Development of mathematical model for chip serration frequency in turning of stainless steel 304 using RSM

Chatter is defined as the self-excited violent relative dynamic motion between the cutting tool and work piece. Chatter is detrimental to all machining operations. In metal turning operations it leads to inferior surface topography, reduced productivity, and shortened tool life. Avoidance of chatter has mostly been through reliance on heuristics such as: limiting material removal rates (to stay within the dynamic stability boundary) or selecting low spindle speeds and shallow depth of cuts. However, the correct understanding of the mechanism of chatter formation in metal cutting reveals that chip morphology and segmentation play a predominant role in chatter formation during machining. Chatter is found to appear as a resonance phenomenon when the frequency of chip serration is equal to or integer multiple of the prominent natural frequency/frequencies of the system component(s). Hence, it is important to study the chip serration frequency. At lower cutting speeds the chip is often discontinuous, while it becomes serrated as the cutting speed is increased. It has been identified that the chip formation process at higher speeds also has a discrete nature, associated with the periodic shearing process of the chip. In this paper a statistical technique is proposed to predict the frequency of chip serration as a function of cutting parameters for two different tool overhang values in turning of stainless steel AISI 304 using Response Surface Methodology (RSM)

Influence of magnetic field on reduction chatter and of surface roughness in end milling of Titanium Alloy - Ti-6Al-4V

One of the most challenging issues in machining process is understanding the chatter phenomenon. Chatter mechanics is still not fully understood. It is inconsistent in character, making it difficult to analyze and predict. This research work investigates the influence of permanent magnets on chatter suppression in end milling of Titanium alloy (Ti-6Al-4V) using uncoated WCCo insert. The experiments were designed based on the Response Surface Methodology (RSM) approach using DESIGN EXPERT (DOE) software. The experiments were performed under two different conditions: under normal condition and under the application of magnetic fields from two permanent magnets located in opposite direction. Ti-6Al-4V was used as the work material. The resultant average surface roughness was found to be reduced by a maximum of 50% due to magnet application. Scanning Electron Microscope (SEM) was used to analyze the chip morphology. The microphotographs showed the evidence of more stable chip formation under the influence of magnetic fields

Application of permanent magnets for chatter control in end milling of titanium alloy Ti-6Al-4V

Machining of metals is generally accompanied by a violent relative vibration between work and tool, known as chatter. Chatter is undesirable due to its adverse effects on product quality, operation cost, machining accuracy, tool life, and productivity. This paper presents an innovative approach to chatter control during end milling of titanium alloy Ti-6Al-4V using ferrite permanent magnets to reduce the unwanted vibrations. A special fixture was fabricated and mounted on a Vertical Machining Center‘s spindle for holding the permanent magnet bars, used in suppressing the vibration amplitudes. DASY Lab 5.6 was used for signal analysis and processing to compare the intensity of chatter under normal and magnet application conditions. Fast Fourier Transform (FFT) was subsequently used to transform the vibration data to a function of frequency domain. The experiments focused on monitoring the vibration amplitudes and analysis of chip formation process during metal cutting. It was observed that the magnetic fields contributed to reduction of chatter amplitudes. It was apparent that a reduction of chatter amplitude would result in improved surface finish of the work-piece and lead to uniform chip formation

Optimization of surface roughness in end milling of titanium alloy TI-6AL-4V under the influence of magnetic field from permanents magnets

This paper presents the effect of cutting parameters on surface roughness in end milling of Titanium alloy Ti-6Al-4V under the influence of magnetic field from permanent magnets. Response Surface Methodology (RSM) with a small central composite design was used in developing the relationship between cutting speed, feed, and depth of cut, with surface roughness. In this experiment, three factors and five levels of central composite with 0.16817 alpha value was used as an approach to predict the surface roughness, in end milling of titanium alloy, with reasonable accuracy. The Design-Expert 6.0 software was applied to develop the surface roughness equation for the predictive model. The adequacy of the surface roughness model was validated to 95% by using ANOVA analysis. Finally, desirability function approach was used to determine the optimum possible surface roughness given the capabilities of the end machine

Surface roughness optimization in end milling of stainless steel AISI 304 with uncoated WC-Co insert under magnetic field

Chatter phenomenon is a major issue as it greatly affects the topography of machined parts. Due to the inconsistent character of chatter, it is extremely difficult to predict resultant surface roughness in a machining process, such as end milling. Also, recent studies have shown that chatter can be suitably damped using magnetic fields. This paper, thus, focuses on a novel approach of minimizing surface roughness in end milling of Mild (Low Carbon) Steel using uncoated WC-Co inserts under magnetic field from permanent magnets. In this experiment, Response Surface Methodology (RSM) approach using DESIGN EXPERT 6.0 (DOE) software was used to design the experiments. The experiments were performed under two different cutting conditions. The first one was cutting under normal conditions, while the other was cutting under the application of magnetic fields from two permanent magnets positioned on opposite sides of the cutter. Surface roughness was measured using Mitutoyo SURFTEST SV-500 profilometer. The subsequent analysis showed that surface roughness was significantly reduced (by as much as 67.21%) when machining was done under the influence of magnetic field. The experimental results were then used to develop a second order empirical mathematical model equation for surface roughness and validated to 95% confidence level by using ANOVA. Finally, desirability function approach was used to optimize the surface roughness within the limiting values attainable in end milling

A novel method for chatter control and improvement of surface finish in end milling

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 frequency of instability of chip formation and the natural frequencies (vibration modes) of the machine-system components coincide. Chatter has detrimental effects on tool life, productivity, the topology and dimensional accuracy of the work-piece apart from its other harmful effects. Finishing and grinding operations are usually required in order to improve the quality of the finished products in End milling of alloys such as Ti-6Al-4V in the absence of any chatter control strategy. The researchers of this work have developed a novel technique to address this issue in end milling operation. The setup consisted of a specially designed fixture, to be mounted on a Vertical milling machine or a Machining Center spindle, to locate and clamp two permanet ferrite magnet bars (dimensions: 1″x6″x3″) located at either side of the cutting tool and maintaining a suitable distance (approximately 5mm) from the tool. The fixture is designed to provide uniform magnetic field by the two magnets of strength 2500-2700 Gauss. The fixture design can be adjusted to suit any spindle diameter and the method can be applied to any vertical milling machine or machining center. The advantage of the new method is illustrated in the example of a end milled of a Ti alloy - Ti6Al4V block. The design of the experiments conducted was done using the statistical method - Response Surface Methodology (RSM) utilizing the capabilities of the Design Expert Software. Three variable parameters cutting speed, feed and depth of cut with three levels of these parameters and two response parameters – vibration/chatter amplitude and average surface roughness were considered in this design. Two sets of experiments, with and without magnets application, were conducted adopting the above RSM design of experiments. For vibration monitoring and analysis, a (16 channel rack) DAQ card and Datalog DASY Lab 5.6, with built-in Fast Fourier Transform (FFT), were used and Mitutoyo SURFTEST SV-500 was used to measure the resultant surface roughness. Apart from that the effect of magne appliation on chip serration instability was studied using Scanning Electron Microscope (SEM). It is observed that cutting the presence of magnets leads to an average reductions in vibration amplitude by 20% and surface roughness by 40%. The SEM analysis demonstated that chip formations were more stable while cutting under the presence of permanent magnets. Finally, the reduction in surface roughness eliminated the need for subsequent grinding and polishing. The cost of the fixture and the magnets are low and the method can be applied to any vertical milling operation and can also be adapted to other cutting process. It is a harmless and green technique for improved machinability of materials, both metallic as well as non metallic