All questions of Manufacturing Engineering for Mechanical Engineering Exam

The Purpose of Draft in Pattern Making

Introduction
Pattern making is a crucial step in the casting process. It involves the creation of a replica of the desired final product, called a pattern, which is used to shape the mold cavity. The pattern is typically made from wood, metal, or plastic and is designed with specific features to facilitate the casting process. One of these features is the inclusion of draft.

What is Draft?
Draft, also known as taper, is a slight inclination or angle provided on the vertical surfaces of a pattern. It is measured in degrees and is necessary to ensure the smooth extraction of the pattern from the mold cavity. Draft is typically applied to all vertical surfaces of the pattern, including the core prints, side walls, and bosses.

Reasons for Providing Draft in Pattern Making

1. Easy Withdrawal from Mold Cavity
The primary reason for providing draft in pattern making is to facilitate the easy withdrawal of the pattern from the mold cavity. The inclusion of draft allows the pattern to be smoothly lifted out of the mold without damaging the mold or the pattern itself. Without draft, the pattern would get stuck in the mold, making it difficult to remove and potentially causing damage to both the pattern and the mold.

2. Sand Filling
While draft primarily aids in the withdrawal of the pattern, it also helps in the sand filling process. The inclusion of draft allows for easier and smoother sand filling around the pattern. The draft angle helps prevent the sand from sticking to the pattern, ensuring that it can be easily removed once the mold is formed.

3. Effective Compression
Draft also plays a role in effective compression of the molding sand. When the pattern is pressed into the sand, the draft angle allows for better compaction of the sand particles. This results in a more stable mold cavity with improved dimensional accuracy and surface finish.

4. Easy Solidification of Casting
Additionally, draft contributes to the easy solidification of the casting material. The inclination of the pattern's vertical surfaces allows for uniform cooling and shrinkage of the molten metal during solidification. This helps prevent the formation of defects, such as shrinkage cavities and cracks, in the final casting.

Conclusion
In conclusion, the inclusion of draft in pattern making is essential for several reasons. It facilitates the easy withdrawal of the pattern from the mold cavity, enables smooth sand filling, ensures effective compression of the molding sand, and promotes easy solidification of the casting material. All these factors contribute to the production of high-quality castings with accurate dimensions and improved surface finish.

Explanation:

Surface Finish:
Shot peening is a process used to improve the fatigue strength of metal parts, not the surface finish. Although shot peening can also have some effects on the surface finish of the parts, its primary objective is to enhance other properties.

Ductility:
Shot peening does not primarily aim to improve the ductility of metal parts. Ductility is the ability of a material to deform plastically before fracturing, and shot peening does not directly influence this property.

Fatigue Strength:
The main objective of shot peening is to improve the fatigue strength of metal parts. Fatigue strength is the ability of a material to resist fatigue failure when subjected to cyclic loading. Shot peening induces compressive residual stresses on the surface of the part, which helps to increase its fatigue strength by preventing crack initiation and propagation.

Conclusion:
In conclusion, the correct answer is option C - fatigue strength. Shot peening is a surface treatment process that is specifically designed to enhance the fatigue strength of metal parts by introducing compressive residual stresses on their surfaces.

Shaper and Material Removal

A shaper is a machine tool used for shaping or surfacing metal and other materials. It is used to produce flat or curved surfaces with the help of a single-point cutting tool. The tool is mounted on the ram and reciprocates over the workpiece, removing material during the cutting stroke.

Forward Stroke

During the forward stroke, the cutting tool moves towards the workpiece and removes material. The cutting stroke is the main stroke that removes material from the workpiece. The depth of cut is controlled by the position of the tool and the feed rate. The cutting tool removes material from the workpiece by shearing off small chips.

Return Stroke

During the return stroke, the cutting tool moves away from the workpiece without removing any material. The return stroke is a non-cutting stroke that allows the cutting tool to reposition itself for the next cutting stroke. During the return stroke, the cutting tool is lifted above the workpiece to avoid any damage to the workpiece or the tool.

Conclusion

In conclusion, material is removed during the forward stroke of a shaper. The cutting tool removes material from the workpiece by shearing off small chips during the cutting stroke. During the return stroke, the cutting tool moves away from the workpiece without removing any material. The return stroke is a non-cutting stroke that allows the cutting tool to reposition itself for the next cutting stroke.

Understanding the Role of Gases in MIG Welding
In Metal Inert Gas (MIG) welding, the use of gases such as helium or argon is crucial for creating a stable and effective welding environment. The correct answer to the given question is option 'C': to act as a shielding medium. Let’s explore this in detail.
Shielding Medium Purpose
- Protection Against Contaminants: The primary role of the shielding gas in MIG welding is to protect the molten weld pool from atmospheric contamination. Oxygen and nitrogen from the air can lead to defects such as porosity and oxidation.
- Stable Arc Environment: Shielding gases help maintain a stable arc during the welding process. This stability is essential for achieving consistent weld quality and preventing arc instability.
Properties of Helium and Argon
- Inert Characteristics: Both helium and argon are inert gases, meaning they do not react with the molten metal. This property ensures that the weld remains free from unwanted chemical reactions that could compromise its integrity.
- Thermal Conductivity: Helium has a higher thermal conductivity compared to argon, which can be beneficial for certain welding applications, providing better heat transfer and penetration.
Conclusion
In summary, the primary function of helium or argon in MIG welding is to serve as a shielding medium. This role is vital for ensuring high-quality welds by protecting the weld pool from atmospheric gases and maintaining a stable arc environment. Understanding this function is essential for anyone involved in welding processes in the mechanical engineering field.

B. Improper design of die

- Cold shut is a forging defect that occurs when two portions of metal fail to fuse together properly during the forging process.
- The defect is characterized by a visible line or seam on the surface of the forged part, indicating a lack of proper bonding between the two sections.
- The primary reason for cold shut is the improper design of the die used in the forging process.

Reasons for Cold Shut:
1. Insufficient material flow:
- The die design plays a crucial role in ensuring proper material flow during forging.
- If the die is not designed properly, it may result in restricted material flow, leading to incomplete fusion between the metal sections.
- Insufficient material flow can occur due to improper die cavity design, inadequate draft angles, or incorrect die dimensions.

2. Improper die temperature:
- Another factor contributing to cold shut is the improper cooling of the die during the forging process.
- If the die temperature is too low, it can cause premature solidification of the metal, preventing proper fusion.
- On the other hand, if the die temperature is too high, it can result in excessive material flow and distortion, also leading to cold shut.

3. Inadequate die lubrication:
- Proper lubrication is essential to facilitate smooth material flow and prevent sticking or dragging of the metal on the die surface.
- Insufficient or improper die lubrication can result in uneven material flow, promoting the formation of cold shut defects.

4. Misalignment of the two die halves:
- Cold shut can also occur if there is a misalignment between the two die halves during the forging process.
- Misalignment can create gaps or misfits between the metal sections, preventing proper bonding.

Conclusion:
- While all the mentioned reasons can contribute to cold shut defects, the primary reason is the improper design of the die used in the forging process.
- It is crucial to ensure that the die is designed correctly, taking into account factors such as material flow, die temperature, lubrication, and alignment, to prevent the occurrence of cold shut defects.

Combination Die:
A combination die is a type of die used in metalworking operations such as cutting and forming. It is designed to perform multiple operations in a single die, making it more efficient and cost-effective.

Functions of a Combination Die:
A combination die can perform both cutting and forming operations simultaneously. It is capable of cutting the desired shape in the metal sheet while also forming it into the desired shape. This eliminates the need for separate dies for cutting and forming, saving time and resources.

Advantages of Combination Die:
1. Increased Efficiency: By combining cutting and forming operations in a single die, the overall production process becomes more efficient. This reduces the number of steps required and speeds up the manufacturing process.

2. Cost Reduction: Using a combination die eliminates the need for separate dies for cutting and forming. This reduces the tooling costs associated with multiple dies and also saves on maintenance and storage costs.

3. Improved Accuracy: Since the cutting and forming operations are performed simultaneously in a combination die, the accuracy and precision of the final product are enhanced. This ensures consistent quality and reduces the need for additional finishing processes.

4. Reduced Material Waste: Combination dies optimize the material utilization by minimizing scrap and waste. The integrated design allows for efficient use of the raw material, resulting in cost savings and improved sustainability.

5. Versatility: Combination dies can be designed to perform various cutting and forming operations, making them versatile for different applications. They can be customized to meet specific requirements and produce complex shapes with high precision.

Conclusion:
Combination dies offer numerous advantages in terms of efficiency, cost reduction, accuracy, material utilization, and versatility. By integrating cutting and forming operations in a single die, manufacturers can streamline their production processes and achieve higher productivity.

In drop forging, the forging process involves shaping a workpiece by the repeated striking of a hammer against a die. The correct answer is option 'C', which states that forging is done by dropping the die with the hammer at high velocity. Let's understand this answer in detail.

1. Introduction to drop forging:
- Drop forging is a metalworking process used to shape heated metal stock into desired shapes.
- It is a type of forging method where a hammer is used to strike the workpiece onto a die, which results in the required shape.

2. The purpose of drop forging:
- Drop forging is primarily used to produce parts that require high strength, durability, and accuracy.
- It is commonly used in the automotive, aerospace, and construction industries to manufacture components like crankshafts, connecting rods, gears, and axles.

3. Explanation of option 'A' - The workpiece at high velocity:
- This option is incorrect because the workpiece is not dropped at high velocity in drop forging.
- The workpiece is heated to a specific temperature and then placed on the die.
- The hammer, along with the die, is dropped at high velocity onto the workpiece to shape it.

4. Explanation of option 'B' - The hammer at high velocity:
- This option is incorrect because the hammer alone is not dropped at high velocity in drop forging.
- The hammer is used in conjunction with the die and is dropped as a unit onto the workpiece.
- The high velocity of the hammer's impact generates the necessary force to shape the workpiece.

5. Explanation of option 'C' - The die with hammer at high velocity:
- This option is correct because drop forging involves dropping the die with the hammer at high velocity.
- The die is positioned above the workpiece, and the hammer, attached to the die, is lifted to a certain height.
- The hammer is then released, and gravity causes it to fall rapidly, impacting the die and exerting a force on the workpiece.

6. Explanation of option 'D' - A weight on the hammer to produce the requisite impact:
- This option is incorrect because drop forging does not involve placing a weight on the hammer.
- The hammer itself is designed to have enough weight to generate the required impact force.
- The weight and velocity of the falling hammer are carefully controlled to achieve the desired shaping effect on the workpiece.

In conclusion, drop forging involves dropping the die with the hammer at high velocity onto the workpiece. This method allows for the precise shaping of heated metal stock into strong and durable components.

< b="" />Introduction: < />
A plug gauge is a precision measuring instrument used to measure the size of a hole. It is commonly used in industries such as manufacturing, engineering, and quality control. Plug gauges are designed to provide accurate and reliable measurements of the diameter or size of a hole, ensuring that it meets the required specifications.

< b="" />Explanation: < />
The correct answer to the question is option 'B', which states that a plug gauge is used to measure hole size. Here's why:

< b="" />Shaft size: < />
A plug gauge is not used to measure the size of a shaft. For measuring shaft size, various other tools such as micrometers, calipers, or snap gauges are commonly used. These tools are specifically designed to measure the outer dimensions or diameters of objects like shafts.

< b="" />Wire thickness: < />
A plug gauge is not used to measure wire thickness. For measuring wire thickness, tools like wire gauges or micrometers are commonly used. These tools are specifically designed to measure the diameter or thickness of wires accurately.

< b="" />Depth of threads: < />
A plug gauge is not used to measure the depth of threads. To measure the depth of threads, thread depth gauges or thread micrometers are commonly used. These tools are designed to measure the depth or pitch of threads accurately.

< b="" />Hole size: < />
A plug gauge is primarily used to measure the size of a hole. It consists of a cylindrical body with precisely calibrated dimensions. The gauge is inserted into the hole, and if it fits perfectly without any play or excessive tightness, it indicates that the hole is within the required specifications. The gauge is usually marked with its corresponding size, allowing the user to determine the diameter or size of the hole.

< b="" />Conclusion: < />
In conclusion, a plug gauge is specifically designed to measure the size of a hole. It is not used for measuring shaft size, wire thickness, or depth of threads. By using a plug gauge, manufacturers and engineers can ensure that the holes they produce meet the required specifications, ensuring the quality and functionality of the final product.

Anodising is an oxidising process used for aluminium and magnesium articles. This process involves the formation of a controlled oxide layer on the surface of the metal, which provides improved corrosion resistance, increased durability, and enhanced aesthetic appearance.

Here is a detailed explanation of the anodising process:

1. Introduction to Anodising:
- Anodising is an electrochemical process that converts the surface of aluminium or magnesium into a protective and decorative oxide layer.
- The process involves immersing the metal in an electrolyte solution and applying an electric current to stimulate the formation of the oxide layer.

2. Formation of Oxide Layer:
- The electrolyte solution typically consists of sulfuric acid or chromic acid, which acts as a medium for the anodising process.
- When a direct current is applied to the metal, oxygen ions from the electrolyte combine with the metal atoms to form a layer of aluminium oxide or magnesium oxide on the surface.
- This oxide layer is porous and adheres tightly to the metal, providing excellent corrosion resistance.

3. Benefits of Anodising:
- Corrosion Resistance: The oxide layer formed through anodising acts as a barrier, preventing the metal from coming into direct contact with corrosive substances. This greatly improves the metal's resistance to corrosion.
- Durability: Anodising increases the hardness and wear resistance of the metal surface, making it more resistant to scratches, abrasion, and fading.
- Aesthetic Appearance: The anodising process allows for the incorporation of various dyes and pigments into the oxide layer, resulting in a wide range of vibrant and durable colors. This makes anodised aluminium and magnesium articles highly desirable for architectural, automotive, and consumer product applications.

4. Other Applications:
- Anodised aluminium is commonly used in architectural components, such as window frames, doors, and curtain walls, due to its combination of corrosion resistance and aesthetic appeal.
- Anodised magnesium is utilized in aerospace and automotive industries for lightweight components that require high strength and corrosion resistance.

In conclusion, anodising is an oxidising process used specifically for aluminium and magnesium articles. It involves the formation of a controlled oxide layer on the metal's surface, providing improved corrosion resistance, durability, and aesthetic appearance.

Explanation:

Sintering:
Sintering is a process used to increase the final strength of a material by heating it below its melting point to form a solid mass without melting it completely.

Increasing final strength:
- The main purpose of sintering is to increase the final strength of a material.
- During sintering, the particles in the material are bonded together through diffusion processes, leading to an increase in strength.

How sintering works:
- As the material is heated, the atoms at the surface of the particles diffuse into the adjacent particles, creating bonds between them.
- This bonding results in a denser structure with improved mechanical properties, including higher strength.

Effect on ductility and porosity:
- Sintering can actually decrease the ductility of a material because it leads to a more rigid and dense structure.
- It also helps in reducing porosity by filling in the gaps between particles, thus improving the overall strength of the material.
Therefore, the correct answer is option 'C) Increase the final strength'. Sintering is a crucial process in the manufacturing of various materials, especially in industries like powder metallurgy, ceramics, and additive manufacturing.

Given data:
- Thickness of each steel sheet (t): 2 mm
- Current (I): 5500 A
- Time (t): 0.15 s
- Diameter of electrodes (d): 6 mm
- Resistance of contact (RC): 250 μΩ

Calculating the heat generated:
1. Calculate the resistance of each spot weld:
- Resistance (R) = RC * t
- R = 250 μΩ * 0.15 s = 37.5 μΩ
2. Calculate the heat generated at each spot weld:
- Heat (Q) = I^2 * R * t
- Q = (5500 A)^2 * 37.5 μΩ * 0.15 s
- Q = 1134 J

Therefore, the amount of heat generated in resistance spot welding is 1134 J.

The tool signature of a single point cutting tool used for turning operations consists of several elements that help define the geometry and characteristics of the tool. These elements are essential for proper tool selection, setup, and machining operations. The correct answer is option 'C', which states that there are seven elements in the tool signature.

The elements present in the tool signature are as follows:

1. Back rake angle:
- The back rake angle is the angle between the face of the tool and a line parallel to the base of the tool.
- It helps in controlling the chip flow and reducing cutting forces.

2. Side rake angle:
- The side rake angle is the angle between the side cutting edge of the tool and a line perpendicular to the base of the tool.
- It helps in controlling the chip flow and reducing cutting forces.

3. End relief angle:
- The end relief angle is the angle between the end cutting edge and a line perpendicular to the base of the tool.
- It provides clearance for the tool during the machining process.

4. Side relief angle:
- The side relief angle is the angle between the side cutting edge and a line perpendicular to the base of the tool.
- It provides clearance for the tool during the machining process.

5. Nose radius:
- The nose radius is the radius formed at the intersection of the face and side cutting edge.
- It helps in reducing cutting forces and improving tool life.

6. Width of the tool:
- The width of the tool refers to the distance between the two side cutting edges.
- It determines the amount of material that can be removed in one pass.

7. Cutting edge angle:
- The cutting edge angle is the angle formed by the side cutting edge and a line perpendicular to the base of the tool.
- It affects the cutting action and chip formation.

These seven elements together define the tool signature of a single point cutting tool used for turning operations. Each element plays a crucial role in determining the tool's performance, chip formation, and the quality of the machined surface. It is important to consider these elements while selecting a cutting tool for a specific turning operation to achieve desired results.

Answer:

Arc welding is a commonly used welding process that involves the use of an electric arc to join metal pieces together. Carbon electrodes are often used in arc welding for various applications. When using carbon electrodes, a D.C. welding set with straight polarity is the most suitable equipment.

Explanation:

D.C. Welding Set with Straight Polarity:
- A D.C. welding set with straight polarity refers to a direct current (D.C.) welding machine that has a positive electrode and a negative workpiece connection.
- In arc welding with carbon electrodes, the carbon electrode acts as the positive electrode while the workpiece acts as the negative electrode. This configuration is known as straight polarity or direct current electrode positive (DCEP).
- Straight polarity is preferred when using carbon electrodes because it provides better control over the welding process and improves arc stability. It also reduces the electrode consumption and helps in preventing overheating of the electrode.

Other Equipment Options:
a) A.C. Welding Set:
- A.C. welding sets are not suitable for arc welding with carbon electrodes. A.C. welding sets provide alternating current, which is not ideal for maintaining a stable arc with carbon electrodes. The arc tends to flicker and become unstable, making it difficult to achieve good weld quality.

b) Rectifier:
- A rectifier is a device used to convert alternating current (A.C.) into direct current (D.C.). While rectifiers are used in some welding machines, they are not specifically designed for arc welding with carbon electrodes.

c) Motor Generator:
- A motor generator is a device that converts mechanical energy into electrical energy. While motor generators can be used to generate direct current for welding, they are not specifically designed for arc welding with carbon electrodes.

Therefore, the correct equipment option for arc welding using carbon electrodes is a D.C. welding set with straight polarity. This equipment provides the necessary control and stability required for successful arc welding with carbon electrodes.

Gear hobbing is not a gear finishing process.

Gear hobbing is a gear manufacturing process that involves the use of a hob, which is a cylindrical cutting tool with helical teeth. During gear hobbing, the hob is mounted on a hobbing machine and it rotates while the gear blank is slowly fed against it. As the hob and gear blank rotate, the teeth of the hob gradually cut into the blank, creating the desired gear teeth.

Gear hobbing is a primary gear manufacturing process, not a finishing process. It is typically used to generate the initial gear teeth profile before any finishing operations are performed. The process is capable of producing gears with high accuracy and good surface finish, but it may leave some residual imperfections on the gear teeth surface.

Gear finishing processes, on the other hand, are used to improve the surface finish and dimensional accuracy of gears that have already been formed. These processes are often performed after gear hobbing or other primary gear manufacturing processes. Some common gear finishing processes include gear shaving, gear lapping, and gear grinding.

Gear shaving is a gear finishing process that involves removing a thin layer of material from the gear teeth surface using a shaving cutter. This process helps to improve the surface finish, reduce gear noise, and ensure proper gear tooth contact.

Gear lapping is another gear finishing process that uses a lapping tool, typically a cast iron or bronze wheel, along with a fine abrasive paste to remove small amounts of material from the gear teeth surface. This process helps to improve the surface finish, eliminate any remaining imperfections, and ensure proper gear meshing.

Gear grinding is a gear finishing process that involves the use of a grinding wheel to remove material from the gear teeth surface. This process is used to achieve high precision and tight tolerances, as well as improve the surface finish and gear tooth profile.

In summary, gear hobbing is not a gear finishing process but a primary gear manufacturing process. Gear finishing processes, such as gear shaving, gear lapping, and gear grinding, are performed after the gears have been formed to improve their surface finish and dimensional accuracy.

Boring is the process of enlarging an existing circular hole with a rotating single point tool. It is commonly used in machining operations to achieve precise dimensions and smooth surface finishes. The process involves removing material from the inner diameter of a workpiece to create a larger hole or cylinder.

Boring is typically performed on a lathe or a boring machine. The rotating tool, known as a boring bar, is mounted on the machine and inserted into the existing hole. The workpiece is held securely in place while the tool rotates and removes material.

The process of boring can be divided into the following steps:

1. Selecting the appropriate tool: The boring bar is chosen based on the desired size and accuracy of the hole. It should have the necessary rigidity and cutting capabilities to efficiently remove material.

2. Securing the workpiece: The workpiece is securely clamped or mounted on the machine to prevent any movement during the boring process. This ensures accuracy and stability.

3. Centering the tool: The boring bar is positioned concentrically with the existing hole to ensure proper alignment. This is crucial for achieving accurate results and preventing any deviation from the desired dimensions.

4. Rotating the tool: The machine is activated, causing the boring bar to rotate. As it rotates, the cutting edge of the tool makes contact with the inner surface of the hole, gradually removing material and enlarging the diameter.

5. Monitoring the process: The operator closely monitors the boring process to ensure the desired dimensions are achieved. This may involve measuring the diameter of the hole at regular intervals using precision instruments.

6. Finishing touches: Once the desired size is reached, the operator may use additional tools or techniques to achieve a smooth surface finish. This could involve using a reamer or honing tool to remove any remaining imperfections.

Overall, the process of boring is essential in various industries, including automotive, aerospace, and manufacturing. It allows for precise hole enlargement and ensures the desired dimensional accuracy and surface finish.

**Explanation:**

In a rolling operation, the draft is defined as the reduction in thickness of the workpiece as it passes through the rolling mill. The draft is influenced by various parameters, including the coefficient of friction between the rolls and the workpiece.

When the coefficient of friction is doubled, it means that the frictional force between the rolls and the workpiece is increased. This increased frictional force will result in a higher resistance to the motion of the workpiece through the rolling mill. As a result, the workpiece will experience a higher compressive force during the rolling process.

The draft in a rolling operation is directly proportional to the compressive force applied to the workpiece. Therefore, when the coefficient of friction is doubled, the compressive force acting on the workpiece will also be doubled. This increased compressive force will result in a higher reduction in thickness of the workpiece, leading to an increase in draft.

To calculate the percentage change in draft, we can use the following formula:

% Change in draft = (New draft - Initial draft) / Initial draft * 100

Since the initial draft is not given in the question, we can assume it to be a reference value, such as 100 units. Let's calculate the new draft when the coefficient of friction is doubled:

New draft = Initial draft + (Change in draft)

Since the coefficient of friction is doubled, the change in draft can be calculated as:

Change in draft = (2 * Initial draft) - Initial draft = Initial draft

Therefore, the new draft will be:

New draft = Initial draft + Initial draft = 2 * Initial draft

Now, let's substitute the values in the percentage change formula:

% Change in draft = (2 * Initial draft - Initial draft) / Initial draft * 100

Simplifying the equation, we get:

% Change in draft = Initial draft / Initial draft * 100 = 100%

Therefore, the percentage change in draft when the coefficient of friction is doubled is 100%. This means that the draft will increase by 100% when the coefficient of friction is doubled.

Hence, the correct answer is option C) 300%.