Production Technology IV Metal Forming INTRODUCTION TO METAL

Production Technology IV (Metal Forming)

INTRODUCTION TO METAL FORMING • METAL FORMING includes all manufacturing processes by which the shape of a material is changed without removal or addition of any excess metal by using mechanical force (plastic deformation). v. Advantages of products manufactured by metal forming: 1. 2. 3. 4. Higher strength due to work hardening Reduction in material cost Closing up and welding of cracks, blow holes, and cavities Superior surface finish v. Types of metal forming: 1. Cold forming 2. Hot forming 3. Warm forming 4. Isothermal forming

COLD FORMING VS. HOT FORMING Cold forming • • • Below the recrystallization temp. Is accompanied with work hardening Higher strength Better surface finish Better dimensional accuracy Ø Processes: 1. Deep drawing 2. Wire drawing 3. Rolling 4. Impact extrusion 5. bending Hot forming • Above the recrystallization temp. • No work hardening • Reduce resistance to plastic deformation • To refine grains Ø Processes: 1. Forging 2. Rolling

Warm forming cold 0. 3 Tm warm 0. 5 Tm hot 0. 75 Tm

Metal forming operations Tool design Forces M/C selection Forces Work done

Plastic deformation curve (flow curve) • The flow curve determine the strain required to cause plastic deformation of the metal at a given strain (Ø). σf Ø

Generalized strain measure: •

ε Or Ø • ε Ø Therefore we use Ø instead of ε

* Strain rate (Ø ) •

Temperature and Strain-Rate Dependence • Flow stress depends on strain rate and temperature, usually increasing with strain rate and decreasing with temperature. • The strain-rate effect at constant strain can be approximated by • Where: Ø C is a strength constant that depends upon strain, temperature, and material Øm is the strain-rate sensitivity of the flow stress. For most metals at room temperature, the magnitude of m is quite low (between 0 and 0. 03).

Determination of the flow curve •

Determination of the flow curve by compression test • Stress at no friction Stress at friction

Determination of the flow curve by compression test •

Determination of the flow curve by tension test • Advantages over compression: 1. No friction 2. Availability of tension test machines v σf = k Ø n § K , n : material constants § K: strength coefficient § n: strain hardening exponent § This relation is valid for Ø in the range between 0. 1 - 1

Determination of the flow curve by tension test •

Determination of the flow curve by tension test •