.021/0 mm; the mid-body houses a bearing seat and motor spigot bored to H7/H8 fits with coaxiality within 0.015 mm; and the mounting faces hold flatness within 0.02 mm with 0.03 mm perpendicularity to the datum faces. Because the part is machined across five faces, the five-axis center carries it through multi face fixturing in one or very few setups, so the holes and bores reference each other instead of accumulating setup error.

Cavity milling thins the walls, and thin walls move under cutting heat and residual stress. The route is staged: rough the profile and cavities with finish stock left on, let the part relax, then run the five-axis finishing of the external contour, flange and mounting faces, then precision bore the bearing seat and drill, ream and tap the hole arrays. Every intersecting hole is deburred under magnification, because a burr inside a joint assembly is a failure waiting for assembly day.

The frame is ultrasonically cleaned, fine bead blasted and clear anodized, then verified with a full CMM pass: bearing bore coaxiality, flange PCD position, and perpendicularity and flatness on every datum face, with thread plug gauges in every tapped hole.