* Which of the following is a metal joining process ?
In mechanical industries every worker is working for changing the shape of metals by different methods and maching.
To change the shape of the metals the following metho dy are generally used.
(i) Forging
(ii) Moulding / Casting
(iii) Cutting
(iv) Joining
1. Forging : This is a method used for changing the shape of metals , by heating the metal in a forge and then hammering it on an anvil .
For example forming chixel , punch etc. by blacksmiths.
2. Moulding : This is a method in which the shape of the metal is changed by melting the metal into liquid form and then pouring the same into moulds.
The poured metal takes the shape as per the mould after cooling . For example bench vice , machine beds , frying pans, aluminiura pressure cooker etc.
3. Cutting : This is a method in which the shape of metal is changed by cutting the exter material from a metal piece ar per our requirement . For example fitting turning machining , rehearing , gas cutting etc.
4. Joining :
This is a method in which the shape of the metal is changed by joining two or more pieces of metals as per our requirement . For example making a chair , welding table , metal bridge , bus body , tin container , oilcan etc.
Metal Joining Process
Definition :-
Metal joining process is a process in which the shape of the metal is changed by joining two or more pieces of metals as per our requirement .
Methods :
The following methods are commonly used for joining of metals.
|
Mechanical |
Thermal |
| (i) |
Seaming |
Soldering |
| (ii) |
Bolting |
Brazing |
| (iii) |
Riveting |
Welding
|
1. Seaming : Seaming in a metal joining process in which the edges of thin sheets to be joined are folded , hooked together and then pressed to form a joint . The faint can be opened by unfolding the hooks .
2. Bolting : Bolting is a method of metal joining by drilling a common hole in overlapped pieces and then joining them by using a set of bolt and nut . The Foint can be separated by unserewing the nut .
3. Riveting : Riveting is a method of joining by drilling a common hole in overlapped pieces and then fastening them by putting a rivet and hammering.
This joint can be opened by cutting the rivet head .
4. Soldering : Soldering is a method of metal joining which in applied on thin metals using 'solder' as a joining medium . Solder is generally made of lead and tin in different proportion . The melting point of solder is less than the metals to be joined and generally below 427 ° c . There is no needed to be heated the joining edges of the metals in gold ering before joining.
The soldering joint can be opened by heating upto the solder melting temperature .
5. Brazing : Brazing in a metal joining process in which to joining medium is used called 'spelter' . The melting temperature of spelter is more than 427 ° c , but lower than the melting temperature of the parts to be joined . In case of plain brazing spelter is made of copper and zine . Joining edges of the metals must be heated upto red hot condition before joining . Brazing joint has more strength than soldering joint .
The joint can also be opened by heating unto the melting point of spelter used.
6. Welding : Welding is a metal joining methods in which the joining edges are heated and fused together with or without filler metal to form a permanent on homogeneous bond . The welding joint cannot be opened on separated .
Comparison Between Welding and other Metal Joining Methods
(i) Welding is the only method to join metals permanently .
Riveting , assembling with bolt or bolting , Seaming , Soldering and Brazing- all result in temporary joints .
(ii) Welded joints cannot be separated because it is made homogeneous by heating and fusing the joining edges together .
The temporary joints can be separated if :-
— the head of the rivet is cut .
— nut of the belt is unserewed .
— hook of the seam is opened .
— more heat is given than that required for soldering and Breazing .
