Stability and high performance machining conditions in simultaneous milling (original) (raw)

Comparison of Analytical Milling Stability Analyses with Time Domain Simulation

2016

INTRODUCTION In the past few decades, machine and cutting tool technology has increased in both capability and complexity. Despite the significant advancements, however, self-excited vibrations (or chatter) remain a limiting factor for material removal rates and part quality. In 1965, Tobias showed that chatter is selfexcited vibration which results from regeneration effects on instantaneous chip thickness [1]. The cutting edge removes a chip that was produced by in the previous pass (the prior revolution in turning or tooth in milling). The chip thickness, which affects the force and therefore the vibration response, depends on the phase between the previously cut surface and the current vibration. This understanding led to the development of analytical algorithms which are used to generate a stability map of the limiting axial depth of cut, blim, versus spindle speed, Ω. This map is known as a stability lobe diagram. As an alternative, the governing equations of motion may be solv...

Experimental and simulated milling stability tests

Mechanik

Self-excited vibrations significantly reduce the milling productivity, deteriorate the quality of machined surface and tool life. One of the ways to avoid these vibrations is to modify the cutting parameters based on the stability analysis results. A method of numerical simulation of self-excited vibrations in the time domain can be used for this purpose. A comparison of numerical simulation results with those from experiments conducted using a milling machine is presented. The results confirm the correctness of applied modeling.

Influence of Milling Cutter Dynamics on Stability Lobe Diagrams

2017

In milling, both dimensional accuracy and productivity depend on several parameters of milling. As these parameters influence the material removal rate and the stability of process in terms of vibrations and chatter, it is important to examine the role of these parameters on the level of vibration and chatter. Since 1960s, the researchers have studied chatter problems with a view to understand the mechanism, parameters responsible for this phenomena and its behaviour in milling operation. Out of several methods that can be followed for minimizing and avoiding chatter, stability lobe diagram is considered to be the most reliable way of identifying the cutting parameters for chatter free condition. Since the chatter depends on the interaction of milling cutter with work piece during milling of parts on the milling machine, it is essential to examine the influence of dynamic parameters of milling cutter on the stability of cutting process. This paper covers the generation of stability ...

Chatter Stability of 5-Axis Milling Using Multi-Frequency Solution

5-axis milling is a common manufacturing process especially in machining of complex surfaces. In such operations, chatter is an important problem as it affects the surface quality of the finished part. The application of stability diagrams is an efficient tool to predict chatter free cutting conditions. Although several stability models have been developed for milling operations, they are limited to 3 axis milling applications. In an earlier study by the authors, a stability model for 5 axis milling was presented using single frequency solution. Due to the time varying nature of the milling dynamics, a multi frequency system response may be obtained for cases where radial depth of cut is small. These frequencies show up in the system response in the form of addition and subtraction of the chatter frequency and harmonics of the tooth passing frequency. In the present study, dynamics of 5-axis milling is modelled analytically considering multi-frequency effects. The existence of multi frequency response is demonstrated using experiments and numerical solutions. The effect of multi frequency dynamics on the stability diagrams are shown by the analytical solutions and time domain simulations.

Determining the Milling Technological Parameters Using the Stability Diagrams

2012

Due to the dynamic behavior of the milling machine, the milling operation can proceed from the stable milling domain in the unstable domain although the depth of milling, the cutting speed and feed rate are rigorously calculated. The stable milling domains can be identified through stability charts which are calculated with specific algorithms that use as input data the modal parameters of the milling machine. We calculated and drew the stability diagrams modeling the cutter vibrations as a one degree of freedom oscillator. For this we implemented the semi-discretization algorithm in software written in Pascal language. Keywords: milling machine, stability diagram, semi-discretization algorithm

On stability prediction for milling

International Journal of Machine Tools and Manufacture, 2005

Stability of 2-dof milling is investigated. Stability boundaries are predicted by the zeroth order approximation (ZOA) and the semidiscretization (SD) methods. While similar for high radial immersions, predictions of the two methods grow considerably different as radial immersion is decreased. The most prominent difference is an additional type of instability causing periodic chatter which is predicted only by the SD method. Experiments confirm predictions of the SD method, revealing three principal types of tool motion: periodic chatter-free, quasi-periodic chatter and periodic chatter, as well as some special chatter cases. Tool deflections recorded during each of these motion types are studied in detail.

Generalized Model for Dynamics and Stability of Multi-Axis Milling with Complex Tool Geometries

Journal of Materials Processing Technology, 2016

Multi-axis milling offers increased accessibility in milling of parts having geometrical constraints or free form surfaces, where variety of cutting tools and edge geometries are utilized to improve stability and productivity of the processes. In order to machine the desired geometries effectively, in conjunction with multi-axis orientations, special tools ranging from taper end mills to process specific form tools are utilized. For such cases, the cutter workpiece engagement boundaries (CWEB) and directional force vector definitions are very complex and cannot be defined analytically. Furthermore, irregular cutting edge geometries, such as variable helix, pitch and serrations introduce multiple time delays between successive cuts where the conventional analytical frequency domain stability solution cannot be used. Prediction of stability diagrams for such variety of tool forms and edge geometries requires both the process and the tool to be defined in a generalized manner. In this paper, a numerical frequency domain milling stability solution method is proposed. The CWEB for complex multi-axis cases are calculated by the general projective geometry 2 approach, where the cutting tool envelope and the cutting edges are represented as organized point clouds. Zeroth-Order approximation (ZOA) frequency domain method is adapted by introducing a speed average time delay term to encompass regular and irregular tool geometries. The stability limits are predicted by iterative solution of the eigenvalue problem using the ZOA frequency domain with the proposed revision. The effect of the process damping is also introduced into the generalized stability solution in order to predict the increase in the stability limits at low cutting speeds. A previously proposed approach is used to calculate the average process damping coefficients, which are introduced as modifiers to the modal parameters. The proposed generalized methodology is applied on several cases and it is shown that stability limits can be predicted within a reasonable accuracy for wide variety of cutting tools and milling operations.

Stability limits of milling considering the flexibility of the workpiece and the machine

International Journal of Machine Tools and Manufacture, 2005

High speed machining of low rigidity structures is a widely used process in the aeronautical industry. Along the machining of this type of structures, the so-called monolithic components, large quantities of material are removed using high removal rate conditions, with the risk of the instability of the process. Very thin walls will also be milled, with the possibility of lateral vibration of them in some cutting conditions and at some stages of machining. Chatter is an undesirable phenomenon in all machining processes, causing a reduction in productivity, low quality of the finished workpieces, and a reduction of the machine-spindle's working life.

Stability study of the milling process using an exponential force model in frequency domain

2006

In the last decade the prediction of the stability of different milling processes has experimented a great advance. Part of these advances are related to the successful application of frequency models that provide sufficiently precise analytic solutions for the industrial environment. Most of these models of regenerative chatter are based on lineal models of cutting force. Following these models, the cutting forces vary linearly with the chip thickness; therefore it is supposed that the stability of the process does not depend on the feed rate. In practice, it is easy to find cases where chatter grows with low feed rates and it is eliminated increasing the feed. This effect can be partially considered by means of cutting coefficients that depend exponentially on the average chip thickness. The present work considers an exponential force model that takes into account the variation of cutting coefficients with the instantaneous chip thickness and proposes a way to study stability in frequency domain. Obtained results are compared with time domain simulations.

Analytical models for high performance milling. Part II: Process dynamics and stability

Chatter is one of the most important limitations on the productivity of milling process. In order to avoid the poor surface quality and potential machine damage due to chatter, the material removal rate is usually reduced. The analysis and modeling of chatter is complicated due to the time varying dynamics of milling chatter which can be avoided without sacrificing the productivity by using analytical methods presented in this paper. r