Shot peening is an important and, for safety reasons, essential process in many industrial sectors, primarily in the aerospace and automotive industries.
Peening technique dates back to Bronze Age armorers; although in more recent years, this technique has been used by engineers who worked the surface of a component with a « ball peen hammer » in order to induce internal compressive stress and thus increase service life.
Technological requirements in all industrial sectors, especially the aeronautic and aircraft industries, are becoming more and more extensive, particularly with regards to shot peening.
Check out IST’s Shot Peening System Guide which discusses major components used in shot peeners designed to meet the most stringent of technical requirements found in the Aerospace Industry.
What is Shot Peening?
Shot peening is a cold work process which consists of producing a compressive residual stress layer and modifying the mechanical properties of metals. In order to achieve this, it implies impacting a metallic surface with small spherical abrasive media (round metallic, glass, or ceramic particles) with force sufficient enough to create deformation.
Shot peening machines are not widely different than conventional abrasive blasting machines. The Peening process can occur in sandblast cabinets, abrasive blast rooms, and other traditional sandblast equipment.
Shot peening is a technique used in a broad range of manufacturing processes and applications. For instance, cast iron pans gain their enhanced mechanical and heat transfer properties from shot peening process.
In industries like aircraft, automotive, and railway manufacturing, shot peening is an inescapable process when it comes to forming components with enhanced mechanical strengths while yet using minimal amounts of material to reduce overall weight.
After all, we all know that the fuel or other energy source consumption of a vehicle is strongly correlated with its weight. The idea is similar to using steel rods as reinforcements for concrete in the construction industry – it allows the use of less material to achieve a given mechanical strength.
As mentioned previously, shot peening also enhances the mechanical strength of components and reduces the risk of failure when they are subjected to extreme conditions. For these reasons, drive components (i.e. gears) are often subjected to the shot peening process in order to induce compressive stress, which considerably increases their resistance to fatigue and reduces the risk of cracks during operating life while these components are subjected to multiple tensile and compression stresses.
Standards and Requirements
SAE International (formerly known as the Society of Automotive Engineers) Standards is a US-based association that covers the engineering requirements for shot peening processes and techniques by the impingement of metallic shot, glass beads, or ceramic shot.
Standards prefixed by AMS (Aerospace Material Specification) refer to standards used in the aerospace industry. J relates to general standards which concern abrasive media or quality control methods of treated parts or process parameters used in a variety of general applications (including ground vehicles), while MIL (Military) relates to military equipment and weapons. In some cases, J-prefixed standards can also be used in the aerospace and military industries.
The typical peening processed standard used in a variety of applications covers the engineering requirements for peening surfaces of parts by the impingement of metallic shot, glass beads, or ceramic shot:
- SAE J2441 (Shot Peening)
Shot peening processes could be automated to ensure consistent results:
- AMS 1- 2430 (Shot Peening, Automatic) – requires minimally a PLC controlled process.
- AMS 2432 (Shot Peening, Computer Monitored) – implies a computer controlled and monitored process which allows for better data remote access, sharing and analysis, as well as the implementation of a predefined process parameters upload.
The abrasive media type and size used in the process is also defined in aerospace standards:
- AMS 2431 (Shot Media General Requirements)
- AMS 2431/1 (Cast Steel Shot, Regular Hardness)
- AMS 2431/2 (Cast Steel Shot, High Hardness)
- AMS 2431/3 (Conditioned Carbon Steel Cut Wire Shot, Regular Hardness)
- AMS 2431/4 (Conditioned Stainless Steel Cut Wire Shot)
- AMS 2431/5 (APB Case Hardened Steel Peening Balls)
- AMS 2431/6 (APB Glass Shot)
- AMS 2431/7 (AZB Ceramic Shot)
- AMS 2431/8 (Conditioned Carbon Steel Cut Wire Shot, High Hardness)
The military standards define media and techniques for military vehicles and weapons:
- MIL PRF-9954 (Glass Beads Cleaning Peening)
- MIL PRF-9954B (Glass Beads Cleaning Peening)
- MIL-P-81985 (Peening of Metal)
- MIL-S-13165 A, B, C (Peening Metal Parts)
- MIL-STD-852 (Glass Beads Peening Procedures)
These general standards apply to numerous peening applications, including aerospace and military:
- SAE J2277 (Shot Peening Coverage Determination)
- SAE J2597 (Computer Controlled Shot Peening Saturation Curves)
- SAE J441 (Cut Wire Shot)
- SAE J442 (Test Strip, Holder, and Gage for Shot Peening)
- SAE J443 (Procedures for using Standard Shot Peening Almen Strip)
- SAE J444 (Cast Shot and Grit Size Specifications for Peening and Cleaning)
All shot peening machines manufactured by IST are custom-designed to meet specific standards used in the manufacturing, military, and aerospace industries.
Abrasive Media Used in Shot Peening
By definition, shot peening uses spherical-shaped abrasive media to produce the peening action – called shot. The shot material and size depend on the material composition of the workpiece and the desired result. The most common media used for shot peening are:
- Ceramic Beads
- Glass Beads
- Steel Shot
- Stainless Steel Shot
- Cut Wire Shot
Refer to the IST Media Selection Guide in order to choose the right media for your application.