Fundamentals of Metal Forming 1

Metal Forming

Plastic Deformation is used to change the shape or metal workpieces

Applies stresses that exceed the yield strength of the metal, the metal takes a shape determined by the geometry of…

die

4 Types of Bulk Deformation

Rolling, Forging, Extrusion, Wire and bar drawing

4 types of sheet metalworking

Bending, Deep drawing, cutting, miscellaneous processes

Characterized by significant deformations and massive shape changes. “ “ refers to workparts with low area-to-volume ratios

Bulk Deformation Processes

Rolling

The slab is heated in a furnace and rolled between powered rollers until the plate is made with desirable thickness.

Forging

process of forming metal by impacting/squeezing a preheated part between two halves of a die. succession of dies may be needed to achieve the final shape.

Extrusion

Billets are preheated and forced by a ram through one or more dies to achieve desired cross section. The product is long relative to its cross-sectional dimensions and has a cross section other than that of rod and bar and pipe and tube.

Wire and Bar Drawing

the cross-section of solid rod, wire or tubing is reduced or changed in shape by pulling it through a die.

Sheet Metalworking

Forming and related operations on metal sheets, strips, and coils. High surface area-to-volume ratio of starting metal

Sheet Metal Bending

Straining of metal sheet or plate to take an angle

Deep Drawing

Forming of a flat metal sheet into a hollow or concave shape by stretching the metal

Shearing of Sheet Metal

Cuts the work by using a punch and die

Plastic region

Plastic region of stress-strain curve is primary interest because material is plastically deformed and expressed by the flow curve:

What is flow stress and what is the equation?

instantaneous value of stress required to continue deforming the material

Average Flow Stress equation

How does higher temperature effect K and n in the flow curve

Both strength (K) and strain hardening (n) are reduced at higher temperatures. Ductility is increased at higher temperatures.

What are the three temperature ranges in metal forming?

Cold Working, Warm working, Hot working

What is cold working?

refers to plastic deformation that occurs usually but not necessarily at room temperature.

What is warm working?

Carried out at intermediate temperatures. Acts as a compromise between cold and hot working

What is hot working?

Refers to plastic deformation carried out above the recrystallization temperature.

What processes occur with increasing temperature relative to melting point (T_m)?

Facts about cold working:

Performed at or slightly above room temperatures, important for mass production operations, minimum or no machining required, tends to be near net shape processes.

Advantages of cold forming

Better accuracy, closer tolerances, between surface finish, strain hardening increases strength and hardness, grain flow causes desirable directional properties in product, no heating of work required.

Disadvantages of cold forming

Higher forces and power required in the deformation operation, workpiece must be free of scale and dirt, ductility and strain hardening limit the amount of forming that can be done

Warm Working

Performed at temperatures above room temp but below recrystallization temp, often defined by 0.3 T_m

Advantages of warm working

Lower forces and power than in cold working, more complex work geometries possible, need for annealing e be reduced or eliminated

Hot Working

Deformation occurs at temps above the recrystallization temperature, recrystallization temp about 0.5 of melting point

Why would people use hot wokring?

Capability for substantial plastic deformation of the metal, far more than possible with cold working or warm working. Strength coefficient (K) is substantially less than at room temperature, Strain hardening (n) is zero (theoretically), ductility is significantly increased

Advantages of Hot Working

Workpart shape can be significantly altered, lower forces and power required, metals that fracture in cold working can be hot formed, strengths properties are generally isotropic, no strengthening of part occurs from work hardening

Disadvantages of Hot Working

lower dimensional accuracy, higher total energy required, work surface oxidation, poorer surface finish, shorter tool life