First, the analysis of the product's parts drawings and assembly drawings is essential before compiling the machining process specifications. It is important to thoroughly study the part drawings and the overall assembly drawings to understand the product's function, performance, and working conditions. This helps in identifying the role and position of each component within the product. Additionally, it is crucial to understand the technical requirements and key points, so that appropriate measures can be taken to ensure the development of an effective process plan.
The purpose of process analysis is to evaluate whether the shape, dimensional accuracy, positional accuracy, surface roughness, material, and heat treatment of the parts are reasonable and suitable for processing and assembly. Through this analysis, we gain a deeper understanding of the part’s structure, which is necessary for developing a practical and efficient process specification.
As shown in Figure 3-8, the automobile leaf spring lug is used in such a way that the leaf spring does not come into contact with both sides of the lug. Therefore, the inner surface roughness of the lug can be adjusted from Ra 3.2 μm to Ra 12.5 μm. This allows for rough milling instead of finish milling, reducing the machining time significantly.
As illustrated in Figure 3-9, the square head pin requires a quenching hardness of 55–60 HRC, and the selected material is T8A. There is a hole φ2H7 on the part, which is required during assembly. However, since the part is only 15 mm long and the square head is only 4 mm, fully quenching the entire length of the T8A material would make it impossible to machine the φ2H7 hole. To resolve this issue, using 20Cr steel with carburizing and quenching would be more appropriate.
**Second, structural process analysis**
Structural processability refers to the feasibility and economic efficiency of the designed part, provided it meets the functional requirements. The following analysis will focus on the manufacturability and ease of machining and assembly of the part.
**(I) Machining Requirements for Part Structure**
1. The structure of the part should allow for easy clamping and positioning during machining, minimizing the number of setups. For example, as shown in Figure 3-10a, the original design is difficult to clamp, but changing it to the configuration in Figure 3-10b makes it easier to install the chuck.
2. The part structure should be as standardized as possible to facilitate the use of standard tools and gauges. Attention should also be given to tool clearance and feed direction, ensuring ease of achieving accurate machining and reducing the area of complex surfaces. Figure 3-8b provides an example of a part designed for easier machining.
3. Parts suitable for CNC machining should have features that simplify programming. For instance, if a part uses abstract dimensioning (as shown in Figure 3-11), it may cause difficulties when writing a program in APT language. In such cases, alternative definitions or roundabout methods may be needed, which can complicate the process. Therefore, the dimensioning on the drawing should be designed to support efficient programming.
4. The part structure should also consider ease of measurement. As shown in Figure 3-14, if the parallelism between a measurement hole and a reference plane is hard to measure due to an offset boss, adding a symmetric process boss can make the measurement much easier.
**(B) Assembly and Maintenance Requirements for Part Structure**
The part structure should be easy to assemble and disassemble for maintenance. For example, in Figure 3-15a, the lack of a vent in the left structure makes it difficult to load the pin. The improved right structure solves this problem. Similarly, chamfering the shoulder of a shaft or the opening of a housing ensures better contact between the bearing and the surface. In Figure 3-15c, only one positioning base should be used in a single direction, making the right structure more reasonable. In Figure 3-15d, the left structure has insufficient space for screws, while the right structure improves accessibility.
Figure 3-16 shows an example of a part designed for easy assembly and disassembly. In Figure 3-16a, the inner ring of the bearing cannot be removed because the shoulder is too large. In Figure 3-16b, designing screw holes on the end face of the housing allows the bushing to be ejected easily.
**Third, Technical Requirements Analysis**
The technical requirements for parts include:
1. Shape accuracy of the machined surface (including dimensional accuracy and geometric tolerances);
2. Positional accuracy between major machined surfaces (including distance dimensions and positional tolerances);
3. Surface roughness and other quality requirements;
4. Heat treatment and other special requirements.
By analyzing these technical requirements, it is possible to identify the main surfaces that require high precision and determine the appropriate technological measures. After evaluating both the structural and technical aspects, a preliminary processing route and method can be established, preparing the groundwork for the next step in developing the process specifications.
If during the analysis, certain structural features or technical requirements are found to be problematic, suggestions for design improvements can be made. Once approved by the designer, these changes can be implemented to enhance the overall manufacturing process.
Button Hole And Button Attach And Bar-tacking Series
Single chain stitch, Double lock stitch, High degree of automation
Zhejiang Lejiang Machine Co., Ltd. , https://www.cnlejiang.com