This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Abrasive Jet Micromachining – 2”.
1. Abrasive particles are suspended in the carrier gas.
Explanation: Abrasive particles should be fine enough to remain suspended in the carrier gas. It should have excellent flow characteristics so that narrow and fine areas are reachable to them.
2. SiC is used as abrasive for harder materials.
Explanation: Following are the materials used as abrasive in AJMM:
1) Al2O3: For cleaning, cutting and de-burring
2) SiC: Similar applications as Al2O3 but for harder work materials
3) Glass beads: Matte finish
4) Sodium Bicarbonate: Cleaning, cutting and de-burring of soft material.
3. Which of the following is commonly used as a carrier gas in AJMM?
Explanation: In AJMM, commonly used gases are CO2, nitrogen, and air. Air is mostly preferred due to universal availability, practically at no cost, and its non-toxic nature.
4. The Carrier gas should spread more after discharge.
Explanation: Following are the required properties for the carrier gas:
1) It should be non-toxic
2) It should be cheap
3) It should be easily available.
4) It must not flare excessively when discharged from the nozzle.
5. There should be supersonic air flow velocity in the nozzle.
Explanation: The following requirements have to be fulfilled on nozzle design:
1) Pressure-less constant feeding system
2) Supersonic air flow velocity in the nozzle
3) Homogeneous dispersion of abrasive particles over the width of the nozzle
4) Long life time of the nozzle (It has to withstand the erosive action of abrasive particles).
6. A decrease in stand-off-distance (SOD) _____
a) increases machining time
b) increases energy consumption
c) improves surface finish
d) improves accuracy
Explanation: A decrease in stand-off-distance (SOD):
1) improves accuracy,
2) decreases kerf width and
3) reduces taper in the machined groove.
7. Material removal rate (MRR) in AJMM _____
a) increases with SOD
b) can only decrease
c) first increases upto certain value and then decreases
d) first decreases upto certain value and then increases
Explanation: MRR increases only upto a certain value of abrasive flow rate beyond which it starts decreasing. After a certain value of abrasive flow rate, abrasive flow velocity decreases to the extent that it results in reduction in MRR.
8. MRR increases with abrasive flow rate increase.
Explanation: As abrasive flow rate increases, then the number of abrasive particles cutting the material also increases there by increasing Material removal rate (MRR).
9. In the case of ductile materials, material is removed by plastic deformation.
Explanation: When ductile materials are machined by AJMM, the material is removed by plastic deformation and cutting wear, or plastic strain and deformation wear.
10. In case of ductile materials, plastic deformation starts when yield strength is exceeded.
Explanation: In case of ductile materials, during an impact of the jet, plastic deformation takes place in the vicinity of the impact when the yield strength of the material is locally exceeded. And yield strength increases due to hardening of the material.
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