ME Processing and Manufacturing 1 — Questions and Answers
Question 1: In metal casting, porosity defects are primarily caused by:
- Excessive mold temperature
- Gas entrapment or shrinkage during solidification (Correct answer)
- Slow pouring rates
- Low carbon content
Correct answer: Gas entrapment or shrinkage during solidification
Porosity in castings arises from dissolved gases released during solidification or from volumetric shrinkage as metal contracts when changing from liquid to solid.
Question 2: Hot working of metals is performed above the recrystallization temperature primarily to:
- Maximize work hardening
- Allow dynamic recrystallization, maintaining ductility at high deformation levels (Correct answer)
- Produce fine grain structures at low cost
- Avoid oxidation
Correct answer: Allow dynamic recrystallization, maintaining ductility at high deformation levels
Hot working enables large deformations with lower forces because recrystallization continuously replaces deformed grains with new equiaxed grains, preventing work hardening.
Question 3: Which powder metallurgy step bonds metal powders into a dense solid part using heat and/or pressure below the melting point?
- Compaction
- Sintering (Correct answer)
- Atomization
- Blending
Correct answer: Sintering
Sintering heats compacted powder to typically 70-90% of the melting point, activating diffusion that bonds particles and densifies the compact without melting.
Question 4: The purpose of annealing a cold-worked metal is to:
- Increase dislocation density
- Increase hardness
- Restore ductility by reducing dislocation density via recovery and recrystallization (Correct answer)
- Increase carbon content
Correct answer: Restore ductility by reducing dislocation density via recovery and recrystallization
Annealing heats cold-worked metal to allow recovery (stress relief) and recrystallization (new strain-free grain formation), restoring ductility and reducing hardness.
Question 5: Investment casting (lost-wax casting) is preferred for complex shapes because:
- It uses permanent metal molds for high volume
- It uses an expendable wax pattern to produce intricate, near-net-shape parts (Correct answer)
- It is the lowest cost casting process
- It requires no post-processing
Correct answer: It uses an expendable wax pattern to produce intricate, near-net-shape parts
In investment casting, a wax pattern is coated with ceramic slurry, the wax is melted out, and metal is poured into the cavity, allowing complex geometries with excellent surface finish.
Question 6: In extrusion manufacturing, the extrusion ratio is defined as:
- Exit velocity divided by entry velocity
- Billet cross-sectional area divided by product cross-sectional area (Correct answer)
- Force divided by billet area
- Die angle in degrees
Correct answer: Billet cross-sectional area divided by product cross-sectional area
The extrusion ratio (R) is the ratio of the billet cross-sectional area to the extrudate cross-sectional area, indicating the degree of deformation applied.
ME Processing and Manufacturing 1
In metal casting, porosity defects are primarily caused by: