Deformable Part Research Articles

Investigation of thermal deformation and surface microstructure of wire electrical discharge machining for thin-walled rare-earth gadolinium

Rare-earth gadolinium (Gd) has excellent magnetocaloric properties. High-aspect-ratio arrays of thin-walled parts processed with rare-earth Gd are typical structures for regenerators, which are the core components of magnetic refrigeration. Wire electrical discharge machining (WEDM) offers significant advantages for manufacturing micro-structured parts. However, in WEDM, materials are thermally ablated, which leads to compromised surface quality and significant thermal deformation in thin-walled structures with low stiffness. In this study, the effects of different process parameters on the thermal deformation and surface microstructure of rare-earth Gd thin-walled parts were studied by single-factor experiments. It was found that the pulse-on time, open voltage, and water pressure had prominent effects on thermal deformation. Lowering the pulse energy can effectively reduce the thermal deformation and oxidation of the samples and improve the machined surface quality. Through the SNR analysis of the thermal deformation and surface roughness results for the optimized experimental sample, the optimal processing parameter combination of rare-earth Gd thin-walled structure regenerator with high-aspect-ratio of 38 was determined. It was proved that the thermal deformation of thin-walled parts can be controlled within 20 μm by using the combination of optimal thermal deformation parameters, including a pulse-on time of 0.5 μs, pulse-off time of 25 μs, peak current of 12 A, open voltage of 95 V, and a water pressure of 0.22 MPa.

English translation of Giesekus's famous article on flows with constant velocity gradient and the motion of particles suspended therein. Part I. Spatial flows

Within the framework of a statistical rheology of suspensions, emulsions, and solutions, it is important to obtain an overview of the total set of flows with a constant velocity gradient. Therefore, the solutions of the differential equations of such flows are given and discussed especially with respect to the influence of the deformation and rotation parts of the velocity gradient. Subsequently, the motion of rigid particles in these flows is analyzed. Both the flow types themselves and the types of motion of the suspended particles can be divided into two broad classes. Among those with predominant deformation influence, we have hyperbolic–parabolic flows as well as a setting of the particles in fixed directions. Among those with predominant rotational influence, we have elliptical–spiral flows as well as a non-uniform orbital motion of the particles. The change from one place of motion to the other depends not only on the shape of the flow but also on the shape of the particles. Deformation becomes stronger as the form anisotropy of the particles increase.

Influence of deposition path strategy on residual stress and deformation in weaving wire-arc additive manufacturing of disc parts

Deposition pattern and path-planning deposition strategy have significant impacts on the deformation and residual stress of components during a wire-arc additive manufacturing (WAAM) process. This work comparatively addressed the influence of weaving and non-weaving deposition patterns on the distributions of residual stress and warping deformation during a single-bead-on-plate WAAM process. Further, four path strategies with different deposition sequences (in-out and out-in) and deposition directions (alternate and consistent) were designed for a weaving WAAM process of disc part, and their impacts on temperature history, warping deformation, and residual stress were comparatively analyzed through thermal-mechanical coupling finite element (FE) method. Simulation and experiment results manifest that, compared to the non-weaving pattern, the weaving deposition pattern results in more uniform deformation and lower residual stress on the deposited plate due to wider and shallower molten pool. Comparison results for the four deposition path strategies in the weaving WAAM process of disc part suggest that the out-in deposition sequence exhibits faster heat dissipation and uniform temperature field during the cooling stage, resulting in reduced warping deformation and residual stress on the workpiece. Moreover, uniform deformation is observed across path strategies employing alternate deposition direction. The out-in alternate deposition path strategy was identified as the optimal choice for the weaving WAAM process of disc part. Finally, physical experiments validated the simulated warping deformation of disc parts under different deposition path strategies. This work contributes to the design and optimization of weaving WAAM process for disc-shaped components.

Towards Zero-Defect Manufacturing Based on Artificial Intelligence through the Correlation of Forces in 5-Axis Milling Process

Zero-Defect Manufacturing (ZDM) is a promising strategy for reducing errors in industrial processes, aligned with Industry 4.0 and digitalization, aiming to carry out processes correctly the first time. ZDM relies on digital tools, notably Artificial Intelligence (AI), to predict and prevent issues at both product and process levels. This study’s goal is to significantly reduce errors in machining large parts. It utilizes data from process models and in situ monitoring for AI-driven predictions. AI algorithms anticipate part deformation based on manufacturing data. Mechanistic models simulate milling processes, calculating tool deflection from cutting forces and assessing geometric and dimensional errors. Process monitoring provides real-time data to the models during execution. The research focuses on a high-value component from the oil and gas industry, serving as a test piece to predict geometric errors in machining based on the deviation of cutting forces using AI techniques. Specifically, an AISI 1095 steel forged flange, intentionally misaligned to introduce error, undergoes multiple milling operations, including 3-axis roughing and 5-axis finishing, with 3D scans after each stage to monitor progress and deviations. The work concludes that Support Vector Machine algorithms provide accurate results for the estimation of geometric errors from the machining forces.

CatFormer: Category-Level 6D Object Pose Estimation with Transformer

Although there has been significant progress in category-level object pose estimation in recent years, there is still considerable room for improvement. In this paper, we propose a novel transformer-based category-level 6D pose estimation method called CatFormer to enhance the accuracy pose estimation. CatFormer comprises three main parts: a coarse deformation part, a fine deformation part, and a recurrent refinement part. In the coarse and fine deformation sections, we introduce a transformer-based deformation module that performs point cloud deformation and completion in the feature space. Additionally, after each deformation, we incorporate a transformer-based graph module to adjust fused features and establish geometric and topological relationships between points based on these features. Furthermore, we present an end-to-end recurrent refinement module that enables the prior point cloud to deform multiple times according to real scene features. We evaluate CatFormer's performance by training and testing it on CAMERA25 and REAL275 datasets. Experimental results demonstrate that CatFormer surpasses state-of-the-art methods. Moreover, we extend the usage of CatFormer to instance-level object pose estimation on the LINEMOD dataset, as well as object pose estimation in real-world scenarios. The experimental results validate the effectiveness and generalization capabilities of CatFormer. Our code and the supplemental materials are avaliable at https://github.com/BIT-robot-group/CatFormer.

A preliminary study on multi-material fused filament fabrication of an embedded strain gauge for low-cost real-time monitoring of part strain

Unlike other manufacturing techniques, additive manufacturing enables part consolidation through the production of multi-material parts with enhanced functionality. With reference to the functionality of monitoring the structural integrity of a product during its use, conductive filaments can be used in additive manufacturing. This work aims to investigate the applications of multi-material fused filament fabrication to produce embedded strain gauges for real-time monitoring of part deformations. In layer-by-layer fabrication, conductive filaments can be used to produce strain-sensitive elements inside products at a low cost. This preliminary study demonstrated the feasibility of the proposed approach using tensile samples fabricated through additive manufacturing. The samples were produced using a polyethylene terephthalate glycol filament and an acrylonitrile styrene acrylate filament, while electrically conductive polylactic acid was used for the strain gauge. The characterization and testing activities were conducted by comparing the results of the tensile testing with data acquired through an experimental system set up with an Arduino board, aligning with the resistance-based strain gauge theory. The findings show that the co-fabricated strain gauge successfully traces part deformation, enabling real-time monitoring of strain in the elastic field. Nevertheless, further optimization of the proposed approach is imperative to enhance the reliability and accuracy of the methodology.

Spatiotemporal difference of deformation and failure affected by a large discontinuity in the surrounding rock mass: A case study at the Baihetan underground powerhouse

The deformation and failure of the surrounding rock mass is a key issue during the construction of large‐scale underground powerhouse, and large discontinuities are likely to cause this problem in the presence of complex geological structures. This article takes the right bank underground powerhouse of the Baihetan Hydropower Station as a case study. In this case, deformation mutation of the surrounding rock mass occurred in the south section of the main powerhouse, with the maximum deformation reaching 178 mm, and the deformation and failure of different parts showed differences. A comprehensive study integrating field survey, site monitoring, laboratory test and numerical simulation was carried out. By field survey and monitoring, characteristics of deformation and failure are described, and the spatiotemporal difference in deformation is analysed. The stress evolution during excavation is studied based on numerical simulations, the mechanical response of rock is derived through laboratory tests, and the mechanism of spatiotemporal difference is revealed. The results indicate that the main reason for the spatiotemporal difference is the presence of slightly inclining interlayer shear zone C4. In the south section, the excavation‐induced stress concentration at the arch was enhanced due to C4, with the maximum principal stress exceeding 70 MPa, and the high compressive stress here triggered the deformation mutation of surrounding rock mass. After undergoing a stress path from concentration to unloading, the surrounding rock mass at the downstream sidewall was seriously damaged, and its deformation also mutated under approximately vertical stress. The mutation resulted in the uneven spatial distribution, large increment and time‐dependent feature of deformation.

Enabling fast debinding of ceramic vat photopolymerization prints with supercritical carbon dioxide as a solvent

Thermal debinding of 3D-printed ceramics that include a large fraction of polymeric binders, can take several days to perform, and often includes a long thermal pre-conditioning step. In addition, means to reduce the manufacturing time are limited. This applies for thermal debinding of dense ceramics, such as dental restorations, that have been printed using vat photopolymerization (VPP) based technologies. The thermal debinding of such ceramics can be made faster, more economical, and more ecological by extracting selected slurry components prior to thermal debinding. Thus, creating flow channels for pyrolysis gases originating from the remaining binder polymers to exit the material. Here, supercritical carbon dioxide (scCO2) extraction was used to create such gas flow channels and to study which slurry components can be dissolved from VPP printed polymeric and ceramic/polymeric parts without significant delamination, cracking, or part deformation. The scCO2 extraction resulted in the creation of significant 33 vol% of nanosized porosity in a pure polymeric as-built print, and 21 vol% of nanosized porosity in a ceramic/polymeric composite print, where the ceramic powder remains in the part. These gas flow channels may allow faster thermal debinding while avoiding the creation of other defects. In the process, 90 wt.-% of the dissolvable resin fraction was extracted from the ceramic/polymeric prints already in 2 h without significant delamination, while 70 wt.-% of the dissolvable resin fraction was extracted in 2 h from the pure polymeric prints as a reference. This presents a novel, successful demonstration of a chemistry that allows both VPP printing and scCO2 extraction.

Exploring the possibility of undesirable manufacturing heritage reduction in parts made of composites and their joints

The object of the research is the possibility of improving the quality of parts made of composites (CM) by means of pre-polymerization treatment of the wet package with intensive pulse loading. The existing technologies for forming parts from CM involve the compaction of the collected impregnated package of reinforcement layers and their subsequent polymerization under the influence of pressure and temperature. As a result of this technology, residual thermal and shrinkage stresses occur in the composite package, which lead to undesirable spatial deformations of profile parts, a violation of monolithicity in the areas of the connection of the composite and metal ends. Using the example of an angular composite profile with a profile with doubler on one of the caps, the residual stress calculation is given and the method of choosing rational angles for stacking the reinforcing material is demonstrated in order to reduce the amount of residual thermal stresses that arise in the composite during its polymerization. The dependence of the twisting parameter of a long-dimensional composite profile of constant cross-section along its axis on the modulus of elasticity and the coefficient of linear temperature expansion is plotted. The work explains the mechanism of the emergence of such harmful technological heredity. The value of the residual deformations was estimated. Based on the analysis of the impregnation process of dry reinforcing material with a binder, the task of increasing the maximum contact area of the binder with fibers is formulated and a possible method of its increase is analyzed. Thus, using the model of capillaries between the fibers of the composite, it is concluded that it is necessary to apply additional pressure to the binder for its deeper advancement between the fibers. Using a synergistic method of combining knowledge from various branches of industry and based on experimental data, a process of pre-polymerization loading of the impregnated package with intense impulse loading (shock waves) is proposed. This process greatly improves the quality of parts of the units produced.

Multi-scale simulation of residual stress and deformation of large-size hollow parts fabricated by laser-based powder bed fusion

Hollow structures are widely used in aerospace, automotive, and other fields. Laser-based powder bed fusion (LB-PBF) enables the fabrication of complex parts. However, residual stresses and deformations present challenges for manufacturing high-quality components. This study proposes a modified inherent strain method (MISM) coupled with shear strain and dynamic mechanical properties to capture the asymmetric deformation behavior of the parts. The asymmetric deformation behavior was verified by two typical geometric structure parts, which demonstrated the generality of the phenomenon. The excellent agreement between the experimental and predicted results proved the validity of the extended model. Based on the asymmetric deformation, the effect of different geometries on the stresses was investigated. The results showed that the geometry of the parts affects the stress distribution and magnitude. The proposed numerical model can accurately predict the stress components of the parts, which is helpful to further investigate crack extension and damage in complex thin-walled parts.

High-Compression Crash Simulations and Tests of PLA Cubes Fabricated Using Additive Manufacturing FDM with a Scaling Strategy

Impacts due to drops or crashes between moving vehicles necessitate the search for energy absorption elements to prevent damage to the transported goods or individuals. To ensure safety, a given level of acceptable deceleration is provided. The optimization of deformable parts to absorb impact energy is typically conducted through explicit simulations, where kinetic energy is converted into plastic deformation energy. The introduction of additive manufacturing techniques enables this optimization to be conducted with more efficient shapes, previously unachievable with conventional manufacturing methods. This paper presents an initial approach to validating explicit simulations of impacts against solid cubes of varying sizes and fabrication directions. Such cubes were fabricated using PLA, the most used material, and a desktop printer. All simulations could be conducted using a single material law description, employing solid elements with a controlled time step suitable for industrial applications. With this approach, the simulations were capable of predicting deceleration levels across a broad range of impact configurations for solid cubes.

A Review of Proposed Models for Cutting Force Prediction in Milling Parts with Low Rigidity

Milling parts with low rigidity (thin-walled parts) are increasingly attracting the interest of the academic and industrial environment, due to the applicability of these components in industrial sectors of strategic interest at the international level in the aerospace industry, nuclear industry, defense industry, automotive industry, etc. Their low rigidity and constantly changing strength during machining lead on the one hand to instability of the cutting process and on the other hand to part deformation. Solving both types of problems (dynamic and static) must be preceded by prediction of cutting forces as accurately as possible, as they have a significant meaning for machining condition identification and process performance evaluation. Since there are plenty of papers dealing with this topic in the literature, the current research attempts to summarize the models used for prediction of force in milling of thin-walled parts and to identify which are the trends in addressing this issue from the perspective of intelligent production systems.

Simulation Method for Curing Deformation of Composite Part Considering Tool–Part Interaction

Simulation Method for Curing Deformation of Composite Part Considering Tool–Part Interaction

Fault mechanism and dynamic two-phase flow behavior of liquid slugging in reciprocating compressors

Liquid slugging is a fatal fault for large process compressors, leading to transient overpressure, the deformation and fracture of vital pressure-bearing parts, and even gas leakage or explosion. In the study reported here, to reveal the mechanism of overpressure formation, numerical simulations were conducted by means of the volume-of-fluid method to explore the dynamic evolution characteristics of the two-phase flow pattern. Then, high-speed photography was applied to capture the dynamic changes of the liquid boundary in the modified cylinder from different views, thus realizing the validation of the numerical model. This study reveals the significant influence of increased rotational speed on fluid flow patterns, impeding liquid discharge and exacerbating overpressure events. Additionally, changes in pressure waveform and a distinctive waveform feature were identified as effective diagnostic indicators for detecting fluid slugging. Next, a nondestructive pressure monitoring reconstruction method based on measuring bolt strain was proposed. The strain-based pressure showed good agreement with the simulated results, thereby validating its effectiveness and feasibility as an early warning indicator for liquid slugging. This study offers new perspectives on the failure mechanism of liquid slugging in reciprocating compressors by delving into the behavior of two-phase flow, with the potential to enhance the theoretical foundation of compressor condition monitoring and fault diagnosis.

Adaptive Optimization Method for Prediction and Compensation of Thin-Walled Parts Machining Deformation Based on On-Machine Measurement.

Thin-walled aluminum alloy parts are widely used in the aerospace field because of their favorable characteristics that cater to various applications. However, they are easily deformed during milling, leading to a low pass rate of workpieces. On the basis of on-machine measurement (OMM) and surrogate stiffness models (SSMs), we developed an iterative optimization compensation method in this study to overcome the machining deformation of thin-walled parts. In the error compensation process, the time-varying factors of workpiece stiffness and the impact of prediction model errors were considered. First, we performed machining deformation simulation and information extraction on the key nodes of the machined surface, and an SSM containing the stiffness information of discrete nodes of each cutting layer was established. Subsequently, the machining errors were monitored through intermittent OMM to suppress the adverse impact of prediction model errors. Further, an interlayer correction coefficient was introduced in the compensation process to iteratively correct the prediction model error of each node in the SSM along the depth direction, and a correction coefficient between parts was introduced to realize the iterative correction of the prediction model for the same node position between different parts. Finally, the feasibility of the proposed method was verified through multiple sets of actual machining experiments on thin-walled parts with added pads.

In-situ EBSD observation of texture evolution and lattice rotation behavior in shear deformation of thin-walled aluminum alloy tubes

As shear stress plays a significant role in the deformation of tubular parts with complex shapes, investigation of the microstructue evolution of tubes under the shear stress state is beneficial to understanding the shear deformation mechanism and promoting the prediction accuracy of numerical simulation. In this paper, the shear experiments were conducted on thin-walled 5052 aluminum alloy tubes. The texture evolution and lattice rotation behavior of the tube during shear deformation were studied using in-situ electron back scatter diffraction (EBSD) technology. It is shown that the initial Cube texture remains stable, while a new Rot. Copper texture is formed in the shear deformation zone. The grains with the orientation of <100> parallel to the axial direction (AD) tend to stabilize, while several low-angle grain boundaries (LAGBs) are formed inside the grains with unstable initial orientations. Notably, the orientations of adjacent grains are more similar after shear deformation, and the high-angle grain boundaries (HAGBs) gradually transform to LAGBs showing the characteristics of polycrystalline cooperative deformation. By analyzing the lattice rotation mechanism under shear stress, it is found that the shear stress promotes the lattice rotation to a stable orientation parallel to the direction of the shear stress. This research provides theoretical guidance for predicting the forming of tubular parts with complex shapes.

A stiffness matching-based deformation errors control strategy for dual-robot collaborative machining of thin-walled parts

Thin-walled parts are widely used in aerospace industry. To reduce the deformation errors of such thin-walled parts in machining and also to achieve simultaneous machining of both sides, a novel dual-robot machining system is developed in this paper. In this system, the local rigidity of the thin-walled parts can be enhanced via mutual support between two robots on both sides of the parts, thus reducing the deformation error caused by the low rigidity of the parts effectively. Further, a new concept of dual-robot stiffness matching is introduced, and the deformation of thin-walled parts caused by stiffness mismatching between two robots is analyzed and given a close-form solution. On basis of this solution, a dual-robot posture optimization model, which can satisfy the stiffness matching constraint and improve the normal stiffness of two robots, is developed and then is solved efficiently using the proposed easy-execution sequential algorithm based on the directed node graph and Dijkstra searching, thus the deformation errors of thin-walled parts in machining can be ulteriorly controlled effectively. Finally, the computer simulation and experiments are performed and the results demonstrate that the developed dual-robot machining system and the stiffness matching-based deformation control strategy can effectively reduce the deformation of thin-walled parts in machining.

Machining-induced residual stress and deformation during Mg–Li alloy thin-walled rib-web parts milling

The deformation of thin-walled parts based on the lightweight Mg–Li alloy materials caused by machining-induced stress is an important factor hindering the further development of lightweight in the aerospace field. Prediction of the machining-induced residual stress is the key to understand the deformation and derive low-stress machining scheme. In this study, the equivalent cutting deformation loads were applied to substitute the strongly coupled thermal-mechanical behavior between the tool and part to realize the prediction of the machining-induced stress and deformation of thin-walled rib-web part under different milling conditions. The local regular and complex rib-web parts share a same deformation mode, both behave as in-plane bending deformation of the machined surface. The low-stress milling scheme of up milling combined with cryogenic cooling obtained based on the local regular four rid-web thin-walled part was applicable to the prediction of the complex Mg-Li alloy disk rib-web part. Compared with the initial scheme, the maximum stress and deformation displacement based on the low-stress scheme were reduced from 80 to 36 MPa and from 0.04060 to 0.00814 mm, respectively. Finally, the effectiveness of low-stress milling scheme were verified based on the milling and measurement experiments of the complex thin-walled disk rib-web part. These results indicate the effectiveness of the modeling method for thin-walled rib-web parts and prove the results obtained based on the local model can be extended and applied to large complex parts with the same structural type.

Experimental Study on Warpage Phenomenon of Wax Parts Manufactured by Fused Filament Fabrication.

Warpage is one of the prominent issues in Fused Filament Fabrication. The cause of this is the rapid cooling of the polymer during extrusion. The residual thermal stresses accumulated within the print part result in a shape distortion and subsequent detachment of the object from the print bed. In this study, both experimental and numerical approaches were used to identify the stresses due to thermal shrinking that occurs in soft polymers such as wax. A temperature sweep test was performed using a rotational rheometer to measure the magnitude of axial forces that are generated due to the thermal shrinking of a thin layer of 3D printable wax. The thermal stresses responsible for warpage were computed analytically and using the FEA. It was found that due to thermal processes, the stress magnitude can reach a value of 1.17 MPa. This value is enough to cause the plastic deformation in the wax part having a thin elongated shape. In addition, Taguchi's robust design has identified two major FFF parameters that impact the warpage in amorphous soft polymers. They are the printing speed and the print bed temperature. To achieve a low level of warpage, it is important to make sure that the layer deposition occurs at medium speeds and the print bed temperature is moderately high according to the findings of this study.

Optimization of Fixture Number in Large Thin-Walled Parts Assembly Based on IPSO

There are lots of researches on fixture layout optimization for large thin-walled parts. Current researches focus on the positioning problem, i.e., optimizing the positions of a constant number of fixtures. However, how to determine the number of fixtures is ignored. In most cases, the number of fixtures located on large thin-walled parts is determined based on engineering experience, which leads to huge fixture number and extra waste. Therefore, this paper constructs an optimization model to minimize the number of fixtures. The constraints are set in the optimization model to ensure that the part deformation is within the surface profile tolerance. In addition, the assembly gap between two parts is also controlled. To conduct the optimization, this paper develops an improved particle swarm optimization (IPSO) algorithm by integrating the shrinkage factor and adaptive inertia weight. In the algorithm, particles are encoded according to the fixture position. Each dimension of the particle is assigned to a sub-region by constraining the optional position range of each fixture to improve the optimization efficiency. Finally, a case study on ship curved panel assembly is provided to prove that our method can optimize the number of fixtures while meeting the assembly quality requirements. This research proposes a method to optimize the number of fixtures, which can reduce the number of fixtures and achieve deformation control at the same time.