Prediction Of Distortion Research Articles

A member-based porous method for predicting flow distortions around a lattice tower

In the wind field measurement, the readings of an anemometer mounted on a lattice tower will be influenced by the tower. Therefore, evaluation of the flow distortions generated by a lattice tower is essential for correcting the wind speed data or guiding the arrangement of anemometers. Wall-refined CFD is a powerful tool to simulate the flow field but is quite time consuming for lattice structures. As an alternative approach for improving the computational efficiency of CFD, a member-based porous method was proposed by this article. It employs porous zones to substitute the real members of a lattice tower, so that the computational resources can be considerably saved. Wind tunnel test of two lattice tower segments were conducted to validate the member-based porous method. Models of wall-refined CFD were also established. Results of the member-based porous method are in acceptable agreement with those of test and wall-refined CFD. The method is proved to be an effective way to predict flow distortions of a lattice tower. Both the test and numerical simulations (wall-refined CFD and member-based porous) reveal that disparities exist between the flow field of different measurement planes. The results highlight the need to consider the impacts of member arrangement in predictions of the flow distortion. At last, some crucial issues on the flow distortion effects of a lattice tower were also discussed, results of the classic theoretical methods were compared with those of the member-based porous method.

Methodical procedure of virtual manufacturing for analysing WAAM distortion along with experimental verification

This paper deals with a principal development of virtual manufacturing (VM) procedure to predict substrate distortion induced by Wire Arc Additive Manufacturing (WAAM) process. In this procedure, a hollow shape is designed in a thin-walled form made of stainless steel. The procedure starts with geometrical modelling of WAAM component consisting of twenty-five deposited layers with austenitic stainless-steel wire SS316L as feedstock and SS304 as substrate material. The hollow shape is modelled based on simplified rectangular mesh geometry with identical specimen dimensions during the experiment. Material model to be defined can be retrieved directly from a database or by conducting a basic experiment to obtain the evolution of material composition, characterized using Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) analysis, and generated using advanced modelling software JMATPRO for creating new properties including the flow curves. Further, a coupled thermomechanical solution is adopted, including phase-change phenomena defined in latent heat, whereby temperature history due to successive layer deposition is simulated by coupling the heat transfer and mechanical analysis. Transient thermal distribution is calibrated from an experiment obtained from thermocouple analysis at two reference measurement locations. New heat transfer coefficients are to be adjusted to reflect actual temperature change. As the following procedure prior to simulation execution, a sensitivity analysis was conducted to find the optimal number of elements or mesh size towards temperature distribution. The last procedure executes the thermomechanical numerical simulation and analysis the post-processing results. Based on all aspects in VM procedures and boundary conditions, WAAM distortion is verified using a robotic welding system equipped with a pulsed power source. The experimental substrate distortion is measured at various points before and after the process. It can be concluded based on the adjusted model and experimental verification that using nonlinear numerical computation, the prediction of substrate distortion with evolved material property of component yields far better result which has the relative error less than 11% in a comparison to database material which has 22%, almost doubled the inaccuracy.

Investigation of the right first-time distortion compensation approach in laser powder bed fusion of a thin manifold structure made of Inconel 718

The research work first demonstrates modelling techniques for distortion prediction of laser powder bed fusion (LPBF) using the inherent strain approach implemented in structural finite element analyses. The prediction of distortion is compared with experimentally measured results of a thin manifold structure made of Inconel 718. The predicted distortions were used to verify the right first-time approach for distortion compensation where the thin manifold structure was first simulated. The distortion was then compensated using mapping techniques across different source meshes, and the component was finally manufactured using LPBF. Two components were built, one with compensation and one without compensation. The results showed that the right first-time approach compensated the distortion for the majority of the part. There were areas where the compensation was not accurate due to overpredictions of the distortion.

Welding Distortion Prediction for Multi-Seam Welded Pipe Structures using Equivalent Thermal Strain Method

Distortion prediction of a welded structure is an important way to improve work efficiency and ensure product quality during the fabrication process. Recently, the widely used approaches for evaluating residual deformation include the thermo-elastic-plastic finite element method (TEP-FEM) and the inherent strain method (ISM). The former can accurately simulate the entire welding process with excessive computational time, whereas the latter has great potential in the fast prediction of residual distortion in complex welded components. In this study, an equivalent thermal strain method based on inherent strain theory was proposed to predict residual deformation of the multi-seam welded pipe structures. Moreover, a full 3D TEP-FEM model was also developed to estimate the distributions of inherent strain in longitudinal (L-seam) and circumferential (C-seam) welds. To validate the accuracy of the proposed ISM, the welding distortion predicted by the proposed ISM is compared with the experimental data and TEP-FEM simulation results. It is discovered that the proposed ISM can be used to accurately predict welding-induced deformation in multi-seam welded pipe structures. Furthermore, compared with TEP-FEM simulation, the significant advantage of this approach is that the computing efficiency can be increased by about 50 times.

Method for Rapid Modeling of Distortion in Laser Powder Bed Fusion Metal Additive Manufacturing Parts

The simulation and modeling of part-level distortion and residual stress in diverse metal additive manufacturing (AM) geometries has great potential to enable the rapid adoption of this technology in engineering design. Moreover, the use of additive manufacturing component libraries (CLs) offer a computationally efficient means of quantifying these part-level defects resultant from AM processing. We report on how the individual simulations of simple shapes, potential entries in a CL, can be superimposed to provide an indication of distortion and residual stresses in complex geometries. Laser powder bed fusion AM was used to construct test geometries of varied shapes and their combinations in the form of CLs in an effort to characterize location-dependent and feature-dependent distortion distributions. Blue light scanning was used to experimentally measure 3D distortions in order to investigate the interaction between the component shapes and local boundary conditions. Overall, part-level distortions were highly dependent on test component geometry, local boundary conditions, and shape combination. Commercial finite element software was used to verify experimental trends and to make predictions of distortion. The use of CLs resulted in over 20 times savings in computational cost while reproducing overall trends in distortion for test geometry assemblies. Therefore, it is anticipated that the use of CLs for L-PBF AM geometries has demonstrated potential to facilitate efficient simulations of full component AM assemblies, thereby reducing the need for costly trial-and-error-type experimental analysis.

A Geometry-Based Welding Distortion Prediction Tool.

The prediction of welding distortion requires expertise in computer simulation programs, a clear definition of the nonlinear material properties, and mesh settings together with the nonlinear solution settings of a coupled thermal–structural analysis. The purpose of this paper is to present the validation of an automatic simulation tool implemented in Ansys using Python scripting. This tool allows users to automate the preparation of the simulation model with a reduced number of inputs. The goal was, based on some assumptions, to provide an automated simulation setup that enables users to predict accurate distortion during the welding manufacturing process. Any geometry prepared in a CAD software can be used as the input, which gave us much geometrical flexibility in the shapes and sizes to be modeled. A thermomechanical loosely coupled analysis approach together with element birth and death technology was used to predict the distortions. The automation of the setup enables both simulation and manufacturing engineers to perform welding-induced distortion prediction. The results showed that the method proposed predicts distortion with 80–98% accuracy.

Numerical investigation of tip-vortex cavitation noise of submarine propellers using hybrid computational hydro-acoustic approach

In this study, the hybrid computational hydro-acoustics (CHA) method is applied to predict hydrodynamic noise due to tip vortex cavitation (TVC) of underwater submarine propellers. The hybrid CHA approach consists of two sequential methods: Delayed Detached Eddy Simulation (DDES) technique with adaptive mesh refinement method and the Ffowcs Williams and Hawkings (FW–H) equation. The former is utilized for accurate prediction of TVC of underwater propellers, and the latter is used for efficient prediction of hydro-acoustic pressure due to cavitating flow. The target submarine and propeller are the DARPA suboff submarine and two high skew propellers with skew angles of 17 and 38°. The propellers are designed to investigate the effects of skew angle on TVC and its noise. The corresponding experiments are performed in the Large Cavitation Tunnel (LCT) of the Korea Research Institute of Ships and Ocean Engineering (KRISO). The two preliminary simulations are carried out to confirm the close reproduction of the experimental conditions in the main simulations. First, the flow through the LCT test section is simulated to confirm the accurate reproduction of the wall boundary layer. Its validity is confirmed by comparing the predicted boundary layer profiles with the measured results. Second, the flow over the DARPA suboff submarine without a propeller in the LCT test section is simulated to confirm the accurate prediction of the inflow distortion originating from the boundary layer flow of the submarine body. Its validity is also confirmed by comparing the predicted nominal wake field with the measured one. After the close reproduction of these two effects is confirmed, the cavitating flow of the propellers installed to the DARPA suboff submarine body is simulated by using the DDES technique combined with adaptive mesh refinement, and the TVC noise is predicted by applying the quadrupole-corrected FW-H equation to the surfaces enclosing the propellers. The predicted TVC of the propeller closely follows the measured one. The numerical and experimental results capture the TVC induced by the wake flows due to the submarine body's rudders and sail. The predicted hydro-acoustic pressure spectra due to the propellers' cavitating flow also show excellent agreements with the predicted ones. Besides, both the numerical and experimental results confirm that the lower noise is generated by the propeller with a higher skew angle.

Prediction of angular distortion due GMAW process of thin-sheets Hardox 450® steel by numerical model and artificial neural network

Angular distortions in high-strength steel, Hardox 450®, welded by gas metal arc welding (GMAW) single-pass butt welding process were analyzed in this work on different sizes and thicknesses thin plates. A backpropagation neural network (BPN) predicted the deformations. Finite element (FE) simulations and analytical formulation fed the input data of the neural network for a range of plate dimensions and levels of heat input. The 3D FEM model has been performed using the thermo-elastic-plastic model in Comsol Multiphysics. A sequence of experiments validated the numerical and analytical results, acquiring the geometry in cross-sections of the weld beads, thermal cycles, and structural deformations. This investigation focused on the relationship between the thermal cycle, the dilution percentage of filler metal, and the angular distortion. The results revealed that numerical models and artificial neural networks allow predicting the angular distortion produced in thin-walled Hardox 450® steel sheets according to their dimension for a defined interval of heat input.

Prediction of distortions and residual stresses in narrow gap weld joints prepared by hot wire GTAW and its validation with experiments

The present paper aims to predict distortions and residual stresses in thick plate weld joints of austenitic stainless steel material prepared by automatic hot wire gas tungsten arc welding (GTAW) process and narrow gap technique using finite element analysis (FEA). The prediction has been validated by carrying out experiments. The variables considered in welding of plate joints are narrow groove configuration, high deposition rate leading to lower heat input (hot wire GTAW), and stress relieving treatment. A suitable stress-relieving treatment has been proposed for relaxing residual stresses and preventing sensitization of the heat-affected zone (HAZ) of the ASS weld joint. Predicted and experimental results of temperature distribution, distortions, and residual stresses were found to be in good agreement. The applicability of prediction of residual stresses for higher weld thicknesses has also been verified. The nature of residual stresses across thickness has also been compared with that given in Structural Integrity Assessment Procedures for European Industry (SINTAP) and BS 7910 standards. Details of the above finding are discussed in this paper.

Recent Advances in the Prediction of Weld Residual Stress and Distortion - Part 2

Weld residual stress can contribute to the reduction of structure lifetime and accelerate the formation of fatigue cracks, brittle fractures, or stress corrosion cracking. Distortion can have a significant impact on the dimensional ac-curacy of assembly, structure strength, and fabrication cost. In the past two decades, there have been many significant and exciting developments in the prediction and mitigation of weld residual stress and distortion. This paper reviews the recent advances in mitigation techniques that have been applied in the structure design, manufacturing, and postweld stages. The techniques used in the structure design stage include selecting the type of weld joint and weld groove, using balanced welding, determining appropriate plate thickness and stiffener spacing, and considering distortion compensation. Mitigation techniques used in the manufacturing stage include welding sequence optimization, reducing welding heating input, selecting low-transformation-temperature filler metals, prebending, precambering, constraints, trailing and stationary cooling, in-processing rolling, transient thermal tensioning, and additional heat sources. Postweld mitigation techniques include postweld heating and mechanical treatment. Finally, the remaining challenges and new development needs were discussed to guide future development in the field of mitigating weld residual stress and distortion.

Geometry and Distortion Prediction of Multiple Layers for Wire Arc Additive Manufacturing with Artificial Neural Networks

Wire arc additive manufacturing (WAAM) is a direct energy deposition (DED) process with high deposition rates, but deformation and distortion can occur due to the high energy input and resulting strains. Despite great efforts, the prediction of distortion and resulting geometry in additive manufacturing processes using WAAM remains challenging. In this work, an artificial neural network (ANN) is established to predict welding distortion and geometric accuracy for multilayer WAAM structures. For demonstration purposes, the ANN creation process is presented on a smaller scale for multilayer beads on plate welds on a thin substrate sheet. Multiple concepts for the creation of ANNs and the handling of outliers are developed, implemented, and compared. Good results have been achieved by applying an enhanced ANN using deformation and geometry from the previously deposited layer. With further adaptions to this method, a prediction of additive welded structures, geometries, and shapes in defined segments is conceivable, which would enable a multitude of applications for ANNs in the WAAM-Process, especially for applications closer to industrial use cases. It would be feasible to use them as preparatory measures for multi-segmented structures as well as an application during the welding process to continuously adapt parameters for a higher resulting component quality.

Efficient Simulation Methods for Thermal‐Mechanical Coupled Analysis and Rapid Residual Distortion Prediction of Laser Melting Deposition Process

Herein, an improved thermal‐mechanical coupled analysis is used to increase the calculation efficiency of the detailed laser melting deposition (LMD) process. By optimizing the loading process of the laser heat source and lumping several deposited layers into an equivalent numerical layer, the efficiency is significantly improved. The calculation time is saved by 85% when lumping six layers. Compared with the experimental data, the minimum deviation of predicted maximum distortion reaches 3.2% when lumping four layers. A multiscale method is proposed to predict the distortion result of the large‐sized part efficiently. In this method, the optimal heights of equivalent numerical layers are explored. The comparisons with the experimental result show that the optimal heights of equivalent numerical layers are 1 and 1.5 mm in view of accuracy and efficiency. Based on the multiscale method, the residual distortion of the substrate after depositing a large‐sized eight‐layer line deposition structure is accurately predicted. The deviations of the maximum distortion predicted by the improved thermal‐mechanical coupled simulation and the multiscale method are 3.26% and 6.12%, respectively. Moreover, the calculation time of the latter is 98.8% less than that of the former.

Numerical investigation of novel process planning in the polymeric powder bed fusion

Multiple-laser and matrix-heat source exposures are emerging systems for powder bed fusion (PBF) to improve productivity. However, the newly available process planning such as scanning patterns may induce different transient thermal distribution and distortion in selective laser sintering or melting process. This work proposes novel scanning strategies for digital process planning in polymer PBF, including contour lines and novel inner scanning patterns. It provides detailed predictions of temperature gradient and distortion upon processing and the shrinkage/warping of printed components. Novel scanning strategies of subarea-sequential, subarea-parallel, and matrix-randomized scanning strategies are addressed here. The thermal-recrystallization-mechanical model for laser sintering is employed to reveal the underlying mechanism upon different process planning strategies. Thereafter, the matrix-randomized scanning mode can obviously reduce the building time of each layer into millisecond level. The advanced subarea-sequential scanning pattern is able to minimize shrinkage and warping. The systemic framework of digital process planning is provided through numerical investigation of scanning strategies and multi-physics modeling, which are an important aspect in the advanced digital twin of additive manufacturing.

Recent Advances in the Prediction of Weld Residual Stress and Distortion - Part 1

Residual stresses and distortions are the result of complex interactions between welding heat input, the material’s high-temperature response, and joint constraint conditions. Both weld residual stress and distortion can significantly impair the performance and reliability of welded structures. In the past two decades, there have been many significant and exciting developments in the prediction and mitigation of weld residual stress and distortion. This paper reviews the recent advances in the prediction of weld residual stress and distortion by focusing on the numerical modeling theory and methods. The prediction methods covered in this paper include a thermo-mechanical-metallurgical method, simplified analysis methods, friction stir welding modeling methods, buckling distortion prediction methods, a welding cloud computational method, integrated manufacturing process modeling, and integrated computational materials engineering (ICME) weld modeling. Remaining challenges and new developments are also discussed to guide future predictions of weld residual stress and distortion.

Prediction of part distortion in Fused Deposition Modelling (FDM) of semi-crystalline polymers via COMSOL: Effect of printing conditions

Residual stresses and warpage adversely affect the dimensional accuracy and performance of 3D-printed semi-crystalline polymers in Fused Deposition Modelling (FDM). One of the main challenges in FDM is to understand and relate the impact of printing conditions on part distortion for optimizing the 3D-printing process to achieve good print quality. Hence, the effect of various printing parameters, particularly print bed temperature, layer bonding, layer thickness and raster pattern, on built-up residual stresses and warpage is simulated in this work, by building a relationship between the crystallisation kinetics, viscoelastic and thermo-mechanical properties of the polymer in relation to changes in temperature during FDM using element activation in COMSOL. To the best of our knowledge, this is a novel approach for quantitative prediction of part distortion in FDM of semi-crystalline polymers under various printing conditions. Based on the simulation results, it is observed that a decrease in layer thickness from 0.5 mm to 0.1 mm results in an 89% drop in warpage and a reduction in residual stress of 24%. Applying a line raster pattern reduces warpage and residual stresses by 16% and 36%, respectively in comparison with a zigzag raster pattern. Very good agreement is observed between simulation and experimental results for warpage under various printing conditions. The results of this study can be used to predict and/or minimise part distortion in a semi-crystalline, 3D-printed polymer by simulating the effect of printing parameters on residual stresses during FDM.

Finite Element-Based Simulation of Metal Fused Filament Fabrication Process: Distortion Prediction and Experimental Verification

Building end-use functional metal parts by metal fused filament fabrication (MF3) is an emerging topic in additive manufacturing. MF3 involves extrusion of polymer filaments that are highly filled with metal powder to print three-dimensional parts, followed by debinding and sintering to eliminate the polymer binder and get a fully dense metal part, respectively. Material properties, part design and processing conditions have a significant influence on the quality of MF3 printed parts. Part distortion and dimensional variations are significant quality challenges that hinder the acceptance of printed parts in potential functional applications. Trial-and-error experiments to find the best conditions are commonly used for defect avoidance, though they are time-consuming and expensive. Hence, computational simulation and design solutions are required for MF3 to enable a virtual analysis of the process outcome and reduce dependency on experimental methods. This paper investigates the applicability of a thermo-mechanical model for finite element simulation of the MF3 printing process. The quantitative influence of material properties on MF3 printed part quality was estimated using a simulation platform. The simulation results of two materials, a Ti-6Al-4V filled polymer and an unfilled ABS copolymer, were compared to experiments. It was determined that the unfilled polymer showed greater shrinkage and warpage than the Ti-6Al-4V filled polymer in simulations and experiments. Further, the trend in the distribution of warpage was consistent between experiments and simulation results for both materials. Finally, warpage compensation algorithms showed improvement in dimensional control for both materials in simulations and were consistent with experimental results.

An analytical gm/ID‐based harmonic distortion prediction method for multistage operational amplifiers

SummaryAn analytical stage‐based harmonic distortion (HD) analysis method for multistage operational amplifiers (Op Amps) is developed in this work. This work contributes two fundamental methods that make the analytical HD prediction possible at the circuit level. Firstly, we propose that the traditionally used first order small‐signal transistor quantities gm (transconductance) and go (output conductance) in the gm/ID design methodology for bulk complementary metal‐oxide‐semiconductor (CMOS) technology can be extended to the higher order quantities gm(k) and go(k) ( ). With proper normalization, these quantities become neutral to the device dimensions and operation currents, hence can be precharacterized by sweeping simulations and used as lookup tables. Secondly, we further develop analytical nonlinearity expressions for a set of commonly used amplifier stages, represented as the functions of the nonlinearity parameters gm(k) and go(k) of the transistors that form a stage circuit. A combination of these two fundamental methods on hierarchical nonlinearity modeling enables us to apply the existing analytical HD estimation methods for the stage‐form macromodels to predict the circuit‐level HD behavior, overcoming the need of running repeated simulations under device resizing and rebiasing. The proposed harmonic distortion analysis method has been validated by application to real multistage amplifiers, achieving HD prediction results in excellent agreement to fully transistor‐level circuit simulation results but with substantial speedup.

Effect of clad height, substrate thickness and scanning pattern on cantilever distortion in direct metal deposition

In metal additive manufacturing, moving heat sources cause spatial and time-dependent variations of temperature and strain that can lead to part distortions. Distortion prediction and optimized deposition parameters can increase the dimensional accuracy of the generated components. In this study, an analytical approach for modeling the effect of clad height and substrate thickness is experimentally validated. Additionally, the influence of the scanning pattern as a function of clad height and substrate thickness is determined experimentally. The analytical model is based on the cool-down phase mechanism and assumes the formation of constant thermal shrinking forces for each deposited layer. The model accurately predicts longitudinal cantilever distortion after experimental calibration when compared with similar experimental conditions. For multi-layer deposition, the scanning pattern has the largest influence on distortion for thin-walled substrates. An optimized deposition strategy with longitudinal scanning vectors leads to a distortion reduction of up to 86%. The results highlight the potential of mechanical modeling and scanning strategy optimizations to increase the shape accuracy for industrial applications in the field of additive manufacturing.

In-Situ Distortion Prediction in Metal Additive Manufacturing Considering Boundary Conditions

Undesired distortion often occurs in metal additive manufacturing due to the high temperature gradient resulting from repeated thermal cycles. A good understanding and fast predictions of in-situ distortion are essential to achieve high dimensional accuracy and prevent delamination or failure of build parts. Experimental investigations and numerical methods have been employed to study the in-situ distortion. However, the complex measurement systems and high computational cost limit their applications. An analytical modeling method with closed-form solutions is proposed in this paper to predict the in-situ distortion of laser cladding process without using iteration-based numerical calculations. The effects of build edges and geometry are considered, which include thermal convection and radiation at boundaries. Heat input and heat sink solutions modified from the point moving heat source model are added together to predict the temperature profile of the build and substrate. The die-substrate assembly model is used to calculate the deflection during the manufacturing process. Alloy 625 is selected to test the predictive accuracy and computational efficiency of the presented analytical model. The predicted results are close to the experimental data of in-situ distortion in literature. The computational time is less than 30 s. The good predictive accuracy and low computational cost make the presented method a promising approach to study the full-field temperature and distortion of a geometrically complex part.

Fast additive manufacturing distortion prediction using backward interpolation

Powder Bed Fusion Additive Manufacturing (PBFAM) processes have emerged as important industrial processes that are capable of manufacturing complicated part features, such as hollow designs, lattice structure and other unique design structures. The current state of computing technology requires significant time to predict the part distortion formed during the PBFAM build process. In this paper, a novel Backward Interpolation (BI) model is presented for fast estimation of part distortion based on build process parameters. In the Backward Interpolation approach, we propose the concept of distortion factor that represents the distortion contribution of unit forces on the node to all other nodes that have equal or lower height in the FEM mesh. To start with, the CAD model is meshed in a layer by layer manner and the FEM model is voxelized and sliced for calculating the distortion factor. Next, the as-built distortion before cutoff from the substrate is calculated based on distortion factors and the internal forces generated by the inherent strain of the voxel. Subsequently, the spring back distortion is calculated, and the total part distortion is then finally determined as the summation of part distortion and the spring back distortion. An experimental validation of the methodology was conducted, and the predicted distortion results appeared to agree well with the distortion obtained from the built part. The comparison of distortion obtained from Backward Interpolation and distortion data from published work was further used to validate this algorithm. The computational efficiency of the proposed Backward Interpolation method was evaluated using an example part and demonstrated that the part distortion values were obtained within a few minutes using a desktop computer, confirming the significant decrease in computing time using this approach.