A. K. M. Nurul Amin

Dynamic Modal Analysis of Vertical Machining Centre Components

The paper presents a systematic procedure and details of the use of experimental and analytical modal analysis technique for structural dynamic evaluation processes of a vertical machining centre. The main results deal with assessment of the mode shape of the different components of the vertical machining centre. The simplified experimental modal analysis of different components of milling machine was carried out. This model of the different machine tools structure is made by design software and analyzed by finite element simulation using ABAQUS software to extract the different theoretical mode shape of the components. The model is evaluated and corrected with experimental results by modal testing of the machine components in which the natural frequencies and the shape of vibration modes are analyzed. The analysis resulted in determination of the direction of the maximal compliance of a particular machine component.

Thermally-assisted end milling of titanium alloy Ti-6Al-4V using induction heating

Titanium and its alloys are considered as difficult-to-cut materials due to their inherent properties, such as low thermal conductivity, high cutting temperature, high chemical reactivity and strong adhesion between cutting tool and work material. This paper presents the benefits of thermally assisted machining on machinability improvement in end-milling of titanium alloy by utilising induction coil heating. The effect of online induction heating on the machinability (cutting force, tool life, vibration, and metal removal rate) are widely investigated. End milling tests were conducted on a vertical machining centre. Titanium alloy Ti-6Al-4V bar was used as the workpiece. Machining was performed with a 20 mm diameter end-mill tool holder fitted with a polycrystalline diamond (PCD) inserts. Flank wear was considered as the criterion for tool life and the wear was measured using a Hisomet II toolmaker’s microscope. The tool life tests were conducted until the flank wear exceeded 0.30 mm. Cutting force measurements were conducted using Kistler rotating cutting forced dynamometer. Vibration during cutting was captured using an online vibration monitoring system. The results lead to conclusions that thermally assisted machining significantly increases the tool life, reduces the vibration and cutting force, and increase the metal removal rate.

Surface Integrity in Hot Machining of AISI D2 Hardened Steel

This study presents experimental results of machined surface integrity of die material (AISI D2 hardened steel) when hot machining (induction heating) assisted end milling using coated carbide is applied. The aim of this work was to study the influence of induction heating temperature, cutting speed, and feed on the effects induced by hard milling on surface integrity (microhardness and work-hardening). Microhardness was measured to observe the distribution of the hardness beneath the surface and to determine the effect of induction heating on the micro-hardness distribution and work-hardening phenomena. The behaviour of microhardness induced in the subsurface region when end milling under room and induction heating cutting conditions using coated carbide inserts was also investigated. The surface integrity and subsurface alteration have been investigated by employing scanning electron microscope (SEM) and Vickers microhardness tester.

Heat-Assisted Machining

Heat-assisted machining, which is popularly known as hot machining, has emerged as an alternative method of machining for improving the machinability of difficult-to-cut metals and alloys. This technique has been under consideration since the late nineteenth century. It was observed that metals tend to deform more easily when heated, thus enhancing machinability. Hot machining found widespread application in the manufacture of engineering components in the late twentieth century, a century after it was first introduced. The principle behind hot machining is to increase the difference in hardness of the cutting tool and workpiece, leading to reduced component forces, improved surface finish, and longer tool life.

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).

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.

Performance Evaluation of PCBN in End Milling of AISI D2 Hardened Steel under Room and Preheated Machining Conditions

In this paper, the tool life and tool wear performance of PCBN tool in end milling of AISI D2 hardened steel under room and preheated machining conditions is presented. The tool life and tool wear patterns were examined through tool maker microscope and scanning electron microscope. The results show that the dominant modes of tool wear observed were flank wear, chipping, and notch wear. The main wear mechanisms were abrasion, adhesion, and diffusion promoted by high stress and cutting temperature. It was also observed that longer tool life and higher volume metal removed could be achieved when employing higher preheating temperature.

Investigations of formation of chatter in a non-wavy surface during thread cutting and turning operations

An attempt has been made to investigate the chatter formation during two machining operations namely, turning and thread cutting on a non-wavy surface of plain carbon steel with a view to observing the formative mechanisms of chatter. Investigations have been conducted on the chips and common types of discreteness in the form of serrated/saw teeth have been identified. Mechanisms of formation of these teeth have been studied and the frequencies of their formation have been determined at different cutting speeds. The different modes of the vibrating components have been extracted by modal analysis and the vibration responses during cutting conditions have also been recorded using an online data acquisition system. All the experiment were conducted on a no wavy surface and thread cutting was conducted on nascent surface, the existence of chatter observed during the experiments prove that the regenerative effect from the waviness of the previous pass, as postulated by the ‘Regenerative Chatter Theory’ is not correct in explaining the primary cause of chatter during metal cutting. The analysis of amplitude of chatter during machining indicates that noticeable chatter appears in the system when the chip serration frequency is equal to or integer multiple of the prominent natural frequency of the system components.

Surface Roughness Prediction in High Speed Flat End Milling of Ti-6Al- 4V and Optimization by Desirability Function of RSM

High Speed Machining is applicable for producing parts that require little or no grinding / polishing operations within the required machining tolerances. For achieving required level of quality, selection of cutting tools and parameters in high speed machining is very important. In this study, small diameter flat end milling tool was used to achieve high rpm to facilitate the application of low values of feed and depth of cut to achieve better surface roughness. Machining was performed on a Vertical Machining Centre (VMC) with a high speed milling attachment (HES 510), using cutting speed, depth of cut, and feed as machining variables. Statistical prediction model of average surface roughness was developed using three-level full factorial design of experiments. It was observed that depth of cut is the most dominating factor followed by cutting speed and feed. The developed model was used for optimization by desirability function approach to obtain minimum Ra. Maximum desirability of 95.63% was obtained.

Prediction of Tool Life and Experimental Investigation during Hot Milling of AISI H13 Tool Steel

This paper presents the results of experimental investigations conducted on a vertical machining centre (VMC) using spindle speed, feed rate, and depth of cut as machining variables to ascertain the effectiveness of TiAlN insert in end milling of hardened steel AISI H13, under work-piece preheated conditions and hence a statistical model was developed using the capabilities of Response Surface Methodology (RSM) to predict the tool life. Sufficient number of experiments was conducted based on the small central composite design (CCD) concept of RSM to generate tool life data for the selected machining variables. The adequacy of the model was tested at 95% confidence interval. Meanwhile, a time trend was observed in residual values between model predictions and experimental data, reflecting little deviations in tool life prediction. A very good performance of the RSM model, in terms of agreement with experimental data, was achieved. The model can be used for the analysis and prediction of the complex relationship between cutting conditions and the tool life in flat end milling of hardened materials.