Techno-economic Analysis of Conformal Tooling via Hybrid Manufacturing
Creators: name: Wilson, Neil
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401403
subject: Flexible manufacturing systems
classificationCode: 401607
subject: Metals and alloy materials

description: Injection molding is an important polymer manufacturing process known for its efficiency in producing complex and precise components at high volumes and with good quality. However, the traditional approach to designing advanced injection molding (IM) tools, particularly their in-situ cooling systems, has resulted in inaccurate approximations that are only discovered after prototype tooling is manufactured and tested. Identifying these design failures during operation often leads to expensive redesigns to meet performance metrics such as manufacturing cycle time, part consistency, and part accuracy.

To avoid poor return on investment (ROI) for IM tool purchasers and operators, a superior design optimisation methodology is necessary. The optimisation should focus on maximising and homogenising the performance of the cooling system by optimising the heat flux across the cavity/core surface and the IM process parameters. Conformal cooling channels (CCCs), which follow the cavity surface, have emerged as a critical solution for achieving these goals, but this ‘smart’ design of CCCs is still in its infancy. This thesis proposes a novel generative design (GD) approach to IM tooling that optimises CCC design to enhance performance. This approach reduces design labour and costs, which are particularly high in Australia's manufacturing sector, and significantly increases ROI for IM tool purchasers. The GD algorithm developed here combines evolution-based optimisation methods with iterative routing optimisation based on surface temperature gradients—a novel combination not explored in existing literature. Compared to conventional tools, the GD tool achieved cooling time reductions of 20% (predicted worst case) and over 50% (measured) for a molded polymer part with a simplified geometry.

While advanced IM tool designs with complex CCCs can now be created, manufacturing them is challenging due to their sophisticated internal geometry. Additive manufacturing (AM) technologies can build somewhat sophisticated internal geometries in a near net-shape manner with low raw material wastage, but hybrid manufacturing (HM), which combines additive and subtractive manufacturing technologies, offers increased productivity and potentially reduced costs. This capability is particularly relevant for building GD-designed IM tools with highly complex internal geometries. Therefore, this thesis determines the "manufacturability" requirements that GD-designed tooling must meet to be manufactured using a modern hybrid directed energy deposition (DED) printer. The key aspect is having self-supported profile shapes with a maximum overhang angle of 35° from the vertical. Additionally, process parameters for multimaterial tools are developed, and tool material selection considers composite (bi-metallic) builds suitable for modern AM alloys.

The combined benefits of GD and HM on the predicted and achievable ROI of IM tool designs are substantial. However, the cost analysis of these modern IM tools and their manufacturing is crucial. This thesis provides an economic assessment of GD-designed and hybrid-manufactured IM tooling with CCCs. The assessment includes a whole-of-life costing model and concludes that, for the sample part evaluated, a minimum of 80,000 molded parts is required to offset the higher costs of hybrid manufacturing compared to conventional methods. The predicted ROI for this tool, considering its usage frequency, leads to an estimated 127% ROI within a year for producing 100,000 parts annually, which is relevant to an Australian tool design and manufacturing SME.