Principle of Manufacturing Engineering sheet 4

1) Answer all the following questions:

1. Define casting. What four basic steps are generally involved in making a casting?

*It means pouring molten metal into a refractory mold cavity and allows it to solidify. 

1. Initially a suitable size of molding box for creating suitable wall thickness is selected for a two piece pattern. Sufficient care should also be taken in such that sense that the molding box must adjust mold cavity, riser and the gating system (sprue, runner and gates etc.) .

2.Next, place the drag portion of the pattern with the parting surface down on the bottom (ram-up) board

 3.The facing sand is then sprinkled carefully all around the pattern so that the pattern does not stick with molding sand during withdrawn of the pattern

4. The drag is then filled with loose prepared molding sand and ramming of the molding sand is done uniformly in the molding box around the pattern. Fill the molding sand once again and then perform ramming. Repeat the process three four times,

2.What are the common factors which should be considered before designing a casting?

 *1. Initially a suitable size of molding box for creating suitable wall thickness is selected for a two piece pattern. Sufficient care should also be taken in such that sense that the molding box must adjust mold cavity, riser and the gating system (sprue, runner and gates etc.).

3.Sketch the cross-section through a permanent mold, incorporating all its principal parts.

Describe its construction in detail.

4.Describe the permanent mold casting process and discuss how it differs from the other casting processes.

*This process is commonly known as permanent mold casting in U.S.A and gravity die casting in England. A permanent mold casting makes use of a mold or metallic die which is permanent .

A typical permanent mold is shown in Fig. 5.8. Molten metal is poured into the mold under gravity only and no external pressure is applied to force the liquid metal into the mold cavity .

However, the liquid metal solidifies under pressure of metal in the risers, etc. The metallic mold can be reused many times before it is discarded or rebuilt. These molds are made of dense, fine grained, heat resistant cast iron, steel, bronze, anodized aluminum, graphite or other suitable refractoriness

5.What are the common materials used for making the permanent molds?

*For metallic category, the common materials are cast iron, mild steel and alloy steels. In the non-metallic group molding sands, plaster of paris, graphite, silicon carbide and ceramics are included

6.Mention the Advantage and Disadvantage of casting proses?

*Advantages

(i) Fine and dense grained structure is achieved in the casting .

(ii) No blow holes exist in castings produced by this method .

(iii) The process is economical for mass production .

.(iv) Because of rapid rate of cooling, the castings possess fine grain structure

.(v) Close dimensional tolerance or job accuracy is possible to achieve on the cast product

.(vi) Good surface finish and surface details are obtained

.(vii) Casting defects observed in sand castings are eliminated

.(viii) Fast rate of production can be attained

.(ix) The process requires less labor

Disadvantages

.(i) The cost of metallic mold is higher than the sand mold. The process is impractical for large castings

.(ii) The surface of casting becomes hard due to chilling effect

(iii) Refractoriness of the high melting point alloys.

7.What are the common tests performed on molding sands?

1. Moisture content Test

2. Clay content Test

3. Chemical composition of sand

. 4. Grain shape and surface texture of sand

5. Grain size distribution of sand

6. Specific surface of sand grains

7. Water absorption capacity of sand

8. Refractoriness of sand

9. Strength Test

10. Permeability Test

11. Flowability Test

12. Shatter index Test

13. Mould hardness Test

8.Explain the Permeability Test by drawing?

9.What is a core? What purposes are served by cores?

*Cores are compact mass of core sand (special kind of molding sand ) prepared separately that when placed in mould cavity at required location with proper alignment does not allow the molten metal to occupy space for solidification in that portion and hence help to produce hollowness in the casting. The environment in which the core is placed is much different from that of the mold..

1 Core produces hollowness in castings in form of internal cavities.

2 It must be sufficiently permeable to allow the easy escape of gases during pouring and solidification.

3 It may form a part of green sand mold

4 It may be deployed to improve mold surface.

5 It may provide external under cut features in casting.

6 It may be inserted to achieve deep recesses in the casting.

7 It may be used to strengthen the mold.

8 It may be used to form gating system of large size mold.

2) State which of the following statements is true and which is false:

1- The mold making material can be metallic or non-metallic. ( √ )

2- Molding sands may be of three types. ( x )

3- Core produces hollowness in castings in form of internal cavities. ( √ )

4- Core may not be inserted to achieve deep recesses in the casting. ( x )

5- Complicated jobs and jobs of various sizes cannot be easily shell molded. ( x )

3) Put a line under the correct answer: (MCQ)

1- ……… is defined as the ability of molding sand to withstand high temperatures without breaking down or fusing.

a- Permeability b- Refractoriness c- cohesiveness

2- ………… It is also termed as porosity of the molding sand in order to allow the escape of any air, gases or moisture present.

a- Permeability b- Refractoriness c- cohesiveness

3- ………… The process is economical for mass production.

a- Gravity die casting b- shell molding c- sand casting