This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Abrasive Jet Micromachining – 12”.
1. For which of the following applications, simple water jet machining is not used?
c) Reinforced plastics
d) Nonferrous metallic alloys
Explanation: WJM is typically used to cut easy-to-machine materials like thin sheets and foils, non-ferrous metallic alloys, wood, textiles, honeycomb, polymers, frozen meat, leather etc.
2. For which of the following applications can be machined by processes other than abrasive water jet machining?
c) Metal composites
Explanation: The domain of “harder and “difficult-to-machine” materials like thick plates of steels, aluminium and other commercial materials, metal matrix and ceramic matrix composites, reinforced plastics, layered composites etc., are reserved for AWJM. Soft materials like wood can be machined by simple water jet machining. This saves unnecessary cost incurred in the manufacturing.
3. A standard abrasive water jet machining (AWJM) system contains mixer, accumulator, catcher, etc., modules.
Explanation: Any standard abrasive water jet machining (AWJM) system using entrained AWJM methodology consists of following modules:
• LP booster pump
• Hydraulic unit
• Additive Mixer
• Flexible high pressure transmission line
• On-off valve
• Mixing Chamber
• Focussing tube or inserts
• CNC table
• Abrasive metering device
4. A booster pump increases the pressure of the water to _____ bars before supplying it to the next system.
Explanation: The water may be directly supplied to the small cylinder of the intensifier or it may be supplied through a booster pump, which typically raises the water pressure to 11 bars before supplying it to the intensifier. Sometimes water is softened or long chain polymers are added in additive unit.
5. To counter drops in delivery pressure, _____ to the delivery unit.
a) a thick cylinder is added
b) an opening is provided
c) an air tight seal is added whose thickness varies corresponding to the pressure changes
d) a flexible joint is added
Explanation: As the intensifier works, it delivers high pressure water. Therefore, as the larger piston changes direction within the intensifier, there would be a drop in the delivery pressure. To counter such drops, a thick cylinder is added to the delivery unit.
6. Accumulator is added because of _____
a) leakages in the system
b) pressure drops is the system
c) operating temperatures
d) safety regulations
Explanation: The change in the direction of the piston causes pressure drop in the delivery line. To counter such drops, a thick cylinder is added to the delivery unit to accommodate water at high pressure. This is called an accumulator which acts like a “fly wheel” of an engine and minimises fluctuation of water pressure.
7. Which of the following is not a part of the cutting head?
b) Mixing chamber
c) Focussing tube
Explanation: High-pressure water from the intensifier is then fed through the flexible stainless steel pipes to the cutting head. Cutting head consists of an orifice, mixing chamber and focussing tube or insert where water jet is formed and mixed with abrasive particles to form abrasive water jet.
8. Generally, the flexible pipe used to carry high pressure water to the cutting head has the diameter equal to _____
a) 4 mm
b) 6 mm
c) 10 mm
d) 12 mm
Explanation: Typical diameter of the flexible stainless steel pipes is of 6 mm. Water carried through the pipes is brought to the jet former or cutting head. Point to be noted here, is that such pipes are to carry water at 4000 bar (400 MPa) with flexibility incorporated in them with joints but without any leakage.
9. The orifice is made of _____
Explanation: The orifices are typically made of sapphire. In commercial machines, the life of the sapphire orifice is typically around 100 – 150 hours.
10. Vibratory feeder or toothed belt feeder as used to measure the quantity of the abrasive particles before mixing.
Explanation: Metered abrasive particles are introduced into the mixing chamber through a port. The abrasive particles are metered using different techniques like a vibratory feeder or toothed belt feeder. The reader may consult standard literature on transportation of powders.
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