The resistance of spot welding machine is the basis of internal heat source, resistance heat, is the internal factor of forming welding temperature field, research shows that the heat extraction of contact resistance (average) is about 5%-10% of the internal heat source Q, soft specification may be less than this value, hard specification and precision spot welding is greater than this value, contact resistance R, It is related to the distribution of the real physical contact points of the conductor and the area of the contact points.
That is, it is related to the weldment material, surface state (cleaning method, surface roughness, storage time), electrode pressure and temperature, and sometimes in order to avoid adhesion damage, initial spatter and other bad phenomena, saddle-shaped pressure change curve can be used in the spot welding of thick steel plate, aluminum alloy, etc., to obtain low and uniform contact resistance value, which not only can make full use of electric power, but also can make full use of electric power. The welding quality can also be improved. The double effect of saving electricity.
In the spot welding of thick steel plate, if the spot welding cycle such as preheating current pulse and amplitude modulation current waveform is used, the same effect can be obtained as the saddle-shaped pressure curve, and the cost of the equipment can be reduced because the pressure of the preloaded electrode can be increased.
It should be pointed out that although the heat absorption of the contact resistance accounts for a small proportion of the heat source, and it decreases and disappears soon after the welding begins, this part of the heat is important to establish the temperature field at the initial stage of welding, expand the contact area, and promote the homogenization of the current distribution.
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Post time: May-08-2024