Unconventional Machining Processes MCQ Quiz - Objective Question with Answer for Unconventional Machining Processes - Download Free PDF

Explanation:

Electron Beam Welding

• Electron Beam Welding is a fusion welding in which coalescence is produced by heating the workpiece due to impingement of the concentrated electron beam of high kinetic energy on the workpiece.
• As the electron beam impinges the workpiece the kinetic energy of the electron beam converts into thermal energy resulting in melting and even evaporation of the work material. 
• Electron beam welding joins metals by bombarding a specific confined area of the base metal with highvelocity electrons.
• It is performed in a vacuum without shielding gas to prevent the reduction of electron velocity. 
• Neither an electrode nor a filler rod is used.
• Electron beam welding is focused on the weld spot using the magnetic lens.

• It allows fusion welds of great depth with a minimum width because the beam can be focused and magnified.

Explanation:

Photo Etching Process

• Photo etching, also known as photochemical machining (PCM), is a process used to fabricate metal parts with intricate details by using photoresist and chemical etchants. The process involves the application of a photographic image onto a metal surface and subsequently etching away the exposed areas to create the desired pattern.
• In the photo etching process, a metal sheet is first cleaned and coated with a photoresist material. The photoresist is then exposed to light through a photomask that contains the desired pattern. The areas of the photoresist exposed to the light harden, while the unexposed areas remain soft. The soft areas are then washed away, revealing the metal underneath. The exposed metal is subsequently etched away using a chemical etchant, leaving behind the pattern defined by the hardened photoresist.
• Ultraviolet (UV) light is generally used in the photo etching process. The photoresist material applied to the metal sheet is sensitive to UV light. When exposed to UV light through a photomask, the photoresist undergoes a chemical change, hardening in the exposed areas. This selective hardening allows for the creation of intricate patterns by subsequently washing away the unexposed, soft areas and etching the revealed metal. UV light provides the necessary resolution and precision for the photo etching process, making it the preferred choice for this application.

Advantages:

• Ability to produce highly intricate and precise patterns, making it suitable for applications requiring fine details.
• Non-contact process, minimizing the risk of mechanical damage to the metal parts.
• Suitable for a wide range of metals, including stainless steel, copper, and brass.
• Cost-effective for small to medium-scale production runs.

Disadvantages:

• Limited to relatively thin metal sheets, typically up to 1.5 mm in thickness.
• Chemical waste management is required, as the process involves the use of corrosive etchants.

Applications: Photo etching is commonly used in the production of electronic components, precision instruments, decorative items, and medical devices, where high precision and intricate designs are essential.

Explanation:

Maximum Material Removal Rate (MRR) in EDM Process

• In Electrical Discharge Machining (EDM), the Material Removal Rate (MRR) is defined as the volume of material removed from the workpiece per unit time during the machining process. It is an essential parameter for evaluating the efficiency of the EDM process. The MRR depends on several factors, including the discharge energy, pulse current, pulse duration, and properties of the workpiece material.
• EDM is a non-conventional machining process where material removal occurs due to the erosive effect of electrical discharges (sparks) between the tool electrode and the workpiece. These discharges generate intense localized heat, which melts and vaporizes the material. The molten material is then flushed away by a dielectric fluid.
• The maximum MRR in the EDM process is influenced by the energy per spark, which is determined by the pulse current, pulse duration, and voltage. The higher the energy per spark, the greater the material removal. However, excessive energy can lead to poor surface finish and damage to the tool electrode. Under optimal conditions, the maximum MRR in EDM is approximately 5000 mm³/min.

Factors Affecting MRR in EDM:

• Discharge Energy: Higher discharge energy increases the MRR but may compromise surface quality.
• Pulse Current: Increasing the pulse current enhances the spark energy, leading to higher MRR.
• Pulse Duration: Longer pulse durations result in more material removal per discharge but can affect precision.
• Material Properties: The MRR varies depending on the thermal conductivity, melting point, and electrical resistivity of the workpiece material.
• Dielectric Fluid: The type and flow of the dielectric fluid affect the flushing of debris and influence the MRR.

Concept:

The required current in Electrochemical Machining (ECM) is given by:

$I=\frac{\text{MRR}\times \rho \times Z\times F}{M\times 60}$

Given:

$\text{MRR}=5{\text{cm}}^3/\text{min},\rho =7.8{\text{g/cm}}^3,Z=2,M=56,F=96500\text{C}$

Calculation:

$I=\frac{5\times 7.8\times 2\times 96500}{56\times 60}=\frac{7524000}{3360}\approx 2240\text{A}$

Explanation:

Laser Beam Machining (LBM)

• Laser Beam Machining (LBM) is a non-conventional machining process that uses the thermal energy of a laser beam to remove material from the workpiece. The laser beam is highly focused, coherent, and monochromatic, which allows precise machining with minimal thermal effects on the surrounding material. This process is widely used for cutting, drilling, and engraving hard and brittle materials, as well as materials that are difficult to machine using conventional methods.
• In LBM, a laser beam is generated using a laser source and then focused onto the surface of the workpiece using a lens system. The high-intensity laser beam heats the material to its melting and vaporization point, leading to material removal. The process is highly localized, ensuring minimal damage to adjacent areas. The wavelength of the laser beam determines its energy density and penetration capabilities, which are critical for the machining process.
• The usable range of wavelength of the laser beam in laser beam machining is typically between 0.4 μm and 0.6 μm. This range falls within the visible light spectrum and is suitable for efficient energy absorption and precise machining. This wavelength range ensures that the laser beam has sufficient energy density to melt or vaporize the material while maintaining control over the machining process.

Advantages:

• High precision and accuracy in material removal.
• Ability to machine hard and brittle materials.
• Minimal thermal damage to the surrounding material.
• No physical contact with the workpiece, reducing wear and tear on tools.
• Capability to produce complex shapes and intricate details.

Applications: Laser beam machining is commonly used in industries such as aerospace, electronics, and medical devices for applications like micro-drilling, cutting intricate patterns, and engraving.

Explanation:

Electrochemical Machining: 

In electrochemical machining, the metal is removed due to electrochemical action i.e. Ion displacement where the workpiece is made anode and the tool is made the cathode. A high current is passed between the tool and workpiece through the electrolyte. Metal is removed by the anodic dissolution and is carried away by the electrolyte.

The tool material used in ECM should have the following property

• It should have high electrical conductivity
• It should be easily machinable and it should have high stiffness
• Its corrosion resistance should be high.

The advantages of ECM include

• Complex shapes can be made accurately
• The surface finish is good due to atomic level dissolution
• Tool wear practically absent
• Its material removal rate is the highest.

The limitation of the Electro-Chemical Machining (ECM) process is the use of corrosive media as electrolytes makes it difficult to handle.

Explanation:

Electrochemical Machining:

• In electrochemical machining, the metal is removed due to electrochemical action where the workpiece is made anode and the tool is made the cathode.
• A high current is passed between the tool and workpiece through the electrolyte.
• Metal is removed by the anodic dissolution and is carried away by the electrolyte.

Concept:

In EDM it is assumed that the material removed per spark is directly proportional to the energy released per spark.

i.e. MRR ∝ Energy/spark

The energy released per spark is $E=\frac{1}{2}C{V}_d^2$

where, C = Capacitance, V_d = Discharge voltage

$MRR\propto E\propto V_d^2$

Calculation:

Given:

Actual voltage V_d1 = 40 V, Voltage which was used for calculation V_d2 = 60 V

$\frac{MR{R}_{actual}}{MR{R}_{calculated}}=\frac{V_{actal}^2}{V_{calculate}^2}=\frac{V_{d1}^2}{V_{d2}^2}=\frac{{40}^2}{{60}^2}=\frac{4}{9}$

Explanation:

Ultrasonic machining (USM):

• Ultrasonic machining is an operation that involves a vibrating tool fluctuating at the ultrasonic frequencies to remove the material from the workpiece.
• The process involves an abrasive slurry that runs between the tool and the workpiece.
• It is typically used on brittle materials as well as materials with a high hardness due to microcracking mechanics.

• In ultrasonic machining, a tool of the desired shape vibrates at an ultrasonic frequency (19 ∼ 25 kHz) with an amplitude of around 15 – 50 μm over the workpiece.
• Generally, the tool is pressed downward with a feed force, F.
• Between the tool and workpiece, the machining zone is flooded with hard abrasive particles generally in the form of a water-based slurry.
• As the tool vibrates over the workpiece, the abrasive particles act as the indenters and indent both the work material and the tool.
• The abrasive particles, as they indent the work material, would remove the work material, particularly if the work material is brittle (due to crack initiation, propagation and brittle fracture of the material).

USM MRR vs Feed Force:

• With an increase in the frequency of the tool head, the MRR should increase proportionally. However, there is a slight variation in the MRR with frequency. 
• MRR increases with increasing feed force but after a certain critical feed force, it decreases because the abrasive grains get crushed under heavy load.
• With increases in feed force, the material removal rate MRR is first increases and then decreases.

Explanation:

Abrasive Jet Machining:

• In Abrasive Jet Machining (AJM), abrasive particles are made to impinge on the work material at a high velocity
• The jet of abrasive particles is carried by carrier gas or air. The high-velocity stream of abrasive is generated by converting the pressure energy of the carrier gas or air to its kinetic energy and hence high-velocity jet
• The nozzle directs the abrasive jet in a controlled manner onto the work material, so that the distance between the nozzle and the workpiece and the impingement angle can be set desirably
• The high-velocity abrasive particles remove the material by micro-cutting action as well as brittle fracture of the work material.

Applications:

• For drilling holes of intricate shapes in hard and brittle materials
• For machining fragile, brittle, and heat-sensitive materials

Limitations:

• MRR is rather low
• Abrasive particles tend to get embedded particularly if the work material is ductile
• Tapering occurs due to the flaring of the jet

The metal removal rate for different processes is given:

So from the option, MRR for AJM is low as the lowest MRR is for LBM.

Explanation:

The unconventional machining process and their characteristics and the application areas are discussed in the table below:

Explanation:

Electro-Discharge Machining (EDM):

• Electrical Discharge Machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). 
• Material is removed from the work-piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid which controls spark discharges and subject to an electric voltage.
• In EDM, the workpiece is connected to positive terminal and tool is connected to the negative terminal.
• EDM has the lowest specific power requirement and can achieve sufficient accuracy.

• The accuracy and surface finish which are dependent on the overcut produced can be easily controlled by varying the frequency and current. The over cut is increased by increasing current and by decreasing frequency.
• For optimum metal removal and better surface finish, high frequency and maximum possible current is used.
• For roughing operation, low frequency and high current are used and for finishing application, high frequency and low current settings are used.
• In EDM a fluid is used to act as a dielectric and to help carry away debris.
• Quite often kerosene-based oil is used as dielectric in EDM.
• The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m2 or less to free it from eroded metal particles, it is circulated through a filter and acts as a coolant.

• Only electrically conducting material can be machined by EDM like steel, cast iron, Titanium and some other metals.

Explanation:

Explanation:

Electro-Discharge Machining (EDM):

• Electrical Discharge Machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). 
• Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid that controls spark discharges and is subjected to an electric voltage.
• In EDM, the workpiece is connected to the positive terminal, and the tool is connected to the negative terminal.
• EDM machines are equipped with a servo control mechanism that automatically maintains a constant gap of approximately 0.02 to 0.05 mm between the tool and workpiece.
• EDM has the lowest specific power requirement and can achieve sufficient accuracy.

• The accuracy and surface finish which are dependent on the overcut produced can be easily controlled by varying the frequency and current. The over cut is increased by increasing current and by decreasing frequency.
• For optimum metal removal and better surface finish, high frequency and maximum possible current are used.
• For roughing operation, low frequency and high current are used and for finishing application, high frequency and low current settings are used.
• In EDM a fluid is used to act as a dielectric and to help carry away debris.
• Quite often kerosene-based oil is used as dielectric in EDM.
• The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m2 or less to free it from eroded metal particles, it is circulated through a filter and acts as a coolant.

Concept:

• Computer Numeric Control (CNC) is a computer-assisted process to control general-purpose machining from instruction generated by a processor and stored in a memory system or storage media.
• CNC is a specific form of Control system where the position is Principle Control Variable.
• CNC machine is best suited when:
  • There is batch Production because of their Highly Working
  • When there is no Precise Location
  • When Production Volume is High with a repeated job making
• Advantages of CNC Machine
  • Improves machining accuracy.
  • Enables complex tasks, detail.
  • Creates flexibility in manufacturing.
  • Increases safety.
  • Boosts production volume.
  • Reduces setup-changeover time.
• Precise Location Required more Jigs and Fixture which leads Increase in Operating cost