Laser Shock Peening in Tooling and Manufacturing
Cold pilgering is a metal rolling process using heavy, round dies to produce seamless pipes and tubes. Prefabricated metal tubing is fed through rotating steel dies to reduce the diamter and wall thickness, producing uniform extrusions for various applications. Laser peening has been shown to significantly extend the service lifetime of steel dies when applied to the die grooves.
The cyclic process of rolling a set of pilger dies to produce tubing eventually causes die failure, typically in the grooved region. The dies are subject to repeated loading at pressures up to 1500 megapascals, leading to fatigue, stress cracking, and/or corrosion fatigue in the die groove. The grooves develop cracks or imperfections that transer into the extruded tubing, ultimately forcing the dies to be removed from service.
These expected failure modes can be mitigated, and die life can be extended, by introducing a surface compressive residual stress in the die groove. However, shot peening and other fatigue enhancement methods are often ineffective due to the shallow compressive residual stresses they generate and the difficulty of applying treatment to the complex die geometry.
Laser peening was applied to specified locations on the die rolling surface to generate deep, compressive residual stresses. These enhancements slowed the onset of expected failure mechanisms, and the laser peened dies produced 300% more tubing than the average standard production die set - the longest die life ever measured for these production conditions.
X-ray diffraction analysis showed that laser peened dies retained compressive stresses up to 1.5 millimeters deep, compared to 0.1 millimeter depth for dies that had only been shot peened.
Another benefit demonstrated by laser peening was that the dies could be ground, polished, or "benched" after application of the LSP process. Laser peening produces such deep compressive residual stresses that a layer of surface material can be removed during post-process finishing without reducing the process benefits.
LSPT was named co-recipient of the Federal Laboratory Consortium's Award for Excellence in Technology Transfer for our work enhancing the fatigue life of cold pilger dies. Click here to read a full report of the study.Enhance Your Metal Components