Advantages and limitations of L-PBF

There are enormous benefits of metal L-PBF that enabling efficiencies in different industry sectors (Betatype Ltd, 2020; Burkhalter, 2018; Fitnik, 2020; Herzog et al., 2016 Materialise, 2018; Monash University/Betatype, 2017). There are however several parameters such as material choice, data preparation and quality assurance to be considered in the adoption of any AM that goes beyond just the printable feature.

Printable feature refers to features that can successfully be manufactured with AM.

Defining the limits of printable features alone cannot support the argument of sustainability. There are also some shortcomings to this metal L-PBF that need careful planning and consideration to maximise the benefits. The production costs of components manufactured using metal L-PBF are often perceived to be high. This could be due to the tendency for the economic dimensions of the sustainability of L-PBF to be limited to the manufacturing phase. The advantages and limitations outlined in this thesis only pertain to metal AM/L-PBF to suit the scope of the thesis. The main advantages of L-PBF for making metal components include the following:

• Design freedom: Possibility of manufacturing lighter, strong and complex macro/micro-sized structures that would have been impossible to make using conventional methods. There is only a small limit to part structure as almost all geometries are achievable. Freedom to design complexity must be done per the process design rules for successful application

• On-demand manufacturing: L-PBF allows swift engineering/designing of functional and prototype parts with on-demand manufacturing to swiftly respond to market needs. Changes required in models are quickly and easily made by simply changing the parameters or shapes in the computer 3D models. New models can be designed and printed under very tight schedules as there are no tooling and machining constraints

• Cost-effectiveness: To a certain extent, L-PBF is cost-effective; there is no need to build a mould, which eliminates mould costs and allows swift design changes and an optimised component with enhanced functional value without adding to costs

• Localised manufacturing: There is the element of convenience as design and production can be conducted locally without any delays or extra work if properly planned. Detailed product designs can be electronically shared for local production, reducing transportation-related emissions that would other be generated when distributing the actual part

• Raw material efficiency: Metal L-PBF can manufacture components close to the final shape, thereby saving on raw material. Metal AM can effectively reduce

material wastage as only the regions of the powder bed that conform to the layers of the digital file are melted. This means that only the required metal powder is hit by a laser beam and melted during the build process

• Conformal cooling channels: L-PBF can make components with internal cooling channels. Incorporating a cooling path just below the surfaces of components such as mould tools and heat exchangers enable uniform and rapid cooling, which lowers the cycle time during their use phase

• Customisation: Possibility of creating customised components to meet specific objectives in applications such as aerospace and automobiles. This reduces labour intensity and the number of manufacturing methods often required to make customised components using conventional product design

• Functionally graded materials: Metal L-PBF allows for cost-effective manufacturing of new functionally graded components using multi-materials.

The base material can be printed from inexpensive material and seamlessly coated with functional materials to satisfy functional requirements. The application of L-PBF for making metal components offers different benefits on the various stages of the value chain

Some several limitations/challenges hinder the acceptance of metal AM/L-PBF. Some of these include process and material-induced defects, component size limitations and an inherent large number of affecting processing parameters. Defects in components may include distortion, shrinkage porosity, delamination of layers, poor surface finish, thermal stresses (Chaplais, 2016; C. Chen et al., 2020; Zhai et al., 2014). Some of the inherent process limitations which are insufficient to satisfy all the stringent quality assurance requirements include low process speed, low part quality, high machine and feedstock cost (AMPOWER, 2019), to mention a few (Brockotter, 2021; Daraban et al., 2019; Dutta et al., 2019; Hinebaugh, 2018; Jimo et al., 2019; Menu, 2018; Sculpteo, 2020; Sealy et al., 2018; Yusuf et al., 2019). Some of the commonly discussed limitations of metal AM/L-PBF are summarised in Figure 2.7.

Figure 2.7: Limitations of the L-PBF industrial application.

Figure 2.7 shows the common limitations of L-PBF, particularly in metal applications.

Metal powders are examples of materials that require excessive amounts of energy as input to the system during production. The L-PBF process may be limited in terms of energy efficiency. The high energy consumption in L-PBF is closely associated with the build process or auxiliary activities such as the preheating of powder. The parts produced may, in some cases do not have the expected tolerances and performance to fulfil inspection requirements. In some cases, poor mechanical performance can occur, as a result of, for example, porosity and the presence of thermally induced residual stresses and distortion of the metal component. The numerous affecting process parameters often require a separate set of optimisations. This can increase the difficulty of using L-PBF as there are no fit-for-all rules for the different processing phenomena. Poor part finish quality, prolonged build time, complexities of support structures and incomplete fusion are examples of limitations that can affect the cost and functional requirement.

Metal L-PBF consumes a high amount of energy during components manufacturing (Z.

Y. Liu et al., 2018; Sharif Ullah et al., 2015). This, however, potentially can be reduced with simulation-driven designs and process parameters optimisation. These limitations are anticipated to be overcome with the increase in an academic and industrial effort directed towards design, materials and the building process in metal AM/L-PBF. The industrial uptake of L-PBF has led to the creation of more efficient machines, with high power and multiple lasers to increase build speed. New metal L-PBF systems are

equipped with high lasers and better hardware solutions that are capable to omit some of the earlier existed limitations.

Research suggests that new developments in adaptive and innovative materials (Amelia, 2021), sensors and automation, closed-loop controlled powder handling, multi-layer concurrent printing (Aurora Labs Ltd 2019; Khorasani et al. 2020), multi-lasers (Khorasani et al., 2020), and uniform inert gas flow (Chen, et al., 2020) continue to emerge. These innovations are examples of potential solutions to overcome the current metal L-PBF limitations and to complement the current pace of machine developments.

It is envisaged that the high cost of L-PBF will be reduced with better production efficiencies and will therefore contribute to increased productivity (Amelia, 2021).

Digital thread of metal AM/L-PBF can create optimised designs to enhance energy consumption, materials usage, cost-efficiency and reduce waste which is otherwise impossible with conventional manufacturing.