## 2 Conformal Cooling Channel  
Conformal cooling channels are different from conventional cooling channels. In a conventional cooling channel, the free-form surface of the cavity is surrounded by straight channels. The cooling channels are at different distances from the cavity surface, resulting in uneven cooling. On the contrary, in a conformal cooling channel, the cooling channel is well matched to the cavity surface by maintaining an almost constant distance between the cooling channel and the cavity surface. Many conformal cooling channel layouts [10, 11, 12, 13] have been proposed in previous research. The cooling channel provides better temperature distribution in molded parts than conventional cooling channels. The main purpose of the design of the cooling channel is to keep the cooling channels inside the injection mold as close to the surface of the product as possible, so that the temperature distribution on the surface of the product is more uniform, eliminating heat collection areas, and ultimately resulting in more uniform cooling, shorter molding cycles, and higher molding quality of the part. With the rapid development of 3D printing technology and prototyping technology and the gradual reduction of manufacturing costs, the application of conformal cooling channel design technology has become increasingly mature and common. Conformal cooling channels are often used in the design of cooling systems for injection molded products with large curvature changes and uneven wall thickness distribution. The production of cooling channels mainly uses the following technologies. The first is direct metal laser sintering technology, which uses a laser to sinter metal powder layer by layer to form the cavity or core part of the mold. The second is thermal or pressure fusion technology, which uses heating or pressure to fuse two or more metal plates in a vacuum furnace. The third is laser 3D printing molding technology. Based on computer software layered discrete and CNC molding system, 3D printing and manufacturing of mold inserts are performed by using a high-energy laser beam and high-temperature fusion nozzles to process and manufacture templates with computer-simulated 3D models by stacking and bonding metal, and ceramic powder and special injection molding raw material. The purpose of traditional manufacturing industry is to shape the product through processing and manufacturing methods such as injection molding, lathes, and milling machines, and then to cut excess materials to manufacture injection molded parts. However, 3D printing technology can convert the three-dimensional design in the computer into a physical model, directly manufacture parts or molds, and save materials without removing scraps. It improves the utilization of materials and effectively shortens the product development cycle time. Optimization of the injection mold cooling system is mainly reflected in the improvement of the numerical simulation technology of the injection mold cooling process and the layout optimization of the cooling channels. [PERSON] et al. [14] proposed a method for the optimization of mold cooling systems based on hydrodynamic simulation. They concluded that the selection of cooling system arrangements mainly depends on the temperature reduction of the system, heat transfer rate, and ease of manufacturing and installation, and they verified the feasibility of the method by numerical simulation. [PERSON] et al. [15] from Korea designed an automated optimization method for cooling channels. Using spectacle lenses as the research object and the surface temperature deviation value of the plastic part as the optimization index, the conformal cooling channels were designed and optimized by imitating the growth mechanism of plant roots. This method first decomposes the injection molded part into small areas according to the CVD algorithm and then connects the central part of heat to form the cooling channel module according to the binary branching law.