Numerical analysis of dynamic characteristics in the ultra-high speed grinding spindle system

In this paper, the dynamic characteristics of ultra-high speed grinding spindle system is analyzed by using digital analysis methods. The spindle system is the key components of the machine tool, and its performance directly determines the machining stability and accuracy. Liquid hybrid bearing, with its superior performance has been widely applied to high speed and heavy machine tools. In order to study the spindle system, Fluent software was used to analyze the dynamic characteristics of liquid hybrid bearing. With the increase of the rotational speed, the capacity of liquid hybrid bearing changes significantly, and the relationship between the capacity and rotational is linear in intermediate stage. At the same time, the stiffness and damping of the liquid hybrid bearing has a corresponding increase with the increase of rotational speed. When the rotational speed increase to a certain extent, the dynamic performance of the spindle system will improve. Finally, the concentrated mass method and the finite element analysis method were used to analyze the dynamic characteristics of the spindle system, respectively. The results obtained by the both methods have good consistency, and the critical speed is about 14000 rve/min

The convergence investigation of meshless finite block method and finite element method

The finite element method is one of the most widely used numerical method in engineering analysis, however, the bad convergence and the complexity of meshing reduce the reliability of the simulated results. Therefore, in this work, a meshless finite block method was applied on heat transfer analysis and elastic deformation analysis. It combines the ideas of finite element and boundary element. A better convergence of meshless finite block method than finite element method was proved

Simulation analysis of rock braking mechanism of tunnel boring machine

U svrhu odgovora na pitanja trošenja i oštećenja odvalnog glodala u postupku loma stijene, simulirao se postupak loma stijene pri raznim stanjima loma primjenom metode konačnih elemenata. Odnos između normalne sile, lateralne sile, sila pri valjanju i vremena dobiven je analizom simulacije loma stijene strojem za rezanje s jednom oštricom. Naprezanje stijene se analiziralo na različitim dubinama kad naprezanje dostigne maksimalnu tlačnu čvrstoću stijene. Najbolji prostor za rezanje postignut je na određenoj dubini analizom stanja naprezanja oštrice stroja u različitim prostorima. Učinkom oblika poprečnog presjeka oštrice na trošenje završen je ovaj rad. Istraživanje je pružilo reference vezano za trošenje i optimizirani dizajn glodala na stroju za bušenje tunela.Aiming at answering the questions of wear and failure of hob in the rock breaking process, the rock breaking process was simulated in different broken rock conditions by using finite element method. The relationship between normal force, lateral force, rolling force and time was obtained by rock breaking simulation analysis on the single edge disc cutter. The rock stress was analysed by setting different cutting depth when the stress reaches the maximum compressive strength of the rock. The best cutter space was also obtained in a certain depth by analysing the stress state of the cutter in different cutter space. The paper concluded with the effect of the disc cutter cross section shape on the wear. Therefore the study provided references for the wear and the optimized design of hob on Tunnel Boring Machine

Modelling and experimental study of surface treatment in abrasive waterjet peening of Nickel-based superalloy: Inverse problem

Abrasive waterjet peening (AWJP) is a promising method of surface treatment for modifying mechanical properties of components by introducing compressive residual stress (CRS) to a workpiece surface. Many efforts have been paid so far to modelling and optimisation of the AWJP process, however, most of these studies focus on the forward problems, i.e. estimating the CRS of workpiece surface according to processing parameters. There are still significant challenges in implanting different CRS at target areas in workpiece surface, which is the foundation of implanting uniform distribution of CRS on free-form surface or workpiece with uneven initial stress state. In this paper, a novel temporally and spatially controlled method for AWJP has been proposed, where the distribution of CRS can be adjusted by the optimisation of the abrasive waterjet parameters. That is, to achieve the AWJP system configuration for specific CRS on a target area, an inverse problem of CRS distribution has been modelled and solved, where the pump pressure, traverse speed and centre distance were optimised together to reach a prescribed CRS distribution. The proposed method was validated through experiments of implanting uniform distribution and non-uniform distribution of CRS at target areas. The results revealed that the maximum error between target and experimental CRS was only 14.25% in 18 sets of experiments. In addition, microstructure analysis of the AWJP surface suggested that a relatively low pump pressure and traverse speed can be selected to induce grain refinement and strain hardening layer on the workpiece surface without cracks and heavy surface topography fluctuations

Prediction of 3D grinding temperature field based on meshless method considering infinite element

© 2018, Springer-Verlag London Ltd., part of Springer Nature. A three-dimensional numerical model to calculate the grinding temperature field distribution is presented. The finite block method, which is developed from meshless method, is used to deal with the stationary and the transient heat conduction problems in this paper. The influences of workpiece feed velocity, cooling coefficient, and the depth of cut on temperature distribution are considered. The model with temperature-dependent thermal conductivity and specific heat is presented. The Lagrange partial differential matrix from the heat transfer governing equation is obtained by using Lagrange series and mapping technique. The grinding wheel-workpiece contact area is assumed as a moving distributed square heat source. The Laplace transformation method and Durbin’s inverse technique are employed in the transient heat conduction analysis. The results of the developed model are compared with others’ finite element method solutions and analytical solutions where a good agreement is demonstrated. And the finite block method was proved a better convergence and accuracy than finite element method by comparing the ABAQUS results. In addition, the three-dimensional infinite element is introduced to perform the thermal analysis, and there is a great of advantages in the simulation of large boundary problems.The work was funded by China Scholarship Council, the Fundamental Research Funds for the Central Universities (N160306006), National Natural Science Foundation of China (51275084), and Science and technology project of Shenyang (18006001)

Study on a Chiral Structure with Tunable Poisson’s Ratio

A chiral structure with a negative Poisson’s ratio containing a hollow circle with varying diameters was designed, and the finite element method was used to investigate the variation in the Poisson’s ratio when the hollow circle diameter was varied (d = 0, 1, 2, 3, and 4 mm). The simulation results showed that the Poisson’s ratio was sensitive to the hollow circle diameter, and the minimum Poisson’s ratio was −0.43. Three specimens with different hollow circle diameters (d′ = 0, 1, and 3 mm) were 3D-printed from thermoplastic polyurethane, and the Poisson’s ratio and equivalent elastic modulus were measured. In the elastic range, the Poisson’s ratio increased and the equivalent elastic modulus decreased as the hollow circle diameter increased. The simulation and experimental results showed good agreement. The proposed structure is expected to be applicable to protective sports gear owing to its high energy absorption and the fact that its properties can be modified as required by adjusting the geometric parameters of the unit cell

Simulation Analysis of Knee Ligaments in the Landing Phase of Freestyle Skiing Aerial

The risk of knee injuries in freestyle skiing athletes that perform aerials is high. The internal stresses in the knee joints of these athletes cannot easily be directly measured. In order to ascertain the mechanical response of knee joints during the landing phase, and to explore the mechanism of damage to the cartilage and ligaments, a finite element model of the knee joint was established. Three successful landing conditions (neutral, backward, or forward landing) from a triple kicker were analyzed. The results demonstrate that the risk of cruciate ligament damage during a neutral landing was lowest. A forward landing carried medium risk, while backward landing was of highest risk. Backward and forward landing carried risk of injury to the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), respectively. The magnitude of stress on the meniscus and cartilage varied for all three landing scenarios. Stress was largest during neutral landing and least in backward landing, while forward landing resulted in a medium level of stress. The results also provide the basis for training that is scientifically robust so as to reduce the risk of injury and assist in the development of a professional knee joint protector

Design of Optical Free-Form Surface Milling Machine Based on Mechanical Shunt and Dynamic Analysis

An optical free-form surface milling machine is designed according to the process characteristics and cutting force of optical components manufacturing. The Z-axis column of the milling machine is designed by a mechanical shunt. In this paper, based on the principle of multibody dynamics (MBD), a virtual prototype (VP) of the optical free-form surface milling machine was established by the ADAMS software. The Z-axis characteristics of the milling machine were simulated and studied, and a modal analysis was carried out to obtain the natural frequencies and vibration modes of the milling machine. The simulation results show that the Z-axis of the milling machine has excellent dynamic characteristics when the gravity balance device is not working. The average torque of the Z-axis motor is 0.5 N·m when the gravity balance device is working, the average torque of the Z-axis motor is 0.1 N·m, and the average torque is reduced by 80%; therefore, the gravity balance device can obviously lower the load of the Z-axis motor, and improve the efficiency of the milling machine

Design of Optical Free-Form Surface Milling Machine Based on Mechanical Shunt and Dynamic Analysis

An optical free-form surface milling machine is designed according to the process characteristics and cutting force of optical components manufacturing. The Z-axis column of the milling machine is designed by a mechanical shunt. In this paper, based on the principle of multibody dynamics (MBD), a virtual prototype (VP) of the optical free-form surface milling machine was established by the ADAMS software. The Z-axis characteristics of the milling machine were simulated and studied, and a modal analysis was carried out to obtain the natural frequencies and vibration modes of the milling machine. The simulation results show that the Z-axis of the milling machine has excellent dynamic characteristics when the gravity balance device is not working. The average torque of the Z-axis motor is 0.5 N·m when the gravity balance device is working, the average torque of the Z-axis motor is 0.1 N·m, and the average torque is reduced by 80%; therefore, the gravity balance device can obviously lower the load of the Z-axis motor, and improve the efficiency of the milling machine