Machining Introduction of Output Shaft for Motor Gearbox

I. Core Product Characteristics & Basic Requirements

1. Material Selection

   302 stainless steel is adopted as the base material, which features excellent corrosion resistance, toughness and mechanical strength to meet the working condition requirements of transmission components. It also complies with stringent environmental test standards, ensuring the product's durability in various application scenarios.
2. Performance Indicators

   The product must meet the specified Rockwell hardness standard, with hardness testing conducted at specific structural positions to ensure the strength of key stress-bearing surfaces. It shall pass a 96-hour salt spray test to verify corrosion resistance, and material compliance certification is required to guarantee product quality from the raw material stage.
3. Basic Process Requirements

   The product surface shall be free of scratches, burrs, nicks and other defects, and the straightness must meet high-precision standards. When inspected on special V-blocks, the straightness deviation per inch of length is controlled within an extremely small range to ensure coaxiality and smooth transmission after assembly.
4. Structural Features

   The shaft body is designed with precision spline structures, groove structures and planar structures. The splines are multi-tooth uniformly distributed, serving as the core structure for power transmission. Meanwhile, the shaft body includes multiple precision steps and chamfers, with strict requirements for the positional and geometric accuracy between various structures.

II. Overall Machining Process

1. Raw Material Preprocessing

   Qualified 302 stainless steel bar stock is selected for straightening and flaw detection to eliminate raw material defects. The bar stock is then cut and rough-turned with finishing allowances reserved to ensure the stability of subsequent machining.
2. Semi-Finishing

   CNC turning is used to machine the basic structures such as shaft steps, grooves and outer circles, initially forming each characteristic surface. CNC milling is adopted for the rough machining of spline basic contours with precision grinding allowances reserved.
3. Heat Treatment

   Custom heat treatment is performed according to the product's hardness requirements, with precise control of heating temperature, holding time and cooling rate to ensure the hardness of specified positions meets the standard. Meanwhile, deformation and cracking of the shaft body are avoided, and stress relief treatment is conducted after heat treatment to eliminate internal stress.
4. Precision Finishing

   As the core link of product machining, CNC cylindrical grinding machines are used for precision grinding of outer circles and steps to ensure dimensional accuracy and straightness. Precision spline grinding is completed by spline grinders to guarantee the accuracy of spline tooth profile, tooth orientation and uniformity. Precision machining is applied to chamfers, planes and other structures to ensure the positional accuracy of each structure.
5. Surface Treatment & Deburring

   Special processes are used for full-surface deburring and rounding of the product to remove micro-burrs generated during machining and ensure surface finish. Surface optimization treatment is conducted according to corrosion resistance requirements to improve the pass rate of the salt spray test.
6. Full-Process Inspection & Certification

   100% inspection is implemented from raw materials to finished products, including material compliance certification, hardness testing, dimensional and geometric accuracy testing, salt spray testing, straightness testing, etc. All test data is retained to provide customers with complete compliance certification documents.

III. Core Machining Challenges

1. Difficulty in Controlling High-Precision Geometric Tolerances

   The shaft body has extremely high requirements for straightness and coaxiality. The long machining process, heat treatment and multiple clamping are prone to micro-deformation of the shaft body. Improper deformation control will directly affect assembly accuracy and transmission performance.
2. Difficulty in Precision Spline Machining

   Splines are the core structure for power transmission, with strict requirements for the accuracy of tooth profile, tooth orientation, pitch uniformity and span measurement. The multi-tooth uniform design places high demands on the positioning accuracy and tool accuracy of machining equipment. Meanwhile, tooth surface scratches and dimensional deviations are likely to occur during machining.
3. Difficulty in Balancing Hardness and Deformation

   The specified positions of the product need to meet precise hardness requirements. Due to the material characteristics of 302 stainless steel, thermal deformation of the shaft body is prone to occur during heat treatment. The key challenge is to control the deformation within the finishing allowance while ensuring the hardness meets the standard.
4. Difficulty in Surface Quality and Defect Control

   The product requires a surface free of any nicks, burrs and scratches. However, the shaft structure includes complex structures such as grooves, splines and small chamfers where burrs are easily generated, and micro-burrs are difficult to remove. In addition, tool wear and improper cutting parameters during finishing are prone to surface scratches, affecting product quality.
5. Difficulty in Clamping and Positioning for Multi-Process Machining

   The product undergoes multiple processes such as turning, milling, grinding and heat treatment. Multiple clamping is prone to positioning errors, and the accumulated errors will affect the final product accuracy. Ensuring the consistency and positioning accuracy of clamping in each process is the key to controlling the overall accuracy.

IV. Solutions to Overcome Challenges

1. High-Precision Geometric Tolerance Control Solution

• Adopt the process concept of multi-process machining with one-time clamping to reduce the number of clamping times and positioning errors. In the finishing stage, use high-precision CNC grinding machines combined with CNC straightening equipment. The shaft body is precision-straightened after heat treatment before finishing to eliminate thermal deformation.
• In the inspection link, use high-precision testing tools such as special V-blocks, dial indicators and laser diameter gauges for 100% dimensional inspection of straightness and coaxiality. Adjust machining parameters in a timely manner when deviations are found to ensure compliance with geometric accuracy standards.

2. Precision Spline Machining Solution

• Select imported high-precision spline grinders and special spline machining tools. Tools are regularly inspected and replaced to ensure tooth profile machining accuracy. Precisely calibrate the equipment before machining and optimize the CNC machining program to ensure spline pitch uniformity.
• After spline machining, conduct 100% inspection with special spline gauges and tooth profile measuring instruments to accurately detect tooth surface roughness and tooth profile deviation. Non-conforming items are reworked immediately to ensure the accuracy and smoothness of spline transmission.

3. Hardness and Deformation Balancing Solution

• Custom heat treatment process: According to the material characteristics of 302 stainless steel, adopt the heat treatment method of step heating and isothermal cooling, and fix the shaft body with tooling to reduce deformation during heat treatment. Low-temperature stress relief tempering is conducted after heat treatment to eliminate internal stress and stabilize product dimensions.
• Reserve reasonable finishing allowances: Based on the heat treatment deformation law, reserve targeted grinding allowances in the rough and semi-finishing stages to ensure that deformation can be completely eliminated after finishing and the accuracy of hardness testing positions is guaranteed.

4. Surface Quality and Defect Control Solution

• Adopt a combined method of mechanical deburring + manual fine grinding for deburring. For complex structures such as grooves and splines, use special deburring tools (e.g., rotary files, ultrasonic deburring equipment), followed by manual fine grinding by senior technicians to ensure no residual burrs.
• Optimize cutting parameters in the finishing stage and select high-quality cutting fluid to reduce tool wear and cutting heat, avoiding surface scratches. Implement a dust-free machining environment during processing to prevent iron chips and impurities from scratching the product surface. Meanwhile, adopt anti-static and anti-collision packaging for machined products to avoid surface damage during transportation.

5. Multi-Process Clamping and Positioning Solution

• Design special tooling and fixtures: Customize a unified positioning fixture for the product, which is used for clamping in all processes to ensure the consistency of the clamping datum and reduce the accumulation of positioning errors.
• Establish an inter-process precision inspection mechanism: Inspect key positioning datums and dimensions after the completion of each process to ensure that the previous process meets the precision standards before entering the next process, avoiding error transmission. Regularly calibrate and maintain tooling and fixtures to ensure fixture accuracy.

V. Quality Assurance & Customer Service

1. Raw Material Assurance

   All base materials are 302 stainless steel supplied through formal channels, with complete material certificates and compliance certifications provided to guarantee product quality from the source and meet customers' material certification requirements.
2. Full-Process Inspection

   Implement a four-level inspection system of First Article Inspection + In-Process Inspection + Last Article Inspection + 100% Finished Product Inspection. All test data is recorded and retained in real time, and complete inspection reports and compliance certification documents can be provided to customers.
3. Customized Services

   As a custom non-standard precision machining factory, we can optimize product processes according to customers' working condition and assembly requirements, and provide real-time feedback on product machining progress to meet customers' customization and delivery needs.
4. After-Sales Support

   Comprehensive after-sales technical support is provided after product delivery. In case of assembly or precision problems, we will respond immediately and provide solutions to ensure the progress of customers' production and assembly.