Papers by Keyword: Chatter

Abstract: The electric base load of milling machine tools has a high share of the machine’s total energy consumption. An approach to decrease the energy demand per workpiece is to shorten the machining time by raising the material removal rate. The maximum feed depends on the tool’s wear resistance while the maximum depth of cut is often limited by the chatter stability of the machine. In this paper active damping is used to damp chatter vibrations, which leads to a higher depth of cut. To evaluate the decrease of energy consumption for any workpiece, a modeling methodology for the energy demand of machine tools was developed, which is presented in this paper. The methodology is able to estimate the energy requirements of the spindle during cutting, of the feed drives, of the auxiliary equipment and of the base load. The numerical results were experimentally validated by different 2.5D machining processes, with good agreement between the simulation model and the experimental results. Therefore, the proposed methodology can be used effectively for calculating the total energy required for the machining of any workpiece. In addition, the structural dynamics of the machine tool, the active damping system and the cutting process were modeled in order to simulate the chatter stability. This enables a straightforward determination of the optimum cutting parameters as well as a comparison of different milling part programs, both in terms of the energy demand. Furthermore, it is possible to evaluate the energy conservation by active damping and to point out for which cutting processes active damping is useful.

Abstract: Chatter is a type of intensive self-excited vibration commonly encountered in machining. It reduces productivity and precision, and is more noticeable in the machining of difficult-to-cut alloys like hardened steel. In such cases chatter causes excessive tool wear, especially flank wear, which in turn affects the stability of the cutting edge leading to premature tool failure, poor surface finish, and unsatisfactory machining performance. Nowadays, however, the demand is for fine finish, high accuracy, and low operation costs. Therefore, any technique which significantly reduces chatter is profitable for the industry. This paper demonstrates the viability and effectiveness of a novel chatter control strategy in the turning of (AISI 304) stainless steel by using permanent bar magnets. Reduction in chatter and corresponding tool flank wear are compared from results for both undamped and magnetically damped turning using coated carbide inserts. Special fixtures and keyway were made from mild steel in order to affix the magnets on the lathe’s carriage. The two ferrite magnets (1500 Gauss each) were placed below and beside the tool shank for damping from Z and X directions, respectively. Response surface methodology (RSM) was used to design the experimental runs in terms of the three primary cutting parameters: cutting speed, feed, and depth of cut. A Kistler 50g accelerometer measured the vibrations. The data was subsequently processed using DasyLab (version 6) software. The tool wear was measured using scanning electron microscope (SEM). Results indicate that this damping setup can reduce vibration amplitude by 47.36% and tool wear by 63.85%, on average. Thus, this technique is a simple and economical way of lowering vibration and tool wear in the turning of stainless steel.

Abstract:

Titanium and its alloys have been experiencing extensive development over the past few decades. They have found wide applications in the aerospace, biomedical and automotive industries owing to their good strength-to-weight ratio and high corrosion resistance. Machining performance is often limited by chatter vibrations at the tool-workpiece interface. Chatter is an abnormal tool behaviour which is one of the most critical problems in the machining process and must be avoided to improve the dimensional accuracy and surface quality of the finished product. This research aims at investigating chatter trends in the end milling process and to identify machine parameters that have effects on chatter during machining. The machine parameters investigated include axial feed rate, spindle revolute speed and depth of cut. In this research, experimental data was collected using sensors to analyze the existence of chatter vibrations on each processing condition. This research showed that the combination of the machine parameters, feed rate and spindle speed within certain proportions has an influence on machine vibrations during end milling and if not managed properly, may lead to chatter.

Abstract: The intelligent control strategy of BP neural combined network with classical PID control is mainly studied and simulated. The advantages of the control strategy are discussed. Based on the simulated data, the BP neural network PID control has the stronger adaptive ability.

Abstract: A new kind of damper with magnetic fluid(MRF)/foam metal designed by us is introduced, and it’s damp model is established. Semi-active controlling shock absorber with the damper is designed, and it’s dynamic module is established. Fuzzy control on chatter system is designed by fuzzy controlling theory. Finally, simulation on it is done by matlab /simulink. It is shown that the control system can restrain the chatter very well.

Abstract: Machine tool chatter is a type of intensive self-excited vibration of the individual components in a machine-tool-fixture-work system. Chatter affects the cutting process and may lead to negative effects concerning surface quality, cutting tool life, and machining precision. However, modern manufacturing industries and their end users demand fine surface finish, high dimensional accuracy as well as low operation costs which include the cost of tooling. Therefore, any effective damping technique, which reduces or eliminates chatter, will significantly improve tool life and will be a profitable technique to implement in the industry. This paper presents a novel chatter control method in turning of (AISI 304) stainless steel by using permanent magnets. The study compared tool wear under two different cutting conditions: normal turning and turning with magnetic damping. A specail fixture made of mild steel was designed and fabricated in order to attach a powerful neodymium permanent magnet (4500 Gauss) to the carraige of a Harrison M390 engine lathe. The arrangement ensured that the magnet was placed exactly below the tool shank. The main idea was that the magnet will provide effective damping by attracting the steel tool shank and restricting its vertical vibratory motion during cutting operations. A Kistler 50g accelerometer, placed at the bottom front end of the tool shank was used to sense vibration. The data was then collected using a Dewetron DAQ module and analyzed using Dewesoft (version 7) software in a powerful Dell workstation. Response surface methodology (RSM) in Design Expert software (version 6) was used to design the sequence of experiments needed based on three primary cutting parameters: cutting speed, feed, and depth of cut. The tool overhang was kept constant at 120 mm in order to facilitate the attachment of the magnet fixture. Analysis of the recorded vibration signals in the frequency domain indicated that significant reduction in the vibration amplitude, as much as 86%, was obtained with magnetic damping. Next tool wear was analysed and measured using a scanning electron microscope (SEM). It is found that tool wear is reduced considerably by a maximum of 87.8% with the magnetic damping method. Therefore, this new magnetic damping method can be very cost effective, in terms of vibration reduction and tool life extension, if applied to industrial turning operations of metals.

Abstract: The cutting stability is determined by the dynamics of the tool-workpiece and the cutting process. Several cutting force models have been established by the former researches. Based on the analysis of the cutting process transfer function derived from the cutting force models, the characteristics of these models were analyzed in this work by ploting the function curves in the complex frequency plane. The curve shapes and centers were considered as the indicator to estimate the suitability of a cutting force model. An experimental method was proposed to select suitable cutting force model for a real cutting process.

Abstract: Machining of metals is generally accompanied by a violent relative vibration between work and tool, known as chatter. Chatter arises due to resonance when the vibrations of the instability of chip formation and the natural vibration modes of the machine-system components coincide. This paper focuses on a novel approach of minimizing chatter in end milling of Titanium alloy (Ti6Al4V) under magnetic field from permanent magnets. The method consists of two ferrite permanent magnet bars (dimensions: 1′′ x 6′′ x 3′′), mounted 5mm from the cutting tool using a specially designed fixture, to provide a uniform magnetic field of 2500-2700 Gausses (approximately). A titanium alloy Ti6Al4V block was then end milled using uncoated WC-Co inserts.The experiments were designed using the Design Expert software with three independent variables; cutting speed, feed, and depth of cut. Machining tests were conducted for two different conditions – with and without the application of magnets. Scanning Electron Microscope (SEM) was used to measure the chip segmentations.The SEM analysis of chip serrations demonstrated that the chip formations were more stable while cutting under the presence of permanent magnets due to lower intensity of chatter. Keywords: Chatter, Chip Serration Frequency, Permanent Magnet, Titanium Alloy.

Abstract: By disrupting the regenerative effect, milling cutters with variable-pitch are usually used to improve stability. Since high interrupted cutting processes, such as low radial immersion case, will result in more nonlinear phenomena and some consequent differences of stability chart, in this paper, an improved semi-discretization algorithm is utilized to predict the stability lobes for variable-pitch milling under low radial immersion ratios, the focus of the current manuscript is to investigate the stability trend caused by tool geometries. In addition, the chart differences in the cases of low and high radial immersion milling are also discussed by comparisons. Under certain combinations of parameters, some phenomena, like bunch of isolated island and flip bifurcation region are described, and some influences of tool geometries on stability trends are shown and explained.

Abstract: In the milling process, the dynamic system in the cutting process is composed of the tool, workpiece, and machine tools themselves. Therefore the mill geometric parameter, workpiece material behavior, and the modal parameters of the cutting system all will influence the stability in milling. Using FLN method and convolution force model to predict the chatter stability of milling process, and discussing the effect of milling parameter on the stability in this article. According to the result: with the increase of the tool diameter, stiffness, damping ratio or the reducing of tangential cutting force coefficient and radial width of cut, the stability lobe diagram tends to move upward. With the increase of natural frequency, the stability lobe diagram tends to move to right side. With the increase of the number of tooth, the stability lobe diagram tends to move downward.