Views: 1 Author: Site Editor Publish Time: 2022-01-21 Origin: Site
The friction heat generated by the friction between thermoplastic plastics is melted on the friction surface, and then the pressure is pressed, and the method of cooling under pressure is called friction welding. This method is most suitable for rotating body parts. Similar to friction welding of metals, one piece is fixed while the other rotates and pressure is applied. We will briefly introduce this for you.
When welding solid parts, due to the high linear velocity at the outer edge of the rotating body, the friction heat increases from the center to the outer edge, so that there is welding stress at the joint. Therefore, the welding surface can be made into a spherical shape, so that the friction occurs at the center first, and then gradually pushes to the edge.
For thermoplastics a satisfactory joint can be obtained by welding. In addition to welding in the actual production of plastic can also be bonded and mechanical connection, especially for those who cannot be welded with welding method of plastic can only be bonded and mechanical connection.
In two welding face upon certain axial stress, and have made contact friction exercise, the heat generated in friction, the welding interface is heated to a certain temperature (generally is slightly lower than the melting point of materials, such as carbon steel welding temperature) when rapid stop moving, and upsetting to pressure, make the two welding pieces of metal produces a certain amount of plastic deformation. Thus the two welds are firmly welded together.
1. Combined with the analysis of welding process, friction welding of similar metals can be divided into three stages:
1) The contact surface of two welds begins to rub, first of all, the oxide and impurities attached to the surface are damaged and eliminated, and the uneven surface of the contact surface produces plastic deformation, the grain is damaged, the result is that the contact surface is heated, and reveals a smooth pure metal surface.
2) The contact surface of pure metal continues to carry out friction movement, so that the temperature of the contact surface continues to rise, the plastic deformation increases, and the metal mutual "bonding" phenomenon (that is, local welding) begins to occur. As the friction motion continues, the temperature near the contact surface of the weldment rises rapidly and approaches or reaches the welding temperature.
3) When the welding temperature is reached, the metal is very plastic. When the relative motion is stopped quickly and the forging pressure is very high, the two welds produce a large plastic deformation, the metal atoms on the contact surface are closer to each other, mutual diffusion and intercrystal bonding occur, forming common recrystallization, intermediate compounds and a small amount of recrystallization grains, so as to weld the two welds together.
2. The friction welding of dissimilar metals
For the friction welding of dissimilar metals, the mechanism of friction welding process is different because of the difference of hardness, plasticity and melting point of two metals. For example, in the process of friction welding of copper and aluminum, initially two metal atoms penetrate and diffuse each other under the action of friction heat and pressure. An alloy of two metals is formed on the surface of the joint. This alloy has different properties from the original metal, such as reduced plasticity and increased strength. Therefore, the initial friction between copper and aluminum metal, when the formation of a very thin alloy layer, because its strength is higher than aluminum, on the aluminum side will become the lowest shear strength, so the friction gradually becomes the friction between the alloy layer and aluminum. It can be seen that copper-aluminum friction welding is based on the friction surface of copper. This concept is also borne out by experimental observations, in which it is evident that a very thin layer of copper-bearing alloy has been welded to the copper if friction is not applied to the end, i.e. the two welds are separated. The alloy thickens over time and gradually becomes pure aluminum, at which point the alloy thickness stops growing. Of course, if the final push force is applied, the two are welded together.