Used Tools:

Introduction

The vast use of electromagnetic induction heating in molds is thanks to its advantages of fast heating and high efficiency. Combined with cooling process, induction heating is employed to achieve a dynamic mold temperature control. This study is dealing with 3D and 2D coil designs to analyze the effect of each design on the temperature control of a mold plate. Figure 2 shows the CAD model of each design.

Figure 1 -  Induction heating for injection mold plate [1]

Figure 2 - 3D model of Mold plate with both 3D a) and 2D b) coil 

Problem description and design

The studied models consist of a square mold plate with 3 cooling channels located at 10 mm from the top surface, and two inductor coils made of copper with 8mm diameter. For both designs, the distance from the coil to the mold surface is 3 mm. Table1 contains the detailed dimensions of each component.

The main goal of this analysis is to compute the temperature distribution across the mold plate for both designs to achieve a better temperature control during the heating mold process.

Table1 - Components’ dimensions

3D coil
2D coil
Mold plate

Simulation Setup

The induction heating process is simulated in EMS using AC Magnetic module coupled with transient thermal. It is used to compute and visualize the temperature distribution versus time, across the studied mold plate.
The simulation setup consists of the following steps:

1. Select the appropriate materials: 

Table2 - Material properties

Part	Material	Density (Kg/)	Magnetic permeability	Electrical resistivity (m)	Thermal conductivity (W/m.K)	Specific heat capacity (J/Kg.K)
Coil	Copper (Cu)	8940	0.99	1.71 E-07	400	392
Mold	Stainless steel 420 (ISO 683/134)	7700	200	5.5 E-07	14	448

2. Electromagnetic Inputs: 

The inductor coils are defined assolid coils (3D coil: 9 turns, 2D coil:4 turns ) supporting a maximum current of 1500 A rms and a frequency of 75 kHz.

3. Thermal Inputs:

The mold plate is pre-heated with an initial temperature of 40°C. A thermal convection is applied on the air body at ambient temperature of 25°C with a coefficient set to 10 W/m²K .

Meshing

Since the eddy currents are mostly located in the skin depth of the top face of mold plate, a small mesh size is needed for accurate results. EMS allows to use a mesh control feature on edges, faces and bodies.
Figure 3 shows the meshed models with two different mesh controls applied on the mold plate face.

Results

For each coil design, EMS enabled to predict and visualize the temperature distribution across the top surface of the mold plate after 2s of heating. Higher temperature zones are located in the center of the mold when using the 3D coil, which confirms the experimental results [1].
On the contrary, the center area of the mold plate sees the lowest temperature values for the second, 2D coil, design. Consequently, this temperature distribution is not adequate for the heating process in injection molding field.

Figure 4 - Temperature distribution across the mold plate for 3D coil  a). and 2D coil b)  design after 2s of heating.

The figure below shows the three measuring positions T1, T2 and T3 on the top surface of the mold plate.

 

The obtained simulation results from the three measuring points illustrate that the temperature difference between them is higher in the 2D coil design than in the 3D coil one. The latter is then confirmed to be more suitable for mold temperature control by induction heating.
Simulation results obtained from EMS have been found close to the experimental results given by the reference. Table 3 shows a comparison of the EMS results versus reference[1].

Conclusion

Choosing the right coil design to easily control the temperature in injection molding has been achieved through a visual comparison of temperature distribution using EMS simulation tool. The latter allowed to accurately model, analyze and select from different designs of induction heating coils.

References

[1]. Minh, Pham Son. "EFFECT OF 2D AND 3D COIL ON THE DYNAMIC MOLD TEMPERATURE CONTROL BY INDUCTION HEATING." Vietnam Journal of Science and Technology 52.4 (2014): 409.