Test artefacts for additive manufacturing: A design methodology review

PurposeThis study aims to evaluate and compare the macroscopic properties of commercial acrylonitrile-butadiene-styrene (ABS) processed by two different types of additive manufacturing (AM) machines. The focus is also on the effect of multiple closed-loop recycling of ABS.Design/methodology/approachA conventional direct-drive, Cartesian-type machine and a Bowden, Delta-type machine with an infrared radiant heating system are used to manufacture test specimens molded in ABS. Afterward, multiple closed-loop recycling cycles are conducted, involving consecutive AM (four times) and recycling (three times). The rheological, mechanical, morphological and physicochemical properties are investigated.FindingsThe type of machine affects the quality of the produced parts. The machine containing an infrared radiant system in a temperature-controlled chamber produces parts showing higher mechanical properties and filling fraction, although it increases the yellowing. Closed-loop recycling of ABS for AM is applicable for at least two cycles, inducing a slight increase in tensile modulus (ca. 5%) and in tensile strength (ca. 13%) and a decrease in the impact strength (ca. 14%) and melt viscosity. An increase in the filling fraction of the AM parts promotes an increase in tensile strength and tensile modulus, although it does not influence the impact strength. Furthermore, multiple closed-loop recycling does not affect the overall chemical structure of ABS.Practical implicationsControlling the environmental temperature and using infrared radiant heating during AM of ABS improves the quality of the produced parts. Closed-loop recycling of ABS used in AM is feasible up to at least two recycling steps, supporting the implementation of a circular economy for polymer-based AM.Originality/valueThis study shows original results regarding the assessment of the effect of different types of AM machines on the main end-use properties of ABS parts and the influence of multiple closed-loop recycling on the characteristics of ABS fabricated by the most suited AM machine with an infrared radiant heating system and a temperature-controlled environment.

PurposeIn this era of Fourth Industrial Revolution, also known as Industry 4.0, additive manufacturing (AM) has been recognized as one of the nine technologies of Industry 4.0 that will revolutionize different sectors (such as manufacturing and industrial production). Therefore, this study aims to focus on “Additive Manufacturing Education” and the primary aim of this study is to investigate the impacts of AM technology at selected South African universities and develop a proposed framework for effective AM education using South African universities as the case study.Design/methodology/approachQuantitative research approach was used in this study, that is, a survey (questionnaire) was designed specifically to investigate the impacts of the existing AM technology/education and the facilities at the selected South African universities. The survey was distributed to several students (undergraduate and postgraduate) and the academic staffs within the selected universities. The questionnaire contained structured questions based on five factors/variables and followed by two open-ended questions. The data were collected and analyzed using statistical tools and were interpreted accordingly (i.e. both the closed and open-ended questions). The hypotheses were stated, tested and accepted. In conclusion, the framework for AM education at the universities was developed.FindingsBased on different literature reviewed on “framework for AM technology and education”, there is no specific framework that centers on AM education and this makes it difficult to find an existing framework for AM education to serve as a landscape to determine the new framework for AM education at the universities. Therefore, the results from this study made a significant contribution to the body of knowledge in AM, most especially in the area of education. The significant positive responses from the respondents have shown that the existing AM in-house facilities at the selected South African universities is promoting AM education and research activities. This study also shows that a number of students at the South African universities have access to AM/3D printing lab for design and research purposes. Furthermore, the findings show that the inclusion of AM education in the curriculum of both the science and engineering education is South Africa will bring very positive results. The introduction of a postgraduate degree in AM such as MSc or MEng in AM will greatly benefit the South African universities and different industries because it will increase the number of AM experts and professionals. Through literature review, this study was able to identify five factors (which includes sub-factors) that are suitable for the development of a framework for AM education, and this framework is expected to serve as base-line or building block for other universities globally to build/develop their AM journey.Research limitations/implicationsThe survey was distributed to 200 participants and 130 completed questionnaires were returned. The target audience for the survey was mainly university students (both undergraduate and postgraduate) and the academics who have access to AM machines or have used the AM/3D printing lab/facilities on their campuses for both academic and research purposes. Therefore, one of the limitations of the survey is the limited sample size; however, the sample size for this survey is considered suitable for this type of research and would allow generalization of the findings. Nevertheless, future research on this study should use larger sample size for purpose of results generalization. In addition, this study is limited to quantitative research methodology; future study should include qualitative research method. Irrespective of any existing or developed framework, there is always a need to further improve the existing framework, and therefore, the proposed framework for AM education in this study contained only five factors/variables and future should include some other factors (AM commercialization, AM continuous Improvement, etc.) to further enhance the framework.Practical implicationsThis study provides the readers and researchers within the STEM education, industry or engineering education/educators to see the importance of the inclusion of AM in the university curriculum for both undergraduate and postgraduate degrees. More so, this study serves as a roadmap for AM initiative at the universities and provides necessary factors to be considered when the universities are considering or embarking on AM education/research journey at their universities. It also serves as a guideline or platform for various investors or individual organization to see the need to invest in AM education.Originality/valueThe contribution of this study towards the existing body of knowledge in AM technology, specifically “AM education research” is in the form of proposed framework for AM education at the universities which would allow the government sectors/industry/department/bodies and key players in AM in South Africa and globally to see the need to invest significantly towards the advancement of AM technology, education and research activities at various universities.

MILP models to minimise makespan in additive manufacturing machine scheduling problems

In most industrial additive manufacturing (AM) applications a set of AM machines (AM-Fleet) are used in parallel. An AM-Fleet often consists of machines from various vendors and may include different AM processes. AM processes often suffer from poor repeatability within a single build, between builds on the same machine, and from machine to machine. AM's lack of robustness is often attributed to insufficient in-process monitoring and feedback control, as well as unknown modeling dynamics, and a lack of process standards. To effectively monitor and control AM-Fleets, system-level approaches must be devised. In this work, a centralized approach is proposed for the system-level control and management of AM-Fleets. Integrating such an approach has advantages in terms of system-level intelligent decision making for AM-Fleets. Key problems that needs to be solved and the challenges for a centralized approach are discussed in this work. The architecture of the proposed framework is presented with discussions on the individual components. A discrete event model for the system-level monitoring and control of AM machines is also proposed to support the presented framework. The use of discrete event models creates an abstract representation of the AM machine that enables the supervision of the physical system. An illustrative example that demonstrates a system-level run-to-run anomaly detection case is discussed. The proposed framework will provide an analytical foundation for systematic anomaly detection, scheduling, and decision making in AM-Fleets.

Despite more than three decades since the beginning of Additive Manufacturing (AM), many challenges and issues prevent the industrialization of this technology. In fact, productivity is related to repetitive production of the same part under the same fabrication conditions. Currently, it is difficult to guarantee this repetitive production due to uncertainty issues, which represents the main obstacle of AM industrialization. In this paper, the uncertainty issues can be divided into two levels. The first level is related to the used AM machine itself which can be considered as robot of 3 degrees of freedom (x, y and z). In addition to its movement in three directions, this robot (AM machine) extrudes melted materials. The second level is related to the associated robots with 3D printing machines. In addition to summarizing some previous works and reviews, this mini review has the objective to provide new ideas to develop new strategies to overcome some uncertainty issues to contribute to the industrialization of AM technology. Furthermore, it paves the way to establish a concurrent AM / robotics loop in order to use AM for robotics and robotics for AM. The different developments should lead to elaborating Industrialization Standard for AM (IS4AM) where the different findings and recomm

Additive manufacturing (AM) has gained notoriety for offering advantages over traditional manufacturing methods, such as increased design complexity and flexibility. However, it has not found widespread use beyond rapid prototyping. One hindrance to the acceptance of AM processes in industry is the time and cost of fabrication per component. While metal AM by itself can be inexpensive, extra manufacturing steps in the form of subtractive manufacturing (SM) may need to be performed to reach final part tolerances, leading to hybrid additive-subtractive manufacturing (HASM) of a part, which increases time and cost. A potential area to reduce cost is through increasing the efficiency of the HASM process by conducting additive and subtractive manufacturing simultaneously. Usually, HASM is performed in a process where AM is completed in one machine or cell and transferred to another machine or cell for SM in a sequential assembly line process. This efficiency decreases part cost, but high aspect ratio parts or parts with internal geometry that require interleaved additive deposition and machining cannot be produced. One unexplored solution to simultaneous HASM that allows for interleaved operations is to operate the deposition head and machining spindle concurrently within the same machine envelope, known as concurrent HASM (CHASM). In this type of process, both AM and SM occur simultaneously on a batch of small parts or a single large part, maintaining a high efficiency without sacrificing the full range of complex geometries that AM allows for. A potential approach to the single-machine method could be to combine a robot and mill within the same envelope. A challenge to this approach, however, is control of both systems. Most machine controllers have limited external communication or, if a robot has been integrated, only offer movement of either the robot or mill at any given time. As a result, systems must pause either the AM or SM process to switch between them rather than working simultaneously. The present work investigates the positional accuracy of such a CHASM system comprised of a robotic arm and a 3-axis mill. Open-loop tests with limited communication between machines are performed on the system to verify positional error during concurrent robot-mill movements. Under certain conditions, it is demonstrated that position error can stay within 2 mm for the duration of a single layer; however, these tests show that, generally, the open-loop positioning performance of the system is inadequate for CHASM without part-specific hand-tuning of parameters. Based on these results, a set of requirements for successful robot-CNC CHASM is proposed for future integrations.

Additive manufacturing of biomedical implants: A feasibility assessment via supply-chain cost analysis

Additive manufacturing (AM) can enable complex and novel designs that are otherwise infeasible with traditional metal manufacturing techniques. In low-volume production scenarios, particularly for specialized applications which can benefit from customized designs, traditional metal manufacturing techniques may be limited by costs associated with tooling. The ability to produce novel designs is particularly interesting in heat exchanger (HX) design where performance is often largely based on the achievable geometry. However, consequences of the AM process such as surface roughness, deviation from specified dimensions, and defects such as cracks and voids could also affect HX performance. These effects may vary between identically designed AM parts based on AM machine settings. The goal of this work is to gain a better understanding of the performance variations across several different implementations of the same heat exchanger design. More specifically, the objective of this work is to experimentally compare the thermal and hydraulic performances of a traditionally manufactured, stamped-aluminum aircraft oil cooler and three geometrically equivalent, additively manufactured counterparts. Compared to the traditionally manufactured heat exchanger, the AM HXs exhibited significantly higher air-side pressure loss and higher heat transfer despite having nominally similar geometries. Between AM HXs, there were slight differences in surface roughness characteristics based on optimal profilometry measurements. In addition, the thickness of the air-side fins varied as much as 15 percent between the AM HXs. The net effect, without the contribution of each cause clear, was higher air-side pressure loss and slightly higher heat transfer for the AM HX with thicker fins. This study indicates that functional heat exchangers built using AM vary in performance even when the same digital model is used to print them, and that AM HXs as a group perform considerably differently than their traditional counterparts. Thus, there is a need to account for anticipated surface roughness, geometric deviations, and potential defects when designing HXs. Proper consideration could result in improved thermal performance for future heat exchangers.

In recent years, additive manufacturing has been gaining ground among traditional manufacturing methods in many different applications. This is mainly due to its ease of prototyping, material savings and above all the highly complex geometries that can be achieved. Despite its many advantages, the use of additive manufacturing in electrical machines has been limited. The lack of maturity of the manufacturing processes and the increase in losses when applying additive approaches to some parts, mainly stators, have led little implementation in the field of electrical machines. The geometric freedom offered by additive manufacturing paves the way for the use of novel optimisation techniques, such as topology optimisation. Traditionally, topology optimisation has not been widely used because the complex geometries obtained by these algorithms are not easily produced by traditional manufacturing methods. However, thanks to additive manufacturing, topology optimisation has started to be used, mainly for mechanical applications and it has demonstrated its ability to reduce weight without compromising mechanical stability in several cases. Nevertheless, topology optimisation for physics other than mechanical has not been thoroughly studied, let alone for the simultaneous optimisation of different physics. In view of the scenario described, this thesis investigates the benefits that additive manufacturing and topology optimisation can bring to the design of electrical machines. For the additive manufacturing of electrical machines, a thorough literature review is carried out on the application of this manufacturing approach to different parts of electrical machines, active and non-active. Two main case studies are presented: in the first, the rotor, the shaft, the stator and the housing of an aerospace actuator are manufactured by L-PBF in FeCoV and the assembled actuator is tested. In the second case, a rotor is manufactured in FeSi by LP- DED. Finally, not considered an additive manufacturing case study itself in this thesis, but two electrical conductor prototypes are manufactured in CuCr1Zr and an additional geometry is manufactured in AlSi10Mg by L-PBF. With regard to topology optimisation of electrical machines, a description of the main topology optimisation methods used is given and their application to electrical machine components is presented. In a similar way to additive manufacturing, two case studies are analysed. First, a novel multiphysics - mechanical and electromagnetic - topology optimisation method is presented, in which the rotor and the stator of a permanent magnet motor are optimised simultaneously. This method is compared with two methods found in the literature, SIMP and on-off. Secondly, another topology optimisation method is described and applied to an electrical conductor model. The proposed algorithm involves a multiphysics - thermal and electromagnetic - hybrid parametric topology optimisation approach. Two reduced length geometries and one full length prototype are built via additive manufacturing. Finally, conclusions regarding additive manufacturing and topology optimisation of electrical machines are drawn from the work presented in this thesis. Future lines of work for additive manufacturing and topology optimisation of electrical machines are also presented.

Increasing the industrial uptake of additive manufacturing processes: A training framework

Lack of industrially available materials for additive manufacturing (AM) of metallic materials along with the promises of materials with improved or unique properties provides a strong drive for developing new process/material combinations. As powder bed technologies for metallic materials are relatively new to the market, and to some extent are only maturing, developers of new process/material combinations have certain challenges to overcome. Firstly, basic knowledge on the behavior of materials (even those well established for other applications) under extreme conditions of melting/solidification with beam-based AM methods is far from being adequate. Secondly, manufacturing of the equipment is up to date driven by industrial application, thus optimization of the AM machines for small test batches of powders is still belongs to research and development projects. Also, majority of the powder manufacturers are primarily driven by the market development, and even they are well aware of the demands imposed by the powder bed AM machines, availability of small test batches of adequate powders may be problematic or at least quite costly for the R&D oriented users. Present paper describes the experiences in developing new materials for EBM A2 machine by Arcam EBM, modified for operating with powder batches of 100-200 ml and less. In particular it discusses achievements and challenges of working with powders from different materials with specifications far beyond the range suggested by machine manufacturer. Also it discusses the possibility of using blended rather than pre-alloyed powders for achieving both composite-like and alloyed materials in the same part by steering electron beam energy deposition strategy.

A dynamic volumetric heat source model for laser additive manufacturing

The growth of additive manufacturing as a disruptive technology poses nuclear proliferation concerns worthy of serious consideration. Additive manufacturing began in the early 1980s with technological advances in polymer manipulation, computer capabilities, and computer-aided design (CAD) modeling. It was originally limited to rapid prototyping; however, it eventually developed into a complete means of production that has slowly penetrated the consumer market. Today, additive manufacturing machines can produce complex and unique items in a vast array of materials including plastics, metals, and ceramics. These capabilities have democratized the manufacturing industry, allowing almost anyone to produce items as simple as cup holders or as complex as jet fuel nozzles. Additive manufacturing, or three-dimensional (3D) printing as it is commonly called, relies on CAD files created or shared by individuals with additive manufacturing machines to produce a 3D object from a digital model. This sharing of files means that a 3D object can be scanned or rendered as a CAD model in one country, and then downloaded and printed in another country, allowing items to be shared globally without physically crossing borders. The sharing of CAD files online has been a challenging task for the export controls regime to manage over the years, and additive manufacturing could make these transfers more common. In this sense, additive manufacturing is a disruptive technology not only within the manufacturing industry but also within the nuclear nonproliferation world. This paper provides an overview of additive manufacturing concerns of proliferation.

<p>Additive Manufacturing (AM), more popularly known as 3D Printing, is a process for producing functional artifacts by adding layers of materials from data generated directly from 3D solid CAD models. Additive Manufacturing (AM) is the formalized term for what used to be called Rapid Prototyping and what is commonly referred to as 3D Printing. The key to how AM works is that parts are made by adding layers of material; each layer corresponding to a thin cross-section of the part derived from the original CAD data. Although most AM machines produce parts using polymers, there are an increasing number of machines that can directly fabricate in metals. The majority of these machines fabricate from raw material in powder form using a directed energy beam to create a local melt zone. Total hip replacement is recommended for people who have medical issues related to excessive wear of the acetabular, osteoarthritis, accident or age. Researches have shown that large numbers of hip arthroplasties (where the articular surface of a musculoskeletal joint is replaced), hip remodelling, or realignment are carried out annually and will increase in the next few decades. Manufacturing of acetabular shells by using AM is a promising and emerging method that has a great potential to improve public health. Lost wax casting or investment casting is currently used to produce acetabular shells followed by lengthy and complex secondary processes such as machining and polishing. Living organs and medical models have intricate 3D shapes that are challenging to identity in X-ray CT images. These images are used for preparing treatment plans to improve the quality of the surgeries regarding waiting and surgery time per procedure and care regime. For instance, a limited number of hip replacement procedures can be carried out on each acetabulum due to a decrease of bone thickness. Rapid prototyping is a suitable treatment planning tool in complex cases to enhance the quality of surgical procedure and provide long-term stability that can be used to customize the shape and size of the acetabular shell. In this paper, to analyse the manufacturing of a prosthetic acetabular shell, built-up lines resulting from a thermal stress flow and process stopping during the selective laser melting (SLM) AM process, with regarding Gibbs free energy, interfacial energy, and equilibrium temperature will be discussed. Geometrical measurements showed 1.59% and 0.27% differences between the designed and manufactured prototype for inside and outside diameter respectively. Experimental results showed that thermal stress flow in outer surfaces are compressive, but for inner surfaces are tensile, so built-up lines in inner and outer surfaces appear as a groove and dent respectively. The results also indicate that SLM is an accurate and promising method for fabrication of acetabular cup.</p>

Beam-based additive manufacturing (AM) is an innovative technique in which parts are built layerwise, starting from the material in powder form. As a developing manufacturing technique, achievement of excellent mechanical properties in the final part is of paramount importance for the mainstream adoption of this technique in industrial manufacturing lines. At the same time, AM offers an unprecedented opportunity to precisely control the manufacturing conditions locally within the part during build, enabling local influence on the formation of the texture and microstructure. In order to achieve the control of microstructure by tailoring the AM machine parameters, a full understanding and modeling of the heat transfer and microstructure evolution processes is needed. Here, we show the implementation of the non-equilibrium equations for phase formation and dissolution in an AM modeling framework. The model is developed for the Ti6Al4V alloy and allows us to show microstructure evolution as given by the AM process. The developed capability is applied to the cases of electron beam melting and selective laser melting AM techniques to explain the significantly different microstructures observed in the two processes.