How Does Shot Peening Work?

 

Introduction

Shot peening is one of those manufacturing processes that quietly transforms how long a metal component can survive in the real world—yet most people outside engineering have never heard of it. Whether it's an aircraft landing gear absorbing thousands of takeoffs, a transmission gear enduring constant torque reversals, or a suspension spring taking millions of road impacts, these components succeed because their surfaces are engineered to resist fatigue. Shot peening machine is the process that makes this possible.

In my work at Vibra Finish Ltd., I’ve seen how a precisely controlled stream of small spherical media can fundamentally improve the durability, reliability, and performance of critical parts. By using high-velocity impacts to reshape the top microns of a metal surface, shot peening introduces beneficial compressive stress that delays crack formation and extends the life of the component. It’s simple in concept yet incredibly powerful in practice — and in this article, I’ll break down exactly how it works, why it matters, and where it delivers the most value.

What exactly is shot peening and why is it used?

Shot peening is a mechanical surface-treatment process in which small spherical media—such as steel shot, ceramic beads or glass beads—are propelled at high velocity onto a metal surface. The repeated impacts plastically deform the surface layer, creating compressive residual stresses that dramatically improve fatigue resistance.

Most metals accumulate tensile stresses during machining, grinding, bending or forming. These tensile stresses make the surface more vulnerable to fatigue cracks. By converting surface tension into compression, shot peening slows or eliminates crack initiation, extending component life.

At Vibra Finish Ltd., this principle is fundamental: even a thin compressive layer can significantly increase durability in aerospace, automotive, and general manufacturing applications.

How does the physical mechanism work?

Each shot impact creates a tiny indentation in the surface. When this happens:

• The material at the impact site undergoes plastic deformation.

• Surrounding material resists the deformation's recovery, locking in compressive stress.

• Thousands of overlapping impacts build a uniform compressive layer.

Because cracks require tensile stress to grow, this compressed zone acts as a barrier. The microstructural refinement and cold working also help increase hardness, improving resistance to wear, contact fatigue and pitting.

In short: Impact → Plastic deformation → Compressive stress → Crack prevention.

What are the main steps and equipment used in shot peening?

1. Surface Preparation

Surfaces must be clean, free of coatings and contaminations. In some cases, masking is required.

2. Media and Parameter Selection

• Media: steel shot, cut-wire shot, ceramic or glass beads.

• Parameters: shot size, pressure/velocity, coverage, Almen intensity, angle, number of passes.

3. Application Method

Common shot peening systems include:

• Air-blast peening – high control, ideal for precision components.

• Wheel-blast peening – high-volume, high-speed applications.

• Lance or internal-diameter peening – for bores and internal features.

• Robotic/CNC peening – provides unparalleled consistency and accuracy.

At Vibra Finish, robotic peening is used to achieve uniform coverage and meet strict aerospace and industrial specifications.

4. Quality Assurance

You cannot “see” compressive stress, so validation matters. Technicians verify:

• Intensity using Almen strips

• Coverage visually or with automated scanning

• Process parameters through real-time monitoring and data logs

5. Post-Peening Handling

Parts are cleaned, inspected, and prepared for coating or final finishing if needed.

Which industries and components benefit most from shot peening?

Shot peening is essential in sectors where components face cyclic loading or high stress:

• Aerospace: landing gear, turbine components, brackets, fasteners

• Automotive: gears, crankshafts, springs, connecting rods

• Manufacturing & Heavy Industry: hydraulic rods, shafts, dies, wear components

The most common result? Reduced failures, greater reliability, and longer service life.

What modern advancements are shaping the future of shot peening?

The biggest shift in recent years is the rise of robotic and CNC-controlled peening. These systems provide:

• Automated coverage verification

• Repeatable intensity levels

• Closed-loop feedback control

• Traceable data for aerospace and defence certifications

They also eliminate operator variability, making the process more reliable and scalable.

What should you consider when specifying shot peening?

Before implementing shot peening, verify:

• Material suitability (metals only — composites cannot be peened)

• Required depth and intensity for the intended fatigue performance

• Geometry complexity and whether robotic/lance peening is needed

• Surface roughness tolerance after peening

• Documentation requirements for your industry

• Cost vs. life-cycle benefit

Peening is often a small cost compared to the benefits of longer service intervals and fewer failures.

FAQ (400 words)

1. Can shot peening repair an already damaged part?

Peening is preventive, not a repair technique. If cracks or deep damage already exist, they must be addressed before peening. The process is designed to stop cracks from forming, not fix existing ones.

2. How deep does shot peening affect the material?

Typical compressive layers range from 0.1 mm to several millimeters, depending on intensity, media and material. Higher intensities and larger media can create deeper stress profiles for heavy-duty parts.

3. Does shot peening increase surface roughness?

Yes. Shot peening leaves a controlled, dimpled texture. For components where a smoother finish is needed—like sealing surfaces—a follow-up polishing step may be required.

4. Is shot peening environmentally friendly?

Very much so. It is a mechanical, cold-working process that uses recyclable media and no chemicals. Closed-loop systems minimize waste and environmental impact.

5. What’s the difference between peening and sandblasting?

Sandblasting cleans or textures a surface using abrasive media. Shot peening, however, uses spherical media to improve mechanical properties by inducing compressive stress. They serve different purposes.

6. Can shot peening be used on composites or plastics?

No. The process relies on plastic deformation in metals. Composites, ceramics and plastics do not deform in the same way and therefore cannot benefit from shot peening.

7. Why is shot peening so critical in aerospace applications?

Aerospace components endure extreme cyclic loading. Shot peening ensures these parts resist cracking, operate longer, and meet strict safety standards. Robotic peening adds traceability and precision required for certification.