The results you obtain from simulating induction heating are critically dependent on the care you take to set up the analysis.
- When simulating induction heating with Autodesk Moldflow Insight, you will need to specify mold materials for the entire mold, because the accuracy of the induction solution depends entirely upon the relative magnetic permeability and electrical resistivity in the mold. You will also need to specify the thermal conductivity, density and specific heat. Only specific mold materials can be used for induction heating in order to get the full benefit of the technology; ordinary mold materials are not highly magnetic and will not be very efficient in induction heating applications.
- Accurately model the exact geometry of the entire mold, including the induction coils, to get optimum induction heating at the part's surface. Induction heating relies on the geometry of the entire mold and on strategically placed inserts in the mold of different magnetic properties. Usually induction heating molds have a nickel based insert touching the part in order to enhance the skin effect. If the molds geometry and choice of materials can be a done precisely induction heating of molds can be very efficient.
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Induction heating relies solely on the skin effect, which depends upon the material properties in the mold and the frequency of the alternating current in the mold. You should calculate the skin effect thickness on all the bodies in the mold before meshing. The mesh size should be set to at least the skin thickness size for each insert or body to be meshed. Place enhancement layers in the inserts such that the element height is at least one third of the skin thickness. If these rules are followed then the heat generated in the skin thickness should be captured entirely resulting in a very accurate solution.
- Due to the skin effect, the induction heating simulations are very sensitive to the mesh size. The frequency chosen and the mesh size are mutually dependent. If the frequency is too high for the mesh size, then the system of equations are no longer diagonally dominant resulting in an ill-conditioned matrix. The ill-conditioned matrix will not solve and the analysis will exit with an error. In such instances the mesh needs to be made finer. A lower frequency will aid matrix diagonal dominance; however this may not suit the mold design specifications.
- Once in the simulation environment, set the property of the induction coils CAD body to Induction coil (3D). The high and low potential terminals on this coil body are set as a boundary condition. On the high potential terminal, specify the source current being applied to the terminal or the voltage that is applied to it. Set the frequency of the alternating current, applied to the coil, on the Induction coil (3D) body itself.
- With induction heating, the current strength dictates the amount of power the mold will be heated by; the higher the frequency the thinner the skin depth. This means that with a higher frequency a thinner skin depth will be heated up faster and be hotter than the rest of the body. A lower frequency will ensure that a thicker skin depth region will be heated up slower and be cooler than if the frequency were higher. This phenomenon can be very useful in rapid heating and cooling applications if applied correctly at the design stage. Thin regions of the mold touching the part can be targeted for heating, resulting in the bulk of the mold remaining very cold throughout the injection molding cycle and reducing the cooling stage of the process.
- With the coils defined, boundary conditions and frequency set, and with the mold meshed to the correct mesh size, the analysis can be started. The solver solves the Maxwell equations at the start of the Cool analysis and calculates the Joule heating and stores it in memory. After the solution of the Maxwell equations the ordinary Cool (FEM) analysis is performed. When the heaters are turned on in the simulation, the Joule heat calculated previously is applied as the source term. When the heaters are turned off, the source term is ignored in the analysis.