With the development of science and technology, mechanical manufacturing technology has undergone profound changes.
Due to the stronger social demand for product diversification and the obvious increase in the proportion of multi variety, small and medium-sized batch production, the use of traditional ordinary 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 kinds of CNC systems. Choosing the appropriate system is the key to choose CNC machine tools.
Finally, the drive unit is also the key to machine tool control.
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.
CNC system is the control center of CNC machine tools, known as the “brain” of machine tools. The machine tools equipped with CNC system greatly improve the accuracy, speed and efficiency of parts processing.
The function of CNC system is undoubtedly an important restrictive factor for the design and selection of CNC machine tools.
The following important factors must be considered in the selection of CNC system:
1. Driving capacity
2. Full closed loop demand and dual drive demand
3. Five axis control requirements
4. RTCP, there will be a large choice.
At the same time, for the NC system suppliers that may be involved in the five axis function, they must also seriously consider the export license, after-sales service, etc.
The following analysis is made from the aspect of CNC system:
Selection of CNC system
CNC system is the “brain” of CNC machine tool, which calculates and processes the control information of machine tool.
According to the principle of numerical control system, it can be divided into economic numerical control system and standard numerical control system.
Economical numerical control system from the perspective of control method, economical numerical control system generally refers to open-loop numerical control system, which has the advantages of simple structure, low cost, convenient maintenance and debugging, low operation and maintenance cost, but the improvement of performance is limited by the mutual restriction between the torque frequency characteristics and accuracy, feed speed and torque of stepping motor.
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 the NC transformation of ordinary machine tools.
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 driving 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 is not in place, but when the system has reached the specified position, the machining accuracy of the machine tool will be greatly reduced.
However, due to its simple structure, rapid 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) of the servo motor of the machine tool fed back 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 of the servo motor of the machine tool, the full closed-loop NC system also has the position signal of the position detection device of the machine tool workbench (usually with grating ruler) fed back to the system, so as to form all position follow-up control.
The system automatically detects and compensates 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 are extremely difficult, and the price of the system is very high.
It is only suitable for medium and high-grade 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 should consider the proportion of the NC system in the price cost of the whole 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 closed-loop control system.
Problems needing attention when purchasing CNC machine tools
Select the CNC machine tool according to the product specification, size and accuracy.
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 accuracy and complete functions will lead to the more complex and low reliability of the system.
The purchase cost and maintenance cost will increase, which will increase the processing cost accordingly.
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 shall be reasonable.
The numerical control system that can meet the requirements of various performance parameters and reliability indexes shall be considered in detail, and it shall 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.
Necessary accessories and cutting tools must be configured.
In order to give full play to the role of NC machine tools and enhance their processing capacity, necessary accessories and cutting tools must be configured.
Do not 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 of dozens 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 250000 US dollars depends largely on the performance of an end mill worth 30 US dollars.
It can be seen that CNC machine tools are equipped with tools with good performance.
It is one of the key measures to reduce costs and obtain the maximum comprehensive economic benefits.
Generally, NC machine tools should be equipped with enough tools to give full play to the functions of NC machine tools, so that the selected NC machine tools can process multiple product varieties and prevent unnecessary idleness and waste.
Pay attention to the installation, debugging and acceptance of NC machine tools.
After entering the factory, NC machine tools should 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 and carefully study the technical training and on-site guidance of suppliers.
The geometric accuracy, positioning accuracy, cutting accuracy and machine performance of NC machine tools shall be fully accepted.
Carefully check the supporting technical data, operation manual, maintenance manual, accessory instructions, computer software and instructions, and keep them properly.
Otherwise, some additional functions will not be developed in the future and it will be difficult to maintain the machine tool.
Finally, the after-sales service, technical support, personnel training, supporting materials, software support, installation and commissioning, supply of spare parts, tool system and machine tool accessories of CNC machine tool manufacturers should be fully considered.