Did You Know?
In vacuum, when similar metals come in contact with one another, they form a strong joint. In presence of atmosphere, an oxidized layer forms at the joint that prevents formation of such strong bonds.
In the manufacturing industry there is a high demand for various metallic structures. These structures can be made of a single metal or a variety of metals. Such components, that are made up of two or more metals are known as hybrid components. There are various ways in which these hybrid components or even structures are held together and some of these methods include use of fasteners or a nut-bolt assembly.
The above mentioned ways of assembling the heterogeneous components is not permanent and can be dismantled easily. Not to forget that these techniques also can compromise the structural stability as well as the quality of the joint and of the structure as well. This leads to the need of techniques that are able to form strong and lasting joints between metals. It is not a requirement for only those structures which have a variety of constituents but such joints are also needed for structures that are made using same metal.
There are various methods that can create more lasting joints that also ensure that the integrity of the structures is maintained. These techniques are brazing, soldering, and welding. Given below is an overview of these three methods that are used for forming joints.
Brazing is used when different types of metals are to be used. These metals that are to be joined are known as base metals. A brazing torch is used in brazing to form joints. This process includes use of a third metal to form the joint, which is known as the filler metal. The brazing torch is used to heat the filler metal a little above its liquidus temperature, which is its melting temperature. This temperature, however, must be below the solidus temperature of the base metals. The solidus temperature is the minimum temperature at which the metals exists in completely solid form.
The filler metal that is applied over the joint will melt and cover the joint completely by capillary action in the general area of the joint. The capillary action is the ability of a liquid to reach in places that do not have easy access without any help and in face of opposing forces like gravitational force.
The cooling of the filler metal results in formation of metallurgical bonds between the filler and base metals. A bond that is formed due to a chemical reaction between base metals and the filler metal is known as a metallurgical bond. The temperature required for brazing is above 800 on a Fahrenheit scale.
Advantages of Brazing
- The joint formed by the brazing process is cleaner as the process does not require melting of base metals, and hence the base metals retain their physical properties too.
- Formation of a non-distorted, integral joint eliminates the need of any follow-up procedures on the joint.
- As there aren't much variations, the entire process can easily be automated and used for mass production.
- Brazing can be employed for joining base metals with different melting points in a cost-effective manner.
Disadvantages of Brazing
- As the liquidus temperature of the filler metal cannot be high, soft metals have to play the role of filler metals.
- The use of soft metals, that is metals with lower melting temperature, will create limitation for using these joints at higher temperatures.
Welding does not involve use of a third metal to connect two base metals and this is one of the major difference between brazing and welding. Another differentiating factor between the two methods is that the workpieces are melted in welding. Welding forms joints on the surface, whereas, brazing forms a layer of filler metal at the joint, between the two base substrates. In the welding process, the two components that are to be welded together are connected after melting them down at the joints. The bond thus formed, once the joint cools down, is a strong one. Also, the welded joints have the ability to withstand higher temperatures as compared to brazing. A welding torch is what one needs for welding two metals together.
Advantages of Welding
- Joints of high strengths can be formed through welding.
- These joints have tolerance to higher temperatures.
- The joints formed through this process are rigid.
Disadvantages of Welding
- Once a joint is formed, it cannot be altered.
- These joints cannot withstand vibrations.
The process of soldering is very much similar to the process of brazing. The difference, however, lies in the temperatures that are required for the two procedures. In case of soldering it is much lower than what is required for brazing. The temperature that is required for soldering hovers below 800°F scale.
Similar to brazing, the process of soldering involves melting of filler metal over base metals. One of the most common fillers used in this process is lead. One would need a solder gun, which is also known as a soldering iron, to create joints using this procedure that is a few thousand years old.
Advantages of Soldering
- The bonds that are formed by this procedure are strong.
- The joints are good conductors of electricity.
Disadvantages of Soldering
- These joints do not have much tolerance to high temperatures.
- They have lead in them which is a harmful substance. In the recent years, lead-free soldering has been employed in the electronics industry. Nevertheless, the fumes released in the process of soldering is considered to be toxic.
Brazing is mainly used in packing together electronic systems, while the major applications of soldering are in plumbing and in making electronic circuits. Welding is used majorly in construction and fabrication industry.