Humanoid Robot Harmonic Reducer Input Shaft CNC Precision Machining Case Study - CNC Machining China

As a technician long responsible for precision component manufacturing, I am honored to share our successful batch machining case of harmonic reducer input shafts for a well-known humanoid robot company. This project fully demonstrates our technical strength and process accumulation in ultra-high precision CNC machining.

The customer, a technology company focused on high-end humanoid robot R&D, presented extremely stringent requirements for the harmonic reducer input shaft in its joint modules:

• Extremely High Dimensional Accuracy and Geometrical Tolerances: Shaft journal diameter tolerance required ±0.002mm, roundness and cylindricity errors needed to be less than 0.001mm.

• Excellent Surface Quality: Key mating surface roughness needed to achieve Ra ≤ 0.2μm to ensure optimal friction and wear characteristics.

• Outstanding Mechanical Properties: A combination of high surface hardness (≥HRC60) and a tough core was essential to guarantee long service life under high speed and heavy load.

• Stringent Dynamic Balance Requirements: The input shaft needed to run smoothly at operating speed (6000r/min), requiring a dynamic balance grade of G2.5.

• Consistent Batch Stability: High quality consistency for every product in large-volume production had to be ensured.

Facing these challenges, our process team developed a detailed CNC machining plan:

1. Material Selection and Pre-processing: Selected high-quality high-strength bearing steel GCr15 as the blank. Ultrasonic flaw detection was performed on incoming materials to ensure no internal defects. Precision cold drawing or centerless grinding processes were used to prepare bar stock, ensuring straightness and dimensional consistency of the blank, laying a solid foundation for subsequent finishing.
2. Precision CNC Turning Forming:
   • Utilized original imported Japanese CNC turning centers equipped with high-rigidity hydraulic tool turrets and precision servo live tools.
   • Adopted a "Rough Turning - Semi-Finish Turning - Finish Turning" process route to gradually eliminate machining stress and approach the final dimensions.
   • For the finishing stage, CBN (Cubic Boron Nitride) inserts were selected for fine turning with high speed, small depth of cut, and large feed, effectively ensuring form accuracy and achieving excellent surface finish.
3. Critical Process: Precision Grinding:
   • Cylindrical grinding employed German-brand high-precision CNC cylindrical grinders. The grinding wheels were finely balanced, and the machines were installed in a constant temperature (20±1°C) workshop.
   • Using a "Rough Grinding - Finish Grinding - Spark-Out Grinding" process, through micron-level feed control and spark-out grinding, the required h6 tolerance (±0.002mm) and surface roughness of Ra 0.2μm were consistently and stably achieved.
   • To guarantee roundness ≤ 0.001mm, we optimized the center hole grinding process to ensure the accuracy and reliability of the machining datum.
4. Core Control of Heat Treatment Process:
   • Used controlled atmosphere sealed quench furnaces for quenching and tempering treatment to obtain a uniform and fine sorbitic structure, ensuring core strength and toughness (HRC28-32).
   • Applied super audio frequency induction hardening to key mating surfaces like journals and keyways. By precisely controlling the inductor shape, heating power, time, and cooling rate, a uniform hardened layer with hardness HRC60-62 and depth of 1.0-1.5mm was achieved with minimal distortion.
5. Dynamic Balancing Correction and Final Inspection:
   • Each input shaft underwent two-plane dynamic balancing correction on a vertical dynamic balancing machine. Residual unbalance was strictly controlled within G2.5 grade by mass removal (micro-drilling at specific locations) or rarely mass addition, ensuring smooth high-speed operation.
   • Final inspection involved 100% checking of all dimensions and geometric tolerances using a UK LK Coordinate Measuring Machine (CMM), supplemented by random checks with a surface roughness tester and a digital Rockwell hardness tester. All data was recorded in the MES system for full-process quality traceability.

Through the above precision manufacturing process, we successfully delivered harmonic reducer input shafts that fully met the customer's requirements:

• Full Compliance with Accuracy Requirements: All dimensional, geometric tolerances, and surface roughness met or even exceeded design requirements.
• Excellent and Reliable Performance: Customer testing showed fatigue life exceeded design specifications by 30%, with noise and vibration levels significantly lower than expected.
• High Batch Stability: The first batch of 500 pieces achieved a pass rate of 99.8%, strongly supporting the mass production of the customer's humanoid robots.

Customer feedback indicated that our input shafts contributed to more precise power transmission, smoother motion performance, and higher reliability for their humanoid robot joints, particularly excelling in high-dynamic performance applications like shoulder and hip joints.

This precision machining technology and service are suitable for:

• High-Precision Humanoid Robot Joint Modules: Such as high-load or high-precision requirement joints like shoulders, elbows, hips, and knees.
• Industrial Robot Joints: Rotary joints for six-axis collaborative robots (COBOTs) and SCARA robots.
• Precision Automation Equipment: High-precision transmission fields such as semiconductor manufacturing equipment (e.g., wafer handling robotic arms), precision optical instruments, and medical equipment.
• Aerospace Field: Drive mechanisms with extreme requirements for weight, reliability, and precision, such as satellite antenna pointing mechanisms.

We provide in-depth customized CNC machining services:

• Processing According to Drawings or Samples: Machining based on drawings or samples provided by customers.
• Material and Process Customization: Recommend and customize materials (e.g., stainless steel for corrosion resistance) and heat treatment processes based on operating conditions (load, speed, environment).
• Special Structure Design Optimization Consultation: Provide design optimization suggestions for stress concentration areas like shaft shoulder transitions, undercuts, and keyways to improve fatigue life.
• Full-Process Support: Offer one-stop services from precision forged blank preparation → machining → heat treatment → surface treatment → assembly.

• Technical Team Liaison: Dedicated engineers provide technical consultation and process solution support.
• Rapid Prototyping Service: Quick prototype manufacturing to shorten customer R&D cycles.
• Comprehensive Quality Documentation: Provide complete quality documents including material certificates, heat treatment reports, and full inspection reports (FAI) with shipments.
• Continuous Improvement and Stable Supply: Establish continuous quality improvement mechanisms to ensure product performance stability and on-time delivery.