12-04-2011, 03:53 PM
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1. INTRODUCTION
A very and potentially world beating solid phase welding method duly named FRICTION STIR WELDING (FSW) was invented in 1991 by Wayne Thomas and colleagues at The Welding Institute (TWI) UK originally for use with aluminum but is now feasible for harder metals such as steels, it is a one or two sided solid phase joining process and can be used for long butt, "T" and lap joints.
Friction stir welding is currently being used to produce components in the Delta family of rockets, as well as in shipbuilding rail car manufacturing, construction and other related industries.
Friction stir welding is a relatively simple process a specially shaped cylindrical tool with a profiled probe, made from a hard and wear resistant material relative to the materials being welded is rotated and plunged into the abutting edges of the parts to be joined. After entry of the profiled probe to almost the thickness of the materials and to allow the tool shoulder to just penetrate into the plate, the rotating tools develops frictional heating of the materials causing it to the plasticized and flow from the front of the tool to the back where it cools and consolidates to produce a high integrity weld in the solid phase.
The process proves predominance for welding non heat treatable or powder metallurgy aluminum alloys, to which the fusion welding can not be applied friction stir welding is highly significant advancement in aluminium welding technology that can produce stronger, lighter and more efficient welds that any previous process without smokes and protective guards by FSW m/c up to 16m long welds can be achieved.
2. NECESSITY OF FRICTION STIR WELDING
The increasing demand for the weight optimization and the recyclability of the materials in aerospace, marine, railways and automotive sectors have pushed the demand for lighter materials like aluminium. Until recently, the production of long butt and lap welded joints in aluminium alloy has only been possible by fusion welding processes (i.e. arc, electron-beam laser, TIG, MIG etc). When applied to the aluminium, the fusion welding processes are expensive and often difficult to use. Also whole process is time consuming, cumbersome. Mismatch can lead to porosity, crack, inclusion and voids. As process involves the melting of materials to be joined, the shrinkage is one of the major problems. This leads to metallurgical changes in the characteristics of the parents materials such as ductility, hardness, and could leave residual; stresses. Fusion welding also involves a heats source and a filler matter. The process starts with the surface preparation.
Comparatively, the FSW does not suffer from these hassles. The need for surface preparation, gas shelled and in process precaution are eliminated as is solid state process. In such a way all these problem look to FSW process for possible solution.
3. MACHINE PROCEDURE
Friction Stir Welding is a highly significant advancement in aluminium welding technology that can produce stronger, lighter and more efficient welds than any previous process. The welds are created by the combined frictional heating and mechanical deformation due to rotating tool. The tool has a circular section except at the end where there is threaded probe or more complicated flute, the junction between the cylindrical portion and the probe is known as the shoulder. The probe penetrate the workpiece whereas the shoulder rubs with the surface. The heat is generated primarily by friction between a rotating-translating tool, the shoulder of which rubs against the workpiece.
This heat causes the latter to soften without reaching the melting points and allows travels from the leading edge of the tool to the trailing edge of the tool probe and is forged by the intimate contact of the tool shoulder and the pin profile it leaves a solid phase bond between the two pieces after cooling.
The process can be regarded as a solid phase keyhole welding technique since a hole to accommodate the probe is generated, then filled during the welding sequence/Also `Auto Adjustable pin tool for friction stir welding addresses the keyhole closeout issue. This disclosure provides the capability to retract the pin while keeping the shoulder in contact with the material being joined, thus closing out the FSW keyhole.
3.1 TOOL
Some types of tools are illustrated above. Each tool has a shoulder whose rotation against the substrate generates most of the heat required for welding. The pin of the tool is plunged in to the substrate and helps stir the metal in the solid state
4. COMPONENTS OF FSW SYSTEM
This FSW system includes seven sub components:
1. A base foundation unit (BFU).
2. A hydraulically controlled elevation platform (EP).
3. The hydraulically adjustable pin tool (HAPT)
4. Fixturing
5. A roller mechanism
6. The real time adaptive computer numerical control (CNC) and
7. Automatic process control system (APCS)
1. The Base Foundation Unit is unique to accommodate the internal mechanical entities of the system. It is designed to operate under the radial and axial loads associated with the FSW process.
2. The hydraulically controlled Elevation Platform is the result of novel applications of existing technologies to create and elevation feature with three axes of movement, specially designed to function under operating pressures. This movement is necessary to attain the proper pin tool location with respect to the center of the weld joint.
3. The HAPT is stand - alone piece of hardware, which was integrated into the FSW system.
4. The Automatic process control system component was specially designed to function as an integrated controller for a variety of functions and data gathering operations.
5. The novelty of the FSW system for welding and weld repair is the fact that the seven sub components act as one integrated welding system.
Also the maintenance of this equipment is minimal requiring no special or operator maintenance training. In addition, this machine tool is ideal suited to automation and integration with other machine tool operations.
Another advantages of this equipment is extremely energy efficient. This can weld sheet of thickens 3mm to 50mm in a single pass with speeds upto 750 mm/min depending upon thickness of material. These machines can accommodate the lengths upto 16m long.
1. INTRODUCTION
A very and potentially world beating solid phase welding method duly named FRICTION STIR WELDING (FSW) was invented in 1991 by Wayne Thomas and colleagues at The Welding Institute (TWI) UK originally for use with aluminum but is now feasible for harder metals such as steels, it is a one or two sided solid phase joining process and can be used for long butt, "T" and lap joints.
Friction stir welding is currently being used to produce components in the Delta family of rockets, as well as in shipbuilding rail car manufacturing, construction and other related industries.
Friction stir welding is a relatively simple process a specially shaped cylindrical tool with a profiled probe, made from a hard and wear resistant material relative to the materials being welded is rotated and plunged into the abutting edges of the parts to be joined. After entry of the profiled probe to almost the thickness of the materials and to allow the tool shoulder to just penetrate into the plate, the rotating tools develops frictional heating of the materials causing it to the plasticized and flow from the front of the tool to the back where it cools and consolidates to produce a high integrity weld in the solid phase.
The process proves predominance for welding non heat treatable or powder metallurgy aluminum alloys, to which the fusion welding can not be applied friction stir welding is highly significant advancement in aluminium welding technology that can produce stronger, lighter and more efficient welds that any previous process without smokes and protective guards by FSW m/c up to 16m long welds can be achieved.
2. NECESSITY OF FRICTION STIR WELDING
The increasing demand for the weight optimization and the recyclability of the materials in aerospace, marine, railways and automotive sectors have pushed the demand for lighter materials like aluminium. Until recently, the production of long butt and lap welded joints in aluminium alloy has only been possible by fusion welding processes (i.e. arc, electron-beam laser, TIG, MIG etc). When applied to the aluminium, the fusion welding processes are expensive and often difficult to use. Also whole process is time consuming, cumbersome. Mismatch can lead to porosity, crack, inclusion and voids. As process involves the melting of materials to be joined, the shrinkage is one of the major problems. This leads to metallurgical changes in the characteristics of the parents materials such as ductility, hardness, and could leave residual; stresses. Fusion welding also involves a heats source and a filler matter. The process starts with the surface preparation.
Comparatively, the FSW does not suffer from these hassles. The need for surface preparation, gas shelled and in process precaution are eliminated as is solid state process. In such a way all these problem look to FSW process for possible solution.
3. MACHINE PROCEDURE
Friction Stir Welding is a highly significant advancement in aluminium welding technology that can produce stronger, lighter and more efficient welds than any previous process. The welds are created by the combined frictional heating and mechanical deformation due to rotating tool. The tool has a circular section except at the end where there is threaded probe or more complicated flute, the junction between the cylindrical portion and the probe is known as the shoulder. The probe penetrate the workpiece whereas the shoulder rubs with the surface. The heat is generated primarily by friction between a rotating-translating tool, the shoulder of which rubs against the workpiece.
This heat causes the latter to soften without reaching the melting points and allows travels from the leading edge of the tool to the trailing edge of the tool probe and is forged by the intimate contact of the tool shoulder and the pin profile it leaves a solid phase bond between the two pieces after cooling.
The process can be regarded as a solid phase keyhole welding technique since a hole to accommodate the probe is generated, then filled during the welding sequence/Also `Auto Adjustable pin tool for friction stir welding addresses the keyhole closeout issue. This disclosure provides the capability to retract the pin while keeping the shoulder in contact with the material being joined, thus closing out the FSW keyhole.
3.1 TOOL
Some types of tools are illustrated above. Each tool has a shoulder whose rotation against the substrate generates most of the heat required for welding. The pin of the tool is plunged in to the substrate and helps stir the metal in the solid state
4. COMPONENTS OF FSW SYSTEM
This FSW system includes seven sub components:
1. A base foundation unit (BFU).
2. A hydraulically controlled elevation platform (EP).
3. The hydraulically adjustable pin tool (HAPT)
4. Fixturing
5. A roller mechanism
6. The real time adaptive computer numerical control (CNC) and
7. Automatic process control system (APCS)
1. The Base Foundation Unit is unique to accommodate the internal mechanical entities of the system. It is designed to operate under the radial and axial loads associated with the FSW process.
2. The hydraulically controlled Elevation Platform is the result of novel applications of existing technologies to create and elevation feature with three axes of movement, specially designed to function under operating pressures. This movement is necessary to attain the proper pin tool location with respect to the center of the weld joint.
3. The HAPT is stand - alone piece of hardware, which was integrated into the FSW system.
4. The Automatic process control system component was specially designed to function as an integrated controller for a variety of functions and data gathering operations.
5. The novelty of the FSW system for welding and weld repair is the fact that the seven sub components act as one integrated welding system.
Also the maintenance of this equipment is minimal requiring no special or operator maintenance training. In addition, this machine tool is ideal suited to automation and integration with other machine tool operations.
Another advantages of this equipment is extremely energy efficient. This can weld sheet of thickens 3mm to 50mm in a single pass with speeds upto 750 mm/min depending upon thickness of material. These machines can accommodate the lengths upto 16m long.
