Question 1
_____ can be fabricated by AJMM.
A. Annealed glass
B. Toughened glass
C. Mirrored glass
D. Pyrex glass wafers
View Answer
Answer: Option D
Explanation:
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).
Question 2
A decrease in stand-off-distance (SOD) _____
A. increases machining time
B. increases energy consumption
C. improves surface finish
D. improves accuracy
View Answer
Answer: Option D
Explanation:
A decrease in stand-off-distance (SOD):1) improves accuracy,2) decreases kerf width and3) reduces taper in the machined groove.
Question 3
A standard abrasive water jet machining (AWJM) system contains mixer, accumulator, catcher, etc., modules.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Any standard abrasive water jet machining (AWJM) system using entrained AWJM methodology consists of following modules:• LP booster pump• Hydraulic unit• Additive Mixer• Intensifier• Accumulator• Flexible high pressure transmission line• On-off valve• Orifice• Mixing Chamber• Focussing tube or inserts• Catcher• CNC table• Abrasive metering device• Catcher.
Question 4
Accumulator is added because of _____
A. leakages in the system
B. pressure drops is the system
C. operating temperatures
D. safety regulations
View Answer
Answer: Option B
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.
Question 5
Adhesion between particles can be increased by moisture.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Inter particle adhesion is further enhanced by moisture that adsorbs readily onto these hygroscopic (having a tendency to absorb moisture) surfaces.
Question 6
After treatment with UV light, resist is washed away by the developer solution.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The exposed resist, after UV treatment is washed away by the developer solution, leaving windows of the bare underlying material. In other words, “whatever shows, goes.” The mask, therefore, contains an exact copy of the pattern which is to remain on the wafer.
Question 7
AJM applications include drilling, engraving of glass, etc. operations.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Typical AJM applications include drilling, cutting and engraving of glass, ceramics and some hard materials. It can also be used to etch labels in plastics and metals, deburr, deflash and clean materials after conventional machining.
Question 8
AJM nozzles are made from which of the following materials?
A. Low carbon steel
B. HSS
C. WC
D. Stainless steel
View Answer
Answer: Option C
Explanation:
Generally, the nozzle is made of;• Material – WC / sapphire• Diameter – (Internal) 0.2 ~ 0.8 mm• Life – 10 ~ 300 hours.
Question 9
AJMM can also machine poly methyl methacrylate (PMMA).
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
AJMM can machine much steeper side walls and flatter bottom section in PMMA than those in glass. For PMMA, there is only a small probability of a particle rebounding from the steep side wall and hitting the opposite side.
Question 10
AJMM can be used for de-burring and polishing plastic.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
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.
Question 11
AJMM generates no heat.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Following are the few advantages of AJMM;• The process generates no heat and does not change the material properties of the work-piece• Very high pattern densities are possible• Process works well with metalized parts• Features can be of any 2D shape: square, round, designed shapes, and connected channels.
Question 12
AJMM is capable of machining anisotropic patterns.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
In contrast to conventional micro-fabrication methods, such as wet and dry etching, AJMM is capable of machining anisotropic patterns and suspended structures with high erosion rate and relatively low cost.
Question 13
AJMM is widely used for machining of glass and silicon.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Abrasive Jet Micro Machining (AJMM) is a relatively new approach to the fabrication of microstructures. AJMM is a promising technique to three-dimensional machining of glass and silicon in order to realize economically viable micro-electro-mechanical systems (MEMS).
Question 14
As the stand-off distance increases, the depth of penetration in AJM _____
A. increases
B. decreases
C. does not change
D. initially increases and then remains steady
View Answer
Answer: Option B
Explanation:
The depth of penetration varies inversely with the stand-off distance. In AJM, generally, the abrasive particles of around 50 μm grit size would impinge on the work material at a velocity of 200 m/s from a nozzle of I.D. of 0.5 mm with a stand-off distance of around 2 mm.
Question 15
At higher angle of impact, the material removal involves _____ failure.
A. plastic
B. ductile
C. brittle
D. tensile
View Answer
Answer: Option A
Explanation:
At higher angle of impact, the material removal involves plastic failure of the material at the sight of impact, which was studied initially by a person named Bitter.
Question 16
At higher particle velocities, adhesion between the mask and the workpiece material becomes weak.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The adhesion is significantly weaker for complex patterns and higher particle velocities that may cause a release of the foils from the substrate. Their applicability is limited to single workpieces and feature sizes down to 75μm.
Question 17
Behaviour of elastomer materials is dependent on temperature.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
In contrast to ductile or brittle materials, elastomers behaviour is dependent on temperature, rate of deformation and particle velocity. Thus elastomers can show ductile, elastic and brittle behaviour.
Question 18
Brittle fracture can occur due to indentation rupture.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Brittle fracture may take place due to:1) Indentation ruptures2) Elastic–plastic deformation3) Critical plastic strain theory4) Radial cracking and propagation or surface energy criterion.
Question 19
By AJMM, holes of intricate shapes can be drilled easily.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Following are the advantages of AJMM process;• For drilling holes of intricate shapes in hard and brittle materials• For machining fragile, brittle and heat sensitive materials• AJM can be used for drilling, cutting, de-burring, cleaning and etching.• Micro-machining of brittle materials.
Question 20
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
View Answer
Answer: Option B
Explanation:
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.
Question 21
Dimensional tolerances of very less microns are possible with AJMM
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
With AJMM, feature location and dimensional tolerances down to +/-25 microns are possible. Also, features of any 2D shape: square, round, designed shapes, and connected channels can be machined.
Question 22
During blasting, the workpiece is exposed to an abrasive air jet pressure of _____ MPa.
A. 0—1
B. 0—0.2
C. 0.2—0.8
D. >1
View Answer
Answer: Option C
Explanation:
During blasting, the workpiece is exposed to an abrasive air jet pressure of 0.2-0.8 MPa and abrasive particles average diameter of 10-100 μm. The scan strategy and the particle beam profile of the nozzle are of great importance.
Question 23
During first half cycle, mixing chamber is at ___________
A. atmospheric pressure
B. 2 atm
C. 2 bar
D. vacuum
View Answer
Answer: Option A
Explanation:
During the first half cycle the powder in the chamber is forced out of the nozzle. At this point, the reservoir is still pressurized, but the mixing chamber is at atmospheric pressure due to the open nozzle. This creates a pressure differential that forces the powder down through the orifice at the bottom of the reservoir and into the mixing chamber.
Question 24
During powder feeding, the oscillating valve is open for the first half of the operation cycle.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
During the first half of the operation cycle, the oscillating valve is open, allowing air to flow from the pressure regulator to the mixing chamber while some enters the powder reservoir and the rest flows out through the opened nozzle.
Question 25
During the first half cycle in pressurized powder feed system, powder that has entered the mixing chamber is _____
A. forced out of the nozzle
B. heated to a specific temperature
C. mixed with air
D. mixed with cutting fluid
View Answer
Answer: Option A
Explanation:
It is during this first half cycle that any powder that has entered the mixing chamber is forced out of the nozzle. In the second half of the cycle, the oscillating valve is closed, stopping air flow through the system.
Question 26
Elastomer masks are provided in the form of foils.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
These types of mask usually provided in the form of ready-made foil with self-adhesive properties. Besides, elastomers can show ductile, elastic and brittle behaviour and experiments have to be carried out under relevant practical conditions.
Question 27
Elastomers are suitable for high air pressures.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Elastomer foils are easy to pattern and allow a high complexity of the design but the procedure is somewhat time consuming. They are not suitable for high air pressures due to their elastic deformation behaviour.
Question 28
Erosion mechanism in elastomer materials is based on fatigue.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The erosion mechanism of this class of materials is based on fatigue; therefore they display a good erosion resistance. The photosensitive materials can be patterned accurately using lithography. Photosensitive-elastomer can be a good option.
Question 29
Erosion rate is directly proportional to velocity of the jet.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The principal empirical relation between erosion rate Erate, expressed as the quotient of mass loss and amount of abrasive, and particle velocity is given as a power function byErate α vk , where k= velocity coefficient.
Question 30
Feature width is the major drawback of metal masks.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The limiting factors for all metal masks are the feature width and the structuring procedure where no free-standing contours are possible. Metal masks should be applied preferably for medium and large sizes.
Question 31
For metal, velocity coefficient ranges from_____
A. 0.5—1
B. 1.8—3
C. 2.3—3
D. 2—4
View Answer
Answer: Option C
Explanation:
velocity coefficient k commonly reported for,1) for metals – between 2.3 and 3,2) for glasses – between 2 and 4 and3) for elastomers – between 1.8 and 3.2.
Question 32
For which of the following applications can be machined by processes other than abrasive water jet machining?
A. Ceramic
B. Steel
C. Metal composites
D. Wood
View Answer
Answer: Option D
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.
Question 33
For which of the following applications, simple water jet machining is not used?
A. Textiles
B. Polymers
C. Reinforced plastics
D. Nonferrous metallic alloys
View Answer
Answer: Option C
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.
Question 34
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
View Answer
Answer: Option B
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.
Question 35
High aspect ratios are not possible with SU-8 material.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
A good compromise in terms of feature size and imaging accuracy gives the epoxy based photo-resist SU-8. Since the maximum thickness of an SU-8 layer is about 300μm, no high aspect ratio is achievable and its application is limited to shallow cavities.
Question 36
How many types of catcher are there?
A. 2
B. 3
C. 4
D. 5
View Answer
Answer: Option A
Explanation:
Moreover the catcher can be of pocket type or line type. In pocket type, the catcher basin travels along the jet. In line type, the catcher basin only travels along one axis of the CNC table and its length covers the width of the other axis of the CNC table.
Question 37
How many types of materials can be used during AJMM?
A. 1
B. 3
C. 8
D. there is no compulsion on the material
View Answer
Answer: Option B
Explanation:
Three groups of mask materials can be applied to AJMM:• Ductile materials such as metals.• Elastic materials such as elastomer sand.• Photo-resists as used in IC-industry.
Question 38
Humidity can affect_____
A. machining time required
B. powder flowability
C. metal mask thickness
D. Powder stratification
View Answer
Answer: Option B
Explanation:
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.
Question 39
If air is used as a carrier gas, the pressure of the air is maintained at around_____
A. 1 bar
B. 3 bar
C. 5 bar
D. 3.5 bar
View Answer
Answer: Option C
Explanation:
In AJM, air is compressed in an air compressor and compressed air at a pressure of around 5 bar is used as the carrier gas. Gases like CO2, N2 can also be used as carrier gas which may directly be issued from a gas cylinder. Generally, oxygen is not used as a carrier gas.
Question 40
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
View Answer
Answer: Option A
Explanation:
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.
Question 41
In AJMM, abrasive particles are accelerated in a gas stream.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Fine micro abrasive particles are accelerated in a gas stream (commonly air at a few times atmospheric pressure). The particles are directed towards the focus of machining (less than 1mm from the tip).
Question 42
In AJMM, as the jet fracture off the surface after striking it.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
As the particles impact the surface, they fracture off the surface and create cavities. As the particle impacts the surface, it causes a small fracture, and the gas stream carries both the abrasive particles and the fractured (wear) particles away.
Question 43
In AJMM, impingement angle is kept approximately in range of_____
A. 100 ~ 200
B. 300 ~ 450
C. 600 ~ 900
D. 500 ~ 600
View Answer
Answer: Option C
Explanation:
Generally, abrasive jet has,• Velocity : 100 ~ 300 m/s• Mixing ratio : mass flow ratio of abrasive to gas = mass of abrasive/ mass of carrier gas• Stand-off distance : 0.5 ~ 5 mm• Impingement Angle : 600 ~ 900.
Question 44
In AJMM, material removal starts when the fracture strength is reached.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
During AJMM, plastically deformed surface layer is formed near the eroded surface, and therefore, the yield strength of the material increases. Upon further deformation, the yield strength at the surface of the material will eventually become equal to its fracture strength. The surface becomes brittle and its fragments may be removed by subsequent impacts.
Question 45
In AJMM, metals masks can be applied to the workpiece by electroplating.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
In order to combine the low erosion rate of a metal, and the high resolution of a lithographic process, a metal mask can be applied to the target by electroplating. Copper is used by this method, while Zinc mask can be made by electro-forming.
Question 46
In AJMM, the powder is fed _____
A. through air stream
B. through a water pipe
C. along with a gel, which improves the adhesion between particles
D. in the form of batches
View Answer
Answer: Option A
Explanation:
The powder is fed through the air stream from a pressurized reservoir through an orifice and mixing chamber. The system utilizes an oscillating valve that splits the operation cycle into two halves.
Question 47
In AJMM, the substrate has to be shielded by a mask.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
In AJMM, the substrate has to be shielded by a wear resistant mask that is patterned with the desired contour. The mask determines the accuracy of the dimensions in the plane of the desired structure.
Question 48
In AJMM, there is initial weight gain in the workpiece.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Especially at normal impact angle, particles tend to embed in the material, resulting in an initial gain in weight of the specimen. After this incubation time steady-state erosion is established and mass loss from the eroded material is proportional to the amount of abrasive particles.
Question 49
In AJMM, workpiece is exposed to abrasive action of the particles.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
It employs a mixture of a fluid (air or gas) with abrasive particles. In contrast to direct blasting, the surface is exposed completely to the erosive action of the particle beam. Hence, before processing, the substrate material has to be partially shielded by applying an erosion resistant mask.
Question 50
In AWJM of ductile materials, material is mainly removed by _____ impact by abrasive particles.
A. low angle
B. 50o —60o
C. 65o —70o
D. 70o —82o
View Answer
Answer: Option A
Explanation:
Mechanism of material removal in machining with water jet and abrasive water jet is rather complex. In AWJM of ductile materials, material is mainly removed by low angle impact by abrasive particles leading to ploughing and micro cutting.
Question 51
In AWJM, mixing process takes place in _____
A. intensifier
B. mixing table
C. mixing chamber
D. mixing line
View Answer
Answer: Option C
Explanation:
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.
Question 52
In case of AWJM of brittle materials, the material is removed due to crack formation.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
In case of AWJM of brittle materials, other than the above two models, material would be removed due to crack initiation and propagation because of brittle failure of the material.
Question 53
In case of ductile materials, plastic deformation starts when yield strength is exceeded.
A. TRUE
B. FALSE
View Answer
Answer: Option A
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.
Question 54
In fluidized bed powder spray system, the air flow from the bottom of the reservoir creates_____
A. pressure in the system
B. a cloud of powder particles
C. vacuum in the system
D. high turbulence to increase the effectiveness
View Answer
Answer: Option B
Explanation:
In this system, upward high-speed air flow from the bottom of the reservoir through the powder bed created a cloud of suspended particles. Some of which settled into a collection funnel at the top of the reservoir that is connected to the air stream leading to the nozzle.
Question 55
In powder feeding systems, powder bridging, compaction, and agglomeration are desirable.
A. TRUE
B. FALSE
View Answer
Answer: Option B
Explanation:
Introducing a vibrator to a screw system improve the steadiness of the powder feed But the improvement diminishes with fine, more cohesive materials such as zeolites and cement powders due to phenomena such as powder bridging, compaction, and agglomeration.
Question 56
In suspension AWJM, mixture of water and abrasive particles is pumped to high pressure.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
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.
Question 57
In the case of ductile materials, material is removed by plastic deformation.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
When ductile materials are machined by AJMM, the material is removed by plastic deformation and cutting wear, or plastic strain and deformation wear.
Question 58
Limitations in feature size are the major drawback of the metal masks.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The disadvantages of this mask type are the limitations in feature size (approximately 50 μm) and pattern constraints (circular patterns cannot be used because the inner side should be supported).
Question 59
Manufacturing of capillary electrophoresis chips has an application of which of the following process?
A. Ultrasonic machining
B. Chemical Milling
C. Abrasive jet machining
D. Electron beam machining
View Answer
Answer: Option C
Explanation:
The device consists of a glass chip which contains a single separation channel as well as an integrated conductivity detection cell. In contrast to most micro-fluidic glass devices, the channels are not wet etched in HF but machined by AJMM which allows the creation of micro-structures below 100μm, and additionally makes parallel holes machining at very low costs outside the clean room environment.
Question 60
Abrasive jet machined features have tapered sidewalls ranging from _____
A. 5—10˚
B. 22—28˚
C. 15—30˚
D. 18—26˚
View Answer
Answer: Option D
Explanation:
Unlike vertical side walls produced by ultrasonic machining, abrasive blasting machined features have tapered sidewalls ranging from 18 to 26˚, depending on several factors.
Question 61
Abrasive particles are suspended in the carrier gas.
A. TRUE
B. FALSE
View Answer
Answer: Option A
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.
Question 62
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
View Answer
Answer: Option D
Explanation:
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.
Question 63
Material removal in AJM of glass is around_____
A. 0.1 mm3/min
B. 15 mm3/min
C. 15 mm3/s
D. 1500 mm3/min
View Answer
Answer: Option B
Explanation:
Following are the limitations of AJMM;• MRR is rather low (around ~ 15 mm3/min for machining glass)• Abrasive particles tend to get embedded particularly if the work material is ductile• Tapering occurs due to flaring of the jet• Environmental load is rather high.
Question 64
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
View Answer
Answer: Option C
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.
Question 65
Material removal takes place in AJM due to _____
A. electrochemical action
B. mechanical impact
C. fatigue failure of the material
D. sparking on impact
View Answer
Answer: Option B
Explanation:
In Abrasive Jet Machining (AJM), abrasive particles are made to impinge on the work material at a high velocity. The high velocity abrasive particles remove the material by micro-cutting action as well as brittle fracture of the work material.
Question 66
Maximum possible aspect ratio in AJMM is_____
A. 1:2
B. 1.5:3
C. 2:1
D. 3:1
View Answer
Answer: Option D
Explanation:
In AJMM, maximum aspect ratio is 3:1 (Thickness: Diameter). Therefore, its applications are restricted to brittle materials because of low MRR in case of ductile materials.
Question 67
Mechanical properties of powder are influenced by _____
A. humidity
B. carrier gas
C. air velocity
D. type of mask used
View Answer
Answer: Option A
Explanation:
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.
Question 68
Monolithic suspended micro-structure in glass was realized using _____
A. oblique AJMM
B. ion beam technique
C. photo chemical technique
D. laser beam technique
View Answer
Answer: Option A
Explanation:
Complex three-dimensional and monolithic suspended microstructure in glass was realized using normal and oblique AJMM. By controlling the under etching induced by oblique AJMM blasting, millimetrer high microstructure single as scan be fabricated with an aspect ratio of 5:10, as well as free-standing monolithic 100-μm-wide structures, suspended over many millimeters.
Question 69
Mounting a variable speed rotary electric mixer above the reservoir can reduce powder compaction.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
In order to reduce powder compaction in the reservoir of the pressurized powder feed system, the system can be modified by mounting a variable speed rotary electric mixer above the reservoir with the shaft passing through a pressure-seal bearing that had been mounted into the reservoir cap.
Question 70
Movement of powder leads to stratification.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
It is well known that the movement of powder leads quickly to stratification and the creation of gradient of particle size and/ or shape. Such problems result in alteration of the powder mass flow rate during the course of AJMM experiments.
Question 71
MRR increases with abrasive flow rate increase.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
As abrasive flow rate increases, then the number of abrasive particles cutting the material also increases there by increasing Material removal rate (MRR).
Question 72
Photo-resists are _____ materials.
A. photogenic
B. photosensitive
C. photo-dissociate
D. photo-emissive
View Answer
Answer: Option B
Explanation:
Photo-resists are photo-sensitive materials. There are two types of photo-resists; positive and negative. The major drawback is that it needs Expensive equipment to prepare the mask.
Question 73
Performance of the AJMM process is dependent on the quality of the mask.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The quality of the mask influences the performance of AJMM. The main qualification for a good mask material is a low erosion rate. It also requires the capability of an accurate and easy pattern transfer, and the ability to retain the irresistance in discontinuous layers.
Question 74
Positive resists are formed when resist is exposed to UV light.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
For positive resists, the resist is exposed with UV light wherever the underlying material is to be removed. In these resists, exposure to the UV light changes the chemical structure of the resist so that it becomes more soluble in the developer.
Question 75
Powder compaction is desirable during AJMM.
A. TRUE
B. FALSE
View Answer
Answer: Option B
Explanation:
This phenomenon usually happens in the pressurized powder feed system. The powder is firmly compacted during the course of AJMM process. Due to this cavities are formed in the supply line, which is not at all desirable.
Question 76
Powder feed control of micro-blasting systems is divided into _____
A. 2
B. 3
C. 4
D. 5
View Answer
Answer: Option A
Explanation:
The powder feed control of two micro-blasting systems is considered into two types.• Pressurized powder feed system• Fluidized bed powder spray system.
Question 77
Powder flowability is affected by particle size and surface texture.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Powder flowability and compatibility are greatly influenced by particle size, size distribution, moisture content, and surface texture.
Question 78
Powder mass flow rate is controlled by _____________
A. regulating the air flow rate
B. nozzle diameter
C. size of the mixing chamber
D. cycle time
View Answer
Answer: Option A
Explanation:
Limited control of the powder mass flow rate is possible by regulating the air flow rate through the reservoir, by changing the orifice bypass, and the size of the reservoir orifice.
Question 79
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
View Answer
Answer: Option C
Explanation:
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.
Question 80
Refilling the reservoir is another way to get good results in AJMM.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
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.
Question 81
Relative humidity can affect adhesive forces.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The relative humidity of stored air can have a major influence on the adhesive forces at the interface of particles. But one of the major difficulties with the AJMM process is the handling of very fine abrasive particles.
Question 82
SiC is used as abrasive for harder materials.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Following are the materials used as abrasive in AJMM:1) Al2O3: For cleaning, cutting and de-burring2) SiC: Similar applications as Al2O3 but for harder work materials3) Glass beads: Matte finish4) Sodium Bicarbonate: Cleaning, cutting and de-burring of soft material.
Question 83
Striation factor is an important product quality parameter in AWJM.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
In AWJM, following are the important product quality parameters;• striation formation• surface finish of the kerf• tapering of the kerf• burr formation on the exit side of the kerf.
Question 84
Structures with high aspect ratios are possible with _____
A. photo-resist material
B. metals
C. elastomers
D. porous silicon
View Answer
Answer: Option B
Explanation:
Stainless steel masks are very suitable for high particle velocities and fast machining operations. Structures with high aspect ratios are achievable due to the low erosion rate of steel. Attention has been paid to the adhesive layer, which should not only stick the two materials together but also avoid under etching.
Question 85
SU-8 is most commonly used negative resist.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Negative resists behave in just the opposite manner as that of the positive resists. Epoxy-based SU-8 is one of the good negative resists. It is able to provide features with high aspect ratios (>10) with UV-lithography.
Question 86
The choice of abrasive varies with the type of machining.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The choice of abrasive particles depends on the type of machining operation. The abrasives should have a sharp and irregular shape for better performance.
Question 87
The degree of powder stratification is not affected by_____
A. mixing time
B. powder mass flow rate
C. air flow velocity
D. diameter of the funnel in the mixing chamber
View Answer
Answer: Option A
Explanation:
Powders stratify as they flow and it depends on particle size. Mixing time did not appear to affect the degree of particle stratification significantly.
Question 88
The erosion mechanism of rubber-like materials is same as that of brittle materials and ductile materials.
A. TRUE
B. FALSE
View Answer
Answer: Option B
Explanation:
The erosion mechanism of rubber-like materials differs essentially from that of brittle materials or ductile materials. No lateral cracks are formed in elastomers as found in brittle materials. Neither do any evidence of cutting or ploughing wear as found in metals.
Question 89
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
View Answer
Answer: Option A
Explanation:
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 factorR= loading factor= mass flow rate of abrasive/ mass flow rate of waterVwj= velocity of water jet.
Question 90
The mask using SU8, _____ is applied as a micro-pattern for AJMM process.
A. SU6
B. SU7
C. SU8
D. SU9
View Answer
Answer: Option C
Explanation:
A passive micro-mixer with3-dimensional feature fabricated by AJMM process by employing photo-polymer as a mask on a glass slide target. The mask using SU8, a photo-sensitive polymer is applied as a micro-pattern for AJMM process. The fabrication process involved three glass target slides and conducted multi-masking processes with four different mask patterns.
Question 91
The mass flow rate of abrasive entering the chamber is independent of the amplitude of vibration of the sieve (in the mixing chamber).
A. TRUE
B. FALSE
View Answer
Answer: Option B
Explanation:
The abrasive particles enter the chamber from a hopper through a metallic sieve. The sieve is constantly vibrated by an electromagnetic shaker. The mass flow rate of abrasive (15 gm/min) entering the chamber depends on the amplitude of vibration of the sieve and its frequency. The abrasive particles are then carried by the carrier gas to the machining chamber via an electro-magnetic on-off valve.
Question 92
The mass loss of workpiece is proportional to_____
A. power supplied
B. nozzle diameter
C. amount of abrasive
D. carrier gas
View Answer
Answer: Option C
Explanation:
The mass loss of workpiece is proportional to the amount of abrasive.Mass loss = (Kρmv2)/(2H), where, K (> 2) is a dimensionless factor, m and v amount and velocity ofparticles, and ρ and H are density and hardness of the eroded material, respectively. The above relation is true for brittle erosion but not for softer materials (elastomers and some metals) due to time variant erosion behaviour.
Question 93
The mixing chamber is immediately followed by _____
A. intensifier
B. on-off valve
C. catcher
D. focussing tube
View Answer
Answer: Option D
Explanation:
The mixing chamber is immediately followed by the focussing tube or the inserts. The focussing tube is generally made of carbide materials.
Question 94
The operation cycle is activated when the entire system is pressurized.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The operation cycle is activated by a switch only after the entire system, including reservoir, has initially been pressurized by closing the nozzle end and opening the oscillating valve to the main air supply.
Question 95
The orifice is made of _____
A. iron
B. zinc
C. sapphire
D. graphite
View Answer
Answer: Option C
Explanation:
The orifices are typically made of sapphire. In commercial machines, the life of the sapphire orifice is typically around 100 – 150 hours.
Question 96
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
View Answer
Answer: Option A
Explanation:
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.
Question 97
The taper angle of the kerf can be_____ of the AWJ
A. reduced by increasing the cutting ability
B. increased by increasing the cutting ability of the
C. reduced by decreasing the cutting ability of the
D. taper angle is not a function of the cutting ability of the jet
View Answer
Answer: Option A
Explanation:
The taper angle of the kerf can be reduced by increasing the cutting ability of the AWJ. It can be said that the surface quality at the top of the kerf is rather good compared to the bottom part. At the bottom there is repeated curved line formation.
Question 98
The usability of the mask is affected by imaging accuracy.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Each material used for making mask, needs a sufficient erosion resistance related to the substrate especially at normal blast angles. Furthermore, the achievable imaging accuracy determines the usability of a mask and minimum achievable features size.
Question 99
There are _____ different types of suspension abrasive water jet (AWJ).
A. 2
B. 3
C. 5
D. 7
View Answer
Answer: Option B
Explanation:
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.
Question 100
There are variations in the powder mass flow rate due to_____
A. powder compaction
B. size of the powder particles
C. air flow rate inside the mixing chamber
D. pressure build-up in the chamber
View Answer
Answer: Option A
Explanation:
Due to powder compaction, cavities often form in the vicinity of the orifice, likely causing variations in the powder mass flow rate as the cavity walls collapse randomly, injecting bursts of powder into the nozzle.
Question 101
There is appearance of the dimples during AJM.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Appearance of the dimples during AJM for 10s. for various machining sets of abrasives and ceramic materials. Properties of the dimples do not differ in terms of the removed volume, but also the roughness of the struck face for different combination of abrasive particles and workpiece material.
Question 102
There should be supersonic air flow velocity in the nozzle.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The following requirements have to be fulfilled on nozzle design:1) Pressure-less constant feeding system2) Supersonic air flow velocity in the nozzle3) Homogeneous dispersion of abrasive particles over the width of the nozzle4) Long life time of the nozzle (It has to withstand the erosive action of abrasive particles).
Question 103
This method is used for _____
A. making finished surfaces
B. thread finishing
C. making grooves
D. cutting
View Answer
Answer: Option C
Explanation:
This method is used for making accurate shallow holes or grooves, and, with the use of masks, patterns on target material.
Question 104
To apply metal mask plate for AJMM, magnetic clamps are used.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Metals having low erosion rates are suitable for making masks for AJMM. To apply metal mask plate for AJMM, it can be magnetically clamped directly to the target or by introducing an intermediate protection/ adhesion layer.
Question 105
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
View Answer
Answer: Option A
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.
Question 106
Tungsten carbide is used because of its abrasive resistance.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
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.
Question 107
Vibratory feeder or toothed belt feeder as used to measure the quantity of the abrasive particles before mixing.
A. TRUE
B. FALSE
View Answer
Answer: Option A
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.
Question 108
Vibratory or screw feeding systems are another approach to control the powder mass flow rate.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Other approaches to the control of powder mass flow rate include vibratory and screw or auger feeding in which the powder is fed to the conveying air through an auger (similar to the tool used for boring earth).
Question 109
Water Jet Machining (WJM) and Abrasive Jet Micromachining (AJMM or AWJM) can be achieved using how many different approaches?
A. 10
B. 5
C. 7
D. only one approach is there
View Answer
Answer: Option C
Explanation:
WJM and AWJM can be achieved using different approaches and methodologies as enumerated below: WJM – Pure WJM – with stabilizer AWJM – entrained – three phase – abrasive, water and air AWJM – suspended – two phase – abrasive and water Direct pumping Indirect pumping Bypass pumping.
Question 110
Which of the following assumption is true about AJMM?
A. Abrasives are irregular in shape.
B. The abrasive particles are characterised by the mean grit diameter
C. Brittle materials are considered to fail due to fatigue
D. The kinetic energy of the abrasives is partially lost in overcoming the friction in the nozzle
View Answer
Answer: Option B
Explanation:
Modelling in AJMM is done with the following assumptions:(i) Abrasives are spherical in shape and rigid. The particles are characterised by the mean grit diameter(ii) The kinetic energy of the abrasives are fully utilized in removing material(iii) Brittle materials are considered to fail due to brittle fracture and the fracture volume is considered to be hemispherical with diameter equal to chordal length of the indentation(iv) For ductile material, removal volume is assumed to be equal to the indentation volume due to particulate impact.
Question 111
Which of the following have a low erosion rate?
A. Ductile materials
B. Malleable materials
C. Hardened materials
D. Low melting point materials
View Answer
Answer: Option A
Explanation:
Ductile materials, like metals, have a low erosion rate, especially at perpendicular impact. This makes them suitable to be used as a mask material. It can be used by means of a thin plate (e.g. stainless-steel).
Question 112
Which of the following is commonly used as a carrier gas in AJMM?
A. O2
B. He2
C. N2
D. H2
View Answer
Answer: Option C
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.
Question 113
Which of the following is correct about AJMM?
A. It requires no cleaning
B. It has very high accuracy
C. It tends to pollute the environment
D. The nozzle has very less wear
View Answer
Answer: Option C
Explanation:
Following are the limitations of AJMM;• Sometimes additional cleaning operation is required to machine parts to remove abrasives from the surface• Machining accuracy is poor• Nozzle wear rate is high• The process tends to pollute the environment.
Question 114
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
View Answer
Answer: Option B
Explanation:
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.
Question 115
Which of the following is not a part of the cutting head?
A. Orifice
B. Mixing chamber
C. Focussing tube
D. Accumulator
View Answer
Answer: Option D
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.
Question 116
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
View Answer
Answer: Option A
Explanation:
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.
Question 117
Which of the following is not true about entrained type AJWM?
A. Sapphires is used for orifice
B. Pressure range = 2500-4000 bars
C. Impact angle < 50o
D. Depth of cut reached is 1—250 mm
View Answer
Answer: Option C
Explanation:
The general domain of parameters in entrained type AWJ machining system is given below:• Orifice – Sapphires – 0.1 to 0.3 mm• Focussing Tube – WC – 0.8 to 2.4 mm• Pressure – 2500 to 4000 bar• Abrasive – garnet and olivine – #125 to #60• Abrasive flow – 0.1 to 1.0 Kg/min• Stand-off distance – 1 to 2 mm• Machine Impact Angle – 60o to 90o• Traverse Speed – 100 mm/min to 5 m/min• Depth of Cut – 1 mm to 250 mm.
Question 118
Which of the following is true about AJMM?
A. It is a low cost method
B. It is toxic towards the environment
C. It is hazardous to human health
D. It is not capable of anisotropic machining
View Answer
Answer: Option A
Explanation:
Advantages of AJM:(1) low capital and operating costs,(2) environment-friendly process,(3) no major health hazards, and(4) ability to machine anisotropic and suspended structures on the same substrate.
Question 119
Which of the following is true about AJMM?
A. It is a high maintenance process
B. It is a time consuming process
C. Depths upto few microns are not possible
D. Multiple features can be machined in one operation
View Answer
Answer: Option D
Explanation:
Following are the few advantages of AJMM;• Minimal tooling cost• Quick turn-around for prototyping and development work• Feature sizes down to 100 μm and featured depths to just a few microns are possible• Multiple features can be machined in one operation.
Question 120
Which of the following is true about AWJM?
A. At the bottom of the kerf, the material removal is by low angle impact of the abrasive particles
B. At the top of the kerf, the material removal is by low angle impact of the abrasive particles
C. At the top of the kerf, the material removal is by plastic failure
D. Striation formation occurs due to excess use of abrasive particles
View Answer
Answer: Option B
Explanation:
At the top of the kerf, the material removal is by low angle impact of the abrasive particle; whereas at the bottom of the kerf it is by plastic failure. Striation formation occurs due to repeated plastic failure.
Question 121
Which of the following is true about powder flow rate in fluidized bed powder system and other systems?
A. First has higher flow rate the other
B. First has lower flow rate the other
C. There is no relation as it is dependent on nozzle parameters
D. Powder flow rate in is not a measurable parameter
View Answer
Answer: Option A
Explanation:
Fluidized bed powder spray is operated at significantly higher powder mass flow rate than the pressurized powder feed system. The mass flow rate could be regulated to some extent by changing the diameter of the funnel.
Question 122
Which of the following is used as abrasive in AJMM?
A. Al2O3
B. HNO3
C. FeC
D. CaCO3
View Answer
Answer: Option A
Explanation:
Abrasive used in AJMM is:• Material – Al2O3 / SiC / glass beads• Shape – irregular / spherical• Size – 10 ~ 50 μm• Mass flow rate – 2 ~ 20 gm/min.
Question 123
Which of the following issues is not of much concern in AWJM?
A. Coolant recovery
B. Abrasive recovery
C. Spent water disposal
D. Chip recovery
View Answer
Answer: Option A
Explanation:
Nowadays, every manufacturing process is being re-evaluated in terms of its impact on the environment. The environmental issues relevant to AWJM are,• water recycling• spent water disposal• chip recovery• abrasive recovery and reuse.
Question 124
Which of the following materials is used for focusing tubes?
A. Chromium
B. Titanium
C. Nickel
D. Tungsten
View Answer
Answer: Option D
Explanation:
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.
Question 125
Which of the following technology is used for ferrite substrates?
A. Powder coating
B. Powder blasting
C. Sintering
D. Continuous powder processing
View Answer
Answer: Option B
Explanation:
Another possible application of the powder blasting technology is the micro-structuring of ferrite substrates. In this case, powder blasting proved to be not only the most appropriate but also a very fast and cheaper way to get such structures.