RESUMEN
Modern machining requires reduction in energy usage, surface roughness, and burr width to produce finished or near-finished parts. To ensure high surface quality in machining processes, it is crucial to minimize surface finish and minimize burr width, which are considered as significant parameters as specific cutting energy. The objective of this study was to identify the optimal machining parameters for milling in order to minimize surface roughness, burr width, and specific cutting energy. To achieve this, the research investigated the impact of feed per tooth, cutting speed, depth of cut, and number of inserts on the responses across three intervals using Taguchi L9 array. Observing the responses by varying these parameters, underlined the need for multi objective optimisation. Machining conditions of 0.14 mm/tooth f z , 350 m/min V c and 2 mm ap using 1 cutting insert (exp no 9) was identified as the best machining run using grey relational analysis owing to its highest grey relational grade of 0.936. ANOVA examination identified cutting speed as the leading factor impacting the grey relational grade with 31.07 % contribution ratio, with the number of inserts, depth of cut, and feed per tooth also making notable contributions. Conclusively, machining parameters identified through response surface optimisation resulted in 21.69 % improvement in surface finish, 11.39 % reduction in specific energy consumption, and 6.2 % decrease in burr width on the down milling side albeit with an increase of 9 % in burr width on the up-milling side.
RESUMEN
Due to the increasing demand for higher production rates in the manufacturing sector, there is a need to manufacture finished or near-finished parts. Burrs and surface roughness are the two most important indicators of the surface quality of any machined parts. In addition to this, there is a constant need to reduce energy consumption during the machining operation in order to reduce the carbon footprint. Milling is one of the most extensively used cutting processes in the manufacturing industry. This research was conducted to investigate the effect of machining parameters on surface roughness, burr width, and specific energy consumption. In the present research, the machining parameters were varied using the Taguchi L9 array design of experiments, and their influence on the response parameters, including specific cutting energy, surface finish, and burr width, was ascertained. The response trends of burr width, energy consumption, and surface roughness with respect to the input parameters were analyzed using the main effect plots. Analysis of variance indicated that the cutting speed has contribution ratios of 55% and 47.98% of the specific cutting energy and burr width on the down-milling side, respectively. On the other hand, the number of inserts was found to be the influential member, with contribution ratios of 68.74% and 35% of the surface roughness and burr width on the up-milling side. The validation of the current design of the experiments was carried out using confirmatory tests in the best and worst conditions of the output parameters.
RESUMEN
Aluminum alloy (Al6061-T6) is an alloy with strong corrosion resistance, excellent disassembly, and moderate strength, which is widely used in the fields of construction, automobile, shipping, and aerospace manufacturing. Researching on the influence of machining precision and surface quality on the micro-milling process of thin-walled structures of Al6061 is highly significant. Combined with the two simulations (DEFORM-3D simulation and interactive finite element numerical simulation (FEM)) and milling experimental verification, the deformations, errors, and surface quality of milling thin-walled Al6061 were analyzed. The simulations and experimental results show that the deformation of milling a micro thin-walled structure was caused by the vertical stiffness of the thin-walled structure and the cutting force. Surface micromorphology further characterized and showed a poorer quality area, top burr, and concave defects, which directly affect machining quality. It is necessary to improve the surface quality, reduce the surface defects, and increase the stiffness at the top of thin-walled structures in future work.
RESUMEN
When a longitudinal wave passes through a contact interface, second harmonic components are generated due to contact acoustic nonlinearity (CAN). The magnitude of the generated second harmonic is related to the contact state of the interface, of which a model has been developed using linear and nonlinear interfacial stiffness. However, this model has not been sufficiently verified experimentally for the case where the interface has a rough surface. The present study verifies this model through experiments using rough interfaces. To do this, four sets of specimens with different interface roughness values (Ra = 0.179 to 4.524 µm) were tested; one set consists of two Al6061-T6 blocks facing each other. The second harmonic component of the transmitted signal was analyzed while pressing on both sides of the specimen set to change the contact state of the interface. The experimental results showed good agreement with the theoretical prediction on the rough interface. The magnitude of the second harmonic was maximized at a specific contact pressure. As the roughness of the contact surface increased, the second harmonic was maximized at a higher contact pressure. The location of this maximal point was consistent between experiments and theory. In this study, an FEM simulation was conducted in parallel and showed good agreement with the theoretical results. Thus, the developed FEM model allows parametric studies on various states of contact interfaces.
RESUMEN
The corrosion performance and electrical contact resistance were investigated for a trivalent chromium passivation layer and a cobalt-free version of that same passivation layer on γ-ZnNi-coated Al 6061-T6. Both passivation layers had a similar surface morphology, were amorphous, had similar thicknesses, and contained pores within the passivation layer. The cobalt-containing passivation layer initially had an exchange current density of 9.5 × 10-4 A/cm2 and a polarization resistance of 290 Ω/cm2. The cobalt-free passivation layer initially had an exchange current density of 10.6 × 10-4 A/cm2 and a polarization resistance of 116 Ω/cm2. After 500 h of exposure to neutral salt spray, the cobalt-containing passivation layer showed no visible corrosion and had an exchange current density of 2.9 × 10-4 A/cm2 and a polarization resistance of 136 Ω/cm2. The cobalt-free passivation layer showed uniform corrosion and had an exchange current density of 5.2 × 10-4 A/cm2 and a polarization resistance of 80 Ω/cm2. After 500 h of exposure to neutral salt spray on specimens which were scribes down to the Al substrate, the cobalt-free passivation layers were uniformly corroded, but scribed specimens with the cobalt-containing passivation layers were only partially corroded. Both the cobalt-containing and cobalt-free passivation layers were found to be viable alternatives to hexavalent chromium as per the requirements of cobalt-containing MIL-DTL-81706 offering protection comparable to hexavalent chromium and cobalt-free offering less. The presence of cobalt in the TCP layer was found to improve corrosion performance and suggested that an intermediate species such as cobalt is beneficial to the oxidation of Cr(III) to Cr(VI).
RESUMEN
The ultrasonic nonlinearity parameter derived for one-dimensional propagation of a longitudinal wave in an isotropic material has been considered useful in the evaluation of material degradation. To demonstrate this, many researchers have reported on the correlation with the yield strength obtained from a tensile test. However, there is an essential issue with this procedure - which is that the ultrasonic nonlinearity parameter is derived in a state where the lateral strain is restrained, whereas the tensile test to measure the yield strength is carried out under uniaxial stress conditions, where lateral deformation is free. In this study, to address this issue, the authors have defined the ultrasonic nonlinearity parameter under uniaxial stress conditions which were the same as the tensile test, and showed that the correlation with the yield strength was higher than the currently used ultrasonic nonlinearity parameter. To verify the validity of the proposed ultrasonic nonlinearity parameter, experiments were carried out for Al6061-T6 alloy specimens heat-treated with different aging times. Results showed that the proposed ultrasonic nonlinearity parameter exhibited a much higher correlation with yield strength than the currently used nonlinearity parameter.
RESUMEN
The ultrasonic nonlinearity parameter (ß) is determined from the particle displacement amplitudes of the fundamental and second-order harmonic components in an ultrasonic wave propagated through a material. This parameter is generally referred to as the absolute parameter. However, measuring the second harmonic component is especially difficult because its amplitude is usually much smaller than those of signals in typical ultrasonic measurements. For this reason, most studies use the relative parameter determined using the measured electric signal amplitudes of the fundamental and second harmonic ultrasonic waves. However, in many occasions, the absolute parameter is needed for a quantitative assessment of material degradation. This study proposes a method to estimate the absolute parameter from a measured relative parameter along with a proportionality constant between normalized absolute and relative parameters. This method is based on the observed fact that the ratio of between normalized relative and absolute parameters is identical after compensating proportionality constant. The method was experimentally validated for Al6061-T6 alloy specimens heat-treated for different aging times. The parameter determined through the proposed method were compared with the absolute parameters which were measured separately. The results show that these two parameters were close to each other within the measurement errors.