Short Answer:

Shot peening is a surface treatment process used to improve the strength and fatigue life of metal components. In this process, small spherical particles called shots are bombarded onto the surface of a material at high velocity. This creates tiny indentations and introduces compressive stresses on the surface layer, which help prevent crack formation and failure during operation.

It is commonly used in mechanical and aerospace industries for components like springs, gears, shafts, and turbine blades. Shot peening enhances wear resistance, reduces stress corrosion, and extends the overall service life of metal parts.

Detailed Explanation :

Shot Peening

Shot peening is a mechanical process that involves striking the surface of a metal component with small spherical media, called shots, which can be made of steel, glass, or ceramic materials. These shots are propelled using air pressure, centrifugal force, or mechanical devices at high velocity toward the surface of the part. When each shot hits the surface, it produces a small plastic deformation, which causes the surface layer to compress. This compressive stress layer counteracts the tensile stresses that are responsible for fatigue cracks, thereby improving the durability and performance of the component.

Shot peening is not a material removal process like machining or grinding. Instead, it is a cold working process where the metal’s surface is plastically deformed, leading to beneficial changes in mechanical properties. This process is widely used in automotive, aerospace, and manufacturing industries to improve the fatigue strength, hardness, and wear resistance of critical parts.

Principle of Shot Peening

The working principle of shot peening is based on plastic deformation caused by repeated impact of small spherical shots on the surface. When these shots strike the surface, they create overlapping dimples. Each impact produces a small dent and causes the surface layer to stretch plastically. However, the underlying material resists this deformation, leading to the creation of residual compressive stresses on the surface.

These compressive stresses play an important role in increasing fatigue strength because cracks generally initiate and propagate under tensile stress. By applying compressive stress, the shot-peened surface becomes more resistant to crack formation, thereby enhancing the part’s fatigue life and overall reliability.

Process of Shot Peening

1. Preparation of Surface:
   Before peening, the surface is cleaned to remove rust, dirt, and grease so that the process can be effective.
2. Selection of Shot Material and Size:
   Depending on the application, shots can be made from steel, glass beads, or ceramic materials. The size and hardness of the shot determine the intensity of peening.
3. Peening Operation:
   The shots are directed toward the surface using compressed air or centrifugal force. The speed and duration of peening are carefully controlled to achieve uniform coverage and desired compressive stress.
4. Inspection and Testing:
   After the process, the surface is inspected to ensure proper peening coverage. Tests like Almen strip tests are used to measure the intensity of shot peening.

Applications of Shot Peening

• Automotive Industry: Used for crankshafts, connecting rods, and springs to increase fatigue life.
• Aerospace Industry: Used for turbine blades, landing gear parts, and gear teeth to resist fatigue failure.
• Manufacturing Tools: Improves wear resistance of cutting tools, dies, and molds.
• Springs and Shafts: Reduces failure due to repeated loading and enhances load-carrying capacity.

Advantages of Shot Peening

• Improves fatigue strength of components.
• Reduces risk of stress corrosion cracking.
• Increases wear and abrasion resistance.
• Extends the service life of parts without altering dimensions significantly.
• Produces compressive stress that delays crack formation.

Limitations of Shot Peening

• Requires precise control of shot size, velocity, and coverage.
• Improper peening may cause surface damage or uneven stresses.
• Not suitable for very thin or brittle materials.
• Increases surface roughness slightly, which may require post-processing.

Conclusion

Shot peening is an effective surface treatment method that enhances the mechanical properties of metals by introducing beneficial compressive stresses. It increases the fatigue life, wear resistance, and durability of components used in demanding mechanical applications. Although the process requires careful control, its benefits in improving part performance make it an essential step in manufacturing high-stress components in aerospace, automotive, and industrial machinery.