0.01mm Coaxiality 6061 Aluminum Robot Arm Segment Modular Hollow Articulated Arm Module

A modular articulated arm only works if its modules are interchangeable. That is an interface problem before it is a machining problem: if two arm segments made six months apart do not share the same bolt pattern, dowel fit and bore alignment, the arm cannot be reconfigured, and the customer keeps a spare inventory instead of a modular product line.

Dongguan Changxinda Precision Technology Co., Ltd. has machined robot arm structures 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.

A hollow arm segment is a thin-wall box with two heavy interfaces at the ends. Removing the material in the middle is easy; keeping the two ends aligned after removing it is the work. Three effects drive the process:

• Stiffness drop: cutting a cavity reduces the section modulus, so any residual stress released by the cut bows the part after the cavity is opened.
• Wall deflection: a 2.5 mm wall pushes away from the cutter, so wall thickness varies unless the cutter path is planned with the deflection in mind.
• Interface distortion: boring the end interfaces before the cavity is opened means the bore closes slightly once the middle is removed.

The order below exists specifically to protect the two end interfaces, which are what the next module bolts to.

Two modules that both measure within tolerance can still fail to interchange, because tolerance is per part while interchangeability is a relationship between parts.

• Interface bores are bored in one setup from a common datum on each part, and the same fixture and program are reused for every batch.
• Bore diameter, roundness and bore-to-bore centre distance are measured and reported per part, not only as a pass or fail.
• Dowel hole true position 0.01 mm relative to the bore, and the dowel pair is reamed with the mating module present on prototype sets.
• Interface face flatness 0.01 mm and squareness to the bore 0.01 mm, since a face error tilts the next module.
• First article report includes an interface summary sheet that the customer can file with the module drawing.
• For repeat production, one reference module is kept at the plant as a checking master.

• Interface bore diameter and roundness 0.01 mm, checked at two depths to catch taper.
• Bore-to-bore coaxiality 0.01 mm across the segment, measured with the part supported as in service.
• Interface face flatness 0.01 mm, squareness to bore 0.01 mm.
• Dowel hole true position 0.01 mm, bore-to-dowel centre distance 0.01 mm.
• Wall thickness 2.5 mm nominal with variation held to 0.1 mm, checked with an ultrasonic gauge at marked points.
• Overall length between interfaces 0.02 mm, since length error accumulates along the arm.
• Surface roughness Ra 1.6 as machined, Ra 0.8 on interface faces for clamped joints.
• Metrology room at 20 degrees Celsius, CMM resolution 0.001 mm.

• Segment length 100 mm to 800 mm, cross section 40 x 40 mm to 200 x 200 mm, wall from 2 mm.
• Materials: 6061-T6 and 7075-T6 aluminum, 304 and 316L stainless, 40Cr for loaded joints, carbon fiber inserts on request.
• Interface patterns matched to your joint module, including bolt circle, dowel pair, spigot diameter and cable pass-through.
• Cable routing: internal channels, grommet holes, strain relief brackets and connector cut-outs machined in the same setup as the cavity.
• Finishes: clear, black and hard anodizing, chromate-free conversion coating, with interface faces and bores masked.
• Weight targets: ribs and pocket depth adjusted to a stated mass, with the achieved mass reported per part.
• Laser marking of module number and revision letter on a non-functional face.
• Drawing input in STEP, IGES, X_T, DWG, DXF or PDF, or a sample module for measurement.
• Prototype quantity from one piece, design feedback within 24 hours.

Arm architecture is often the most sensitive part of a robot program. 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 segment: 6 to 10 working days including first article inspection.
• Batch of 10 to 100 pieces: 12 to 20 working days including anodizing.
• Recurring module releases: reserved machine capacity with the same fixture and the same checking master, so module N and module N+50 interchange.
• 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 interface faces protected by rigid caps, so a module arrives with its bores untouched.