How to ensure coaxiality and positional accuracy of both sides in CNC machining of automation equipment accessories, and avoid errors introduced by secondary clamping?
Publish Time: 2026-02-17
In the manufacturing of automation equipment accessories, especially structural components used in precision transmission, sensing, or positioning systems, strict alignment of holes, contours, or features on both sides is often required. Coaxiality and positional tolerances often need to be controlled within ±0.01mm. However, double-sided CNC machining inevitably involves workpiece flipping and secondary clamping, which can easily introduce cumulative errors due to datum offset, fixture deformation, or human error. To overcome this technological challenge, modern CNC machining systems systematically ensure the geometric consistency of double-sided machining through four strategies: "datum unification, process integration, intelligent clamping, and online compensation."
1. Unified Process Datum: "Zero-Conversion" Positioning from Blank to Finished Product
The core of double-sided machining of automation equipment accessories lies in "one-time datum, full-process reuse." In the roughing stage, a set of high-precision process datum surfaces are precision milled on the workpiece or standard positioning holes are embedded. These datums serve as the sole clamping reference for all subsequent processes—including finishing after stress relief. Some companies employ a "process boss" design, reserving removable positioning ears in non-functional areas to ensure the original coordinate system can still be used during finishing. Thus, even after intermediate steps such as flipping and stress relief, the CNC system can still be programmed based on the same theoretical coordinate system, fundamentally avoiding error sources caused by datum conversion.
Automation equipment accessories traditional manual clamping relies on operational experience, making it difficult to guarantee repeatability. Modern machining commonly uses pneumatic/hydraulic flip fixtures or modular zero-point positioning systems. These systems, through conical surface + end face dual constraints, combined with high-precision positioning pins, can achieve repeatability within ±0.002mm. After the workpiece is initially clamped, the fixture records its spatial orientation; during flipping, simply loosen the quick-change mechanism, flip the workpiece 180°, and relock it to automatically return to the original coordinate system. Some high-end production lines integrate automated flipping robots, combined with vision alignment, to completely eliminate human intervention variables.
3. Online Measurement and Closed-Loop Compensation: Real-Time Correction of Clamping Deviations
Even with high-precision fixtures, minor thermal deformation or burrs can still affect the actual fit. The in-machine probe automatically executes a "alignment cycle" after secondary clamping: the probe touches a preset reference point, the system calculates the actual coordinate system offset in real time, and dynamically compensates the toolpath. For example, if the Z-axis deviation is 0.015mm after flipping, the program will automatically move down the entire machining depth. This "measurement-compensation-machining" closed-loop mechanism ensures that the final coaxiality no longer depends on the absolute accuracy of the fixture, but is guaranteed by measurement feedback, significantly improving the yield rate.
4. Material and Process Synergy: Reducing Deformation Interference Caused by Internal Stress
For easily deformable materials such as aluminum alloys and engineering plastics, the release of residual stress after rough machining may cause slight warping of the workpiece. Even with precise clamping, the machined surface may still deviate from the theoretical position. Therefore, arranging the process flow as "rough machining → stress relief → fine datum adjustment → double-sided finishing" is crucial. Especially for insulating materials, rough milling with a 1.0mm allowance and allowing it to stand allows for full release of internal stress; before finishing, lightly mill the datum surface to ensure it accurately reflects the current deformation state, thus guiding the CNC system to cut according to the "actual shape" rather than the "ideal model."
5. Integrated Programming and Simulation Verification: Preemptively Avoiding Interference and Error Accumulation
In CAM software, the machining paths for both sides are integrated into the same program file, sharing the same workpiece coordinate system. Through virtual machine simulation, the risk of interference between the tool and fixture after flipping can be detected in advance, and the tool feed direction can be optimized. Simultaneously, the system can simulate contour deviations caused by slight clamping misalignments, guiding engineers to adjust tolerance allocation strategies.
In summary, ensuring high coaxiality in double-sided CNC machining does not rely on a single technology, but rather on the system integration of datum design, intelligent fixtures, online measurement, material processing, and digital simulation. It embodies the core concept of modern precision manufacturing: "using testing to replace assembly and using software to supplement hardware," providing a solid guarantee for the high performance and high reliability of automation equipment accessories.
