Shot peening can significantly improve the fatigue performance of metal components, and the shot medium is the core parameter. Its selection and process control directly determine the fatigue improvement effect and process consistency. Bullets have six key characteristics: size, shape, hardness, density, wear resistance, and material, all of which need to be strictly controlled.
The size affects the shot blasting intensity. When the speed remains constant, the larger and heavier the shot, the higher the intensity. Commonly used screening tests can also be used for batch measurement of particle size and roundness through visual analysis systems, resulting in more stable data. Experiments have shown that uniformly sized round steel wire pellets have higher shot peening intensity and better consistency.
A circular shape is preferred and sharp edges should be avoided. Damaged particles can damage the surface of the workpiece and reduce fatigue life. Automatic shape analysis can reduce manual errors and ensure process stability.
In terms of hardness, it is recommended that the hardness of the projectile should not be lower than the hardness of the workpiece and the Almen test piece to obtain stable residual compressive stress. Low hardness can lead to low arc height and saturation point, which is not conducive to process control.
Density reflects the internal density of particles. High density results in greater kinetic energy, better resistance to fragmentation, longer service life, stable maintenance of shot peening intensity, and reduced surface damage. Particles with multiple internal defects have low density and are prone to breakage, resulting in sharp corners and affecting the quality of reinforcement.
Wear resistance refers to the ability of pellets to maintain shape and size, which directly affects the fatigue resistance of workpieces, dust emissions, equipment wear and tear, and usage costs. Data shows that stainless steel wire cutting pellets have the longest grinding life and the least dust; Cast steel shot has a short lifespan, high dust content, and higher overall usage cost. Choosing high wear-resistant pellets can reduce overall costs and maintenance frequency.
The material determines the applicable scenario. Cast steel shot and steel wire cutting shot are suitable for ordinary steel parts; Stainless steel pellets, ceramic pellets, and glass beads are commonly used for non-ferrous metals such as aluminum alloys, which can reduce the risk of iron residue and corrosion. The iron residue test shows that the residual amount of stainless steel shot is much lower than that of cast steel shot, making it more suitable for components with high cleanliness requirements.
In summary, in order to stably improve fatigue performance, the selection of pellets should follow the following principles: uniform and stable size; Round in shape and not easily broken to produce sharp corners; The hardness shall not be lower than that of the workpiece and the Almen test piece; High density and few internal defects; Strong wear resistance and long service life; Match the material with the workpiece and control surface residue. Strictly controlling the above points is necessary to achieve stable, reliable, and repeatable shot peening effects.