Shot peening consists of bombarding a metal surface with thousands of small spherical steel media. As the media, or “shot,” hit the metal, they act as tiny compacting agents. This energy transfer creates a subsurface compression layer that significantly reduces failures such as fatigue cracks and defects related to stress corrosion.
This strengthening process carries through various applications in the automotive and aviation industries and has been refined at Sonaca Wichita. Sonaca offers two methods of shot peening for optimum quality, including Saturation Peening to strengthen wing skins and other aviation parts, and Peen Forming to provide various contours, from the most basic structures to the more complex integrated stringer panels.
Sonaca Wichita also uses the shot peening process to form metals into exacting configurations. This single-piece construction process eliminates the need for dies and presses, reduces costly joints, and extends intervals between inspections.
Shot peening consists of bombarding a metal surface with thousands of small metal pellets. As the pellets, or “shot,” hit the metal they act as tiny peening hammers. The peening process is especially suited to aviation manufacturing because it works to eliminate tension loads that fatigue metals. As a result, the fatigue life of the part is greatly increased by several thousand per cent.
The initial Saturation Peening process is specifically designed to relieve internal stresses and reduce crack propagation. A second saturation is sometimes needed after forming operations for cosmetic purposes, as well as to ensure an even, compressive layer in the material. The changes in the surface properties caused by the impact of the shot relieve stress and increase the fatigue life of the metal significantly.
Peening also makes the material highly resistant to impact and stress corrosion while improving surface roughness and cosmetic appearance.
Sonaca Wichita’s saturation machine is one of the largest in the world and can accommodate parts up to 10 feet wide and 65 feet long.
The peen forming process was developed to apply contours into complex configurations such as prestressed arcs and dihedral breaks. At Sonaca Wichita, this forming process can even be performed on complicated wing skins that contain integrated stringers.
There are two main advantages to peen forming: proficiency and cost. Peen forming provides an efficient alternative for creating complex aerodynamic curvatures in large metal surfaces without the use of costly dies, cuts, or multi-part compositions. Techniques have been developed by Sonaca that involve the stretching or “growing” of one side of the panel in order to induce a curvature. This may be accomplished in conjunction with the saturation process by peening the outer side at a higher intensity than the inner side, thereby forcing a permanent bowing effect.
Additionally, the peen forming process generally has lower manufacturing costs because there is no need for dies and presses or subsequent thermal processes. Forming integrated stringer wing skins not only provides a weight savings, but also greatly reduces costly joints and assembly time. Curves and contours that would be cost prohibitive through machining processes are quickly, easily and efficiently achieved by peen forming. Once the process parameters have been determined, it is easily reproducible for larger quantities.
