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Justin Sand - 1/28/2015

Shot is fired from a blasting gun at a ceramic leaf spring to adjust its structure. Image: Fraunhofer IWM, Felicitas Gemetz

Shot peening is a cold work process used to alter the surface layer of a metal, while at the same time modifying the mechanical properties of the material. The process involves, repeatedly blasting the part with particles creating a residual stress layer which strengthens the material, increases fatigue life, and resists corrosion.

The particles used to blast the metal may consist of steel, ceramics, or glass.

Purpose of shot peening

Shot peening allows manufactures in any industry to create lighter parts without sacrificing strength. The main goal of shot peening is to reduce the risk of microcracks forming on the surface of the part.

When the material is repeatedly impacted with "shot" small indents or dimples are formed across the entire surface of the material. These small indents form a compressive stress layer, on the surface, that will change the properties of the material. This layer of compressive stress along the surface will greatly reduce the risk of microcracks forming and therefore increase strength and improve lifespan. It is, also, the most economical and effective way of doing this.

While this process has a vast array of benefits, some of the most common benefits include:

• Increased strength
• Longer fatigue life
• Corrosion resistance
• Increased aerodynamics
• Surface finishing
• Cosmetic effect

Applications

Parts

In the Blancpain Calibre 69F9 watch, the bridges are shot peened and then plated with pink gold to bring out the texture. © BLANCPAIN

Shot peening has a multitude of uses in the automotive field where manufactures strive to create strong and lightweight parts. It is used on gear parts, transmission disk springs, camshafts, hose clamps, stabilizer bars, and leaf and suspension springs. It can also be used for surface finishing or deburing of engine blocks and cylinder heads.

A large number of Apple stores are covered in stainless steel that has been shot with glass beads to obtain the satin finish.

There are also many uses in the aerospace industry where strength, weight, and aerodynamics are huge factors. The process is used on helicopter blades, wing flaps, and access panels. It can also be used to form or distort aerospace parts to a desired shape or structure. Examples of this include skins, sections of the fuselage, ribs, and spars.

Other companies have utilized shot peening to create a cosmetic effect for a piece. One example of this is a watchmaker who uses moderate shot peening to add texture to certain parts of their watches. They often paint or otherwise finish the surface after shot peening, which creates an interesting and unusual effect. Other companies cover their building in metals that have undergone the process, leaving them with an elegant, soft, and glare-free look.

Companies

There is great variance in the types of companies that utilize this process and the materials that they produce. Almost all auto-part manufactures such as Toyota, Honda, Nissan, Acura, Ford, and Fisker utilize this for more than one car part. Aerospace employers, such as the U.S. Military, use this process on their helicopters. Other companies such as Blancpain (watchmaker) and Apple have used this to change the appearance of their products or their state of the art buildings.

Shot peen machine

The shot peen machine, in a moderate volume manufacturing facility, consists of a cabinet and a cyclonic reclaimer. Parts are brought inside the cabinet on a conveyor system. The cabinet doors close and the blasting begins. When the shot particles hit the parts, they rebound and fall onto the floor of the cabinet. The floor contains a funnel system that will return the shot to the cyclonic reclaimer. Dust particles or pieces of shot that have become too small will be sorted by the machine and sent to a connected trash bin. The rest of the shot is then recycled and again blasted at the parts in a continuous cycle.

Development

Shot peening started in the 1920's and 1930's in Germany and the United States. In the early stages, it was used for leaf and suspension springs as well as valve spring covers. In the 1920's and 1930's it involved beating the part by hand with a small hammer, instead of blasting with particles.

As time progressed, new machinery made the process more efficient and more types parts began to undergo this process.

Today, it is widely used across the United States, Germany, and at other manufacturing plants across the world.

See also

• Steel Belt: Shot Peening
• Cut Wire Shot

Further reading

• "SHOT PEENING." (n.d.): n. pag. Web. 25 Jan. 2016. "SHOT PEENING"

External links

• Shot Peening Benefits and History