In recent years, in parallel with the widespread adoption of advanced aluminium alloys and high-strength steels, additive manufacturing (AM) technologies have emerged as a transformative approach within the automotive industry. Initially introduced primarily for rapid prototyping and tooling applications, additive manufacturing is now progressively being adopted for the production of functional components, including structural and semi-structural parts. The key advantage of AM lies in its exceptional design freedom, which enables the realization of highly optimized geometries, topology-optimized structures, internal channels, and lightweight lattice architectures that cannot be manufactured using conventional subtractive or formative processes. These capabilities align closely with the automotive industry’s ongoing pursuit of weight reduction, improved fuel efficiency, and enhanced overall vehicle performance.

From a materials and structural standpoint, additive manufacturing allows engineers to place material only where it is strictly necessary, thereby maximizing stiffness-to-weight and strength-to-weight ratios. This is particularly relevant for electric and hybrid vehicles, where mass reduction directly translates into extended driving range and improved energy efficiency. Nevertheless, despite these advantages, the widespread use of additively manufactured components in load-bearing automotive applications remains limited by several material- and process-related challenges.

One of the most critical issues associated with additive manufacturing is the surface integrity and residual stress state of AM parts. The layer-by-layer fabrication process, characterized by rapid melting and solidification cycles and steep thermal gradients, often results in tensile residual stresses, anisotropic microstructures, and relatively high surface roughness. Additionally, process-induced defects such as lack-of-fusion porosity, unmelted particles, and micro-cracks can act as stress concentrators, significantly compromising fatigue performance. These issues are particularly detrimental in components subjected to cyclic loading, which is a typical operating condition for many automotive structural elements.

Furthermore, additive manufacturing is increasingly being combined with traditional manufacturing techniques in hybrid production routes, where AM components are welded or mechanically joined to conventionally manufactured parts. While such approaches offer enhanced design flexibility and cost efficiency, they also introduce additional critical zones, as welded joints in AM materials may inherit both the intrinsic defects of the additive process and the residual stresses induced by welding. As a result, fatigue resistance and long-term durability become key concerns that must be addressed through appropriate post-processing strategies.

In this context, shot peening represents a particularly attractive post-treatment for additively manufactured components, both for standalone AM parts and for hybrid welded AM structures. The primary mechanisms of shot peening, namely the introduction of compressive residual stresses in the near-surface region and the induction of localized plastic deformation leading to surface work hardening, directly counteract the tensile residual stresses and surface-related defects typical of additive manufacturing. By reducing the effective driving force for crack initiation and early crack propagation, shot peening can substantially enhance the fatigue strength and service life of AM components.

In addition, shot peening can play a complementary role when combined with other post-processing techniques such as machining, polishing, or laser remelting. When surface irregularities and geometrical imperfections are first reduced through these processes, shot peening can further improve mechanical performance by acting on a more homogeneous and defect-controlled surface. This synergistic approach is particularly relevant for high-performance automotive components, where reliability and repeatability are essential.

However, as already observed for welded components made from high-strength steels and aluminium alloys, the application of shot peening to additively manufactured parts cannot rely on standard or generalized process parameters. The effectiveness of the treatment is strongly influenced by several AM-specific factors, including the material system, build orientation, layer thickness, internal porosity distribution, surface condition, and component geometry. Peening parameters developed for conventionally manufactured materials may lead to insufficient stress profiles or, conversely, to surface damage if directly applied to AM parts.

For this reason, comprehensive investigations are required to optimize shot peening treatments specifically for additively manufactured components. These investigations should include both theoretical modeling—aimed at understanding the interaction between AM-induced microstructures and peening-induced stress fields—and experimental validation, focusing on fatigue life, crack initiation behavior, and long-term durability. Such studies are essential for establishing reliable correlations between additive manufacturing parameters, shot peening conditions, and final mechanical performance.

Ultimately, the integration of shot peening into the post-processing chain of additively manufactured and hybrid welded–AM automotive components would support the development of robust design guidelines and standardized procedures. This would not only increase confidence in the structural integrity of AM parts but also accelerate their broader adoption in the automotive sector and in other industries where lightweight, high-performance materials are increasingly required.

Shot Peening in the Automotive Industry

by Mario Guagliano

Contributing Editor MFN and 

Full Professor of Technical University of Milan

20156 Milan, Italy

E-mail: mario@mfn.li