Fifth, the choice of CNC system
As market demands diversify, machine tool builders often offer the choice of multiple CNC options for the same machine tool or multiple selection options for the CNC system.
The numerical control system of the machine tool configuration provided by the machine tool manufacturer is divided into the mainstream system and the adaptable system. The mainstream system is relatively technically mature, but the user should have other requirements, such as the pursuit of the quality of the brand-name system, hope There are better after-sales technical conditions in China, and the numerical control system used in the user unit is relatively concentrated in several requirements, so as to use the mastering and maintenance parts preparation, so the user unit is willing to configure the CNC system that is trustworthy or relatively familiar.
In the system of choice, the performance difference is very large, which directly affects the price structure of the equipment. Therefore, it is not possible to pursue high-level and new systems one-sidedly, but should mainly meet the performance of the host, and make a comprehensive analysis of system performance and price. Choose the right system. At present, the most famous numerical control systems in the world include Japan's FANUC, Germany's SINUMERIK, France's NUM, Italy's FIDIA, Spain's FAGO, and the United States' A-B. Major machine tool manufacturers also have their own systems, such as MAZAK, OKUMA, etc. There are also CNC system suppliers such as Aerospace Group, Electromechanical Group, Huazhong University of Science and Technology, Liaoning Blue Sky, Nanjing Dafang Group, and North Kaiqi. Each company also has a series of products of various specifications.
The basic principle of the user selection system is: the performance price ratio is higher, the post-purchase use and maintenance are convenient, and the system has a long service life (the system cannot be eliminated, otherwise the repair spare parts will not be found after several years of use).
In addition to the basic functions, there are many functions to choose from in the CNC system. For the system equipped with the machine tool, the CNC system selection function required for the basic requirements of the machine tool has been selected by the manufacturer. Users can select some according to their own production management, measurement requirements, tool management, programming requirements, etc. The function is included in the order form, such as the DNC interface networking requirements.
Sixth, automatic tool change equipment (ATC), automatic exchange workbench (APC) and tool holder selection configuration
1. ATC's choice
On some CNC machine tools with comprehensive processing capabilities, such as machining centers, turning centers and CNC punching machines with exchange punches, automatic switching devices are the basic features of these devices. The quality of their work is directly related to the quality of the machine. It is also an important part of the investment in equipment (10% to 30% of the cost of the whole machine). Therefore, it is necessary to pay attention to the working quality and tool storage of the ATC automatic tool changer when selecting the host device. At present, the automatic tool changer of the machining center is more standardized. The following is an example of the ATC device of the machining center.
Field experience shows that about 50% of the faults in the machining center are related to the ATC device, but ATC is the basic component to improve the processing efficiency of the equipment. Therefore, it is recommended that the user should choose the structure as simple and reliable as possible. The high ATC can also lower the price of the whole machine accordingly.
The main technical parameters related to the ATC device are described below.
(1) Tool holder model
The tool holder type depends on the specifications of the tool spindle mounting hole. At present, most of the machining center machine spindle holes are made of ISO 7:24 taper holes, commonly used are No. 40, No. 45, No. 50, etc., and there are also No. 30 and No. 35. The smaller the machine tool size, the smaller the tool holder size should be, but the small size tool holder is not good for processing large size holes and long holes. Therefore, if a machine tool with large specifications can be selected, it should be as large as possible. However, the size of the magazine and the time of tool change will be affected. In recent years, both machining centers and CNC milling machines have been developed in the direction of high speed. Many experimental data show that when the spindle speed exceeds 10000r/min, the 7:24 taper hole will increase due to the centrifugal force, which affects the positioning accuracy of the tool holder. To this end, one view is to recommend the HSK series of short taper shank recommended by German VDI. In addition, the tapered taper shank that has been contacted by both the tapered surface and the end surface of some products in Japan, but in centering accuracy and repetition In terms of positioning accuracy, the HSK series is better, and there are currently few manufacturers in China.
For the same tapered surface, there are Japanese BT standard, American CAT standard, German VDI standard, etc. They stipulate that the size of the clamping jaw of the robot is different, and the size of the clamping nail of the shank is also different, so it must be considered when selecting. Complete, for users who already have a certain number of CNC machine tools or users who are going to purchase a batch of CNC machine tools, they should choose a single standard tool holder series that can be used universally.
(2) Tool change time
The tool change time refers to the tool change time, that is, the total time for replacing the used tool and loading a new tool from the spindle. There are two ways to specify the subdivision, namely the tool to tool and the chip to chip. The total tool change time includes the old tool after machining and leaving the machining area to the tool exchange. The time between the new tool entering the new machining. At present, the fastest pure tool change time is about 0.7s, the total tool change time is between 3 and 12s, and the vertical machine tool change time is generally shorter than the horizontal type. Short tool change times mean high machine productivity.
(3) Maximum tool weight
The maximum tool weight refers to the maximum tool weight allowed in the case of automatic tool exchange. The maximum allowable weight of the shank of the 40th taper is 7~8kg, the handle of the 50th handle is 15kg, and some heavy tools can reach 25~30kg. The tool change speed should be slower. The maximum tool diameter and length are primarily limited by the size of the magazine.
(4) Tool magazine capacity
The tool magazine capacity of some machining center machines is often available in several specifications, from a dozen to 40, 60, 100, etc. Some flexible machining units (FMC) have a tool storage capacity of nearly 1,000 after configuring the central tool magazine. As long as the capacity of the tool magazine can meet the basic needs, it is generally not suitable to choose too large, because the capacity is large, the cost of the tool magazine is high, the structure is complex, the failure rate is correspondingly increased, and the tool management is also complicated. In the use of a single machine, when replacing a new workpiece, the operator should clean the tool magazine according to the new process data. The more irrelevant tools in the tool magazine, the more the finishing work will be. The more prone to human error. Therefore, the user should generally calculate the number of tools to be used according to the process analysis of a typical workpiece, and then determine the capacity of the tool magazine. If not considered in a flexible machining unit or a flexible manufacturing system, the general machine tool magazine is used as a basis for selecting the total number of shanks required for one workpiece to be clamped at a time. According to the foreign process analysis of typical workpieces for small and medium-sized machining centers, it is believed that the storage capacity of small and medium-sized machine tools should be between 4 and 48.
In the machine tool incorporated into the flexible manufacturing unit, in order to meet the requirements of multi-work, multi-process simultaneous machining, it is necessary to configure a large-capacity tool magazine. At this time, corresponding tool management measures should be added.
2. Tool holder and tool selection
After the main machine and the automatic tool changer (ATC) are determined, the required tool holder and tool (cutting tool) are selected. The series of tool holders used in CNC machine tools have been standardized, especially for tool holders used in machining centers, such as CAT in the US, BT in Japan, and JT in China. The machining of workpieces by CNC machine tools depends on the cutting tool. However, the connection between the cutting tool and the machine tool, and the clamping position provided to the manipulator when the tool is automatically exchanged must be solved by the tool holder. Therefore, the selection of the tool essentially includes the cutting tool and the knife. The configuration of the handle. The selection of the cutting tool depends on the processing requirements. After the cutting tool is determined, the corresponding tool holder must be configured. For example, the process requires drilling a small hole with a diameter of 6 mm. The cutting tool is a 6 mm diameter straight shank twist drill, and then a picking bit can be selected. Tool holder. Some of the shanks are now equipped with special cutting tools, such as fine shank handles. In short, most of these accessories have been standardized, supplied by specialized production plants, and machine tool users should be reasonably selected according to specific processing objects. Since the range of tool holders is wide, the selection will increase the investment. If the selection is less, it will affect the starting rate of the machine tool, so it should be treated with caution.
For some workpieces with a total batch size of more than several thousand pieces and repeated production, the compound tool can be considered in the process arrangement, that is, the main cutting power of the CNC machine tool is large, the machine tool has good rigidity, and the multi-tool is used for the compound tool. Multi-blade, powerful cutting for increased productivity and reduced production tempo. But a composite tool is much more expensive and becomes a special tool that must be considered when the number of workpieces is sufficient.
In recent years, many new products have been developed on the tools used in CNC machine tools, which greatly enrich the machining process of CNC machine tools, such as universal vertical milling heads, anti-scratch tools, deburring tools, speed increasing heads, thread milling cutters and internal cooling. Tools, etc. (see product catalog for details).
3. Automatic exchange workbench
The automatic exchange workbench is an accessory configured on the host. The number of configurations is 2, 4, 6, 10, etc., except for the dual exchange workbench, which is mainly configured with a flexible manufacturing unit. The configuration of the double exchange workbench can greatly save the auxiliary time of the loading and unloading of the complex parts and improve the starting rate of the machine tool. However, if the equipment is added, the investment must be at least 100,000 yuan. The multi-quantity exchange workbench is used for flexible manufacturing units. It is suitable for 24 hours of people or unmanned management. It is suitable for the alternate production and processing of multi-variety workpieces. Here, we should pay attention to increase the quality inspection measures, otherwise the investment growth of 20% to 50% is uneconomical. of.
Seven, machine selection function and accessories selection
When purchasing CNC machine tools, in addition to the functions and basic components that meet the basic requirements, you should also fully consider the selection function and accessories. The selection principle is: comprehensive configuration, give full play to the maximum potential of the host, and consider the benefits in the near future. For some price increases, but for the convenience of use, it should be fully equipped. The accessory package should ensure that the machine tool can be put into use immediately after it arrives at the scene. It is forbidden to spend hundreds of thousands of dollars or even millions of machines purchased. After the arrival of the goods, the lack of a tens or hundreds of yuan attachments can not be used for a long time. happened.
The selection function of the numerical control system should be practical, not necessarily too much, especially the equipment incorporated into the mass production line should be as simple as possible. For the multi-variety and small-batch production methods, the selection of programming functions should be strengthened, such as Random programming (background programming), motion graphics display, human-machine dialog programming (GPS), macro programming, etc., although the speed of programming can be accelerated, but the cost should be increased accordingly. Another configuration scheme is to simplify the function of programming the CNC system. The automatic programming machine and the communication interface with the CNC system are separately configured. The program processing is done in advance on the programming machine, and then takes a few minutes to be sent to the CNC system. This will further increase the machine start rate.
Many accessories have been developed in improving the processing quality and work reliability, such as automatic measuring devices, contact probes and corresponding measuring software, tool length and wear detection, machine tool thermal deformation compensation software and other accessories. These accessories are selected to require work. Reliable, not one-sided pursuit of novelty. For some auxiliary function accessories, such as cooling, protection and chip removal, the equipment is mainly determined according to the requirements of the field use and process requirements in the future. For example, considering the requirements for processing large-size cast iron parts in the future, it is necessary to use a high-sealing protective cover and a large Flow shower cooling method, paper coolant filter device, etc. In short, choose accessories that are compatible with production capacity.
Eight, technical services
As a high-tech product, CNC machine tools contain multi-disciplinary professional content. It is not enough to apply and repair the complex technical equipment. The application unit itself is not enough, and it is difficult to do. Rely on and utilize the professional team in society. Therefore, when purchasing equipment, you should also consider the purchase of pre-sales and after-sales technical services around the equipment. The purpose is to make the equipment work as soon as possible.
For some new CNC machine users, the most difficult thing is not the lack of funds to buy equipment, but the lack of a high-quality technical team, so new users from the beginning of the selection of equipment, including the subsequent equipment arrival and acceptance, equipment Manpower and technical support are required for operations, programming, mechanical and electrical maintenance. It is very difficult for these conditions to be solved by users in a short period of time. At present, various machine tool manufacturers have generally paid attention to pre-sales and after-sales services of products, assisting users in process analysis of typical workpieces, performing process feasibility tests and undertaking complete sets of technology. Services, including process equipment development, programming, installation and commissioning, trial cutting of the workpiece, until the full production into production, quickly respond to warranty services, for the user to hold various types of technical personnel training.
In short, CNC machines can be used reasonably in enterprises that attach importance to the construction of technical teams and attach importance to the improvement of the quality of employees. Therefore, when selecting a machine tool, it is recommended that users spend a portion of the funds to purchase technical services for their own shortages, so that the equipment can function as soon as possible.
