MCE2120_Manufacturing Process upto Grinding.pdf

Question 1

What are the two primary types of metal casting processes?

Answer 1

1. Expendable Mould Casting: Uses molds that are destroyed after each casting (e.g., sand casting, investment casting).
2. Permanent Mould Casting: Utilizes reusable molds (e.g., die casting, centrifugal casting).

Question 2

What are the advantages of expendable mould casting?

Answer 2

Expendable mould casting can produce complex shapes, it’s cost-effective for small production runs, and allows for intricate designs using materials like sand or plaster.

Question 3

What are the benefits of permanent mould casting?

Answer 3

Permanent mould casting offers better surface finish, closer dimensional accuracy, and is more economical for high-volume production since the mold can be reused multiple times.

Question 4

What is centrifugal casting, and what are its applications?

Answer 4

Centrifugal casting involves rotating a mold around its axis while pouring molten metal. It is used for producing cylindrical objects like pipes, gun barrels, and bushings, which benefit from enhanced mechanical properties due to directional solidification.

Question 5

What is Shrinkage Allowance in casting, and why is it necessary?

Answer 5

Shrinkage allowance compensates for the natural contraction of metal as it cools from its pouring temperature to solidification and finally to room temperature. Different metals have varying shrinkage rates, and this allowance ensures the final dimensions are accurate.

Question 6

What is Machining Allowance, and when is it applied?

Answer 6

Machining allowance refers to the extra material added to the casting to account for the material that will be removed during the finishing (machining) process. It ensures the final casting meets the required tolerances and surface finish after machining.

Question 7

Explain Draft Allowance in casting.

Answer 7

Draft allowance refers to the taper applied to vertical surfaces of a casting pattern. This allows easy removal of the pattern from the sand mold without damaging the mold cavity. Typical draft angles range from 0.5 to 2 degrees.

Question 8

What is Distortion Allowance in casting?

Answer 8

Distortion allowance compensates for warping or changes in shape that occur due to internal stresses during cooling. It is provided particularly in castings with asymmetrical or thin sections.

Question 9

What are the key properties of green sand used in molding?

Answer 9

Green sand is a mixture of silica sand, clay, and water. It offers good moldability, collapsibility (after casting), and thermal stability. However, green sand molds can deform easily under high pressure or weight of the molten metal.

Question 10

What are dry sand molds and when are they preferred over green sand molds?

Answer 10

Dry sand molds are created using sand mixed with a binder and baked in an oven to harden. These molds are stronger and more accurate than green sand molds and are used when more precise dimensional accuracy is needed, such as in large castings.

Question 11

What is core sand used for in casting?

Answer 11

Core sand is a special type of molding sand used to make cores, which form hollow cavities in castings. Core sand must have high collapsibility to allow easy removal after casting solidification.

Question 12

What is the primary purpose of a gating system in casting?

Answer 12

The gating system controls the flow of molten metal into the mold cavity, ensuring that the mold is filled smoothly and completely without causing defects such as turbulence, porosity, or misruns.

Question 13

What is the role of a sprue in the gating system?

Answer 13

The sprue is the vertical passage in a mold through which molten metal flows from the pouring basin to the runner and then into the mold cavity. It helps control the flow rate and reduces turbulence.

Question 14

What is a riser and why is it important in casting?

Answer 14

A riser is a reservoir in the mold that feeds molten metal into the casting during solidification to compensate for shrinkage. This ensures that the final casting is free of voids or porosity.

Question 15

What is the purpose of a chill in a casting process?

Answer 15

Chills are metallic objects placed in the mold to increase the cooling rate in specific areas. This helps achieve directional solidification and prevents shrinkage defects.

Question 16

What are some common shrinkage defects in casting, and how can they be prevented?

Answer 16

Shrinkage defects include shrinkage cavities and porosity. They can be prevented by using proper riser placement, adding chills to the mold, and optimizing the gating system for directional solidification.

Question 17

What causes misruns in casting and how can they be avoided?

Answer 17

Misruns occur when molten metal solidifies before completely filling the mold. They can be avoided by ensuring adequate metal pouring temperature, proper gating system design, and minimizing turbulence.

Question 18

What is cold shut, and what are its causes?

Answer 18

Cold shut is a defect that occurs when two streams of molten metal meet but do not fuse properly, resulting in a weak joint. Causes include low pouring temperature and poor gating design.

Question 19

How does gas porosity occur in castings, and what remedies can prevent it?

Answer 19

Gas porosity occurs when trapped gases (like hydrogen or nitrogen) form bubbles in the casting. Remedies include using degassing techniques, proper venting of the mold, and controlling the temperature and humidity during molding.

Question 20

What is radiographic inspection in casting and what does it detect?

Answer 20

Radiographic inspection uses X-rays or gamma rays to detect internal defects such as voids, cracks, and porosity within castings. It is a common non-destructive testing method.

Question 21

What is the purpose of magnetic particle inspection in castings?

Answer 21

Magnetic particle inspection detects surface and near-surface defects like cracks or inclusions in ferromagnetic materials by applying a magnetic field and using ferromagnetic particles to indicate discontinuities.

Question 22

What does pressure testing involve in casting inspection?

Answer 22

Pressure testing involves applying internal pressure to the casting (e.g., using air or fluid) to check for leaks, porosity, or weaknesses in the casting walls.

Question 23

How are cutting machine tools classified?

Answer 23

Cutting machine tools are classified based on the operation they perform:

Turning machines (e.g., lathes),
Milling machines,
Drilling machines,
Grinding machines.

Question 24

What is the difference between lathe machines and milling machines?

Answer 24

A lathe machine rotates the workpiece against a stationary cutting tool, primarily used for turning operations. A milling machine rotates a cutting tool against a stationary workpiece, ideal for producing flat surfaces and complex shapes.

Question 25

What are shaping machines and what are their applications?

Answer 25

Shaping machines use linear reciprocating motion of the tool to remove material. They are used to produce flat surfaces, grooves, and keyways on small to medium workpieces.