Welding refers to the metal fabrication that joins metals or thermoplastics to fuse the parts together. Most welding methods use high heat to melt the materials and cool down the finished parts. However, there are also metal joining methods that can be performed at a lower temperature without melting the base materials, such as friction welding, brazing, and soldering. A variety of electrical, chemical and other types of energy sources can be utilized for welding process, including frictions, electric arcs, lasers, ultrasounds and also electron beams.
Friction welding machines can be used to perform “solid-state” welding processes. In the friction welding (FRW) process, the heat is generated from mechanical friction between relative motion between work pieces. The heat plus the lateral force can effectively displace and fuse the metals or other materials without melting, creating permanent connections. Welding in friction welding machines is more like forge welding than fusion welding since the process requires no melting parts. Friction welding process often involves “rotation” of one piece against another until a high temperature has been achieved. Friction welding machines can work on thermoplastics and metals for a wide range of industries such as aerospace and automotive applications. In some cases. Friction welding is also used for wood materials.
As mentioned above, the friction welding machine produces the parts in a solid state and join the materials by the heat obtained from friction. The friction is introduced by the sliding motions between rubbing work parts. The materials have to be gripped firmly together under pressure.
There are 2 common variations of the friction welding process, and more types of friction welding will be discussed later. In one of the manners, which is also called rotary friction welding (RFW), one piece is gripped stationary while another is spinned by a motor which keeps a consistent rotational rate. Two pieces are moved in contact under a specific pressure. As the rotation ceases, the friction welding process finishes. This style can be precisely regulated when speed, pressure, and exact contact period of time are set.
Another manner is called inertia friction welding, which requires the flywheel which rotates by the motor at a commanded speed and rotates the work pieces that are going to be welded in turn. When the rotation rate of the work piece is reduced, the flywheel will stop after the predetermined time passes. Similar to general friction welding, additional pressure is required in the process.
Without melting the metal base parts at a high temperature, friction welding machines can produce high-quality welded products in a short cycle time. Also, the equipment structure is relatively simple and easy to operate. The friction welding machine can be used to join most of the common metals, which include some combinations of dissimilar metals. There is little heat-affected area compared to conventional welding machines. Friction welding machine requires no gas, filler metal and flux to complete the metal welding. Also, the process eliminates the slags which might cause contaminations and other imperfections during the operations.
As mentioned above, rotary friction welding uses friction to weld not separable parts by utilizing the frictional heat. It is the classic method used in friction welding machines. Dissimilar, composite, or other non-metallic materials can also be welded in this method with solid state.
Rotary friction welding is widely used across the manufacturing industries, for example, the production of turbine shafts, automotive parts, steel truck axles, valves, pistons, pipes, and a large range of cutting tools. They are also popular in some medical manufacturing applications.
The materials are positioned in contact under predetermined pressure. An outer vibration force will be utilized to slip the parts, which is perpendicular to the pressure. The pieces are vibrated with a small amplitude range from 0.1 to 0.2 cm and a high frequency of 200 Hz or amplitude ranges from 0.2 to 0.4 cm at a low frequency of 100 Hz on the surface of the connecting joint. Linear vibration welding is commonly used in the automotive industry and more.
Friction stir welding is also a solid-state welding process. The friction between the spinning tool and the work parts causes a softened area near the friction stir welding tool. During the period that the FSW tool is travelling along the joint, the tool can mechanically fuse the two metal parts. It is much like joining clay, or dough other than melting the metals and fusing them under heat and pressure. This method is mainly used on wrought or extruded aluminum, joining copper alloys, titanium alloys, mild steel and so on.
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