Class 2 - Solid State Welding PDF

Advanced Joining Processes Solid state welding Eduardo A. S. Marques Eduardo Marques Advanced Joining Processes – Welding Processes 1  Contents Introduction to solid state welding Friction stir welding...

Advanced Joining Processes Solid state welding Eduardo A. S. Marques Eduardo Marques Advanced Joining Processes – Welding Processes 1  Contents Introduction to solid state welding Friction stir welding (FSW) Difusion welding (DW) Forge welding (FW) Explosive welding (EW) Ultrasonic welding (UW) Eduardo Marques Advanced Joining Processes – Welding Processes 2 2  Introduction to solid state welding Eduardo Marques Advanced Joining Processes – Welding Processes 3 3  Solid state welding Introduction Source: Khaledi, K., et al. (2019), Khalfallah, F., et al. (2020) Unlike fusion welding, solid state welding is carried out below the melting point of the materials being joined. Eduardo Marques Advanced Joining Processes – Welding Processes 4 4  Solid state welding Introduction Solid state welding processes always rely on temperature, pressure or a combination of both; Although no fusion occurs, the materials become sufficiently plastic that they can intermix and create a joint; No filler material is usually necessary; Heat affected zone still exists, but it is usually quite minor; Distortion is greatly minimized. Eduardo Marques Advanced Joining Processes – Welding Processes 5 5  Friction stir welding Eduardo Marques Advanced Joining Processes – Welding Processes 6 6  Friction stir welding Introduction Process description Advantages and disadvantages Equipment and tooling Process parameters Dissimilar joining Eduardo Marques Advanced Joining Processes – Welding Processes 7 7  Friction stir welding Introduction Friction stir welding (FSW) uses a non-consumable tool to join two adjacent workpieces without fusing the base material. The friction between the rotating tool and the workpiece material generates heat and softens the region near the FSW tool. Eduardo Marques Advanced Joining Processes – Welding Processes 8 8  Friction stir welding Introduction Friction stir welding (FSW) uses a non-consumable tool to join two adjacent workpieces without fusing the base material. The friction between the rotating tool and the workpiece material generates heat and softens the region near the FSW tool. Eduardo Marques Advanced Joining Processes – Welding Processes 9 9  Friction stir welding Introduction Joint geometries possible with FSW Eduardo Marques Advanced Joining Processes – Welding Processes 10 10  Friction stir welding Process description Shoulder Probe Stages of a FSW process Source: Ferreira Magalhães, A. C. (2020) Eduardo Marques Advanced Joining Processes – Welding Processes 11 11  Friction stir welding Process description Different zones affected by the friction stir welding process Eduardo Marques Advanced Joining Processes – Welding Processes 12 12  Friction stir welding Process description Source: Ferreira Magalhães, A. C. (2020) Eduardo Marques Advanced Joining Processes – Welding Processes 13 13  Friction stir welding Advantages As a solid-state welding process, FSW is a largely defect free joining method with no hot cracking, porosity or solidification cracks; Due to the low temperatures there is a reduction in shrinkage and distortion in the material being joined; No filler materials, flux or shielding gas requirement for aluminium alloys; FSW is more environmentally friendly as it produces no fume, spatter, or UV radiation. Eduardo Marques Advanced Joining Processes – Welding Processes 14 14  Friction stir welding Advantages Uses machine tool technology, making the process easy to automate, highly repeatable and reducing need for skilled welders; Can work in any position since there is no molten metal pool; Good mechanical properties, which for aluminium alloys typically equals or exceeds those obtainable by competing processes; Energy efficient process, with lower temperatures; Able to join many ‘non-weldable’ aluminium alloys, such as those from the 2xxx and 7xxx series; No requirement for special edge preparation in most applications. Eduardo Marques Advanced Joining Processes – Welding Processes 15 15  Friction stir welding Advantages Source: Riftec Gmbh Process with extremely low energy consumption and CO2 emissions Eduardo Marques Advanced Joining Processes – Welding Processes 16 16  Friction stir welding Disdvantages Exit hole left after withdrawing tool from the materials to be joined. However, this can usually be accounted for in the design of the part or by using run on/off tabs; The need for significant down force and traversing forces means that clamping on the parts to be joined is more substantial than for arc welds; Gaps between the parts to be joined needs to be tightly controlled as no filler material is used in the process; Eduardo Marques Advanced Joining Processes – Welding Processes 17 17  Friction stir welding Equipment and tooling FSW was initially developed for use in conventional milling machines. However, these often suffer from limited power and low stiffness for handling high strength materials Eduardo Marques Advanced Joining Processes – Welding Processes 18 18  Friction stir welding Equipment and tooling Gantry machine Six-axis robot Industrially, friction stir welding is now carried out in a dedicated XYZ gantry machine (if the joint line is on one plane) or a six-axis robot (for three-dimensional joint lines). Eduardo Marques Advanced Joining Processes – Welding Processes 19 19  Friction stir welding Equipment and tooling Source: Riftec Gmbh Eduardo Marques Advanced Joining Processes – Welding Processes 20 20  Friction stir welding Equipment and tooling Source: Fanuc Eduardo Marques Advanced Joining Processes – Welding Processes 21 21  Friction stir welding Process parameters The main variables of the friction stir welding process are: welding (travel) speed tool rotation speed axial force on the tool the tilt angle of the tool tool design These variables determine the peak weld temperature, linear force, torque and power. Eduardo Marques Advanced Joining Processes – Welding Processes 22 22  Friction stir welding Process parameters Source: Ferreira Magalhães, A. C. (2020) Eduardo Marques Advanced Joining Processes – Welding Processes 23 23  Friction stir welding Process parameters Peak weld temperature increases significantly as rotation speed increases and axial pressure increases. High pressures lead to overheating and thinning of the joint, while low pressures may lead to insufficient heating and void formation. Higher travel speeds generate excessive linear force, leading to erosion and breakage of the tool. The power Source: Rajiv Sharan and Mishra, P. S. D., Nilesh requirement also increases as axial pressure increases. Kumar Eduardo Marques Advanced Joining Processes – Welding Processes 24 24  Friction stir welding Process parameters The torque depends on several parameters, such as: Axial force. Tool design. Tilt angle. Friction coefficients. Slippage between the tool and workpiece. Local shear stress at the tool-workpiece interface Eduardo Marques Advanced Joining Processes – Welding Processes 25 25  Friction stir welding Process parameters Peak temperature is not significantly affected by travel speed. High travel speeds tend to reduce heat input applied to the workpieces during friction stir welding. Torque increases only slightly with increasing travel speed, since material flow becomes somewhat more difficult at slightly lower temperatures. Eduardo Marques Advanced Joining Processes – Welding Processes 26 26  Friction stir welding Process parameters Source: D Lohwasser, Zhan Chen (2010) Eduardo Marques Advanced Joining Processes – Welding Processes 27 27  Friction stir welding Process parameters As the tool is rotated and moved, the thread form on the probe (pin) body disrupts the softened weld zone material, crushes and disperses the oxide film at the joint interfaces. Forging and extrusion occurs. Softened material is transferred from the leading edge to the trailing edge of the probe (180º) under the effect of temperature and pressure. Source: TWI Eduardo Marques Advanced Joining Processes – Welding Processes 28 28  Friction stir welding Process parameters The first FSW tool consisted of a simple parallel-sided (cylindrical) threaded probe body. This same tool design was also the first to be industrially adopted, in 1995. Source: TWI Eduardo Marques Advanced Joining Processes – Welding Processes 29 29  Friction stir welding Process parameters The tapered probe body and the three equally spaced helical flutes, displace much less material during the weld cycle than the original cylindrical body probe and thus much faster welding speeds could be achieved, whilst maintaining high quality. The three flutes also create a more active disruption of weld zone materials and more rapid generation of frictional heating. Source: TWI Eduardo Marques Advanced Joining Processes – Welding Processes 30 30  Friction stir welding Process parameters Source: Zhang, Y., et al. (2012) Eduardo Marques Advanced Joining Processes – Welding Processes 31 31  Friction stir welding Process parameters The tool is often tilted such that the trailing edge of the shoulder penetrates the workpiece and applies additional forging pressure. Scroll shoulders are also used, in which a scroll feature is machined into the face of the shoulder. This spiral shape pulls in material from the outer edge of the shoulder to the root of the probe. This allows for faster welding of some aluminium alloys. Source: TWI Eduardo Marques Advanced Joining Processes – Welding Processes 32 32  Friction stir welding Defects Tunnel defect Flash defect Void defect Cavity defect Kissing bond Root defect Eduardo Marques Advanced Joining Processes – Welding Processes 33 33  Friction stir welding Defects Tunnel defect - occurs in the advancing side due to insufficient heat input and metal flow of the material Eduardo Marques Advanced Joining Processes – Welding Processes 34 34  Friction stir welding Defects Flash defect - generated heat thermally softens the material near the boundary of tool shoulder and expels the large volume of material in the form of flash Eduardo Marques Advanced Joining Processes – Welding Processes 35 35  Friction stir welding Defects Void defect - Voids are defects with variable size and orientation. Voids occur due to insufficient forging pressure and with faster welding speeds. Eduardo Marques Advanced Joining Processes – Welding Processes 36 36  Friction stir welding Defects Cavity defect - Voids are defects with variable size and orientation. Voids occur due to insufficient forging pressure and with faster welding speeds. Eduardo Marques Advanced Joining Processes – Welding Processes 37 37  Friction stir welding Defects Oxide layer Kissing bond- oxide layer breaks partially due to insufficient stirring of the metal and low heat input, causing reduced flowability of plastic material. Broken oxide particles are included in the form of zigzag line or a kissing bond defect Eduardo Marques Advanced Joining Processes – Welding Processes 38 38  Friction stir welding Defects Root defects - developed due to insufficient heat input or due to incomplete breakup of surface oxide layers and insufficient pin length for the thickness of the workpiece leads to the formation of crack-line root defect Eduardo Marques Advanced Joining Processes – Welding Processes 39 39  Friction stir welding Joining of dissimilar materials Joining of dissimilar materials is a very challenging procedure. This is mainly due to two different factors: Different melting temperatures, which influences the way the two different materials flow and intermix. Formation of intermetallic compounds. Hard and brittle compounds which form in the interface of the two materials and greatly decrease the mechanical properties of the joint. Eduardo Marques Advanced Joining Processes – Welding Processes 40 40  Friction stir welding Joining of dissimilar materials Intermetallic phases An intermetallic compound is a type of metallic alloy that forms an ordered solid- state compound between two or more metallic elements. Intermetallics are generally hard and brittle, with good high-temperature mechanical properties. Eduardo Marques Advanced Joining Processes – Welding Processes 41 41  Friction stir welding Joining of dissimilar materials Eduardo Marques Advanced Joining Processes – Welding Processes 42 42  Friction stir welding Joining of dissimilar materials Friction stir spot welding process. Formation of hook, that connects both materials mechanically. Eduardo Marques Advanced Joining Processes – Welding Processes 43 43  Friction stir welding Joining of dissimilar materials Aluminium and magnesium Application in transportation industries Similar characteristic: Melting point, thermal expansion, thermal conductivity Different characteristics: Crystal structure and formability Eduardo Marques Advanced Joining Processes – Welding Processes 44 44  Friction stir welding Joining of dissimilar materials Aluminium and magnesium Eduardo Marques Advanced Joining Processes – Welding Processes 45 45  Friction stir welding Joining of dissimilar materials Aluminium and copper Fusion welding processes used to join Al−Cu are not recommended because of solidification and liquefaction cracking and the tendency to form large hard and brittle IMCs. FSW is still challenging, but possible since it reduces energy input. Eduardo Marques Advanced Joining Processes – Welding Processes 46 46  Friction stir welding Joining of dissimilar materials Aluminium and copper Eduardo Marques Advanced Joining Processes – Welding Processes 47 47  Friction stir welding Joining of dissimilar materials Steel and aluminium Friction stir welding of steel and aluminium is a complex procedure due to highly dissimilar properties of these materials. The use of offset pin is employed, allowing to explore the larger plastic flow of aluminum. Eduardo Marques Advanced Joining Processes – Welding Processes 48 48  Friction stir welding Joining of dissimilar materials Steel and aluminium Eduardo Marques Advanced Joining Processes – Welding Processes 49 49  Friction stir welding Joining of dissimilar materials Steel and aluminium This combination is also highly susceptible to the formation of intermetallic compounds, which form a layer full of discontinuities. These discontinues can be reduced with a heat-treating process. Eduardo Marques Advanced Joining Processes – Welding Processes 50 50  Friction stir welding Joining of dissimilar materials Titanium and aluminium Titanium and aluminium welding has the same characteristics as steel and titanium, requiring the use of a pin offset. Eduardo Marques Advanced Joining Processes – Welding Processes 51 51  Friction stir welding Joining thermoplastics Thermoplastics soften and flow as they are heated, and then regain their stiffness as they cool which makes them suitable for FSW. Thermoplastics are composed of long chain molecules rather than individual atoms, with very different flow characteristics, making the process more complex. Process parameters and tool designs for the FSW of thermoplastics are therefore quite different from those required for metals. Source: Moochani et al. (2018) Eduardo Marques Advanced Joining Processes – Welding Processes 52 52  Diffusion welding Eduardo Marques Advanced Joining Processes – Welding Processes 53 53  Diffusion welding Introduction Diffusion bonding or diffusion welding is a solid-state welding technique, capable of joining similar and dissimilar metals. Solid-state diffusion occurs where the atoms of two solid metals surfaces intersperse themselves over time under high pressure and temperature. Eduardo Marques Advanced Joining Processes – Welding Processes 54 54  Diffusion welding Introduction Diffusion welding has been utilized to join very high strength and refractory metals that are either difficult or impossible to weld by other means. Operation temperature is 50 to 75% of the fusion temperature of the metal. Eduardo Marques Advanced Joining Processes – Welding Processes 55 55  Diffusion welding Advantages Simple process with limited costs of operation; Joint has the same characteristics as the base material; Joints are clean and free from discontinuities and porosity; Diffusion bonding allows joining similar and dissimilar materials; Has good dimensional tolerance, suitable to produce high precision components and complex shapes; Plastic deformation is limited under diffusion. Eduardo Marques Advanced Joining Processes – Welding Processes 56 56  Diffusion welding Disadvantages Although the running cost are low, the initial setup cost is high; Compared to other welding techniques, it is very time-consuming; Surface preparation is critical and may be difficult; The available equipment limits the size of the weld; Very difficult to adapt to mass production; Extreme dependence on the welding parameters, such as temperature, pressure, metal surface finish and the welding material. Eduardo Marques Advanced Joining Processes – Welding Processes 57 57  Diffusion welding Applications Micro-heat exchanger design Source: Vacuum Process Engineering Eduardo Marques Advanced Joining Processes – Welding Processes 58 58  Forge welding Eduardo Marques Advanced Joining Processes – Welding Processes 59 59  Forge welding Introduction In forge welding, two pieces of metal are joined by heating them to a high temperature and then hammering them together. It is one of the simplest methods of joining metals, being versatile and able to join both similar and dissimilar metals. Eduardo Marques Advanced Joining Processes – Welding Processes 60 60  Forge welding Advantages Very simple and basic process; Uses very inexpensive equipment (for small scale work); Can work with similar and dissimilar materials; Welded area has properties similar to the base material; Does not require additional material. Eduardo Marques Advanced Joining Processes – Welding Processes 61 61  Forge welding Disadvantages Manual process is only suitable for small components; Large joints require large expensive presses and furnaces; Requires a skilled operator to avoid damaging the welded material; High likelihood of defects in the weld; More suitable for iron and steel; Relatively slow process. Eduardo Marques Advanced Joining Processes – Welding Processes 62 62  Forge welding Applications Shafts Fasteners Eduardo Marques Advanced Joining Processes – Welding Processes 63 63  Explosive welding Eduardo Marques Advanced Joining Processes – Welding Processes 64 64  Explosive welding Principle In explosive welding, a compression force created by detonation of explosives is used to join overlapping metal sheets. Joining happens continuously by local plastic deformation of the contact area Eduardo Marques Advanced Joining Processes – Welding Processes 65 65  Explosive welding Principle Source: NOV.com Eduardo Marques Advanced Joining Processes – Welding Processes 66 66  Explosive welding Advantages Can join dissimilar and even unweldable metals; Allows to reduce manufacturing costs, by applying thin coatings of an expensive material to a larger component of a cheaper material; Requires simple jigs and fixtures; Suitable for very large joining areas; Works with a wide range of thickness values; There is no change the mechanical properties of the metal. Eduardo Marques Advanced Joining Processes – Welding Processes 67 67  Explosive welding Disdvantages Base metals must be ductile to resist the impact; Noisy and potentially dangerous, requires the use of special chambers or sand/water protection; Only suitable for simple geometries, such as plates or cylinders; Requires thorough cleaning and preparation of the surfaces to be joined Use of explosives is limited and strictly regulated. Eduardo Marques Advanced Joining Processes – Welding Processes 68 68  Explosive welding Applications Pressure vessels (steel, titanium clad) Large heat exchangers, (steel, super duplex clad) Eduardo Marques Advanced Joining Processes – Welding Processes 69 69  Magnetic pulse welding Eduardo Marques Advanced Joining Processes – Welding Processes 70 70  Magnetic pulse welding Introduction A component (1) is fixed in the machine, surrounded by an outer component (2). A large alternating current (up to one million amps) is fed to a conductive coil (3), creating a magnetic field that forces the outer component to accelerate toward the interior, reaching up to 800 m/s A weld is made when the parts collide, driven by kinetic energy and heat generated. Eduardo Marques Advanced Joining Processes – Welding Processes 71 71  Magnetic pulse welding Advantages Weld is stronger than the weakest base material; No protecting atmosphere, filler materials or other aid materials; No heat affected zone is created, and no loss of material properties takes place; Workpieces can be unclamped immediately after welding and can be further processed immediately; Very fast production rates; Green welding process, with no heat, radiation, gas or welding fume release. Eduardo Marques Advanced Joining Processes – Welding Processes 72 72  Magnetic pulse welding Disdvantages The outer material should possess a good electrical conductivity; Surfaces to be joined can only be positioned in an overlap configuration; Geometry of parts may require changes to suit the magnetic pulse process; If the parts cannot fully fit into the coil, this might require a more complex multi-part coil; The large mechanical shock can damage or break brittle materials; Large setup cost versus low cost of the manufactured part. Eduardo Marques Advanced Joining Processes – Welding Processes 73 73  Magnetic pulse welding Applications Electrical conductors Gears Eduardo Marques Advanced Joining Processes – Welding Processes 74 74  Ultrasonic welding Eduardo Marques Advanced Joining Processes – Welding Processes 75 75  Ultrasonic welding Principle Ultrasonic welding, for thermoplastic injection moulded components, is a process that uses mechanical vibrations above the audible range. Vibrations, soften or melt the thermoplastic material at the joint line. Eduardo Marques Advanced Joining Processes – Welding Processes 76 76  Ultrasonic welding Principle Ultrasonic welding equipment consists of: press; control system with generator, converter or transducer; booster; sonotrode or horn; component support tooling. Eduardo Marques Advanced Joining Processes – Welding Processes 77 77  Ultrasonic welding Principle Setup: The two pieces to be joined are assembled in the fixture. Horn contact: The horn, also known as the sonotrode, is placed in contact with the upper part of the piece, transmitting mechanical vibration. Pressure applied: Pressure is applied to the setup using a pneumatic or electric driven press. Weld time: The horn is vibrated vertically at a high frequency (~20 kHz), generating heat that softens or melts the parts. Retraction: After the weld cools, pressure is released, and the horn is retracted, allowing the welded part to be removed from the fixture. Eduardo Marques Advanced Joining Processes – Welding Processes 78 78  Ultrasonic welding Advantages Exceptionally fast process as the material welds and cools very quickly; Extremely safe as the ultrasonic energy is highly targeted; Ultrasonic welding equipment will function with a high level of reliability with minimal human intervention; Produces a very clean and precise joint, with no plastic flash or deformation; Can be applied to a variety of materials, such as thermoplastics and several metals; Very cost-effective, with low material usage. Eduardo Marques Advanced Joining Processes – Welding Processes 79 79  Ultrasonic welding Disadvantages Does not work with all thermoplastics and requires a low moisture content in the materials that it welds; Ultrasonic energy is not enough to produce large joints, greater than 250 mm in length since this requires very large power; Ultrasonic welding can only be used on lap joints; Very slow setup time, requiring custom tooling and tuning work; Significantly more expensive than traditional welding equipment. Eduardo Marques Advanced Joining Processes – Welding Processes 80 80  Ultrasonic welding Applications Shoes Printed circuits Electrical connectors Medical equipment Eduardo Marques Advanced Joining Processes – Welding Processes 81 81  Thank you [email protected] Eduardo Marques Advanced Joining Processes – Welding Processes 82 82