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CAD modeling and CAE simulation and analysis are the important tools to support design process, fine-tune and verify the result. The systematic procedure of applying computer-aided design and CAE simulation for cooling channels design optimization can be presented as follows (see Fig. 14). First of all, based on the results obtained from the analytical analysis step, approximate cooling channels are modeled by projecting cooling channels layout from a plane to the offset surfaces of the molded part. Subsequently, the coordinate of cooling channels are generated and stored in a text file. Next, the conformal cooling channels are imported to CAE environment and meshed automatically by an Application Programming Interface (API) via Visual Basic Scripting (VBS) language. After that, cooling simulation is performed to obtain the exact results of average mold temperature and temperature distribution of the molded part. Finally, the temperature of all elements or considered elements are queried and stored in a text file to support data for optimization process. The third step to the last step are looped until the optimal conditions are satisfied. This process is controlled automatically by an optimizer programmed by Matlab and VBS language. 5. Case study In order to prove the applicability and the feasibility of the milled groove conformal cooling channels, various practical cases had been carried out. In this section, a typical case study is presented. The molded part is a plastic car fender with the bounding box dimensions and thickness are 348×235×115 mm and 2.5 mm respectively as shown in Fig. 15. The polymer material is Noryl GTX979 which can suffer a high temperature up to 180°C in online painting process. Material properties of polymer, mold, and coolant are shown in Table 2. The molding parameters are recommended by material manufacturer as shown in Table 3. Filling time was obtained by performing filling simulation using Moldflow software. The cooling time was calculated analytically by using the formula (11). Mold opening time was estimated by the ratio of mold opening distance and mold opening velocity. According to formula (20) and the required length of milling tool to machine the cooling groove, the cooling diameter was selected as 12 mm. The range of pitch x was selected from 4d to 5d due to a high level of ejection temperature and requirement of reducing the number of cooling paths. By applying the solver tools, the results of analytical method are shown in Table 4. Table 2 Material properties Material Water (25°C) Steel (P20) PlasticDensity (kg/m3) 996 7800 930Specific heat (J/kg.°K) 4177 460 4660Thermal conductivity (W/m.°K) 0.615 29 0.25Viscosity (mm2/s) 0.801 - - Fig. 15 A plastic car fender with free-form shape The results from analytical method were used to deploy the conformal cooling channels as an initial design. Subsequently, Moldflow software was used to perform the cooling analysis. The simulation results for the first run showed that the average mold cavity surface temperature is 98.6°C. This figure nearly approaches the target mold temperature ( W T = 100°C). To approach the target mold temperature, the pitch x of cooling channels was fixed and the depth y of both core side and cavity side were adjusted. Linear interpolation method was used as a strategy to reduce the number of iteration of simulation. The final results were obtained rapidly after performing three more simulations. The average mold temperature is 100.4°C. The maximum temperature at the middle layer of the part is 221.2°C at the end of cooling time, so it can allow ejecting the molded part safely without distortion. The temperature on the part distributes quite uniform even though the free-form shape of the part is complex (see Fig. 16). The simulation result shows that the time to freeze the part to ejection temperature is 6.1 second. This result agrees well with the cooling time calculated by formula (11) (6.3 second). This means that the cooling design results satisfy the optimality conditions. The optimum values of the distances from the cooling channels to the part surface are 46.0 mm and 46.9 mm for the core side and cavity side of the mold, respectively. We compared the cooling effect of an un-optimized design and the optimized design and found that the range between maximum and minimum temperature in the case of optimized conformal cooling channel is always smaller than that of the un-optimized one (see Fig. 17 as an example). In addition, the comparison of the warpage between the best straight cooling channel and the conformal one was also carried out. The simulation result shows that conformal cooling channel reduces 15.7% warpage for this case study (see Fig. 18). The effect of conformal cooling channel varies according to the complexness of the molded part. In general, conformal cooling channels always offer a better uniform cooling Table 3 Molding parameters Parameters Value Unit Melt temperature TM 305 °C Ejection temperature TE 247 °C Average mold temperature W T 100 °C Filling time tf (obtained by simulation) 1.9 s Cooling time tc 6.3 s Mold opening time to 3 s Velocity of cooling water u 1.0 m/s Temperature of cooling water TC 25 °C