Spot welding( RIHUI Ceramic Welding Backing)

                                                                             Spot welding

                                                                                                 Supplied  By   RIHUI Ceramic Welding Backing

Spot welding is a resistance welding method used to join two to four overlapping metal sheets which are up to 3 mm thick each. In some applications with only two overlapping metal sheets, the sheet thickness can be up to 6 mm. Two copperelectrodesare simultaneously used to clamp the metal sheets together and to pass current through the sheets. When the current is passed through the electrodes to the sheets, heat is generated due to the higher electrical resistance where the surfaces contact each other. As the heat dissipates into the work, the rising temperature causes a rising resistance, and the heat is then generated by the current through this resistance. The surface resistance lowers quickly, and the heat is soon generated only by the materials' resistance. The water cooled copper electrodes remove the surface heat quickly, since the copper is an excellent conductor. The heat in the center has nowhere to go, as the metal of the workpiece is a poor conductor of heat by comparison. The heat remains in the center, melting the metal from the center outward. As the heat dissipates throughout the workpiece in less than a second the molten, or at least plastic, state grows to meet the welding tips. When the current is stopped the copper tips cool the spot weld, causing the metal to solidify under pressure. Some coatings, such as zinc, cause localized heating due to its high resistance, and may require pulsation welding to dissipate the unwanted surface heat into the copper tips.

If excessive heat is applied, or applied too quickly, the molten area may extend to the outside, and with its high pressure (typically 30,000 psi) will escape the containment force of the tips with a burst of molten metal called expulsion. When this occurs, the metal will be thinner and have less strength than a weld with no expulsion. The common method of checking a weld is a peel test, technically called "coach peel", as expulsion weakens the material by thinning, and makes it pass the peel test easier. A better test is the tensile test, which is much more difficult to perform, and requires calibrated equipment.

The advantages of the method include efficient energy use, limited workpiece deformation, high production rates, easy automation, and no required filler materials. When high strength in shearis needed, spot welding is used in preference to more costly mechanical fastening, such as riveting. While the shear strengthof each weld is high, the fact that the weld spots do not form a continuous seam means that the overall strength is often significantly lower than with other welding methods, limiting the usefulness of the process. It is used extensively in the automotive industry— cars can have several thousand spot welds. A specialized process, called shot welding, can be used to spot weld stainless steel.

                                                                                                      Supplied  By   RIHUI Ceramic Welding Backing

Date: 2023-04-10     hits: 814    Return