Search

The paper deals with the issue of chatter reduction by modification of both the cutting tool geometry and the machining strategy. Tool wear, cutting forces, surface roughness, and flatness of milled thin-walled parts produced by WAAM (Wire and Arc Additive Manufacturing) technology are evaluated. The machining strategy and parameters of the cutting tool macrogeometry were designed on the basis of experimental machining. Due to the combination of custom geometry of the cutting tool and adapted machining strategy, it is possible to significantly reduce chatter during milling and thereby reduce the roughness of the machined surface, as well as improve machining precision. The experimental results contribute to the effort to expand the knowledge in the field of machining thin-walled parts. [ABSTRACT FROM AUTHOR]

Investigation of a new process and method to control the planarity of thin-walled parts can provide an important theoretical and application foundation for the high-precision, high-quality fabrication of thin-walled components in aerospace and other areas. A planarity control method based on ice fixation for the milling of thin-walled parts is proposed for thin-walled aluminum alloy 7075 flat parts. The heart of the method is the application of a low temperature of about −5 °C to a flat thin-walled part using a freezing tray to hold the workpiece in place in order to control the flatness of the thin wall face grinding process. Investigation of the influence of the machining process and workpiece shape parameters on the machining flatness of thin-walled parts was conducted based on the practicality and efficiency of the method. Experimental results demonstrate that: compared to traditional milling (non-ice fixation), this method of fixing the ice can significantly improve the milling flatness of thin-walled parts, with the reduction of flatness ranging from 16.4% to 60.0%; however, the reduction of flatness is accompanied by the phenomenon of increasing milling force, with the mean increase in milling strength ranging between 5.8% and 40.3%; the flatness of the machining process decreases with increasing workpiece thickness (15.6%–65.0%) and increases with an increasing aspect ratio of the workpieces (17.4%–48.7%). The orthogonal test results show that the best-machined flatness can be achieved at large spindle speed, high feed rate, and low cutting depth working conditions, i.e. spindle speed 3000r·min−1, feed rate 350 mm·min−1, and cutting depth 0.01 mm.

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. [ABSTRACT FROM AUTHOR]

Ti-6Al-4 V titanium alloy has high strength, low density, good heat resistance, high fatigue life and excellent corrosion resistance. It is a preferred material for important parts such as aeroengine fans, compressors, roulette and blades. However, thin-walled titanium alloy parts are easy to deform in the milling process, which affects the machining accuracy. It is necessary to propose appropriate milling parameters. Using finite element software, the stress of thin-walled parts in the milling process was simulated, and the transient stress and the stress rules were analyzed. To predict the stress deformation effects of mutual coupling multiple process parameters during milling thin-walled titanium alloy parts, a set of orthogonal simulation experiments were carried out. The actual milling experiment of thin-walled Ti-6Al-4 V parts was conducted by optimal process parameters. The surface roughnesses in the bottom and the side are Ra 437 nm and Ra 738 nm respectively. [ABSTRACT FROM AUTHOR]

Thin-walled components have extensive usage in the aviation, aerospace, automotive, and energy sectors. Wire Arc Additive Manufacturing (WAAM) additive technology is a technology that is used to produce thin-walled components by adding layers by layers. MIG/MAG welding technology is used in WAAM. The milling of thin-walled components often results in chatter, which causes waves on the milled surfaces. The variable helix angle reduces chatter during milling. The study found that a constant helix angle of 30°-30°-30° caused the active part of the wall to deflect towards the cutting tool, resulting in the least desirable outcomes. In contrast, cutting tools with 30°-30°-25° and 30°-30°- 35° helix angles produced comparable results with minor surface waves. [ABSTRACT FROM AUTHOR]

Chatter in thin-walled parts is easy to occur in the process of machining, so the analysis of the stability of thin-walled parts has always been a research hotspot. In this paper, considering the influence of cutter eccentricity on milling force first, the coefficients of milling force were able to be identified by combining the milling force model with genetic algorithm. The results show that this method can obtain the milling force coefficients only by one experiment, and the accuracy is higher. Then the tool point Frequency Response Function (FRF) for a given combination can be calculated by using the Receptance coupling substructure analysis (RCSA) method that uses Timoshenko beam theory. Finally, the milling system can be divided into three types by aspect ratio. That is, when aspect ratio is less than 0.03, the system is considered to be a rigid tool-flexible workpiece system, but aspect ratio is between 0.03 and 0.2, the system is considered to be a flexible tool-flexible system, then aspect ratio is greater than 0.2, the system is considered to be a flexible cutter-rigid workpiece system. [ABSTRACT FROM AUTHOR]

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.

Milling, as a common machining method, is widely used in rough machining and final finishing of various materials. In this paper, according to the milling temperature produced in the milling process, the formula of heat distribution coefficient for workpiece milling is established. By means of Deform-3D finite element software to carry out orthogonal cutting simulation of workpiece, the influence of different machining parameters on milling heat distribution coefficient is studied, the optimal machining parameters are determined, and the milling temperature experiment is carried out to verify the simulation temperature. The experimental results show that the simulation temperature is very close to the experimental workpiece temperature, and the error is very small, which verifies the accuracy of the method. At the same time, the influence of different initial temperature of workpiece on the milling force and stability is also studied. The results show that proper heating of the workpiece can effectively improve the milling stability of the thin-walled parts. [ABSTRACT FROM AUTHOR]

The process parameters chosen for high-performance machining in the milling of a thin-walled workpiece are determined by a stability prediction model, which needs accurate modal parameters of the machining system. However, the in-process modal parameters are different from the offline modal parameters and are difficult to precisely obtain due to material removal. To address this problem, an accurate time-dependent autoregressive moving average with an exogenous input (TARMAX) method is proposed for the identification of the modal parameters in the milling of a thin-walled workpiece. In this process, a TARMAX model considering external force excitation is constructed to characterize the actual condition in the milling of a thin-walled workpiece. Then, recursive method and sliding window recursive method are used to identify TARMAX model parameters under time-varying cutting conditions. Subsequently, a three-degree of freedom (3-DOF) time-varying structure numerical model under theoretical milling forces and white-noise excitation is established, and the computational results show that the predicted natural frequencies using the proposed method are in close agreement with the simulated values. Finally, several experiments are designed and carried out to validate the effectiveness of the proposed method. The experimental results show that the predicted accuracy of the proposed method using actual cutting forces is 95.68%. Good agreement has been drawn in the numerical simulation and machining experiments. Our further research objectives will focus on the prediction of the damping ratios, modal stiffness, and modal mass. [ABSTRACT FROM AUTHOR]

Machining thin-walled structures introduces challenges in terms of process stability due to the varying in-process workpiece dynamics. For the first time in the literature, this study compares the effectiveness and performance of standard, variable-pitch, and crest-cut tools on chatter suppression in milling thin-walled parts. The novel stability maps are generated based on varying stability limits caused by in-process workpiece dynamics. Using the obtained stability maps, the performance of different cutting strategies is compared considering productivity and surface finish quality. The experimentally verified results demonstrate the superiority of crest-cut tools as a robust solution for overcoming chatter in thin-wall machining. [ABSTRACT FROM AUTHOR]

The process parameters chosen for high-performance machining in the milling of a thin-walled workpiece are determined by a stability prediction model, which needs accurate modal parameters of the machining system. However, the in-process modal parameters are different from the offline modal parameters and are difficult to precisely obtain due to material removal. To address this problem, an accurate time-dependent autoregressive moving average with an exogenous input (TARMAX) method is proposed for the identification of the modal parameters in the milling of a thin-walled workpiece. In this process, a TARMAX model considering external force excitation is constructed to characterize the actual condition in the milling of a thin-walled workpiece. Then, recursive method and sliding window recursive method are used to identify TARMAX model parameters under time-varying cutting conditions. Subsequently, a three-degree of freedom (3-DOF) time-varying structure numerical model under theoretical milling forces and white-noise excitation is established, and the computational results show that the predicted natural frequencies using the proposed method are in close agreement with the simulated values. Finally, several experiments are designed and carried out to validate the effectiveness of the proposed method. The experimental results show that the predicted accuracy of the proposed method using actual cutting forces is 95.68%. Good agreement has been drawn in the numerical simulation and machining experiments. Our further research objectives will focus on the prediction of the damping ratios, modal stiffness, and modal mass.

The system dynamic model is essential for chatter prediction in milling of thin-walled structures, which is largely affected by the estimation precision of dynamic modal parameters. This paper presents a method of dynamic modal parameter identification from response signals through operational modal analysis (OMA). To avoid omission of the modes and improve recognition accuracy, multichannel least square complex exponential (LSCE) method and multichannel autoregressive moving average (ARMA) method are applied to identify the modal parameters by processing multiple sets of response signals simultaneously. The convergence characteristics of the damping stability diagram at different natural frequencies are employed to eliminate the false modes caused by harmonics and model order. After that, the predicted stable boundaries of the milling system are estimated by an extended semi-discretization method, which incorporates the effects of multi-modes, multi-point contact, and regeneration chatter caused by the interaction between tool and thin-walled part. Through the milling experiment validation, it is shown that the dynamic modal parameters can be identified accurately, and chatter can be well predicted. [ABSTRACT FROM AUTHOR]

The dimensional tolerance of flexible, thin-walled aerospace parts can be violated by the excessive static deflections during milling. This paper proposes a method to predict the dimensional surface form errors caused by deflections of both flexible workpiece and slender end-mill in five-axis flank milling of thin-walled parts. The end-mill is modeled as a cantilevered beam. The stiffness of the thin-walled part varies as the metal is removed and the tool-part contact location changes. The time varying stiffness of the thin-walled part is predicted by an efficient structural stiffness modification method that only needs the FE model of the initial workpiece and avoids re-meshing the part at each cutter location. The cutting forces are distributed over both the cutting tool and the part in the engagement zone, and the effect of deflections on the immersion is calculated. The effect of radial runout of the tool is considered in chip thickness, hence in the cutting force prediction. Finally, the cutter and the workpiece deflections are considered to predict the surface errors left on the finished part. The proposed method has been proven in five-axis blade milling experiments. [ABSTRACT FROM AUTHOR]

A new information-localization strategy for machining large thin-walled parts is presented in this paper. This strategy uses sub-areas and fiducials calibration methods to improve processing precision of large thin-walled parts, which are of poor machinability, low rigidity, and poor deformation coupling. In our experiments, the large thin-walled part is firstly divided into several sub-areas based on the actual state of the workpiece sampled by a binocular vision sensor. And then each divided sub-area is calibrated by the machining benchmark fiducials. Finally, the machining error of each sub-area is automatically compensated based on the measurement results of fiducials in each sub-area by the touch probe. Two verification experiments show that the proposed strategy is feasible and efficient. [ABSTRACT FROM AUTHOR]

As the main factor, residual stress undoubtedly restricts the long-term stability of high-precision machining quality parts, arresting an extensive attention on studying its control method. Therefore, a model is meticulously proposed, along with the optimization method of the overlap rate of cutting tool path. In the roughing, the selection of a larger magnitude of overlap coefficient K is found to be necessary for the optimization of the surface machined residual stress, followed by an indispensable selection of smaller K values in the finishing. The shrinking overlap coefficient K echoes with the decreasing influence of the deformation affected by the residual stress distribution, inevitably accompanied by the lowering material removal rate. Based on all the optimization results, an aerospace thin-walled part is adopted in the application case to verify the proposed approach. [ABSTRACT FROM AUTHOR]