In the field of metal processing, the shrink fitting process is a common and important forming technology, widely used in industries such as automotive parts, aerospace, home appliances, and daily necessities. The basic principle of the shrink fitting process is to apply pressure to pipes or cylindrical parts through molds, so that their diameters gradually decrease to achieve the required geometric dimensions and shapes. In this process, the selection of mold angles has a crucial impact on the forming quality, material flow, forming force, and mold life. Therefore, reasonably selecting mold angles is one of the key factors for achieving efficient and stable shrink fitting processing.



First, the definition and classification of mold angles



Mold angle usually refers to the semi-angle of the conical part of the shrink fit mold, that is, the angle formed from the mold center line to the inner wall of the mold. The common range of mold angles is between 5° and 30°, which can be divided into small angle molds (such as 5°~10°), medium angle molds (such as 12°~18°), and large angle molds (such as 20°~30°) according to the forming requirements.



Second, the influence of mold angles on the forming process



1. Material flow characteristics

The smaller the mold angle, the more uniform the flow speed of the metal material during plastic deformation, which is conducive to reducing local stress concentration and reducing the risk of cracking; however, an excessively large angle may lead to uneven material flow, causing wrinkles or cracking.



2. Forming force and energy consumption

Although small angle molds are helpful for uniform material deformation, they will increase the friction area, thereby requiring greater forming force and higher energy consumption; on the other hand, large angle molds can reduce forming resistance, but are prone to material instability.



3. Mold life and wear

Large angle molds have more intense wear on the mold surface during the processing process, which is easy to cause the mold life to shorten. In contrast, small angle molds are relatively more conducive to extending the mold service life.



Third, the selection principles of mold angles



1. Selection based on material characteristics

For materials with good plasticity (such as low carbon steel, copper alloys, etc.), a larger angle can be appropriately selected to improve production efficiency; for materials with poor plasticity (such as high carbon steel, stainless steel), a smaller angle should be chosen to prevent cracks from occurring.



2. Consider the shrinkage ratio (the diameter ratio before and after the shrink fit)

When the shrink fit is large, a smaller mold angle should be selected to ensure that the material has good fluidity and stability during the deformation process; when the shrink fit is small, the mold angle can be appropriately increased to improve processing efficiency.



3. Combine process conditions with equipment capabilities

If the equipment pressure is large, a smaller angle mold can be selected to obtain better forming quality; if the equipment capability is limited, a larger angle mold should be chosen to reduce the demand for forming force.



Fourth, optimization suggestions in practical applications



- In practical applications, it is common to compare and analyze the forming effects under different mold angles through experimental methods or finite element simulation methods, thereby selecting the best angle.

- The best mold angle with comprehensive performance is usually between 12° and 18°, suitable for most shrink fitting forming occasions.

- In continuous production, it is necessary to regularly inspect the mold wear condition and adjust mold parameters or replace the mold in a timely manner according to the degree of wear.



Conclusion



In summary, the selection of mold angles in the shrink fitting process is not only related to product quality and production efficiency, but also directly affects the mold life and processing cost. Therefore, it is necessary to scientifically and reasonably select mold angles according to material characteristics, structural parameters, equipment capabilities, and process requirements in order to achieve efficient, stable, and economic shrink fitting processing goals. In the future, with the development of digital manufacturing and simulation technology, the optimization of mold angles will be more precise, bringing greater improvement space to metal forming processes.