Category: Manufacturing Engineering Objective Questions

Manufacturing Engineering Multiple Choice Questions on “Metal Casting Defects”.

1. The major defects of casting are __________
a) gas defects
b) shrinkage cavities
c) molding material defects
d) all of the mentioned
Answer: d
Clarification: Following are the major defects, which are likely to occur in casting:
i) gas defects
ii) shrinkage cavities
iii) molding material defects
iv) pouring metal defects
v) mold shift.

2. The defects caused by trapping a gas in molten metal or by mold gases while pouring the melt is known as?
a) Gas defects
b) Shrinkage cavities
c) Molding material defects
d) Pouring defects
Answer: a
Clarification: Shrinkage cavities are caused by liquid shrinkage occurring during the solidification of the casting while gas defects are a condition existing in a casting caused by the trapping of gas in the molten metal or by mold gases evolved during the pouring of the casting.

3. The causes of gas defects are ___________
a) metal contains gas
b) mold is too hot
c) poor mold burnout
d) all of the mentioned
Answer: d
Clarification: The lower gas-passing tendency of the mold, which may be due to lower venting, lower permeability of the mold or improper design of the casting. The lower permeability is caused by finer grain size of the sand, high percentage of clay in mold mixture, and excessive moisture present in the mold.
Metal contains gas
Mold is too hot
Poor mold burnout.

4. The defects caused by liquid shrinkage during the solidification of the casting?
a) gas defects
b) shrinkage cavities
c) molding material defects
d) hot tears
Answer: b
Clarification: Shrinkage cavities are caused by liquid shrinkage occurring during the solidification of the casting while gas defects are a condition existing in a casting caused by the trapping of gas in the molten metal or by mold gases evolved during the pouring of the casting.

5. In casting, which of the following are not material defects?
a) cut and washes
b) metal penetration
c) fusion
d) hot tears
Answer: d
Clarification: The defects in this category are cuts and washes, metal penetration, fusion, and swell.

6. The defect caused when the melt is unable to fill the mold cavity completely and thus leaves cavities is termed as?
a) cold shut
b) misrun
c) hot tear
d) porosity
Answer: b
Clarification: A mis-run is caused when the metal is unable to fill the mold cavity completely and thus leaves unfilled cavities and a cold shut is caused when two streams while meeting in the mold cavity, do not fuse together properly thus forming a discontinuity in the casting.

7. The defect caused when two streams do not fuse together (while melting), thus forming discontinuity in casting is termed as?
a) cold shut
b) misrun
c) hot tear
d) porosity
Answer: a
Clarification: A mis-run is caused when the metal is unable to fill the mold cavity completely and thus leaves unfilled cavities and a cold shut is caused when two streams while meeting in the mold cavity, do not fuse together properly thus forming a discontinuity in the casting.

8. A casting defect which occurs near the ingates as rough lumps on the surface of a casting is?
a) Shift
b) Sand wash
c) Swell
d) Hot tear
Answer: b
Clarification: Swell is caused under the influence of metallostatic forces, the mold wall may move back causing a swell in the dimension of the casting whereas Sand wash is a casting defect which occurs near the ingates as rough lumps on the surface of a casting.

9. A casting defect which occurs due to improper venting of sand is known as?
a) Cold shuts
b) Blow holes
c) Shift
d) Hot tear
Answer: c
Clarification: The mold shift defect occurs when cope and drag or molding boxes have not been properly aligned and a cold shut is caused when two streams while meeting in the mold cavity.

10. Scabs are casting defects which?
a) result in a mismatch of the top and bottom parts of a casting
b) result near the ingates as rough lumps on the surface of a casting
c) occur as rough and irregular projections on the surface of the casting
d) occur as smooth and regular projections on the surface of the casting
Answer: c
Clarification: A casting defect which occurs near the ingates as rough lumps on the surface of a casting is sand wash and scabs are casting defects which occur as rough and irregular projections on the surface of the casting.

Manufacturing Science Puzzles on “Heat Transfer-2”.

1. Ratio of rate of heat conduction to the rate of internal energy storage is in solid is known as?
a) Biot number
b) Drag coefficient
c) Eckert number
d) Fourier number
Answer: d
Clarification: Fourier number is the ratio of heat conduction to the rate of heat storage. The significance of Fourier number is 1. It signifies the degree of penetration of heating or cooling effect, 2. It is a measure of heat conducted through a body relative to heat stored.

2. Ratio of pressure drop for internal flow through ducts is known as?
a) Friction factor
b) Grashof number
c) Colburn factor
d) Nusselt number
Answer: a
Clarification: Friction factor (µ) is defined as the ratio between the force required to move a section of pipe and the vertical contact force applied by the pipe on the seabed, in simpler terms, it is the ratio of pressure drop for internal flow though ducts.

3. Ratio of buoyancy to viscous forces is known as?
a) Prandtl number
b) Grashof number
c) Colburn factor
d) Nusselt number
Answer: b
Clarification: Grashof number in natural convection is analogous to the Reynolds number is forced convection. Grashof number indicates the ratio of the buoyancy force to the viscous force. Higher Gr number means increased natural convection flow.

4. Which of the following is known as the dimensionless heat transfer coefficient?
a) Friction factor
b) Grashof number
c) Colburn factor
d) Weber number
Answer: c
Clarification: Colburn factor obtained from the Reynold-Colburn analogy relates to the local skin friction coefficient (from fluid mechanics) to the local convective heat transfer coefficient.

5. Which of the following is known as the dimensionless heat transfer coefficient?
a) Friction factor
b) Grashof number
c) Nusselt number
d) Prandtl number
Answer: c
Clarification: Nusselt number is a dimensionless number and it is defined as the ratio of convective heat flux to the conductive heat flux (where fluid is in rest). Convection in fluid = conduction in fluid + advection in fluid (occurs due to motion of fluid). So, practically we can understand it as a comparison of heat taken by fluid due to moving fluid and heat taken by a static fluid when flowing over a heated plate (or inside a pipe).

6. Ratio of convection heat transfer to conduction is known as?
a) Friction factor
b) Grashof number
c) Colburn factor
d) Nusselt number
Answer: a
Clarification: The Nusselt number is the ratio of convective to conductive heat transfer across a boundary.
Nu = (frac{hl}{k}), where, h = heat transfer coefficient, l = characteristic length and k = thermal conductivity.

7. Product of Prandtl number and Reynolds number is also known as?
a) Peclet number
b) Prandtl number
c) Rayleigh number
d) Biot number
Answer: a
Clarification: Peclet number is the product of Prandtl number and Reynolds number, in other sense, it is the ratio of the heat transfer by convection to the heat transferred by conduction. So, you can consider a pipe with some wall thickness. The wall conducts heat to the fluid. While the heat can also be carried away by the fluid in motion which is called as advection. If the advection term is dominant, then the Peclet number is going to large and thus the hat transfer from the wall is of less importance. Conversely, the heat transfer form the wall to the fluid can be of higher importance in the case of a smaller Peclet number.

8. Ratio of molecular diffusivity to thermal diffusivity is also known as?
a) Biot number
b) Prandtl number
c) Rayleigh number
d) Biot number
Answer: b
Clarification: Prandtl number as explained by others here, is a dimensionless number, which is the ratio of molecular diffusivity of momentum to molecular diffusivity of heat. It shows the relative thickness of the velocity boundary layer to the thermal boundary layer.

9. Product of Grashof and Prandtl is known as?
a) Peclet number
b) Biot number
c) Rayleigh number
d) Reynolds number
Answer: c
Clarification: Rayleigh number is the product of Grashof and Prandtl number.

10. Ratio of inertia to viscous forces is known as?
a) Stanton number
b) Prandtl number
c) Rayleigh number
d) Reynolds number
Answer: d
Clarification: The Reynolds number is the ratio of inertial forces to viscous forces. The Reynolds number is a dimensionless number used to categorize the fluids systems in which the effect of viscosity is important in controlling the velocities or the flow pattern of a fluid.

To practice puzzles on all areas of Manufacturing Science,

Manufacturing Processes Multiple Choice Questions on “Electromagnetic Forming”.

1. Which of the following is not used in electromagnetic forming process?
a) A capacitor bank
b) A forming coil
c) A foeld shaper
d) Stiffening ribs
Answer: d
Clarification: The EMF process uses a capacitor bank, a forming coil, a field shaper, and an electrically conductive workpiece to create intense magnetic fields that are used to do the useful work.

2. Which of the following is true about EMF process?
a) Intense electric field is produced using capacitors and coils
b) Heavy current is made to flow through the workpiece
c) Intense magnetic field is produced for few microseconds
d) Principle of electromagnetic induction is used to pre-heat the workpiece
Answer: c
Clarification: In EMF process, very intense magnetic field is produced by the discharge of capacitor bank into a forming coil, which lasts for only a few microseconds.

3. In EMF process, eddy currents are induced in a conductive workpiece.
a) True
b) False
Answer: a
Clarification: In EMF process, eddy currents are induced in the workpiece which is placed close to the coil. When these eddy currents interact with the magnetic field, cause mutual repulsion between the workpiece and the forming coil due to which workpiece is stressed beyond its yield strength, resulting in permanent deformation.

4. In EMF process, forming pulse rate is kept as high as possible
a) True
b) False
Answer: b
Clarification: As the workpiece surface moves inward under the influence of the pressure generated by the repulsive force, it absorbs energy from the magnetic field. To apply most of this available energy to forming, and to reduce energy loss due to permeation of the workpiece material, the forming pulse is kept short. In most forming aplications, pulses have a duration between 10 to 100 seconds.

5. For EMF process, resistivity of the workpiece material should be _____________
a) greater than 10 micro-ohm-cm
b) less than 8 micro-ohm-cm
c) less than 15 micro-ohm-cm
d) in the range 10-20 micro-ohm-cm
Answer: c
Clarification: The efficiency of the magnetic pulse forming depends upon the resistivity of the metal being formed. For good results, the resistivity of the material should be less than 15 micro-ohm-cm.

6. Which of the following is not true about EMF?
a) Leaves tool marks
b) Does not require lubrication
c) Does not require any cleanup
d) It is primarily applied in the forming of good conducting materials
Answer: a
Clarification: In EMF pressure is applied by a magnetic field, unlike other mechanical processes in which a tool contacts a workpiece. Therefore, it requires no lubrication, leaves no tool marks and requires no cleanup after forming.

7. Springback effect of the workpiece material is eliminated in EMF process.
a) True
b) False
Answer: a
Clarification: In EMF, the material is loaded into its plastic region, resulting in permanent deformation, so that the springback associated with mechanical processes is vertually eliminated because there is no mechanical contact.

8. The maximum pressure applied by the compression coil is approximately _______________
a) 300 MPa
b) 340 MPa
c) 375 MPa
d) 400 MPa
Answer: b
Clarification: The maximum pressure that can be applied by standard compression coils is approximately 340 MPa, thus process is restricted to a relatively thin-wall tube or sheet products.

9. Electromagnetic forming is rarely used to form tubular shapes.
a) True
b) False
Answer: b
Clarification: Electromagnetic forming is chiefly used to expand, compress, or form tubular shapes. It is occasionally used to form flat sheet, and it is often used to combine several forming and assembly operations into a single step.

10. The die used in electromagnetic process should be made of material with _________________
a) high electrical conductivity
b) low electical conductivity
c) low ductility
d) high creep resistance
Answer: b
Clarification: The die used in the electromagnetic process should be made of low electrical conductivity to minimize the magnetic cushion effect. Dies are generally made of steel or epoxy resin.

11. The EMF process allows increased ductility for______________ alloys.
a) Chromium – molybdenum
b) aluminium
c) nickel
d) chromium – mangnese
Answer: b
Clarification: The EMF process allows increased ductility for certain aluminium alloys because of the lack of mechanical stress and friction normally encountered with mechanical processes.

12. Tooling for EMF process is relatively inexpensive.
a) True
b) False
Answer: a
Clarification: The machine and the work coils required in EMF process can be viewed as general-purpose tooling. Therefore it can be said that the tooling for this process is inexpensive.

13. EMF is primarily used for which of the following material?
a) Silver
b) High carbon steel
c) Chromium alloys
d) Martensitic steel
Answer: a
Clarification: This process is primarily applied in the forming of good conducting materials such as copper, aluminium, silver and low carbon steel. It can also be used to form a poor conductor like stainless steel.

Manufacturing Processes Multiple Choice Questions on “Electrochemical Etching – 11”.

1. mpSi and μpSi structures are used to develop distributed Bragg reflectors.
a) True
b) False
Answer: a
Clarification: Multilayered mpSi and μpSi structures can be used to develop distributed Bragg reflectors (DBR). Basically, a pSi-based DBR structure consists of multiple layers of pSi with different porosity levels and thicknesses.

2. The structure of the mpSi- or μpSi-based DBR affects their refractive indices.
a) True
b) False
Answer: a
Clarification: The interfaces between two consecutive layers of dielectric material reflect incident light due to the effective refractive index contrast. Therefore, constructive light interference can be engineered by designing the structure of the mpSi- or μpSi-based DBR (i.e. by designing the porosity and thickness of each layer).

3. DBR structures based on_____ can be implemented into Fabry–Pérot filters.
a) mpSi
b) pSi
c) SiO₂
d) graphite
Answer: a
Clarification: DBR structures based on mpSi and μpSi can be implemented into Fabry–Pérot filters, also called optical microcavities, which are composed of two parallel DBRs with a space layer of different effective refractive index in between.

4. The effective optical thickness of the space layer is taken equal to _____
a) frequency
b) wavelength
c) amplitude
d) product of refractive index and density of the material
Answer: b
Clarification: The effective optical thickness of the space layer (i.e. product between the physical thickness and the effective refractive index of the layer) is typically engineered as the wavelength of the incident light or half of it.

5. Microcavities based on mpSi and μpSi can be used to develop optical pass-band filters.
a) True
b) False
Answer: a
Clarification: The reflectivity spectrum of microcavities based on mpSi and μpSi shows a narrow pass-band centred at the wavelength where the light is reflected with the highest intensity. Therefore, the structural design of microcavities based on mpSi and μpSi makes it possible to develop optical pass-band filters and sensors.

6. The effective refractive index of mpSi and μpSi are modulated to produce rugate filters.
a) True
b) False
Answer: a
Clarification: If the current density profile is modified in a sinusoidal manner in the course of the electrochemical etching, the effective refractive index of mpSi and μpSi can be modulated to produce rugate filters, which are another type of optical structure used in optoelectronic and sensing applications.

7. Which of the following is one of the important optical property of mpSi and μpSi structure?
a) Photo-conductivity
b) Stimulated emission
c) Photo-luminescence
d) Photo-emissivity
Answer: c
Clarification: Another important optical property of mpSi and μpSi structure is their photo-luminescence (PL), which has been extensively studied during the last decades. Bulk crystalline silicon presents a very weak PL peak at 1100 nm.

8. The discovery of bright red-orange photoluminescence was the origin for the use of mpSi materials for optoelectronic devices.
a) True
b) False
Answer: a
Clarification: Photo-luminescence limits the use of silicon to develop optoelectronic devices, which are aimed at converting light into electricity (e.g. photodetectors, solar cells, etc.). However, the discovery of bright red-orange photoluminescence and the identification of confinement effects in the absorption spectrum of pSi were the starting point of a flood of studies focused on the development of optoelectronic devices based on mpSi and μpSi structures such as switches, displays and lasers.

9. PL properties of mpSi and μpSi structures depend on _____
a) temperature
b) etching conditions
c) light intensity
d) refractive index
Answer: b
Clarification: PL properties of mpSi and μpSi structures depend on the etching conditions. The different PL bands in pSi can be tuned from blue-green, red-orange to infrared by adjusting the etching conditions.

10. An increment of the current density can lead to blue shifts in the PL peak of mpSi.
a) True
b) False
Answer: a
Clarification: An increment of the current density, a decrease in the concentration of HF or an increase of the illumination intensity lead to blue shifts in the PL peak of mpSi and μpSi. In addition, it is worth stressing that PL in pSi is dependent on the porosity level as well as the doping density.

Manufacturing Processes written test Questions & Answers on “Abrasive Jet Micromachining – 7”.

1. 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
Answer: a
Clarification: 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.

2. During first half cycle, mixing chamber is at ___________
a) atmospheric pressure
b) 2 atm
c) 2 bar
d) vacuum
Answer: a
Clarification: 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.

3. 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
Answer: a
Clarification: 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.

4. 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
Answer: b
Clarification: 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.

5. 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
Answer: a
Clarification: 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.

6. The powder mass flow rate is dependent on_____
a) fineness of powder particles
b) type of mask used during the process
c) carrier gas
d) amount of powder
Answer: d
Clarification: The powder mass flow rate is dependent on the amount of powder in the reservoir. The powder mass flow rate obtained by fluidized system decreased rapidly as the powder in the reservoir chamber is consumed.

7. Powder compaction is desirable during AJMM.
a) True
b) False
Answer: b
Clarification: 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.

8. 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
Answer: a
Clarification: 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.

9. Mounting a variable speed rotary electric mixer above the reservoir can reduce powder compaction.
a) True
b) False
Answer: a
Clarification: 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.

10. 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
Answer: a
Clarification: Powders stratify as they flow and it depends on particle size. Mixing time did not appear to affect the degree of particle stratification significantly.

To practice all written questions on Manufacturing Processes,

Manufacturing Processes Multiple Choice Questions on “Electron Beam Machining – 1”.

1. Mechanism of material removal in Electron Beam Machining is due to _____
a) mechanical erosion due to impact of high of energy electrons
b) chemical etching by the high energy electron
c) sputtering due to high energy electrons
d) melting and vaporisation due to the thermal effect of impingement of high energy electron
Answer: d
Clarification: EBM is typically used with higher power density to machine materials. The mechanism of material removal is primarily by melting and rapid vaporisation due to intense heating by the electrons and laser beam respectively.

2. Electron beam machining is a/an _____ process
a) adiabatic
b) thermal
c) iso-thermal
d) isentropic
Answer: b
Clarification: Electron Beam Machining (EBM) is a thermal process considering the mechanisms of material removal. However electrical energy is used to generate high-energy electrons in case of Electron Beam Machining (EBM).

3. Electron beam machining is carried out in _____
a) high pressure vessel
b) thermally insulated area
c) vacuum
d) in a room at atmospheric pressure
Answer: c
Clarification: Electron Beam Machining is required to be carried out in vacuum. Otherwise, the electrons would interact with the air molecules, thus they would lose their energy and cutting ability.

4. During EBM _____ is kept under vacuum.
a) electron gun
b) whole setup
c) the workpiece
d) laser generation setup
Answer: c
Clarification: The workpiece to be machined is located under the electron beam and is kept under vacuum. The high-energy focused electron beam is made to impinge on the workpiece with a spot size of 10 – 100 μm.

5. As the electrons strike the work material _____
a) heat energy is converted to kinetic energy
b) atomic energy is converted to heat energy
c) kinetic energy is converted to heat energy
d) electrical energy is converted to heat energy
Answer: c
Clarification: The kinetic energy of the high velocity electrons is converted to heat energy as the electrons strike the work material. Due to high power density instant melting and vaporisation starts and “melt – vaporisation” front gradually progresses.

6. The gun in EBM is used in _____ mode.
a) wave guide
b) biasing
c) pulsed
d) high intensity
Answer: c
Clarification: Unlike in Electron Beam Welding, the gun in EBM is used in pulsed mode. Holes can be drilled in thin sheets using a single pulse. For thicker plates, multiple pulses would be required. Electron beam can also be manoeuvred using the electromagnetic deflection coils for drilling holes of any shape.

7. Which of the following is not a function of electron beam gun?
a) generation of electrons
b) accelerating the electrons
c) focusing the beam
d) absorbing the electron beam
Answer: d
Clarification: Electron beam gun is the heart of any electron beam machining facility. The basic functions of any electron beam gun are to generate free electrons at the cathode, accelerate them to a sufficiently high velocity and to focus them over a small spot size. Further, the beam needs to be manoeuvred if required by the gun.

8. ______ is used to make cathode for electron beam gun.
a) Aluminium
b) Rubidium
c) Molybdenum
d) Tantalum
Answer: d
Clarification: The cathode is generally made of tungsten or tantalum. Such cathode filaments are heated, often inductively, to a temperature of around 2500⁰C.

9. Heating to a high temperature leads to thermo-ionic emission.
a) True
b) False
Answer: a
Clarification: In EBM, temperature in the electron beam gun is around 2500⁰C. Such heating leads to thermo-ionic emission of electrons, which is further enhanced by maintaining a very low vacuum within the chamber of the electron beam gun.

10. In the electron beam gun, cathode cartridge is highly negatively biased.
a) True
b) False
Answer: a
Clarification: In the electron beam gun, cathode cartridge is highly negatively biased so that the thermo-ionic electrons are strongly repelled away from the cathode. This cathode is often in the form of a cartridge so that it can be changed very quickly to reduce downtime in case of failure.