Design Rules For Conformal Cooling Channels In Plastic Injection Moulds Produced Through Direct Metal Laser Sintering Of Maraging Steel

Abstract

Additive Manufacturing (AM) is fast becoming a common process in the manufacturing and tooling industry at large. Subsequently, AM has been identified as one of the key technologies in Industry 4.0 through the design freedom and versatility in the possible shortened lead times offered.The application of AM has recently become quite appealing in the Injection Moulding (IM) industry. The development of metal powders for Selective Laser Melting (SLM) has created the potential for SLM to be used for the manufacture of high-volume production IM tooling inserts. The design capabilities of tool designers have been enhanced through the use of AM in the tool making environment by lending its greatest advantage: freedom of design. Since AM offers virtual freedom of design, this has led to the implementation of conformal cooling channels for tooling, which has shown to be instrumental in enhancing productivity and ultimately increasing profitability. The cooling of IM tools is a vital stage in the IM process which has a direct impact on the profitability and productivity of the process. The efficiency of injection mould tooling is positively influenced by an enhanced cooling rate achieved through conformal cooling, which in turn has a positive influence on the quality of the parts produced. The aim of this study was to further enhance the use of AM in the IM industry through the refinement of design rules for conformal cooling channels. By utilizing Finite Element Analysis (FEA)-based techniques and practical experiments, the end goal has been achieved through the determination of physical limitations of conformal cooling channels built through the Direct Metal Laser Sintering (DMLS) process, an AM technique used to fuse metal powders through application of a high-power-density laser. Furthermore, one of the challenges faced during this study led to the development of a stress-relieving heat treatment for maraging steel components built using the DMLS process. This was achieved through subsequent applications of a combination of heat treatments followed by 3D-scanning techniques and hardness measurements. This process was iterated until a virtually stress-free component was achieved. Ultimately, the refined design rules were applied to an IM toolset in an attempt to compare the cooling efficiency and productivity of conformal cooling channels produced using AM and that of conventionally machined cooling channels.The results indicated that conformal cooling has a significant impact on the reduction of cycle times resulting in an improved cooling efficiency. In a broader perspective, a design process was documented to further augment the design thought process as applied AM in the IM tooling industry. Together with the documentation of the refined design rules for conformal cooling channels, this provides a valuable tool to the IM design industry at large.