Proceedings of the Institution of Mechanical Engineers,Part B: Journal of Engineering Manufacture

Ti6Al4V is the most widely used titanium alloy and is a demanding material in applications requiring high specific strength and corrosion resistance, that is, aerospace, automobile and biomedical industries. However, the poor machinability of this alloy, resulting from its low thermal conductivity, high hardness at elevated temperatures, high chemical reactivity with the cutting tool and low elastic modulus, restricts its usage. As a result, the tool life in machining of Ti6Al4V is substantially less than conventional materials such as steel and aluminium. This work reviews the various techniques employed in improving the machinability of Ti6Al4V alloy, from the perspective of cutting tool technology. The focus is onto the parameters affecting tool life in machining of Ti6Al4V alloy with some trending techniques and their feasibility, considering the economics to develop the best techno-economic method.

The perennial challenge for the industry is to make parts, assemblies and machinery lighter and more efficient. This has led to progressively wider application of composites due to their excellent strength, stiffness and corrosion resistance properties. Composite components are assembled predominantly by fastening, which makes drilling a common machining process for such components. Delamination of the component surface at entry and exit of the drill is a drilling defect frequently encountered. Assessment of the severity of the delamination is necessary for correction and improvement of the performance of the parts and assemblies. Over a period of time, several factors have been suggested as the index of delamination for comparison and control. Also, various techniques are being adopted to measure the extent and severity of delamination so as to calculate the assessment factor. This study aims to present and review the different means and methods for the assessment of delamination.

Error compensation technology as an economical and effective method for improving the machining accuracy of the machine tools has been widely applied in the manufacturing. How to quickly and accurately obtain machine tool error is an important prerequisite for achieving the above task. A laser tracker is adopted the multi-station and time-sharing measurement principle to achieve quick and accurate identification of the geometric errors of the machine tool. In this article, the error of single-station measurement of laser tracker is analyzed first, and then the principle and algorithm of multi-station and time-sharing measurement are given. Based on the kinematic model of the machine tool, the mapping relation equations between the space motion error and individual geometric error of the machine tool are established, and two different identification algorithms are derived, respectively. Meanwhile, the identification accuracy of two algorithms and the impact of different measurement areas and squareness errors on two algorithms are compared and analyzed in depth. The experiment results indicate that higher identification accuracy can be obtained by the second algorithm, and individual geometric error of the machine tool can be quickly and accurately separated by this algorithm.

To provide a suitable rotation rate for different machining processes, a single machine tool spindle should work over a wide range of speeds. This study considered the effects of speed on dynamic behaviour of ball bearings and combined the fatigue life model and ball bearing internal load distribution model to determine the appropriate preload. First, the influence of speed on internal load distribution and ball bearing contact angles was analysed. The preload was calculated using a ball bearing internal load distribution model. Next, assuming constant bearing fatigue life, the theoretical preload curves were determined using the fatigue life model by changing the reliability factor. Finally, at low speeds, the maximum designed preload (design value) was set as the initial preload. With the increase in speed, the optimum preload was hierarchically obtained within the internal region between the theoretical preload curves. An experimental test rig for the optimum preload of ball bearings, which can automatically adjust the preload, was developed. The proposed method for determining the optimum preload was verified using the measured performance indicators, including the temperature, motor currents, and vibration of ball bearings. The results showed that the optimum preload suggestion made the test ball bearings exhibit excellent behaviour.

Off-axis aspheric mirror is an important component widely used in optical system and precision measurement instrument. Off-axis parabolic surface is one typical shape of off-axis aspheric mirrors which can enlarge focal length and widen field-of-view. Two typical ultra-precision turning methods which are turning the cylindrical blank by revolving around the axis of parabolic surface (TPS) and revolving around the axis of cylindrical surface (TCS) are analyzed and compared for off-axis parabolic surface in this article. Three-axis (X, Z, C) turning machine is applied and kinematic analyses of two linear axes (X, Z) are studied during cutting with the single point diamond turning. The tool paths are generated and installation errors are analyzed under two different conditions. Primary experiments are conducted to verify the effectiveness of theoretical analyses. The obtained results demonstrate that the surface machined with TPS method has better machining quality than the one machined with TCS method.

As for the gantry-type machine tools, the forces of the slide blocks supporting the beam are different for different saddle locations, which would further affect the stiffness of the slider–guide joints and the dynamic characteristics of the whole machine tools. Therefore, the beam kinematic joints (the slider–guide joints) on the gantry-type machine tools are crucial for the dynamics prediction of traveling bridge systems. In this article, considering the effect of axis coupling force on the slider–guide joints’ stiffness, an equivalent dynamic model of traveling bridge systems for the gantry-type machine tools is established using hybrid element method. The additional load variation in the four slider blocks is analyzed for different locations of the saddle, and the variation in the slider–guide joints’ stiffness and traveling bridge system natural frequency are also studied. Finally, validation experiments are conducted on the traveling bridge systems of the gantry-type milling machine tools, and the results show that the dynamic modeling proposed in this article can reach a higher accuracy.

This work investigates the areal effect, a smoothing of the surface areal topography in measurements from optical instruments that arises from the use of discrete pixels. Two-dimensional and three-dimensional models for the process of acquiring areal topography data were developed and applied to three-dimensional reference surface textures of various traditional machined surfaces that were measured by an atomic force microscope. Sets of reference surface areal data were stitched by a three-dimensional stitching method prior to their use in simulations. Roughness parameters and cumulative power spectra of areal topography of the specimen surfaces measured by coherence scanning interferometry were calculated and compared to the results from the simulated profiles. The results from the simulated data profiles showed good agreement with profiles measured by a coherence scanning interferometry microscope. Finally, the relationship between the pixel size of the optical instruments and the resulting reliability of the high-frequency components of the acquired surface profiles was investigated with spectral analysis. Selection criteria for the magnification of the objective lens are proposed, which allow determination of the appropriate sensor spatial resolution for measurements based on the surface texture characteristics of the specimen.

Energy conservation is one of the most important aspects of electrical discharge machining process in which the material removal is by means of spark erosion. Metal removal in wire electrical discharge turning is a complex erosion mechanism which involves melting, vaporization and rapid cooling of molten material. In this work, the significance of discharge energy on the performance of wire electrical discharge turning process, namely, material removal rate, surface finish, thickness of recast layer and surface crack, is analyzed. New model to estimate material removal rate and surface finish in wire electrical discharge turning process have been proposed. Erosion energy and kinetic energy imparted by electrons and average physio-thermal properties of work material are utilized for the modeling. Proposed models are validated by conducting experiments on AISI 4340 steel material. The results obtained from the model are well in agreement with the experimental values. The influence of discharge energy on surface crack and recast layer thickness is analyzed using scanning electron microscope micrographs and energy-dispersive x-ray spectroscopy analysis. Surface crack is observed at higher discharge energy. The thickness of recast layer increases with the increase in discharge energy. Three-dimensional surface topography reveals the turbulent nature of machining process resulted from transient erosion phenomena of wire electrical discharge turning process. Higher material removal rates of the order of about 0.06 g/min with consistent average roughness in the range of 4.5–5.5 µm at the expense of 1.6–2.6 J of discharge energy are achieved in this work. The proposed models can be utilized for machining of difficult to machine material by effective utilization of energy that leads to energy conservation in wire electrical discharge turning process.

Hybrid machining processes growing popularity in the processing of difficult-to-cut materials due to their distinct merits over individual machining processes attributed by an amalgamation of two or more machining mechanisms simultaneously. This research study deals with the response surface methodology and artificial neural network with backpropagation algorithm–based mathematical modeling of electro-discharge diamond grinding of Inconel 718 superalloy. The matrix experiments were designed based on central composite design. The wheel speed, current, pulse-on-time, and duty factor were chosen as control factors, while material removal rate and average surface roughness (R_a) were chosen as performance parameters. The analysis of variance test shows that the wheel speed is the major factor influencing both the material removal rate and the R_a and contributes 89.03% and 79.10% on material removal rate and R_a, respectively, followed by current which contributes 4.43% and 8.38% on material removal rate and R_a, respectively. The modeling and predictive abilities of developed artificial neural network model (4-24-2) were related to the response surface methodology model using root mean square error and absolute standard deviation. The predicted values of material removal rate and R_a by response surface methodology and artificial neural network are in close agreement with the actual experimental results.

The use in motor vehicles of lightweight metals such as aluminium and titanium provides a high strength-to-weight ratio, thereby lowering overall weight and reducing energy consumption and CO₂ emissions. Aluminium alloys have thus become an important structural material especially high strength and ultra-high strength alloys such as AW 7020. Many studies have shown that the presence of an aluminium oxide (Al₂O₃) thin film formed naturally on aluminium alloys is detrimental to welding. This article further investigates the specific effect of the Al₂O₃ thin film on welding AW 7020 alloy. An analytical experiment of welded AW 7020 alloy using a pulsed metal inert gas (MIG) robotic weld machine is carried out. Four specimens were cut, butt welded, and examined. The weld parameters included pre-weld cleaning of the Al₂O₃, pre-, and post-weld heat treatment. Al₂O₃ was removed by wire brushing; preheating was conducted at a temperature of 130 °C; and natural ageing was conducted by post-weld heating at 480 °C for 2 h, followed by quenching in water at 90 °C for 8 h, reheated, and sustained at 145 °C for 15 h. The result shows that the presence of Al₂O₃ layer appears not to be detrimental to the weld with new welding technologies, therefore suggesting that it is not necessary to grind off the Al₂O₃ layer before welding. This finding implies that welding costs can be lowered and weld quality improved when new welding technologies are applied in the welding of high-strength aluminium alloys.

Edge stretchability refers to a sheet metal’s capability to resist edge cracking during edge forming and flanging. In this article, a quantitative method has been proposed to evaluate the effect of punching or trimming of sheet metals on the degradation of their edge stretchability. This method adopts the Marciniak and Kuczynski concept to quantify edge damages due to punching or trimming. A novel index, the effective failure strain ratio, is introduced. Effective failure strain ratio is strain-based, and it is defined as the ratio of the actual edge failure strain to the theoretical edge failure strain. The algorithm to calculate effective failure strain ratio based on hole-expansion simulations is detailed. The magnitude of effective failure strain ratio depends on the damage value, which corresponds to the edge damage caused by preprocessing such as punching. Numerical studies are conducted to demonstrate the applicability of this method. The results show that the degradation of edge stretchability of materials with higher hardening exponent (n-value in power hardening law) is more sensitive to edge damage. Hole-expansion experiments using two grades of dual-phase steels are conducted to validate the conclusions deduced from the simulations. The comparison between the experimental and numerical results shows that the proposed method is able to predict phenomena appearing in the experiments. The quantitative relationship between damage value and the punching clearance has not been established in this work yet, which requires extensive experimental investigation. However, a qualitative link has been clearly demonstrated, and this method provides a new perspective to express the pre-damage and its effect straightforwardly.

Surface integrity determines the performance and quality of the end product. It often needs to change the input parameters, such as cutting parameter, cutting tool geometry and material, and tool coating, to obtain the best machining surface integrity. This article presents and demonstrates the effectiveness for the multi-objective optimization of cutter geometric parameters for surface integrity of milling Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy via grey relational analysis coupled with the Taguchi method, entropy weight method, and analytic hierarchy process. The main influence factors are chosen as radial rake angle, primary radial relief angle, and helix angle, while surface roughness and residual stress are taken as performance characteristics. Based on the Taguchi method, an L16 (4³) orthogonal array is chosen for the experiments. The effect of cutter geometric parameters on surface roughness and residual stress is analysed by signal-to-noise ratio. Then, the multiple objectives optimization problem is successfully converted to a single-objective optimization of grey relational grade with the grey relational analysis. The weight coefficient for grey relational grade is determined by entropy weight method integrated with analytic hierarchy process. The results show that the order of importance for controllable factor to the milling surface integrity, in sequence, is radial rake angle, primary radial relief angle, and helix angle. The validation experiment verifies that the proposed optimization method has the ability to find out the optimal geometric parameters in terms of milling surface integrity.

Anti-glare coatings on glass substrates were prepared by a silk-screen printing machine using a glass frits paste. The proposed method was achieved by dispersion control of the glass frits using silk-screen printing equipment, and the glass frits used was ZnO-B₂O₃-SiO₂. To implement an anti-glare effect using ZnO-B₂O₃-SiO₂ during tempering of liquid crystal display cover glasses, the specific parameters related to the anti-glare effect were analysed, and the performance of the proposed method in terms of the clarity and anti-glare effect was compared with that of an anti-glare film solution.

We report a new method for tool positioning in micro-electro-discharge machining with multiple electrodes for generating parallel spark employing a combination of stepper motor and piezoactuator-based co-actuation method. The stepper motor was used for coarse positioning and the inequality arising due to difference in the tool size of multiple tools used in micro-electro-discharge machining was equated employing piezoactuation followed by electrical continuity test. Simultaneous sparks for two different electrodes could be observed employing this method. The voltage waveforms across the tool–workpiece interface also confirm the generation of simultaneous and parallel sparks across both the electrodes.