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

Explanation:

Planetary Internal Grinder Machine

• A planetary internal grinder machine is a specialized type of grinding machine used for grinding the internal surfaces of a workpiece. It employs a planetary motion, where the grinding wheel rotates around its own axis while simultaneously moving around the axis of the bore being ground. This dual motion allows for precise and efficient grinding of complex internal geometries.
• The planetary internal grinder machine operates by having the grinding wheel mounted on a spindle that rotates around its axis. This spindle is also part of a larger mechanism that rotates around the axis of the workpiece bore. This planetary motion enables the grinding wheel to cover the entire internal surface of the bore, ensuring uniform material removal and high precision.

Advantages:

• High precision and accuracy in grinding internal surfaces.
• Capability to grind complex and irregular shapes.
• Efficient material removal due to the dual motion of the grinding wheel.

Disadvantages:

• Complexity in design and operation, requiring skilled operators.
• Higher initial cost compared to simpler grinding machines.

Applications: Planetary internal grinder machines are commonly used in industries where precision grinding of internal surfaces is critical, such as in the manufacturing of bearings, gears, and hydraulic components.

Explanation:

Drill Chuck in Drilling Machines

Definition: A drill chuck is an essential component of a drilling machine, designed to securely hold the drill bit in place during the drilling operation. It is a mechanical device that clamps onto the shank of the drill bit, ensuring it remains stable and aligned while the machine operates. The drill chuck is typically mounted on the spindle of the drilling machine and can accommodate various sizes of drill bits, making it a versatile tool in both industrial and home workshops.

Working Principle: The drill chuck operates by tightening around the shank of the drill bit using a key or a hand-tightening mechanism. When the drilling machine is activated, the spindle rotates, and the chuck transmits this rotary motion to the drill bit. This motion allows the drill bit to cut into the material being worked on, creating holes of various sizes and depths. The chuck's design ensures that the drill bit remains firmly in place, preventing slippage and ensuring precise and accurate drilling.

Types of Drill Chucks:

• Keyed Chucks: These chucks use a key to tighten and loosen the grip on the drill bit. The key engages with teeth on the chuck, allowing for a secure and tight grip on the drill bit.
• Keyless Chucks: These chucks do not require a key for operation. They can be tightened and loosened by hand, making them more convenient for quick bit changes. However, they may not provide as secure a grip as keyed chucks.
• Jacobs Chucks: A common type of keyed chuck, known for its reliability and durability. Jacobs chucks are widely used in various drilling machines and are available in different sizes to accommodate a range of drill bits.

Advantages:

• Versatility in holding different sizes and types of drill bits.
• Secure grip on the drill bit, preventing slippage during operation.
• Ease of use, especially with keyless chucks for quick bit changes.
• Durability and reliability, particularly with high-quality chucks like Jacobs chucks.

Disadvantages:

• Keyed chucks require a key, which can be inconvenient and may be misplaced.
• Keyless chucks may not provide as tight a grip as keyed chucks, leading to potential slippage in heavy-duty applications.
• Regular maintenance is required to keep the chuck in good working condition, such as cleaning and lubrication.

Applications: Drill chucks are used in a wide range of applications, including metalworking, woodworking, construction, and DIY projects. They are essential in tasks that require precise and accurate drilling, such as creating holes for fasteners, dowels, and electrical wiring. Drill chucks are also used in specialized drilling machines, such as bench drills, pillar drills, and CNC drilling machines, to accommodate different drilling needs.

Correct Option Analysis:

The correct option is:

Option 3: holds the drill bit.

This option correctly identifies the primary function of a drill chuck, which is to hold the drill bit securely in place during the drilling operation. The drill chuck ensures that the drill bit remains stable and aligned, allowing for precise and accurate drilling. Without a proper chuck, the drill bit would not be able to perform its task effectively, leading to poor quality holes and potential damage to the workpiece and the machine.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: transmits rotary motion to the drill spindle at a number of speeds.

This option is incorrect because the drill chuck itself does not transmit rotary motion to the drill spindle. Instead, the spindle of the drilling machine transmits rotary motion to the chuck, which then transmits this motion to the drill bit. The spindle is responsible for the variable speeds and rotary motion, not the chuck.

Option 2: rests on the base and supports the head and the table.

This option is incorrect because the drill chuck does not rest on the base or support the head and the table of the drilling machine. These functions are typically performed by other components, such as the column, base, and table of the drilling machine. The chuck's primary role is to hold the drill bit, not to provide structural support.

Option 4: holds electric motor, V-pulleys, and V-belt.

This option is incorrect because the drill chuck does not hold the electric motor, V-pulleys, or V-belt. These components are part of the power transmission system of the drilling machine, responsible for driving the spindle and providing the necessary rotary motion. The chuck's role is to secure the drill bit, not to hold these power transmission components.

Conclusion:

Understanding the role and function of a drill chuck is essential for correctly identifying its importance in a drilling machine. The drill chuck is designed to hold the drill bit securely, ensuring precise and accurate drilling. While the chuck does not transmit rotary motion or provide structural support, its ability to clamp onto the drill bit is crucial for effective drilling operations. By evaluating the other options, it is clear that option 3 accurately describes the primary function of the drill chuck, making it the correct choice.

Explanation:

Cubic Boron Nitride (CBN)

Definition: Cubic Boron Nitride (CBN) is a synthetically produced material that is used as an abrasive in grinding processes. It is known for its exceptional hardness, second only to diamond, and is primarily used in applications that require high precision and durability.

Properties: CBN is characterized by its high thermal stability, chemical resistance, and hardness. These properties make it an excellent material for cutting and grinding tools, particularly when working with hard and ferrous materials.

Manufacturing Process: CBN is produced by transforming hexagonal boron nitride (hBN) into its cubic form under high-pressure and high-temperature conditions. The process involves placing hBN in a press, subjecting it to pressures of around 5-10 GPa and temperatures of about 1500-2000°C. This transformation alters the crystal structure, resulting in the formation of CBN.

Advantages:

• Hardness: CBN is one of the hardest known materials, making it highly effective for grinding and cutting applications.
• Thermal Stability: It retains its hardness at high temperatures, which is crucial for maintaining performance during high-speed grinding processes.
• Chemical Resistance: CBN is chemically inert with ferrous materials, preventing reactions that could degrade the tool or the workpiece.
• Longevity: Tools made with CBN have a longer lifespan compared to those made with conventional abrasives, reducing the frequency of tool replacement and downtime.

Applications: CBN is widely used in various industrial applications, including:

• Grinding: CBN grinding wheels are used for precision grinding of hardened steels and superalloys.
• Cutting Tools: It is used in the production of cutting tools for machining hard metals.
• Finishing: CBN is used for finishing operations where high precision and surface quality are required.

Correct Option Analysis:

The correct option is:

Option 4: Cubic boron nitride

This option correctly identifies the full form of "CBN," which is Cubic Boron Nitride. CBN is an abrasive material used in grinding processes due to its exceptional hardness and thermal stability.

Important Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Calcium bi nitrous

This option is incorrect as "Calcium bi nitrous" does not refer to any known abrasive material used in grinding processes. It is not related to the term "CBN."

Option 2: Carbon boron nitrate

This option is incorrect because "Carbon boron nitrate" is not the correct full form of CBN. Additionally, it is not a material used in grinding processes. The correct term is Cubic Boron Nitride.

Option 3: Copper boron nitride

This option is incorrect as "Copper boron nitride" does not exist as a commonly known material in grinding processes. The term CBN specifically refers to Cubic Boron Nitride, not a compound involving copper.

Conclusion:

Understanding the correct full form of CBN is essential for recognizing its significance in industrial applications. Cubic Boron Nitride (CBN) is a critical material used in grinding and cutting tools due to its exceptional hardness, thermal stability, and chemical resistance. It is important to distinguish CBN from other materials and understand its specific properties and applications to appreciate its role in manufacturing and precision engineering.

Explanation:

Centerless Grinding:

• Centerless grinding is a machining process that uses abrasive cutting to remove material from a workpiece. Unlike traditional grinding processes that require the use of centers to hold the workpiece, centerless grinding holds the workpiece between two wheels – a grinding wheel and a regulating wheel – and a work rest blade. The process is typically used to create cylindrical parts with precise dimensions and smooth surface finishes.

Working Principle: In centerless grinding, the workpiece is supported by a work rest blade and is positioned between a high-speed grinding wheel and a slower-speed regulating wheel. The grinding wheel performs the cutting action, while the regulating wheel controls the rotational speed and the feed rate of the workpiece. The workpiece is rotated and fed axially through the wheels, allowing for continuous and efficient grinding.

Role of the Regulating Wheel:

• The regulating wheel is a key component in the centerless grinding process. It provides the necessary horizontal force to the workpiece, ensuring that it is held securely and fed through the grinding wheel at the correct speed and orientation. The regulating wheel's speed and angle of inclination can be adjusted to control the feed rate and the amount of material removed during the grinding process.

Advantages of the Regulating Wheel:

• Ensures consistent feed rate and rotational speed of the workpiece, leading to precise and uniform grinding results.
• Allows for continuous processing of workpieces without the need for manual intervention or repositioning.
• Enables the grinding of complex shapes and profiles with high accuracy and repeatability.

Explanation:

Climb Milling

Definition: Climb milling, also known as down milling, is a milling process where the direction of the cutter rotation is the same as the feed direction of the workpiece. In this process, the cutter engages the workpiece at the top of the cut and removes material in a downward direction, moving with the feed of the workpiece.

Working Principle: In climb milling, the cutter rotates in the same direction as the feed. As the cutter tooth starts to engage the workpiece, it cuts from the surface to the bottom, which means the chip thickness decreases from the beginning to the end of the cut. The cutting force is directed into the workpiece, which helps to hold the workpiece against the machine table.

Advantages:

• Improved Surface Finish: The cutter in climb milling provides a cleaner cut as it shears the material, leading to a better surface finish.
• Longer Tool Life: Due to the direction of cutting and the way the material is removed, the tool experiences less friction and wear, extending its operational life.
• Better Chip Evacuation: The chips are thrown behind the cutter, making chip evacuation easier and reducing the chances of re-cutting chips.
• Reduced Work Hardening: Climb milling reduces work hardening of the material because the cutter engages the material with less friction.

Disadvantages:

• Requires Rigid Setup: The process can cause the workpiece to be pulled into the cutter, demanding a more rigid machine setup to prevent backlash and ensure precision.
• Not Suitable for All Materials: Certain materials, especially those that are harder or brittle, may not be suitable for climb milling due to the aggressive nature of the cut.

Applications: Climb milling is widely used in CNC machining, especially for finishing cuts and precision work where a high-quality surface finish is desired. It is also preferred in scenarios where tool life is a critical factor, such as in high-production environments.

Concept:

Table speed in mm/minute = ft × Z × N

where, N = RPM, Z = no. of teeth, ft = Feed per tooth

Calculation:

Given:

Z = 10, N = 150 rpm, ft = ?, f_m = 400 mm/min

Table speed in mm/minute, 400 = 150 × 10 × ft

Explanation:

Glazing: When a surface of the wheel develops a smooth and shining appearance, it is said to be glazed. This indicates that the wheel is blunt, i.e. the abrasive grains are not sharp.

• Glazing is caused by grinding hard materials on a wheel that has too hard a grade of bond. The abrasive particles become dull owing to cutting the hard material. The bond is too firm to allow them to break out. The wheel loses its cutting efficiency.
• Glazing of grinding wheel is more predominant in hard wheels with higher speeds. With softer wheels and relatively lower speeds, this effect is less prominent.

Concept:

Abrasive grains are held together in a grinding wheel by a bonding material. The bonding material does not cut during the grinding operation. Its main function is to hold the grains together with varying degrees of strength. Standard grinding wheel bonds are silicate, vitrified, resinoid, shellac, rubber and metal.

Rubber bond (R): 

• Rubber-bonded wheels are extremely tough and strong.
• Their principal uses are as thin cut-off wheels and driving wheels in centerless grinding machines.
• They are used also when extremely fine finishes are required on bearing surfaces.

Silicate bond (S): 

• This bonding material is used when the heat generated by grinding must be kept to a minimum. 
• Silicate bonding material releases the abrasive grains more readily than other types of bonding agents. 
• This is the softest bond in grinding wheel.

Vitrified bond (V): 

• Vitrified bonds are used on more than 75 per cent of all grinding wheels.
• Vitrified bond material is comprised of finely ground clay and fluxes with which the abrasive is thoroughly mixed.

Resinoid bond (B): 

• Resinoid bonded grinding wheels are second in popularity to vitrified wheels.
• The phenolic resin in powdered or liquid form is mixed with the abrasive grains in a form and cured at about 360F.

Shellac bond (E): 

• It's an organic bond used for grinding wheels that produce very smooth finishes on parts such as rolls, cutlery, camshafts and crankpins.
• Generally, they are not used on heavy-duty grinding operations.

Metal bond (M): 

• Metal bonds are used primarily as binding agents for diamond abrasives.
• They are also used in electrolytic grinding where the bond must be electrically conductive.

Explanation:

• Grinding involves an Abrasive action and while removing material abrasive also wears out and when the rubbing force reaches the threshold, the worn-out abrasives are pulled out of the wheel.
• Thereby giving chance to a fresh layer of abrasives for removing material. This is known as the self-sharpening behavior of the grinding wheel.
• The ratio of the volume of material removed to the volume of wheel wear is known as grinding ratio.

\(Grinding\;ratio = \frac{{{V_m}}}{{{V_w}}} = \frac{{l \times b \times d}}{{\frac{\pi }{4} \times w \times \left( {D_i^2 - D_f^2} \right)}},\;where\;w = width\;of\;wheel\)

• The grinding ratio varies from 1.0 - 5.0 in very rough grinding.

Explanation:

Abrasives are classified into two categories:

Natural Abrasives:

• Garnet, Corundum, Emery (impure corundum), Calcite (calcium carbonate), Diamond dust, Novaculite, Pumice, Rouge, Sand, Sandstone, Tripoli, Powdered feldspar, Staurolite

Synthetic Abrasives:

• Boron carbide, Borazon (cubic boron nitride or CBN), Ceramic, Ceramic aluminium oxide, Ceramic iron oxide, Dry ice, Glass powder, Steel abrasive, Zirconia alumina, Slags

Concept:

A grinding wheel consists of the abrasive that does the cutting, and the bond that holds the abrasive particles together.

A standard marking system is used to specify and identify grinding wheels.

The following is the sequence of arrangement:

Abrasive type – Grain size – Grade of bond – Structure – Bond type

The number ‘46’ specifies the average grit size in inch mesh. For a very large size grit, this number may be as small as 6 whereas for a very fine grit the designated number may be as high as 600. 

• Abrasive type: ‘A’ for aluminium oxide, ‘C’ for silicon carbide
  • A =  Aluminium oxide
  • B = Cubic boron nitride
  • C = Silicon carbide
  • D = Diamond
• Grain size: They are indicated by a number ranging from 10 (coarse) up to 600 (very fine)
• Grade of bond: The grades range from ‘A’ indicating light or ‘soft’ bond to ‘Z’ indicating a firm or ‘hard’ bond
• Structure: This structure is indicated by a number from 1 to 12. The higher numbers indicate a progressively more open structure
• Bond type: V – Vitrified, S – Silicate, B – Resinoid, R – Rubber, E – Shellac, O – Oxychloride

Explanation:

The helix angle is the angle between the leading edge of the land and the axis of the drill. Sometimes it is also called a spiral angle.

1. The helix results in a positive cutting rake. This angle is equivalent to the back rake angle of a single-point cutting tool.
2. The usual range of helix angle used in the drill is 20° to 35°.
3. Large helix angle 45° to 60° suitable for deep holes and softer work materials.
4. The small helix angle of less than 45° is suitable for harder and stronger materials.
5. Zero helix angles are used in spade drills for high production drilling, micro‐drilling, and hard work materials.

Important Points

1. An increase in helix angle is given for more quick removal of chips but a decrease in helix angle will give greater strength of cutting edges.
2. The larger the value of helix angle lesser will be the power required in drilling.

Explanation:

Centre Lathe → Knurling

Milling → Slotting

Grinding → Dressing

Drilling → Counter-boring

Knurling

Knurling is the operation of producing a straight-lined, diamond-shaped pattern or cross lined pattern on a cylindrical external surface by pressing a tool called knurling tool. Knurling is not a cutting operation but it is a forming operation.

A lathe is used for many operations such as turning, threading, facing, grooving, Knurling, Chamfering, centre drilling

Counter - boring

Counter - boring is an operation of enlarging a hole to a given depth, to house heads of socket heads or cap screws with the help of a counterbore tool.

Dressing:

When the sharpness of grinding wheel becomes dull because of glazing and loading, dulled grains and chips are removed (crushed or fallen) with a proper dressing tool to make sharp cutting edges.

The dressing is the operation of cleaning and restoring the sharpness of the wheel face that has become dull or has lost some of its cutting ability because of loading and glazing.

Slot Milling:

Slot milling is an operation of producing slots like T - slots, plain slots, dovetail slots etc.

Concept:

Drilling time can be calculated by;

\(T = \frac{L}{{f ~×~ N}}\)

where T = Machining time in min, L = (Approach Length + Thickness of plate) in mm, f = Feed (mm/rev), N = Speed in rpm (revolution per min)

\(Approach\ Length= \frac{D}{2\ tanθ}\)

Where θ = Half drill bit angle, D = diameter of the hole

∵ The angle of a drill bit is not given in the question hence we will take approach length zero.

∴ L = Thickness of the plate

Calculation:

Given:

Thickness of plate (L) = 30 mm, Feed (f) = 1 mm/rev, Speed (N) = 60 rpm, Hole diameter (d) = 25 mm

\(T = \frac{30}{{1 × 60}}\)

T = 0.5 min

T = 0.5 × 60 sec

T = 30 sec

Hence drilling time will be 30 sec.

Important Points

If in the ques it is given that "Neglect approach and over travel" OR "Drill bit angle is not given" then effective length equal thickness of the workpiece.

Explanation:

Grinding:

• Grinding is the process of removing metal by the application of abrasives which are bonded to form a rotating wheel. When the moving abrasive particles contact the workpiece, they act as tiny cutting tools, each particle cutting a tiny chip from the workpiece.
• It is a common error to believe that grinding abrasive wheels remove material by a rubbing action; actually, the process is as much a cutting action as drilling, milling, and lathe turning.

Grain size:

• The grain or grit size of your grinding wheel influences the material removal rate and the surface finish and the grain size varies from 8 to 600 (8 is coarse and 600 is very fine).
• The grinding wheel grain size controls the possible amount of depth of cut. Bigger grain size protrudes more on the grinding wheel periphery or face resulting in a higher depth of cut and smaller grains protrude less resulting in a lower depth of cut. Hence the size of the chip is fine in the case of smaller grain size wheels.
• Large grain size grinding wheel is used for ductile materials.