Abstract:
This article mainly introduces the design and verification analysis process of the gear milling process for aerospace transmission spiral bevel gear. By utilizing the R&D V-model, the traditional continuous gear milling process is decomposed into stages such as demand analysis, preliminary design, and detailed design. Based on theoretical analysis and in conjunction with mainstream gear-specific software, it interprets the static and dynamic relationships that require calculation and analysis by process designers among gear milling workpieces, tools, and equipment. This aids process designers in establishing gear milling process designs and verification schemes oriented towards new product development, as well as in the development of enterprise digital solutions.
1. Introduction
Spiral bevel gear (hereinafter referred to as bevel gear) is core components in aerospace engine mechanical systems, engine reducers, helicopter transmission systems, and other components/subsystems. They have high technical requirements and provide crucial support for these components/subsystems to meet demands such as power load, speed reduction and direction change, paralleling, accessory drives, as well as indicators such as weight, strength life, transmission efficiency, vibration noise, and survival capability (dry running). The spiral bevel gear milling process is a core process for bevel gears, typically conducted after semi-finishing of the spiral bevel gear blank and before heat treatment, playing a significant role in ensuring the final finishing process of grinding for the characteristics. Balancing processing costs while taking into account processing quality and efficiency is crucial. Traditional aerospace manufacturing enterprises organize production based on manufacturing resources. This article aims to provide process designers with a comprehensive understanding of process design from a process-level design and verification perspective, assisting enterprises in refining forward-looking R&D operations during the implementation of digital transformation.
2. Framework Design
Considering the process design as a small system, and leveraging the R&D V-model, the traditional process design stages such as drawing review, preliminary process design, and detailed process design are mapped to demand analysis, preliminary design, and detailed design, respectively, to clarify the associated validation process solutions. For process design, the solutions should encompass not only the corresponding processes in the “process specification” but also process specifications, operating specifications, Standard Operating Procedures (SOPs), process design modeling and calculation analysis software, processing and inspection programs, etc., for that process.
Table 1: Correspondence Between Traditional Process Design Stages and V-Model Stages
| Traditional Process Design Stages | V-Model Stages |
|---|---|
| Drawing Review | Demand Analysis |
| Preliminary Process Design | Preliminary Design |
| Detailed Process Design | Detailed Design |
In actual production, the businesses of process design, tooling design, and on-site processing overlap on the process designer, who plays a central role. It is necessary to not only meet the system requirements arising from the spiral bevel gear milling processing scenario itself but also to meet the requirements posed by processes such as the machining of the tooth transfer area and heat treatment, while the direct relationship between the preceding process of spiral bevel gear blank machining and the tools, equipment, and auxiliary materials directly affects machinery’s operational efficiency and safety.
3. Design and Verification
3.1 Demand Analysis and Verification
At the demand analysis level, the spiral bevel gear milling process design needs to satisfy the grinding process design requirements with spiral bevel gear tooth meshing marks as the comprehensive performance verification result and the characteristics of structures such as tooth surfaces, tooth roots, and tooth root fillets as the physical performance verification results. This is the most fundamental requirement. Specific mating test pieces are designed for spiral bevel gear tooth meshing for verification, mainly involving tooth thickness reduction and adjustment of the mounting distance. However, the acceptance criteria for gear milling marks should differ from those for grinding meshing marks. For standard gears, meeting the trends in length, width, and basic shape suffices.
In recent years, gear-specific software such as GEMS from Gleason Corporation (USA), KIMOS from Klingberg, and CHIMES from Zhongda Chuangyuan has been widely used in production to calculate theoretical spiral bevel gear tooth models and morphologies, with specific parts collected using gear-specific measuring machines for comparative analysis, which can be used for cross-verification with meshing marks.
Figure 1: Schematic Diagram of Gear-Specific Software
The assembly area of spiral bevel gear generally also requires heat treatment strengthening. Therefore, the calculation of the spiral bevel gear tooth mounting distance needs to consider the grinding allowance. Factors such as spiral bevel gear structure, spiral bevel gear tooth parameters, and heat treatment strengthening layers collectively determine that various tooth profiles in the transfer area need to have burrs and chips produced during gear milling removed to prevent damage during grinding or fitting processes due to the brittleness of the strengthened layer.
3.2 Preliminary Design and Verification
At the preliminary design level, it is necessary to clarify the technical state of traditional elements involved in gear milling operations.
(1) Calculation of Gear Blank Geometric Parameters
Geometric parameters such as cone distance, tooth length (tooth width), and full tooth height should be calculated. For spiral bevel gears with a volume-to-accuracy relationship of approximately 10–103 mm in volume and 10-2–10-3 mm in accuracy, the outer conical surface and related areas of spiral bevel gear blank may require grinding. Therefore, gear blank geometric parameters cannot be calculated solely based on nominal values; differences considering tolerances must be incorporated, and if discrepancies are large, they need to be verified in coordination with drawing designers.
Traditional gear blank tolerances are relatively high, which may adversely affect grinding finishing. Therefore, stricter accuracy is required for related gear blank processing steps. Calculations of parameters such as the root cone can provide intuitive insights into whether spiral bevel gear tooth processing interferes with fixtures or the workpiece itself, thereby necessitating optimization of spiral bevel gear blank processing or fixture structure.
(2) Calculation of Gear Tooth Geometric Parameters
In traditional design drawings, the complete set of geometric parameters for spiral bevel gear teeth is often not provided. Instead, only basic parameters such as tooth count, modulus, and tooth thickness are supplied to meet fundamental calculation requirements. However, for the precise processing of spiral bevel gear teeth, a more comprehensive set of geometric parameters is necessary. These parameters include, but are not limited to, tooth root cross-sections in various directions, tooth groove width, tooth bottom fillet, arc tooth thickness, chord tooth thickness, and corresponding tooth height.
To obtain these detailed geometric parameters, calculations based on gear handbook size charts are typically required. The process involves:
- Reference to Gear Handbook: Utilize a comprehensive gear handbook, which provides detailed size charts and formulas for various types of gears. This handbook serves as a critical resource for calculating the required geometric parameters.
- Basic Parameters Input: Begin with the basic parameters provided in the design drawing, such as tooth count, modulus, and tooth thickness. These parameters serve as the foundation for further calculations.
- Cross-Sectional Calculations: Calculate the cross-sectional dimensions of the tooth root, including the tooth groove width, tooth bottom fillet, and other relevant dimensions. These calculations are crucial for ensuring the correct shaping and clearance of spiral bevel gear teeth.
- Arc and Chord Tooth Thickness: Determine the arc tooth thickness and chord tooth thickness, which are essential for the strength and durability of spiral bevel gear teeth. These calculations help ensure that the teeth can withstand the loads and stresses they will encounter in operation.
- Tooth Height Calculations: Calculate the corresponding tooth height, which is critical for maintaining the proper engagement and alignment of spiral bevel gear teeth.
- Consideration of Tolerances: Incorporate tolerances into the calculations to account for manufacturing variations and ensure that the final spiral bevel gear teeth meet the required specifications.
- Optimization and Verification: After performing the calculations, use gear-specific software to simulate and verify the designed spiral bevel gear teeth. This step ensures that the calculated parameters result in a functional and durable gear.
By following these steps, the geometric parameters required for spiral bevel gear tooth processing can be accurately calculated. These parameters are crucial for the successful manufacturing and operation of spiral bevel gear in aviation transmission systems.