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

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 

where, C = Capacitance, V_d = Discharge voltage

Calculation:

Given:

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

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:

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

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:

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