Shot Peening vs. Laser Peening

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Laser shock peening emerged as a necessary application for parts requiring greater fatigue enhancement than shot peening and other technologies could provide.

What is Shot Peening?

Shot peening is a cold work, surface modification process aimed to improve the fatigue life of metal components through inducing compressive residual stresses. It is used when components experience metal failure due to high-cycle operating conditions.

Shot peening is commonly seen in the aerospace, automotive, heavy machinery, and power generation industries.

What is the Process of Shot Peening?

The process of shot peening involves accelerating a steel shot or other hard media (metal, ceramics, glass) toward a component’s metal surface at high velocities. The impact of the media with the metal surface causes a plastic deformation which changes the mechanical properties of the surface. The mechanical change of the metal surface produces compressive residual stresses and crack initiation is prevented or slowed down.

Does Shot Peening Improve Fatigue Life?

When the shot hits the surface of a metal part, an indentation is created which generates the beneficial compressive residual stress. Once the residual stress is induced, the surface is more resistant to cracking and failure because tensile stresses are removed.

Fatigue improvement is often determined by parameters like density, material, size, hardness, geometry, distance, and angles. Shot peening fatigue improvement is best implemented in metal parts that require compressive residual stresses at shallow depths.

SO WHY LASER PEENING OVER SHOT PEENING?

Advantages of Laser Peening

Why would you consider using laser peening? Because it’s being used today to improve the safety and reliability for components in industries that are counted on for commercial, residential, and government use.

Laser peening provides a trusted solution unmatched by common technology. Laser peening has impoved the fatigue strength in a wide-range of metals including titanium alloys, stainless steel, aluminum alloys, and nickel alloys. The short laser pulse provides precision, depth, and power to areas of components that experience high fatigue.

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Laser peening has been shown to provide over 10x life increases for components that had previously only been shot peened. This type of service life extension is unparalleled among surface enhancements, and has the power to revolutionize many industry practices. Not only will laser peened parts last longer, but they can be manufactured with less material to reduce costs and improve efficiency.

Beyond enhanced fatigue resistance and service life, laser peening has proven superior to shot peening across a number of performance-related applications:

Retains compressive residual stresses to higher temperatures
Reducing crack growth rates (da/dN)
Improving life of welded components
Improved fretting damage resistance
Improved galling resistance
Improved spallation resistance
Improved stress corrosion (SCC) resistance

Laser peening consistently outperforms shot peening when it comes to the material enhancement properties associated with compressive residual stresses.

Other Surface Enhancement Technologies

Shot peening is one of the original surface modification technologies developed for improving fatigue life via induced compressive stress. The process of shot peening involves accelerating a hard media (metal, ceramics, etc.) toward a part surface at high velocities. Impacts of the media with the part surface induce plastic deformation and resulting compressive residual stresses. Shot peening continues to be a popular surface modification technology; however, the depths and magnitudes of residual stress benefits obtained with shot peening are greatly exceeded by laser peening.
Deep rolling is a surface burnishing process that creates a high degree of cold work. Resulting residual stresses are frequently deeper than shot peening. Like other burnishing processes, deep rolling requires sufficient access to an area and is limited on geometric areas that can be processed. The high degree of cold work also limits the process for elevated temperature applications. Limitations of the burnishing process make laser peening a better option for many applications.
The low plasticity burnishing (LPB) process is similar to other burnishing processes in which a metal object in contact with the surface of a part is forcefully passed over the desired area. The end result is usually a surface compressive stress and finer surface finish than when the process was initiated. In LPB, the ball is maintained in a spherical socket with fluid supplied to the top of the ball. Fluid pumped to the socket applies the force and helps prevent the ball from contacting the socket directly. A fluid film allows the ball to roll across the surface of a part and helps to reduce the risk of the ball seizing in the socket.
Ultrasonic peening is a surface enhancement process that uses electro-mechanical methods to generate stress waves in a material. Stress waves are induced into the material by vibrating steel pins attached to a calibrated frequency controller. Most ultrasonic peening tools are handheld apparatuses and the technology has been heavily used in the welding industry.

Advantages of the process include the ability to be highly transportable, leading to the ability to reach austere environments.

Disadvantages include a need for physical contact with a surface, limiting the process to open geometries and generally flat surfaces. The use of handheld tools also poses difficulties with repeatability and consistency. Ultrasonic treatments roughen the surface finish considerably. In comparison to laser peening, ultrasonic peening has been unable to reach similar compressive stress depths.
Water jet peening and cavitation peening are terms used to refer to generally the same process. This type of peening uses a jet of high pressure water to impinge the part surface. Upon contact with the surface, the water droplets cavitate and induce stress into the part surface. The advantage of water jet peening over shot peening is due to the limited effect upon surface finish. The water jet peening system also requires only water as a media and has some environmental benefits. Disadvantages of water jet peening include the potential for erosion and cavitation damage, material loss and limited residual stress profiles.

The Laser Peening Difference

See real-world examples of how laser peening outperforms other surface enhancement technologies, like shot peening.

Where Does Laser Peening Fit in the Metal Finishing Process?

David Lahrman is a certified trainer for Metal Finishing News International (MFN). David provides insights and instruction on metal finishing for this worldwide network, and he wrote a feature article for the July 2017 issue of MFN Magazine.

Fatigue Enhancement with Power and Control

Laser peening is a very controlled and precise surface enhancement treatment. LSPT can customize the process for specific parts or materials by manipulating parameters like power density and spot coverage.

Shot Peening Falls Short of Laser Peening in Residual Stress Comparison

Laser peening imparts significantly deeper compressive residual stresses than shot peening

Metal Fatigue Improvement with Stress Waves

The stress wave generated during laser peening is the mechanism which imparts residual strength and fatigue resistance into a metal part.

Laser Peening is the Superior Solution

When other technologies aren’t cutting it, it’s time time to consider the leading technology for metal surface enhancement. Laser peening has a proven reliability when it comes to providing fatigue cracking resistance. Our technology is being called upon across a variety of industries due to the unmatched compressive residual stress profiles.

The potential cost savings and benefits of increasing component lifetimes extend far beyond the value of the part itself.

Let’s talk about implementing laser peening into your process.