Imagine a raw piece of metal, like uncut jade, brimming with potential yet plagued by insufficient strength and brittleness. How can it be transformed into an industrial cornerstone capable of withstanding heavy loads and enduring prolonged use? The answer may lie in a metalworking process known as "shot peening."

In their natural state, metal materials often prove inadequate for demanding manufacturing applications. To enhance strength, fatigue resistance, and overall reliability, metal processors typically employ various modification techniques. Shot peening, as a crucial cold working method, has emerged as a solution to these challenges by altering metal surfaces' physical properties to significantly improve mechanical performance.

Before delving into shot peening, we must first understand why metals require strengthening and the challenges they face in practical applications:

Ideal metal materials must possess sufficient strength to bear loads while maintaining adequate toughness to prevent brittle fractures. However, increasing strength often comes at the expense of toughness, and vice versa. Achieving this balance remains a fundamental challenge in metal material design and application.

Under cyclic loading, metals can experience fatigue failure even when stresses remain well below their yield strength. This failure typically begins with microscopic surface cracks that gradually propagate, ultimately causing material fracture. Fatigue failure represents one of engineering structures' most common and dangerous failure modes.

During service, metal materials suffer from wear (gradual surface material loss due to friction) and corrosion (material degradation through chemical or electrochemical reactions with the environment).

This phenomenon occurs when metals crack under combined tensile stress and corrosive environments. Its sudden and rapid nature can lead to catastrophic failures.

Shot peening, also called shot blasting, is a cold working process that improves metal surfaces' physical properties through controlled impact. The core principle involves bombarding metal surfaces with high-velocity pellets (typically metal, ceramic, or glass beads) to induce plastic deformation. This deformation creates a compressive stress layer that effectively inhibits crack initiation and propagation, enhancing fatigue strength, wear resistance, and stress corrosion cracking resistance.

Unlike heat treatment and other metal strengthening methods, shot peening operates at or near room temperature, avoiding potential issues like grain growth and oxidation while better preserving the metal's original microstructure and dimensional accuracy.

Shot peening's origins trace back to ancient hammering techniques where blacksmiths hardened metal surfaces through repeated strikes. Modern industrial advancements have developed several peening variants:

The oldest and simplest form, using manual or mechanical hammering to induce plastic deformation. While inexpensive and equipment-simple, it suffers from low efficiency and inconsistent results. Modern applications are limited to small-batch, low-precision scenarios like hand tool manufacturing or large component spot treatment.

The most widely used method today, employing compressed air or centrifugal force to propel pellets at high speeds. Parameters like pellet size, velocity, angle, and duration can be precisely controlled for optimal results.

• Air Blast Peening: Uses compressed air for propulsion. Advantages include simple equipment and lower costs, making it suitable for small-to-medium production. Disadvantages include lower energy efficiency and relatively weaker peening intensity.
• Centrifugal Peening: Utilizes centrifugal force to hurl pellets. Benefits include higher energy efficiency and adjustable intensity for mass production. Drawbacks involve complex equipment and higher costs.

This emerging technology employs high-energy laser pulses to vaporize metal surfaces, creating plasma whose rapid expansion generates powerful shockwaves that form compressive stress layers. Laser peening offers unparalleled precision, non-contact operation, and cleanliness, making it ideal for aerospace and medical applications where performance demands are extreme.

Shot peening improves metal performance through several mechanisms:

The most significant effect, surface compressive stresses counteract external tensile stresses, reducing actual stress exposure and inhibiting crack formation—especially crucial for fatigue life extension under cyclic loading.

Pellet impacts cause surface grain plastic deformation and refinement, simultaneously increasing strength/hardness while improving toughness/ductility.

Enhanced surface hardness improves wear resistance for friction-prone components like gears and bearings.

Peening can produce smoother surfaces that reduce friction coefficients, lowering energy losses and improving mechanical efficiency.

With its unique advantages, shot peening has found widespread use across industries:

Critical components like engine blades, landing gear, and airframe structures benefit from enhanced fatigue strength and reliability.

Crankshafts, connecting rods, gears, and suspension springs see improved wear resistance and fatigue life, extending vehicle longevity.

Propellers and hull structures gain corrosion and fatigue resistance for safer navigation.

Gears, bearings, and springs across industrial equipment achieve greater strength, wear resistance, and operational lifespan.

Casings and connectors obtain improved strength, wear resistance, and aesthetic quality.

Peening effectiveness depends on multiple factors: pellet material/size/shape, velocity, angle, duration, and pressure. Optimal results require precise parameter control and iterative testing for refinement.

Ongoing technological advancements are driving several trends:

• Computer-controlled intelligent systems for enhanced precision and efficiency
• Robotic automation to reduce labor costs and increase productivity
• Nano-peening using nanometer-scale pellets for superior hardness and finish
• Hybrid techniques combining peening with other treatments like heat treatment for synergistic performance gains

As a vital metalworking process, shot peening plays an irreplaceable role in enhancing material performance. From traditional hammer peening to advanced laser methods, these techniques provide effective solutions for metal modification. Continuous technological progress will further refine peening methods, delivering higher-quality, more reliable metal components to support industrial advancement across sectors.