Laser peening is a metalworking process in which pulses from a laser are directed onto the surface of a metal object to improve its mechanical properties. It is similar to shot peening, which uses very small metal or ceramic balls to bombard the surface of a metal object. The corrosion resistance, fatigue strength, residual stresses, and wear resistance of a metal item can all generally be improved by laser peening.
Prior to treatment, a component is prepared for laser peening by the application of two overlays. First, an overlay that is opaque to the laser is applied, and then one that is transparent to the laser is applied. The laser is directed through the transparent overlay but cannot pass through the opaque overlay.
At this point, the energy from the laser vaporizes a layer of this overlay. The vapor remains trapped between the transparent overlay and the surface of the component. As this vapor absorbs more energy from the laser, it heats up and expands rapidly in the small space where it is trapped. Pressure rises rapidly in this area and causes a shock wave to propagate into the component. The shock wave rather than the heat of the vapor causes changes to the material’s properties, so the process of laser peening is mechanical rather than thermal.
This process is similar to shot peening, which uses small ceramic or metal balls, known as shot, to create numerous overlapping indentations on the surface of a metal component. Such indentations form a surface layer that is highly resistant to mechanical failure modes such as cracking, corrosion, and fatigue. Laser peening has similar results but replaces the repetitive impacts to the metal of the shot with pulses of light from a high-energy laser.
Many metals and alloys can be worked by laser peening. These include such materials as steels and cast iron, aluminum and titanium alloys, and more. The improved mechanical properties of such materials makes laser peening a desirable technique for application in the manufacture of high cost parts or where fatigue resistance is critical.
Applications that may utilize laser peened parts include fatigue-critical components in automotive or aircraft construction. Components that are difficult to transport and maintain such as large wind turbine blades may also be improved with this process to maximize service life. Hip implants, which are best replaced as infrequently as possible due to the risks of surgery, may be subjected to this process to extend service life.
Components that are laser peened may also be made thinner and lighter due to their improved mechanical characteristics. This saves on material costs in the manufacturing process. It can also save costs due to lower energy requirements when operating vehicles or other machinery.