Deformation Of Thin-walled Parts 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.

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.

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.

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.

316L Stainless Steel Thin-Walled Parts Hybrid-Layered Manufacturing Process Study.

Additive manufacturing technology overcomes the limitations imposed by traditional manufacturing techniques, such as fixtures, tools, and molds, thereby enabling a high degree of design freedom for parts and attracting significant attention. Combined with subtractive manufacturing technology, additive and subtractive hybrid manufacturing (ASHM) has the potential to enhance surface quality and machining accuracy. This paper proposes a method for simulating the additive and subtractive manufacturing process, enabling accurate deformation prediction during processing. The relationship between stress distribution and thermal stress deformation of thin-walled 316L stainless steel parts prepared by Laser Metal Deposition (LMD) was investigated using linear scanning with a laser displacement sensor and finite element simulation. The changes in stress and deformation of these thin-walled parts after milling were also examined. Firstly, 316L stainless steel box-shaped thin-walled parts were fabricated using additive manufacturing, and the profile information was measured using a Micro Laser Displacement Sensor. Then, finite element software was employed to simulate the stress and deformation of the box-shaped thin-walled part during the additive manufacturing process. The experiments mentioned were conducted to validate the finite element model. Finally, based on the simulation of the box-shaped part, a simulation prediction was made for the box-shaped thin-walled parts produced by two-stage additive and subtractive manufacturing. The results show that the deformation tendency of outward twisting and expanding occurs in the additive process to the box-shaped thin-walled part, and the deformation increases gradually with the increase of the height. Meanwhile, the milling process is significant for improving the surface quality and dimensional accuracy of the additive parts. The research process and results of the thesis have laid the foundation for further research on the influence of subtractive process parameters on the surface quality of 316L stainless steel additive parts and subsequent additive and subtractive hybrid manufacturing of complex parts.

Perspectives on Developing Burn Resistant Titanium Based Coatings-An Opportunity for Cold Spraying.

Titanium alloys are crucial lightweight materials; however, they are susceptible to spontaneous combustion under high-temperature and high-pressure conditions, limiting their widespread use in aerospace engines. Improving the burn resistance of Ti alloys is essential for the structural safety and lightweight of aerospace equipment. Burn-resistant Ti alloys, such as Ti-V-Cr and Ti-Cu, however, face limitations such as high cost and low specific strength. Surface coatings provide a cost-effective solution while maintaining the high specific strength and good processability of the base material. Conventional surface treatments, such as laser cladding, result in defects and deformation of thin-walled parts. Cold spray technology offers a promising solution, as it uses kinetic energy to deposit coatings at low temperatures, avoiding defects and deformation. In this paper, we review the current research on burn-resistant surface technologies of Ti alloys and propose a new method of bimetallic coating by cold spraying and low-temperature heat treatment, which has the potential to solve the problem of spontaneous combustion of aerospace engine parts. The strategy presented can also guide the development of high-performance intermetallic compound-strengthened metal matrix composite coatings.

Study on milling flatness control method for TC4 titanium alloy thin-walled parts under ice fixation

Thin-walled parts are characterized by weak rigidity and are very prone to deformation during machining, which directly affects the machining accuracy and performance of the parts, so controlling the machining deformation of thin-walled parts is an urgent process problem to be solved. To address such problems, this paper proposes a flatness control machining method based on ice holding of workpieces. The method uses frozen suction cups to solidify liquid water to achieve stress-free clamping of workpieces. We conducted a low-temperature tensile test to investigate the low-temperature mechanical properties of the material. Comparative tests of ice-free and low-temperature ice-fixed milling were conducted to compare and analyze the changes of flatness and milling force in the two working conditions, to investigate the influence of machining parameters on the flatness of thin-walled parts, and to reveal the mechanism of low-temperature milling of ice-fixed workpieces. In addition, the low-temperature milling performance of titanium/aluminum alloy based on ice-fixation was compared. The results show that TC4 has good plasticity, high flexural strength ratio and strong resistance to deformation at low temperatures. Compared with no ice-holding, ice-holding machining effectively improves the flatness of the workpiece, and the order of the machining parameters affecting flatness is: feed rate > milling depth > spindle speed. The milling forces under ice-holding conditions were all greater than those without ice holding. The stiffness and hardness, resistance to damage and deformation of titanium alloy at low temperature are greater than those of aluminum alloy. This method provides a new method for high-precision machining of thin-walled parts.

The effect of rescanning strategy on residual stress and deformation of laser-based powder bed fusion of 316L stainless steel thin-walled parts

Purpose Laser-based powder bed fusion (LPBF) is a new method for forming thin-walled parts, but large cooling rates and temperature gradients can lead to large residual stresses and deformations in the part. This study aims to reduce the residual stress and deformation of thin-walled parts by a specific laser rescanning strategy. Design/methodology/approach A three-dimensional transient finite element model is established to numerically simulate the LPBF forming process of multilayer and multitrack thin-walled parts. By changing the defocus amount, the laser in situ annealing process is designed, and the optimal rescanning parameters are obtained, which are verified by experiments. Findings The results show that the annealing effect is related to the average surface temperature and scan time. When the laser power is 30 W and the scanning speed is 20 mm/s, the overall residual stress and deformation of the thin-walled parts are the smallest, and the in situ annealing effect is the best. When the annealing frequency is reduced to once every three layers, the total annealing time can be reduced by more than 60%. Originality/value The research results can help better understand the influence mechanism of laser in situ annealing process on residual stress and deformation in LPBF and provide guidance for reducing residual stress and deformation of LPBF thin-walled parts.

Non-uniform machining allowance planning method of thin-walled parts based on the workpiece deformation constraint

In order to reduce the machining deformation of thin-walled parts during milling, a non-uniform allowance planning method for thin-walled parts based on the workpiece deformation constraint with the idea of adding materials in reverse material removal sequence is proposed in this paper. This method does not require accurate deformation prediction and extensive experiments compared to traditional error compensation methods. It strives to maximize the allowance to enhance the stiffness of the in-process workpiece. First, a cutting force threshold calculation method is proposed according to the finite element method. The cutting force threshold at different positions is calculated by obtaining the local stiffness characteristics at the cutter-contact point under the constraint of allowable deformation. And then, the maximum machining allowance at the cutter-contact point is calculated depending on the cutting force model. Considering that the stiffness of the workpiece is position-dependent and affected by material removal, the stiffness of the workpiece is updated by adding elements in the reverse cutting direction, and the finishing stock is obtained by surface fitting. Experimental results show that compared with the traditional uniform allowance method, the error of the proposed method is reduced by about 83%, which can effectively reduce the deformation and improve the machining accuracy.

An efficient prediction method for the dynamic deformation of thin-walled parts in flank milling

Severe deformation may occur in the flank milling of thin-walled parts due to their low rigidity. Considering the varying stiffness resulting from the moving cutting force and the material removal effect, finite element-based methods have been developed to compute the deformation and generate compensated tool paths. However, they are time-consuming since they require solving the full-scale deformation equation at each cutting location. Therefore, an efficient deformation prediction method is firstly proposed in this study, in which the workpiece stiffness matrix is reduced and dynamically modified to avoid re-meshing meanwhile decreasing the computational scales of the solving process. Then, considering the coupling effect between the compensation value and the deformation error, a compensation strategy without the iteration process is developed to obtain the compensation value with high accuracy and efficiency. The flank milling of four comparison sets of thin-walled aluminum alloy blocks was conducted to validate the proposed method. The experiment results revealed that the proposed method obtained similar accuracy to the finite element methods, but cost less than 62.0% of their computational time. And the machining error ranges of four comparison sets were reduced by more than 58.7% after compensation. The proposed method shows great potential for efficiency and accuracy improvement in the 5-axis flank milling of thin-walled freeform surface parts. • A novel deformation prediction method for the milling of thin-walled parts is proposed to improve computational efficiency. • Compared with other FEM-based methods, the proposed method obtains similar accuracy but greatly decreases computation time. • Considering the coupling effect between the compensation values, a compensation strategy without iterations is developed. • The proposed method is validated through milling experiments, in which the machining errors were greatly reduced.

A material constitutive model-based prediction method for flank milling force considering the deformation of workpiece

Milling force is an important factor that affects the machining deformation of thin-walled parts. In order to improve the predictive accuracy of milling forces by considering the time-varying contact relationship between workpiece and tool, a modeling method of cutting force in flank milling considering deformation of workpiece is proposed. Milling force is modeled for infinitesimal elements based on bevel cutting theory, and converted to be expressed in the workpiece coordinate system. A material constitutive model coupled with temperature, strain and strain rate is used to describe the deformation behavior of the shear zone material. According to the Euler-Bernoulli beam theory, the deformation of the workpiece at any cutting depth is calculated. Flow stress and workpiece deformation are computed in the modeling process to update the covariates in the model to ensure the accuracy of the milling force model. The comparison between the prediction results and the experimental results of the flank milling shows that the average error of the proposed method in this paper is less than 10 %, which is 27.8 % and 31.2 % lower than the error in X and Y directions without considering the deformation model, respectively. The validity of the proposed model is verified.

Optimization of the number and positions of fixture locators for curved thin-walled parts by whale optimization algorithm

Optimizing the fixture layout of the locating element is an important method to reduce the clamping deformation of thin-walled parts. A method for optimizing the fixture layout based on whale optimization algorithm is proposed in this paper, the number and positions of the fixtures for curved thin-walled parts are optimized. Firstly, the multi-point flexible locating tooling for curved thin-walled parts is developed based on the multi-point support technology. Then the strain energy is used to describe the deformation of the curved thin-walled parts in all directions, and an optimization model that takes the position of the locating element as a decision variable and minimum strain energy as the goal is established. Combined with the whale optimization algorithm and the parameterized finite element analysis, the optimal design of the number and positions of fixture locators for curved thin-walled parts are realized. Finally, the effectiveness of the proposed method is validated by the aircraft skin locating layout optimization, and a multi-point flexible locating and deformation measurement platform is constructed to verify the results of finite element calculations.

Post-Machining Deformations of Thin-Walled Elements Made of EN AW-2024 T351 Aluminum Alloy as Regards the Mechanical Properties of the Applied, Rolled Semi-Finished Products

The paper presents an evaluation of post-machining deformations of thin-walled elements as regards the mechanical properties of the applied, rolled semi-finished products. Nowadays, wrought aluminum alloys, supplied primarily in the form of rolled plates, are widely applied in the production of thin-walled integral parts. Considering the high requirements for materials, especially in the aviation sector, it is important to be aware of their mechanical properties and for semi-finished products delivered after plastic working to take into account the so-called “technological history” concerning, inter alia, the direction of rolling. The study focused on determining the influence of the ratio of the tension direction to the rolling direction on the selected mechanical properties of the EN AW-2024 T351 aluminum alloy depending on the sample thickness and its relation to the deformation of thin-walled parts. Based on the obtained results, it was found that the sample thickness and the ratio of the tension direction to the rolling direction affected the mechanical properties of the selected aluminum alloy, which in turn translated into post-machining deformations. Summarizing, the textured surface layer had a significant impact on the mentioned deformation. Greater deformations were noted for samples made of a semi-finished product with a thickness of 5 mm in comparison to 12 mm. It was the result of the influence of the surface layer, which at lower thickness had a higher percentage of contents than in thicker samples.

Digital twin-driven clamping force control for thin-walled parts

Clamping quality is one of the main factors that will affect the deformation of thin-walled parts during their processing, which can then directly affect parts’ performance. However, traditional clamping force settings are based on manual experience, which is a random and inaccurate manner. In addition, dynamic clamping force adjustment according to clamping deformation is rarely considered in clamping force control process, which easily causes large clamping deformation and low machining accuracy. To address these issues, this study proposes a digital twin-driven clamping force control approach to improve the machining accuracy of thin-walled parts. The total factor information model of clamping system is built to integrate the dynamic information of the clamping process. The virtual space model is constructed based on finite element simulation and deep neural network algorithm. To ensure bidirectional mapping of physical-virtual space, the workflow of clamping force control and interoperability method between digital twin models are elaborated. Finally, a case study is used to verify the effectiveness and feasibility of the proposed method.

Deformation Prediction and Experimental Study of 316L Stainless Steel Thin-Walled Parts Processed by Additive-Subtractive Hybrid Manufacturing.

The hybrid process integrates two or more different processes, such as additive and subtractive manufacturing, which have gained appreciable consideration in recent years. The deformation of hybrid manufacturing is an essential factor affecting machining quality. The purpose of this paper is to study the effect of milling on stress release and surface deformation of additive manufacturing (AM) specimens in the process of additive and subtractive hybrid manufacturing (ASHM) of 316L stainless steel thin-walled parts, so as to effectively improve the forming quality of thin-walled parts manufactured by the combined processing of ASHM. To this end, a series of experiments were carried out to study the relationship between stress distribution and thermal stress deformation of 316L stainless steel thin-walled parts prepared by LMD, and the changes of stress and deformation of these thin-walled parts after subsequent milling. An infrared camera and laser distance sensor were used to record the temperature field data and deformation data to analyze the influence factors of temperature and stress on the machining results. Then, the finite element software was used to simulate the stress and deformation of the thin-walled parts in the additive manufacturing process and the subsequent milling process. Meanwhile, the model was verified through the experiments. In addition, the relationship between the milling force and the milling parameters of the AM parts was studied by orthogonal test and regression analysis.

Study on the surface grain state, residual stress and their influence on the deformation of thin-walled parts under ultra-precision cutting

Thin-wall parts have the advantages of light weight and high structural strength and are widely used in industrial fields. As the increasing requirements for the form accuracy and surface quality, ultra-precision cutting has been increasingly used to manufacture thin-walled parts. However, due to the small effect range (less than 10 [Formula: see text]m) of residual stress caused by ultra-precision cutting, it cannot be accurately measured by the conventional methods. Therefore, the research on the residual stress and deformation of thin-walled parts under ultra-precision cutting are currently restricted. In this paper, we first introduced the GIXRD method to solve the technology absence for measuring the ultra-precision cutting conducted residual stress. Based on GIXRD, TEM and dynamic interferometer measurement, the relationship between grain state, residual stress and deformation of thin-walled parts was established. The research works had shown that reducing the cutting depth within a certain range was beneficial to reduce residual stress and deformation. However, there was an extreme point of the cutting parameter. If this extreme point was exceeded, the cutting action would gradually transform from shearing to pressing and pushing, resulting in an increase in residual stress. Therefore, there was an extremely small cutting parameter that minimized residual stress and deformation of the thin-walled member. The results were helpful to understand the mechanism of deformation of thin-walled parts from the perspective of grain size and residual stress, and accordingly established a deformation control method.

A new in-processes active control method for reducing the residual stresses induced deformation of thin-walled parts

Abstract It is usually deformed severely for thin-walled workpiece when the fixture is removed after machining, which is mainly caused by the redistribution of internal stress and machining induced residual stress (MIRS). Previous works have tried to relax the fixture in-processes to release the residual stresses (i.e. internal stress and MIRS), and perform the following machining operation after re-fasten the workpiece at its totally relaxed state. However, the totally relaxed state is only an equilibrium of residual stresses and the MIRS on the top layer of the workpiece will be changed after the following machining process. The residual stresses of the workpiece become imbalance again and thus will lead to the deformation of final component. In this paper, a novel research work of actively controlling the in-processes deformation of thin-walled part is presented, which is aimed at balancing the internal stress/MIRS and preventing the redistribution of residual stresses after last machining step. Firstly, the variations of internal stress, MIRS and clamping force during machining are analyzed through a simplified in-process model of blade. An equilibrium equation is established by taking the residual stresses as the equivalent loads of clamping point. Next, to achieve the proposed in-processes active control method, a mathematical model of how to actively adjust the fixture between machining operations is established. And then, the finite element method (FEM) is used to calculate the MIRS induced deformation, in which the MIRS is measured through experiment. A prototype of active control fixture for blade part is developed to adjust the in-process deformation. Finally, three groups of machining experiments on a simplified blade with three different treatments on the fixture after the rough machining – no relaxing the fixture at all, totally relaxing the fixture in-process, and actively controlling the deformation in-process– are carried out. The validation demonstrates that the proposed in-process active control method could decrease machining deformation significantly. The maximum deformation reduced to 18.3 % and 42.9 % compare to the no relaxing and totally relaxing the fixture after rough milling.

Deformation and control method of thin-walled part during laser powder bed fusion of Ti–6Al–4V alloy

The large thermal stress caused by the high temperature gradient leads to part deformations which are the important factor restricting the rapid development and wide application of the laser powder bed fusion (LPBF) technology. In the present study, a layer-by-layer model based on the finite element method was developed to study the thin-walled part deformation and the effect caused by the part dimension during LPBF of Ti–6Al–4V alloy. The deformation along the length direction dominated for the thin-walled parts, and the maximum deformation occurred at the middle of the thin-walled part. A mechanism built in the present study revealed the deformation evolution of the thin-walled part. With the increase of the part height and length, the maximum deformation increased first and then tended to be stable. However, the maximum deformation decreased with an increase of the part thickness. Furthermore, a method of compensation design was used to effectively reduce the deformation of the thin-walled part. The simulated results and the deformation control method were validated by the experimental data. The investigated results of this research provide a significant understanding of the part deformation during the LPBF process.

A semi-analytical model for predicting the machining deformation of thin-walled parts considering machining-induced and blank initial residual stress

A prediction model for machining deformation considering machining-induced residual stress (MIRS) and initial residual stress (IRS) of the blank is proposed in the present study based on the equivalent stiffness numerical calculation and elastic mechanics. The deflections of six thin-walled parts (includes two thin-walled specimens designed in the present study and four cases in the literature [1]) are predicted using the proposed model, and the corresponding finite element analysis (FEA) and experiments are implemented to verify the model. The machining deformation can be ultimately expressed by MIRS and IRS with the influence coefficients on the basis of the proposed model, and the effects of MIRS and IRS on the machining deformation are analyzed. It is shown that the predicted deformation by the proposed model has a good consistency with the FEA and experiment results. By comparison with the model only considering IRS in literature [1], the prediction accuracy visibly increases when both MIRS and IRS are considered. The contribution ratio of MIRS and IRS on the machining deformation is affected by the stress magnitude and depth, equivalent bending stiffness, and material removal rate. Also it can be easily gotten based on the proposed model.

Study on the Deformation Control and Microstructures of Thin-Walled Parts Repaired by Laser Cladding

To reduce the deformation and improve the quality of thin-walled parts repaired by laser cladding, a three-factor, three-level orthogonal experimental scheme was employed to clad Ni60 powder on thin-walled parts with a thickness of 3.5 mm. To measure the deformation of the thin-walled parts, a method of combining the meshing of the backs of the thin-walled parts and fixing one end of the parts during cladding was used. The effects of the powder feed rate, laser power, and scanning speed on the deformation of the thin-walled parts were studied via visual analysis and analysis of variance, and the process parameters that resulted in the minimum deformation were determined. The deformation process of the thin-walled parts and the causes of cladding stress were also studied, and the microstructure of the cladding layer with the minimum deformation was analyzed via scanning electron microscopy (SEM). The results reveal that the deformation of the thin-walled parts increased with the increase of laser power. The increases of the scanning speed and powder feed rate were found to reduce the deformation of thin-walled parts; the laser power was found to have a significant effect, and the powder feed rate was found to have no significant effect, on the deformation of thin-walled parts. The order of the influence of factors on the deformation of thin-walled parts from greatest to least was determined to be as follows: laser power > scanning speed > powder feed rate. The optimal parameters to obtain the minimum deformation and good metallurgical bonding of thin-walled parts were found to be a powder feed rate of 1.4 r/min, a laser power of 1100 W, and a scanning speed of 8 mm/s. From the bottom to the top, the crystal structure of the coating with the minimum deformation was found to be coarse dendrite, dendritic crystal, and equiaxed crystal.