0.01mm Parallelism Dual Flange Connecting Link in 6061-T6 Aluminum with One Datum Machining for Robot Connecting Link Assembly

A dual flange link has one job: present two mounting faces that are parallel, at the right distance apart, with bores that line up with the joints at both ends. When it is right, nobody notices it. When the two faces are 0.03 mm out of parallel, the arm pulls to one side through its travel, and the fault gets blamed on the reducer or the controller for weeks.

Dongguan Changxinda Precision Technology Co., Ltd. has machined structural links to drawing since 2008. The plant runs 4-axis and 5-axis machining centers, turn-mill combined lathes and precision CNC lathes, employs more than 90 people, holds ISO 9001:2015, and exports 50 to 60 percent of output to robot, automation and medical buyers.

The difficulty is not machining a flat face — it is machining the second face so that it is parallel to the first. Most shops do this by flipping the part and indicating it in, which works until the part is long, thin and springy, and then the flip introduces an error that cannot be measured until the part is finished.

• Flip error: re-clamping on the second side never repeats exactly, so parallelism is set by the fixture and the operator rather than by the machine.
• Stress release: removing material from one side unbalances the part, so it bows towards the side that still has stock.
• Clamping force: a link is a lever, so a clamp at one end lifts the other end by more than the tolerance being held.
• Spacing control: the flange-to-flange distance is what sets the assembly width, and it drifts whenever the part is re-fixtured.

The aim is to touch each critical face once, from a datum that does not change.

• Face-to-face parallelism 0.01 mm over the full flange width
• Flange spacing 0.01 mm, measured at four points around each flange and reported as a set
• Bore-to-bore centre distance 0.01 mm, which is what sets the joint geometry
• Bore-to-face squareness 0.01 mm; bore diameter and roundness 0.01 mm
• Bore-to-bore axis parallelism 0.01 mm, measured with the part supported as in service
• Web thickness and wall variation 0.1 mm, checked at marked points to catch a thin side
• Surface roughness Ra 1.6 as machined, Ra 0.8 on flange faces that clamp
• Metrology room at 20 °C, CMM resolution 0.001 mm, ballooned first article report

• Flange diameter 30 mm to 200 mm, centre distance 80 mm to 600 mm, spacing 20 mm to 300 mm
• Materials: 6061-T6 and 7075-T6 aluminum, 304 and 316L stainless, 40Cr for loaded links, titanium on request
• Flange pattern matched to your joint module: bolt circle, dowel pair, spigot diameter, counterbore or through hole
• Web geometry: straight, offset, tapered, or with weight-reduction slots placed to a stated stiffness
• Cable pass-through or clamp bosses machined in the same setup as the faces
• Finishes: clear, black and hard anodizing, chromate-free conversion coating, with faces and bores masked
• Laser marking of part number, batch and revision on a non-functional face
• Drawing input in STEP, IGES, X_T, DWG, DXF or PDF, or a sample link for measurement
• Prototype quantity from one piece, design feedback within 24 hours

A link carries the arm's reach and joint spacing, which is often the part of a robot program a customer does not want visible. On request, this family runs on confidential terms: mutual NDA before drawings move, restricted file access with named staff, no photographs of the part for marketing, sub-suppliers bound by the same terms, neutral marking and neutral packing, and programs and fixtures reserved to that customer. Mention it at enquiry stage and the quotation is issued under those terms.

• Prototype link: 5 to 8 working days including first article inspection
• Batch of 10 to 200 pieces: 10 to 18 working days including anodizing
• Recurring releases: reserved machine capacity with the same fixture and the same program, so spacing repeats batch to batch
• A named project engineer per account, weekly status update with photographs unless the program is confidential
• Written notice at least 5 working days before the ship date if any step is at risk
• Packing with rigid caps on flange faces and bores, so a link arrives without a damaged clamp face