Sheet Metal Forming Processes - Yola

Sheet Metal Forming Processes Introduction Ratio Surface Area:Volume is very high for sheet metal process. Plates thickness > 0.25 inches Boilers, bridges, ships, etc. use relatively thick plates Usually sheet forming is done on relatively thin material.

Shapes can be of various size Beverage can, car body Sheet metal forming includes many widely used processes. Sheet Metal Characteristics Formability Methods Sheet metal is formed as coils of sheets (by

rolling) or plates. Blanks are created for required shapes. Shearing sheets Flame cutting - plates Sheet Metal Characteristics Main forces acting in sheet metal forming tensile No (or very low) compressive load. Can lead to buckling or folding and wrinkling.

What is the big difference between bulk deformation and sheet metal? What factors affect stretching and bending? Elongation, Yield point elongation, anisotropy, grain size, residual stresses, springback, wrinkling. Elongation

Uniform elongation region Postuniform elongation region n True stress, true strain: K Necking begins at n

Uniform strain strain hardening index n Large n, uniform elongation is better. Necking occurs at an angle Localized Diffuse Depends on strain rate sensitivity m of the material. Postuniform elongation is higher with

higher values of m. Total elongation n and m. Yield Point Elongation

Low carbon steel Certain points elongate more in the specimen. Strain rate elongation Grain size Y.P. elongation Leuders bands = stretcher strain marks May not be acceptable in many cases To avoid: skin rolling (cold rolling) Reduces thickness of sheet 0.5 to 1.5 % Strain aging can cuase the Y.P elongation to

appear after a few days. Residual Stresses Because of non uniform deformation. Cause distortion if some parts are removed. Stress corrosion cracking Springback Thin considerable springback

Wrinkles Due to compressive load in certain areas. Anisotropy Previous history of the sheet metal can cause anisotropy. Crystallographic grain orientation Mechanical Fibering - alignment of impurities, inclusions

Grain Size Mechanical properties Appearance: coarse grain causes rough surface appearance (orange peel)