Integrated process chain for first-time-right mould components production using laser powder bed fusion metal additive manufacturing

This thesis is dedicated to research and development that goes beyond the current state-ofthe- art of tool manufacturing for injection moulding and that uses additive manufacturing (AM) technologies, in particular laser powder bed fusion (LPBF). The main objective of this PhD project was to conduct research that takes a holistic approach and therefore takes the full process chain into account.

The work therefore focuses not only on what happens inside the LPBF machine, but also on the whole industrial manufacturing line. This includes pre-process such as part design, simulation, the LPBF process, and potential improvements such as the implementation of a monitoring solution. It also includes post-processes and the final performance of the tool in its intended application.

An extensive and thorough review of both the academic and industrial literature was first carried out. A number of aspects within the corresponding process chain were then investigated, using the newest technologies available in LPBF technology, a detailed research plan being developed for each step.

The state-of-the-art in additive manufacturing, moulding technology and Industry 4.0 was first determined from published scientific literature. An in-depth review was at the same time carried out into the use of additive manufacturing in the industry and its current status. This literature review represents the foundation and the background knowledge for the projects, and helped define which directions to explore and which issues to address.

The first research developed a detailed description of how a current production line works, including the technologies required and production costs. This exploration was essential to the definition of the current status of the technology, and the extent to which it is exploited. Another important aspect at this stage was the comparison of the process chain for additive manufacturing technologies with the chain for conventional subtractive technologies.

Conventional technologies are still, by far, the most widely used adopted in today's manufacturing industry. The results also show that conventional technologies are capable of producing parts at a higher throughput than AM, because of the machines times of some of the steps (in particular printing and heat treatment).

However AM mould's components have more competitive production costs and better performance. Productivity can also be greatly improved within a few years from research into increasing the speed of printing (by adding more lasers in the machine) and through optimising and automating some of the post-process steps, such as heat treatment.

Defining the capabilities and limitations of the LPBF technologies available in the market was also very important. An extensive and thorough benchmarking research was therefore designed, planned and executed. This involved both LPBF machine manufacturers and endusers, both equipped with the newest LPBF machines.

A 10-year old LPBF machine was also included comparison also a 10-year old LPBF machine was included in the benchmarking, to give a better understanding of the development of the technology in the last decade. The results demonstrated the importance of user experience. It also demonstrated the need to focus more on increasing the maturity of LPBF production for the industrial environment, for example through determining how the repeatability of the process can be improved.

The research also focussed on the final application, beginning with the exploration of new possibilities to exploit the as-built surface in moulds. The moulded plastic part was analysed and a detailed investigation of the differences between this and part conventionally manufactured using electrical discharge machining (EDM), was carried out.

The investigation showed that an as-built LPBF surface and its moulded plastic part present roughness of the same amplitude as some EDM manufactured surfaces and their relative plastic replica. Products produced by LPBF are notorious for presenting characteristics that differ from those of conventional cast and machined parts.

A detailed examination was therefore also carried out to understand the effect of residual porosity, which is typical for AM parts. The results identified the source of the defects and how they were replicated on the moulded part. The defects did no, however, generate aws that are crucial for consumer goods products.

These investigations overall helped define the existing gap between injection moulding requirements and what LPBF technologies can deliver today. The main objective of this Ph.D. project was to present a potential integrated process chain. Different solutions for first-time-right production were therefore investigated.

Two of the tools explored were analysed in more detail and their potentialities defined. The two tools were real-time process monitoring and process simulation. These two solutions together can help forecast AM part properties and any issues in fabrication. Real-time monitoring, in particular, helps develop a deeper knowledge of the phenomena taking place in the building chamber of the machine.

Such understanding allows a correlation between process monitoring data and product quality to be developed. The final research involved the development of an overall roadmap for the research and solutions that need to be built, to achieve an integrated process chain that can produce firsttime-right mould components based on LPBF technologies in an production environment.

Challenges and benefits were identified and are presented, this including a comprehensive description of the structure that the manufacturing line should include to take into account the Industry 4.0 framework.