Papers by Keyword: Friction Model

Abstract: In this study, hot ultrasonic assisted machining of Hastelloy-X material was compared using two different finite element software (DEFORM and AdvantEdge). The results obtained from the two software were compared in terms of maximum cutting tool temperature, average cutting force and maximum effective stresses. The simulations were performed in 2D. The results obtained from the two software were compared with the experimental study in terms of maximum cutting tip temperatures.

Abstract: Built-up Layer (BUL)/Built-up Edge (BUE) formed on the tool surface can be treated as a protective, thermal barrier or lubricant films especially in the extreme severe conditions when machining the metal materials, which can sustain the tool effective and wear resistance. In order to have a thorough understanding of the adhesion effect during machining, experiments have been carried out to investigate the performance and the formation mechanisms of adhering layer on the carbide tool in machining of aluminium alloys A6063, carbon steel S45C and difficult-to-cut hardened steel S45C (H-S45C). The morphology of tool adhered surface was examined by employing Scanning Electron Microscopy (SEM), the dimensions of adhering layer were measured by Laser Scanning Microscopy (LSM) and the elements on the tool were analyzed by Electron Probe Micro Analyser (EPMA), respectively. The atomic-scale cluster adhesive friction model is proposed to explain the tool-chip contact conditions, which considers the nature of the shear strain, shear strain rate and temperature distribution in the secondary deformation zone. The model is a dynamic model and the rate equation approach can be applied to estimate the formation process of adhering layer during machining. Results have shown that the adhering layer will give rise to BUL on the tool rake face and the BUE on the cutting edge and clearance face.

Abstract: Cutting force, cutting heat and tool wear are closely related to the friction characteristics of tool-chip interface in the process of metal cutting. The variation of the cutting speed and temperature have been analyzed by the distribution of stress and strain in the primary and the secondary shear zone. A new friction model has been established to analyze the contact length between cutting tool and chip and local friction coefficient at the sliding zone. Cutting experiments have been performed in the process of carbide tools cutting the titaniumTi6Al4V, the contact length of sticking zone and sliding zone and friction coefficient have been analyzed by measured cutting force. The simulation of cutting process has been carried out based on Deform software, then the simulation results have been compared with the test ones, which verifies the accuracy of the established model.

Abstract: After modifying the Wahime/Bay friction model, a new friction model suitable for micro-forming process without lubrication is established. In this model, it is shows that the friction coefficient is a function of strain hardening exponent, the normal pressure and the initial yield stress of material. Based on the experimental data, the micro-upsetting process is simulated using the proposed friction model. The simulation results are used to investigate the size effect on the dry friction behavior. It is found that the Coulomb’s friction coefficient is dropping with miniaturization of specimens when the amount of reduction is not too large.

Abstract: To determine the impact of dynamic recrystallization on frictional behaviour in the tool-chip interface, a specific friction test called the Warm and Hot Upsetting Sliding Test (WHUST) is implemented. This friction bench simulates tests with contact pressure, sliding velocity, contactor and specimen temperatures similar to industrial ones. Several tests are performed on specimens at different sliding speed, penetrations and work-piece temperatures to reach different dynamically recrystallized states. A numerical model of this test using Arbitrary Lagrangian Eulerian (ALE) method is implemented. Thanks to a specific rheological model, we are able to predict the evolution of the volume fraction of recrystallized grains.

Abstract: The aim of this paper is to compare the predicting ability of the orthogonal cutting models developed by three commonly used finite element softwares, namely commercial explicit dynamic code Abaqus/explicit, Thirdwave AdvantEdge and implicit finite element codes Deform 2D. In all proposed models, the chip formation was simulated through adaptive remeshing and plastic flow of work material around the round edge of the cutting tool. Therefore, there was no need for a chip separation criterion which made the physical process simulation more realistically. Predicted cutting, feed force and shear angle were compared with experimental results. In addition, the effect of friction coefficient on the chip morphology was investigated as well.

Abstract: In order to improve the performance of the electro-hydraulic servo system, considering the special structure of servo motor, nonlinear model of the servo motor was established in time domain. Several friction models commonly used in project were introduced and applied to the simulation analysis of servo motor with friction torque. The simulation curves show the relationship between driving torque, friction torque, angular velocity and angular displacement. The result confirms the influence of the different friction torque model on the performance of motor, and the LuGre friction model is identified which is fit for the friction torque compensation. This study lays the foundation for the friction torque compensation of electro-hydraulic servo motor.

Abstract: A novel modified LuGre friction model is proposed by taking pressure of the cylinders into consideration. And a practical identification method to estimate the parameters associated with the modified friction model is presented. The validity of the modified model is investigated experimentally. It is shown that the modified LuGre model can demonstrate the comprehensive friction behaviors of the forging machine with a fairly good accuracy.

Abstract: Generally, pressures resulted from roller during leveling process in selective laser sintering has the effect of densification of powder materials. But extra frictions due to them become the forces which always deteriorate the surface of the part and mark it with several lines trace. Sometimes, the manufacturing can even not continue if these forces accumulate to a large extent to move the whole part. Therefore, the whole forming process will be obliged to stop owing to the displacement of part from above mentioned damage. In this work, the emerging reason and related variation factors of these forces were studied mathematically, the mathematical and physical model of friction force was also built to describe the connections between the leveling process parameters and them. How to control the influence factor of friction to abate their damages to surfaces and promote the forming quality were also discussed based on these models. This will provide a common reference for the application of selective laser sintering technology.

Abstract: In order to reduce the influence of frictional interference and measurement noise on stabilized platform tracking performance, disturbance observer (DOB) is applied to platform servo system. In view of the non-ideal performance of classical disturbance observer about suppressing measurement noise, a novel improved DOB which uses an additional control signal to compensate system outputs is proposed based on the structure of classical DOB, and robust stability of the improved DOB when existing model perturbation is analyzed in detail. Simulation results show that the improved DOB can suppress external disturbances and model perturbation well, and the suppression performance of measurement noise is improved, too.