The Define Of Friction Welding Process
What is friction welding? Friction welding refers to a method of welding by using the heat generated by the friction of the contact surface of the workpiece as a heat source to cause the workpiece to plastically deform under the action of pressure.
Under the action of pressure, under the action of constant or increasing pressure and torque, the relative motion between the welding contact end surfaces is used to generate frictional heat and plastic deformation heat in the friction surface and its surrounding area, so that the temperature of the surrounding area rises to In the temperature range close to but generally lower than the melting point, the deformation resistance of the material is reduced, the plasticity is improved, and the oxide film at the interface is broken. Solid-state welding method to achieve welding.
The Process Characteristics Of Friction Welding Process
- The welding construction time is short and the production efficiency is high. For example, the productivity of the engine exhaust valve double-head automatic friction welding machine can reach 800 to 1200 pieces/h. For the welding of oil drill pipes and joints with an outer diameter of Φ127mm and an inner diameter of Φ95mm, it only takes ten seconds for continuous drive friction welding.
- The welding deformation caused by the welding thermal cycle is small, the dimensional accuracy after welding is high, and there is no need to correct the shape and eliminate the stress after welding. Diesel engine pre-combustion chamber produced by friction welding, the overall length error is
±0.1mm; the special welding machine can ensure that the length tolerance after welding is ±0.2mm, and the eccentricity is 0.2mm.
- High degree of mechanization and automation, and stable welding quality. When the welding conditions are given, the operation is simple and does not require special welding technicians.
- It is suitable for welding of various dissimilar materials, and can be welded to aluminum-steel, aluminum-copper, titanium-copper, intermetallic compound-steel, etc. that cannot be welded under conventional melting.
- Welding of rods and pipes with the same diameter and different diameters can be realized.
- No smoke, arc light and harmful gases are generated during welding, and it does not pollute the environment.
At the same time, compared with flash welding, electric energy is saved by 5 to 10 times. However, friction welding also has the following disadvantages and limitations.
- It is difficult to weld non-circular sections, and the required equipment is complicated; for thin disc-shaped parts and thin-walled pipe fittings, welding is also difficult because it is not easy to clamp.
- For components whose shape and assembly position have been determined, it is difficult to achieve friction welding.
- The joint is prone to flash, and must be machined after welding.
- The clamping part is prone to scratches or clamping marks.
The Connector Form Design Of Friction Welding Process
Continuous drive friction welding can realize reliable connection of bar-to-bar, tube-to-tube, bar-to-tube, bar-to-plate and tube-to-plate. The shape of the joint is very important to obtain a high-quality joint, and Figure 12 shows the common joint forms. The joint form in Figure 12a has joint surfaces of the same shape. If it is made of the same material, the heat generation and heat dissipation of the two are the same, and the temperature field is symmetrical, so that wider welding parameters can be obtained and joints with high reliability can be obtained. If it is a connection of dissimilar materials, due to the different physical properties of the materials, the heat generation and heat dissipation are different, and the temperature field is asymmetrical. It is necessary to work hard to find suitable welding parameters and quality. In actual production, there are many types of joints similar to Figure 12b, and the diameters of the two parts to be welded are different. At this time, the material with the larger diameter needs to be processed into a boss before welding, so that the shape of the joint is the same. In order to save the production cost of pre-welding processing, the joint form shown in Figure 12c can be used for direct welding, but the large-diameter joint surface should not be inclined; at the same time, to increase the friction pressure, the relative movement must be stopped in a short time. The equipment is required to have good rigidity. The friction welding joint form of sheet and bar is shown in Figure 12d, which requires high concentricity of the equipment. If it is a dissimilar material connection, the base metal with good high temperature strength should use a smaller diameter. 12e is a joint form with a certain slope, which is mainly used for friction welding of gears in mechanical equipment. The 3-12f joint allows a certain amount of flash, which is mainly used in the manufacture of diesel engine combustion chamber nozzles and lower moving wheels of bulldozers.
The design of the continuous drive friction welding joint mainly follows the following principles:
- Among the two workpieces of rotary friction welding, at least one workpiece must have a revolving section.
- The welding workpiece should have greater rigidity, and the clamping is convenient and firm, and the use of thin tube and thin plate joints should be avoided as much as possible.
- The cross-sectional dimensions of two weldments of the same material should be the same as possible to ensure that the welding temperature distribution is uniform and the thickness of the deformed layer is the same.
- Generally, the inclined joint should form an inclined plane of 30° to 45° with the center line.
- When welding dissimilar materials with large differences in forging temperature or thermal conductivity, in order to make the upsetting of the two parts relatively balanced, the relative size of the interface should be adjusted; in order to prevent the workpiece end face metal with low strength at high temperature from producing too much Deformation loss requires the use of a mold to seal the joint metal.
- In order to increase the weld area, the weld can be designed as a lap joint or a dimension joint.
- When welding large-section joints, in order to reduce the peak value of heating power, the method of chamfering the welding end face can be used to gradually increase the friction area.
- For rod-rod and rod-plate joints, more energy is consumed when the material in the center is extruded to form flash, and the center of the weld bears little torque and bending stress. Therefore, if the workpiece is When conditions permit, one or two parts can be machined with a central hole, so that a less powerful welder can be used and productivity can be increased.
- Nitriding and carburizing should be avoided on the surface to be welded.
- While designing the joint form, attention should also be paid to the length, diameter tolerance of the workpiece, the verticality, unevenness and surface roughness of the welding end face.