Lens focal distance and auxiliary gas type utilized in CO2 laser cutting are two important parameters affecting process measures such as cuts width and quality at desired cutting speeds. This research work focuses on cuts width and quality in CO2 laser cutting with a power of 4000W on two types of steel sheets at different focal distance values and using different types of auxiliary gas. The effect of focal distances of 5” and 7.5” as well as utilizing oxygen and nitrogen as auxiliary gas on cut width and quality in 304L stainless steel and St37 steel sheets were investigated. The size of cut widths was measured using an optical microscopy. The results demonstrate that cuts performed at the focal distance of 7.5” are wider than those created at the focal distance of 5”. It is also observed that with increased workpiece thickness, the use of focal distance of 7.5” is more feasible because cuts are faster; need lower laser power, and use less amount of auxiliary gas. When using oxygen as auxiliary gas, the main factor affecting the cutting efficiency is the oxidation reaction, whereby oxidation energy is added to laser power which results to an increased energy level in the cutting region. This means that using oxygen as auxiliary gas makes it possible to cut thicker sheets at higher cutting speeds as compared to that of nitrogen. However, when using oxygen as auxiliary gas, the quality of cuts appears to be lower and their width larger as compared to cuts performed by nitrogen auxiliary gas. پرونده مقاله

Micro ultrasonic machining (Micro-USM) is a process with a great capability to generate micro features in hard and brittle materials. Despite some developments in micro-USM process, issues such as precision measurement and control of the machining force, which is crucial for stable machining conditions, need further investigations. In this paper, the precision measurement and control of the machining force is studied using a newly-developed force measurement configuration. The results of the force measurement for different levels of static force, abrasive particle size and amplitude of vibration demonstrated that the variation of measured machining force increases at higher static forces. Furthermore, a better control over the static load was acquired when feeding the abrasive slurry with particle size of 0.37 mm as compared to 1 mm and 3 mm particles leading to more stable machining conditions in micro-USM process. Finally, applying lower levels of vibration amplitude to the workpiece resulted in more stable machining conditions and lower static load errors. پرونده مقاله

This paper presents a model to predict Material Removal Rate (MRR) in Micro Ultrasonic Machining (micro-USM). The proposed model is developed based on the ductile-mode of material removal in micro-USM process. The correlation between ductile material removal rate and process parameters including frequency and amplitude of the ultrasonic vibration, particle size, and slurry concentration is presented. The proposed predictive model is verified by performing micromachining experiments using two types of workpiece materials including silicon and quartz at various process parameters levels. The results show that the MRR increases with a rise in vibration amplitude for both silicon and quartz materials. The experimental MRR values follow a trend similar to that of predicted MRR values. However, the predicted MRR values are higher than the measured MRR values for both silicon and quartz materials. The measured MRR values for ductile removal mode were found to have a considerable increase at vibration amplitudes of 2 mm and 2.4 mm for silicon and quartz, respectively, which is in favour of increasing the accuracy of the model prediction. پرونده مقاله

Gas turbine disks usually operate at very high temperatures and rotate at very high angular velocities under normal working conditions. High temperature in turbine disks causes changes in their properties. High angular velocity creates a large centrifugal force in the disk and high temperature reduces the strength of the material and causes deformation. Complexity of these parameters has turned the determination of stress distribution in gas turbine disks to one of the bottlenecks in the analysis, design and manufacturing of turbine engines. Therefore, using an applicable method for stress analysis is essential in order to better determine stress distribution in turbine disks. In this study, the finite element method (FEA) is used for predicting the behavior of rotating disks under mechanical and thermal stresses. In order to increase the certainty of simulation, gas turbine disk is first simulated and analyzed based on dimensions and loading conditions extracted from previous studies. Then, the results are compared with previous studies in order to determine the accuracy of analysis method applied in ANAQUS software. Afterwards, gas turbine disks are evaluated under both rotational movement and temperature gradient. The results show that the presence of angular velocity and centrifugal force cause expansion to the disk radius. The results show an acceptable correlation between the results of empirical and numerical studies. According to the results, the approach proposed in this study is a suitable method for analysis of the stress, temperature and displacement in turbine disks and other components with similar functions. پرونده مقاله

Surface quality including surface roughness and edge chipping is a key process measure in microultrasonic machining (Micro-USM) as an efficient process for micromachining of hard and brittlematerials. Process parameters such as ultrasonic vibration amplitude, static load, type of toolmaterial, type and size of abrasive particles and slurry concentration can influence the surfacequality. However, there is limited study on the parametric effects on the surface quality in micro-USM. The objective of this study is to investigate the effects of the workpiece material as well asprocess parameters including abrasive type, particle size and vibration amplitude on surfaceroughness and edge chipping in micro-USM. Silicon, alumina ceramics and soda-lime glass wereselected as workpiece materials and polycrystalline diamond and alumina as abrasives. Particle sizeranging from 0.3 to 3 μm and vibration amplitude ranging from 0.8 to 3 μm were selected in thisstudy. Results indicate that workpiece material and vibration amplitude have significant effects onsurface roughness. Workpiece material was found to be the most significant parameter with apercentage contribution of about 45 % in the variation of mean Ra, followed by vibration amplitudeand particle size of about 28 % and 5% contributions, respectively. Results also show that aluminaceramic is a material capable of achieving better surface quality in micro-USM as compared tosilicon and soda-lime glass. پرونده مقاله

Grinding is finishing process aimed at achieving surface quality and dimensional accuracy in workpieces with tight tolerances especially from materials with a high degree of hardness and strength. The grinding process of superalloys is faced with problems and challenges caused by the generation of excessiveheatas well as the adhesion of workpiecematerialon the grinding tool. Therefore, in-depth research is still under way to introduce and develop new techniques for optimization of output parameters in the grinding of superalloys. One of such techniques is to apply minimum quantity lubrication (MQL) using nanofluids.In this research, we study the effect of using a type of mixed nanofluid comprising multiwall carbon nanotubes (MWCNT) and nano-aluminum oxide (Al2O3) on the surface quality in the grinding process of Inconel 600.For this purpose, the input parameters of the process are first determined. Following that, the design of experiments were performed based on full factorial method and the, grinding experiments were conducted accordingly to study the effect of various parameters including the nanoparticles size , volume concentration, and mixing ratio on surface quality of the workpiece. Based on the results obtained from this study, while using the vegetable oil for MQL with nanofluids, the highest surface quality with Ra=0.15µm is achieved by applying a nanofluid with a mixing ratio of 75% -25% for Al2O3 -MWCNT nanoparticles, volume concentration of 0.6%, and with size of 20 nm and 15 nm for Al2O3and MWCNT nanoparticles, respectively. پرونده مقاله