Introduction to Laser Shock Peening (LSP) Process
Since the early middle ages, mankind has always struggled to increase the hardness and flexibility of metals, thereby improving the durability and reliability of metal tools and parts. From the Damascus steel smiths to the swordsmiths of medieval Japan, the method of cold-working metal by the application of precise mechanical pressure, such as hammer blows, has a glorious history. In modern times, this concept reached its apex with industrial surface hardening using shot peening. In the peening process, thousands of small lead shot pellets are fired at a metal surface, compressing and hardening the surface, to improve its durability. With the advent of high power laser systems, an improved peening process developed, called laser shock peening.
Laser Peening (LP) or Laser Shock Peening (LSP) is a process in the field of surface engineering. A pulsed high-power laser beam generates residual stresses in materials to improve their properties related to failure resistance (such as fatigue and stress corrosion cracking), strengthening thin sections, and hardening the material surface.
Unlike most material processing applications that utilize the laser’s thermal power to achieve the desired results, LSP is a mechanical process that utilizes the momentum of the laser beam. The high-power laser beam strikes the surface of the target workpiece at high rate, short pulses.
The beam strikes the metal workpiece surface and immediately vaporizes a thin layer to the plasma state, which applies shock wave pressure on the target workpiece. Sometimes, an additional thin layer of an opaque overlay material is placed on the workpiece, so the opaque material will be vaporized instead of the metal. To increase the pressure, another transparent overlay or inertial tampering layer (typically water) is used to capture the plasma.
The plasma creates a shock-wave effect, reshaping the workpiece surface microstructure at the strike point. This in turn creates a chain reaction of expanding and compressing metal, which results in deep compressive stresses that extend the life of components.
LSP has been used in many industrial applications since the 1990s including: aeronautics, automotive, power generation, drilling and more. Developments in the field have decreased process costs and increased throughput.
Developments in recent years in automation and in the laser industry have helped to reduce labor costs and energy costs. The sharp decrease in cost per watt and the increase in energy availability now enable shaping the laser beam using beam shaping optics to increase the throughput and further optimize the process.
Laser beam shaping in LSP
There are several different laser beam shaping applications available to optimize the LSP process:
- A Broadband Diffuser (BD) is a special, high efficiency, micro-refractive flat top laser beam shaper that generates controlled output shapes, resembling a microlens array.
- A Diffractive Diffuser (HM) is a Diffractive Optical Element (DOE) designed to generate any freeform output shape with uniform, homogenic, and flat top profile from a multimode input beam.
- A Diffractive Top Hat (TH) is a DOE designed to generate controlled output shape with flat top energy distribution and very sharp transfer region.
- A Diffractive Beam Splitter (also known as Multispot) generates any number of output beams with identical characteristics to the input beam at a controlled arrangement and separations. Such an element can generate an array of >10,000 spots and cover large areas with good uniformity.
Holo/Or offers customized laser beam shaping solutions that can encompass more than one optical function on the same flat element.
For more information about this or other Holo/Or products, contact Holo/Or.