ME Manufacturing Processes and Surface Engineering 1 — Questions and Answers
Question 1: In metal casting, porosity defects are primarily caused by:
- Excessive mold temperature
- Gas entrapment and solidification shrinkage (Correct answer)
- Too slow a pouring rate
- Use of green sand molds
Correct answer: Gas entrapment and solidification shrinkage
Porosity in castings arises from dissolved gases released during solidification and from volumetric shrinkage as the metal transitions from liquid to solid.
Question 2: Hot working of metals is defined as plastic deformation carried out at temperatures:
- Below the recrystallization temperature, preserving strain hardening
- Above the recrystallization temperature, so recrystallization occurs concurrently (Correct answer)
- At exactly the melting point of the alloy
- At room temperature under high strain rates
Correct answer: Above the recrystallization temperature, so recrystallization occurs concurrently
Hot working occurs above the recrystallization temperature, so new strain-free grains continuously replace deformed grains, preventing strain hardening and allowing large deformations.
Question 3: In powder metallurgy, sintering after compaction serves to:
- Remove alloying elements from the compact
- Bond powder particles together and reduce porosity via solid-state diffusion (Correct answer)
- Increase the density of the powder before pressing
- Coat particles with a protective oxide layer
Correct answer: Bond powder particles together and reduce porosity via solid-state diffusion
Sintering heats the powder compact below its melting point, allowing solid-state diffusion to bond particles at contact points and reduce porosity, increasing density and strength.
Question 4: Which welding process uses a non-consumable tungsten electrode and an inert shielding gas to weld reactive metals like titanium and aluminum?
- Shielded Metal Arc Welding (SMAW)
- Gas Metal Arc Welding (GMAW/MIG)
- Gas Tungsten Arc Welding (GTAW/TIG) (Correct answer)
- Flux-Cored Arc Welding (FCAW)
Correct answer: Gas Tungsten Arc Welding (GTAW/TIG)
GTAW (TIG welding) uses a non-consumable tungsten electrode with inert gas shielding (Ar or He), providing precise, clean welds ideal for reactive metals and thin materials.
Question 5: Electroplating deposits a metal coating on a substrate by:
- Physical vapor deposition in vacuum
- Thermal spraying of molten metal droplets
- Electrolytic reduction of metal ions from solution onto the cathode (workpiece) (Correct answer)
- Chemical vapor deposition from a metal halide precursor
Correct answer: Electrolytic reduction of metal ions from solution onto the cathode (workpiece)
In electroplating, the workpiece is the cathode; metal ions in the electrolyte are reduced and deposited onto it by passing an electrical current through the solution.
Question 6: Anodizing of aluminum creates a surface layer of:
- Pure aluminum deposited from an electrolytic bath
- Aluminum oxide (Al2O3) formed by controlled electrochemical oxidation (Correct answer)
- Zinc chromate conversion coating
- Nickel phosphate for corrosion protection
Correct answer: Aluminum oxide (Al2O3) formed by controlled electrochemical oxidation
Anodizing uses electrochemical oxidation in an acidic bath to grow a thick, porous Al2O3 layer on the aluminum surface, improving corrosion and wear resistance.
ME Manufacturing Processes and Surface Engineering 1
In metal casting, porosity defects are primarily caused by: