Part Distortion Research Articles

Study on the effect of multi-point stretch-bending processing conditions on the section distortion of complex cross-sectional parts

Section distortion is a common defect in plastic forming, however, excessive section distortion will affect the actual use of the workpiece. In this paper, the finite element software ABAQUS is used to simulate the multi-point flexible stretch-bending process. Processing parameters are important factors in the forming process of the profile, so this paper discusses the effects of three processing parameters, namely the effects of pre-stretching amount, pro-stretching amount and friction coefficient on section distortion under different bending radius, taking the complex cross-sectional T-profile as an example. And the validity of the simulation results is verified by comparing with the experimental results and the simulation results. At the same time, the upper limit value of section distortion is given according to the actual assembly and use of aluminium profile components of high-speed train head frame, and the minimum bending radius (i.e., processing limit) for which the section distortion does not exceed the given value under different process parameters is explored and used for practical production guidance.

A numerical formalism towards finding a good component orientation in laser powder bed fusion

• Mathematical formulation of several of objectives considered when deciding how to orient a part during LPBF. • Consideration of printing cost as a metric affecting orientation decisions. • Reduction of complex distortion and residual stress results to a representative variable manageable by multi-objective optimization. • Discontinuity in distortion and residual stress results make it difficult to use machine learning tools. Monte-Carlo optimization is not as sensitive to discontinuities. • The frequency of distortion computations is analyzed to achieve reasonably reliable predictions with least possible computational effort. Several manufacturing constraints and objectives are considered when choosing a build orientation for laser powder bed fusion (LPBF) parts. Some of them are inversely proportional to one another making it necessary to formalize an optimization scheme with weighting factors enabling engineers to decide which of them is most relevant for the application under consideration. Several of the considered cost functions are quick to calculate (e.g. down skin area). The reduction of residual stresses and distortion are on the other hand computationally intensive and are not easily considered in an optimization scheme. Solution sampling in 3 angular directions is therefore utilized to create a response surface describing the part distortion in arbitrary orientations. The response surface accuracy is studied before applying it together with 7 other cost functions within a multi-objective Monte-Carlo optimization scheme.

Aortic root reinforcement using the Florida sleeve technique in a patient with acute aortic dissection type A

Stanford type A acute aortic dissection is an inherently lethal condition that is regarded as a surgical emergency. The Bentall procedure is considered the gold standard for patients requiring aortic root replacement. However, this method can be technically difficult for less-experienced surgeons. Complications encountered after composite graft replacement include distortion of the proximal part of the coronary artery, bleeding from the conduit implant site, and reattached coronary artery origins caused in general by a consumption coagulopathy. In cases for which aortic valve preservation is not applicable and the root is not dissected or dilated, surgeons often opt for less complicated techniques like aortic valve and supracoronary ascending aortic replacement. Nevertheless, these patients carry a high risk of late aortic root dilatation and subsequent reoperation. The goal of aortic root reinforcement by the Florida sleeve technique is to encase the aortic root to prevent any further dilatation and perioperative bleeding.

Influence of Ambient Temperature on Part Distortion: A Simulation Study on Amorphous and Semi-Crystalline Polymer.

Semi-crystalline polymers develop higher amounts of residual stress and part distortion (warpage) compared to amorphous polymers due to their crystalline nature. Additionally, the FDM processing parameters such as ambient temperature play an important role in the resulting residual stresses and part distortion of the printed part. Hence, in this study, the effect of ambient temperature on the in-built residual stresses and warpage of amorphous acrylonitrile-butadiene-styrene (ABS) and semi-crystalline polypropylene (PP) polymers was investigated. From the results, it was observed that increasing the ambient temperature from 50 °C to 75 °C and further to 120 °C resulted in 0.22-KPa and 0.37-KPa decreases in residual stress of ABS, but no significant change in the amount of warpage. For PP, increasing ambient temperature from 50 °C to 75 °C led to a more considerable decrease in residual stress (0.5 MPa) and about 3% increase in warpage. Further increasing to 120 °C resulted in a noticeable 2 MPa decrease in residual stress and a 3.4% increase in warpage. Reduction in residual stress in both ABS and PP as a result of increasing ambient temperature was due to the reduced thermal gradients. The enhanced warpage in PP with increase in ambient temperature, despite the reduction in residual stress, was ascribed to crystallization and shrinkage.

Numerical Simulation of Welding Distortion in Laser Metal Deposition Additive Manufacturing Process

The article presents the simulation of part distortion during laser metal deposition and a comparison of its results with the deposition performed in experiment. A numerical methodological approach to simulation is viewed which involves dividing the deposited material into primitive solids and further heating and cooling of each primitive solid along the deposition trajectory instead of simulating a moving heat source.

Reducing lateral stair-stepping defects in liquid crystal display-based vat photopolymerization by defocusing the image pattern

Vat photopolymerization-based additive manufacturing (AM) technology has emerging success in efficiently fabricating complex and high-resolution objects. However, the lateral and vertical stair-stepping defects limit vat photopolymerization in manufacturing smooth surfaces, such as optical components. Vertical stair-stepping was mitigated by thinner layer thickness or layer-less fabrication. It is still challenging to reduce the lateral stair-stepping defects caused by the pixelated projection pattern, especially for Liquid Crystal Display (LCD) projection whose pixels are disconnected. To tackle this lateral stair-stepping issue, we propose to defocus the curing image pattern by increasing the gap between the LCD screen and the resin vat. This gap intentionally blurs the disconnected pixels to create a continuous and smooth projection pattern. Experiments verified that the smoothened LCD pattern led to an average 81.2% reduction in surface roughness, which was much more effective than grayscale pixels. The gap between the LCD screen and the resin vat also enabled blowing air to dissipate the heat from LCD and the resin polymerization, reducing the part distortion and printing failure due to the thermal stress. The present approach improved the surface roughness and paved the way for vat photopolymerization in fabricating smooth micro-optics, microfluidic channels, and functional curved surfaces.

Uncertainty calibration and quantification of surrogate model for estimating the machining distortion of thin-walled parts

Uncertainty calibration and quantification of surrogate model for estimating the machining distortion of thin-walled parts

Characterization and modeling cure- and pressure-dependent thermo-mechanical and shrinkage behavior of fast curing epoxy resins

A fast crosslinking reaction is crucial for the economical production of automotive components in liquid composite molding (LCM) processes. Although a large number of works have focused on modeling of shrinkage induced surface waviness and part distortions and the underlying phenomena an accurate determination of material properties under consideration of processing parameters still represents a major challenge for fast-curing epoxy resins. Fast-curing epoxy polymers allow manufacturing of thermoset composite parts in minutes while entailing a highly exothermic heat generation. Cure is carried out under elevated temperatures and pressures and is accompanied by a change in density due to chemical shrinkage and followed by thermal contraction. In the present study, comprehensive results on the characterization of thermo-mechanical properties, pressure dependent reaction kinetics and shrinkage are presented for a fast curing epoxy resin. The obtained results give important advice for improved process modeling and facilitate prioritisation for future characterisation of fast-curing epoxy resins.

Finite element simulation on residual stress during immersion quenching and pre-stretching of Al7055 thick plates

During the immersion quenching process, severe temperature changes and significant temperature differences between the core and superficial area can give rise to high residual stresses within the aluminum alloy thick plate to cause subsequent machining distortion of the thin-walled part. Reducing the residual stress within the thick plate can effectively minimize the distortion in part. In this research, ABAQUS software was adopted to simulate the internal temperature and stress fields of thick plates of Al7055 alloy during the quenching and pre-stretching processes, sequentially and respectively. In addition, the x-ray residual stress measurement method was used to measure and characterize the surface residual stress of the plates. The results indicate that the medium temperature affects residual stress inside the thick plate significantly during the immersion quenching process. The level of which inside the plate gradually increases as the medium temperature decreases. Further, the pre-stretching treatment can effectively reduce residual stresses within the thick plate, and the residual stress level gradually decreases with the pre-stretching ratio increasing. The experimental results verify the feasibility of numerical simulation to predict the status of quenching stress in thick plates. Subsequently, a simulation study for material removal processes was carried out based on the above studies. The results reveal that the thin-walled part’s machining distortion degree improves as the raw thick plate’s initial quench residual stress level decreases.

Predicting part distortion field in additive manufacturing: a data-driven framework

Predicting part distortion field in additive manufacturing: a data-driven framework

Development of High-Entropy Alloy Coating by Additive Technology

In this research study, various additively fabricated coatings and bulk 3D-printed parts were prepared, using the mechanical and corrosion-resistant properties of CrMnFeCoNi (Cantor alloy) and AlCrMnFeNi high-entropy alloys (HEAs). The coatings were applied to an EN 1.0038 carbon steel substrate using direct metal laser sintering. We attempted to optimize the 3D printing parameters of HEA alloys. The effect of volumetric energy density (VED) on the microstructure was investigated by scanning electron microscopy. We also examined the change of relative concentration of alloys in the direction of 3D printing (z-axis) as well as the volumetric failures (cracks and gaps). Standard salt spray tests were performed to test the corrosion resistance of various coatings after 3D printing. The use of both raw materials applied as thick films was successful; they retained their corrosion-resistant properties even with a change in their composition. Regarding the crystal structure, no difference was found between the base material and the material applied as a coating on the basis of X-ray diffraction investigations. Bulk HEA printing experiments need further optimization concerning their structural integrity and density in the case of the Cantor alloy. Bulk 3D printing experiments of the AlCrMnFeNi alloy did not yield satisfactory results because of the formation of dendritic microstructure and brittle BCC phase, and the residual internal stress resulted in part distortion and improper printing.

Precise machining based on Ritz non-uniform allowances for titanium blade fabricated by selective laser melting

Selective laser melting (SLM) is an increasingly concerned trend in Ti-6Al-4V blade manufacturing, while the SLMed Ti-6Al-4V blade cannot be used directly because of poor surface integrity and high residual stresses. Precise machining after SLM is a feasible solution but also a challenge. The low rigidity of the blade will lead to deformation when machining. The deformation can lead to surface error and may make defect parts. Two-step machining processes to address the problems were proposed in this paper. First, a non-uniform allowances distribution was allocated and optimized in semi-finishing based on Ritz solution to elastic deformation. The blade was simplified as a cantilever thin plate with various thicknesses, and the thicknesses of finishing allowances were designed and optimized on the premise of ensuring the thin-wall stiffness of the blade, so as to realize the design of Ritz non-uniform allowances. Then, finishing machining was conducted to achieve precise parts. A blade deformation model was established to evaluate part distortions with cutting force moving and changing. Finite element analysis (FEA) and experimental validation in ball-end milling of a blade were conducted. FEA results and experimental results showed dimensional errors have been reduced up to 50%. Further surface tests demonstrated that the mean surface roughness reduced from 7.88 to 0.815 μm. And the residual surface stresses of the SLM samples changed after semi-finishing machining due to the residual stresses relaxation and redistribution. The results demonstrated that the proposed method enhanced the surface quality of the blade fabricated by SLM.

A low-cost open-source automated shot peen forming system

The aerospace industry relies on shot peen forming to form sheet metal parts and correct distortion in machined parts. The shot peen forming community is developing simulation and planning methods to meet the industrial need for automation. Researchers need to invest in expensive industrial robots contained in large blasting cabinets to perform the experimental validations of their proposed methods. To bypass this need for expensive industrial-grade equipment, this work presents a low-cost shot peen forming system that enables researchers to validate their methods experimentally on small samples. Conventional installations can cost a few 100,000 USD while the proposed prototype only costs 400 USD to produce. Such a prototype can operate on a tabletop with conventional electrical installations. The use of small samples for validation further reduces the cost of experiments and allows for faster development.

Experimental and simulative determination of residual stress during heat treatment of 7075-T6 aluminum

Part distortion is caused by the release and redistribution of the residual stresses generated by machining and manufacturing processes applied before machining. This work aims to simulate part distortion in machining of 7075-T6 aluminum alloy. A model of heat treatments (quenching and tempering) has been developed by FEM and validated using the removal layer and contour methods. This model was applied to predict the residual stresses distributions generated by heat treatments. These stresses distributions were used in a machining model to simulate part distortion. Then, the comparison between the simulated and measured distortions permitted to validate the methodology.

Distortion discrepancy of large-scale components in electron beam melting processes

Amongst many factors that hinder the industry from adopting additive manufacturing technology, dimensional printing error and thermal distortion are crucial, especially for large-scale components (length > 100 mm). Although residual stress in an electron-beam melting (EBM) printed part is relatively low, part distortion cannot be neglected in quality control and post-processing. To investigate distortion rules of EBM parts along the X and Y direction of the build plate, a series of L shape beams, with a length of 130 mm in both X and Y, were designed, printed, and characterized. Both 3D scanning and multi-functional coordinate-measuring machine (CMM) were used to measure designed hexagonal marks with a 10 mm interval along part gauge length. The dimensional error between designed and printed parts was calculated and analyzed. Results showed that the beams shrank orthotopically in terms of X and Y directions in discrepant rules. In the X direction, total shrinkage was around 0.7 %, accumulating with a stable increment. While in the Y direction, the shrinkage was indistinctive without apparent accumulation. We observed a slight wall thickness effect on shrinkage non-uniform accumulation in the X direction. Thin wall structures (T = 1 mm and 2.5 mm) distorted more at the beginning 40 mm of the part length from the origin point than the rest to the rear end. On the other hand, thick wall (T = 10 mm) distorted more at the rear end.

Assessment of the cartesian and layered tetrahedral mesh strategies in the thermomechanical simulation of the selective laser melting process

Selective Laser Melting (SLM) is an Additive Manufacturing (AM) process aimed for the fabrication of complex metallic parts. Due to the inherent to the process rapid thermal cycles and the developed high temperature gradients, residual stresses are formed which result to part distortion and may lead to preliminary failure during its building. Current thermomechanical modelling methods of the SLM process aim at the prediction of residual stress and strain fields in an efficient manner. Meshing schemes such as uniform or adaptive cartesian and layered tetrahedral meshing have been utilized in thermomechanical modelling but their accuracy has not been evaluated yet. The present study quantitively assess the meshing strategies in the simulation of SLM process with the focus placed on the characteristics of layered tetrahedral meshing. Although it is shown both meshing strategies lead to accurate results for a relatively small element size, layered tetrahedral meshing strategy can achieve convergence with relative coarse mesh and better discretization of curvature regions.

Investigation of residual stresses and microstructure effects on the fatigue behaviour of a L-PBF AlSi10Mg alloy

Al-Si alloys produced by Laser Powder Bed Fusion (L-PBF) techniques allow the fabrication of lightweight free-shape components that find space in aerospace, automotive, biomedical and military applications. Due to the high cooling rates occurring during the building process, L-PBF AlSi10Mg alloys exhibit an ultra-fine microstructure that leads to superior mechanical properties in the as-built condition compared to conventional cast Al-Si materials. Nevertheless, L-PBF processing induces high thermal gradients, leading to deleterious residual stress levels that must be considered to avoid part distortion and unpredicted failures. In order to relax detrimental residual stress and to increase the ductility, post-processing stress relief treatments are generally performed. In as-built condition the hypoeutectic AlSi10Mg microstructure consist of fine α-Al cells containing uniformly dispersed silicon nanoparticles, which are, in addition, surrounded by a eutectic Si network. Above 260°C the silicon interconnectivity starts to breakdown into spheroidized particles and to coarsen. At the same time, the heating residual stresses are relieved.The objective of the contribution is to investigate, under different heat treatment conditions, the evolution of microstructure and residual stresses in view of optimizing the fatigue performance of the alloy. To this purpose various heat treatments in a range of temperatures between 265°C and 300°C for a duration between 15 minutes and 2 hours are performed. The microstructure modifications are analysed using a scanning electron microscope and the residual stress state is measured by laboratory X-ray diffraction.

Residual stress characterization during laser-based Directed Energy Deposition using in-situ digital image correlation based on specular light reflection on as-built surfaces of thin walls

Residual stresses present one of the major challenges within additive manufacturing as they lead to part distortion and cracking, production issues, scrapped parts and mechanically underperforming components. The current work presents a method to determine full-field residual stress information by deploying in-situ Digital Image Correlation during the Directed Energy Deposition process of thin walls. In an attempt not to disturb the process to apply the typical ‘speckle pattern’, the correlation analysis is based on the specular light reflection of active lighting on the as-built surface of thin walls under construction. This approach allows the continuous monitoring of the thermally induced stresses, both during the actual deposition process as well as during the subsequent cooldown phase. The method presents significant time-savings while providing maximized insight in the formation process of residual stresses. The manuscript presents the used test configuration, initial proof-of-concept results along with an accuracy estimation of the used method.

Towards Geometry Prediction in Additive Manufacturing by Considering Variation in the Inherent Strain

The inherent strain method is commonly employed to predict part distortion in the additive manufacturing (AM) process simulations. However, mean inherent strain values are considered which could hinder the prediction accuracy. Therefore in this paper, variation in inherent strain values are considered to predict the geometric distortion. In the first step, a five layer mesoscale thermo-mechanical model is employed to estimate the varying inherent strain values in each of the five layers. This serves as an input to the inherent strain method to predict geometric distortion at the part level. A comparison between mean versus varying inherent strain approach is shown to highlight the differences in geometric distortion prediction accuracy.

Crystal mechanics-based thermo-elastic constitutive modeling of orthorhombic uranium using generalized spherical harmonics and first-order bounding theories

In earlier works, a mathematical procedure for invertible microstructure-property linkages was developed using computationally efficient spectral methods for polycrystalline cubic and hexagonal metals. This paper formulates such invertible microstructure–property linkages for orthorhombic polycrystalline metals relying on the generalized spherical harmonics (GSH) spectral basis. The procedure is used to compute property closures of orthorhombic polycrystals. The closures represent the complete set of theoretically possible combinations of effective properties for a selected material. The procedure relies on the first-order bounding theories and considers orientation distribution functions (ODFs) as the main microstructural descriptor influencing homogenized properties. Numerous examples of these closures involving second-rank thermal expansion and fourth-rank elastic stiffness tensorial properties over a broad range of temperatures are presented for α-uranium (α-U). In doing so, certain key properties of these closures are exploited to facilitate their computation with drastically reduced computational effort. Along with the recently developed GSH-based interpolation procedure for ODFs from coarsely spaced experimental measurement grids to finely spaced finite element mesh resolution grids presented in Barrett et al., the developed computationally efficient ODF-effective property linkages are used to establish a crystal mechanics-based simulation framework coupled with the finite element method (FEM). The ODF dependent thermal expansion and elastic stiffness tensors are efficiently calculated at every integration point and used by the FEM to predict the overall distortion of a hemispherical part made of α-U during heating. It is shown that the developed framework can be used to simulate microstructurally heterogeneous components under thermo-mechanical loadings in a computationally efficient manner.