- Detail

Research on virtual machining modeling

1 Introduction

at present, the manufacturing industry is facing great challenges. At the same time, the economic development also puts forward higher requirements for the manufacturing industry. The emergence of virtual manufacturing technology is to meet this challenge. Using virtual manufacturing technology can evaluate the performance, appearance and quality of products in the product design stage, so as to shorten the development cycle of products and improve production efficiency. As one of the keys of virtual manufacturing technology, virtual machining technology has been paid more and more attention. The key to realize the virtual machining of maximum torque, torsional strength, upper yield strength and lower yield strength is virtual machining modeling. Only by reasonably modeling the machining process can we better realize the prediction and control of machining quality in virtual machining, and better realize the reality and immersion of virtual machining

2 virtual machining modeling

virtual machining process is to simulate the machining process of parts in an all-round way with the help of virtual reality technology and computer simulation technology. Milling is an important means of machining complex parts, and the study of milling process is of great universal significance. Next, take the milling process as an example to illustrate the virtual machining simulation modeling. A simplified model of the milling system is shown in Figure 1. The system is simplified as vibration in two mutually perpendicular directions. The dynamic equation of the system is

where: the mass, damping and stiffness X and y of MX, CX, KX X and Y directions are the displacement FX (T) in X and Y directions respectively, and FY (T) the cutting force varying with time converts formula (1) into the following form

where XX, WNx, KX, XY, wny and KY are the structural damping ratio, natural frequency and stiffness in X and Y directions respectively. When solving the vibration displacement in two directions, these six parameters are measured first, so that the deformation of the system is only related to the cutting force. Different processing methods have different calculation methods of cutting force. In terms of milling force, the calculation methods are generally similar. The following takes ball end milling cutter as an example to calculate the milling force (see Figure 2). The cutting edge is divided into countless small segments along the edge line, and each segment is regarded as a turning tool. According to the oblique angle orthogonal cutting theory circle, the micro element cutting force

is obtained. In the formula: DFR micro element cutting force TS shear strength of materials DAC micro element instantaneous cutting area (related to instantaneous cutting thickness) AE effective rake angle shear angle B friction angle. Among them, the shear angle, shear strength and friction angle can be used to establish empirical formulas for different materials by experimental methods. Decompose DFR in the follow-up coordinate system o'x'y'z'where the cutter tooth is located into DFX, dfy and DFZ, and convert them into the whole tool coordinate system oxyz, and get the formula:

where: the micro cutting force of the i-th edge line of DFI (q), DFX, dfy, DFZ, the component force of DFR in o'x'y'z', DFX, dfy, DFZ, the component force of DFR in oxyz, Q the included angle of the edge line in oxyz, y the rotation angle of the milling cutter, and then integral along the cutting edge line, Get the vector sum of the cutting force on the whole edge line, and add all the forces on the edge line participating in the cutting. A more intuitive interface produces a complete solution. In the formula,

: fi cutting force vector on the i-th edge line j number of edge segments participating in the cutting on the i-th edge line qjl the lower integral limit qju of the infinitesimal participating in the cutting in this segment qju the upper integral limit of the infinitesimal participating in the cutting in this segment can be seen from the above formula, After obtaining the equation of the cutting edge line of the curve, the cutting force can be obtained by integrating along the cutting edge line. However, the number of segments and the upper and lower limits of the cutting edge line involved in cutting need to be obtained, which needs to be provided by geometric simulation. It can be seen from the above analysis that to realize the integration of physical simulation, it is necessary to calculate the number of cutting segments and cutting in and cutting out angles when the cutting edge intersects the workpiece. These parameters can be obtained by geometric simulation. The geometric simulation of the machining process is that elastic materials such as rubber are lined in the fixture, which is essentially the process of intersection between the tool scanning volume and the workpiece. In the geometric simulation, the workpiece is represented by B-rep modeling method. In this paper, the method of polyhedron approximation is used to describe the workpiece and the cutting material. For ball end milling cutter, the edge line equation of cutting edge is

, in which: coordinate of X, y, Z edge line R radius of ball cutter an effective rake angle of tool Q the included angle between tool edge line and coordinate axis. For each tool interpolation position, the intersection section between tool tooth edge line and workpiece entity can be obtained. The specific steps are as follows:

intersect the tool scanning body and workpiece entity to obtain two parts of entity, namely, the material body and workpiece have been cut

intersect the cutting edge line with the cut material body to obtain the line segment of the cutting edge line in the cut material body

calculate the cut-in angle and cut-out angle of these line segments and substitute them into equation (5) for solution

3 simulation experiment

from the vibration displacement diagram, when the regenerative vibration intensifies, the vibration displacement also increases with the increase of the angle. This is mainly because the dynamic cutting force increases with the increase of instantaneous cutting thickness, which leads to the increase of vibration displacement. At the same time, it can be seen that the simulation can well simulate the aggravation of regenerative vibration and is in good agreement with the experimental results

4 conclusion

modeling with the combination of physics and geometry can more truly represent the whole machining process, which can provide a basis for part machining error analysis, surface morphology simulation, part characteristic analysis, parameter setting and optimization, and machining state prediction and analysis

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