Study regarding the influence of material type on economic objectives in MEX fabrication

Material Extrusion has been used extensively as an additive manufacturing technology for a variety of applications like visual models, functional prototypes, tooling components, patterns for castings, and final parts. The current research paper proposes a study on the material type influence on economic objectives in material extrusion fabrication of complex assemblies. Three economic objectives have been analysed, namely, estimated fabrication time, material usage and material cost, whilst two commercial additive manufacturing machines have been considered for the simulation. Cura and ZSuite slicing software were used for the generation of Gcode and project files. Five filaments were selected from the same manufacturer and all components of the selected assembly were included in the analysis. Throughout the study, the additive manufacturing parameters were kept constant, as well as the component layout on the build platform of the two machines. Study results were analysed in correspondence with the manufacturing requirements and the optimum fabrication scenario was selected. Further research includes the analysis of multiple material manufacturers, in order to evaluate the influence of chemical composition on economic outputs.


Introduction
Developing a new product involves understanding the needs and desires of customers, the competitive environment and the market typology [1]. Cost, time and quality are the main variables that drive customer needs. Based on these three variables, companies are continually developing techniques and strategies to better meet customer requirements and to increase their market share by constantly developing new products [2]. The process of product development has undergone a huge evolution in recent years, at the same time with the increase of the rate of adoption of additive manufacturing (AM) technologies, themselves already having an age of maturity of more than 30 years. New AM equipment is small in size and can produce real objects in a relatively short period of time. The advantages of AM technologies have made the product development process include, almost invariably, a rapid prototyping step [3]. Many specialists consider AM technologies to be the next disruptive step in technology, similar to the emergence of personal computers, offering everyone the opportunity to imagine, design and create custom products [4,5,6]. Others claim that these technologies will continue to be used primarily for prototyping applications [7]. This is driven by the current inability of AM technologies to effectively meet, in terms of costs, the global demand for production applications. Other opinions show that AM will revolutionize manufacturing processes and the economic and social environment [4,7]. Regardless of the point of view, it is a certainty that in the last decade AM technologies have undergone a spectacular evolution in terms of the functionality of the manufacturing systems, the ease of use, the cost efficiency and the adoption rate in multiple industrial sectors [3]. There is also an obvious change in the applicability of AM technologies, from rapid modelling and prototyping to rapid manufacturing of finished products [8]. If the future evolution will follow the same upward trend, the role of AM technologies in the manufacturing value chain will be a key one in terms of purpose, scale and complexity. It is expected that these technologies will reach their full potential in the next 15-20 years [3,8,9]. During this period, it is preferable for most companies to analyse their potential benefits in the proposed performance, development and innovation targets.
Compared to traditional prototype manufacturing technologies, AM technologies significantly shortens the development process from concept to prototype or finished product. For specific applications and when using competent personnel, the process of developing prototypes and medical products can be shortened from weeks to days or even hours [10,3].
The costs involved in developing prototypes with traditional methods are also significantly reduced when using the optimal AM technologies for the studied applications. Thus, it can be said that these technologies are easily adaptable and are more efficient in the case of prototypes and personalised medical products of small or unique series, especially in comparison with the traditional methods of injection moulding, casting or mechanical processing [11,12]. One of the most affordable and readily available AM technologies is Material Extrusion (MEX), hence the plethora of research studies undertaken in this area. The selection of an AM technology is influenced by a variety of factors, such as: the functional role of the part, the work environment of the part, the characteristics of the technology, the experience of the company that makes the part, etc. In the report "The state of 3D printing 2018" [9], Sculpteo researchers state that Fused Deposition Modelling (a proprietary name for MEX by a leading international AM company) was the most used technology in 2017 (36%) and 2018 (46%) with an ascending general trend.
In this context, the current research paper proposes a study on the material type influence on three economic objectives in MEX fabrication. The importance of this research relies on the benefits which could be brought to companies in the early product development stages.

Materials and methods
Three economic objectives have been analysed, namely, estimated fabrication time, material usage and material cost. Their choice was directly corelated with the capabilities of the software to provide measurable outputs. To evaluate the influence of the material type on these three economic objectives, two commercial AM machines have been considered for the simulation. The first one is a low-cost Creality CR 20-Pro, chosen to represent the hobby and DIY market segment. A Zortrax M300+ AAM machine was chosen to represent the professional market segment with a capacity of a medium series production volume. Cura and ZSuite slicing software were used for the generation of Gcode and project files. Using Cura the files obtained were *.gcode and *.3mf files and using ZSuite the files obtained were *.zcodex and *.zprojx. Throughout the study, the optimised AM parameters were kept constant, as well as the component layout on the building platform of the two machines. Ten filaments were selected from the same two manufacturers and all components of the selected assembly were included in the analysis. For the Creality CR 20-Pro PLA, ABS, PETG, PC, NYLON filaments were used from Polymaker. The Zortrax M300+ equipment was simulated with Z-PLA, Z-ABS, Z-PETG, Z-PCABS, Z-NYLON from Zortrax. The diameter size is the same for all ten filaments, namely 1.75 mm. Table 1 shows the material characteristics used for all simulations. The assembly used for the study is a concept model ( Figure 1) for an automatic wiping board [13]. The main mechanical components of the assembly are presented in Table 2. The electronics and software modules do not represent the target of the study, but their specific characteristics, functions and overall dimensions influenced the design of the concept model and its' assembly pattern.  Five build plates were created to optimise the AM economic objectives within three specific sets requirements, namely: -Manufacturing requirements: two available AM machines (Creality CR 20-Pro, Zortrax M300+); 5 filament types from Zortrax; 5 filament types from Polymaker; heated build plates; 8-hour shift; one shift per working day; one technician; one engineer; -Client requirements: 5 working days delivery time; one batch production; -Functional requirements: the assembly is set to be used as a testing concept in an experimental stand.
Using Cura and ZSuite the five optimised build plates are presented in Figure 2 below. Optimisation of the build plates was done in correspondence with the requirements and with the AM design rules imposed by the MEX technology.

Results and discussions
Based on the optimised build plate layouts, all AM build parameters were optimised in order to meet the requirements. Table 3 presents the optimised parameters for five build plates generated on Creality CR20-Pro using PLA. Similarly, in Table 4 the optimised parameters are detailed for manufacturing of the five build plates in the Zortrax M300+ using Z-PLA. The optimisation process was undertaken for a total of 50 build plates.  Next, the support structures were added (where necessary) and the slicing software was run for all 50 simulations, using two AM machines. Thus, for the Creality CR 20-Pro Table  5 was compiled, and for the Zortrax M300+ Table 6 was put together.  Study results were analysed in correspondence with the manufacturing requirements and the optimum fabrication scenario was selected.
Graphical representations were used to discuss the best choice of manufacturing for the assembly, and are presented in Figures 3, 4 and 5 for both types of AM equipment utilised. Figure 3 shows that the estimated fabrication time of the selected concept model is considerably lower overall and across all build plates if Zortrax M300+ is used for manufacturing. Also, on this equipment, PLA has the quickest cumulative fabrication time out of all building platforms, with almost 200 minutes ahead of all other materials. The Zortrax M300+ is faster than the Creality CR20-Pro with an average of 4347 minutes (approximately 3 days).
From Figure 4, is possible to state that the lowest material consumption is achieved by using the Zortrax M300+ for manufacturing of the automatic wiping board concept model. Across all build platforms the lowest material usage is registered for PC and the highest for PETG. The consumption distribution for material type on all platforms is similar for the Creality CR20-Pro.    Overall material costs ( Figure 5) were higher for the Zortrax supplier in comparison with Polymaker, with PETG having the top value with 93.56 Euros for building the entire concept model. The lowest value on this machine is attributed to PLA.

Fig. 5. Estimated material cost for manufacturing the automatic wiping board concept model
Based on the restrictions and on the functional role of the concept model the best choice of manufacture was using the Zortrax M300+ AM machine with PLA filament (Figure 6). Two of the three economic objectives have scored better values in the analysis undertaken for this equipment. Cost-wise, the average difference represents only 16.79 Euro, which is acceptable to the client if the imposed time frame is met.