Improving the Dynamic Characteristics of Precision Lathes Used in the Repair of Agricultural Machinery

A model of a friction unit of a lathe in the form of a thin layer of material of a honeycomb structure is described to determine the dynamic characteristics of a movable carriage to guide joint. The analysis of the mathematical model of friction for different sliding pairs with varying load and sliding speed is performed. It is shown that the presence of an abrasive impurity in the lubrication of the guide enhances the effect of the low-frequency component of the carriage vibrations on the dynamics of the machine tool and the presence of pockets for retaining the lubricant in the joint of the guide makes it possible to reduce the amplitude of the longitudinal vibrations of the carriage to 30-50 %.

Analysis and Revision of Torque Formula for Hydro-viscous Clutch

Hydro-viscous clutch is a speed-regulating device for heavy fans and water pumps. It has important engineering significance in the fields of soft-start for rotating machinery. More and more attention has been paid to its torque and control characteristics. This paper is focused on the torque formula for hydro-viscous clutch (HVC), assuming that multi-friction plates distribute ununiformly with different oil film thickness. A mathematical model of friction plates was constructed, then the distribution formula of the oil film thickness was obtained. A new expression was presented using a modified factor. Parameters such as pressure, viscous torque, and oil film thickness were obtained. The results show that each clearance of friction plates is not the same and the distribution of oil film thickness is influenced by pressing force, groove depth, angular ratio of groove/non-groove, and static friction force. To verify the proposed expression, relevant experiments were carried out on an HVC with multi-friction plates, and the experimental results indicate that the new expression is more accurate compared to the original one.

A Semi-Analytical Solution for Temperature Distribution in Friction Stir Welding

In this paper, a semi-analytical thermal model of friction stir welding processes is developed in which the heat-generating regions are divided into many elements as point heat sources. The heat generation in each element involves the friction and plastic deformation, and the temperature rise caused by each element is calculated by solving the heat conduction equation of a moving heat source in a solid body. The heat loss through the top and bottom surfaces are considered in the model as heat sinks. The asymmetric distribution of the temperature is calculated through the whole process and over the whole volume of the workpiece by integrating the effects of all heat sources and sinks. The temperature-dependent material properties are updated by a numerical routine. The comparison between the calculated results and the experimental data clearly approved the validity of the proposed method for some aluminum and steel alloys.

The micro contact model of friction materials in friction hoisting-and-transport cars at different temperatures

In the paper there is proposed computer model of the contact of friction materials in the brake devices of building road machines and lifting transport machines at different temperatures. The contact surface is modeled by a microrelief composed of a set of elements in the form of rods. As a result of modelling, there are such contact characteristics as rapprochement, distribution of contact pressure, real contact area and the gap between the surfaces. The obtained dependencies are compered with the finite element method. Keywords computer model of contact at diggerent temperatures, temperature influence, contact of friction material, actual contact area, contact pressure distribution

Verification of Friction Models Implemented in the Simulation Software

Modern approaches in simulations of sheet metal stamping processes are based on definition the friction coefficient as not constant, but the different value in different regions, considering the nature of the actual deformation process in each individual region. In this contribution the regression and analytical models to determine the friction coefficients under blankholder and on the die drawing edge by strip drawing test are presented. These models were verified by experimental strip drawing test under the same contact conditions. Zn coated steel sheets for the automotive industry were used in experiments and simulations – extra deep drawing quality DX54D and high strength steel TRIP. The results indicate, that friction coefficients are not constant and depend on the pressure on the die contact surfaces. Friction coefficients were determined also at the cup test by the regression model of drawing versus blankholding force. Conformity of friction coefficients obtained by the cup and the strip tests was confirmed. Model of friction applied in FEM simulation was verified by cup test and good conformity was found out.

The redistribution of temperature-induced interface friction in friction-type high-strength bolted joint after bolt fracture

For the friction-type high-strength bolted joint, the bolt fracture can cause redistribution of interface friction, which will seriously endanger the connection safety of structural members. However, current study scarcely focuses on the redistribution of interface friction after bolt fracture. Therefore, this paper will specifically carry out finite element analysis on the redistribution of interface friction caused by fractured bolts. Firstly, the refined finite element model of friction-type high-strength bolted joint is used to investigate the variation of interface friction with uniform temperature and the distribution of interface friction in different areas. Furthermore, stochastic finite element method is introduced to explain how the quantity and location of fractured bolts influence the redistribution of interface friction. Finally, the mathematical model of friction redistribution is built to describe the redistribution of temperature-induced interface friction in the friction-type high-strength bolted joint after bolt fracture. After validation, the mathematical model can well describe the redistribution of interface friction caused by fractured bolts.