Frictional energy is generated when the stirring tool comes in contact with the workpiece. This results in the generation of heat that is used to create a weld between two workpieces, hence the process is known as friction stir welding.
"Friction" is the mode of energy and "stir" resembles the rotation of the tool. Friction stir welding is a solid-state welding process, This means no melting of the workpiece takes place during the process.
Friction stir welding is an eco-friendly process of welding metals together using a non-consumable tool. No filler metals are used in the process of friction stir welding. Aluminum materials used in industries like automobiles and aviation are welded using friction stir welding.
History of Friction stir welding:
The Welding Institute (TWI) was the first organization to file a patent for friction stir welding in the year 1991. The places where TWI patented FSW were the US, Japan, Australia, and Europe. In 1992 TWI launched a project with the name "Development of new friction stir welding technique for welding aluminum". The project was divided into three phases each had different objectives to be fulfilled.
- Phase1. This phase focused on proving the technique realistic. Following welding of 6000 series aluminum alloys.
- Phase2. Focused on practical use of FSW on ships, aircraft, and automobiles.
- Phase3. The last phase focused on developing data for further industrialization of the process.
Nowadays friction stir after gaining all the attention throughout the world is used for many industrial purposes.
Elements and construction of Friction stir welding:
The Construction of friction stir welding is very simple and effective. Motor and guide mechanisms are connected to a power supply. The workpiece is kept on the worktable and the worktable is attached to the base. Workpieces are clamped using fixtures to restrict their degrees of freedom. The position of the tool is adjusted using the guide mechanism.
Following are the important elements used in the basic friction stir welding setup:
- Guide Mechanism
- Table and Base
The Tool is the most important element in the setup of friction stir welding. A non-consumable tool is used for welding workpieces in the case of FSW. The tool is made of high-carbon steel.
Advantages of high carbon steel:
- It protects the tool against wear and increases its machine life.
- Provides better machinability.
- Do not lose its properties at high temperatures.
The pins used in friction stir welding can be of different types. Some of the generally used pins are. Straight cylindrical, tapered cylindrical, threaded cylindrical, square cylindrical, etc.
Fixtures used in friction stir welding must be highly accurate. If there's an error with the fixture used, the force developed during the rotation of the tool may dislocate the workpiece. This will result in the formation of improper weld.
A motor is used to convert electrical energy to rotational motion of non-consumable tools.
#4. Table and base:
Base and table provide a platform for the welding operation to take place.
#5. Guide mechanism:
A guide mechanism is used to guide the rotating tool on the given workpiece.
Few important parameters should be taken under consideration before moving on to the working of friction stir welding.
Tool material is an important parameter while working on a friction stir welding machine. The tool must be strong enough to withstand high temperatures and pressure. Damage to the tool should be nil or minimal.
It should retain its properties at high temperatures. Generally, tools are made of high carbon steel to fulfill the above requirements.
There are 2 types of tool speeds involved in friction stir welding: one is the rotational speed of the tool expressed in RPM and the other is the linear speed of the tool, generally expressed in mm/min. RPM of the tool must vary from 200 to 2000. Lower and upper limits for linear speed are 10mm/min and 500mm/min respectively.
To produce a good quality weld the tool must be tilted to an angle of 2 to 5 degrees. This prevents the joints from being affected due to the force applied in the downward direction.
Working Principle of Friction stir welding:
The weld formed in the case of friction stir welding is due to the intermolecular bonding of metals at the time of heat diffusion. This is the basic working principle of friction stir welding.
The non-consumable tool creates shear stress and friction on the surface of the workpiece. Due to this heat generation takes place at the interface of the tool and the workpiece.
The heat generated is sufficient enough to create an intermolecular bond between the two workpieces without Melting the respective metal.
Given below is the step-wise working of friction stir welding:
- The workpiece to be welded is clamped using fixtures so that the degrees of freedom of the workpiece should be restricted. The operator must manually check if the workpiece is clamped tightly.
- The workpiece should be kept in an abutting position (there must be a small gap between them).
- The tool must be kept in the correct position, that is the pin must be inserted in the gap between the workpieces. And the shoulder must touch the joint.
- After the tool is placed in the correct position, the rotation of the tool begins.
- Friction is created due to which heat is generated. Because of heat and force applied in a downward direction weld is created between the two workpieces.
- The weld is moved forward with the linear motion of the tool w.r.t to the workpiece.
- When the required area is welded the tool is moved upwards and the welding stops.
- The workpiece is then removed by loosening the fixtures.
Materials that can be manufactured using friction stir welding are aluminum and its alloys, copper and its alloys, titanium, nickels, and plastics.
Advantages of Friction stir welding:
1. High accuracy: Accuracy is important while working on different industrial products. Dimensional stability in the case of friction stir welding is high and weld formation is extremely accurate.
2. No cracking: Cracks are developed on the workpiece due to traditional welding methods. But in the case of friction stir welding, there is no generation of cracks because no Melting of the workpiece takes place and the weld is created due to plastic Melting of the workpiece.
3. No loss of metal: There is a loss of metal in different welding processes. But in friction stir welding there is no generation of Arc hence the loss of metal is negligible. Hence no parent metal is lost during friction stir welding.
4.Clean process: There are no waste materials formed in friction stir welding. The process is clean and hence it is said to be an eco-friendly process of welding metals.
5. Non-consumable tool: The use of a non-consumable tool also gives environmental benefits to the process of friction stir welding. As there are no harmful fumes produced during the welding operation.
6. Surface finish: Excellent surface finish is obtained by friction stir welding. This results in a smooth welded surface and eliminates the requirement of grinding.
7. Automation:The process of friction stir welding has an advantage over traditional welding methods as it can be fully automated. The operator just needs to clamp the workpiece, further the process can be automated.
8. Safe process: Once the workpiece is clamped there is no need to touch the workpiece with hands. This ensures the safety of the operator performing the welding operation.
Friction stir welding Disadvantages:
1. Clamping: Clamping of the workpiece in case of friction stir welding is a crucial operation. As the forces applied during the welding may dislocate the workpiece from its desired position. For this heavy fixtures are used to hold the workpiece and clamping should be rechecked before starting the process.
2. Slow process: One of the drawbacks of friction stir welding is that the process is sometimes slower than other welding processes. This results in a decreased production rate of the plant.
3. High tool cost: The non-consumable tool used in FSW is made of high carbon steel and hence is expensive. The tool is specially designed for a specific purpose which makes it costlier.
4. Keyhole is left: When the process of welding is stopped the tool leaves an unfilled keyhole. This is not desired in some of the products, hence is considered as a drawback.
5. Large downward force: A large downward force is required a the initial stage to insert the pin in the abutting workpiece.
Friction stir welding Application and Uses:
The following application includes:
- Many shipbuilding companies have adopted the friction stir welding process for joining bigger parts of ships.
- FSW is used in aviation industries to weld huge parts like the wings of an aircraft.
- Friction stir welding is also used in the railway industry for the welding of large aluminum panels.
- In automotive industries for welding chassis made of aluminum friction stir welding is used over other welding processes due to its high tolerance.
- Fabrication of metals and their alloys can also be done using friction stir welding.
So this is all about Friction Stir Welding, I hope you enjoyed this article. I also wrote articles on some other welding processes do check out those too. And moreover do not forget to share the article on your favourite social platform.
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