Layered Manufacturing Process Research Articles

Characterization of additively manufactured parts for direct screwing

The combination of additive manufacturing and direct screwing can minimize the limitations in additive manufacturing such as long manufacturing times and high costs for expanding building spaces. Direct screwing allows smaller components to be assembled into larger components and attachable to assemblies with high functional integration. Thus, large building spaces can be avoided, and integration of additive components into serial production is possible. Although there are guidelines for direct screwing of injection-molded thermoplastic components by the Deutscher Verein für Schweißen und verwandte Verfahren e.V. (German Welding Society), there are currently no recommendations that can be directly applied to additively manufactured components. The layered manufacturing process of additively manufactured components is highly anisotropic as the strength of the components strongly depends on the build orientation. Thus, the compatibility of additive manufactured components for direct screwing was investigated at the Kunststofftechnik Paderborn. The characterization of additively manufactured screw bosses was considered with respect to the existing guidelines. For the characterization, screw domes were additively manufactured according to the geometry recommendations of the guidelines with the fused deposition modeling and the selective laser sintering. To account for the anisotropy, the screw domes were built in three different orientations. The compatibility of additively manufactured screw domes was evaluated through a comparison to injection-molded screw bosses. For the comparison, the joining parameters, the pull-out strength, and the component strength were investigated. The results showed there are significant differences in the investigated criteria based on the manufacturing technique and the build orientation.

Tensile properties of sandwich-designed carbon fiber filled PLA prepared via multi-material additive layered manufacturing and post-annealing treatment

Abstract Polylactic Acid (PLA) experiences widely spread applications in Fused Filament Fabrication (FFF) owing to its relatively high stiffness, strength, and environmentally friendly biodegradability. Reinforcing inclusions like short carbon fibers are introduced to virgin PLA feedstock aiming to improve the mechanical performance of FFF-made products. Nevertheless, the rigid fibers significantly reduce the ductility of the overall fabricated parts. This study prepares sandwich specimens with PLA as core and its 10 wt% chopped carbon fiber reinforced composites (i.e., CF/PLA) as shell via a low-cost FFF-based multi-material additive layered manufacturing method. The sandwich specimen has three layers, which are changed according to different material volumes, which is able to design the local strength and toughness performances of a printed part. Tensile properties of these sandwich samples printed in the different volumetric rates of virgin PLA constituents are measured. It is found that the strength of sandwich specimens with 20% vol of PLA reduces noticeably as compared to the full CF/PLA specimens. The 80% vol specimens exhibit a competitive strength as compared to the 40% and 60% vol specimens, while its toughness increases notably as compared to the other cases. Finite element simulations of the layered manufacturing process show that the thermal residual stresses of 20% vol sandwich accumulates most significantly. We also explore the effects of thermal annealing on the prepared sandwiches. Experimental results indicated that the post-annealing process improved the strength and stiffness of the sandwich specimens, while enhancing the stability of the mechanical properties of the FFF printed sandwich.

Effect of layer orientation on behaviour of 3D-printed rock specimens in indirect tensile testing

The mineralogical composition, texture and fracture of natural rocks can be complicated due to the inherent heterogeneity of geomechanical properties, making it challenging to understand their behaviour. Due to the intrinsic layer by layer manufacturing process, 3D printing technology enables to create rock-like materials and specimens with known and controllable inhomogeneity. In this study, disc specimens of a rock-like material are fabricated using 3D printing of cement mortar for testing to understand fabric orientation effect on fracture behaviour better. For the first time, a novel technique, named AUSBIT (Adelaide University Snap-back Indirect Tensile test), for Brazilian disc tests is applied for obtaining both strength and snap-back post-peak behaviour of the 3D printed rock-like materials. Adopting Digital Image Correlation (DIC) technique, in conjunction with the use of AUSBIT, allows obtaining full-field strains and their evolutions, showing strong effects of fabric orientation on strain distributions and both pre-and post-peak responses.

Improving the surface integrity of additively manufactured curved and inclined metallic surfaces using thermo-electric energy assisted polishing

Laser powder bed fusion (LPBF) is an advanced layer by layer manufacturing process gaining increased interest in industrial sector owing to its complex design flexibility. However, the parts produced using LPBF are not directly used in practical applications due to the geometrical inaccuracy and poor surface quality resulting from surface irregularities and defects. The established methods for post-processing LPBF parts/components such as laser polishing, abrasive polishing, chemical polishing and conventional finishing methods have inherent limitations depending on the variation in geometric shape/profile of the components. Hence, the present study analyses the effectiveness of a low energy wire electrical discharge polishing (WEDP) method in improving the surface quality and form accuracy of curved and inclined AlSi10Mg samples fabricated using laser powder bed fusion (LPBF). A geometrical model is proposed in the study for estimating the depth of material removed in each polishing pass. The developed model is capable of predicting the number of polishing passes required for the removal of irregularities on the surface. The geometrical form accuracy of metallic AM samples was improved significantly after WEDP with more than 68 % reduction in cylindricity error and 75 % reduction in flatness error. In addition, the samples exhibited uniform surface finish after WEDP with ~50–60 % reduction in as-built roughness. The SEM analysis conducted in the study reveals that WEDP is capable of eliminating the stair stepping surface defect with enhancement in geometrical profile. Furthermore, the EDS analysis confirmed the formation of oxide layer on the LPBF surface after WEDP post-processing.

Tetrabromobisphenol A (TBBPA) generation and removal paths analysis in printed circuit board (PCB) industrial wastewater: Lab-scale investigations

With the rapid development of printed circuit board (PCB) industry, the problem of the release of tetrabromobisphenol A (TBBPA) during PCB manufacturing processes was recognized and harmful to the receiving water body. In this study, TBBPA generation paths, fates in industrial wastewater in the PCB manufacturing processes were analyzed. Gas chromatograph-mass spectrometer (GC-MS) scanning results showed that the raw materials including solder mask ink, character ink and dry film mainly contained TBBPA. The PCB fabrication procedures, mainly including development, etching, stripping of inner layer manufacturing process, and pattern plating, tin-plating of outer layer manufacturing process, and development during the forming and surface treatment process would introduce TBBPA into wastewater. Flocculation and activated sludge process (ASP) that were commonly used for industrial wastewater treatment were selected to assess their removal capability for TBBPA in the wastewater, both which could remove more than 80% TBBPA. Low pH below 7, increased PAC and PAM dosages, and proper dosing during the slow-stirring stage could enhance the TBBPA removal of flocculation-sedimentation process. The ASP removes TBBPA mainly by the path of adsorption. High activated sludge concentration, low pH, medium-temperature and limited competitive adsorbates (NH4+, Cu2+) were beneficial to remove TBBPA by the ASP.

A Review on Additive Manufacturing Technology

Additive manufacturing is a new, rapidly emerging technique in the industrial sector. This is the process of creating parts by adding layer by layer material, hence it is called as 'Layer Manufacturing Process.’ This process is also called ‘Rapid Prototyping’ or ‘3DPrinting.’ This is a tool-less manufacturing method that produces parts in less time and with high precision. This process provides freedom for designing the parts and their complexity. Additive manufacturing has many advantages over conventional manufacturing processes like low production cost, no residual stresses, no wastage of material, etc. Nowadays, so much research work is going on in this additive manufacturing field. This manufacturing technology is going to replace the conventional manufacturing techniques in the upcoming days. In this paper, we discuss about the various additive manufacturing methods, its principles, applications, advantages, and challenges to industrial use.

Development of the Platform for Three-Dimensional Simulation of Additive Layer Manufacturing Processes Characterized by Changes in State of Matter: Melting-Solidification.

A new platform for three-dimensional simulation of Additive Layer Manufacturing (ALM) processes is presented in the paper. The platform is based on homogeneous methods—the Lattice Boltzmann Method (LBM) with elements of Cellular Automata (CA). The platform represents a new computer-based engineering technique primarily focused on Selective Laser Melting (SLM) technology. Innovative computational strategies and numerical algorithms for simulation and analysis of entire powder bed-based technology with changes in state of matter (melting-solidification) are presented in the paper. The models deal mainly with heat transfer, melting and solidification, and free-surface flow. Linking LBM and CA into a complex holistic model allows for complete full-scale simulations avoiding complicated interfaces. The approach is generic and can be applied to different multi-material powder bed-based SLM processes. A methodology for the adaptation of the model to the real material (Ti-6Al-4V alloy) and processing parameters is presented. The paper presents the first quantitative results obtained on the platform and shows the ability of the model to simulate and analyze a very complex technology, entirely without a complicated interface between the sub-models. It solves the large-scale problem connected with computer-aided design and analysis of new multi-passes and multi-materials processes.

An experimental investigation into influences of build orientation and specimen thickness on quasi-static and dynamic mechanical responses of Selective Laser Melting 316L Stainless Steel

Additive Layer Manufacturing (ALM) processes like Selective Laser Melting (SLM) enable the conception of complex designs with a high precision and equal or enhanced mechanical properties compared to Conventionally Manufactured (CM) structures. Nevertheless, this process, which consists in melting metallic powders layer by layer with a laser beam, greatly influences the microstructure and therefore the mechanical properties. While some studies have considered the effects of the thickness and/or the building direction of 316L Stainless Steel (SS) specimens produced by SLM on the quasi-static mechanical behavior, the strain rate effect for crash or impact applications on these two parameters has not been fully investigated. To complete the actual knowledge, the present work proposes to analyze the mechanical behavior of 316L SS tensile specimens produced by SLM with different build orientations (0°, 45° and 90°) and thicknesses (0.5, 0.75, 1 mm) and submitted to dynamic loadings at various strain rates up to 103 s−1. In addition, the microstructure and the fracture surfaces are analyzed to give a more detailed comprehension of the mechanical tests. It results that the SLM 316L SS achieves better Yield Stress (YS), similar Ultimate Tensile Stress (UTS) and equal or lower failure strain compared to the CM material. This is mainly a result of microstructure refinement. Anisotropy is observed at the macroscopic level with higher tensile stress and lower failure strain for horizontal specimens, which is explained by the different shapes, orientation and size of the grains at the microscopic level. The mechanical properties greatly decrease as the thickness reduces from 1 to 0.5 mm, by 14% for the YS and 16% for the UTS for a quasi-static loading. A minimum thickness of 0.75 mm is advised to at least recover the mechanical properties of the CM 316L SS. A positive strain rate sensitivity, higher than the CM material, is observed for all configurations, with the exception of 0.5 mm thickness. For strain rates ranging from to 10−3 to 103 s−1, there is an increase of 20% of the UTS. The material anisotropy is not affected by the strain rate sensitivity whereas the latter increases with the thickness.

A process optimization of additive layer manufacturing processes for the production of polymer composite-based components

The way additive layer manufacturing works is that materials are added in layers to create components. Every layer represents a narrow cross section of the component generated from the CAD data file. Each layer in ALM must have a defined part thickness, and the final part will be an estimate of the actual data. The last element will be the thinner surface of each layer that is formed. Modern and sophisticated ALM machines operate on a layer-based philosophy and methodology, which differs from traditional processes in terms of the materials utilised in component manufacture, the final layers formed, and how the layers are bonded to one another. These margins will look at things like the end part's correctness, as well as its material and mechanical qualities. We will determine several criteria in this study, such as how quickly the part can be manufactured utilising various ALM procedures. We also explore the beginnings of additive layer manufacturing and introduce the basic notion of additive layer manufacturing in this work. It will also go over the design process for additive layer manufacturing as well as the whole production of polymer composite based components tools. For functional engineering environments, polymer material is commonly employed to create hard and robust plastic parts. This material is extremely long-lasting, and it can be made or even welded if necessary. A minor change in the characteristics of the same material can make a big difference. ALM can be helpful at this point since it allows the designer to create a tangible model of the product to show its use and functions.

Machine learning in predicting mechanical behavior of additively manufactured parts

Although applications of additive manufacturing (AM) have been significantly increased in recent years, its broad application in several industries is still under progress. AM also known as three-dimensional (3D) printing is layer by layer manufacturing process which can be used for fabrication of geometrically complex customized functional end-use products. Since AM processing parameters have significant effects on the performance of the printed parts, it is necessary to tune these parameters which is a difficult task. Today, different artificial intelligence techniques have been utilized to optimize AM parameters and predict mechanical behavior of 3D-printed components. In the present study, applications of machine learning (ML) in prediction of structural performance and fracture of additively manufactured components has been presented. This study first outlines an overview of ML and then summarizes its applications in AM. The main part of this review, focuses on applications of ML in prediction of mechanical behavior and fracture of 3D-printed parts. To this aim, previous research works which investigated application of ML in characterization of polymeric and metallic 3D-printed parts have been reviewed and discussed. Moreover, the review and analysis indicate limitations, challenges, and perspectives for industrial applications of ML in the field of AM. Considering advantages of ML increase in applications of ML in optimization of 3D printing parameters, prediction of mechanical performance, and evaluation of 3D-printed products is expected.

Surface finish of Additively Manufactured Metals: biofilm formation and cellular attachment

Powder bed fusion techniques enable the production of customized and complex devices that meet the requirements of the end user and target application. The medical industry relies on these additive manufacturing technologies for the advantages that these methods offer to accurately fit the patients’ needs. Besides the recent improvements, the production process of 3D printed bespoke implants still requires optimization to achieve the optimal properties that can mimic both the chemical and mechanical characteristics of the anatomical region of interest. In particular, the surface properties of an implant device are crucial to obtain a strong interface and connection with the physiological environment. The layer by layer manufacturing processes lead to the production of complex and high-performance substrates but always require surface treatments during post-processing to improve the implant interaction with the natural tissues and promote a shorter assimilation for the fast recovery and wellness of the patient. Although the surface finishing can be tailored to enhance cells adhesion, proliferation and differentiation in contact with a metal implant, the same surface properties can have a different outcome when dealing with bacteria. This work aims to provide a preliminary analysis on how different post-processing techniques have distinct effects on cells and bacteria colonization of 3D printed titanium implants. The goal of the paper is to highlight the importance of the identification of an optimized methodology for the surface treatment of Ti6Al4V samples produced by Selective Laser Melting (SLM) that improves the implant antimicrobial properties and promotes the osseointegration in a long-term period.

A New Adaptive Slicing Algorithm Based on Slice Contour Reconstruction in Layered Manufacturing Process

Computer-Aided Design and Applications is an international journal on the applications of CAD and CAM. It publishes papers in the general domain of CAD plus in emerging fields like bio-CAD, nano-CAD, soft-CAD, garment-CAD, PLM, PDM, CAD data mining, CAD and the internet, CAD education, genetic algorithms and CAD engines. The journal is aimed at all developers and users of CAD technology to ptovide CAD solutions for various stages of design and manufacturing. The journal publishes all about Computer-Aided Design and Computer-Aided technologies.

Conformal Geometry and Multimaterial Additive Manufacturing through Freeform Transformation of Building Layers.

3D printing, formally known as additive manufacturing, creates complex geometries via layer-by-layer addition of materials. While 3D printing has been historically perceived as the static addition of build layers, 3D printing is now considered as a dynamic assembly process. In this context, here a new 3D printing process is reported that executes full degree-of-freedom (DOF) transformation (translating, rotating, and scaling) of each individual building layer while utilizing continuous fabrication techniques. Transforming individual building layers within the sequential layered manufacturing process enables dynamic transformation of the 3D printed parts on-the-fly, eliminating the time-consuming redesign steps. Preserving the locality of the transformation to each layer further enables the discrete conformal transformation, allowing objects such as vascular scaffolds to be optimally fabricated to properly fit within specific patient anatomy obtained from the magnetic resonance imaging (MRI) measurements. Finally, exploiting the freedom to control the orientation of each individual building layer, multimaterials, multiaxis 3D printing capability are further established for integrating functional modules made of dissimilar materials in 3D printed devices. This final capability is demonstrated through 3D printing a soft pneumatic gripper via heterogenous integration of rigid base and soft actuating limbs.

Comparative evaluation of supervised machine learning algorithms in the prediction of the relative density of 316L stainless steel fabricated by selective laser melting

To find a robust combination of selective laser melting (SLM) process parameters to achieve the highest relative density of 3D printed parts, predicting the relative density of 316L stainless steel 3D printed parts was studied using a set of machine learning algorithms. The SLM process brings about the possibility to process metal powders and built complex geometries. However, this technology’s applicability is limited due to the inherent anisotropy of the layered manufacturing process, which generates porosity between adjacent layers, accelerating wear of the built parts when in service. To reduce interlayer porosity, the selection of SLM process parameters has to be properly optimized. The relative density of these manufactured objects is affected by porosity and is a function of process parameters, rendering it a challenging optimization task to solve. In this work, seven supervised machine learning regressors (i.e., support vector machine, decision tree, random forest, gradient boosting, Gaussian process, K-nearest neighbors, multi-layer perceptron) were trained to predict the relative density of 316L stainless steel samples produced by the SLM process. For this purpose, a total of 112 data sets were assembled from a deep literature review, and 5-fold cross-validation was applied to assess the regressor error. The accuracy of the predictions was evaluated by defining an index of merit, i.e., the norm of a vector whose components are the statistical metrics: root mean square error (RMSE), mean absolute error (MAE), and the coefficient of determination (R2). From this index of merit, it is established that the use of gradient boosting regressor shows the highest accuracy, followed by multi-layer perceptron and random forest regressor.

Fused Deposition Modelling of Fibre Reinforced Polymer Composites: A Parametric Review

Fused deposition modelling (FDM) is a widely used additive layer manufacturing process that deposits thermoplastic material layer-by-layer to produce complex geometries within a short time. Increasingly, fibres are being used to reinforce thermoplastic filaments to improve mechanical performance. This paper reviews the available literature on fibre reinforced FDM to investigate how the mechanical, physical, and thermal properties of 3D-printed fibre reinforced thermoplastic composite materials are affected by printing parameters (e.g., printing speed, temperature, building principle, etc.) and constitutive materials properties, i.e., polymeric matrices, reinforcements, and additional materials. In particular, the reinforcement fibres are categorized in this review considering the different available types (e.g., carbon, glass, aramid, and natural), and obtainable architectures divided accordingly to the fibre length (nano, short, and continuous). The review attempts to distil the optimum processing parameters that could be deduced from across different studies by presenting graphically the relationship between process parameters and properties. This publication benefits the material developer who is investigating the process parameters to optimize the printing parameters of novel materials or looking for a good constituent combination to produce composite FDM filaments, thus helping to reduce material wastage and experimental time.

Selective Laser Melting and Electron Beam Melting of Ti6Al4V for Orthopedic Applications: A Comparative Study on the Applied Building Direction.

The 3D printing process offers several advantages to the medical industry by producing complex and bespoke devices that accurately reproduce customized patient geometries. Despite the recent developments that strongly enhanced the dominance of additive manufacturing (AM) techniques over conventional methods, processes need to be continually optimized and controlled to obtain implants that can fulfill all the requirements of the surgical procedure and the anatomical district of interest. The best outcomes of an implant derive from optimal compromise and balance between a good interaction with the surrounding tissue through cell attachment and reduced inflammatory response mainly caused by a weak interface with the native tissue or bacteria colonization of the implant surface. For these reasons, the chemical, morphological, and mechanical properties of a device need to be designed in order to assure the best performances considering the in vivo environment components. In particular, complex 3D geometries can be produced with high dimensional accuracy but inadequate surface properties due to the layer manufacturing process that always entails the use of post-processing techniques to improve the surface quality, increasing the lead times of the whole process despite the reduction of the supply chain. The goal of this work was to provide a comparison between Ti6Al4V samples fabricated by selective laser melting (SLM) and electron beam melting (EBM) with different building directions in relation to the building plate. The results highlighted the influence of the process technique on osteoblast attachment and mineralization compared with the building orientation that showed a limited effect in promoting a proper osseointegration over a long-term period.

The effect of processing parameters on the mechanical characteristics of PLA produced by a 3D FFF printer

3D printing by fused filament fabrication (FFF) provides an innovative manufacturing method for complex geometry components. Since FFF is a layered manufacturing process, effects of process parameters are of concern when plastic materials such as polylactic acid (PLA), polystyrene and nylon are used. This study explores how the process parameters, e.g. build orientation and infill pattern/density, affect the mechanical response of PLA samples produced using FFF. Digital image correlation (DIC) was employed to get full-field surface-strain measurements. The results show the influence of build orientation and infill density is significant. For on-edge orientation, the tensile strength and Young’s modulus were 55 MPa and 3.5 GPa respectively, which were about 91% and 40% less for the upright orientation, demonstrating a significant anisotropy. The tensile strength and Young’s modulus increased with increasing infill density. In contrast, different infill patterns have no significant effect. Considering the influence of build orientation, based on the experimental results, a constitutive model derived from the laminate plate theory was employed. The material parameters were determined by tensile tests. Results demonstrated a reasonable agreement between the experimental data and the predictive model. Similar anisotropy to tension was observed in shear tests; shear modulus and shear strength for 45° flat orientation were about 1.55 GPa and 36 MPa, whereas for upright specimens they were about 0.95 GPa and 18 MPa, respectively. The findings provide a framework for systematic mechanical characterisation of 3D-printed polymers and potential ways of choosing process parameters to maximise performance for a given design.

Variable-width contouring for additive manufacturing

In most layered additive manufacturing processes, a tool solidifies or deposits material while following pre-planned trajectories to form solid beads. Many interesting problems arise in this context, among which one concerns the planning of trajectories for filling a planar shape as densely as possible. This is the problem we tackle in the present paper. Recent works have shown that allowing the bead width to vary along the trajectories helps increase the filling density. We present a novel technique that, given a deposition width range, constructs a set of closed beads whose width varies within the prescribed range and fill the input shape. The technique outperforms the state of the art in important metrics: filling density (while still guaranteeing the absence of bead overlap) and trajectories smoothness. We give a detailed geometric description of our algorithm, explore its behavior on example inputs and provide a statistical comparison with the state of the art. We show that it is possible to obtain high quality fabricated layers on commodity FDM printers.

Microstructural Characteristics and Mechanical Properties of Repaired Titanium Alloy Blade by Arc Additive Manufacturing Process

To improve repair efficiency and achieve a high‐quality repair layer, wire and arc additive manufacturing process is used in this study to repair missing‐angle Ti‐6Al‐4V blade. The deposition layer with a mixed equiaxed β and columnar grain can be obtained by optimizing the deposition speed and single layer height. According to the characteristics of β grain, the typically repaired thin‐walled part is divided into four representative areas, including heat affected zone (HAZ), bottom layer, middle layer, and top layer. The bottom layer consists of coarsely near‐equiaxed β grains with martensite α′ and basket‐weave structure, and the columnar β grains grow perpendicularly from middle layer to top layer. The heat accumulation in HAZ continues to increase which resulted in a certain degree of cooling rate reduction, resulting in the martensite α′ decomposed to α dots and rods in HAZ near the layer band. The fine near‐equiaxed β grains (78 ± 28 μm), martensite α′ structure, and fine lamellar α structure are presented in HAZ, causing the fracture transition from the HAZ to bottom region. The characteristic of ductile rupture is observed in repaired thin‐wall, the maximum tensile strength is 991 MPa, and the elongation reaches about 10%.

SCIENTIFIC AND TECHNOLOGICAL CHALLENGES OF LAYER MANUFACTURING PROCESSES FOR POLYMER COMPONENTS PRODUCTION

Purpose of study: Additive manufacturing processes taking the basic information form computer-aided design (CAD) file to convert into the stereolithography (STL) data file. Today additive layer manufacturing processes are playing a very vital role in manufacturing parts with high rate of effectiveness and accuracy. CAD software is approximated to sliced containing information of each layer by layer that is printed. The main purpose of the study is to discuss the scientific and technological challenges of additive layer manufacturing processes for making polymer components production through various technological parameters and problem-solving techniques of layer manufacturing processes.
 Main findings: Additive layer manufacturing is simply another name for 3D printing or rapid prototyping. As 3D printing has evolved as a technology, it has moved beyond prototyping and into the manufacturing space, with small runs of finished components now being produced by 3D printing machines around the world. Additive layer manufacturing (ALM) is the opposite of subtractive manufacturing, in which material is removed to reach the desired shape
 Methodology Used: The continuous and increasing growth of additive layer manufacturing processes to discuss with different experimental behavior through simulations and graphical representations. In ALM, 3D parts are built up in successive layers of material under computer control. In its early days, 3D printing was used mainly for rapid prototyping, but it is now frequently used to make finished parts the automotive and aerospace sectors, amongst many others.
 The originality of study: At the present time, the technologies of additive manufacturing are not just using for making models with the plastics but using polymer materials. It is possible to make finished products developed with high accuracy and save a lot of time and there is the possibility of testing more models.