How to ensure high precision in precision five axis machining for customized robot joint shells and robot structural parts with irregular shapes

Customizing a robot joint shell, the easiest pit to step on is not the high processing cost, but whether the sample can be seen to fit - the hole position does not match, the lid is sewn, and there is a jamming noise when rotating. The joint shell is a typical structural component of irregular robots, with curved surfaces, inclined holes, thin walls, and bearing sockets all squeezed together. The three-axis is flipped and clamped several times, and errors naturally accumulate. These types of parts require high-precision customization, relying on precision five axis machining to create multi-faceted features in one clamping. Let's take this article apart. What are the difficulties in customizing robot joint shells and how to maintain accuracy in five axes.

1、 Why is the joint shell the most difficult type of structural component to serve

The joint shell of a robot is not an ordinary casing. It needs to accommodate servo motors, harmonic or RV reducers, bearings, and wiring inside, and accurately dock with adjacent arm segments on the outside. It is a highly integrated shaped component. Compared to regular installation boards and end caps, it has three headache inducing features:

Dense spatial features - bearing holes, mounting surfaces, oblique threaded holes, and irregular inner cavities often face in different directions, with alternating curved and flat surfaces. It is difficult for three-axis cutting tools to cover everything in one cutting.

Thin and uneven walls - In order to create space for the motor and reducer while controlling weight, the housing is extensively made thin and partially hollowed out, resulting in poor rigidity. The clamping and cutting forces can deform slightly, and even rebound after release.

The coordination relationship is interdependent - any deviation in the coaxiality of the bearing holes at both ends, the flatness of the mating surface, and the positional accuracy of the locating pin holes will be amplified into jamming, abnormal noise, or displacement during joint rotation.

Because of this, the requirements for craftsmanship for this type of shell are much higher than those for general appearance parts, which also determines that it is more suitable for high-precision customization using precision five axis machining.

2、 Customization first review: eliminate risks during the drawing stage

The biggest difference between customized irregular parts and batch standard parts is that the weight of the preliminary process review is particularly heavy. A reliable manufacturer, upon receiving the drawings, will not immediately quote for start-up. Instead, they will first conduct a manufacturability evaluation: which holes require one-time clamping and processing, which thin walls require auxiliary support, where rounded corner tools cannot reach, and where strict tolerance design will significantly increase costs.

This step is particularly valuable for robot structural components. For example, if the bearing holes on both sides of the shell are clamped and processed twice, the coaxiality basically depends on luck; The five axis plan will arrange them to be precisely drilled in the same positioning. For example, if the inner cavity corner is designed as a clear corner, even if the tool radius is small, it will still leave residue. When reviewing, it should be changed to a reasonable rounded corner, which can be processed without affecting assembly.

Solving these problems in the drawing stage is much more convenient than making waste samples and then modifying the drawings. This is also the key difference between high-precision customization and "processing based on the drawings".

3、 How to do five axes: one-time clamping, short knife cutting, thin-walled anti deformation

The core advantage of precision five axis machining is most directly reflected in the joint shell. Five axes have two more rotation axes than three axes, allowing the workpiece or tool head to deflect angles. Complex surfaces, inclined holes, and deep cavities can be continuously completed in one clamping, without the need for repeated flipping and alignment - the number of clamping times is reduced, and the accumulated error and waiting time are also reduced.

There are several key points specific to the process. One is to unify the standards, with design standards, process standards, and measurement standards overlapping as much as possible. The bearing holes and positioning surfaces on both sides are completed under the same positioning, ensuring coaxiality and positional accuracy. The second method is to use a short knife. When machining the side wall of a deep cavity, the axis of the knife is swung in and a shorter knife is used for cutting. The short knife has good rigidity, making the knife smaller and significantly reducing vibration patterns and tool marks. The third is to separate coarse and fine machining. First, rough machining should be carried out to remove excess material and arrange stress relief. Then, semi precision and fine machining should be carried out to avoid subsequent dimensional drift of the shell caused by internal stress.

The clamping of thin-walled parts is also very particular. Usually, vacuum suction cups, imitation soft supports, or auxiliary core supports are used to disperse the clamping force, and the clamping points are avoided from the bearing socket and the cover surface, so that the workpiece is firmly attached without being deformed by clamping. Only with this combination can the thin-walled and irregular features of the robot joint shell be made both stably and effectively.

4、 Testing and mass production: Single piece qualification does not equal assembly qualification

Irregular parts are most prone to situations where the report data is complete but the installation is not smooth, because the inspection only measured isolated dimensions against the drawing and did not align with the assembly relationship. What really matters is the coaxiality of the bearing holes at both ends, the positional accuracy between the holes and the installation surface, the flatness of the closing surface, and the rebound amount of the thin-walled part after releasing the clamping - these must align the detection benchmark and the assembly benchmark so that the data can directly serve the assembly.

Shenzhen Huiwen Zhizao uses Zeiss three coordinate system for form and position tolerance detection on such parts, combined with imaging instruments and online measuring heads, to set detection points for key dimensions in each process, rather than relying solely on final inspection.

In terms of equipment and system, the Huiwen factory covers an area of approximately 20000 square meters and has more than 370 processing and testing equipment, equipped with multiple five axis machining centers. The precision machining area has a turning capacity of ± 0.005mm and milling capacity of ± 0.01mm, and has passed IATF16949 and ISO9001 system certifications. From R&D sampling to small and medium batch production, the precision five axis machining program and benchmark can be stably replicated to ensure consistency and interchangeability between multiple parts.

Based on the technical background of the Chinese Academy of Sciences, Huiwen adopts a combination process of "new materials+new molds+precision machining" to provide integrated design, intelligent manufacturing, and assembly services. In high-precision customized parts such as joint shells, it has cooperated with Huawei, Xinsong, Xiaomi ecological chain enterprises, Beijing Institute of Technology, Chinese Academy of Sciences and other enterprises and research institutions, and has experience in matching such robot structural parts from single piece sampling to batch climbing.

4、 How to choose a manufacturer for customized joint shells

Choose a customized manufacturer for irregular parts, don't just look at the number of devices, focus on three things:

Looking at the process review ability - can you point out the risks of thin walls, inclined holes, and inner cavity corner cleaning before starting work, and provide suggestions for modifying drawings or clamping, directly determining whether the first piece can be produced.

Second, let's take a look at the five axis and clamping skills - whether there is a real five axis equipment and thin-walled irregular parts solution, and whether the key bearing holes can be clamped in one go, instead of struggling with three axes and dividing heads.

Three checks on testing and fit - whether to provide reports on geometric tolerances such as coaxiality, positional accuracy, and flatness, and whether willing to cooperate with R&D iterations and find problems together during assembly review.

For teams still in the prototype iteration stage, factories that can provide continuous support in DFM review, small batch rapid response, and assembly problem review have much more value than just processing itself. The precision of special-shaped parts such as joint shells is never a one size fits all solution, but rather a combination of craftsmanship, clamping, and testing. If you need precision five axis machining solutions and quotations for robot joint shells or robot structural parts with irregular shapes, please feel free to provide 2D drawings, 3D models, and technical requirements consultation.