Deposition Path Research Articles

Thermal analyses for optimal scanning pattern evaluation in laser aided additive manufacturing

Laser aided additive manufacturing (LAAM) is one of the key metal 3D printing technologies for surface cladding or fabrication of near-net shape parts. The study of LAAM scanning pattern is important to understand their relationship with residual stress and part distortion. This paper proposed a framework to both simulate and evaluate laser scanning paths. Firstly, an efficient 3D thermal history analysis finite element (FE) model was developed to predict temperature field evolution for arbitrary scanning patterns. Subsequently, a thermal field based evaluation method was established to determine the optimal scanning pattern with minimal distortion. The effectiveness of the framework was validated experimentally by depositing a rectangular clad on a cuboid substrate with five different scanning patterns. Experiments showed width-wise Zigzag scanning pattern yielded largest distortion. This method with 5 criteria and two evaluation levels were effective to identify an improved width-wise Zigzag scanning pattern by adjusting the deposition paths sequence, while determining the length-wise scanning as the optimal pattern. This work also demonstrated that the temperature field can be used to make qualitative evaluation of LAAM induced distortion which further reduces computational costs.

A Topology Optimization Method for Hybrid Subtractive–Additive Remanufacturing

This paper presents a hybrid subtractive–additive remanufacturing oriented topology optimization method. This method provides a design-for-remanufacturing approach, which offer solutions for product upgrade or repair. To be specific, a used part is first machined to remove material, and then additively deposited of materials on top. In this way, either the function of the part is upgraded or the broken part is repaired. Beneficially, the used part is economically and environment-friendly recycled. This method is developed under the level set framework and innovatively, the layer-wise level set representation of the additive manufacturing part is adopted for self-support and material anisotropy control. Especially for the latter point, the hybrid deposition path, a combination of contour-offset and zig–zag path patterns, is adopted for deposition path planning, which will be concurrently optimized for the best material anisotropy distribution. Therefore, what will be presented in this paper is a novel combination of structural topological design and process planning to derive the optimal hybrid remanufacturing strategy. This is a very novel trial and we have performed experiments to verify its effectiveness.

Insight into the Mechanism of Ethylene Decomposition Over Co(0001) Surface: Formation of Carbon Species

Ethylene decomposition over Co(0001) surface has been systematically studied by spin-polarized density functional theory calculations aiming to investigate the detail mechanism at the atomic level. All C–H bond and C–C bond scission reactions were computed and all the intermediates were considered. It is concluded that the C–H bond breaking reaction is always advantageous for a species possessing both C–H scission and C–C scission modes. C2 cluster is practicable formed during ethylene decomposition, which is coincide with experiment results. However, the high activated barrier blocks the C–C bond scission reaction of C2. After comparative analysis, two pathways of C2 cluster formation and two pathways of carbon monomer formation were proposed. These results provide novel information on ethylene decomposition over Co(0001), deepening our understanding of relevant catalytic reactions such as the carbon deposition and initial path to graphene formation.

Wire + Arc Additive Manufacture of 17-4 PH stainless steel: Effect of different processing conditions on microstructure, hardness, and tensile strength

Wire + Arc Additive Manufacture (WAAM) is receiving increasing attention as it offers a way to fabricate meter scale parts, with relatively low capital cost, lower material wastage and logistical advantages. A wide range of metallic alloys could be manufactured using this process. Martensitic grade precipitation-hardening stainless steel 17-4 PH offers excellent combination of high strength and corrosion resistance. Hence, it is important to investigate the behaviour of this alloy in WAAM. In the present work, the effect of different process variables such as shielding gas, deposition path and post-fabrication heat treatment, on microstructure and mechanical properties were studied. A number of specimens were manufactured by WAAM using the Fronius Cold Metal Transfer (CMT) process under different controlled processing conditions. These specimens were subsequently characterized by optical and electron microscopy and mechanical properties in terms of tensile strength and hardness. It was found that using shielding gases that result in higher heat input reduces the amount of retained austenite in the as-deposited microstructure. It has been demonstrated that the required tensile properties can be achieved by applying post-deposition heat treatment. However, it is suggested that direct aging in as deposited condition resulted in formation of harmful intermetallic phases which embrittles the deposit.

Automatic multi-axis path planning for thinwall tubing through robotized wire deposition

Metal wire deposition is a promising additive technology to produce low-cost near shape blanks for large and complex parts. Combined with robotic arms, multi-axis deposition presents new opportunities and challenges regarding deposition path planning and tool axis determination, especially to avoid support material use.In this work, an automated algorithm that calculates the deposition path, the tool orientations and the local inter-layer distances is presented. Then, an adaptive travel speed strategy is applied to adjust the bead morphology to the local layer height. Finally, two multi-axis deposition strategies are compared numerically and experimentally for manufacturing cantilever thinwall tube geometries.

Residual Stress Modeling and Simulation of Direct Metal Laser Sintered Ti-6Al-4V Alloy

Abstract Additive Manufacturing is able to accurately create layer wise deposition of a variety of materials from three dimensional CAD models. It is a competitive technology for the future as compared to subtractive manufacturing. This paper presents a Finite Element model of Ti-6Al-4V alloy popularly used for aerospace applications. Ti-6Al-4V alloy manufactured by the Direct Metal Laser Sintering (DMLS) technique was used to estimate the residual stresses developed in the specimen. It was found that the residual stress developed along the deposition path was always lower than the yield strength of the alloy. The process parameters are taken as per DMLS technique because this technique is popularly used for metals and their alloys specifically. The effect of laser parameters on the Ti-6Al-4V alloy was studied and the residual stresses generated in the DMLS technique were estimated by Finite Element Modelling.

Cold Metal Transfer (CMT) Based Wire and Arc Additive Manufacture (WAAM) System

The forming system of wire and arc additive manufacture (WAAM) based on cold metal transfer (CMT) is a high build rate system for production of near-net shape components layer by layer, which is composed of industrial robot operation system and 3D path simulation software. In the 3D path simulation software, the working layout of the off-line virtual robot is carried for the imported three-dimensional model to screen the model wall thickness, correct process library, set process parameters, slice, layer, plan deposition path, form simulation and upload program to execution system. Among the whole system, the 3D path simulation software provides essential database for process control and an innovative planning path to coordinate industrial robot platform to build parts layer by layer. Furthermore, the experiment is also performed to study the stability of aluminum alloy forming using the WAAM-CMT system by establishing different experimental models and changing process parameters and process modes of industrial robot and Fronius digital welding machine embedded on robot operation platform.

Additive manufacturing of polyethylene terephthalate glycol /carbon fiber composites: An experimental study from filament to printed parts

This research focuses on the definition and application of a characterization methodology to determine the characteristics of fused deposition modeling 3D printing materials. Commercial short fiber reinforced and unreinforced polyethylene terephthalate glycol parts were tested achieving comparison terms. The presented methodology is composed of three classes: thermal analysis, mechanical testing, and material morphology. Filament was tensile tested with specially developed setup for determining the mechanical properties of raw materials. Standardized flexural and tensile samples were printed 100% dense in both materials and tested. Differential scanning calorimetry results showed that the thermal properties of both materials do not change with successive heating cycles. Thermogravimetric analysis allowed to understand the thermal stability of materials and quantify the amount of fiber in the matrix. Tensile tests indicated that the addition of fibers increases the Young’s modulus by 70.10% but there is lesser withstanding of stress by 28.21%. Flexural tests exhibited an increase in flexural modulus of 191.38% and 5.14% in flexural strength for the reinforced polyethylene terephthalate glycol, due to the presence of fiber. Microscopic analysis revealed a 12% of void spots and fiber alignment accordingly to the deposition path.

Feature based three axes computer aided manufacturing software for wire arc additive manufacturing dedicated to thin walled components

WAAM (Wire-Arc-Additive-Manufacturing) is a metal additive manufacturing process using arc welding to create large components with high deposition rate. The workpiece quality and the process productivity are strongly dependent both on the process parameters (wire feed speed, voltage and current) and on the selected deposition path. Currently, the CAM (Computer-Aided-Manufacturing) software dedicated to WAAM rely on a multi-pass strategy to create the component layers, i.e. each layer is built overlapping multiple welding passes. However, since WAAM can create wide layers, a single pass strategy can improve the process efficiency when dealing with thin walled components. This paper proposes CAM software dedicated to WAAM, using a single pass strategy. The proposed solution uses a midsurface representation of the workpiece as input, to generate the deposition toolpath. A feature recognition module is proposed, to identify the critical features of the part, such as free end walls, t-crossings, direct-crossings and isolated tubulars. A specific strategy is developed and proposed for each one of the selected features, with the aim of minimizing the geometrical errors and to ensure the required machining allowances for the subsequent finishing operations. The effectiveness of the proposed strategy is verified manufacturing a test case.

Challenges in Three-Dimensional Printing of High-Conductivity Copper

With recent advancements in additive manufacturing (AM) technology, it is possible to deposit copper conductive paths and insulation layers of an electric machine in a selective controlled manner. AM of copper enables higher fill factors that improves the internal thermal conduction in the stator core of the electric machine (induction motor), which will enhance its efficiency and power density. This will reduce the motor size and weight and make it more suitable for aerospace and electric vehicle applications, while reducing/eliminating the rare-earth dependency. The objective of this paper is to present the challenges associated with AM of copper coils having 1 × 1 mm cross section and complex features that are used in producing ultra-high efficiency induction motor for traction applications. The paper also proposes different approaches that were used by the authors in attempts to overcome those challenges. The results of the developed technologies illustrate the important of copper powder treatment to help in flowing the powder easier during deposition. In addition, the treated powder has higher resistance to surface oxidation, which led to a high reduction in porosity formation and improved the quality of the copper deposits. The laser powder direct energy deposition (LPDED) process modeling approach helps in optimizing the powder deposition path, the laser power, and feed rate that allow the production of porosity free thin wall and thin floor components. The laser powder bed fusion (LPBF) models identify the optimum process parameters that are used to produce test specimens with >90% density and minimum porosity.

Light-weight shape and topology optimization with hybrid deposition path planning for FDM parts

FDM (fused deposition modeling) parts demonstrate anisotropic properties between the in-layer raster and transverse directions. However, structural optimization of FDM parts has rarely taken the deposition path and thus the anisotropic material properties into consideration. This work proposes a methodology that integrates optimal hybrid deposition paths with the shape and topology optimization and brings all aspects under a unified level set framework. A dedicated sensitivity analysis is performed on both the shape and path variables, which ensures the optimality of the derived design solutions. Effectiveness of the proposed method is demonstrated through a number of 2D and 3D numerical examples.

Influence of dipping cycle on SILAR synthesized NiO thin film for improved electrochemical performance

NiO thin films have been successfully synthesized using by successive ionic layer absorption and reaction (SILAR) technique which is simple, cost-effective and low-temperature wet chemical process. Influences of deposition cycle on structural and morphological property were investigated using XRD and FESEM. Surface morphological study shows formation of highly porous network which provides more active sites and deposition path for electrolyte ions. NiO thin film based electrode provides highest specific capacitance of 1341 Fg−1 at the voltage scan rate of 2 mVs−1 for the film deposited at 40 deposition cycle. From charging -discharging curve of NiO electrode, specific capacitance value of 877 Fg−1 at current 1 Ag−1for the film deposited at 40 deposition cycle was observed. It shows highest specific energy of 64.8 Wh Kg−1. The NiO electrode exhibited long-term cycle stability with 90% capacitance retention after 1000 cycle. Such attractive electrochemical performance of the formed electrode is suitable for the manufacturing of the good quality supercapacitors for commercial application.

Extrusion-based additive manufacturing process for producing flexible parts

The processing of elastomers through fused deposition modeling (FDM) is challenging task due to low column strength and high melt viscosity. Ethylene vinyl acetate (EVA) is an elastomer which is widely used for fabricating flexible objects. However, the potential of this material has not been explored in the FDM process. Pre-fabricated EVA filament cannot be processed in standard filament feed extrusion mechanism of commercial FDM machine due to buckling of the filament. However, development of pellet-based extrusion additive manufacturing (AM) may eliminate the issues caused by elastomer filament. The current study demonstrates the development of pellet-based AM system for processing EVA material. The developed system is compatible with the three-axis CNC milling machine, which provides high precision positioning to the deposition path and required power for screw rotation. Details about hardware and software related to the developed system have been presented. Flexible parts using EVA pellets have been fabricated successfully, which shows the capability of the developed extrusion AM system. Experiments have been performed for tuning process parameters. Further, mechanical characterization has been done to analyze the dimensional accuracy, flexibility, strength and hardness of printed parts. Obtained results show that EVA demonstrates approx. 300–550% higher elongation as compared to ABS and PLA materials, which indicates EVA can be used to make highly flexible parts. The outcome of this study will be helpful to the engineers for the development of low-cost flexible parts for those applications where customized flexible parts are needed in short span of time.

Effect of inter layer idle time on thermal behavior for multi-layer single-pass thin-walled parts in GMAW-based additive manufacturing

Components fabricated in gas metal arc welding (GMAW)-based additive manufacturing undergo a special thermal process with many reheating cycles, resulting in the complicated thermal behavior. Many process variables can affect the thermal history in GMAW-based additive manufacturing, especially the interlayer idle time. In this paper, three-dimensional transient models were established to research the effect of interlayer idle time on thermal process in GMAW-based additive manufacturing. Meanwhile, a confirmatory test was conducted to verify the effectiveness of the model. The results indicate that the total maximum temperature gradients of the molten pool at the middle points in the models with the interlayer idle time of 2 min, 5 min, and cooling to room temperature are approximately consistent after the fourth layer, and those in the case with continuous deposition decrease gradually. As the deposition height increases, the maximum temperature gradient in molten pool along the deposition path keeps steady in the model with cooling to room temperature. At the deposition ending moment, with the increasing interlayer idle time, the total temperature gradients at the middle points of the layers decrease in the first eight layers and increase in the ninth and tenth layers, while the circumferential temperature gradients increase progressively.

A framework for future CAM software dedicated to additive manufacturing by multi-axis deposition

Deposition processes, such as Wire & Arc Additive Manufacturing (WAAM), have important perspectives in industry, due to their capacity to produce large near-shape parts with high productivity. Beyond process-material issues, deposition path planning is one of the major challenges to allow a wide use of these processes using multi-axis machines or robots. Early CAM software solutions dedicated to multi-axis additive manufacturing have been already commercialised. However, few elementary deposition strategies are currently available. In this article, the possibilities of multi-axis deposition and the developments needed to improve deposition path generation are highlighted through the analysis of a hollow half-sphere as a case study. Deposition strategies are experimentally tested on two different robotised polymer deposition systems. Based on the comparison of the trials, the issues related to the portability of technology from a specific machine setup to a different one are discussed. Finally, a framework for future Computer-Aided Multi-Axis Additive Manufacturing (CAMAAM) software is proposed.

Study on the role of deposition path in electron beam freeform fabrication process

PurposeThe present work aims to reveal the effect of deposition paths on transient temperature, transient stress, residual stress and residual warping in the electron beam freeform fabrication (EBF) process.Design/methodology/approachSix typical deposition paths were involved in the finite element (FE) simulations of EBF process by implementing a specially written program.FindingsThe results showed that the deposition path had a remarkable influence on heat transfer and transient temperature distribution in the scanning process, resulting in different residual stress and residual warping after cooling to room temperature. The largest and smallest temperature gradients were obtained from the zigzag and alternate-line paths, respectively. Meanwhile, the temperature gradient decreased with the increase of deposited layers. The optimum deposition path, namely, the alternate-line pattern, was determined with respect to the residual stress and residual warping.Originality/valueAlthough some researcher revealed the importance of deposition path through FE analysis and experimental observation, their studies were usually confined within one type of deposition pattern. A complete investigation of typical deposition paths and comparison among them are still lacking in literature. To address the aforementioned gap, the present work started by extensive FE simulations of EBF process involving six representative deposition paths, namely, the alternate-line, zigzag, raster, inside-out spiral, outside-in spiral and Hilbert. For each deposition path, the transient temperature field, residual stress and residual deformation were obtained to optimize the deposition path.

Enhanced beads overlapping model for wire and arc additive manufacturing of multi-layer multi-bead metallic parts

Wire and arc additive manufacturing (WAAM) is a competitive technology for fabricating metallic parts with complex structure and geometry. It enables the fabrication of multi-layer multi-bead (MLMB) parts. The basis of planning the deposition paths is the beads overlapping model (BOM). The existing overlapping models consider only the geometric area of adjacent beads, but ignore the spreading of the melted weld beads. The objective of the research was to develop an enhanced BOM (E.BOM) for WAAM, which takes the spreading of the weld beads into consideration. A deposited bead spreads to the already deposited neighboring bead and as a consequence, its center point deviates from the center point of the fed (to be melted) wire. Experiments were designed to explore the relationships between the geometries of the beads, and the offset distance between the center of a weld bead and the center of the fed wire. An artificial neural network was used to predict the offset distance of a certain weld bead based on the results of the experiments. In addition, a reasoning algorithm was implemented to calculate the optimal distance between the centers of adjacent deposition paths in order to achieve a planned center distance between adjacent beads. This enables the control of the actual center distance of the adjacent beads according to an expected value. The E.BOM has been tested by validation experiments. On the one hand, it improves the surface flatness of layers of MLMB parts produced by WAAM. On the other hand, it prevents formation of defects inside the parts.

Finite Element mesh coarsening for effective distortion prediction in Wire Arc Additive Manufacturing

WAAM (Wire Arc Additive Manufacturing) is a metal AM (Additive Manufacturing) technology that allows high deposition rates and the manufacturability of very large components, compared to other AM technologies. Distortions and residual stresses affecting the manufactured parts represent the main drawbacks of this AM technique. FE (Finite Element) modeling could represent an effective tool to tackle such issues, since it can be used to optimize process parameters, deposition paths and to test alternative mitigation strategies. Nevertheless, specific modeling strategies are needed to reduce the computational cost of the process simulation, such as reducing the number of elements used in discretizing the model. This paper presents an alternative technique to reduce the number of elements required to discretize the substrates of WAAM workpieces. The proposed technique is based on dividing the substrate in several zones, separately discretized and then connected by means of a double sided contact algorithm. This strategy allows to achieve a significant reduction of the number of elements required, without affecting their quality parameters. The geometry and dimension of the mesh zones are identified through a dedicated algorithm that allows to achieve an accurate temperature prediction with the minimum element number. The effectiveness of the proposed technique was tested by means of both numerical and experimental validation tests.

Special Issue on “Additive Manufacturing Technologies and Applications”

Additive Manufacturing (AM) is a well-known technology, first patented in 1984 by the French scientist Alain Le Mehaute [...]

Concurrent deposition path planning and structural topology optimization for additive manufacturing

PurposeStructural performance of additively manufactured parts is deposition path-dependent because of the induced material anisotropy. Hence, this paper aims to contribute a novel idea of concurrently performing the deposition path planning and the structural topology optimization for additively manufactured parts.Design/methodology/approachThe concurrent process is performed under a unified level set framework that: the deposition paths are calculated by extracting the iso-value level set contours, and the induced anisotropic material properties are accounted for by the level set topology optimization algorithm. In addition, the fixed-geometry deposition path optimization problem is studied. It is challenging because updating the zero-value level set contour cannot effectively achieve the global orientation control. To fix this problem, a level set-based multi-step method is proposed, and it is proved to be effective.FindingsThe proposed concurrent design method has been successfully applied to designing additively manufactured parts. The majority of the planned deposition paths well match the principle stress direction, which, to the largest extent, enhances the structural performance. For the fixed geometry problems, fast and smooth convergences have been observed.Originality/valueThe concurrent deposition path planning and structural topology optimization method is, for the first time, developed and effectively implemented. The fixed-geometry deposition path optimization problem is solved through a novel level set-based multi-step method.