We know that the formula of the Heat Input of a moving heat source in welding operation is:
Heat Input = (Voltage X Ampere X Process Efficiency)/(Weld Speed)
Is this formula is really accurate??!!
I mean should we include the material's thermal conductivity in that formula?!! Don't you think so!!
If we think in one material that has a high thermal conductivity then we should expect some heat loss in the weld pool area due to fast thermal conductivity, While in other materials with poor thermal conductivity the heat in the weld pool will be trapped and build up where the heat input from the source is the same, which means the longer weld line the higher the heat input will be created in the weld pool. In other words, the beginning of the weld line will form a weld pool with lower heat input than the end of the weld line since the amount of heat coming from the source is constant and as well as the weld speed.
What do you think?!! Please share your opinion
Good day, Abdulaziz Albannai !
The proposed formula for calculating rate of energy input is accurate. It considers the flow of energy to the surface of the structure to be welded. In turn, the energy flux from the surface to the material is equal to the lambda dT/dx and indeed includes the thermal conductivity of the particular material. But this is a reaction of the material, not a feature of welding heat source. If you integrate your temperature field to assess the total enthalpy, it should equal the total heat input, regardless of conductivity.
As for your long weld example. You don't take into account heat dissipation, which increases with temperature (T^4 for radiation and T^1 for conduction), so for long weld the liquid pool size finds its equilibrium state.
An interesting questions. We can discuss it from two perspectives.
1. The line energy of welding process is defined by the equation you mentioned. It determines how many energy will be applied on the unit length of weld structure. While, the heat generation just has relationship with the heat source, which is not affected by the materials itself.
2. After the energy is loaded on material, the thermal behaviors, such as temperature variation, thermal conduction and thermal loss, are influenced by the thermal property of materials. E.g. the density and specific heat capacity determines the temperature variation. The thermal conduction is influenced by the conductivity and dT.
Indeed, when you solve the FEM formula to calculate transient temperature and its rate, the equivalent heat and thermal properties matrix are located at the two sides of equation. Both of them can affect the accuracy of thermal analysis, but they are individual with each other.
For your case, if we used a same line energy to make a long welding bead, the maximum temperature at the start and end are different. It is induced by the average temperature of the whole structure. Some Joule heat is employed to heat the material with lower average temperature at start, thereby the maximum temperature and weld pool size are lower. The situation at the end is opposite. This phenomenon is induced by the heat transfer rather than the heat generation.
please read,
1.https://weldinganswers.com/how-to-calculate-heat-input/
Plz read https://www.researchgate.net/publication/357861670_The_Effect_of_Heat_Input_Parameters_on_Residual_Stress_Distribution_by_Numerical_Simulation_You_may_also_like_Experimental_study_on_the_evolution_law_of_residual_stress_in_the_fatigue_process_of_induc
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The formula for calculating heat input in welding is generally accurate, but its accuracy depends on several factors, including the specific welding process, materials being welded, and the method of measurement. The formula for heat input is typically given as:
HI=SV⋅I
Where:
- HI is the heat input in joules per unit length (J/mm) or some other appropriate unit.
- V is the welding voltage in volts.
- I is the welding current in amperes.
- S is the welding speed in millimeters per second (mm/s).
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