Thin-walled Deformation Research Articles

Research on optimization of micro-milling process for curved thin wall structure

In order to satisfy the increasing fabrication quality requirements of micro curved thin wall structures, deformation, burrs height and dimensional errors in micro-milling processes of curved thin walls are studied. At first, the finite element analysis of curved thin wall deformation is carried out, it shows that complex elastic-plastic deformation and recutting occur in each micro-milling layer. Appropriate radial depth of cut, smaller spindle speed and axial depth of cut are beneficial to reduce deformation. Then, the influence of key process parameters in micro-milling as the speed of spindle n, feed engagement fz, radial depth of cut ae and axial depth of cut ap on milling force (Fn), burrs height (H) and dimensional errors (△w) are analyzed using the response surface method (RSM). To facilitate the quantitative analyses, mathematical models of burrs height and dimensional errors are established considering the interactions and quadratic effects of key parameters. It shows that the interactions among key parameters cannot be ignored. Therefore, cutting parameters should be delicately selected. The multi-objective particle swarm optimization (MOPSO) experiments are carried out based on the established prediction model. The results show that the combination of the optimized parameters identified by this method can effectively reduce the burr height and the dimensional error. Finally, under the guidance of this method, high-quality curved thin wall parts are fabricated.

Mitigation of cutting point deviation by generating provisional corrugations during milling of thin walls

The nominal cutting contour for the thin wall deviates in response to the cutting forces during the end milling process. Elimination of mass in the milling process links to loss of stiffness, which favors the wall to deflect and promote error. This article proposes a novel way of generating rigidity during the process of milling. The tool paths were drafted to mill away mass in the central region and make corrugations at the edges simultaneously. This approach mitigated the thin wall deformation. Comparison experiments were conducted to analyze between open wall conventional type (OWC) and end corrugated pillar type (ECP). Force polygons were constructed to evaluate the effectiveness of machining. The experiments resulted in 36% more effectiveness in up milling and with 93% in down milling. An increase in the cutting effectiveness exhibited error-free and minimized cutting point deviation at the top of the wall. Eventually, the error diminished as the tool traversed to the bottom edge of the wall.

Study on deformation and compensation for micromilled thin walls with high aspect ratios

In order to further improve the dimensional accuracy of micromilled thin walls with high aspect ratios, the machining process should be actively controlled. A device for active cutting force measurement and cutting parameter compensation is developed to realize the real-time measurement of radial cutting forces and compensation of radial cutting parameters in thin wall cutting process. Firstly, a mathematical model is established to calculate the deformation and cutting force of thin walls based on the cantilever beam deformation theory. The thin wall deformation in the cutting process is estimated by measuring the cutting force. Then, the obtained incremental thin wall deformation is to be compared with the compensation threshold, which is set at 0.5 μm. If the value of the incremental deformation is less than 0.5 μm, compensation will not be processed. Otherwise, the incremental deformation is used as the compensation value for iterative compensation, until the incremental deformation of the thin wall is less than 0.5 μm. At last, a contrast experiment is carried out. The experimental results show that the introduced device and compensation method are feasible. Machining quality of the thin wall has been obviously improved in dimension precision after the cutting parameter compensations.

A state-of-art review on chatter and geometric errors in thin-wall machining processes

Thin-wall components are some critical parts that are extensively used in modern industries due to their high structural efficiency and low specific weight. However, precision machining of flexible thin-wall components has been a challenging task accompanied by many inevitable issues such as unexpected chatter vibration and large surface form errors. To solve these inherent problems and improve the machining quality, plenty of research has been carried out in the last decades. In this paper, a comprehensive review of previous studies on thin-wall machining process and issues has been conducted; The state-of-the-art technologies recently developed are introduced, and an in-depth discussion of both chatter vibration and thin-wall deformation have been presented in terms of the theories, mechanisms, the prediction, monitoring and elimination methods. Finally, development trends are summarized, and recommendations for future works are proposed based on the extensive review and the analysis of practical problems.

On-Line Compensation for Micromilling of High-Aspect-Ratio Straight Thin Walls.

In order to improve the machining quality and reduce the dimensional errors of micro high-aspect-ratio straight thin walls, the on-line cutting parameter compensation device has been introduced and corresponding micromilling processes have been investigated. Layered milling strategies for the micromilling of thin walls have been modeled and simulated for thin walls with different thicknesses based on the finite element method. The radial cutting parameters compensation method is adopted to compensate the thin wall deformation by raising the radial cutting parameters since the thin wall deformation make the actual radial cutting parameters smaller than nominal ones. The experimental results show that the dimensional errors of the thin wall have been significantly reduced after the radial cutting parameter compensation. The average relative dimensional error is reduced from 6.9% to 2.0%. Moreover, the fabricated thin walls keep good shape formation. The reduction of the thin wall dimensional error shows that the simulation results are reliable, which has important guiding significance for the improvement of thin wall machining quality, especially the improvement of dimensional accuracy. The experimental results show that the developed device and the machining strategy can effectively improve the micromilling quality of thin walls.

Deformation mechanism in wax supported milling of thin-walled structures based on milling forces stability

At mesoscale, dynamic alternating milling forces and relative stiffness of thin wall are the main factors affecting the deformation of thin-walled structures. To improve the machining accuracy and effectively control the thin wall deformation, this paper investigates the control strategies of dynamic milling forces and deformation mechanism in milling of different thin-walled structures. The instantaneous deformation of thin wall in high temperature casting wax supported milling is analyzed. A deformation control method of thin wall based on the dynamic stability of micro milling forces is proposed in high-speed milling process. Three representative milling experiments on microchannel cold plate with cantilevered boundary, single impeller blade with mixed boundaries, and cantilevered structure shaped like variable curvature wavy line are presented. The milling deformation mechanisms of these three thin-walled structures with different target thickness are further investigated in free milling and casting wax supported milling. Compared with free milling, the milling forces and thickness dimension of thin wall machined under different control strategies are analyzed. By monitoring the milling forces in milling of different micro-walled structures, the small difference and fluctuation of milling forces at different positions, together with the reduced thickness errors verify the effectiveness of the control strategies, using high temperature precision casting wax as auxiliary support in reducing the thin wall deflection. Additionally, the optimal milling control strategy of thin wall is determined.

Prediction of mesoscale deformation in milling micro thin wall based on cantilever boundary

The micro channel cold plate is very suitable for the application environment of high heat consumption liquid cooling such as PCB plate and multi-layer components. However, at mesoscale, the titanium alloy micro channel cold plate is micro thin-walled structure of cantilever boundary with weak stiffness, which leads to significant deformation and resultant poor machining accuracy during micro milling. To effectively control and reduce micro thin-walled deformation, a 3D FE cantilever model is established to predict dynamic milling deformation of micro thin wall. The constitutive model of titanium alloy (Ti-6Al-4 V) that includes the strain gradient to consider size effect in micro milling, the edge geometry of milling cutter, the thin-walled microstructure, and micro milling parameters is involved in milling modeling of thin wall. Moreover, a series of micro milling experiments for micro thin wall of titanium alloy at different machining parameters were carried out to investigate the law and mechanism of thin wall deformation in milling micro thin wall subjected to dynamic alternating forces. By comparing numerical and experimental deformation of micro thin wall in micro milling, the accuracy and validity of the prediction model based on cantilever boundary are verified, which provides theoretical support and model basis for the deformation control in milling micro channel cold plate at mesoscale.

Research on deformation law and mechanism for milling micro thin wall with mixed boundaries of titanium alloy in mesoscale

At mesoscale, the blade of micro impeller with Ti-6Al-4V titanium alloy (micro thin wall with mixed boundaries) is a thin-walled structure, characterized by small size, low stiffness, high surface precision, complex boundaries, and difficult-to-control machining deformation. To control and reduce the deformation of micro thin wall, it is necessary to study the micro-deformation mechanisms during milling micro thin-wall parts. In side milling of micro thin wall with mixed boundaries, the micro thin wall suffers from dynamic alternating forces, and the deformation modes are complex, so the direct and accurate theoretical modelling is difficult to make. Since the feed speed in milling micro thin wall is less, the small deformation of micro thin wall can be described based on the flexure deformation model of the thin plate subjected to elastic loadings. Firstly, accompanied by the reciprocal theorem of work for a curved thin plate, Kirchhoff-Love small deformation model of micro thin wall is used to establish the deformation equation and boundary conditions of micro thin wall with mixed boundaries under concentrated milling forces. Thus, the obtained boundary conditions are mainly applied to the subsequent finite element simulation of three-dimensional milling deformation of micro thin wall. Then a three-dimensional deformation simulation of the micro thin wall under different milling parameters is carried out by considering the micro-walled structure, material elasto-plastic constitutive model, the stiffness and geometric structure of micro milling tools in finite element method. In the workpiece constitutive modelling, considering the strain gradient plastic model in micro milling of Ti-6Al-4V titanium alloy, the workpiece plastic constitutive model is modified by introducing the intrinsic characteristic length of the material to describe the size effects in mesoscale micro milling. Finally, a series of the corresponding experiments on the milling of titanium alloy micro thin walls are carried out. By comparing and analyzing the experimental values and finite element numerical results of the micro thin-walled deformation, the micro deformation mechanisms in milling of thin wall are revealed. It also verifies the accuracy and effectiveness of this established milling finite element model of thin wall, and provides theoretical basis and technical support for controlling the milling deformation of micro thin-walled parts.

Micro milling of copper thin wall structure

A mathematical model of cutting force is established to illustrate the characteristics in micro milling process of copper thin wall structure. The deformation of thin wall is predicted by means of finite element analysis. Experiments are carried out to confirm the validity of the model in which a diamond-coated micro milling cutter with a 0.5-mm diameter is used. Deformation and micro burrs are induced using different parameters and machining methods. Experimental results show that the proposed mathematical model and analysis methods can effectively predict the machining deformation of a micro thin wall. There is a close correspondence between the position of applied load and deformation of a thin wall. Not only the sizes of burrs and deformation are smaller but also the quality is better for the down-milling of copper thin wall structure than the up-milling. With decreasing the cutting thickness, the surface quality is improved.

Influence of Cutting Data on the Thin Wall Deformation in Milling of Difficult to Cut Materials<sup></sup>

The paper presents the results of milling tests of aluminum alloy with a sintered carbide tool. For selected sets of cutting data, the thin wall deformation of the workpieces was analyzed. Theoretical calculations were compared with the experimental measurements, using the high speed camera and FEM analysis.

Analiza odkształcenia cienkiej ścianki w systemie NX w obróbce HPC

Analiza odkształcenia cienkiej ścianki w systemie NX w obróbce HPC

The effects of tool edge radius on drill deflection and hole misalignment in deep hole gundrilling of Inconel-718

Straightness control in gundrilling of deep, thin-walled holes on Inconel-718 is challenging due to insufficiently explored phenomena governed by the tool edge radius effects. Such effects are activated by conservative drilling conditions for Inconel-718, which transforms the chip formation mode to a thrust-dominated mechanism. Critical changes in force generation are thus resulted, which affect the characteristics of drill deflection and thin wall deformation. In consequence, the drill's self-piloting capability deteriorates – leading to uncontrollable deflection and hole misalignment. A mechanistic model uniting the underlying force, drill deflection, wall deformation and process kinematics is proposed and substantiated, as well.

Locating and clamping of complex geometry workpieces with skewed holes in multiple-constraint conditions

Purpose – The purpose of this paper is to propose a general model for locating and clamping workpieces of complex geometry with two skewed holes under multiple constraints. Design/methodology/approach – Numerous constraints related to application of the proposed model are discussed as prerequisite to design of fixture solution. Based on theoretical model, a fixture was designed and successfully tested in experimental investigation. Experimental results were also verified using FEM simulations. Findings – This study showed that, opposed to conventional approach, novel solution results in significantly smaller fixture dimensions, while providing greater stability. Insertion of mandrels and supports element sub-assemblies into the workpiece holes significantly increases workpiece stiffness through an increased moment of inertia, while the internal support elements largely diminish the problem of thin wall deformation in the workpiece. Practical implications – The fixture designed in this case was actually us...

Cutting Parameters Optimization in Machining Thin-Walled Characteristics of Aircraft Engine Architecture based on Machining Deformation

The machining of thin-wall characteristic is the key point of framework-part of aircraft enginealltime. This paper took the deformation of thin-walled processing as objective, and the experience formula of milling force on aeronautical aluminum alloy 7475-T7351 was set up, which provided support for finite element analysis of machining deformation on the web-plate and thinwalled part subsequently. The finite element simulation model of deformation of the thin-wall processing is established. The law of machining deformation of thin-walled characteristic was analyzed and experimental results verified the correctness of this rule. The results show that in machining process, using high spindle speed conditions with large radial cutting depth, small axial cut deep cutting parameters can reduce the thin-walled machining deformation efficiently. According to the law of deformation of thin wall, genetic algorithm was used to optimize cutting parameters. The parameters can reach the quality requirements of the thin-wall processing.

Numerical Simulation Study of High-Speed Milling Thin-Wall Part

According to the weak rigidity characteristics of thin-walled parts, the material parameters and deformation tools are taken into account. In this paper, the finite element model of high-speed milling process is systematically studied by a large-scale finite element analysis (FEA) software DEFORM-3D with the modified Johnson-Cook model. The simulated results of cutting force, chip morphology, effective stress, effective strain and cutting temperature in deformation zones of thin-wall part are analyzed. On the basis of simulation results, cutting force of high speed milling on thin-wall part is verified. Comparing to the experimental results, the simulated results of cutting force, chip morphology, effective stress and cutting temperature in deformation zones of high speed peripheral milling indicate good consistence and the models established can be used to accurately predict the thin wall deformation. Therefore, numerical simulation method for the thin wall milling deformation control and provide a new way of compensation.

Study on Static Assembly Interference Pressure between a Thin-Wall Flexible Cup and a Hollow Flexible Shaft

Distribution of static interference pressure between a thin-wall flexible cup and a flexible shaft fluctuates heavily along the axis of the cup and is quite different from pressure distribution of common interference styles. In this article, aiming at solving distribution of static interference pressure between a thin-wall flexible cup with much thicker bottom and a hollow flexible shaft, mechanical model and mathematical model of solving the problem were built based on classic thin shell theory. Special difference is that precise special solution of bending equation of thin cylindrical shell was used to substitute the special solution which is original from bending deformation of thin cylindrical shell in no moment status. And a brand new general solution, the relational expression between bending deformation of thin wall of the cup and distribution of the static interference pressure, was obtained. Then, a method used to solve the pressure distribution was presented by solving integral equation and applying superposition principle for the first time. Through using the method to solve an example and comparing calculated results with FEM results, it was proved that the method is correct and effective.