ME Manufacturing Processes and Surface Engineering 2 — Questions and Answers
Question 1: The heat-affected zone (HAZ) in welding is the region that:
- Has been melted and resolidified to form the weld nugget
- Was not melted but experienced microstructural changes due to welding heat (Correct answer)
- Remains completely unaffected by the welding process
- Contains the highest concentration of weld defects
Correct answer: Was not melted but experienced microstructural changes due to welding heat
The HAZ is the base metal adjacent to the fusion zone that did not melt but whose microstructure and properties were altered by the welding thermal cycle.
Question 2: Shot peening improves the fatigue life of metal components by:
- Removing surface material to eliminate microcracks
- Introducing compressive residual stresses in the surface layer that retard fatigue crack initiation and growth (Correct answer)
- Depositing a hard coating to increase surface hardness
- Heating the surface to relieve tensile residual stresses
Correct answer: Introducing compressive residual stresses in the surface layer that retard fatigue crack initiation and growth
Shot peening bombards the surface with small spherical media, causing localized plastic deformation that induces beneficial compressive residual stresses, which oppose tensile fatigue stresses.
Question 3: Investment casting (lost-wax casting) is preferred for:
- High-volume production of large, simple iron castings
- Near-net-shape production of complex, high-tolerance parts in superalloys and stainless steel (Correct answer)
- Casting non-metallic materials like ceramics
- Continuous casting of steel slabs
Correct answer: Near-net-shape production of complex, high-tolerance parts in superalloys and stainless steel
Investment casting uses an expendable wax pattern coated in ceramic to produce intricate, near-net-shape parts with excellent surface finish, suitable for superalloys and aerospace components.
Question 4: Cold drawing of metal wire through a die produces a product with:
- Reduced strength and increased ductility due to annealing
- Increased strength and hardness due to strain hardening, but reduced ductility (Correct answer)
- No change in mechanical properties
- Improved corrosion resistance due to surface oxidation
Correct answer: Increased strength and hardness due to strain hardening, but reduced ductility
Cold drawing at room temperature plastically deforms the wire, increasing dislocation density (strain hardening), which raises strength and hardness while reducing ductility.
Question 5: Chemical vapor deposition (CVD) is commonly used to apply hard coatings (e.g., TiN, TiC) to cutting tools because:
- It can deposit coatings at room temperature without any heating
- It produces dense, adherent coatings with excellent uniformity even on complex geometries at elevated temperatures (Correct answer)
- It is the lowest-cost coating method available
- It only works with polymer substrates
Correct answer: It produces dense, adherent coatings with excellent uniformity even on complex geometries at elevated temperatures
CVD deposits hard, wear-resistant ceramic coatings by thermally decomposing gas-phase precursors on the heated tool substrate, producing dense, conformal coatings with strong adhesion.
Question 6: Extrusion of metals involves:
- Rolling a billet between two rotating rolls to reduce its cross-section
- Forcing a heated billet through a shaped die orifice by ram pressure to produce a continuous profile (Correct answer)
- Drawing a wire through successively smaller dies
- Hammering a billet between flat dies to shape it
Correct answer: Forcing a heated billet through a shaped die orifice by ram pressure to produce a continuous profile
In extrusion, a ram forces a heated metal billet through a shaped die, producing long continuous profiles such as rods, tubes, and complex structural shapes.
ME Manufacturing Processes and Surface Engineering 2
The heat-affected zone (HAZ) in welding is the region that: