With the development of science and technology, mechanical manufacturing technology has undergone profound changes.
Due to the greater social demand for product diversification and the obvious increase in the proportion of batch production of small and medium varieties, the use of traditional common processing equipment has been difficult to meet the processing requirements of high efficiency, high quality and diversification .
When purchasing CNC machines, three aspects can be considered:
The first is whether the machine tool body can meet its own processing requirements and the quality of the machine tool.
Secondly, there are many types of CNC systems. Choosing the appropriate system is the key to choosing CNC machine tools.
Finally, the drive unit is also the key to controlling the machine tool.
Different drive units can achieve different machining accuracy.
When selecting the drive unit, select the appropriate drive unit according to the accuracy requirements of the workpiece.
The CNC system is the control center of CNC machine tools, known as the “brain” of the machine tools. Machine tools equipped with CNC system greatly improve the accuracy, speed and efficiency of parts processing.
The function of the CNC system is undoubtedly an important constraining factor for the design and selection of CNC machine tools.
The following important factors should be considered when selecting the CNC system:
1. Driving ability
2. Full closed loop demand and dual drive demand
3. Five-axis control requirements
4. RTCP, there will be a big choice.
At the same time, for NC system suppliers who may be involved in the five-axis function, they should also seriously consider export license, after-sales service, etc.
The following analysis is made of the appearance of the CNC system:
CNC system selection
The CNC system is the “brain” of the CNC machine tool, which calculates and processes the control information of the machine tool.
According to the principle of numerical control system, it can be divided into economic numerical control system and standard numerical control system.
Economic numerical control system from the perspective of control method, economic numerical control system generally refers to the open-loop numerical control system, which has the advantages of simple structure, low cost, convenient maintenance and debugging, low operation cost and maintenance but improvement Performance is limited by the mutual constraint between the torque and precision frequency characteristics, feed speed and torque of the stepper motor.
The economical CNC system is often used in CNC wire cutting and some economical CNC lathes and milling machines with low speed and accuracy requirements.
It is also widely used in NC transformation of common machine tools.
The open-loop CNC system means that the CNC system itself does not have a position detection device.
The CNC system sends a certain number and frequency of command pulses and the drive unit locates the machine tool.
In the open loop system, under the influence of external factors, the machine tool does not act or the action does not occur, but when the system reaches the specified position, the machining accuracy of the machine tool will be greatly reduced.
However, due to its simple structure, quick response, stable and reliable operation, convenient debugging and maintenance, and very low price, it still has the largest market in China.
Standard CNC System Standard CNC system includes semi-closed loop CNC system and full closed loop CNC system.
Semi-closed loop CNC system generally refers to the position signal (photoelectric encoder) from the machine tool servo motor returning to the CNC system.
The system can automatically detect the position and compare the error, and compensate and control some errors.
Therefore, its control accuracy is higher than that of the open-loop CNC system, but lower than that of the full closed-loop CNC system.
In addition to the position feedback from the machine tool servo motor, the full closed-loop NC system also has the position signal from the machine tool bench position detection device (generally with grid ruler) returned to the system, so how to form all position tracking control.
The system automatically detects and compensates for all position errors in the machining process.
The machining accuracy of the full closed-loop CNC system is the highest, but the debugging and maintenance of this system is extremely difficult, and the price of the system is very high.
It is only suitable for medium and high-end CNC machine tools.
Because the price of the open-loop control system is much lower than that of the closed-loop control system, when selecting the NC system, we must consider the proportion of the NC system in the price cost of the entire NC machine tool, and then, According to the configuration of the machine tool and the requirements of the machine tool itself, the medium and low-grade machine tools adopt the open-loop control system, and the medium and high-grade machine tools adopt the open-loop control system closed circuit.
Problems that need attention when purchasing CNC machine tools
Select the CNC machine tool according to the product specification, size and precision.
When selecting the function of the CNC machine tool, excessive pursuit of the number of coordinate axes of the CNC machine tool, large power of the worktable and motor, high machining precision and complete functions will lead to more complex and low reliability of the system.
The purchasing cost and maintenance cost will increase, which will increase the processing cost correspondingly.
Only when the CNC machine tool has the characteristics of high flexibility and strong adaptability can it achieve the best processing effect.
Therefore, before choosing equipment, we must first determine the typical parts to be processed.
The selection of numerical control system must be reasonable.
The numerical control system that can meet the requirements of various performance parameters and reliability indexes should be considered in detail and should be convenient for operation, programming, maintenance and management.
Try to be centralized and unified.
If it is not a special case, try to select the same series of CNC systems familiar to the unit and produced by the same manufacturer for future management and maintenance.
The necessary accessories and cutting tools must be set up.
To fully play the role of NC machine tools and increase their processing capacity, the necessary accessories and cutting tools must be configured.
Don't buy a machine tool that costs hundreds of thousands of yuan or millions of yuan.
It cannot be used normally due to the lack of an accessory or cutting tool worth tens of yuan. When purchasing the host, purchase some vulnerable parts and other accessories.
Foreign metal cutting experts believe that the efficiency of a CNC machine tool worth 250,000 US dollars largely depends on the performance of an end mill worth 30 US dollars.
It can be seen that CNC machine tools are equipped with good performance tools.
It is one of the main measures to reduce costs and obtain maximum comprehensive economic benefits.
Generally, NC machine tools must be equipped with sufficient tools to fully perform the functions of NC machine tools, so that the selected NC machine tools can process multiple varieties of products and avoid unnecessary idleness and waste.
Pay attention to the installation, debugging and acceptance of NC machine tools.
After entering the factory, NC machine tools must be installed and debugged carefully, which is very important for future operation, maintenance and management.
During the installation, commissioning and trial operation of CNC machine tools, technicians actively participate in and carefully study technical training and local guidance from suppliers.
The geometric accuracy, positioning accuracy, cutting accuracy and machine performance of NC machine tools must be fully accepted.
Carefully check the supporting technical data, operation manual, maintenance manual, accessory instructions, computer software and instructions and store them properly.
Otherwise, some additional functions will not be developed in the future and it will be difficult to maintain the machine tool.
Finally, after-sales service, technical support, personnel training, supporting materials, software support, installation and commissioning, spare parts supply, tool systems and machine tool accessories of CNC machine tool manufacturers must be fully considered.
