Coplanarity 0.05mm Machined Aluminum Robot Truss Grid Frame for Large Format Automation

• ISO 9001:2015
• 4-Axis / 5-Axis & Turn-Mill Capacity
• First Article Report With Every Shipment
• Exporting Since 2008

A truss grid frame is a flatness problem disguised as a welding problem. The frame looks simple in a drawing: a rectangular grid of rails with machined node pads where the joints, motors or rails bolt on. In service the requirement is unforgiving, because the pads have to be coplanar and the node positions have to be right to a fraction of a millimetre across a metre or two of span. Every millimetre of error shows up as a rail that binds or a joint that preloads unevenly.

Dongguan Changxinda Precision Technology Co., Ltd. has machined frame and node geometry 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.

• Node coplanarity: each pad can be flat and still be at a different height. The frame then becomes a twisted plane, and the rail mounted on it wears on one side.
• Diagonals: a grid that is square by the outer dimensions can still be a parallelogram. The diagonal measurement is what catches it.
• Release distortion: a frame machined flat while clamped to a table springs when the clamps come off, because the part was never flat — it was held flat.
• Weld and assembly stress: where a frame is welded or bolted from segments, the joint pulls the pads out of plane after machining.
• Thermal length: a 1500 mm aluminum frame grows about 0.034 mm per degree Celsius, so the shop temperature at the moment of measurement is part of the tolerance.

1. Rough all faces, rails and pad stock with 1.2 mm left, in a sequence that removes material symmetrically so the part does not bow to one side.
2. Stress relief after roughing, then a stabilising period before finishing.
3. Establish the primary datum: the largest pad face is finished first and becomes the reference for everything else.
4. Machine the grid pocket with the part supported at the nodes rather than at the corners, because support position decides where the part springs.
5. Finish the node pads in one continuous cycle where the machine envelope allows, so all pads share one thermal state and one tool path.
6. Drill and ream node holes from the finished pads, with position taken from the pad datum rather than from the outline.
7. Check diagonals and pad heights on the CMM, then re-check after a settling period at 20 degrees Celsius.
8. Mask pads, anodize, re-check. Coating on a pad changes the height, so pads are either masked or pre-compensated.

• Node pad flatness 0.02 mm per pad, and pad-to-pad coplanarity 0.05 mm over the frame
• Pad height spread 0.05 mm, measured on every pad and reported as a table
• Node hole position 0.02 mm from the pad datum, hole diameter and roundness 0.01 mm
• Diagonal difference 0.05 mm over 1000 mm, which is what keeps the grid square
• Overall frame length and width 0.1 mm, since these are outer dimensions that carry no function
• Rail straightness 0.05 mm per 500 mm for machined rails
• Pad surface roughness Ra 1.6, with Ra 0.8 available for rail mounting faces
• Metrology at 20 degrees Celsius, CMM resolution 0.001 mm, pad map report shipped with the frame

• Frame envelope up to 1500 × 800 mm in one piece, larger on request as machined modules
• Materials: 6061-T6 and 7075-T6 aluminum, 304 and 316L stainless, 40Cr pads for loaded joints
• Grid pitch from 100 mm, rail section 40 × 40 mm to 100 × 100 mm, pad sizes to the customer's joint footprint
• Node features: bolt patterns, dowel pairs, spigot bores, counterbores, cable pass-through, sensor mounting bosses
• Mirror pairs: left-hand and right-hand frames machined as a matched set, with the pair checked together
• Finishes: clear, black and hard anodizing, chromate-free conversion coating, with pads and bores masked
• Marking: node numbering and axis letters laser marked so assembly follows the drawing without interpretation
• Drawing input in STEP, IGES, X_T, DWG, DXF or PDF, or a sample frame for measurement
• Prototype quantity from one piece, design feedback within 24 hours

A frame carries the layout of a robot cell, which often reveals the product being built. On request, this family runs on confidential terms: mutual NDA before drawings move, restricted file access with named staff, no photographs of the frame 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 frame: 8 to 12 working days including stress relief and first article inspection
• Batch of 5 to 50 frames: 15 to 25 working days including anodizing
• Recurring releases: reserved machine capacity with the same fixture and program, so pad heights repeat 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 in a braced crate with the frame supported at the nodes, since a frame supported at its corners arrives bowed

Machined to drawing in the same plant, with the same tolerance and inspection standard.