peen forming - Metal Improvement Company

The majority of aircraft in production with aerodynamically
formed aluminum alloy wingskins employ the peen forming
process.
Metal Improvement Company has developed computer
modeling techniques that allow feasibility studies of
particular designs. The program takes three-dimensional
engineering data and, based on the degree of compound
curvature, calculates and illustrates the degree of peen
forming required. It also exports numerical data to define the
Figure 10-4 Computer Modeling of
peening that is required to obtain the curvatures. A
significant advantage of these techniques is that MIC can
Peen Forming Operation
assist aircraft wing designers in the early stages of design. These techniques insure that the desired
aerodynamic curvatures are met with economically beneficial manufacturing processes (Figure 10-4).
C O N T O UR C O R R E C TION
Shot peening utilizing peen forming techniques can be used to correct unfavorable geometry conditions.
This is accomplished by shot peening selective locations of parts to utilize the surface loading from the
induced compressive stress to restore the components to drawing requirements. Some examples are:
• Driveshaft/crankshaft straightening
• Roundness correction of ring shaped geometry
• Aircraft wing stiffner adjustment
• Welding distortion correction
The peen forming process avoids the unfavorable tensile residual stresses produced by other straightening
methods by inducing beneficial compressive residual stresses.
W ORK H A R D E N I N G
A number of materials and alloys have the potential to work harden through cold working. Shot peening
can produce substantial increases in surface hardness for certain alloys of the following types of materials.
• Stainless steel
• Aluminum
• Manganese stainless
steels
• Inconel
• Stellite
• Hastelloy
This can be of particular value to
parts that cannot be heat treated but
require wear resistance on the
surface. The following table
illustrates examples of increases in
surface hardness with shot peening.
Material Before After Percent
Shot Peen Shot Peen Increase
Cartridge Brass 50 HRB 175 HRB 250
304 Stainless 243 HV 423 HV 74
316L Stainless 283 HV 398 HV 41
Mn Stainless 23 HRC 55 HRC 139
Inconel 625 300 HV 500 HV 67
Stellite 42 HRC 54 HRC 29
Hastalloy C 18 HRC 40 HRC 122 *
Hastalloy C 25 HRC 45 HRC 80 **
* Wrought condition ** Cast condition
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