Ultrasonic welding is an industrial process whereby high-frequency ultrasonic acoustic vibrations are locally applied to work pieces being held together under pressure to create a solid-state weld. It is commonly used for plastics and metals, and especially for joining dissimilar materials. In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together. When used to join metals, the temperature stays well below the melting point of the involved materials, preventing any unwanted properties which may arise from high temperature exposure of the metal.
Plastic welding is welding for semi-finished plastic materials, and is described in ISO 472 as a process of uniting softened surfaces of materials, generally with the aid of heat. Welding of thermoplastics is accomplished in three sequential stages, namely surface preparation, application of heat and pressure, and cooling. Numerous welding methods have been developed for the joining of semi-finished plastic materials. Based on the mechanism of heat generation at the welding interface, welding methods for thermoplastics can be classified as external and internal heating methods, as shown in Fig 1.
Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex cross-sections; and to work materials that are brittle, because the material encounters only compressive and shear stresses. It also creates excellent surface finish and gives considerable freedom of form in the design process.
Friction welding (FWR) is a solid-state welding and bonding process that generates heat through mechanical friction between workpieces in relative motion to one another. This process is used with the addition of a lateral force called "upset" to plastically displace and fuse the materials. No melting occurs, friction welding is not a fusion welding process, but a solid-state welding technique more like forge welding. Friction welding is used with metals and thermoplastics in a wide variety of aviation and automotive applications.
Friction stir welding (FSW) is a solid-state joining process that uses a non-consumable tool to join two facing workpieces without melting the workpiece material. Heat is generated by friction between the rotating tool and the workpiece material, which leads to a softened region near the FSW tool. While the tool is traversed along the joint line, it mechanically intermixes the two pieces of metal, and forges the hot and softened metal by the mechanical pressure, which is applied by the tool, much like joining clay, or dough. It is primarily used on wrought or extruded aluminium and particularly for structures which need very high weld strength. FSW is capable of joining aluminium alloys, copper alloys, titanium alloys, mild steel, stainless steel and magnesium alloys. More recently, it was successfully used in welding of polymers. In addition, joining of dissimilar metals, such as aluminium to magnesium alloys, has been recently achieved by FSW. Application of FSW can be found in modern shipbuilding, trains, and aerospace applications.
Spin welding is a friction welding technique used on thermoplastic materials, in which the parts to be welded are heated by friction. The heat may be generated by turning on a lathe, a drill press, or a milling machine, where one part is driven by the chuck, and the other is held stationary with the spinning part driven against it. This is continued until the heat of friction between the parts reaches a sufficient level for the parts to weld. The stationary part is then released to spin as well, while pressure is applied along the axis of rotation, holding the parts together as they cool.
Strapping, also known as bundling and banding, is the process of applying a strap to an item to combine, stabilize, hold, reinforce, or fasten it. A strap may also be referred to as strapping. Strapping is most commonly used in the packaging industry.
Plastics extrusion is a high-volume manufacturing process in which raw plastic is melted and formed into a continuous profile. Extrusion produces items such as pipe/tubing, weatherstripping, fencing, deck railings, window frames, plastic films and sheeting, thermoplastic coatings, and wire insulation.
Drill pipe, is hollow, thin-walled, steel or aluminium alloy piping that is used on drilling rigs. It is hollow to allow drilling fluid to be pumped down the hole through the bit and back up the annulus. It comes in a variety of sizes, strengths, and wall thicknesses, but is typically 27 to 32 feet in length. Longer lengths, up to 45 feet, exist.
Hot plate welding, also called heated tool welding, is a thermal welding technique for joining thermoplastics. A heated tool is placed against or near the two surfaces to be joined in order to melt them. Then, the heat source is removed, and the surfaces are brought together under pressure. Hot plate welding has relatively long cycle times, ranging from 10 seconds to minutes, compared to vibration or ultrasonic welding. However, its simplicity and ability to produce strong joints in almost all thermoplastics make it widely used in mass production and for large structures, like large-diameter plastic pipes. Different inspection techniques are implemented in order to identify various discontinuities or cracks.
Vibration welding refers to a process in which two workpieces are brought in contact under pressure, and a reciprocating motion (vibration) is applied along the common interface in order to generate heat. The resulting heat melts the workpieces, and they become welded when the vibration stops and the interface cools. Most machinery operates at 120 Hz, although equipment is available that runs between 100–240 Hz. Vibration can be achieved either through linear vibration welding, which uses a one dimensional back and forth motion, or orbital vibration welding which moves the pieces in small orbits relative to each other. Linear vibration welding is more common due to simpler and relatively cheaper machinery required.
Laser welding of polymers is a set of methods used to join polymeric components through the use of a laser. It can be performed using CO2 lasers, Nd:YAG lasers, Diode lasers and Fiber lasers.
Extrusion welding is one of the processes used to weld thermoplastics and composites, developed in the 1960s as an evolution of hot gas welding. It can be a manual or automated process.
Aluminium alloys are often used due to their high strength-to-weight ratio, corrosion resistance, low cost, high thermal and electrical conductivity. There are a variety of techniques to join aluminium including mechanical fasteners, welding, adhesive bonding, brazing, soldering and friction stir welding (FSW), etc. Various techniques are used based on the cost and strength required for the joint. In addition, process combinations can be performed to provide means for difficult-to-join assemblies and to reduce certain process limitations.
Ultrasonic welding is a method of joining thermoplastic components by heating and subsequent melting of surfaces in contact. Mechanical vibration with frequency between 10 and 70 kHz and amplitude of 10 to 250 μm is applied to joining parts. After ultrasonic energy is turned off, the parts remain in contact under pressure for some time while the melt layer cools down creating a weld.
Advanced thermoplastic composites (ACM) have a high strength fibres held together by a thermoplastic matrix. Advanced thermoplastic composites are becoming more widely used in the aerospace, marine, automotive and energy industry. This is due to the decreasing cost and superior strength to weight ratios, over metallic parts. Advance thermoplastic composite have excellent damage tolerance, corrosion resistant, high fracture toughness, high impact resistance, good fatigue resistance, low storage cost, and infinite shelf life. Thermoplastic composites also have the ability to be formed and reformed, repaired and fusion welded.
Radio-frequency welding, also known as dielectric welding and high-frequency welding, is a plastic welding process that utilizes high-frequency electric fields to induce heating and melting of thermoplastic base materials. The electric field is applied by a pair of electrodes after the parts being joined are clamped together. The clamping force is maintained until the joint solidifies. Advantages of this process are fast cycle times, automation, repeatability, and good weld appearance. Only plastics which have dipoles can be heated using radio waves and therefore not all plastics are able to be welded using this process. Also, this process is not well suited for thick or overly complex joints. The most common use of this process is lap joints or seals on thin plastic sheets or parts.
IR welding is a welding technique that uses a non-contact heating method to melt and fuse thermoplastic parts together using the energy from infrared radiation. The process was first developed in the late 1900s, but due to the high capital cost of IR equipment the process was not commonly applied in industry until prices dropped in the 1990s. IR welding typically uses a range of wavelengths from 800 to 11,000 nm on the electromagnetic spectrum to heat, melt, and fuse the interface between two plastic parts through the absorption and conversion of the IR energy into heat. Laser welding is a similar joining process that applies IR radiation at a single wavelength.
Implant induction welding is a joining method used in plastic manufacturing. The welding process uses an induction coil to excite and heat electromagnetically susceptible material at the joint interface and melt the thermoplastic. The susceptible material can be contained in a gasket placed between the welding surface, or within the actual components of a composite material. Its usage is common for large, unusually shaped, or delicate parts that would be difficult to weld through other methods.
Rotary friction welding (RFW) one of the methods of friction welding, the classic way of which uses the work of friction to create a not separable weld. Typically one welded element is rotated relative to the other and to the forge. The heating of the material is caused by friction work and creates a permanent connection. In this method, the materials to be welded can be the same, dissimilar, or composite and non-metallic materials. The friction welding methods of are often considered as solid-state welding.
