Tooling Through Laser Sintering In Maraging Steel For High-Volume Plastic Injection Moulding

Abstract

Existing techniques to manufacture conventional tool steel inserts for the plastic injection moulding process are expensive and time-consuming. Complex mould inserts, difficult to manufacture with conventional processes, can be produced using Direct Metal Laser Sintering (DMLS). DMLS is an additive manufacturing (AM) process that can produce complex functional metal components directly from computer aided design (CAD) data. Recent advances in materials and laser sintering technologies make it possible to process high-performance metals suitable for production components. Maraging Steel MS1, an AM material made available by EOS GmbH Electro Optical Systems (EOS), is a DMLS metal powder designed for tooling applications. It is an ultra-high-strength alloy that is resistant to corrosion, has good thermal conductivity properties and can be hardened with a thermal age-hardening process. Maraging Steel MS1 can be, and is easily machined and EDM spark-eroded in its ‘as-built’ state. Unlike conventional methods traditionally used in the manufacturing of metal components, DMLS can produce complex inner structures (such as conformal cooling) that can be beneficial for the tooling sector. This dissertation describes an investigation into the possible heat transfer benefits of conformal cooling channels using Maraging Steel MS1 inserts which could result in a reduction of cycle times, cost per product as well as improving part quality by eliminating defects such as warpage and heat sinks. Two AM inserts for an interlocking floor tile with different conformal cooling channel designs were compared using ANSYS® CFD and SIGMASOFT® virtual moulding to determine the most efficient cooling channel design. During the simulations, factors such as heat transfer rates and turbulent flow inside the cooling channels were considered and the most efficient design was selected based upon these factors. A comparison between the most efficient AM insert design and an insert manufactured through conventional manufacturing techniques was conducted. Simulation results showed that an AM insert with conformal cooling channels can remove heat more effectively than conventionally manufactured cooling channels. By considering the increased solidification rate of the part produced through the AM insert, a reduction in cycle time of 10.7% was possible from the simulation results. Actual IM trials were conducted and temperatures inside both the AM and conventionally manufactured inserts were recorded. The temperature results recorded from the trials were within 4% of the simulated values. The outcomes from the experimental trials confirmed the simulated results, indicating that simulation software can successfully be used to analyse different cooling channel designs to identify the most efficient cooling channel layout. After benchmarking the experimental results with the simulation results, the same simulation principles and methodology were applied to an industrial application. Both an AM and conventional insert design were simulated and compared in a virtual injection moulding situation. From the simulated results it was evident that the AM insert with conformal cooling channels was able to remove heat more efficiently than the insert designed for conventional manufacturing, resulting in a reduction of mould temperature and cycle times. A manufacturing cost and lead-time comparison was conducted. For both cases considered, it indicated that the conventionally manufactured insert reached its break-even point after fewer IM cycles compared to the AM insert due to its lower manufacturing costs. During high-volume production, the AM insert will be more profitable due to its lower running costs and cycle time. From the research results it was concluded that the AM inserts with conformal cooling channels could result in a benefit for high-volume plastic injection moulding, resulting in shorter production times to produce a product.