A Brief History of

The Benefits of Shot Peening

What is Shot Peening

Shot peening is a cold metalworking method that involves bombarding a metal surface with enough force to create a plastic deformation. This process is known to be a shot using a small, spherical media such as metal, glass or ceramic. The shot creates dimples on the metal surface, causing considerable compressive stress in the area immediately beneath the dents. The atoms on the surface are pushed outwards by the stress and they strive to restore the surface to its former shape by pressing the grain boundaries of the surface material together. The stretched surface drags the atoms in the metal deeper into the metal, bringing them closer to the surface. The deeper atoms resist the pull and the resulting tension harmonizes the compressive stress on the surface, making it stronger.

Shot peening is not a new technique, when in fact evidence of mechanical pre-stressing procedure dates back to 2700 BC in Mesopotamia. Peening hammers have been used throughout history, but it was not until the late twentieth century that the peening process began to advance, with the increased usage of shots and more precise impacts.

The Advantages

The most significant advantage of shot peening is an increase in the metal part’s fatigue life. Internal stress concentrations can be caused by precise machining, forging, die casting, or dynamic loading after a metal part has been formed, resulting in fatigue failure, porosity, decreased strength, and corrosion. The underlying tensile strength is enhanced by increasing the compressive stress layer on the surface. Furthermore, because cracks normally form on a metal part’s surface, the reinforced surface helps to avoid stress cracking and corrosion to a large extent. Other advantages of shot peening include a more uniform surface for platings and special coatings, reduced casting porosity and straightening components and deformities.

Its Significance on Gears

Gears are extremely affected by continuous stress by their sheer nature and therefore also benefit immensely from shot peening. Peening improves the gear’s lubricity and oil retention, notably when utilized in engine pistons and cylinder walls. Shot peening procedure will protect and also aids in the elimination of continuous machine markings on the gear tooth flank, decreasing stress risers. Shot peening allows manufacturers to employ alternative, less expensive materials to get the same amount of hardness necessary for the application by enhancing the metal’s strength. This allows manufacturers to meet customer and government demands for more production, durable and light in weight vehicles that result in less consumption of fuel. Given that a gear tooth is essentially a supported beam, it is only natural that the root fillets of the gear would bear the brunt of the cyclical stress, making them the most crucial section of the gear to be shot-peened. Peening the root fillets results in less pitting and longer gear life as well as increased bending strength.

In Conclusion

Unfortunately, many production procedures result in a drop in fatigue strength, which leads to a reduction in material durability. Because of this, shot peening has become the industry standard to restore the strenghth of the product. These mechanisms have been shown in numerous academic research to restore the bulk of the fatigue strength that is lost during the other stages. Shot peening is the industry leader in terms of strength, durability and safety.

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