Nugget Coating Equipment Heating Process

- Aug 28, 2017 -

The nugget is the product of condensing the liquid metal, nugget coating equipment so the central part of the nugget has been heated to the melting point of the metal, nugget coating equipment the boundary is the highest temperature is the melting point of the isothermal surface, the study of the internal temperature distribution of the weld to understand the nugget formation process There's important meaning.

According to the principle of heat conduction, nugget coating equipment the temperature change of each point from the point of instantaneous input, the difference between the output heat and the calorific value of the point itself caused by the algebra. The heat input or output is caused by its temperature difference from the adjacent point. The heat of each point is the current through the generated resistance heat. As the current density, resistivity varies with temperature, the heat of each point is also changing. nugget coating equipment To this end, it is extremely complicated to calculate accurately. At present, only a simple model can be used to estimate the finite element method on a large computer.

1. Current distribution during spot welding For the most commonly used cone-shaped electrode spot welding and other thickness of the steel plate, nugget coating equipment you can ignore the contact resistance, for computer calculations, can be drawn at the beginning of the electric field distribution and current density distribution.

With the heating process of the weldment, nugget coating equipment the temperature increases unevenly, the resistivity of each point is different, the central temperature is higher, the resistivity is larger, the current flows to the periphery, and the current density distribution will change. After the central melting, nugget coating equipment due to the mechanical metal resistivity jump, the current distribution is also a step-like changes in the current more to the external diffusion, this phenomenon is called the flow phenomenon.

2. Spot welding temperature distribution of heating at the beginning, nugget coating equipment the welds of the same degree of overflow, no heat conduction, so the temperature rise of each point is proportional to the heat at all points, the highest current density of the highest temperature. Further heating, the temperature rise will depend on the combination of heat and heat conduction at all points. nugget coating equipment Heat is always transferred from the high temperature zone to the low temperature zone, and the greater the temperature difference, the faster the heat conduction. Finally, when the heat and heat to balance, the temperature is no longer rising.

The temperature distribution of the weld zone at spot welding can not be measured directly, but can be plotted with a calculated model on a large computer. nugget coating equipment For normal spot welding models, excluding contact resistance. The maximum temperature zone at each stage of the temperature rise is different. Such as the rapid heating, in the initial phase of the temperature that is to melt, nugget coating equipment and then cooling can be obtained ring nugget. Under normal circumstances, spot welding is recommended to use a nearly balanced heating mode,nugget coating equipment  which can be achieved on the impact of minimal fluctuations in the power of a good repeatability of the nugget size.

3. Thermal time constant Since the beginning of heating to reach the heat balance takes some time, the length of this time and the material of the thermal physical and thickness related. In order to determine the heating law of the plate spot welding, a Japanese scholar proposed to charge the heating process analog capacitor, which proposed the concept of hot time constant. nugget coating equipment That the heating is similar to the charge, nugget coating equipment the temperature exponentially curve rise, when reached 3r that has reached the welding parameters under the equilibrium temperature of 0.95. And that more than 3r of time the heating is basically no longer warming, but a waste of energy.

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