The essence of bonding/welding process is to heat the contact surfaces so that they become plastic (dough-like) and then press them together. Only a small volume of the contact surfaces is plasticised. Depending on the method used, pressure is applied first and then heat, or vice versa, heat is applied first and then surface pressure is added.
In terms of the nature of the phenomenon causing the joint, bonding/welding is divided into:
- electric resistance welding – the parts to be joined are connected to the secondary circuit of a transformer and, as a result, during the flow of the electric current, the places where the electrodes come into contact with the material and the parts to be joined are heated locally very strongly. In addition, in most cases, it is necessary to apply temperature and pressure simultaneously to carry out the welding process;
- electric resistance welding with accumulated energy – the materials are joined by the heat released in them during the flow of the welding current, created from previously accumulated energy (e.g. capacitors);
- induction welding – involves the phenomenon of heating electrical conductors placed in an alternating electromagnetic field due to the formation of high-frequency eddy currents and magnetic hysteresis in the conductors;
- friction welding – uses the conversion of mechanical energy into thermal energy as a result of friction between two surfaces with simultaneous axial pressure force. A variation of this process is Friction Stir Welding (FSW), in which a weld is formed by forcing a rotating arm, which ends with a specially shaped mandrel, along the surfaces of the plates that are in contact with each other;
- ultrasonic welding – materials are joined by the simultaneous action of pressure and ultrasonic mechanical vibration;
- explosive welding – joining of materials as a result of dynamic pressure on the surfaces to be joined caused by the energy released when the explosive is detonated;
- crush welding – involving the local and instantaneous application of a large pressure force to the parts to be joined, which may be exerted either statically or dynamically, without using an additional heat source;
- diffusion welding – based on the phenomenon of mutual diffusion of the materials to be joined (with minimum plastic deformation), heated to a temperature close to the melting point and in a state of close adhesion.
