All questions of Manufacturing Engineering for Mechanical Engineering Exam

Explanation:

The correct answer to the given sentence is "had been sleeping" because it is in past perfect continuous tense. This tense is used to describe an action that was ongoing in the past before another action took place.

Here is a detailed explanation of the sentence:

- The sentence is in the past tense, as indicated by the word "woke" which is the past tense of "wake".
- The action of sleeping started before the moment of waking up and continued until that moment.
- The past perfect continuous tense is formed using the auxiliary verb "had" in the past perfect tense, the main verb "been" in the present participle form, and the main verb "sleep" in the base form with "-ing" added to the end.
- The sentence can be rephrased as "By the time I woke him up, he had been sleeping for three hours."
- The use of past perfect continuous tense emphasizes the duration of the action of sleeping that had been happening before the moment of waking up.

In summary, the correct answer "had been sleeping" indicates that the action of sleeping had started before the moment of waking up and had been ongoing for a duration of three hours until that moment.

Given data:
Stroke of a shaping machine = 250 mm
Number of double strokes per minute = 30

To find: Overall average speed of operation

Formula used:
Overall average speed of operation = (length of stroke x number of double strokes per minute) / 1000

Calculation:
Substituting the given values in the formula, we get
Overall average speed of operation = (250 x 30) / 1000
= 7.5 m/min

Therefore, the correct answer is option C, i.e., 7.5 m/min.

Explanation:
The overall average speed of operation of a shaping machine is the distance traveled by the tool in one minute. As the machine makes 30 double strokes per minute, the tool travels a distance of 250 mm x 30 = 7500 mm or 7.5 m in one minute. Hence, the overall average speed of operation is 7.5 m/min.

Ra

Taylor Equation for Tool Life:
The Taylor equation is used to determine the relationship between cutting speed and tool life. The equation is as follows:

VT^n = C

where,
V = cutting speed
T = tool life
n, C = constants

Calculating the Percentage Increase in Tool Life:
Given, n = 0.5 and C = 400

Let's assume the initial cutting speed is V1 and the corresponding tool life is T1. When the cutting speed is reduced by 50%, the new cutting speed becomes V2 = V1/2.

Using the Taylor equation, we can find the new tool life T2.

T1 = C/V1^n

T2 = C/V2^n
= C/(V1/2)^n
= C/(2^n * V1^n)
= (1/2^n) * (C/V1^n)
= (1/2^(0.5)) * T1
= 0.707 * T1

Therefore, the new tool life T2 is 0.707 times the initial tool life T1.

The percentage increase in tool life is given by:

((T2 - T1)/T1) * 100
= ((0.707T1 - T1)/T1) * 100
= -29.3%

However, we need to calculate the percentage increase in tool life when the cutting speed is reduced by 50%. This can be found as follows:

Percentage increase in tool life = |((T2 - T1)/T1) * 100|
= |((-0.293) * 100)|
= 29.3%

Therefore, the percentage increase in tool life when the cutting speed is reduced by 50% is 29.3%. This is option 'D'.

Shrinkage allowance is the difference in dimensions between the pattern and the final casting due to the shrinkage of the metal during solidification. The amount of shrinkage allowance required is dependent on the material being used for casting.

Explanation:

Steel has the highest shrinkage allowance among the given materials. This is due to the following reasons:

1. High melting point: Steel has a high melting point compared to other materials. This means that it takes longer for the metal to cool and solidify, resulting in more shrinkage.

2. High carbon content: Steel has a higher carbon content than other materials. Carbon is a strong carbide former, which can lead to a reduction in the solidification range of steel, resulting in more shrinkage.

3. Low thermal conductivity: Steel has a lower thermal conductivity than other materials. This means that heat is retained for a longer time, resulting in a longer solidification time and more shrinkage.

4. High density: Steel has a higher density than other materials. This means that it will shrink more during solidification.

Therefore, steel requires the highest shrinkage allowance among the given materials.

Aluminum is not a strongest materials to compare these three material so it not suitable for wire material

Sintering is a process used in the manufacturing of metal parts, where powdered metal is compacted into a desired shape and then heated to a temperature below its melting point. During sintering, the metal particles are bonded together to form a solid object. The sintering time required for different materials can vary based on their properties and composition.

The correct answer for the minimum sintering time is option 'A', which is iron.

Here is an explanation of why iron has the minimum sintering time compared to the other options:

1. Iron:
- Iron has a relatively low melting point compared to other materials like stainless steel, alnico alloy, and tungsten carbides. This lower melting point allows for faster sintering because less time is required to heat the iron powder to the necessary temperature for bonding.
- Iron also has good sintering properties, meaning it can be easily compacted and bonded during the sintering process. This further reduces the required sintering time.

2. Stainless Steel:
- Stainless steel is an alloy composed of iron, chromium, and other elements. It has a higher melting point compared to pure iron, which means it requires more time to reach the sintering temperature during the heating process.
- Additionally, stainless steel has higher hardness and strength compared to iron, which can make it more difficult to deform and bond the particles during sintering. This may also increase the required sintering time.

3. Alnico Alloy:
- Alnico alloy is a type of permanent magnet alloy composed of aluminum, nickel, cobalt, and iron. It has a higher melting point compared to iron, similar to stainless steel.
- The complex composition of alnico alloy can make it more difficult to sinter compared to pure iron. The different elements in the alloy may have different melting points and sintering behaviors, requiring more time to achieve proper bonding.

4. Tungsten Carbides:
- Tungsten carbides are a group of hard and brittle materials composed of tungsten and carbon. They have a very high melting point, making them the most challenging to sinter.
- The high melting point of tungsten carbides requires a longer sintering time to reach the necessary temperature for bonding. Additionally, the hardness and brittleness of tungsten carbides can make it more difficult to deform and bond the particles during sintering.

In conclusion, the sintering time is minimum for iron compared to stainless steel, alnico alloy, and tungsten carbides. This is due to the lower melting point and better sintering properties of iron.

The correct answer is option 'C', which states that tool signature is the procedure adopted for describing various tool angles. In the field of mechanical engineering, tool signature plays an important role in understanding and identifying the characteristics of a cutting tool. It consists of a set of numbers and symbols that provide information about the angles and dimensions of the tool.

The tool signature is used to describe the various angles associated with a cutting tool. These angles include:

1. Rake angle: It is the angle between the rake face of the tool and the normal to the machined surface. It determines the direction of chip flow and affects the cutting forces and tool life.

2. Relief angle: It is the angle between the flank of the tool and a line perpendicular to the machined surface. It provides clearance for the tool, reducing friction and minimizing the chance of built-up edge formation.

3. Side cutting edge angle: It is the angle between the side cutting edge of the tool and the machined surface. It determines the direction of cutting forces and affects the chip thickness and surface finish.

4. End cutting edge angle: It is the angle between the end cutting edge of the tool and the machined surface. It affects the cutting forces and surface finish.

5. Nose radius: It is the radius of curvature at the tip of the tool. It reduces the stress concentration and improves tool life.

The tool signature also includes information about the dimensions of the tool, such as the tool height, tool width, and nose radius. These dimensions are important for selecting the appropriate tool for a specific machining operation.

By using the tool signature, engineers and machinists can easily identify and select the right tool for a particular machining operation. It helps in optimizing cutting conditions, reducing tool wear, and improving productivity. Moreover, the tool signature is also useful in tool regrinding or replacement, as it provides a reference for restoring the original tool angles.

In conclusion, the tool signature is a procedure adopted for describing various tool angles. It is an essential tool in the field of mechanical engineering, providing valuable information for tool selection, optimization of cutting conditions, and tool maintenance.

Explanation:

When pouring molten metal into a mould, it is important to ensure that the metal fills the entire cavity without any defects or voids. The use of risers is a common technique to prevent shrinkage defects in castings. A riser is an additional volume of molten metal that is connected to the casting through a channel, and it serves as a reservoir of molten metal that can compensate for the shrinkage during solidification.

If the molten metal does not appear in the riser during pouring, it indicates that a sound casting will be produced. This is because the molten metal has completely filled the cavity without any defects or voids, and there is no need for additional molten metal from the riser. This is a desirable situation, as it indicates that the casting will have good dimensional accuracy and mechanical properties.

If the molten metal does not appear in the riser, it rules out the possibility of the other three options:

- An obstruction between sprue and riser: If there was an obstruction, the molten metal would not have been able to flow freely into the cavity, and there would be defects or voids in the casting.
- Insufficient molten metal to fill the cavity: If there was insufficient molten metal, the cavity would not have been completely filled, and there would be defects or voids in the casting.
- Either insufficient molten metal to fill the cavity or an obstruction between sprue and riser: This is a combination of the previous two options, and it is also ruled out by the absence of molten metal in the riser.

Thus, the absence of molten metal in the riser during pouring is a good sign that a sound casting will be produced.

Riser in Casting Processes

Riser is an integral part of casting processes. It is a reservoir of molten metal that compensates for the shrinkage that occurs during solidification. This shrinkage can lead to various casting defects, such as porosity, shrinkage cavities, and cracks.

Purpose of Riser

The primary purpose of the riser is to feed the molten metal to the casting in order to compensate for the shrinkage. When the molten metal is poured into the mould cavity, it begins to solidify from the surface towards the centre. As the metal solidifies, it shrinks and creates a void or a cavity in the casting.

The riser compensates for this shrinkage by providing additional molten metal to the casting. The molten metal in the riser solidifies after the metal in the casting has solidified. This solidification of the riser provides an additional source of metal to compensate for the shrinkage in the casting.

Other Purposes of Riser

Apart from compensating for the shrinkage, the riser also serves other purposes in the casting processes. These include:

1. Acting as a reservoir for the molten metal: The riser acts as a reservoir for the molten metal and ensures that there is enough metal available to fill the mould cavity.

2. Providing a source of feeding: The riser provides a source of feeding to the casting by supplying additional molten metal.

3. Reducing the risk of defects: The riser reduces the risk of defects in the casting by compensating for the shrinkage and ensuring that the casting is filled with metal.

Conclusion

In summary, the primary purpose of the riser in casting processes is to compensate for the shrinkage that occurs during solidification. It provides additional molten metal to the casting to ensure that the casting is filled with metal and reduce the risk of defects.

The impurities in true centrifugal casting get collected in the middle portion in between the inner and outer surface. This is because of the unique nature of the centrifugal casting process, which involves the use of centrifugal force to distribute the molten metal and impurities.

Explanation:
1. The Centrifugal Casting Process:
- Centrifugal casting is a casting process that uses the principle of centrifugal force to distribute the molten metal and impurities.
- In this process, a mold is rotated at high speeds while the molten metal is poured into it.
- The centrifugal force generated by the rotation of the mold pushes the molten metal towards the outer surface of the mold, while the impurities tend to move towards the inner surface.

2. Movement of Impurities:
- As the molten metal is poured into the rotating mold, the centrifugal force acts on it, causing it to move towards the outer surface of the mold.
- At the same time, the impurities present in the molten metal also experience the centrifugal force and tend to move towards the inner surface.
- However, due to their higher density compared to the molten metal, the impurities are not able to move as easily as the molten metal.
- As a result, the impurities get trapped in the middle portion of the casting, which is in between the inner and outer surface.

3. Collection of Impurities:
- The impurities that get collected in the middle portion of the casting are typically in the form of slag, oxides, or other non-metallic contaminants.
- These impurities are undesirable in the final casting as they can weaken the material and affect its mechanical properties.
- To minimize the presence of impurities, various techniques can be used, such as the use of proper gating systems, filtering the molten metal, and controlling the pouring temperature.

In conclusion, in true centrifugal casting, the impurities get collected in the middle portion in between the inner and outer surface. This is due to the movement of the molten metal towards the outer surface under the influence of centrifugal force, while the impurities, being denser, tend to remain in the middle portion. Proper control and techniques can be employed to minimize the impurities and ensure a high-quality casting.

Seam Welding Process Explanation:

Seam welding is a type of welding process that involves making a series of overlapping spot welds to form a continuous seam. Here is an explanation of why seam welding is considered a continuous spot welding process:

Continuous Spot Welding:
- Seam welding is a variation of spot welding where the electrodes move along the joint, producing a continuous weld rather than individual spot welds.
- The electrodes apply pressure and current to the workpieces, creating a series of overlapping welds along the seam.

Advantages of Seam Welding:
- Seam welding is a high-speed process that can create a leak-proof and hermetic seal along the entire length of the seam.
- It is commonly used in the automotive industry for welding fuel tanks, exhaust systems, and other components where a continuous, watertight seal is required.

Comparison with Other Welding Processes:
- Seam welding differs from arc welding processes like MIG or TIG welding, which use a continuous electrode to create a molten pool of metal that solidifies into a weld bead.
- It is also distinct from multi-spot welding processes, which involve making multiple individual spot welds at different locations along the joint.

In conclusion, seam welding is categorized as a continuous spot welding process because it involves creating a series of overlapping spot welds to form a continuous seam. This process is widely used in industries where leak-proof and continuous welds are required.

Degrees. The diameter of the regulating wheel is 254 mm.

To find the rotational speed of the regulating wheel, we can use the formula:

Rotational speed = Surface speed / Circumference

The circumference of the regulating wheel can be calculated using the formula:

Circumference = π * diameter

Circumference = 3.14 * 254 mm
Circumference = 798.36 mm

Now, we can calculate the rotational speed:

Rotational speed = 127 mm/s / 798.36 mm
Rotational speed ≈ 0.159 radians/s

Therefore, the rotational speed of the regulating wheel is approximately 0.159 radians/s.

Shrinkage Allowance in Materials

Introduction
Shrinkage allowance is the amount of additional material that needs to be added to a casting pattern to compensate for the shrinkage that occurs during the solidification and cooling process. The shrinkage allowance ensures that the final casting dimensions are accurate and match the desired specifications. Different materials have different shrinkage rates, which is why different shrinkage allowances are required for different materials.

Explanation
Among the materials mentioned in the options (Cl, Lead, Brass, and Aluminium alloy), the material with the highest shrinkage allowance is Brass.

Shrinkage Allowance Factors
Several factors influence the shrinkage allowance in a material, including:
1. Cooling rate: Faster cooling rates tend to increase shrinkage.
2. Solidification time: Longer solidification times lead to higher shrinkage.
3. Alloy composition: Different alloy compositions can result in varying shrinkage rates.

Shrinkage Allowance Comparison
Let's analyze the shrinkage allowances for each material:

1. Cl (Chlorine)
Chlorine is not a casting material but a chemical element. Therefore, it does not have a shrinkage allowance.

2. Lead
Lead is a soft and malleable material with a relatively low melting point. It exhibits minimal shrinkage during the cooling process. Therefore, the shrinkage allowance for lead is relatively low compared to other materials.

3. Brass
Brass is an alloy composed of copper and zinc. It has a higher melting point compared to lead. Due to the different thermal properties of copper and zinc, brass experiences a significant amount of shrinkage during cooling. Consequently, a larger shrinkage allowance is required for brass castings.

4. Aluminium Alloy
Aluminium alloys are widely used in various industries due to their lightweight and excellent mechanical properties. They have a relatively low shrinkage rate compared to materials like brass. Therefore, the shrinkage allowance for aluminium alloy castings is lower compared to brass.

Conclusion
Among the materials mentioned in the options, brass has the highest shrinkage allowance. This is because brass, being an alloy of copper and zinc, experiences significant shrinkage during the cooling process. It is important to consider the shrinkage allowance when designing casting patterns to ensure accurate final dimensions in the castings.