Advances in Manufacturing

Determination of optimal geometrical parameters of peripheral mills to achieve good process stability

Min Wan, Heng Yuan, Ying-Chao Ma, Wei-Hong Zhang

2018, 6(3): 259-271. doi:10.1007/s40436-018-0226-9

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This paper focuses on optimization of the geometrical parameters of peripheral milling tools by taking into account the dynamic effect. A substructure synthesis technique is used to calculate the frequency response function of the tool point, which is adopted to determine the stability lobe diagram. Based on the Taguchi design method, simulations are first conducted for varying combinations of tool overhang length, helix angle, and teeth number. The optimal geometrical parameters of the tool are determined through an orthogonal analysis of the maximum axial depth of cut, which is obtained from the predicted stability lobe diagram. It was found that the sequence of every factor used to determine the optimal tool geometrical parameters is the tool overhang length, teeth number, and helix angle. Finally, a series of experiments were carried out as a parameter study to determine the influence of the tool overhang length, helix angle, and teeth number on the cutting stability of a mill. The same conclusion as that obtained through the simulation was observed.

The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0226-9.pdf

Efficient determination of stability lobe diagrams by in-process varying of spindle speed and cutting depth

Christian Brecher, Prateek Chavan, Alexander Epple

2018, 6(3): 272-279. doi:10.1007/s40436-018-0225-x

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The experimental determination of stability lobe diagrams (SLDs) in milling can be realized by either continuously varying the spindle speed or by varying the depth of cut. In this paper, a method for combining both these methods along with an online chatter detection algorithm is proposed for efficient determination of SLDs. To accomplish this, communication between the machine control and chatter detection algorithm is established, and the machine axes are controlled to change the spindle speed or depth of cut. The efficiency of the proposed method is analyzed in this paper.

The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0225-x.pdf

Optimal cutting condition determination for milling thin-walled details

Anton Germashev, Viktor Logominov, Dmitri Anpilogov, Yuri Vnukov, Vladimir Khristal

2018, 6(3): 280-290. doi:10.1007/s40436-018-0224-y

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This paper presents an approach for determining the optimal cutting condition for milling thin-walled elements with complex shapes. The approach is based on the interaction between the thin-walled detail and its periodic excitation by tooth passing, taking into account the high intermittency of such a process. The influence of the excitation frequency on the amplitude of the detail oscillation during milling was determined by simulation and experiments. It was found that the analytical results agreed with experimental data. The position of the detail when the tooth starts to cut was evaluated through experiments. The influence of this parameter on the processing state is presented herein. The processing stability is investigated and compared with the proposed approach. Thereafter, spectral analyses are conducted to determine the contribution of the vibrating frequencies to the detail behavior during processing.

The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0224-y.pdf

Integrated in-process chatter monitoring and automatic suppression with adaptive pitch control in parallel turning

Shuntaro Yamato, Yuki Yamada, Kenichi Nakanishi, Norikazu Suzuki, Hayato Yoshioka, Yasuhiro Kakinuma

2018, 6(3): 291-300. doi:10.1007/s40436-018-0222-0

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Simultaneous processes such as parallel turning or milling offer great opportunities for more efficient manufacturing because of their higher material removal rates. To maximize their advantages, chatter suppression technologies for simultaneous processes must be developed. In this study, we constructed an automatic chatter suppression system with optimal pitch control for sharedsurface parallel turning with rigid tools and a flexible workpiece, integrating in-process chatter monitoring based on the cutting force estimation. The pitch angle between two tools is tuned adaptively in a position control system in accordance with the chatter frequency at a certain spindle speed, in a similar manner as the design methodology for variable-pitch cutters. The cutting force is estimated without using an additional external sensor by employing a multi-encoder-based disturbance observer. In addition, the chatter frequency is measured during the process by performing a low-computational-load spectrum analysis at a certain frequency range, which makes it possible to calculate the power spectrum density in the control system of the machine tool. Thus, the constructed system for automatic chatter suppression does not require any additional equipment.

The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0222-0.pdf

Point-based tool representations for modeling complex tool shapes and runout for the simulation of process forces and chatter vibrations

P. Wiederkehr, T. Siebrecht, J. Baumann, D. Biermann

2018, 6(3): 301-307. doi:10.1007/s40436-018-0219-8

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Geometric physically-based simulation systems can be used for analyzing and optimizing complex milling processes, for example in the automotive or aerospace industry, where the surface quality and process efficiency are limited due to chatter vibrations. Process simulations using tool models based on the constructive solid geometry (CSG) technique allow the analysis of process forces, tool deflections, and surface location errors resulting from fiveaxis machining operations. However, modeling complex tool shapes and effects like runout is difficult using CSG models due to the increasing complexity of the shape descriptions. Therefore, a point-based method for modeling the rotating tool considering its deflections is presented in this paper. With this method, tools with complex shapes and runout can be simulated in an efficient and flexible way. The new modeling approach is applied to exemplary milling processes and the simulation results are validated based on machining experiments.

The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0219-8.pdf

Use of inverse stability solutions for identification of uncertainties in the dynamics of machining processes

Lutfi Taner Tunc, Orkun Ozsahin

2018, 6(3): 308-318. doi:10.1007/s40436-018-0233-x

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Research on dynamics and stability of machining operations has attracted considerable attention. Currently, most studies focus on the forward solution of dynamics and stability in which material properties and the frequency response function at the tool tip are known to predict stable cutting conditions. However, the forward solution may fail to perform accurately in cases wherein the aforementioned information is partially known or varies based on the process conditions, or could involve several uncertainties in the dynamics. Under these circumstances, inverse stability solutions are immensely useful to identify the amount of variation in the effective damping or stiffness acting on the machining system. In this paper, the inverse stability solutions and their use for such purposes are discussed through relevant examples and case studies. Specific areas include identification of process damping at low cutting speeds and variations in spindle dynamics at high rotational speeds.

The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0233-x.pdf

Chatter prediction for uncertain parameters

Michael Löser, Andreas Otto, Steffen Ihlenfeldt, Günter Radons

2018, 6(3): 319-333. doi:10.1007/s40436-018-0230-0

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The occurrence of chatter in milling processes was investigated in this study. The prediction of the stability lobes of metal cutting processes requires a model of the cutting force and a model of the dynamic machine tool behavior. Parameter uncertainties in the models may lead to significant differences between the predicted and measured stability behavior. One approach towards robust stability consists of running a large number of simulations with a random sample of uncertain parameters and determining the confidence levels for the chatter vibrations, which is a time-consuming task. In this paper, an efficient implementation of the multi frequency solution and the construction of an approximate solution is presented. The approximate solution requires the explicit calculation of the multi frequency solution only at a few parameter points, and the approximation error can be kept small. This study found that the calculation of the robust stability lobe diagram, which is based on the approximate solution, is significantly more efficient than an explicit calculation at all random parameter points. The numerically determined robust stability diagrams were in good agreement with the experimentally determined stability lobes.

The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0230-0.pdf

Prediction of machining chatter in milling based on dynamic FEM simulations of chip formation

Ehsan Jafarzadeh, Mohammad R. Movahhedy, Saeed Khodaygan, Mohammad Ghorbani

2018, 6(3): 334-344. doi:10.1007/s40436-018-0228-7

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Chatter vibration is a major obstacle in achieveing increased machining performance. In this research, a finite element model of chip formation in a 2D milling process is used to predict the occurrence of chatter vibrations, and to investigate the effects of various machining parameters on this phenomenon. The dynamic properties of the machine tool at the tool tip are obtained based on experimental modal analysis, and are used in the model as the cutter dynamics. The model allows for the natural development of vibration as the result of the chiptool engagement, and accounts for various phenomena that occur at the chip-tool interface ultimately leading to stable or unstable cutting. The model was used to demonstrate the effects of the machining parameters, such as the axial depth of cut, radial immersion, and feed rate, on the occurrence of chatter. Additionally, the phenomenon of jumping out of the cut region could be observed in this model and its effect on the chatter process is demonstrated. The numerical model is verified based on comparisons with experimental results.

The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0228-7.pdf

Stability of turning processes for periodic chip formation

Gergely Gyebrószki, Daniel Bachrathy, Gábor Csernák, Gabor Stepan

2018, 6(3): 345-353. doi:10.1007/s40436-018-0229-6

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The prediction of chatter vibration is influenced by many known complex phenomena and is uncertain. We present a new effect that can significantly change the stability properties of cutting processes. It is shown that the microscopic environment of chip formation can have a large effect on its macroscopic properties. In this work, a combined model of the surface regeneration effect and chip formation is used to predict the stability of turning processes. In a chip segmentation sub-model, the primary shear zone is described with a corresponding material model along layers together with the thermodynamic behavior. The surface regeneration is modeled by the timedelayed differential equation. Numerical simulations show that the time scale of a chip segmentation model is significantly smaller than the time scale of the turning process; therefore, averaging methods can be used. Chip segmentation can decrease the average shear force leading to decreased cutting coefficients because of the non-linear effects. A proper linearization of the equation of motion leads to an improved description of the cutting coefficients. It is shown that chip segmentation may significantly increase the stable domains in the stability charts; furthermore, by selecting proper parameters, unbounded stability domains can be reached.

The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0229-6.pdf

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