Technical Bulletin on Laser Peening

Originally published in Technical Bulletin No. 1, 2002

Authored by Dr. Allan H. Clauer

INTRODUCTION
What Does It Do?
Laser Shock Processing (LSP) produces a number of beneficial effects in metals and alloys. Foremost among these is increasing the resistance of materials to surface-related failures, such as fatigue, fretting fatigue and stress corrosion cracking. It does this by driving compressive residual stresses deep into metals and alloys. Much deeper than shot peening. For these applications the process is referred to as laser shock peening.
There are a number of other reasons to use LSP besides increasing fatigue strength and fatigue life; it can be used to strengthen thin sections, work-harden surfaces, shape or straighten parts, break up hard materials, possibly to consolidate or compact powdered metals, and still others remaining to be discovered.

Applying LSP
LSP can often be applied to the finished surface of a part, or just prior to the final finishing step. In machine components, tooling and other parts, application to external surfaces and internal surfaces with line-of-sight access is straightforward. Application to internal surfaces without line-of-sight access is quite possible, but the method used is application specific and requires some development for each application.
LSP works by exerting a mechanical force on the part surface; the surface is not affected thermally. However, process options can be selected which have a limited thermal effect and offer potential cost benefits. The effects of the mechanical force on the surface itself are minimal. In softer alloys, a very shallow surface depression occurs, which decreases in depth in harder materials. For example, in aluminum alloys, the depression is about 250 inches (6 m) deep, but on machined surfaces of harder alloys, it is difficult to see where the surface was laser shocked. The depth of the depression does increase with increasing intensity of shock peening.

With LSP, treating just the fatigue critical area(s) on a part without masking the area around it is easily accomplished. This enables localized treatment around holes, and in and along notches, keyways, fillets, splines, welds, and other highly stressed regions.
The intensity of LSP can be easily controlled and monitored, allowing the process to be tailored to the specific service and manufacturing requirements demanded by the part. The flexible nature of the process accommodates a wide range of part geometries and sizes. It can also be used in combination with other treatments, e.g., shot peening or coatings, to achieve the most beneficial property and cost advantages for each part.
LSP can also be used in manufacturing processes requiring a high, controllable, mechanical impact over a defined area, where mechanical punches are limited in how they can be adapted to the task. The impact area could have a variety of shapes.
The first production application of laser shock peening began in 1997 on a military gas turbine engine blade. More production applications will begin in 1998.

Benefits
The use of LSP to obtain increased strength and resistance to failure offers several advantages. After applying LSP to failure-prone areas on troublesome parts, the service life of the parts and the maintenance intervals of machinery can be increased and downtime decreased, without changing the design. Alternatively, a part or machine can be redesigned to make them lighter, easier to manufacture, or less expensive, using LSP to upgrade the properties to meet the original design performance requirements.
It is a new manufacturing tool that could offer more control, flexibility or unique effects for upgrading current products or developing new ones than other methods.
LSP Technologies, Inc. provides commercial laser shock processing services and equipment. We are the only company providing LaserPeenTM laser peening services to industry, and building LaserPeenTM equipment specifically for laser shock processing applications. In 2000 we will be introducing our new RapidPeenTM process and associated RapidPeenTM equipment for increased throughput and lower cost. In 2001 we will introduce a factory-floor ready laser shock peening system.
LSP Technologies’ key management and staff have many years of experience in the development and use of laser-generated shock waves for a wide variety of applications. Our staff’s experience dates back to the early 1970’s, when we began developing the technology at Battelle Memorial Institute in Columbus, Ohio.
The company is located in Dublin, Ohio, a suburb of Columbus, in new facilities for production processing of parts and development of new applications. The facility has two laser shock peening systems that provide flexibility for processing a wide variety of parts.

Learn More: Laser Shock Processing