Showing papers on "Rotational speed published in 2020"

A multi-objective optimization of the friction stir welding process using RSM-based-desirability function approach for joining aluminum alloy 6063-T6 pipes

Abstract: In this study, a multi-objective optimization technique involving response surface methodology (RSM)-based desirability function approach is used in optimizing the process parameters for friction stir welding of AA6063-T6 pipes. Two process parameters, namely, tool rotational speed and weld speed, are optimized for achieving a weld joint having superior tensile properties, viz., maximum yield, and ultimate tensile strength and maximum % of elongation. A regression model, with a 95% confidence level, is developed using response surface methodology to predict the tensile strength of the weld joint. ANOVA technique is used to determine the adequacy of the developed model and identify the significant terms. The desirability function is used to analyze the responses and predict the optimal process parameters. It is found that tool rotational speed and weld speed have equal influence over the tensile strength of the pipe weld. Tool rotational speed 1986 rpm and weld speed 0.65 rpm have yielded a maximum ultimate tensile strength of 167 MPa, yield strength of 145 MPa, and % elongation of 8.3, under considered operating conditions. Microstructural attributes for superior weld properties are also discussed.

Compound Bearing Fault Detection Under Varying Speed Conditions With Virtual Multichannel Signals in Angle Domain

Abstract: Mechanical fault diagnosis under varying speed conditions has gradually become an important issue in rotating machinery monitoring, especially the research on compound fault diagnosis is still rare. Order analysis is one of the most effective and widely used methods to eliminate the effects of speed fluctuations; however, it is difficult to extract compound fault features directly. Moreover, there are often many restrictions on the number and locations of sensors to be installed in practice, which also brings great challenges to compound fault diagnosis under varying speed conditions. In this article, a novel compound fault detection method with virtual multichannel signals in the angle domain is proposed to solve these problems for rolling bearing monitoring under varying speed conditions. First, we aim to use only a vibration acceleration sensor and a noncontact rotational speed sensor to adapt to limitations on sensor installation in practical applications. However, this may result in an underdetermined problem when trying to detect a compound fault with only a single-channel vibration signal. Then we make it up through constructing virtual multichannel signals based on variational mode decomposition theory, before which the nonstationary vibration signal is converted from the time domain into a stationary signal in the angle domain with computed order tracking to eliminate speed fluctuations. Finally, these virtual signals can be easily taken as input to a normal independent component analysis, and different faults can be detected in the order spectrum of each independent component. Case studies on rolling bearing experiments verified the advantages of the proposed method in compound fault detection under varying speed conditions.

Q-Learning based Maximum Power Extraction for Wind Energy Conversion System With Variable Wind Speed

Abstract: This paper presents an intelligent wind speed sensor less maximum power point tracking (MPPT) method for a variable speed wind energy conversion system (VS-WECS) based on a Q-Learning algorithm. The Q-Learning algorithm consists of Q-values for each state action pair which is updated using reward and learning rate. Inputs to define these states are electrical power received by grid and rotational speed of the generator. In this paper, Q-Learning is equipped with peak detection technique, which drives the system towards peak power even if learning is incomplete which makes the real time tracking faster. To make the learning uniform, each state has its separate learning parameter instead of common learning parameter for all states as is the case in conventional Q-Learning. Therefore, if half learned system is running at peak point, it does not affect the learning of unvisited states. Also, wind speed change detection is combined with proposed algorithm which makes it eligible to work for varying wind speed conditions. In addition, the information of wind turbine characteristics and wind speed measurement is not needed. The algorithm is verified through simulations and experimentation and also compared with perturbation and observation (P&O) algorithm.

A stacked electromagnetic energy harvester with frequency up-conversion for swing motion

Abstract: This paper undertakes theoretical and experimental investigations of a stacked magnetic modulation harvester with frequency up-conversion for energy harvesting performance enhancement from swing motion. The harvester includes stacked rings including a coil ring, an energy harvesting magnetic ring, a ferromagnetic ring, and a frequency up-conversion magnetic ring with a proof mass, which are axially designed in the same rotating axis to increase the rotation speed of the magnetic field due to swing excitations from human motion. The magnetic flux density produced by frequency up-conversion mechanisms is calculated to derive the governing theoretical model for harvester performance prediction. The rotation speeds and inductive voltages of theoretical results show good agreement with the experimental results in a range of rotational speeds. A range of motion speed tests on a treadmill are performed to demonstrate the advantage of the stacked electromagnetic harvesters on harvested energy from human motion. The average output power improves from approximately 1.5 mW to 11.8 mW when motion speed increases from 4 km/h to 8 km/h. The maximum power density under human motion is 61.9 μW·g−1, with a total weight of 190.7 g.

Discrete Element Simulation of the Effect of Roller-Spreading Parameters on Powder-Bed Density in Additive Manufacturing.

Abstract: The powder-bed with uniform and high density that determined by the spreading process parameters is the key factor for fabricating high performance parts in Additive Manufacturing (AM) process. In this work, Discrete Element Method (DEM) was deployed in order to simulate Al2O3 ceramic powder roller-spreading. The effects of roller-spreading parameters include translational velocity Vs, roller's rotational speed ω, roller's diameter D, and powder layer thickness H on powder-bed density were analyzed. The results show that the increased translational velocity of roller leads to poor powder-bed density. However, the larger roller's diameter will improve powder-bed density. Moreover, the roller's rotational speed has little effect on powder-bed density. Layer thickness is the most significant influencing factor on powder-bed density. When layer thickness is 50 μm, most of particles are pushed out of the build platform forming a lot of voids. However, when the layer thickness is greater than 150 μm, the powder-bed becomes more uniform and denser. This work can provide a reliable basis for roller-spreading parameters optimization.

Parameter Optimization of Rotary Ultrasonic Machining on Quartz Glass Using Response Surface Methodology (RSM)

Abstract: In the current research, rotary ultrasonic machining was used to drill holes in quartz material. The effect of different RUM parameters namely tool feed rate, tool rotational speed and ultrasonic power on material removal rate and surface roughness has been studied experimentally. The response surface methodology with central composite design has been used to design the experiments. From the desirability approach, the optimum setting of the rotary ultrasonic machining parameters was found to be the tool rotational speed of 4968 rpm, feed rate of 0.55 mm/min, and ultrasonic power of 80% for achieving the maximum MRR of 0.2135 mm3/s and minimum SR of 0.3685 μm. Microstructure analysis of the machined surface was performed by using scanning electron microscopy in order to study the mechanisms of material removal under the different settings of RUM parameters. It was observed that at very low feed (0.08 mm/min) and high rpm (5681) the material is predominantly removed by plastic deformation whereas at high feed (0.92 mm/min) and low rpm (2318) the material is removed by brittle fracture.

Evaluation of the formation of intermetallic compounds at the intermixing lines and in the nugget of dissimilar steel/aluminum friction stir welds

Abstract: A relatively successful dissimilar joint between 1050 pure aluminum and annealed low carbon steel is achieved by using friction stir welding. Most studies of joining aluminum to steel have been performed by using low rotational speed with high traverse speed to minimize heat in weld zones and to minimize the thickness of the intermetallic compounds (IMCs). Although the minimized heat may reduce the formation of brittle IMCs but the steel side may not be strongly influenced by this heat which affects the stirring action on both sides. The novelty of this analysis is applying great generated heat by employing a combination of a low traverse speed and a high rotational speed to accomplish the joints. In this study, a high rotational speed of 1550 rpm, a low traverse speed of 17 mm/min, a tilt angle of 1°, a pin length of 1.6 mm, and a deep shoulder surface penetration of 0.2 mm on 1.9 mm sheet thickness is the best set obtained to maximize both the frictional heat and the joint strength. The theory used exhibits more stirring of steel on aluminum than previous studies. The major contribution obtained from this study is knowing a new evaluation of the effect of the thicknesses of the IMCs formed at the interface and on the nugget. It is shown that the effect of the thickness of IMCs formed has a very little impact on the joint strength of about 1.3% at a very high difference in the IMCs thickness obtained between 7.5−8 μm and 8−36 μm. The joint strength depends on how the wide intermixing of steel edge on the aluminum side creates and the size/shape of steel particles.

Simulation of heat transfer and analysis of impact of tool pin geometry and tool speed during friction stir welding of AZ80A Mg alloy plates

Abstract: Peak temperature arising during the joining of metals by friction stir welding (FSW) needs to be investigated along with other process parameters of FSW to understand their inevitable impact on joint quality. This investigational and experimental analysis aims to determine the impact of pin geometry and its rotational speed by formulating thermic mechanical process-based models to anticipate peak temperature and to compare it with actual values. Three distinctive pin geometries rotated at three speeds were used while other parameters were unchanged. The fitness and suitability of the model were verified by comparing the anticipated values with the experimental values. Macrographic and micrographic observations revealed that flawless joints with improved mechanical properties were fabricated at a peak temperature of 616 K (80 % melting temperature) when a taper cylindrical pin with a rotational speed of 818 rpm was employed. In addition, SEM analysis of the fractured specimen confirmed that failure of the defect free weldment occurred in brittle mode, indicating that preferred fusion of grains and their constituents occurred during the joining process.

Prediction of temperature and residual stress distributions in friction stir welding of aluminum alloy

Abstract: A thermal model considering the heat generated by friction and plastic deformation is developed for friction stir welding. The proportion of heat-generated between friction and plastic deformation depends on the contact states determined by the temperature and velocity of the tool. The model is verified by welding experiment, and the numerical results agree with the experimental data. Then, the effects of process parameters on temperature and residual stress are investigated using the validated model. These process parameters involve the welding speed, rotational speed, and axial force. The results show that the temperature increases with the increase of the rotational speed and axial force, and decreases with the increase of the welding speed. The increase of the axial force and welding speed will lead to larger tensile stress in the weld zone. Furthermore, the relationship between peak temperature, peak residual stress, and process parameters are established though regression method.

Experimental studies on controlling of process parameters in dissimilar friction stir welding of DH36 shipbuilding steel–AISI 1008 steel

Abstract: In the present work, DH36 steel and AISI 1008 steel sheets were joined using friction stir welding (FSW) process to investigate the influence of the rotational speed, traverse speed, and tool offset on temperature distribution, z-force, microstructure, and mechanical properties of the welded specimens. At a traverse speed (v) of 50 mm/min with a rotational speed (ω) of 600 rpm and tool offset of 2 mm, the maximum impact toughness and hardness were obtained due to higher grain refinement. The transverse tensile test specimens fractured in the weaker material (i.e., AISI 1008 steel) and exhibited the ultimate tensile strength values at least on the level of the weaker material. The impact toughness and hardness were highly dependent on the grain size variation. The effect of pitch ratio (ω/v) on grain size variation was more as compared with that on tool offset. Increasing the pitch ratio reduced the grain size and improved the impact toughness and hardness. Stir zone exhibited the acicular-shaped bainitic ferrite in DH36 steel and Widmanstatten ferrite grains in AISI 1008 steel. The higher hardness values were observed in thermo-mechanically affected zone of both steels due to significant grain refinement. Increasing the rotational speed and decreasing the traverse speed result in a higher welding temperature, which reduced the z-force.

A revisit of the tonal noise of small rotors.

Abstract: In this study, asymptotic analysis of the frequency-domain formulation to compute the tonal noise of the small rotors in the now ubiquitously multi-rotor powered drones is conducted. Simple scaling laws are proposed to evaluate the impacts of the influential parameters such as blade number, flow speed, rotation speed, unsteady motion, thrust and observer angle on the tonal noise. The rate of noise increment with thrust (or rotational speed) is determined by orders of blade passing frequency harmonics and the unsteady motion. The axial mean flow influence can be approximated by quadratic functions. At given thrust, the sound decreases rapidly with the radius and blade number as the surface pressure becomes less intensive. The higher tonal harmonics are significantly increased if unsteady motions, although of small-amplitude, are existed, as indicated by the defined sensitivity function, emphasizing that the unsteady motions should be avoided for quiet rotor designs. The scaling laws are examined by comparing with the full computations of the rotor noise using the frequency-domain method, the implementation of which has been validated by comparing with experiments. Good data collapse is obtained when the proposed scaling laws, which highlights the dominant influence of the design parameters, are incorporated.