Manufacturing Processes Multiple Choice Questions on “Abrasive Jet Micromachining – 13”.
1. In AWJM, mixing process takes place in _____
a) intensifier
b) mixing table
c) mixing chamber
d) mixing line
Answer: c
Clarification: Mixing means gradual entrainment of abrasive particles within the water jet. This is done in the mixing chamber. Finally, the abrasive water jet comes out of the focussing tube or the nozzle.
2. Abrasive water jet velocity increases with (keeping all other parameters unchanged) _____
a) increasing traverse velocity of the job
b) decreasing mass flow rate of abrasive
c) decreasing traverse velocity of the job
d) increasing mass flow rate of abrasive
Answer: d
Clarification: Assuming no losses, abrasive water jet velocity for a given pressure is calculated by formula; where p= pressure. Now mass flow rate is calculated by formula; mw = ρ*A*Vw, where A= area of cross section of the jet.
3. In an environment friendly development concerning AWJM, which of the following is used as abrasive?
a) dry ice
b) cubic boron nitrite
c) diamond
d) tungsten carbide
Answer: a
Clarification: In this case, liquid nitrogen replaces the water phase and dry ice crystals (solid CO2 crystals) replace the abrasive phase leading to no need of disposal or waste generation. The removed work material in the form of microchips can be collected much easily reducing the chances of environmental degradation.
4. The mixing chamber is immediately followed by _____
a) intensifier
b) on-off valve
c) catcher
d) focussing tube
Answer: d
Clarification: The mixing chamber is immediately followed by the focussing tube or the inserts. The focussing tube is generally made of carbide materials.
5. Which of the following materials is used for focusing tubes?
a) Chromium
b) Titanium
c) Nickel
d) Tungsten
Answer: d
Clarification: The focussing tube is generally made of tungsten carbide (powder metallurgy product) having an inner diameter of 0.8 to 1.6 mm and a length of 50 to 80 mm.
6. Tungsten carbide is used because of its abrasive resistance.
a) True
b) False
Answer: a
Clarification: Tungsten carbide is used for its abrasive resistance. Abrasive particles during mixing try to enter the jet, but they have reflected away due to an interplay of buoyancy and drag force. They go on interacting with the jet and the inner walls of the mixing tube until they are accelerated using the momentum of the water jet.
7. The formula for abrasive jet velocity considering the momentum loss is _____
a) Vawj = η*(1/(1+R))*Vwj
b) Vawj = η*(1+R)*Vwj
c) Vawj = R*(1/(1+ η))*Vwj
d) Vawj = η*(1+ η)*Vwj
Answer: a
Clarification: As during mixing process momentum loss occurs as the abrasives collide with the water jet and at the inner wall of the focussing tube multiple times before being entrained, velocity of abrasive water jet is given as,
Vawj = η*(1/(1+R))*Vwj.
Where η= momentum loss factor
R= loading factor= mass flow rate of abrasive/ mass flow rate of water
Vwj= velocity of water jet.
8. There are _____ different types of suspension abrasive water jet (AWJ).
a) 2
b) 3
c) 5
d) 7
Answer: b
Clarification: In suspension AWJM the abrasive water jet is formed quite differently. There are three different types of suspension AWJ formed by direct, indirect and Bypass pumping method.
9. In suspension AWJM, mixture of water and abrasive particles is pumped to high pressure.
a) True
b) False
Answer: a
Clarification: In suspension AWJM, preformed mixture of water and abrasive particles is pumped to sufficiently high pressure and store in pressure vessel. Then the premixed high-pressure water and abrasive is allowed to discharge from a nozzle to form abrasive water jet.
10. Catcher is used to_____
a) increase the residual energy of the AWJ
b) absorb the residual energy of the AWJ
c) focus the jet on the target
d) collect the residual part of the machined component
Answer: b
Clarification: Once the abrasive jet has been used for machining, they may have sufficiently high level of energy depending on the type of application. Such high-energy abrasive water jet needs to be contained before they can damage any part of the machine or operators. “Catcher” is used to absorb the residual energy of the AWJ and dissipate the same.