On the basis of ordinary CNC machine tools, the past CNC machine tools mainly developed along the two tracks of precision/ultra-precision CNC machine tools and high-speed processing machine tools. In order to meet the new requirements of workpiece materials, part geometry, precision and surface quality in the CNC machining process, and to improve the competitiveness of China CNC machining tool products, since the mid-1990s, a combination of high precision and high speed High-performance CNC machine tools in all aspects are highly valued. Since the beginning of the 21st century, High Performance Cutting and its main supporting technology-Virtual CNC Machining technology has become a new hot spot for scholars and engineers in the field of CNC cutting.
Virtual CNC machining technology becomes a new hot spot in the field of high-performance CNC machine tools
The International Society of Production Engineering (CIRP) held the first and second international conferences on high-performance cutting in 2004 and 2006, respectively, on machine tool dynamics modeling, control, CAM, cutting theory, Milling/drilling/grinding, micro-cutting and other directions have been discussed, and important conferences on advanced manufacturing technology held in China have also listed high-performance CNC machine tools and processing technology as one of the topics. It can be said that high-performance CNC machine tools R&D and supporting technology research and application have become a new trend in the development of CNC machine tools.
This article combines domestic and foreign literature and part of the research work of the author and his team, focusing on introducing and discussing the requirements of high-performance CNC machining equipment and technology, the research and application of key technology of high-performance CNC machine tools, virtual CNC machining technology and part-oriented process characteristics The virtual numerical control machining mechanics simulation method research and so on.
High-performance parts processing requirements for CNC cutting equipment and technology
The characteristics of high-performance parts in modern equipment and products are reflected in the following aspects.、
(1) Structural characteristics
There are various types of parts and structures, such as car and engine boxes, cylinders/cylinder heads, disks, shafts and other parts, aircraft wall panels, beams, frames, ribs, flanges, girders and joints and skeletons and other structural parts, aircraft engines Blades/disks/impellers, casings, disk rings, etc. In addition, due to the design requirements of high performance, light weight and high reliability, the proportion of parts adopting the overall structure and the complex surface structure has been greatly increased, so the parts have large geometric dimensions, complex shapes, many process features, and small wall thickness.
(2) Material characteristics
Metal material parts are the main objects of CNC machining. Various steels and machining aluminum alloys account for a large proportion. Titanium alloys and high-temperature alloys also have a certain proportion. The metal material blanks can be cast, forged, pre-stretched, rolled and other processes. In addition, the numerical control processing volume of non-metallic material parts (mainly composite materials and optical hard and brittle materials) also shows an increasing trend.
(3) Process characteristics
Due to the characteristics of material selection and structural design, high-performance parts have the characteristics of high machining accuracy, large material removal during machining, and difficult control of machining deformation during CNC cutting. High demands were put forward. In addition, the development of modern manufacturing must also ensure that the parts processing process meets the increasingly stringent environmentally friendly requirements.
In high-performance CNC cutting, high-performance CNC machine tools, high-performance cutting tools, high-performance CNC programming and simulation systems (virtual CNC machining technology), cutting parameters and process optimization techniques and tools are its key supporting technologies. Due to space limitations, the focus of this article is on high-performance CNC machine tools and virtual CNC machining technology.
The characteristics of materials, structures and processes of high-performance product parts put forward higher requirements on processing quality, efficiency, cost and environmental protection. High-performance cutting is a new concept proposed to meet the above requirements. The so-called high-performance cutting refers to the comprehensive consideration of machine tools, tools, workpieces, programming, processing technology and parameters and their interactions in the process of CNC cutting, using geometric simulation and mechanical simulation methods. The analysis of the characteristics of the “parts-tool” process system, NC programming, cutting parameters, tool path, etc., comprehensively optimizes the cutting process to achieve high-quality, efficient, low-cost and green CNC machining.
Research and application of high-performance CNC machine tools
1. Main features of high-performance CNC machine tools
In order to meet the requirements of high-performance CNC cutting, high-performance CNC machine tools should have the following main features:
(1) High-speed spindle
The maximum spindle speed is higher than 12000r/min and can be as high as 42000r/min or even higher. At the same time, the spindle should also provide sufficient power and torque. The high-speed spindle is used in conjunction with a high-performance tool system to achieve high-speed cutting. For example, in the high-speed CNC machining of aircraft large aluminum alloy structural parts, the cutting linear speed is generally 1000-4000m/min, and the maximum cutting linear speed can reach more than 5000m/min. At the same time, the high spindle speed reduces the feed per tooth during cutting, thereby reducing the cutting load on the cutter teeth.
(2) Multi-axis linkage
Generally, it is four-axis or five-axis multi-axis linkage, or on the basis of five-axis linkage control, more axes can be controlled and compound machining linkage control can be realized. The introduction of A/B, A/C coordinates of multi-axis linkage can easily solve the processing problems of complex structures and profiles, such as the processing of blades, complex cavities, pump bodies, polyhedrons, etc.; compounding based on multi-axis linkage CNC machining can greatly shorten the auxiliary working time such as workpiece positioning and clamping, and improve the machining efficiency of the machine tool.
(3) High dynamic response feed system
The linear feed axis speed can reach 30 ~ 60m/min or higher, the feed acceleration of the new type CNC machine tool can reach 1 ~ 2g, and the small CNC machine tool can reach higher. The high-performance CNC machine tool adopts the linear axis motion driven by the linear motor and the swing axis motion driven by the torque motor, which can greatly simplify the mechanical transmission structure and realize the so-called “zero transmission”, and the speed, acceleration and acceleration rate of change in the axis motion controller The control profile (Profile) is optimized to suppress the resonance during the movement and obtain a very high dynamic response characteristic to achieve high-speed feed under the conditions of frequent acceleration and deceleration during the processing of complex profiles and cavities.
(4) High rigidity
The spindle system, feed system and machine tool structure should have good static and dynamic stiffness and thermal stability. High enough static stiffness can resist the machine tool deformation caused by the gravity of the machine tool parts and the cutting force during the machining of the parts, and ensure the static displacement of the tool and the workpiece during the cutting process; excellent dynamic characteristics can prevent and reduce the dynamic process during the cutting process. Forced vibration and self-excited vibration generated during the cutting process to meet the dynamic displacement requirements of the tool and the workpiece during the cutting process; good thermal stability allows the machine tool to undergo thermal deformation as much as possible when it is subjected to cutting heat and environmental temperature changes during processing small. Ultimately, the high static and dynamic stiffness and thermal stability of the machine tool will enable parts to be machined to obtain good surface quality and high cutting efficiency.
(5) High precision
Linear axis positioning accuracy is in the order of microns (μm), and can achieve higher position accuracy. Since the feed servo uses a linear motor drive, a high-precision and high-rigidity motion component motion control system, and considers the electromechanical coupling effect in the feed system, full closed-loop feedback control, PID+feedforward control is used, and even more complex and advanced control The digital servo control and compensation control of the algorithm further improve the smoothness and precision of the movement of the coordinate axes of CNC machine tools.
Intelligence is an important feature of a new generation of CNC machine tools. Intelligentization is mainly manifested in two aspects: on the one hand, the intelligentization of machine tool control, such as the introduction of advanced control strategies such as feedforward control, predictive control, and robust control in machine tool axis motion control, and the introduction of adaptive control in machining process control , Learning control, etc.; on the other hand, the expert system, automatic detection and automatic compensation functions are embedded in the CNC system, such as automatic programming and simulation, machine tool status monitoring, fault diagnosis, automatic tool management and compensation, machine tool thermal The functions of deformation/vibration monitoring and compensation make CNC machine tools more “intelligent” and improve the control performance of the CNC system, thereby realizing intelligent and optimal control of the machine tool and the machining process.
Virtual CNC machine tool and virtual machining technology
1. Virtual CNC machine tool
At the 2005 meeting of the International Society of Production Engineering, well-known scholars in the field of manufacturing technology such as Y. Altintas, C. Brecher, M. Weck, and S. Witt jointly published the paper “Virtual Machine Tool”, which carried out virtual machine tool technology, research progress and challenges. A comprehensive discussion.
The virtual machine tool VMT (VirtualMachineTool) is a computer simulation model of the actual machine tool product, also known as the virtual prototype of the machine tool. It can be used for demonstration, analysis and testing like a real machine tool. During the design process, the virtual model of the machine tool can be changed repeatedly, and various designs can be simulated and verified until the performance of the machine tool meets the requirements. This virtual machine tool technology can greatly shorten the development cycle of machine tool products and significantly reduce development costs.
The integrated development environment for developing modern CNC machine tools using virtual prototype technology mainly includes:
- ● Finite element analysis and optimization of machine tool structure;
- ● Finite element calculation of machine tool parts;
- ● Performance simulation matching and testing.
- ● Flexible multi-body coupling simulation;
- ● 3D computer-aided design and kinematics optimization test;
VMT is a powerful tool for analysis and simulation of CNC machine tools and design optimization. The key issues that need to be solved in the current VMT research are:
- ● Analysis and calculation method of dynamic characteristics of the joint surface of mechanical parts;
- ● “rigid body + flexible body” coupling modeling and analysis method;
- ● “Mechanical structure-servo system-cutting process” coupling modeling and analysis method;
- ● “Mechanical structure + servo system” coupled electromechanical system dynamic characteristics modeling and analysis;
- ● 3D solid model-based performance prototype modeling and analysis method.
2. Virtual CNC machining
Before the actual parts are processed, the machine tool kinematics, dynamics, numerical control system, space accuracy, cutting force, spindle torque/power, machining errors, etc. are considered in the virtual environment to realize the simulation and optimization of the machining process, so that the correct, The first qualified part is processed economically and efficiently. The essence of virtual machining can be regarded as geometric simulation and mechanical simulation of the NC machining process, and on the basis of the two simulations, the cutting parameters and process of the NC machining are optimized. CAM simulation software, virtual machine tools and cutting process dynamics are important supporting tools for virtual machining.
- ● Simulation of machine tool structural characteristics: simulation of machine tool structural dynamics, statics and overall performance (whole machine feed and spindle drive);
- ● NC program geometric simulation: mainly solves the tool path interference, collision check, dimensional path error caused by NC programming errors, etc., and can also partially optimize the NC program from the aspect of geometric motion;
- ● Machining process optimization: Calculate and simulate the cutting force, torque, power, vibration, generating surface, etc. under various cutting conditions, and optimize the cutting parameters and processing technology through iterative comparison. Geometric simulation software that uses CAM simulation software to perform NC tool path trajectory simulation verification, interference verification, etc. has been commercialized and is widely used in domestic manufacturing companies. At present, the focus of virtual CNC machining research is on the mechanical simulation of the “machine tool + workpiece + process (cutting process)” system in the cutting process.
- ● Simulation of machining dynamics: simulation of trajectory generation, interpolation, feed, etc. under the consideration of machine tool dynamics and cutting process disturbance;
3. Virtual CNC machining mechanics simulation research oriented to process characteristics
In order to further adapt to the diversity of part structure and process characteristics in the actual CNC machining process, after solving the basic problems of dynamic simulation in the milling process, we further carried out virtual NC machining mechanical simulation oriented to the process technology features, the main goal is to face the part machining Geometrical characteristics (such as side walls, deep cavities, corners, etc.) and different cutting directions (such as straight lines, circles, spirals, cycloids, etc.), considering the dynamic characteristics of CNC machine tools and the characteristics of workpiece materials, under different cutting parameters, Carry out calculation and simulation of cutting force, spindle torque/power, machining vibration, tool deformation/workpiece deformation, surface morphology, etc. in the CNC machining process, according to different optimization goals, realize cutting parameters and machining process optimization, and can be a virtual CNC machine tool And virtual CNC machining process provides mechanical simulation methods and data support.
For example, one of the common geometrical characteristics of milling processing-mechanical simulation is carried out during deep side milling such as right-angle corners. After the parameters of the tool geometry, milling method, milling amount, cutting force coefficient, tool modal and other parameters are given, the simulation calculation The cutting force, chip thickness, spindle torque/power, stability curve, etc. can be obtained.
Carrying out mechanical simulation on the cutting process of CNC machining is the basis of virtual machine tool and virtual CNC machining. The team led by the author independently developed “CNC milling machining dynamics simulation system (SimuCut)” and “CNC machining dynamics characteristic test and analysis system (DynaCut)”, which has been applied to more than 40 aviation, aerospace, marine, electronics, The CNC machining workshops in the military industry, such as weapons, provide a new idea and a set of quick methods and tools for the rapid optimization of milling cutting parameters and improve the cutting efficiency of machine tools. The speed-up and efficiency-increasing of a machine tool has achieved obvious results.
The research and development of high-performance CNC machine tools and their supporting technologies have become an important trend in the development of CNC machine tools, and will play an important role in improving the quality and efficiency of swiss machining of high-performance parts such as aviation, aerospace, automobiles, and molds. Virtual machine tool technology provides a new way to shorten the development cycle of new CNC machine tool products and reduce development costs. However, VMT is not just a virtual function prototype, nor a simple 3D model. It is difficult to directly complete modeling and analysis using existing CAD and CAE software. The most important thing is to solve each link or component in the machine tool structure and system And the coupling relationship between it and the dynamics of the cutting process. Virtual CNC machining technology will provide important basic methods and basic data for virtual machine tool modeling analysis, cutting parameter optimization, cutting process optimization, etc.
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