What are the difficulties in machining joint parts for embodied robots? Practical disassembly of five axis CNC process

Many engineers involved in the development of embodied robots have stepped this pitfall: when joint shell drawings are sent out samples are made, single piece inspections are all qualified, but when installed on the entire machine, there are lagging, abnormal noises, insufficient positioning accuracy. is the problem? Joint parts are ordinary structural components, their requirements for form position tolerances, surface quality, batch consistency are one order of magnitude higher than ordinary parts. Using conventional machining methods is likely to cause problems. Based on the practical processing experience of thousands of robot joint parts, Huiwen Zhizao explains the core difficulties solutions clearly.

1、 The Three Core Difficulties in Joint Component Processing

Difficulty 1: Thin walled structures are prone to deformation

For the purpose of lightweighting, the wall thickness of joint shells is usually only 1.5-3mm, for dexterous hand joints, it can even be as thin as 0.8mm. There are two sources of deformation in thin-walled parts processing: one is elastic deformation caused by clamping force during clamping, dimensional rebound exceeds the tolerance after loosening; The second reason is that cutting heat causes the material to expand, after cooling, it shrinks deforms. Ordinary processing plants use hard pressure plates to directly clamp, after processing, it looks qualified. After a day of testing, the hole position flatness will change.

Difficulty 2: Difficulty in ensuring the positional accuracy of multi-faceted hole systems

A joint shell usually requires machining more than 5 faces, each face bearing holes, mounting holes, locating pin holes. The motor stop of the hip joint shell, the installation surface of the reducer, the positioning reference of the encoder have strict requirements for the spatial position relationship of the hole system in three directions, the coaxiality is usually within 0.01mm. Using three-axis machining requires multiple flips, each re alignment introduces errors. After three clamping cycles, the accumulated errors can easily exceed the tolerance.

Difficulty 3: Batch consistency is difficult to manage control

It is difficult to produce one two high-precision products during the prototype stage, but the difficulty is that each product is stable during mass production. Tool wear, environmental temperature changes, differences in blank allowance can all cause dimensional fluctuations. The batch qualification rate of joint parts in ordinary factories in the industry is about 80%, which means that 2 out of every 10 pieces are scrapped, directly increasing the cost by more than 25%.

2、 Five axis linkage+process optimization: solving accuracy problems the source

In response to the above difficulties, the core solution of Huiwen Zhizao is "five axis one-time clamping+coarse fine separation+full process detection":

Firstly, the five axis linkage completes multi-faceted machining in one clamping. We have configured a Demagi five axis machining center with sufficient hardware performance, but we place more emphasis on process implementation. By relying on the RTCP tool tip tracking capability of the equipment combining it with our self-developed robot component programming strategy, we perform collision interference checks optimize cutting parameters for thin-walled parts. With a single clamping, we can complete all the features of multi-faceted parts eliminate the cumulative errors caused by multiple flipping clamping. High end equipment is just the foundation, the process sedimentation of processing robot components is the key to making good joint shells.

Secondly, rough fine processing separation+natural aging. Rough machining removes most of the excess, leaving 0.3-0.5mm for precision machining, then the workpiece is removed left to stand for 4-8 hours to fully release the internal stress generated by cutting clamping. During precision machining, gentle parameters such as small cutting depth low feed rate are used to reduce clamping force by 30% -50% compared to rough machining, avoiding secondary deformation. This "three-stage" process can stably control the thin-walled deformation within 0.005mm.

Thirdly, vacuum suction cup+imitation soft support clamping. Abandoning traditional hard pressing plates, using vacuum suction cups to distribute clamping force, fitting irregular contours with soft claws, adding adjustable support pins near the hole system. The core principle is to evenly distribute the clamping force, rather than concentrating it on a few points.

3、 Material selection: Deeply cultivate the processing of aluminum alloy components, match titanium alloy as needed

The material selection of joint parts essentially involves finding a balance between strength, weight, processing cost. Huiwen Zhizao is deeply involved in the processing of various aluminum alloy components. Currently, the mainstream in the industry is 7075-T6 aluminum alloy, with a yield strength of 503MPa, high specific strength, a density of only 2.81g/cm ³. It is widely used in the shells of main load-bearing joints such as hip joints knee joints. 7075 has a high cutting speed material removal rate, but its thin-walled structure is prone to tool vibration requires sharp cutting tools high-pressure internal cooling.

For areas such as dexterous hands wrist joints that require extreme weight strength, TC4 titanium alloy is more suitable. Titanium alloy has a specific strength equivalent to 7075, but it has higher absolute strength better corrosion resistance, allowing for thinner wall thickness. The disadvantage is that the processing difficulty is high - the thermal conductivity is only 1/10 of aluminum alloy, the cutting heat is concentrated on the blade, the tool wear is fast, the cutting speed needs to be reduced to about 1/3 of aluminum alloy. Huiwen Zhizao adopts a special coating tool+high-pressure internal cooling scheme to control the tool life machining accuracy of titanium alloy joint parts within an acceptable range.

4、 Quality control: Each process must be inspected

The accuracy of joint parts is determined by final inspection, but by controlling each process. Huiwen Zhizao has established a three-level testing system, equipped with Zeiss coordinate measuring equipment: checking the material hardness blank size of incoming materials; Conduct spot checks on key benchmarks after rough machining before precision machining, promptly compensate for any deviations found; After the completion of the finished product, a full-size inspection will be conducted using Zeiss coordinate system, a test report will be issued before delivery.

In the mass production stage, we will also make seasonal parameter adjustments - the cutting parameters cooling scheme need to be adjusted accordingly due to the different environmental temperatures in summer winter. Reserve temperature adaptation time before processing large-sized parts to avoid dimensional drift caused by uneven blank temperature after processing. Through these detailed controls, the batch qualification rate of Huiwen Zhizao's joint parts has remained stable at over 95%.

As a precision parts service provider specializing in the field of robotics, Huiwen Zhizao has a factory area of 20000 square meters over 370 processing equipment, equipped with Demagi five axis machining centers Zeiss three coordinate systems. It has full process service capabilities design, manufacturing to assembly, can meet the needs of parts such as humanoid robots, mechanical dogs, flexible robotic arms single piece sampling to medium to large-scale production. At present, we have provided processing services to multiple clients such as Huawei, Xinsong, Xiaomi Ecological Chain Enterprises, Beijing Institute of Technology, Chinese Academy of Sciences, our accuracy stability have been unanimously recognized.

If you need a machining plan quotation for articulated robot parts, please feel free to provide drawings for consultation.