Shot Peen Forming

Shot Peen Forming uses the compressive stresses induced by controlled shot peening to alter the stress pattern, magnitude and depth to deliberately create a change in the component shape. Gentle curves within the elastic range of the material are regularly formed to consistent tolerances.

Varying curvature requirements, material thickness, cut outs, reinforcements and pre-existing distortion can all be processed with Shot Peen Forming.

Parts formed by peen forming exhibit increased resistance to flexural bending fatigue and where peen formed pieces are processed on one side only, the result causes both sides to have compressive stress. These compressive stresses serve to inhibit stress corrosion cracking and to improve fatigue resistance.

Process

Curtiss-wright’s shot peen forming service is a dieless process performed at room temperature, whereby small round steel shot impact the surface of the work piece. Every piece of shot acts as a tiny peening hammer, producing elastic stretching of the upper surface and local plastic deformation that manifests itself as a residual compressive stress. The combination of elastic stretching and compressive stress generation causes the material to develop a compound, convex curvature on the peened side.

Laser peening is an alternative technique for the introduction of residual compressive stresses. It has the advantage over conventional shot peening in that it induces these stresses to greater depths, consequently a tighter radius of curvature can be achieved or performed on thicker materials.

Applications & benefits for Shot peen forming

The shot peen forming process is ideal for forming large panel shapes where the bend radii are reasonably large and without abrupt changes in contour. Shot peen forming is best suited for forming curvatures where radii are within the metal’s elastic range. Although no dies are required for shot peen forming, for severe forming applications, stress peen fixtures are sometimes used. Shot peen forming is effective on all metals, even honeycomb skins and ISO grid panels.

Shot peen forming is often more effective in developing curvatures than rolling, stretching or twisting of metal. Saddle-back shapes also are achievable. Because it is a dieless process, shot peen forming reduces material allowance from trimming and eliminates costly development and manufacturing time to fabricate hard dies. The shot peen forming process also is flexible to design changes, which may occur after initial design. Curtiss-Wright can make curvature changes by adjusting the shot peen forming process.

Shot peening of parts that have been cold formed by other processes overcomes the harmful surface tensile stresses set up by these other forming processes.

Correction of distortion

A very successful method of correcting distortion caused during manufacturing for example through casting, rolling, forging and heat treatment, is using controlled shot peening to stretch the material on the concave side of the distorted component to bring the component back to pre-manufacture specification.

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