How to choose CNC and EDM processes for precision machining of robot parts in Shenzhen?

Many engineers who work on precision parts machining for robots are confused about choosing between CNC or EDM technology. Which one should they choose? In fact, the two are complementary rather than substitutive, and depending on the specific processing requirements of the parts, they are generally combined with two different process routes. As a high-end robot full industry chain service provider specializing in the field of robotics in Shenzhen, Huiwen Zhizao combines thousands of practical processing experiences to explain the selection logic of two types of processes.

Why do robot parts machining require CNC and EDM collaboration?

The requirements for precision, strength, and consistency of robot core components are much higher than those of ordinary mechanical parts. For example, the joint bearing seat requires dimensional tolerance control within ± 0.02mm, the reducer housing needs to be heat treated to maintain dimensional stability, and many parts need to balance complex shapes and micro internal features. A single CNC or EDM cannot meet both efficiency and precision requirements.

Firstly, we clarify the basic positioning of two processes: CNC machining (including five axis CNC milling) relies on tool mechanical cutting to remove materials, which is suitable for most shape processing and three-dimensional surface processing, and has high material removal efficiency; EDM relies on the instantaneous high-temperature erosion of materials through pulse discharge, without relying on tool hardness or mechanical cutting force, making it suitable for handling special features that CNC cannot achieve.

From the actual processing requirements of robot parts, the complementarity between the two processes is very obvious:

1. Many robot parts require heat treatment to increase strength, resulting in an increase in material hardness after heat treatment. The difficulty of CNC machining increases sharply, while EDM can complete precision machining without considering material hardness;

2. The core components of robots often have matching inner right angles, and CNC cannot achieve corner cleaning due to tool diameter limitations. EDM can easily process inner sharp angles within R0.02;

3. Complex shapes are efficiently completed by CNC, and special features are supplemented by EDM, resulting in lower costs and more stable accuracy compared to a single process.

The core technical difficulties of CNC and EDM in robot parts processing

In the actual processing of robot core components, the difficulty of two process collaboration lies not in the process itself, but in the precision connection and tolerance control. Huiwen Zhizao has summarized three core difficulties in years of processing:

Difficulty 1: Deformation control after heat treatment

Robot structural components generally require quenching treatment to improve wear resistance. After quenching, the parts will undergo a deformation of 0.02-0.05mm. If CNC is directly machined to the final size and then quenched, the size will exceed the tolerance after deformation. If all the material is left for EDM processing, the amount of material removed will be too large, and the processing cycle will be extended by 3-5 times, resulting in a significant increase in cost.

Taking the joint pin shaft of an industrial robot processed by Huiwen Zhizao as an example: the material is 40CrNiMoA, and the required hardness after quenching is HRC58-62, with a dimensional tolerance of ± 0.008mm. Our solution is to leave a precision machining allowance of 0.2-0.3mm after CNC rough machining, and then use EDM precision machining to achieve the final size after quenching. This not only uses CNC to remove most of the material, but also avoids the influence of quenching deformation on the final accuracy. The accuracy qualification rate has increased from 72% to over 98%.

Difficulty 2: Control of Cumulative Accuracy Error in Multiple Processes

CNC machining of external shapes and EDM machining of internal features can result in positioning errors during two clamping processes. If the accumulated positioning errors exceed the part tolerance, the final size will be non-conforming. The fitting tolerance of robot joint parts is usually within 0.01mm, and a positioning error exceeding 0.005mm will lead to assembly failure.

The solution of Huiwen Zhizao is to use a unified reference design fixture. During CNC machining, EDM positioning reference surfaces are reserved, and the same reference fixture is directly used during EDM machining to avoid errors in secondary alignment. In addition, we use Zeiss three coordinate inspection throughout the process, and control the accuracy of each process. The final cumulative error can be controlled within ± 0.003mm, far less than the part tolerance requirements.

Difficulty 3: Control of EDM recast layer

After EDM machining, a discharge recast layer with a thickness of 2-20 μ m will be formed on the surface. The recast layer has high hardness but high brittleness. If it is a mating surface, the recast layer will affect the wear resistance after assembly. For robot moving parts, microcracks in the recast layer may also pose a risk of fatigue fracture.

Our process control method is to lower the pulse energy during the precision machining discharge stage, reduce the thickness of the recast layer, and add a grinding process to remove the recast layer for high demand mating surfaces. This not only retains the accuracy advantage of EDM machining, but also solves the surface quality problem.

Common Collaborative Solutions between CNC and EDM in Robot Parts Processing

Based on Huiwen Zhizao's years of experience in processing core robot parts, we have summarized four of the most commonly used collaborative process routes, covering the vast majority of robot part processing scenarios:

Plan 1: CNC rough machining → quenching → EDM precision machining

This is the most commonly used process route for hard robot parts, suitable for quenched reducer housings, joint shafts, and mold tooling parts. The process is: CNC rough machining to remove most of the excess, leaving 0.2-0.3mm unilateral allowance → quenching heat treatment → EDM precision machining to the final size. The advantage of this solution is that it solves the problem of quenching deformation, EDM machining is not limited by hardness, and the final dimensional accuracy is stable.

Option 2: CNC machining shape → EDM corner cleaning

This scheme is suitable for joint bearing seats and slider parts with inner right angle mating surfaces: CNC completes the machining of the outer shape and cavity body, leaving a corner allowance for the inner angle → EDM uses forming electrodes to clean the inner angle and machine a right angle that meets the requirements. Taking the linear module slider of a certain robot we processed as an example: the design requires the inner angle of the T-shaped groove to be within R0.05, but CNC machining with a diameter of 0.1mm milling cutter still cannot meet the requirement. Finally, EDM corner cleaning was used to achieve the inner angle requirement of R0.02, perfectly meeting the assembly and fitting requirements. As a local robot full industry chain service provider in Shenzhen, Huiwen Zhizao has over 370 processing equipment, including multiple five axis machining centers and supporting EDM equipment. The 20000 square meter factory can meet the collaborative processing needs of bulk parts.

Plan 3: CNC machining all features → wire cutting machining irregular through holes

This scheme is suitable for parts with irregular cross-section through holes on the main structural components, such as connector mounting seats and servo motor fixing plates: CNC completes all external, planar, and threaded hole processing → slow wire cutting completes the processing of irregular through holes. The precision of slow wire cutting for through-hole machining is higher than that of CNC milling, with better surface roughness, especially suitable for through-hole with irregular cross-sections. The slow wire cutting equipment used by Huiwen Zhizao can achieve an accuracy of ± 0.002mm, meeting the requirements of high-precision assembly.

Plan 4: Five axis CNC machining of complex surfaces → EDM machining of fine features

For robot end effector parts with complex surfaces, five axis CNC can complete complex surface machining in one clamping, with much higher efficiency and accuracy than EDM. For micro grooves and sharp corners on the surface, EDM can be used to supplement machining, which not only leverages the advantages of five axis CNC machining complex surfaces, but also solves the problem of machining micro features.

Quality control of CNC and EDM collaborative machining of robot parts

The core of quality control in collaborative processing is the precision testing of each process. As a national high-tech enterprise and specialized new enterprise certified by ISO9001 and IATF16949 quality management system, Huiwen Intelligent Manufacturing has established a complete testing process:

1. Incoming material inspection: Check the hardness of the material and the size of the blank to avoid subsequent processing scrap caused by unqualified blanks;

2. Process inspection: After each process is completed, the dimensions are checked using the Zeiss coordinate system, and if they pass the inspection, they flow into the next process;

3. Finished product testing: After the finished product is completed, the tolerance and surface quality are fully inspected, and a testing report is issued before delivery to the customer.

As a service provider specializing in robot parts processing, Huiwen Zhizao can provide full stage OEM services for humanoid robots, mechanical dogs, flexible robotic arms, bionic robots, medical robots and other parts from single piece sampling to medium to large-scale production. At present, Huiwen Zhizao has provided robot parts processing services to many technology innovation enterprises and research institutions such as Huawei, Xinsong, Xiaomi ecological chain enterprises, Beijing Institute of Technology, and Chinese Academy of Sciences, and its accuracy and stability have been unanimously recognized by customers.

Especially for humanoid robots, Huiwen Intelligent Manufacturing innovatively adopts a combination process of "new materials+new molds+precision machining", relying on integrated design, intelligent manufacturing, and assembly full chain services to complete the entire process from research and development to batch delivery in one stop.

If you need a robot parts processing plan or quotation, please feel free to provide drawing consultation.