Fundamentals of Metal Forming

What is forging?

forming metal by impacting and/or squeezing a preheated part between two halves of a die

When work temperature is raised, ductility (_) and yield strength (_)

increases, decreases

What does "bulk" refer to?

low surface area-to-volume ratios

What are the disadvantages of hot working?

lower dimensional accuracy higher total energy required Scaling, poorer surface finish Shorter tool life

What are advantages of warm working?

lower forces and power more complex work geometries need for annealing may be reduced or eliminated

When is sheet metalworking performed?

With metal sheets, strips, and coils with high surface area to volume ratio of starting metal

Strength and strain hardening are (_) at higher temperatures

reduced

Why is hot working done?

Able to perform substantial plastic deformation of the metal This is possible because the strength coefficient is substantially less than at room temperature

What is the shearing of sheet metal?

A shearing operation which cuts the work by using a punch and die.

What does a die do?

Apply stresses that exceed the yield strength of the metal

What are examples of sheet metalworking?

Bending Deep Drawing Cutting

What are some advantages of cold forming?

Better accuracy, closer tolerances Better surface finish Strain hardening increases strength and hardness Grain flow during deformation can cause desirable directional properties in product No heating required

What is extrusion?

Billets are preheated, forced by a ram through one or more dies to achieve the desired cross-section. Product is long in relation to its cross-sectional dimensions

Scale

Black scaly coating of oxide forming on the surface of a metal

Warm Working

Carried out at intermediate temperatures. Compromise between cold and hot working 0.3*Tm

What process is important for mass production operations?

Cold forming

What are the three temperature ranges in metal forming?

Cold, Warm, and Hot working

What is wire and bar drawing?

Cross section of solid rod, wire, or tubing is reduced or changed in shape by pulling in through a die

True or False: machining is required for cold-worked metals

False

What is metal forming?

Group of manufacturing processes in which plastic deformation is used to change the shape of metal workpieces

What are some disadvantages of cold forming?

Higher force and power required Surfaces of starting workpiece must be free of scale and dirt Ductility and strain hardening limit amount of forming

What is flow stress?

Instantaneous value of stress required to continue deforming the metal Y = Kepsi^n

What are desirable material properties for metal forming?

Low yield strength High ductility

Any deformation operation can be accomplished with what?

Lower forces and power at elevated etmperature

What parts and tools are used for sheet metalworking?

Parts are called stamping Tooling used is punch and die

Hot Working

Plastic deformation carried out above recrystallization temperature > 0.5Tm

What region is the primary interest during metal forming?

Plastic region where metal behavior is expressed by k = epsilon^n

What is another term for sheet metal?

Pressworking

Cold Working

Refers to plastic deformation that occurs usually at room temperature

What are examples of bulk deformation?

Rolling Forging Extrusion Wire and bar drawing

What characterizes a bulk deformation process?

Significant deformations and massive shape changes

What is rolling?

Slab is heated then rolled between powered rollers until plate is made with desirable thickness

Why does a metal's strength increase when deformed?

Strain hardening

What is dependent on temperature in the flow curve?

Strength (K) and strain hardening (n)

What is deep drawing?

The forming of a flat metal sheet into a hollow or concave shape, by stretching the metal

What is sheet metal bending?

The straining of a metal sheet or plate to take an angle

True or False: Cold Worked operations are near net processes

True

True or False: Die geometry determines the shape of the metal

True

What is Average Flow Stress?

Where epsi = max strain during deformation

What are advantages of hot working?

shape can be significantly altered lower forces and power required metals that usually fracture in cold working can be hot formed isotropic properties as a result no strengthening of part occurs from work hardening