Abstract Additive Manufacturing Processes Research Articles

Investigation of bio-based and recycled printing materials for additive manufacturing

Additive manufacturing (AM) processes are becoming increasingly important alongside conventional processes. As a result, the consumption of materials is also increasing. The most widespread process in polymer AM is Fused Layer Modelling (FLM). Today, the FDM process often uses synthetically produced materials based on petrochemical processes. However, there is little knowledge about which bio-based and recycled polymer materials are suitable for sustainable polymer AM. The aim of this paper is to carry out investigations of eight selected materials, which are already commercially available, to gain insights into their suitability as materials for polymer AM. These materials are divided into four categories: conventional, recycled, bio-based and fibre-reinforced thermoplastics. The evaluation model consists of a point system in which the materials are evaluated according to various weighted criteria. For technical, economic and ecological evaluation meaningful criterions were developed and applied. Based on the evaluations, three two-dimensional strength diagrams were developed, from which the results of the materials, on two of the evaluations in each case, can be read. These results are combined in a three-dimensional diagram. This representation provides the ability to make a precise selection of bio-based or recycled materials for polymer AM.

Creation and Assessment of a Novel Design Evaluation Tool for Additive Manufacturing

Abstract Additive manufacturing (AM) is a rapidly growing technology within the industry and education sectors. Despite this, there lacks a comprehensive tool to guide AM novices in evaluating the suitability of a given design for fabrication by the range of AM processes. Existing design for additive manufacturing (DfAM) evaluation tools tend to focus on only certain key process-dependent DfAM considerations. By contrast, the purpose of this research is to propose a tool that guides a user to comprehensively evaluate their chosen design and educates the user on an appropriate DfAM strategy. The tool incorporates both opportunistic and restrictive elements, integrates the seven major AM processes, outputs an evaluative score, and recommends processes and improvements for the input design. This paper presents a thorough framework for this evaluation tool and details the inclusion of features such as dual-DfAM consideration, process recommendations, and a weighting system for restrictive DfAM. The result is a detailed recommendation output that helps users to determine not only “Can you print your design?” but also “Should you print your design?” by combining several key research studies to build a comprehensive user design tool. This research also demonstrates the potential of the framework through a series of user-based studies, in which the opportunistic side of the tool was found to have significantly improved novice designers’ ability to evaluate designs. The preliminary framework presented in this paper establishes a foundation for future studies to refine the tool’s accuracy using more data and expert analysis.

Medical Device Hybrid Manufacturing: Translating the Coordinate System From Metal Additive Manufacturing to Subtractive Post-Processing

Abstract Additive manufacturing (AM) has transformed not only how parts can be realized but also their design. Metal additive manufacturing (MAM) has increased AM’s utility toward the manufacture of functional products. This has been seen in several industries including medical device, aerospace, and the automotive industries. The main limitation of MAM continues to be the part dimensional tolerances that can be achieved, and the respective surface finish produced. Hybrid manufacturing processes have been used to address these limitations; however, there remain challenges of how to translate the component’s coordinate system from AM to subtractive post-processes. This paper explores this topic through a medical device case study. A translatable coordinate system was produced by first designing features to serve as a datum reference frame (DRF). These features were introduced by MAM and then finalized with wire-electrical discharge machining (EDM). The produced DRF features successfully prepared the component for translation from the MAM to subtractive post-process. The completed medical device component met the expected requirements with a less than 1% difference on key part nominal dimensions. In addition, the hybrid process exhibited a potential for sustainable manufacturing with a buy-to-fly ratio of 6:1. The study demonstrated that a coordinate system can be translated effectively in hybrid manufacturing by designing part features informed by both AM and wire-EDM processes.

Functional Requirements of Software Tools for Laser-Based Powder Bed Fusion Additive Manufacturing for Metals

Abstract Additive manufacturing (AM) for metals is rapidly transitioning to an accepted production technology, which has led to increasing demands for data analysis and software tools. The performance of laser-based powder bed fusion of metals (PBF-LB/M), a common metal AM process, depends on the accuracy of data analysis. Advances in data acquisition and analysis are being propelled by an increase in new types of in situ sensors and ex situ measurement devices. Measurements taken with these sensors and devices rapidly increase the volume, variety, and value of PBF-LB/M data but decrease the veracity of that data simultaneously. The number of new, data-driven software tools capable of analyzing, modeling, simulating, integrating, and managing that data is also increasing; however, the capabilities and accessibility of these tools vary greatly. Issues associated with these software tools are impacting the ability to manage and control PBF-LB/M processes and qualify the resulting parts. This paper investigates and summarizes the available software tools and their capabilities. Findings are then used to help derive a set of functional requirements for tools that are mapped to PBF-LB/M lifecycle activities. The activities include product design, design analysis, process planning, process monitoring, process modeling, process simulation, and production management. PBF-LB/M users can benefit from tools implementing these functional requirements implemented by (1) shortening the lead time of developing these capabilities, (2) adopting emerging, state-of-the-art, PBF-LB/M data and data analytics methods, and (3) enhancing the previously mentioned AM product lifecycle activities.

X-ray Tomography Investigation of the Quality of Architected Structures Obtained with Additive Manufacturing Processes

Additive Manufacturing (AM) appears to be the best candidate to manufacture random architected materials, as it offers significant freedom in the design of hollowed parts with complex geometry. However, when these structures are needed with thins walls and struts, AM processes may encounter difficulties in properly manufacturing these structures due to their capability limits. This study proposes to characterize the manufacturing of random architected structures to see firstly their fabricability and the capability of the additive manufacturing processes used, such as vat photopolymerization (Stereolithography process (SLA)), material extrusion (Fused Filament Fabrication process (FFF)) and powder bed fusion (Selective Laser Sintering process (SLS)) through tomographic, dimensional, and mass analysis. Several defects specific to each process were identified. A higher predominance of porosities, lack of printing and excess of material manifests as trapped or partially fused powder for SLS and angel hair for FFF. These defects strongly affect the dimensional and geometric accuracy of the struts and, thus, the final mass of the structure obtained with these two processes. The SLA process makes it possible to print thinner details of random architected structures with better material quality and good dimensional and geometric accuracy, under the conditions and protocol used in this study.

Linkage of Macro- and Microscale Modeling Tools for Additive Manufacturing of Steels

Additive manufacturing (AM) offers several benefits including the capability to produce unique microstructures, geometrical freedom allowing for material and energy savings, and easy production lines with fewer post-processing steps. However, AM processes are complex and phenomena occurring at different length and time scales need to be understood and controlled to avoid challenges with, for example, defects, residual stresses, distortions, and alloy restrictions. To overcome some of these challenges and to have more control over the final product, computational tools for different length scales need to be combined. In this work, an 18Ni300 maraging steel part is studied to understand the link between the process parameters and the as-built microstructure. The temperature evolution during laser powder bed fusion is simulated using the MSC simulation software Simufact Additive. This result is then linked to microscale models within the Thermo-Calc software package to predict the elemental micro-segregation, martensite start (Ms) temperature, and martensite fraction. The different values of the key process parameters such as laser speed, laser power, heating efficiency, and baseplate temperature are considered, leading to different thermal histories. The thermal histories affect the elemental segregation across the solidification structure, which in turn results in different Ms temperatures at different locations of the built part. It is found that higher laser energy generally causes higher temperatures and higher cooling rates, which results in a larger degree of elemental segregation and lower Ms temperatures in segregated regions. Furthermore, the segregated regions are predicted to have Ms temperatures below 200°C, which would result in retained austenite when using a baseplate temperature of 200°C. On the other hand, by using a baseplate temperature of 100°C, all regions would reach temperatures below the Ms temperature, and an almost fully martensitic structure would be possible. In summary, it is demonstrated how the linkage of macro- and microscale modeling tools for AM can be used to optimize the process and produce the desired microstructure, thereby achieving the desired mechanical properties.

Wear Analysis of Additively Manufactured Slipper-Retainer in the Axial Piston Pump

Additive manufacturing (AM) of spare parts is going to become more and more common. In the case of hydraulic solutions, there are also some applications of AM technology related to topological optimization, anti-cavitation improvements, etc. An examination of all available research results shows that authors are using specialized tools and machines to properly prepare AM spare parts. The main aim of this paper is to analyze the influence of quick repair of the damaged slipper-retainer from an axial piston pump by using an AM spare part. Hence, it was prepared with a 100-h test campaign of the AM spare part, which covers the time between damage and supply of the new pump. The material of the slipper-retainer has been identified and replaced by another material—available as a powder for AM, with similar properties as the original. The obtained spare part had been subjected to sandblasting only to simulate extremely rough conditions, directly after the AM process and an analysis of the influence of the high surface roughness of AM part on wear measurements. The whole test campaign has been divided into nine stages. After each stage, microscopic measurements of the pump parts’ surface roughness were made. To determine roughness with proper measurements, a microscopical investigation was conducted. The final results revealed that it is possible to replace parts in hydraulic pumps with the use of AM. The whole test campaign caused a significant increase in the surface roughness of the pump’s original parts, which was worked with the AM spare slipper-retainer: (1) from Ra = 0.54 µm to Ra = 3.84 µm in the case of two tested pistons; (2) from Ra = 0.33 µm to Ra = 1.98 µm in the case of the slipper-retainer. Despite significant increases in the surface roughness of the pump’s parts, the whole test campaign has been successfully finished without any damages to the other important parts of the whole hydraulic test rig.

Design for stressed and additively manufactured lightweight structures

Additive Manufacturing (AM) represents a new class of disruptive production and prototyping technologies. Topology optimization has been known to produce a high level of complexity in generated structure designs that is suitable for AM. Design for stress is a major factor in a number of scientific applications, where AM still experiences its own limitations that are unique to it. When such limitations and stress factors are not considered, postprocessing is generally required to modify generated designs such that it adds to cost and reduces performance of optimized structures. Hence, a stress-based optimization framework is proposed in conjunction to an AM model that incorporates the main trait of AM processes. With a density-based framework, the approach can be used with stress clustering to optimize the number of stress factors with a conventional topology optimization solver. The approach ensures the design of structures with restricted AM geometries that does not violate the filtering size constraints by use of stress clusters for compliance-based minimization problems.

Progress of Additive Manufacturing Technology and Its Medical Applications

Abstract Additive manufacturing (AM), also known as three-dimensional (3D) printing, is a disruptive technology that is revolutionizing many industries. It is gaining considerable attention, particularly in the medical field as it renders the possibilities of building new devices or modifying existing devices to match a patient's anatomy and to produce anatomically exact models, supporting health professionals with diagnostics and surgery preparation. In addition, the free-form building capability of AM allows the designer to have a complete control over the internal architecture of the device, along with tailored mechanical properties, such as compression strength, stiffness, and many surface features. As the processes of AM become well-understood, there is more control over the consistency and quality of the printed parts, positioning this technology for medical applications. With more and more medically approved 3D-printed devices entering the market, the purpose of this paper is to give an overview of the regulatory pathway to the Food and Drug Administration approval of a medical device, along with common AM processes used in the medical industry. To conclude, medical devices that are enabled by AM technology and associated companies will be highlighted.

Manufacturing of Tool Steels by PBF-EB

Additive manufacturing (AM) of metals is stimulating the tool making industry. Moreover, besides the production of lost forms, AM processes are now being used to directly generate tools, molds or parts, leading to massive time savings. In the case of material development for AM, the challenge is to operate with carbon-containing iron-based materials distinguished by high strength and hardness, as well as high corrosion resistance and thermal conductivity. Often, those materials are susceptible to crack formation during processing. Using Electron Beam Powder Bed Fusion (PBF-EB), the challenge of crack formation can be overcome by using high process temperatures in the range 800–900 °C. In this paper, results on the processing of a cold-working tool steel (X65MoCrWV3-2) and a hot-working steel (X37CrMoV5-1) will be presented. These include the processing window, processing strategies to minimize the density of cracks and properties with respect to microstructure and hardness.

Anisotropic Cutting Force Characteristics in Milling of Maraging Steel Processed Through Selective Laser Melting

Abstract Additive manufacturing (AM) process of maraging steel has been studied for high value parts in aerospace and automotive industries. The hybrid additive/subtractive manufacturing is effective to achieve tight tolerances and surface finishes. The additive process induces anisotropic mechanical properties of maraging steel, which depends on the laser scanning direction. Because anisotropy in the workpiece material has an influence on the cutting process, the surface finish and the dimension accuracy change according to the direction of the cutter feed with respect to the laser scanning direction. Therefore, the cutting parameters should be determined to control the cutting force considering material anisotropy. The paper discusses the cutting force in milling of maraging steel stacked with selective laser melting, as an AM process. Anisotropic effect on the cutting forces is proved with the changing rate of the cutting force in milling of the workpieces stacked by repeating laser scanning at 0/90 deg and 45/−45 deg. The cutting forces, then, are analyzed in the chip flow models with piling up of orthogonal cuttings. The force model associates anisotropy with the shear stress on the shear plane. The changes in the cutting forces with the feed direction are discussed in the cutting tests and analysis.

Impact of the LACKS of Fusion Induced by Additive Manufacturing on the Lubrication of a Gear Flank

Additive Manufacturing (AM) is becoming a more and more widespread technology. Its capability to produce complex geometries opens new design possibilities. Despite the big efforts made by the scientific community for improving the AM processes, this technology still has some limitations, mainly related to the achievable surface quality. It is known that AM technologies promote the formation of LACKS of fusion inside the material. In some cases, the external surfaces are finished with traditional machining. This is the case of AM-produced gears. While the grinding operation aims to reduce the surface roughness, the presence of porosities just below the surface of the wrought component, could lead, after grinding, to the exposure of those porosities leading to a pitted surface. This phenomenon is surely not beneficial in terms of structural resistance, but can help the lubrication promoting the clinging of the lubricant to the surface. The aim of this paper is to study this effect. Micro-Computer-Tomography (μ-CT) analyses were performed on a 17-4 PH Stainless Steel (SS) produced via Selective Laser Melting (SLM). The real geometry of the pores was reproduced virtually and analyzed by means of multiphase CFD analyses in the presence of centrifugal effects.

The technology, economy, and environmental sustainability of isotropic superfinishing applied to electron-beam melted Ti-6Al-4V components

Additive manufacturing (AM) processes allow complex geometries to be produced with enhanced functionality, but technological challenges still have to be dealt with, in terms of surface finish and achieved tolerances. Among the consolidated powder-bed fusion processes, electron beam melting (EBM), which allows almost stress-free parts to be manufactured with a high productivity and minimum use of support structures, suffers from a poor surface quality. Thus, finishing processes have to be performed. The same geometrical complexity, which is considered one of the benefits of AM, becomes an issue when finishing is applied, in particular when internal features are present. Unconventional isotropic superfinishing processes could be a solution to this problem since they can generate a low surface roughness on complex geometries. However, the performance characteristics, with regard to the environmental sustainability and economic aspects, need to be evaluated since they are key factors that must be considered for decision-support tools when selecting a finishing process. The technological feasibility of the isotropic superfinishing (ISF) process, applied to Ti-6Al-4V parts produced by electron beam melting, is investigated in this paper by considering the dimensional and geometrical deviations induced by the finishing treatment, and from observations of the surface morphology. A significant reduction in surface roughness, Sa, to around 4 μm, has been observed on the most irregular surfaces, although the original shape is maintained. Environmental sustainability has been analyzed for all the manufacturing steps, from powder production to part fabrication, to the finishing process, and both the cumulative energy demand and material waste have been accounted for. The economic impact of the whole manufacturing chain has been evaluated, and the advantages of the ISF process are pointed out.

An Integrated Computational Materials Engineering Predictive Platform for Fatigue Prediction and Qualification of Metallic Parts Built With Additive Manufacturing

Abstract Additive manufacturing (AM) processes create material directly into a functional shape. Often the material properties vary with part geometry, orientation, and build layout. Today, trial-and-error methods are used to generate material property data under controlled conditions that may not map to the entire range of geometries over a part. Described here is the development of a modeling tool enabling prediction of the performance of parts built with AM, with rigorous consideration of the microstructural properties governing the nucleation and propagation of fatigue cracks. This tool, called DigitalClone® for additive manufacturing (DCAM), is an Integrated Computational Materials Engineering (ICME) tool that includes models of crack initiation and damage progression with the high-fidelity process and microstructure modeling approaches. The predictive model has three main modules: process modeling, microstructure modeling, and fatigue modeling. In this paper, a detailed description and theoretical basis of each module is provided. Experimental validations (microstructure, porosity, and fatigue) of the tool using multiple material characterization and experimental coupon testing for five different AM materials are discussed. The physics-based computational modeling encompassed within DCAM provides an efficient capability to fully explore the design space across geometries and materials, leading to components that represent the optimal combination of performance, reliability, and durability.

Ceramics Processing by Additive Manufacturing

Additive manufacturing (AM) can be a game changer of ceramic industry by opening up new avenues in terms of reduction in cost and ushering in to the domain of designing complicated structure without having dependence on exotic tools. Unlike polymers and metals where AM technology is growing up rapidly, growth of the same in ceramic industry is rather slow due to several technical challenges. However, AM of ceramics is growing steadily as there is considerable urge for producing fully dense defect-free ceramic components with complex geometry for which AM technology comes very handy. Consequently, many AM technologies have been used to fabricate ceramic components with varying results depending upon the nature of the material, AM technology, and part complexity. Thus, beside the nature of the processed ceramic, it is of paramount interest to select right kind of AM process for a particular application in terms of complexity, size density, and surface finish. This review gives present status in AM of ceramics along with some relevant properties of parts produced by AM technology followed by challenges and future prospects of ceramic AM.

A Robust Design Perspective on Factors Influencing Geometric Quality in Metal Additive Manufacturing

Abstract Additive manufacturing (AM) for metals is a widely researched, continuously enhanced manufacturing process and is implemented across various industries. However, the AM process exhibits variation that affects the geometric quality of the end product. The effect of process variation on geometric quality is rarely considered during the design stages. In this paper, sources that influence the geometric quality in a metal AM process are reviewed from a robust design perspective and further sorted into control factors and noise factors. A framework for geometric robustness analysis of AM products is presented as an outcome. This framework would facilitate development of methods and tools to produce geometry assured AM products. Also, the prospects of variation simulation to support geometric robustness analysis and the challenges associated with it are discussed.

Investigation of Printing Parameters of Additive Manufacturing Process for Sustainability Using Design of Experiments

Abstract Additive manufacturing (AM) offers many advantages to make objects compared to traditional subtractive manufacturing methods. For example, complex geometries can be easily fabricated, and lightweight parts can be formed while maintaining the parts strength for the low carbon footprint, low material consumption and waste. But there are some areas for AM to improve in sustainability, reliability, productivity, robustness, material diversity, and part quality. Life-cycle assessment studies have identified that the AM printing stage has a big impact on the life-cycle sustainability of 3D printed products. AM building parameters can be properly selected to improve the sustainability of AM. This paper explores the fused deposition modeling (FDM) process parameters for sustainability to reduce the process energy and material consumption. Investigated parameters include the printing layer height, number of shells, material infilling percentage, infilling type, and building orientation. Taguchi design of experiments approach and statistical analysis tools are used to find optimal parameter settings to improve the sustainability of the FDM process. Models formulated in this research can be easily extended to other AM processes.

Additive Manufacturing Review: Early Past to Current Practice

Abstract Additive manufacturing (AM) is a set of manufacturing processes that are capable of producing complex parts directly from a computer model of the part. This review provides a history of the early antecedents of these processes. In addition, the different classes of AM processes and their commercialization are presented and discussed along with their fields of use. This paper emphasizes AM processes that produce production quality parts. The review also addresses design issues and the commercial state of the art for production of polymer, metal, and ceramic parts. A main emphasis of this paper is the development and motivations for AM especially during its nascent years. The paper is written for the general readership of manufacturing professionals and researchers.

Additive Manufacturing Distortion Compensation Based on Scan Data of Built Geometry

Abstract Additive manufacturing (AM) processes such as direct metal laser sintering (DMLS) are highly attractive manufacturing processes due to the ability to create certain geometries which would be prohibitive or even impossible to manufacture by other means. However, with such high thermal gradients which are usually present in these processes, manufacturing distortions may result in the creation of unacceptable parts. This paper presents an approach to compensate input STL files based on registration of the point cloud from sacrificial part builds. A novel strain energy based non-rigid registration algorithm has been developed for robust registration of data points to the original computer-aided design (CAD) model. A neural network based approach is used to learn the deformation of the geometry based on the deviation of the scan geometry. This network is subsequently used to modify the STL file to generate a new compensated STL file. The compensated STL file was validated by building parts and comparing the change in the part distortion.

Quality and productivity trade-off in powder-bed additive manufacturing

Additive manufacturing (AM) is a technology that creates parts directly from 3D CAD files based on a layer-by-layer manufacturing process. Quality and productivity are the two key concerns in powder-bed AM processes, which are one of the most widely used AM in the industry. Because of the keyholes and porosity formation occurring in the object’s structure during a printing process, quality is considered a difficult factor to manage. On the other side, focusing only improving quality could result in higher building cost and inefficient printing operations. Thus, a trade-off between these two concerns is vital for maintaining competitiveness of AM. To the best of our knowledge, there is no study in the literature that has yet considered this trade-off in a systematic way and can provide optimal results for productivity based on a desired quality level. This study combined equations from previous studies in a systematic way to create an empirical model to optimize major process parameters, including laser power, scan speed, layer thickness, hatch distance, and laser spot size for a trade-off between quality and productivity in powder-bed AM processes. The combined and individual effects of all process parameters were analyzed in a numerical experiment to show their significance for the printing process. The case study also showed that the proposed empirical optimization model yielded lower building costs than those from similar studies in the literature and is effective on maximizing productivity at the desired quality level.