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Virtual machining has been around for a long time. With the advancement of science and technology, 3D computer-aided design is widely used in product design. In engineering design, processing design and product assembly level, computer aided development is needed. Technology, particularly in computer-aided engineering (CAE), uses finite element method (FEM) to pre-analyze the structure, thermal conductivity, and programming techniques used to determine tool trajectories using computer-aided manufacturing (CAM). They have penetrated into all areas of engineering and are effectively utilized.
The development trend of cutting simulation technology includes two aspects. One is to develop NC simulation software to display the tool movement trajectory and judge whether the tool, the tool holder and the workpiece and its fixture interfere.
In the end milling process, the most basic task is to cut off the enveloping surface of the cutting edge of the tool through a part of the material to be processed, so that the remaining part becomes the machined surface. The software used to complete this type of processing should include the following: coordination of tools, tool chucks, workpieces, fixtures, etc., the construction of the machine tool spindle and its working range, can truly simulate the movement of the machine tool and tool. Especially in recent years, due to the increasing number of five-coordinate cutting operations, the importance of NC simulation before actual machining has become increasingly prominent. Among these NC simulation softwares, many softwares have extremely excellent performance, such as calculating the machining efficiency from the metal removal volume; determining whether the machining process is overloaded according to the metal removal volume; if the load is fixed, the feed rate is too high. In the event of an overload, the simulation software can adjust the feed rate to prevent overload generation and shorten the cutting time.
Another development trend of the cutting simulation technology is to study and analyze the physical phenomena in the cutting process, such as the heat generated by the plastic deformation of the material to be processed, the material being cut is continuously wiped through the rake face of the tool to form the chip, and then discharged. The cutting edge of the tool cuts off the unnecessary material to form the machined surface on the workpiece, and the series of cutting processes are simulated by computer. There are only a few products that can achieve this ideal goal. Third wave systems' "advantedge" is a software product that uses finite element method to optimize and analyze the cutting process. Compared with the finite element method package for structural analysis, the biggest advantage is that the user interface is excellent, the machining technician It can be easily parsed. The "deform" of the American scientific forming technologies company is a finite element method analysis package for plastic deformation processing such as forging, and has recently been transferred to cutting.
The cutting process is the deformation process of the chip and the elastic deformation and plastic deformation of the material to be processed. Compared with the plastic deformation such as stamping and forging, the deformation speed (the amount of deformation per unit time) is very large, and the plastic deformation energy and the front knife are generated. The energy generated by the friction on the surface will cause heat, which will greatly increase the temperature. The cutting edge breaks the workpiece material in a continuous and narrow range, and separates it into chips and processed surfaces. This is a remarkable feature of the cutting process. These phenomena have complex interactions with each other.
If you use finite element analysis, you need to input the following: physical properties such as material properties and friction state; boundary conditions such as cutting conditions and tool shape. Through the finite element analysis of the rigid equation, the cutting parameters such as cutting force, shear angle and cutting temperature with the characteristics of chip generation state can be output. In this process, no mathematical model or hypothesis is needed. According to the results of the finite element analysis, it is also easy to visualize the physical quantities such as the chip generation process, stress, and deformation.
In order to obtain high-precision analytical results, the most important input is the material properties that reflect the stress-deformation relationship of the material being processed, and the acquisition of material properties is extremely laborious. In the future, as computer power increases, the physical simulation technology of this cutting process will gradually become popular. The key to rapid adoption is the ability to provide users with the material properties of the materials being processed in a timely manner.
Development of cutting simulation technology software on demand
At present, many scientific and technical personnel are conducting research on the most basic cutting technology in production engineering, and most of the research aims to predict the processing process while clarifying the processing phenomenon. If these research contents realize the computer software of the system, it means that a cutting simulation technology software can be formed. For example, the laboratory of the School of Mechanical Engineering of Tokyo University of Agriculture and Technology is conducting several predictive studies on cutting simulation technology software. The process flow and practical simulation adopt a horizontal and vertical matching research system, and the horizontal direction corresponds to the product design to the processing process; in the vertical direction, the higher the practicality, the lower the practicality, and the processing phenomenon. Parse and implement visualizations.
1. Cutting condition selection system using tool information database and analytical simulation technology
In the actual cutting process, the recommended cutting conditions provided by the tool factory should not be copied, but the test cutting should be repeated to correct the cutting conditions according to the specific conditions of the machine tool, tool system, and workpiece loading. At the same time, the effective reference data accumulated in the past processing should be input into the database, and the cutting conditions can be optimized by means of analytical methods while effectively utilizing the data; for new cutting without reference data, it should be developed. The cutting condition selection system associated with this. In this system, vibration, machining accuracy, tool temperature rise, tool life, residual stress, etc. are set as analysis contents, and based on the analysis, the optimum tool can be selected and the cutting conditions can be adjusted. [Page]
The data of this system is roughly divided into three parts: tool information data, tool system composition, and cutting conditions. Effective cutting process parameters can be accumulated in the cutting conditions.
This paper intends to use the legend to illustrate the optimum milling efficiency for the flat end mill machining and to optimize the shape error of the side. Select the required tool and tool holder according to the database, and predict the machining error caused by the bending of the end mill and the tool holder and the rotation change of the joint between the chuck and the spindle taper. The cutting force is predicted by multiplying the cutting force at the tip of the tool by the mode of the cutting resistance. This is the easiest method, but it yields good results with consistent cutting force waveforms and measured values. The amount of deflection of the tool caused by the cutting force at each moment is calculated, and the shape of the machined surface is obtained by connecting it to the displacement of the position of the cutting edge forming the machined surface. Compared with the calculation of the large-scale finite element method, the calculation time is very small, and the machining error can be easily simulated by inputting the tool information and the cutting condition information.
Although the database has a well-adapted cutting process condition, it is still desirable to further reduce the machining error and improve the processing efficiency. The examples show that it is entirely possible to correct the cutting conditions with this simulation and optimization.
2. Tool temperature during end mill machining
In recent years, high-speed milling has become commonplace. It is known from experience that it is suitable for milling conditions with small depth of cut and large feed, and it is quite difficult to grasp the best conditions. Milling is different from turning. The former is interrupted cutting. During the machining process, the tool temperature rise and cooling are repeated at high speed. Since the heat transfer to the tool-chip contact portion is intermittent, the change in tool temperature must be resolved based on this feature. The amount of heat conduction has a great influence on the prediction accuracy, but it does not require large-scale calculation of the deformation of the chip generation state and the thermal analysis, so the analysis result can be quickly obtained. The combination of cutting speed, depth of cut and feed will affect the maximum temperature. When the machining efficiency is constant, the feed rate will be increased and the tool temperature will decrease. The temperature decrease will often increase the feed rate to the limit and increase the feed rate. The machined surface will become rough. Therefore, if the relationship between roughness and temperature can be well balanced, it is possible to select the cutting conditions in which the two are balanced.
3. Physical simulation of cutting process by finite element method
In the physical simulation of the cutting process by the finite element method, the input conditions as the cutting conditions include: cutting speed, cutting thickness, tool rake angle, tool back angle, workpiece material characteristics, and the like. By analyzing these parameters, physical output results such as cutting force, chip shape, temperature distribution on the tool and chip, stress distribution, deformation distribution, and residual stress distribution can be obtained.
This simulation is also applicable to special cutting conditions such as dynamic cutting. The wave generation process of cutting the waveform surface and the waveform generation process of the tool edge vibration edge show that the shear angle becomes small and the deformation is concentrated to cause large deformation during the thinning of the chip thickness. In such a dynamic cutting process, the shear angle changes, and correspondingly, the deformation range of the chip generation also changes, so the cutting force is not proportional to the cutting thickness of the cutting edge. It can be seen from the shear angle change map corresponding to the variation of the cutting edge thickness, even if the cutting edge thickness is the same, the shear angle is larger when the amplitude is increased than when the amplitude is decreased, and the Lissajo pattern is convex below. Half moon shape. According to such analysis results, it is possible to visualize and understand the phenomenon, and to develop a more practical high-precision approximate analysis method.
In addition, the machining of composite metal materials with different material properties, and the machining of tools such as ultrasonic vibration cutting in the cutting direction while interrupting the cutting can be analyzed by physical simulation techniques. As an example of analysis in which the ferrite and the pearlite are distributed in a layer form, it is understood that the state of the chip curl is greatly different due to the difference in the positions of the layers. If the analytical results of the physical simulation can be effectively applied in the material design, it is possible to realize the chip processing without relying on the chip breaker. The cutting force is reduced in ultrasonic vibration cutting because the vibration frequency of the vibration cutting is much higher than the natural vibration frequency of the tool-processed material system. The cutting force obtained by this analysis is the force acting intermittently between the tool and the chip. It is assumed that there is no other factor such as friction reduction, and the cutting force is the same as the normal cutting.
Development trend of virtual cutting processing simulation technology