casting

CASTING

Steps involved in making a casting :-
Casting:- it is the process of obtaining required component by pouring molten metal in the mould cavity and allowing to solidify.
Steds involved in making a casting are,
1.pattern preparation
2.Moulding
3.Melting and pouring the metal
4.solidification
5.removal of casting and fetling
6.machining
7.Heat treatment
8.finishing.

1. pattern preparation :-

A pattern is the replica of the final product required. Therefore, depending upon size, shape and casting process a pattern is prepared with either wood, metal or wax.
Thus, pattern prepared must include all the allowances to obtain a sound.
2. Moulding :-

It is the main step as it involves making of cavity. The steps involved in moulding are as follows

(a) initiay, drag is placed in the inverted position on moulding table.
(b) The pattern is then placed in suitable position inside the drag.
(c) now, parting sand is sprinkled on the pattern and all over drag.
(d) now, facing sand is poured only on pattern and it is pressed thoroughly on the pattern so that every detail of pattern is obtain.
(e) now, backins sand is poured all over the drag and then rammed thoroughly. This is repeated till sand level reaches the surface of drag.
(f) ramming is done all over the drag to get a better mould cavity.
(g) Then, the excess sand is removed using strike- off bar, to maintain a perfect surface level.
(h) using a vent rod, vent holes are made, which allows the air to escape.
(i) now, the drag is again reversed back. This can be seen in figure.
(j) now, cope is placed exactly above the drag and then parting sand is sprinkled again all over the pattern.
(k) now, the sprue and riser are placed in position in the cope.
(l) sprue is placed beside the pattern, where as the riser should be directly above the pattern.
(m) Facing sand is poured around sprue and riser and pressed throughly to obtain steady position.
(n) now, backing sand is poured all over cope and then ramming is done.
(o) Extra sand is removed using strike- off bar.
(p) now sprue and riser are removed and pouring basin is cut using a gate cutter near the sprue
(q) above fig shows the arrangement of cope and drag … etc.
(r) Now, the pattern is slowly removed without disturbing the cavity.
(s) Again cope is placed over the drag thus, moulding is obtain i.e., cavity is obtained.

3.Melting and pouring the metal :-

(a) Required metal is melted in oil furnace and then using the saddles molten metal can be transferred into cavity.
(b) care should be taken that metal is poured with uniform velocity, so as to obtain sound casting.

4. solidification :-

In this step, after moltan metal is poured, it is allowed to cool for certain duration, so that induced stresses can be required. Solidification time actualy depends on volume and surface area of casting.

5.Removal of casting and feting :- After the metal gets solidified, casting is removed from the mould and fetling is done.
Fetling is cleaning operation of the cast using a brush to remove the sand particles on it.

6. Machining :-
(a) The casting so removed has sprue, risers, ingates, basewell and pouring basin.
(b) thus, in this step all these are removed and we remain with only the product required.

7. Heat treatment :- The heat treatment is done to relieve these include stresses.

8.Finishing :-
This is the final step where in fine finishing of components is done so as to obtain the dimensional accuracy and surface finish.

Advantages of casting process :-
Advantages of casting process over other manufacturing procee are,
1.it is the most versatile process.
2.difficult and uneconomical shapes may be achieved by casting.
3.metails like castiron difficult to shape by other processes may be eaisly cast.
4.parts which are small or big with intricate shapes can be produced by casting, which is almost not possible by other processes.
5.There is no restrication to the type of metal to be casting as in other production process there may be restrictions (Eg: welding)
6.Even plastics can be casted.
7.surface finish of the product obtained by casting is too high.
8.machining cost can be reduced.
9.component achieves good mechanical properties after casting.
10.cost of casting can be reduced by using mechanical and automatic casting process.
11.number of castings can be obtained at single time.


Disadvantages of casting process:-
1.making of casting needs so much time.
2.In metal casting metal needs to be melted which is a high energy consuming process.
3.metal casting needs more ladder compare to other process.
4.The productivity is less then the other automatic processes, like rolling.


Limitations of casting process:-
1.this process cannot obtain high dimensional accuracies.
2.it is difficult to remove thr deffects which arise due to mositure present in sand casting.
3.several casting defects may arise when moulding and foundary are not performed property.

Applications:-
1.machine tool beds of lathe .etc..
2.power generaters.
3.Railway crossings.
4.paper mill stock braker parts.
5.air craft jet engine blades.
6.agriculture parts.
7.sanitory fittings to communication,construction and atomic energy applications.
8.turbine vanes(cast iron).
9.mill housings(cast steels).
10.cast parts are used more than 90% in automobile industry and more than 50% of the weight in tractor parts.