Hardware Knowledge Base: Friction Welding

Summary

Under pressure, through the friction interface and the nearby temperature of the workpiece to be welded, the deformation resistance of the material decreases, the plasticity increases, the interface oxide film breaks, along with the plastic flow of the material, diffusion and recrystallization through the interface. Solid welding method for realizing welding.

definition

Definition 1: The frictional heat energy generated by the relative motion between the workpieces heats the joining surface to the forging temperature and forms the solid-state welding method by the plastic deformation and diffusion process of the material under the action of the pre-forging force. Subjects: Aviation Science and Technology (a subject); Aviation Manufacturing Engineering (two subjects)

Definition 2: Use the heat generated by the frictional surfaces of the weldment to make the end face thermoplastic, and then quickly upset to complete a welding method.

Introduce

Under pressure, through the friction interface and the nearby temperature of the workpiece to be welded, the deformation resistance of the material decreases, the plasticity increases, the interface oxide film breaks, along with the plastic flow of the material, diffusion and recrystallization through the interface. Solid welding method for realizing welding.

Friction welding usually consists of the following four steps: 1. Mechanical energy is converted into heat energy; 2. Material is plastically deformed; 3. Thermoplastic under-forging pressure; 4. Intermolecular diffusion and recrystallization.

The biggest difference in friction welding compared to traditional welding is that during the entire welding process, the temperature at which the metal to be welded reaches the elevated temperature does not reach its melting point, ie the metal is in a forged solid-state connection in the thermoplastic state.

Compared with traditional fusion welding, friction welding has high welding joint quality—it can achieve strength such as weld strength and matrix material, high welding efficiency, stable quality, good consistency, and welding of dissimilar materials can be achieved.

After years of development, friction welding technology has developed a wide variety of friction welding classifications: inertial friction welding, radial friction welding, linear friction welding, orbital friction welding, and friction stir welding.

The definition of traditional friction welding: the use of the heat generated by the surface friction of the weldment, so that the end surface to the thermoplastic state, and then quickly upset, a welding method to complete the welding.

Technical features

Friction stir welding, as a new welding method, completed the process from invention to industrial application in a short time. At present, there is no unified technical terminology standard for friction stir welding in the world. Under the influence of the Patent Licensing Association for Friction Stir Welding, the industry has defined and approved common technical terms involved in the friction stir welding method. The main technical terms involved in friction stir welding technology are defined as follows:

Pin tool - welding tool for friction stir welding;

Tool Shoulder - shoulder portion of the agitator head that contacts the workpiece surface;

Tool Pin - the part of the tool inserted into the workpiece;

Advanced Side-side of the weld that matches the direction of rotation of the stirrer shaft;

Retreating Side - The side of the weld that is opposite to the direction of rotation of the stirrer's shoulder;

Axial pressure (Down or Axial Force) - the pressure applied to the stirring head to insert the stirring needle into the workpiece and maintain the contact of the stirring head shoulder with the workpiece surface;

Friction stir welding is a solid-phase connection method under the action of mechanical force and frictional heat. As shown in Fig. 1, during the friction stir welding process, a cylindrical stirrer with special shoulders and needles rotates and slowly inserts the workpiece to be welded. The frictional resistance between the stirrer head and the material to be welded generates frictional heat. The material in the vicinity of the mixing head is thermoplasticized (welding temperature generally does not reach and exceed the melting point of the material being welded), and the thermoplastic metal material is moved backwards from the front edge of the stirring head when the stirring head rotates to move forward. Along the transfer, and under the action of friction heat generation and forging of the surface of the stirring head and the workpiece surface, a dense solid phase connection joint is formed.

Friction stir welding has many advantages suitable for automation and robot operation. For the connection of non-ferrous metal materials (such as aluminum, copper, magnesium, zinc, etc.), it has unparalleled other welding methods in the welding method, joint mechanical properties and production efficiency. Its superiority is that it is a new type of connection technology that is highly efficient, energy-saving and environment-friendly.

However, friction stir welding also has its limitations. For example, there are usually keyholes at the end of the weld (non-porous welding is currently available); the mechanical force during welding is large and the welding equipment needs to have good rigidity; In contrast, the lack of flexibility in welding operations; wire welding cannot be achieved.

Friction stir welding is very adaptable to materials and can weld almost all types of aluminum alloy materials. Due to the low welding temperature and low heat input during the friction stir welding process, the friction stir welding head generally has small deformation and excellent joint performance. Features; can be welded current welding "can not be welded" and the so-called "hard solder" of metal materials such as: Al-Cu (2xxx series), Al-Zn (7xxx series) and Al-Li (such as 8090,2090 and 2195 aluminum Alloy) and other aluminum alloys.

In addition, friction stir welding is also a preferred welding method for joining of magnesium alloys, zinc alloys, copper alloys, lead alloys, and aluminum-based composite materials, such as plate butt joints or lap joints; currently, friction stir welding has also been successfully realized. Excellent connection of stainless steel, titanium alloys and even superalloys.

Friction stir welding can easily achieve the connection of dissimilar materials, such as friction stir welding of aluminum alloy and stainless steel. The use of friction stir welding can more easily achieve the connection between aluminum-steel plates and copper-aluminum composite welding joints.

The initial stage of friction stir welding was mainly to solve the problem of aluminum alloy plate welding with a thickness of 1.2~6mm; in 1996, FSW technology was used to solve the connection of 6~12mm aluminum, magnesium, and copper alloys. In 1997, it was 12~25mm thick. Friction stir welding of aluminum alloy plates, and applied to aerospace structural components. In 1999, friction stir welding was able to weld 50 mm thick copper alloys and 75 mm thick aluminum alloy parts and products. In 2004, the British Welding Institute was able to Single-pass single-sided friction stir welding of 100 mm thick aluminum alloy sheet. Up to now, in the thickness of material, single-pass welding can realize the welding of aluminum alloy material with thickness of 0.8~100mm; double-pass welding can weld 180mm thick butt welding material. Recently, micro-friction stir welding technology that can connect 0.4mm aluminum plate has been developed.

Friction stir welding is the ideal welding method for long and straight regular welds (flat butt joints and lap joints). Friction stir welding can also achieve 2-D, 3-D structural welding, such as circular and longitudinal joints of tubular parts. Can realize all-position space welding, such as horizontal welding, vertical welding, overhead welding and orbital welding at any position and angle. FIG. 2 shows various typical friction stir welding head forms, such as multi-layer butt joints, multi-layer overlaps, T-joints, V-joints, corner joints, and the like.

Compared with traditional TIG welding and MIG welding, friction stir welding has obvious advantages in the mechanical properties of joints. For example, for a 6.4mm thick 2014-T6 aluminum alloy, the FSW weld head performance is 16% higher than that of a TIG weld; for a 12.7mm thick 2014-T6 aluminum alloy, the FSW weld head performs 22% more than the TIG weld. The friction stir welding head Performance data consistency is better, the process is stable, and the quality of welded joints is easily guaranteed.