MATLENG 330 - Chapters 5 & 6

For a strain hardening materials (n=0.3), the maximum possible strain in a wire drawing process is: -0.7 -0.73 -1.3 -2.67 -1

1.3

The maximum ratio of diameters (D0/Df) for wire drawing of a perfectly plastic material is approximately: -0.36 -None of the above -0.63 -2.73 -1.64

1.64

Which of the following statements is FALSE in rolling process? -The roll gap increases with increasing the draft. -Higher friction between the rolls and the workpiece allows for higher reduction in thickness (draft). -Slipping between the rolls and the workopiece in flat rolling process is the highest at the entry and exit points. -Rolled threads have better corrosion resistance than machined threads. -Applying equal front and back tensions simultaneously lowers the location of the neutral point towards the center.

Applying equal front and back tensions simultaneously lowers the location of the neutral point towards the center.

Fastest shrinkage in metal casting processes is most likely to occur during: -A. cooling of the liquid melt -B. liquid-to-solid transformation -C. cooling of the solid to room temperature -B and C -A and C

B. liquid-to-solid transformation

Which of the following sand molds offers the worst performance against hot tearing? -Skin-dried sand molds -Cold-box sand molds -Baked sand molds -Green sand molds -Shell molds

Baked sand molds

Hydrostatic extrusion is commonly used for: -Strain hardening materials -Brittle materials -Perfectly plastic materials -Coaxial extrusion -Ductile materials

Brittle materials

Metal casting processes are often classified based on the following, except: -Processing setup -Mold materials -Mold designs/structure -Casting finish -Mold filling mechanisms

Casting finish

Solidification time is a function of all of the following parameters, except: -Mold material -Casting fluidity -Surface area of the casting -Shape of the casting -Size of the casting

Casting fluidity

The presence of workpiece inclusions is likely to result in one of these defects during deformation: -Rolls deflection -Center cracking in extrusion -Cold-shuts in forging -Residual stresses in rolling -Rolls flattening

Center cracking in extrusion

Which of the following statements is FALSE in forging process? -Initial tooling cost is lower for hot working conditions than cold working conditions. -Flash in closed die forging results in good surface finish. -Barreling defect in open-die forging is less likely under cold forming conditions. -Cold shut defect in closed die forging is mainly due to high porosity in the workpiece. -Barreling in open die forging is affected by the surface finish of the workpiece ends.

Cold shut defect in closed die forging is mainly due to high porosity in the workpiece.

Flash in closed die forging is often used for: -Simple shapes -Complex shapes -Soft metals -Rigid-perfectly plastic metals -High fluidity metals

Complex shapes

The main concern (challenge) in using internal chills over external chills is: -Slower heat transfer -Lower recyclability -Effective bonding/fusion with the melt -Higher microporosity -Higher cost

Effective bonding/fusion with the melt

Assuming all process/mold parameters are the same, ceramic molds have better melt fluidity the plaster molds. -True -False

False

Castings with small specific surface areas require shorter solidification times. (challenge question) -True -False

False

Expendable molds are more likely to result in isotropic material properties in the castings compared to permanent molds. -True -False

False

Expendable molds are used to make only one part (casting) per production cycle. -True -False

False

Investment casting process is most suitable for making large parts at high production volumes. -True -False

False

Laminar flow is more preferred over turbulent flow in metal casting since it is not associated with known casting defects. -True -False

False

Overall, continuous casting involves a simpler setup than conventional casting processes. -True -False

False

Slower cooling rates are more likely to result in isotropic structure. -True -False

False

Some metals will expand during solidification process due to excessive porosity in the castings process. -True -False

False

The maximum amount of shrinkage in metal casting occurs during liquid-to-solid phase transformation. -True -False

False

Unlike external chills, internal chills are more effective in reducing porosity due to turbulent melt flow. -True -False

False

Using fine sand grains in making sand molds reduces the potential for casting porosity. -True -False

False

Which of the following metals experiences expansion during solidification? -Brass -Lead -Low density aluminum -Zinc-Copper alloys -Grey cast iron

Grey cast iron

Which of the following parameters improves melt fluidity? -Higher cooling rate -Higher freezing range -Higher melt viscosity -Higher mold temperature -Higher melt density

Higher mold temperature

In closed die forging, flash can be desired since it: -Increases workpiece strength -Improves tooling useful life -Multiple answers are correct -Improves workpiece ductility -Decreases forging force

Increases workpiece strength

The average flow stress in rolling processes increases with: -Increasing rolling speed -Applying front or back tension -Increasing the roll radius -Increasing draft -Increasing friction

Increasing draft

The most suitable expendable mold casting process for making small parts at a large production volume is: -Expendable pattern (lost foam) -Shell mold casting -Die casting -Investment casting -Sand mold casting

Investment casting

Which of the following expendable mold casting processes can be used with an external force to fill the mold? -Die casting -Squeeze casting -Investment casting -Lost foam/wax patterns -Pressure casting

Lost foam/wax patterns

Which of the following statements is TRUE in wire drawing process? -Low carbon steel (K= 530MPa, n=0.26) has better drawability (i.e., maximum reduction in diameter) than 6061-T6 Aluminum (K=410 MPa, n=0.05). -The average flow stress is corrected for plane strain condition by a factor of 1.15. -The ideal force component can be reduced by modifying the die design. -None of the statements is true. -The reduction in diameter increases with increasing the die angle.

Low carbon steel (K= 530MPa, n=0.26) has better drawability (i.e., maximum reduction in diameter) than 6061-T6 Aluminum (K=410 MPa, n=0.05).

The type of melt flow (laminar versus turbulent) during metal casting is influenced by the following, except: -Melt density -Mold permeability -Melt viscosity -Melt pouring rate -Mold (cavity) geometry

Mold permeability

Chevron cracks in extrusion process can be reduced by: -Modifying the workpiece temperature -Modifying the extrusion speed -modifying the extrusion ratio -Modifying the die design Multiple options are correct

Multiple options are correct

In flat rolling, increasing friction between rolls and workpiece results in: -Increased entry/exit pressure -Increased hot tearing -None of the options -Increased spreading -Increased flash

None of the options

Slow cooling rate in metal casting results in: -Lower microporosity -Lower hot tearing -Higher strength and hardness -Isotropic properties -None of the options

None of the options

In flat rolling, which of the following statements is TRUE about the neutral point? -Overall rolling power is the highest at the neutral point -Roll velocity is the highest at the neutral point -None of the options is correct -Workpiece velocity in the lowest at the neutral point -Rolling draft is the lowest at the neutral point

None of the options is correct

Plane strain conditions are often assumed in the case of: -Low strain wire drawing -High strain wire drawing -Hydrostatic extrusion -None of the options is correct -Closed die forging

None of the options is correct

Which of the following statements is TRUE in rolling process? -The workpiece velocity increases between the entry and the neutral point and then starts to decrease towards the exit point. -As friction increases in rolling process, the roll gap decreases. -Cogging operation is preferred over flat rolling due to its higher speed. -Residual stresses in rolled parts are detrimental to the mechanical properties and surface finish. -None of the statements is true.

None of the statements is true.

Which of the following statements is true for flat rolling? -Roll velocity increases with increasing front tension -Workpiece velocity decreases with increasing friction between the rolls and -workpiece -Roll velocity decreases with increasing back tension -Angle of acceptence increases with rolling pressure -None of the statements is true.

None of the statements is true.

Continuous casting is best performed with: -Sand mold casting -Investment casting -Die casting -Pressure casting -None of these

None of these

Which of the following expendable casting processes is only suitable for low melting point metals? -Plaster mold casting -Aluminum mold casting -Green sand mold casting -Slush casting -Shell mold casting

Plaster mold casting

Which of the following molds has the lowest permeability? -Skin-dried sand molds -Shell molds -Green sand molds -Plaster molds -Baked sand molds

Plaster molds

Porosity due to trapped gas in metal castings can be reduced by: -Pressure casting -Expendable molds -Internal chills -External chills -Internal or external chills

Pressure casting

The main advantage of internal chills over external chills is _____________ in the troubled area. -Improving melt fluidity -Improving mold strength -Increasing casting strength -None of these -Reducing mass of the melt

Reducing mass of the melt

Ideally, when applying back tension in flat rolling, -Rolling draft decreases -Rolling torque decreases -Neutral point shifts down -Approach angle decreases -None of the statements is true.

Rolling torque decreases

In flat rolling, edge cracks are usually associated with: -Stretching of roll stand -Residual stresses -Thermal cambering of the rolls -Rolls flattening -Rolls deflection

Rolls deflection

In flat rolling, which pair of the following problems have opposite effects on the workpiece? -Rolls deflection and rolls thermal cambering -Edge cracks and thermal cambering -Wavy edges and rolls flattening -Thermal cambering and spreading -Rolls flattening and stretching of the roll stand

Rolls deflection and rolls thermal cambering

The type of sand mold which combines high surface rigidity and good collapsability is: -Skin-dried sand molds -Baked sand molds -Cold-box sand molds -Skin-dried cold box sand molds -Green sand molds

Skin-dried sand molds

An advantage of cold forming over hot forming: -Higher production rate in cold forming -Slower tool wear in cold forming -Lower tooling cost in cold forming -Lower forming energy in cold forming -All of the above

Slower tool wear in cold forming

The following metal casting processes use sand as a raw material to make the molds, except: -Vacuum casting -Cold-box molds -Shell mold casting -Expendable pattern (lost foam) -Slush casting

Slush casting

In closed die forging, cold shut defect is mainly attributed to: -High forces and energy -Pre-existing workpiece defects -Heat transfer -Flash design -Tooling design

Tooling design

Hot tearing defect in metal castings can be reduced by increasing the collapsability of sand molds. -True -False

True

Plaster molds offer better fluidity than shell molds for the same mold/cavity design. -True -False

True

Pure metals offer better fluidity than their alloys (under same casting conditions). -True -False

True

Wax patterns in expendable pattern casting process result in worse melt fluidity compared to conventional wood/metal patterns. -True -False

True

Which of the following expendable mold casting processes produces low porosity castings with sharp corner details? -Die casting -Pressure casting -Shell mold casting -Vacuum casting -Ceramic mold casting

Vacuum casting