When the thickness or different materials ranging from spot welding, the nugget will be asymmetric in its interface, but the plate or the electrical conductivity, thermal conductivity and bad side of the offset, the offset of the result will be thin pieces or conductivity, thermal conductivity good penetration rate of the workpiece decreases, the solder joint strength decreased. Nugget is composed of two parts offset heat production and heat conditions are not the same cause. Unequal thickness, the thick side pieces of large resistivity, the interface is far away from the electrode, so less heat and more the heat, resulting in thick pieces of nugget bias; material is not the same time, electrical conductivity, thermal conductivity of materials of poor thermal heat production is easy and difficult, so this material also tend to nugget
Nugget offset adjustment principles are: to increase sheet or conductivity, thermal conductivity and good jobs to reduce their heat production and heat dissipation. Common methods are:
(1) The strong conditions for the contact resistance between the workpiece impact of heat production increases, the impact of lower electrode cooling. Capacitor discharge welding electrode using a large current and a short driving time will be able to weld the workpiece thickness ratio is very obvious example.
(2) with different diameter electrodes in contact with the surface of thin parts or electrical conductivity, thermal conductivity and good side of a smaller diameter of the workpiece to increase this side of the current density, and reduce the heat of the welding rods.
(3) sheets with different electrode materials or electrical conductivity, thermal conductivity and good thermal conductivity of the workpiece side of the poor used copper alloy, to reduce heat loss on this side.
(4) use technology in the thin parts or conductive gasket, thermal conductivity and good thermal conductivity of the workpiece side of the pad by a poor piece of metal gasket (thickness 0.2-0.3mm), in order to reduce this side of the heat .
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