Chapter 18 Manufacturing
Which of the following are advantages and characteristics of hot working relative to cold working (four correct answers): (a) fracture of workpart is less likely, (b) friction is reduced, (c) increased strength properties, (d) isotropic mechanical properties, (e) less overall energy is required, (f) lower deformation forces is required, (g) more significant shape changes are possible, and (h) strain-rate sensitivity is reduced?
(a) fracture of workpart is less likely, (d) isotropic mechanical properties, (f) lower deformation forces is required, (g) more significant shape changes are possible
The coefficient of friction between the part and the tool in cold working tends to be (a) higher, (b) lower, or (c) no different relative to its value in hot working?
(b) lower
Which of the following is typical of the starting work geometry in sheet metal processes: (a) high volume-to-area ratio or (b) low volume-to-area ratio?
(b) low volume-to-area ratio
The flow curve expresses the behavior of a metal in which of the following regions of the stress-strain curve: (a) elastic region or (b) plastic region?
(b) plastic region
Which of the following are bulk deformation processes (three correct answers): (a) bending, (b) deep drawing, (c) extrusion, (d) forging, (e) rolling, and (f) shearing?
(c) extrusion, (d) forging, (e) rolling
Increasing strain rate tends to have which one of the following effects on flow stress during hot forming of metal: (a) decreases flow stress, (b) has no effect, or (c) increases flow stress?
(c) increases flow stress
Hot working of metals refers to which one of the following temperature regions relative to the melting point of the given metal on an absolute temperature scale: (a) room temperature, (b) 0.2Tm, (c) 0.4Tm, or (d) 0.6Tm?
(d) 0.6Tm
The average flow stress is the flow stress multiplied by which of the following factors: (a) n, (b) (1+n), (c) 1/n, or (d) 1/(1+n), where n is the strain-hardening exponent?
(d) 1/(1+n)
what is the difference between deep drawing and bar drawing
Deep- sheet metal operation, cut shaped parts as output. Bar- bulk deform, cylindrical parts of reduced diameter are output
Extrusion is a fundamental shaping process. Describe it
Desired shape by allowing it to pass through an orifice
Why is the term pressworking often used for sheet metal processes?
Due to the use of a press for all sheet metal processes
How does increasing temperature affect the parameters in the flow curve equation
As temperature increases, there is a subsequent decrease in flow stress
Describe the effect of strain rate in metal forming
As the strain rate increases, the material offers a greater resistance to deformation
What is isothermal forming
Both the work and the forming tool are heated to the hot working temperature of the work
What are the differences between bulk deformation processes and sheet metal processes?
Bulk- causes workpiece to deform plastically, pushed to fill die sheet metal is on workpiece of sheets or strips, pushed into a die
Why is friction generally undesirable in metal forming operations?
Causes high residual stress, causes cracks, increased power required, tool wear
Indicate the mathematical equation for the flow curve
Flow stress = Strength strain ^ strain hardening exponent
Indicate some of the advantages of cold working relative to warm and hot working
greater accuracy, better surface finish, high strength and hardness, different properties in different directions, cost efficient
What is sticking friction in metalworking?
sticking causes the work to stick to the tool instead of sliding
