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
