Precision Forming and Enhancement

Laser peen forming is a powerful, laser-based method of shaping metal parts to specific geometric configurations. The process harnesses the power of controlled plastic strain to form and shape components, while also imparting deep compressive residual stresses that increase damage tolerance and improve service life. Laser peen forming maximizes the material benefits of LSP, while attuning the inherent relationship between stress and strain within the metal to create complex, stable shapes.

Complex Curvatures

Model and sample of laser peen formed dual curvature

Finite element model of specimen with dual compound curvatures (top image), and physical specimen processed in accordance with model plan (bottom image).

Laser peen forming is possible thanks to the predictable distributions of plastic strain imparted by the laser peen process. Because these distributions are readily responsive to today’s analytical modeling tools, we can use Finite Element Analysis (FEA) to simulate the imparted plastic strain along with the elastic response of the surrounding material. This allows accurate, scalable predictions that translate into a vast array of unique curvatures and shapes.

Materials processed with laser peen forming include aluminum alloys of varying thicknesses (0.1 inch to 0.5 inch) and heat-treated tempers. LSPT’s modeling capability guides the laser peen forming process to achieve specific part geometries within each variation of material. Validation of the modeling efforts have been completed via physical measurement of post-processed samples, and exhibit physical results that nominally agree with modeling predictions within a 5% accuracy.

Model and sample of laser peen formed compound curvature

Finite element model of specimen with compound curvature (top image), and physical specimen processed in accordance with model plan (bottom image).

Laser Peen Straightening

Another benefit of laser peen forming lies in the selective application of this method to distorted components. The laser peening process can reshape and return non-conforming components to acceptable geometric tolerance bands, without bulk plastic deformation that may otherwise damage the structure. Due to the precision modeling and application capabilities of laser peen forming, it has been used to mitigate distortions in engine crankshafts with eccentric lobes.

Life Improvement and Distortion Correction – Engine Crankshaft

Low performance of bearing journals causes a crankshaft to experience service life limitations. The manufacturing process leads to bowing of the crankshaft, resulting in an unacceptable concentricity runout. LSPT implemented a plan to laser peen the journals to improve fatigue resistance, while also inducing corrective shaping to the crankshaft to meet concentricity requirements. Through FEA analysis, the ideal treatment of the shaft was selected for fatigue improvement and to prevent distortion in the primary shaft. Processing of the shafts and subsequent dimensional analysis confirmed the success of the operation.

  • Shaft runout predicted without corrective laser peening: 0.052 mm
  • Average measured runout without corrective laser peening: 0.05 mm
  • Shaft runout predicted with corrective laser peening: 0.004 mm
  • Average measured runout with corrective laser peening: < 0.010 mm (max spec.)
Finite element models of unbalanced crankshaft deformation

Cross-sectional view of engine crankshaft exhibiting unbalanced residual stresses due to eccentricity (top image), and deformation predicted due to unbalanced residual stresses (bottom image).

 

Finite element models of crankshaft corrected with laser peen forming

Optimization of shaping treatment to correct unbalanced residual stresses identified by red areas at the eccentric lobe fillet (top image). Cross section of crankshaft with predicted deformation when corrective laser peening applied (bottom image).

Laser peen straightening is a service life extension treatment that mitigates component distortion while improving fatigue strength of the part.  LSP Technologies’ successful modeling and application of controlled plastic strain improves both geometric tolerances and residual stress profiles for enhanced reliability and performance.

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