TALAT Lecture 4400: Introduction to Friction, Explosive and Ultrasonic Welding Processes of Aluminium

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This lecture gives a brief introduction to friction, explosive and ultrasonic welding techniques of aluminium; it describes the possibilities and results of joining aluminium to different metals, e.g. stainless steel. General mechanical engineering background and basic knowledge in aluminium metallurgy is assumed.

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  • An example of Ultrasonic welding: UW of titanium alloy TiAl6V4 to an aluminium alloy,http://www.sciencedirect.com/science/article/pii/S1044580314002654 ,http://www.slideshare.net/acezcq/089-46140435
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TALAT Lecture 4400: Introduction to Friction, Explosive and Ultrasonic Welding Processes of Aluminium

  1. 1. TALAT Lecture 4400 Friction, Explosive and Ultrasonic Welding Processes of Aluminium 11 pages, 11 figures Basic Level prepared by Ulrich Krüger, Schweißtechnische Lehr- und Versuchsanstalt Berlin Objectives: − to give a brief introduction to friction, explosive and ultrasonic welding techniques of aluminium − to describe the possibilities and results of joining aluminium to different metals, e.g. stainless steel Prerequisites: − General mechanical engineering background − Basic knowledge in aluminium metallurgy Date of Issue: 1994  EAA - European Aluminium Association
  2. 2. 4400 Friction, Explosive, and Ultrasonic Welding Processes of Aluminium Table of Contents 4400 Friction, Explosive, and Ultrasonic Welding Processes of Aluminium...................................................................................................................2 4400.01 Friction Welding ..................................................................................... 3 Principle of Friction Welding ..................................................................................3 Feasibility of Friction Welding Aluminium with other Materials ...........................4 Tensile Strength of Friction Welded Aluminium-Steel Joints.................................4 Hardness Curves in the Joint Region .......................................................................5 Preparation and Conduction of Friction Welding for an Al-Cr-Ni-Steel Joint........6 Friction Welding Parameters ...................................................................................7 4400.02 Explosive Welding..................................................................................... 7 Principle of Explosive Welding...............................................................................7 Macrostructure of Explosive Welded Joints ............................................................8 4400.03 Ultrasonic welding .................................................................................... 9 Principle of Ultrasonic Welding ..............................................................................9 Joint Forms with Ultrasonic Welding......................................................................9 Material Combinations for Ultrasonic Welding ....................................................10 4400.04 Literature................................................................................................... 11 4400.05 List of Figures............................................................................................ 11 TALAT 4400 2
  3. 3. 4400.01 Friction Welding ♦ Principle of friction welding ♦ Feasibility of friction welding aluminium with other materials ♦ Tensile strength of friction welded aluminium-steel joints ♦ Hardness curves in the joint region ♦ Preparation and conduction of friction welding for an Al-Cr-Ni-steel joint ♦ Friction welding parameters Principle of Friction Welding Friction welding is a process in which mainly rotationally symmetrical parts are rotated while being pressed together, thereby generating heat of friction which causes the parts to weld. There are two main variations of this process: − friction welding with a continuously applied drive − friction welding using a flywheel drive Characteristic for the continuous drive is an externally applied brake. The flywheel drive, on the other hand, delivers its stored energy to the process thereby slowing down itself. Consequently, this leads to differences in behaviour of the two methods regarding torque and the compressive force being brought to bear (Figure 4400.01.01). Principle of Friction Welding with Continuous Drive with Flywheel Drive 1 2 5a 5b 1 5a 5b 4a 4b 6 3 4a 4b 6 Compressive Force Compressive Force Based on Area 1 - Drive Based on Area 2 - Brake RPM Torque 3 - Flywheel, Variable Mass 4a - Gripping Tool, Rotating RPM 4b - Gripping Tool, not Rotating Torque 5a - Work-Piece, Rotating 5b - Work-Piece, not Rotating 6 - Working Cylinder Axial Shortening Axial Shortening Time Time alu Training in Aluminium Application Technologies Principle of Friction Welding 4400.01.01 TALAT 4400 3
  4. 4. Feasibility of Friction Welding Aluminium with other Materials The material data alone are not sufficient to indicate whether friction welding can be successfully employed. Consequently, a number of alloys which cannot be welded by other welding processes, can be welded effectively using friction welding. Parts to be joined by the friction welding process, must have a sufficiently high strength to be able to transmit the axial pressure and frictional moment as well as a sufficient hot forming capacity. Pure aluminium is ideally suited for friction welding. Out of the large number of aluminium alloys and powder metallurgical materials available, there are still some whose suitability for welding has still to be tested (Figure 4400.01.02). Feasibility of Friction Welding Aluminium with Other Materials Steel, High Alloyed Steel, Unalloyed Steel, Austenitic Steel, Alloyed Al, Sintered Magnesium Aluminium Zirconium Mg Alloys Ceramics Zr Alloys Al Alloys Titanium Copper Bronze Nickel Brass Aluminium Al Alloys Al, Sintered Suitable for Friction Welding Partly Suitable for Friction Welding Not Suitable for Friction Welding Not Tested alu Feasibility of Friction Welding Aluminium 4400.01.02 Training in Aluminium Application Technologies with Other Materials The following disadvantages limit the applicability of friction welding : − The creation of low-melting phases or brittle intermetallic compounds. − The softening of aged alloys. − The amount and distribution of non-metallic inclusions. − Hardening effects of the material combinations. Tensile Strength of Friction Welded Aluminium-Steel Joints Experiments with friction welding on different aluminium and steel alloys (for parameters see Figure 4400.01.06) have shown that strengths exceeding the yield stress of aluminium and steel can be attained. There is no straightforward correlation between strength of alloys and strength of friction welded joints (Figure 4400.01.03) TALAT 4400 4
  5. 5. Consequently, one can assume that other factors play an important role here. Such composite joints exhibit brittle fractures with little plastic strain at the joining plane. This is a result of the different mechanical properties of steel and aluminium. The resulting inhibition of plastic deformation at the contact surface which occurs under the influence of multi-axial state of stresses leads to the preferential building of cracks at these sites. Tensile Strength of Friction Welded Aluminium-Steel Joints 400 1 - C 60 2 - St 37 2 N/mm 3 - 25 CrMo 4 4 - X 10 CrNiMoTi 18 10 300 5 - X 5CrNi 18 9 Tensile Strength 200 100 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 AlCuMg 2 AlMgSi 1 AlZn 4,5 Mg 1 AlMg 4,5 Mn Al 99,5 Source: Reiners, Kreye alu Tensile Strength of Friction Welded 4400.01.03 Training in Aluminium Application Technologies Aluminium-Steel Joints Hardness Curves in the Joint Region The short welding times lead to correspondingly high hardness values. For aluminium joints this is less of a problem than for composite joints of aluminium with steel. The very narrow bonding plane, characteristic for the process, shows hardness peaks only in a region of 100 to 200 µm (Figure 4400.01.04). Austenitic steels have a higher strain hardening coefficient than ferritic steel and therefore reach higher hardness values. In heat-treatable alloys the precipitates can go into solution, causing a softening of the alloy. In heat-treatable alloys which respond to natural ageing, a precipitation of the hardening particles occurs at room temperature, causing the hardness to rise again. TALAT 4400 5
  6. 6. Hardness Curves in the Joint Region 400 x x 300 Hardness HV 0,1 x 200 x AlMgSi 1 x x x x x x x x x x x X 10 CrNiMoTi 18 10 100 x x x xx x 0 8 6 4 2 0 2 4 6 8 mm Distance from the Joining Zone Source: Reiners, Kreye alu Hardness Curves in the Joint Region 4400.01.04 Training in Aluminium Application Technologies Preparation and Conduction of Friction Welding for an Al-Cr-Ni-Steel Joint The different thermal properties of the materials have to be taken into account while preparing the welds. The surface area of materials with a low thermal conductivity should be increased, in order to deliver a joining zone with good properties. In this region, the grains are highly deformed (Figure 4400.01.05). Preparation and Conduction of Friction Welding for an Al - CrNi -Steel Joint CrNi -Steel Al before after Friction Welding Friction Welding Macrostructure of the Joint Zone X 10 CrNiMoTi + AlCuMg2 0.05 mm Preparation and Conduction of Friction Welding alu 4400.01.05 Training in Aluminium Application Technologies for an Al - CrNi -Steel Joint TALAT 4400 6
  7. 7. Friction Welding Parameters Friction welding of aluminium with itself and its alloys as well as with steel is characterised by extremely short welding times and high frictional and compressive forces. As a result, the joining plane is kept extremely narrow, so that intermetallic compounds and phases cannot be built. The diffusion zone characteristic for this region is thus kept very small (< 1µm). Friction Welding Parameters Material Diameter Area-based Friction Compress- Circum- (Massive) Friction- Compress- Time ion Time ferential al Force ive Force 2 2 Speed mm N/mm N/mm sec sec m/sec Al 99,5 + Al 99,5 20 10 ... 30 30 ... 80 0,1 ... 4 2 ... 5 2,0 ... 4,0 AlMgSi0,5 + AlMgSi0,5 20 30 ... 80 50 .. 150 0,1 ... 6 2 ... 5 0,5 ... 2,0 Al 99,5 St 37 AlMg4,5Mn C 60 AlMgSi1 + 25 CrMo4 20 40 .. 70 65 .. 250 0,1 .. 1,1 3 ... 4 1,2 ... 2,3 AlZn4,5Mg X5CrNi18 9 AlCuMg2 X10CrNiMoTi18 10 alu Friction Welding Parameters 4400.01.06 Training in Aluminium Application Technologies Short friction times for aluminium are only relevant in connection with a rapidly increasing force the friction and compressive phases (Figure 4400.01.06). 4400.02 Explosive Welding ♦ Principle of explosive welding ♦ Macrostructure of explosive welded joints Principle of Explosive Welding Shock waves (3,000 to 9,000 m/s) can produce pressures of up to 6 x 106 N/cm2. This energy is utilised for explosive welding, especially for plates with large areas. The shock waves spread out and create a "material wave" at the joining plane. At the TALAT 4400 7
  8. 8. collision point a thin jet of material is heated to a high temperature, causing melting and mechanical mixing at the interface (Figure 4400.02.01). Aluminium can be effectively welded with itself and also with steel and copper giving composite joints. Principle of Explosive Welding Detonation Front in Explosive Expanding Products of Detonation (Vapour) Unused Explosive Sheet at Rest Explosive Accelerating Joining Sheet Plated Joining Sheet Joining Sheet Air Shock Wave Air under Normal Pressure Wavy Joining Zone Material Jet at High Velocity Moving Shock Wave Metal Interface Flowing Collision Point, Front in Air Turbulent or Laminar Very High Stress Base Metal under the High Pressure (10,000 - 100,000 bar) alu Principle of Explosive Welding 4400.02.01 Training in Aluminium Application Technologies Macrostructure of Explosive Welded Joints The detonation force waves can be clearly seen as waves in a microsection. "Multiple explosive welding" can be used to join a number of materials of different thicknesses (Figure 4400.02.02). Even here it is possible to join materials which cannot be joined by other processes. Macrostructure of Explosive Welded Joints AlMg2Mn0,3 Al Intermediate Layer St 37 1 mm AlMg4,5Mn Al Intermediate Layer Ni X 3 CrNiMnMo 19 17 1 mm alu Macrostructure of Explosive Welded Joints 4400.02.02 Training in Aluminium Application Technologies TALAT 4400 8
  9. 9. 4400.03 Ultrasonic welding ♦ Principle of ultrasonic welding ♦ Joint forms with ultrasonic welding ♦ Material combinations for ultrasonic welding Principle of Ultrasonic Welding In ultrasonic welding, frictional heat produced by the ultrasonic waves and force is used for the joining process. Ultrasonic waves (15 to 60 kHz) are transferred to the material under pressure with a sonometer. Welding times are lower than 3 s. The welding can proceed with or without the application of external heat (Figure 4400.03.01). Joint Forms with Ultrasonic Welding The principle of the process limits the allowable mass of material on the sonotrode side to a maximum of 10 g. The maximum thickness that can be welded, depends on the self- damping characteristics of the work-piece material. A main advantage while welding aluminium is the fact that the vibrations break the oxide layer and transport it to the boundary regions. As a result, mechanical and chemical surface cleaning is not necessary. Surface coatings (e.g. coated wire) and impurities behave in a similar manner. Consequently, a main application area for ultrasonic welding is the contact joining of wires (Figure 4400.03.02). Principle of Ultrasonic Welding F F Converter Converter Vibrating Tool Sonotrode Sonotrode Vibrating Tool Work-Piece Work-Piece Ultrasonic Vibration Ultrasonic Vibrations Support ( Anvil ) electrically heated Weld Seam US Roller Welding US Spot Welding alu Principle of Ultrasonic Welding 4400.03.01 Training in Aluminium Application Technologies TALAT 4400 9
  10. 10. Joint Forms with US Welding Two Parallel Wires Two Wires with Bridging Wire on Sheet Wire Strand on Sheet Sheet on Sheet T-Profile on Sheet T-Profile on Pipe alu Joint Forms with US Welding 4400.03.02 Training in Aluminium Application Technologies Material Combinations for Ultrasonic Welding Ultrasonic welding is particularly suitable for joining aluminium and its alloys with each other as well as for producing composite joints with other materials (Figure 4400.03.03). In electrical and electronic applications, the frictional energy creates clean welding zones with low contact resistances. Hardness influences the weldability of composite joints with steel. Hard alloys are less suitable, since the plastic formability required for the joining is not sufficient. Very often an intermediate layer is used to overcome this deficiency. Material Combination for US Welding Al Alloys with Al Alloys Copper Brass Gold Germanium Steel, Iron Mg Alloys Mo Alloys Ni Alloys Pd Alloys Pt Alloys Si Ag Alloys Ta Alloys Ti Alloys Sn alu Material Combinations for US Welding 4400.03.03 Training in Aluminium Application Technologies TALAT 4400 10
  11. 11. 4400.04 Literature - Aluminium-Taschenbuch, 14. Auflage, 1984, Aluminium-Verlag, Düsseldorf Neumann, A. und Schober, D.: Reibschweißen von Metallen. Fachbuchreihe Schweißtechnik Bd. 107, Deutscher Verlag für Schweißtechnik 1990, Düsseldorf 4400.05 List of Figures Figure No. Figure Title (Overhead) 4400.01.01 Principle of Friction Welding 4400.01.02 Feasibility of Friction Welding Aluminium with other Materials 4400.01.03 Tensile Strength of Friction Welded Aluminium-Steel Joints 4400.01.04 Hardness Curves in the Joint Region 4400.01.05 Preparation and Conduction of Friction Welding for an Al-CrNi-Steel Joint 4400.01.06 Friction Welding Parameters 4400.02.01 Principle of Explosive Welding 4400.02.02 Macrostructure of Explosive Welded Joints 4400.03.01 Principle of Ultrasonic Welding 4400.03.02 Joint Forms with Ultrasonic Welding 4400.03.03 Material Combinations for Ultrasonic Welding TALAT 4400 11

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