3M™ Roto Peen Mandrel 7211, 1 ea/Case

The 3M Roto Peen Mandrel is a specialized tool designed to provide efficient repair and maintenance to various components of U.S. Army helicopters, such as rotors and rotor hubs. This tool, along with its associated flap assembly, allows for peening action using a die grinder or disc sander. In the early 1970s, the 3M Roto Peen Flap Assembly, also known as TC 330, was qualified and included in military specifications. Its effectiveness soon led to its adoption in other aerospace applications.

Today, the mandrel, when used in conjunction with the flap assembly, is primarily utilized in aerospace applications. It enables the use of a die grinder or disc sander to perform captive shot peening, which is a process used to repair metal surfaces. The assembly consists of tungsten carbide shot bonded to a flexible polymeric flap, which is gripped by the mandrels attached to the power tool. As the flap spins, the captive shot hammers the metal surface with each revolution, effectively strengthening it.

The 3M flap/mandrel assemblies offer portability and are particularly effective for precision in-service rework, manufacturing, and repair of small areas. They can also be used for peening holes with diameters as small as 1/2 inch (12.7mm). Additionally, the flaps can be cut with scissors to peen confined areas or areas with a radius as small as 1/16 inch (1.6mm).

Captive shot peening is employed when repair or limited access work is required, or when the use of free shot is not feasible. By using captive flaps, the shot used for peening metal surfaces can be controlled more effectively, allowing for greater access to areas that require strengthening.

Peening is a process that has evolved from the days of blacksmiths hammering swords. It involves applying compressive surface stress to metals, which enhances their resistance to fatigue fracture and stress corrosion cracking. The aerospace industry has strict peening specifications, and adherence to these specifications often needs to be documented. Failure to meet these specifications can result in part failure.

3M also provides Almen gauges, which are used to measure peening intensities by providing precise readings of strip deflections. The Almen Scale of Peen Intensity, adopted by the Society of Automotive Engineers (SAE), measures the curvature of a standardized steel strip when peened on one side.