Thin-walled Workpiece Research Articles

Design of a mixed robotic machining system and its application in support removal from metal additive manufactured thin-wall parts

Robotic machining could provide a solution for removing supports from metal additive manufactured workpieces, replacing labor-intensive work. However, the robot’s intrinsic weaknesses of low positioning accuracy and structural rigidity primarily restrict its applications. Improving the accuracy of robotic machining remains an unresolved issue. A mixed solution is proposed, in which a portable CNC machine with the capability of visual feature recognition is equipped with a universal industrial robot. The robot implements positioning motions in a large space, while the portable CNC fulfills accurate machining motions on a local feature of the workpiece. A sizeable weight of the portable CNC exerts a moderate load on the industrial robot’s joints, increasing joint stiffness. The mixed machining system exhibits high accuracy and stiffness when milling a steel/titanium alloy workpiece, achieving tolerances up to ±0.04 mm on a 60×80 mm U-shaped path without exciting any structural vibration modes. When the dimension of the workpiece exceeds the machining range of the portable CNC, a combined algorithm of coarse-fine registration based visual identification and robot error compensation is designed to align the spatial coordinates of the machining motion with that of the positioning motion, thereby extending the machining range with high accuracy. Through the proposed mixed robot machining method, experiments of doubling the machining range have been done to verify that the mixed machining robotic system is able to slot a 550 mm-long path with accuracy of ±0.1 mm. Furthermore, the mixed robotic machining system is applied to recognize and remove multiple supports of lattices, grids and ribs from a titanium-alloy additive manufactured thin-wall workpiece with high accuracy and high efficiency.

An electromagnetic semi-active dynamic vibration absorber for thin-walled workpiece vibration suppression in mirror milling

An electromagnetic semi-active dynamic vibration absorber for thin-walled workpiece vibration suppression in mirror milling

Prediction of the cutting forces in milling operation based on multi-objective optimization of the time series analysis parameters

Accurate simulation of the cutting forces in the milling process is extremely complicated because of variations in cutting process parameters, including the change in modal characteristics of the workpiece along the machining path and the high-temperature gradient around the cutting zone, especially for the modeling of milling forces in flexible thin-walled workpieces. Therefore, proposing effective methods for prediction and control of cutting forces is highly important to ensure the high performance and stability of the cutting process as well as the quality of the machined surface. In this article, a novel method is presented for rapid prediction of cutting force signals based on the combination of the multi-variable time series analysis, the Imperialist Competitive Algorithm (ICA) and Multi-View Embedding (MVE) algorithm. A state-space model of the dynamic system is presented in order to quickly predict the instantaneous dynamic characteristics of the cutting process. The maximum error between the amplitude of experimental and predicted force signals (peak-to-peak) in stable and unstable cutting conditions is less than 8% and 17%, respectively. Therefore, it is illustrated that the presented method has remarkable computational accuracy and convergence speed for predicting the future of the cutting forces under both stable and unstable conditions.

AN EFFICIENT ITERATIVE METHOD TO SIMULATE THE VARYING STATIC RECEPTANCE OF A THIN-WALLED WORKPIECE

This paper introduces an accelerated iterative Conjugate Gradient method (CG-method) for simulating the varying static receptance of a thin-walled workpiece. The proposed approach enhances computational efficiency by computing an optimal initial displacement guess for a given cutter location. This guess is based on the previously calculated displacement vector from the preceding cutter location, serving as the start iteration vector for the CG-method. The validation of efficiency gains through this method is demonstrated by a significant reduction in computation time for a numerical example. Moreover, to ensure the accuracy of the accelerated iterative CG-method, comparisons are made with the Cholesky method. The results confirm the precision of the proposed approach.

Prediction of thin-walled workpiece machining error: a transfer learning approach

Prediction of thin-walled workpiece machining error: a transfer learning approach

Quality control of NiCr-Cr3C2-hBN@Ni coating on thin-walled GH4169 alloy surface prepared by plasma spraying

As equipment lightweight trends progress, thin-walled structures have seen extensive application in critical aerospace components. Nevertheless, the aero-engine tail nozzle flaps are exposed to the harsh operating conditions of high-temperature friction, so there is an urgent requirement to prepare wear-resistant, self-lubricating coatings with a wide range of temperatures for their protection. Due to the poor rigidity and weak strength of thin-walled workpieces and complex forms of structural stresses, the processing is extremely difficult. In order to solve the thermal deformation problem of coating workpieces prepared by spraying on the surface of thin-walled workpieces, the effects of spraying path, cooling airflow, and spraying interval on the thermal force field of thin-walled workpieces to prepare NiCr-Cr3C2-hBN@Ni coating are investigated in this study using finite element simulation. As a result, the deformation and stress of thin-walled workpieces can be minimized by adding back-side cooling air during the spraying process and moving the cooling air with the gun in a set interval, with the maximum warpage and maximum stress being less than 2.366 mm and 0.177 GPa, respectively. During the spraying process by simulating the optimum spraying process, no significant warpage of the substrate occurred and the coating was sprayed with uniform thickness. Typically, the thickness error rate is 16.7 %, and the coating hardness reaches 15–20 GPa, with excellent tribological properties in a wear rate of 10−5 mm3·N−1·m−1 and 10−6 mm3·N−1·m−1, which protects the workpiece effectively.

Time-varying vibration characteristics and surface topography of thin-walled cylinders during machining operations

Machining thin-walled cylindrical workpieces is frequently subjected to vibration due to their low rigidity, resulting in complicated surface topography. This paper investigates the vibration characteristics of thin-walled cylinder turning as well as its effect on the machined surface topography comprehensively by means of numerical simulations and experimental measurements. It is seen that the circumferential shell mode of vibration exhibits higher sensitivity to the variation of the wall thickness than the axial beam mode. The features of the vibration characteristics as well as the machined surface textures of thin-walled workpieces are shifting in a cutting pass. The underlying physical mechanism behind this phenomenon was interpreted. By extracting the critical vibration frequency and surface waviness measurement along the cutting path, a hybrid physics and data-driven surface topography was reconstructed, which showed consistency with the real surface topography. The formulated correlation between the vibration characteristics and the surface topography contributes to a holistic understanding of dynamic behaviors of thin-walled cylinder machining, and a tool that utilizes vibration to produce functional microstructures on cylindrical surfaces.

Computational studies of electromagnetic field propagation and deforming of structural elements for a thin-walled curved workpiece and an inductor

Introduction. At the present stage of industrial development, the electromagnetic field is widely used in various technological processes. The force effect of an electromagnetic field on conductive materials is used in a class of technological operations called electromagnetic forming. Problem. Under the conditions of electromagnetic forming, the main element of the technological equipment – the inductor – is simultaneously subjected to the force impact with the workpiece. At certain levels of the electromagnetic field, the deformation of the inductor becomes so significant that it can lead to a loss of its efficiency. Goal. Computational analysis of a thin-walled curved workpiece and a two-turn inductor under the conditions of electromagnetic processing of the workpiece corner zone. Determining the distribution of quantitative characteristics of the electromagnetic field and the stress-strain state and conducting assessments based on them regarding the efficiency of the technological operation. Methodology. Computational modeling using the finite element method as a method of numerical analysis. The results on the distribution of quantitative characteristics of the electromagnetic field and components of the stress-strain state for a thin-walled workpiece and an inductor are obtained. It is shown that for the specified characteristics of the technological operation, the inductor remains operational, and plastic deformations occur in the workpiece. A series of calculations were carried out, in which some parameters of the technological system were varied. Originality. For the first time, the results of the calculation analysis of the quantitative characteristics distribution of the electromagnetic field of the deformation process for the «inductor – thin-walled curved workpiece» system are presented. Practical value. The presented design scheme of a curved thin-walled workpiece and a two-turn inductor, the method of calculation analysis and some obtained results can be used in the analysis of electromagnetic processing of thin-walled structures that contain curved elements.

Исследование влияния элементов режима и шага зубьев фрезы на технологические параметры и температурное поле процесса обработки заготовок тонкостенных деталей

When machining workpieces of thin-walled parts, the temperature field differs from the field, which is formed during massive workpieces treatment. The reason for this is that machining of a thin-walled billet is interfered with its surface, being opposite to the one under machining. It has a significant effect on the temperature field, since the intensity of heat removal from this surface into the environment is significantly less than heat removal into the underlying layers of a massive material blank. In this regard, the problem of finding a rational mode of the machining process of thin-walled workpieces is relevant. The aim of the study is to determine the effects of the elements of the milling mode of thin-walled workpieces and milling cutter teeth space on the technological parameters of the milling process of titanium alloy workpieces and to develop recommendations for choosing this milling mode. For this purpose, a numerical modeling of the technological parameters of the milling process of blanks of massive workpieces and thin-walled parts made of titanium alloy, was performed experiencing various combinations of feed to the milling cutter tooth, cutting speed and milling cutter teeth space. When machining a thin-walled workpiece, due to less intense heat removal from the cutting zone into the workpiece, the temperatures in the areas of chip contact with the front surface of the tooth, the back surface of the tooth with the workpiece and the temperature of the workpiece itself are higher than when in a massive workpiece treatment. The patterns of changes in the parameters of the milling process of thin-walled workpieces depending on the feed, cutting speed and the milling cutter teeth space are established. With a larger tool stepover, the average and maximum temperatures in the areas of chip contact with the front surface of the tooth and the back surface of the tooth with the workpiece are lower in most of the combinations of mode elements used. Equations that establish the effect of feed on the milling cutter tooth, cutting speed and spacing of teeth on the parameters of the machining are obtained. The results of the study will allow choosing a rational milling mode and spacing of teeth in the work on workpieces of thin-walled parts made of titanium alloy.

Numerical evaluation of cutting strategies for thin-walled parts

Static form errors due to in-process deflections is a major concern in flank milling of thin-walled parts. To increase both productivity and part geometric accuracy, there is a need to predict and control these form errors. In this work, a modelling framework for prediction of the cutting force-induced form errors, or thickness errors, during flank milling of a thin-walled workpiece is proposed. The modelled workpiece geometry is continuously updated to account for material removal and the reduced stiffness matrix is calculated for nodes in the engagement zone. The proposed modelling framework is able to predict the resulting thickness errors for a thin-walled plate which is cut on both sides. Several cutting strategies and cut patterns using constant z-level finishing are studied. The modelling framework is used to investigate the effect of different cut patterns, machining allowance, cutting tools and cutting parameters on the resulting thickness errors. The framework is experimentally validated for various cutting sequences and cutting parameters. The predicted thickness errors closely correspond to the experimental results. It is shown from numerical evaluations that the selection of an appropriate cut pattern is crucial in order to reduce the thickness error. Furthermore, it is shown that an increased machining allowance gives a decreased thickness error for thin-walled plates.

Chatter prediction for parallel mirror milling of thin-walled parts by dual-robot collaborative machining system

Thin-walled parts with double-sided features are widely used in the aerospace industry, but the machining of such parts still faces great challenges due to their weak rigid structure and the positioning errors caused by turning/re-clamping of the workpiece. For this purpose, a novel machining approach for parallel mirror robotic milling of thin-walled parts is proposed. Different from conventional single-sided milling, it can simultaneously machine both sides of the workpiece while avoiding the above problems and improving machining efficiency. However, the introduction of multiple cutting excitations makes the vibration behavior of the workpiece more complicated, thus making it difficult for the dynamic modeling of the dual-robot machining system. This paper aims to uncover the dynamic mechanism of chatter phenomenon in parallel mirror robotic milling process in consideration of the interaction of tool-workpiece-tool system. A dual-robot collaborative machining system is first developed for the milling of thin-walled workpiece, and the method of synchronous motion planning for dual robots is described. The slave robot synchronously follows the master robot and the two milling cutters mounted on tool flange of the robot are kept in mirror position. Over a tooth passing period, the engagement state of the cutters and the workpiece is analyzed considering the effect of rotation phase lag (RPL) between the twin cutters. After that, the vibration state and the corresponding instantaneous displacement of the workpiece can be expressed explicitly, then the dynamic resultant cutting force acting on the workpiece is calculated according to the mechanistic force model. Comprehensively considering the dynamic interaction of the tool-workpiece-tool system, multi-mode and position-dependent modal characteristics of thin-walled part, a time-varying delay differential equation is constructed and solved to explore the dynamical behavior of parallel mirror milling process. The predicted stability lobe diagram is validated by a series of parallel mirror milling tests on thin-walled PMMA plates. Comparisons of numerical and experimental results show that the dynamic model successfully predicts the chatter stability for the parallel mirror milling of thin-walled parts.

Improving dynamic process stability in finishing of thin-walled workpieces by optimal selection of stock shape

In 5-axis milling of thin-wall parts, flexibility of the in-process-workpiece (IPW) governs static and dynamic deflections, especially at the semi-finishing and finishing stages. Thus, the near net shape preform, i.e. the stock shape left for semi/finishing is crucial for chatter stability. In this study, a methodology is presented to design the stock shape for improved stability. Coupled process simulation, which includes material removal, finite element analysis (FEA) and process stability simulations, is used to show the effect of stock shape on chatter stability. Spindle speed is optimized along the toolpath based on the varying process dynamic behavior for selected cutter locations (CL). The proposed method is experimentally demonstrated on case studies.

Investigation of the influence of pulse parameters on the resulting weld seam quality in pulsed electron beam welding of AW 6061

Utilizing pulsed lasers in favor of a continuous wave in laser beam welding is a well-established method to achieve higher process efficiency and reduce heat input into the workpiece, which is especially useful for thin-walled workpieces (Steen, 2005). In addition, pulsed processes have shown to lead to smaller grain sizes due to higher cooling rates, which can lead to a reduction in hot cracks in some aluminum alloys (Beiranvand et al., 2019). Since an electron beam can also be pulsed, a technique industrially utilized in electron beam drilling, the same principles apply (Schultz, 2000). However, pulsed electron beam welding is rarely used in industrial welding applications due to the risk of pores, spiking and sputtering resulting from the pulsed process dynamic, especially in the deep welding regime (Kautz, 1991). This study aims to develop a pulsed electron beam welding process for AW 6061 sheet metal, which is susceptible to hot cracking. The influence of the welding and pulse parameters, as well as the combination of a pulsed beam with high frequency beam oscillation is discussed. Furthermore, suitable welding parameters for pulsed electron beam welding of AW 6061 are developed, and the increased efficiency of pulsed welding is shown by comparison to continuous welds.

AN EFFICIENT METHOD TO SIMULATE THE VARYING STATIC RECEPTANCE OF A THIN-WALLED WORKPIECE

A new method to simulate the varying static receptance of a thin-walled workpiece based on the Cholesky decomposition is presented in this paper. In this method, the system stiffness matrix is updated by subtracting the elemental stiffness matrices of the removed elements from the initial system stiffness matrix. The updated system stiffness matrix is permuted by using a novel method based on element removing sequence and considering fill-in reduction. The Cholesky factor of the permuted system stiffness matrix is reused to compute the static receptance of the workpiece for multiple cutter locations. The reduction of computation time by using this new method is proved by a numerical test and the accuracy of the simulation is demonstrated with a machining test.

Top burr thickness prediction model in milling of thin-walled workpiece considering tool and workpiece deformation

Top burr thickness prediction model in milling of thin-walled workpiece considering tool and workpiece deformation

Suppressing Milling Chatter of Thin-Walled Parts by Eddy Current Dampers

Machining vibrations often occur when working with thin-walled workpieces. One effective method to mitigate these vibrations is by using a damper, which can enhance machining accuracy, surface finish, and tool life. However, traditional contact dampers have a drawback in that they require direct contact with the workpiece, leading to friction, wear, increased cutting forces, and reduced machining accuracy. In contrast, electromagnetic eddy current dampers are noncontact dampers that can effectively suppress machining vibrations without the need for physical contact. In this study, a method to suppress machining vibrations in thin-walled workpieces using electromagnetic eddy current dampers is proposed. By establishing a theoretical model for the electromagnetic damper, the damping force and equivalent damping of the damper are determined. Subsequently, the impact of electromagnetic dampers on frequency response functions and machining vibrations are investigated through hammer impact tests. The results indicate that increasing the surface damper voltage and reducing the air gap both enhance the equivalent damping of the electromagnetic eddy current damper. Moreover, cutting experiments are conducted to analyze the surface roughness of thin-walled workpieces with and without dampers. The results demonstrate that the eddy current damper can effectively increase the equivalent damping and provide the necessary damping force to suppress machining chatter. Overall, the proposed method utilizing electromagnetic eddy current dampers presents a promising solution for suppressing machining vibrations in thin-walled workpieces.

Dual PID Adaptive Variable Impedance Constant Force Control for Grinding Robot

High-precision and low-overshoot force control are important to guarantee the material removal rate and surface quality of robot grinding. However, traditional force control methods are subjected to positional disturbance, stiffness disturbance, contact process nonlinearity, and force-position coupling, leading to difficulties in robot constant force control. Therefore, how to achieve smooth, stable, and high-precision constant force control is an urgent problem. To address this problem, a dual PID adaptive variable impedance control is established (DPAVIC). Firstly, PD control is used to compensate for the force error, and PID is used to update the damping parameters to compensate for the disturbance. Secondly, a nonlinear tracking differentiator is used to smooth the desired force and reduce the contact force overshoot. Then, the stability, convergence, and effectiveness of the force control algorithm are verified via theoretical analysis, simulations, and experiments. The force tracking error and overshoot of a conventional impedance controller (CIC), adaptive variable impedance control (AVIC), and DPAVIC are analyzed. Finally, the algorithm is used in grinding experiments on a thin-walled workpiece. The force tracking error is controlled within ±0.2 N, and the surface roughness of the workpiece is improved to Ra 0.218 μm.

Optimized bilateral ultrasonic surface rolling process assisting directed energy deposition of thin-walled medium-entropy alloy with high mechanical performance

Laser directed energy deposition (DED) offers significant advantages for the integral manufacturing of large-scaled thin-walled workpieces. Nevertheless, how to improve the yield strength (YS) and fatigue properties of thin-walled parts fabricated by DED is a crucial issue. As an advanced surface strengthening technology, ultrasonic surface rolling process (USRP) is aimed to improve the mechanical performances of additively manufactured workpieces. In this work, an optimized bilateral USRP parameter (including the load, repeated times, scanning speed, etc.) with high manufacturing efficiency and surface integrity was developed to fabricate thin-walled CoCrNi medium-entropy alloy (MEA) parts (~1.5mm thickness). Compared to the as-deposited sample, the sample treated by USRP shows a good strength-ductility balance (ultra-high YS and ductility with 1026.6MPa and 21.9%, respectively), as well as an impressive improvement in the high-cycle fatigue limit strength of 76.9%. The reasons for high mechanical performance are revealed through multi-scale characterization and calculation. Ultra-high strength is predominantly attributed to the high-density pre-existing dislocations and deformation twins (DTs); Good ductility is related with high hetero-deformation induced stress and the activation of multiple deformation substructures induced by high flow stress, such as dislocations, DTs and hexagonal close-packed phase. Further, the improvement in fatigue performance is ascribed to the closure of manufacturing defects in the surface or subsurface and inhibited surface roughening behavior from stable gradient nanotwinned layer. Finally, the work reveals the quantitative relationship among processing-properties-promotion mechanism (PPP), which provides a criterion to meet the specific mechanical performance of DEDed thin-walled components by precisely tuning the bilateral USRP parameters.

Influence of microphone tilt angle on instability identification in micromilling of thin-walled Ti6Al4V

High speed micromilling is the most preferred manufacturing process to fabricate complex 3D featured thin-walled structures like stents, turbine blades, micro-fins, cabin parts etc., that are extensively used in bio-medical, energy, automobile and aerospace sectors. Fabricating thin-walled structures with high dimensional and geometrical accuracy requires chatter free machining parameters. Different sensors like accelerometer, current sensors, laser based sensors, vibration pick-ups etc. are available for capturing the vibration while machining thin-walled structures. Each sensor has its own advantages and disadvantages, like laser based sensors adds noise to response as chips fly past in the laser path and accelerometer captures deflection of both micro-cutting tool and thin-walled workpiece. Hence, In-process chatter identification is a challenging task in thin-wall micromilling. Also, the Filtering of signals to remove the noise from signals captured via contact type and laser based sensors results in loss of low-amplitude chatter data in high-speed micromilling. Consequently, there is a need of sensor, which functions similar to contact type with less or no loss in low-amplitude chatter data. The proposed work compares vibration signal captured using accelerometer and microphone at different tilt angles for radial milling of thin-walled Ti6Al4V at different radial immersion to analyse the effect of tilt-angle on chatter identification. The recorded signals from both accelerometer and microphone are analysed in time domain by estimation and comparison of statistical parameters, in frequency domain by analysing the distributed frequency and in time–frequency domain by analysing the energy of the signals. Complete characterization of the signals in time, frequency and time–frequency domain/methods indicated that microphone at 60° tilt angle can be used as an alternative sensor for chatter onset identification without loss in chatter data irrespective of cutting condition. Machined surface analysis of thin-walled structures complements the microphone as an effective chatter identification sensor.

Modeling and analysis for time-varying dynamics of thin-walled workpieces in mirror milling considering material removal

Modeling and analysis for time-varying dynamics of thin-walled workpieces in mirror milling considering material removal