Manufacturing Processes Multiple Choice Questions on “Abrasive Jet Micromachining – 8”.
1. The powder distribution changes because of _____
a) powder stratification
b) variation in feed rates
c) variation in nozzle diameter
d) variation in air flow velocity
Answer: a
Clarification: Powders stratify as they flow and it depends on particle size. Therefore, the powder size distribution changes while blasting, as the smaller particles are ejected first, leaving the larger ones to remain in the reservoir.
2. Powder size distribution can be minimised by ___________
a) increasing the carrier gas flow
b) increasing the amount of the powder in the reservoir
c) decreasing the amount of the powder in the reservoir
d) using very fine powder
Answer: c
Clarification: However, in most practical applications, a relatively small amount of powder is used during a single machining operation, and therefore a negligible change in the powder size distribution occurs.
3. Refilling the reservoir is another way to get good results in AJMM.
a) True
b) False
Answer: a
Clarification: The powder size distribution changes while blasting because of powder stratification. Using a relatively small amount of powder during the process can improve powder distribution but to ensure repeatable results, the powder reservoir should be emptied and refilled with fresh powder.
4. Mechanical properties of powder are influenced by _____
a) humidity
b) carrier gas
c) air velocity
d) type of mask used
Answer: a
Clarification: Mechanical properties of powder are influenced by humidity. Increasing humidity decreases the fracture toughness, which can have a large effect on the resulting solid particle erosion rates.
5. Humidity can affect_____
a) machining time required
b) powder flowability
c) metal mask thickness
d) Powder stratification
Answer: b
Clarification: Humidity can also greatly influence the powder flowability and the repeatability of particle mass flow rates since it has a direct effect on inter-particle adhesion.
6. Which of the following is done to minimize the effects due to humidity?
a) Increasing the exposure of the powder to atmospheric air
b) Drying the air before entering the mixing chamber
c) Using photo sensitive mask
d) Using pressurized powder feed system
Answer: b
Clarification: To minimize the effects due to humidity, sacks of desiccant were placed inside the sealed powders to rage bottles, and both a desiccant-based and a refrigeration air dryer are used to dry the compressed air. Achieving a moisture free powder reservoir however, is difficult because of its frequent exposure to atmospheric moisture when it was opened to be refilled.
7. Which of the following is not true about AJMM?
a) It can be used for shallow depth cut on ceramic materials
b) It can be used for medical applications
c) It can be used for pressure sensors
d) It can be used in machining of high strength materials
Answer: a
Clarification: Following are the few applications of AJMM;
• Shallow depth cut on ceramic materials
• Trenches for micro-medical applications
• Mesas to reduce the surface area of chuck and other semiconductor components
• Reference cavities for pressure sensors.
8. AJMM can be used for de-burring and polishing plastic.
a) True
b) False
Answer: a
Clarification: AJMM is used for;
• Thru-holes for air and chemical flow
• Cavities for mechanical locations
• Removing flash and parting lines from injection molded parts
• De-burring and polishing plastic, nylon and Teflon components
• Cleaning metallic mould cavities which otherwise may be inaccessible.
9. _____ can be fabricated by AJMM.
a) Annealed glass
b) Toughened glass
c) Mirrored glass
d) Pyrex glass wafers
Answer: d
Clarification: Cantilever beam in pyrex glass wafers for inertial sensor applications can be fabricated by AJMM. This can be made by erosion process which consists of etching through the complete wafer (sensing mass and thick supporting beam).