1. The development trend of CNC machine tools
CNC machine tools have gone through digital control (NC), direct numerical control (DNC) to computer numerical control (CNC) commonly used in manufacturing today. Its machining accuracy and cutting speed are approximately doubled every 8 years. Positioning accuracy will soon bid farewell to the micron era and enter the sub-micron era. High speed and high precision are the main features of modern CNC machine tools.
Modern machine tools also feature: composite machining, multi-axis linkage, environmentally friendly (green eco-machine tools), intelligent monitoring and compensation, and human-machine communication and autonomous management (smart machine tools), integrated into high-performance CNC machine tools. The overall goal of high-performance CNC machine tools is to significantly improve production efficiency and product quality, energy saving, environmental protection and operator health.
It can be predicted that in the next three to five years, machine tool manufacturers and R&D institutions will compete for the commanding heights in the following areas:
1) Virtual machine tool (NCVerification). Develop mechatronics, hardware and software integration simulation technology to improve the design level and performance of machine tools.
2) Green Eco-Machine. Energy conservation and emission reduction, and strive to minimize the environmental load of the production system.
3) Smart Machining. Improve the reliability, processing accuracy and comprehensive performance of production systems.
4) e-machine tool (AutonomousMachine). Improve the independent autonomy of the production system and the ability to interact with users and managers, so that the machine tool is not only a processing device, but a node in the enterprise management network.
2. What is a green ecological machine tool?
The machine not only consumes energy during use, but also produces solid, liquid and gaseous waste, which directly or indirectly pollutes the working environment and the natural environment. From the perspective of the entire life cycle of the machine tool, how to reduce the impact on the environment of green eco-machine tools has become a hot topic of current research. Green eco machine tools should have the following characteristics:
1) The main parts of the machine tool are made of recycled materials.
2) The weight and volume of the machine tool are reduced by more than 50%.
3) Reduce power consumption by 30-40% by reducing the mass of the mobile and reducing the power of the idle operation.
4) Reduce the waste of the process by 50-60% to ensure a basically non-polluting working environment.
5) After scrapping, the material of the machine tool can be recycled 100%.
2.1 Weight loss and energy saving
According to statistics, the power used to cut metal during the use of machine tools accounts for only about 25%, and various losses account for most of them. The first step in a green eco-machine tool is to build an eco-efficient machine (Eco-efficientMachine) by significantly reducing the weight of the machine and reducing the power required. Green Eco-Machine proposes a new concept: significantly reducing the weight of the machine tool, saving materials; while reducing the energy consumption of the machine tool.
The traditional machine tool design philosophy is "only enough stiffness to ensure machining accuracy, increase the rigidity must increase the weight of the machine." Therefore, 80% of the weight of existing machines is used to “guarantee†the rigidity of the machine, while only 20% is used to meet the kinematics of the machine. Therefore, there is a lot of room for machine structure optimization. The way to achieve this goal is through the adoption of new structures and new materials.
2.2MQL emission reduction
Lubricating coolants during machine tool use are harmful emissions, especially when used in grinding, which is very harmful to the environment and workers' health. Therefore, drastically reducing the use and discharge of coolant is a fundamental feature of green eco-machine tools. There are two ways to achieve this goal:
1) Dry cutting without using coolant. The machine needs to have enough rigidity and sharp tools to be used only for machining some simple milling and turning operations.
2) Minimal lubrication (MQL). MQL has a wide range of applications and can be used in a variety of processing methods, but requires specialized equipment to provide aerosol or low temperature air (cold air), as well as specialized lubricants.
2.3 Tool efficiency
3) Adopt the next generation CNC system. Interfaces and data formats compatible with STEP-NC enable seamless operation of CAD-based machine controls.
4) Condition monitoring and reliability, development of measurement, sensing and analysis methods.
5) A method of directly measuring tool wear and workpiece accuracy during machining.
The essence of smart processing systems is the intelligence and networking of manufacturing systems.
3.1 Advanced Process Control System
The advanced process system (Advanced Process System) is connotation is to monitor the working state of the electric spindle. Because the electric spindle is the heart of a CNC machine, its state is directly related to machining accuracy and machining efficiency. The principle is that an acceleration sensor is installed near the front end bearing in the electric spindle housing, so that the vibration generated during the milling process can be displayed in the form of an acceleration "g load" value.
3.2 intelligent temperature control system
Thermal deformation of machine tools is one of the main factors affecting machining accuracy. There are many factors that cause thermal deformation, mainly from the working environment of the machine tool and the thermal effects inside the machine tool:
1) Environmental impact. Such as temperature distribution and temperature changes in the workshop and air convection; the effects of heat sources such as daylight, heating and adjacent machine tools; and heat transfer from machine tool foundations.
2) The internal influence of the machine tool. Such as the heat of the machine parts (bearings, screws, guides, motors, gears, hydraulic systems, etc.), the heat generated by the cutting process and the heating of the cooling system.
The above thermal influence is a complex heat input to the machine tool structure. It changes with time and machine working state, and is unpredictable. The size and location of the thermal deformation of the machine tool ultimately depend on the thermal properties of the machine structure material. , that is, the thermal expansion coefficient, thermal conductivity and heat capacity of the material and the structural design of the machine tool, ie the shape, quality and distribution of the heat source.
4.e-machine tool
When machining complex 3D contours at high speeds, it is often encountered how to optimize the three interrelated values: speed, accuracy and surface finish. For example, when roughing a mold, the speed should first be considered; when finishing a small precision electrode, accuracy is the most important; while in the case of finishing the mold, the pursuit is the surface finish. How to properly configure and optimize the performance of the machine to achieve the goal in different situations is a complicated problem. Because it involves hundreds of CNC parameters, such as motion control algorithms, servo loop gain, feedforward, smoothing filters, and so on.
The productivity of the machine tool goes up to the tip of the tool. Using advanced tools, selecting reasonable tool geometry and cutting parameters can greatly improve the efficiency of cutting, reduce the power required for the cutting process, and extend the life of the tool, thus achieving greater output with less resource consumption. the goal of.
2.4 Value-added reuse
Metal cutting chips are the main solid waste in the use of machine tools. The traditional method is to sell it as waste to the waste recycling unit and into the social waste recycling cycle. Jiangsu Yangli Group will process thousands of tons of iron filings and steel scraps per year in the enterprise by sorting, briquetting, compounding and melting high-quality ductile iron castings, turning waste into treasure and making crankshafts such as presses. And other key parts.
3. Smart processing system
If the vision of a green eco-machine tool is environmentally friendly, then the goal of a smart machine tool is user-friendliness. The meaning of “user friendly†is to greatly improve work efficiency and work more comfortable and safe. This requires the machine tool to manage itself, automatically identify the processing tasks and processing status, with little or no manual intervention, and can communicate with the operator in a timely manner, become "smart" and open up a new era of CNC machine tools.
Machine tools inevitably produce various errors during the machining process, and modern monitoring and compensation techniques are needed to further improve the performance and communication capabilities of the machine. In 2005, the National Institute of Standards and Technology proposed a research program for the SmartMachining System.
The five goals of a smart processing system are:
1) System dynamic optimization. The relevant process and equipment knowledge are integrated to model and optimize the dynamic performance of the system.
2) Device characterization. Develop characterization methods, models and standards, and measure and communicate machine performance under operating conditions.
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