Tool selection and cutting amount determination is an important part of CNC milling, which is directly related to machining accuracy, machining surface quality and machining efficiency. Choosing the right tool and the amount of cutting allows you to achieve the best processing quality at the lowest cost and in the shortest time. In the machining process, the amount of cutting and the tool have a large influence on the machining accuracy, surface quality, production efficiency and production cost. Fast processing speed and high production efficiency are the advantages of CNC machining compared with traditional cutting. Under the principle of “high quality, high production and low cost”, the cutting amount and the correct selection and use of the tool can give full play to the advantages of CNC machining. Have a greater impact.

First, the selection of CNC machining tools CNC milling machine processing efficiency, processing quality and the choice of milling cutters have a direct relationship. It has great significance in the processing technology of CNC milling machine. CNC milling machine processing requires higher requirements for tools, requiring high precision, high strength, good rigidity, high durability, and requires dimensional stability and convenient installation and adjustment. The correct choice of tool and tool holder should be selected according to the processing capacity of the machine tool, the performance of the workpiece material, the processing procedure, and the amount of cutting. The principle of tool selection should be: easy installation and adjustment, good rigidity, long life and high precision. Under the premise of meeting the processing requirements, try to choose a shorter tool holder to improve the rigidity of the tool processing. (I) Types of Commonly Used Tools for CNC Milling CNC milling tools can be divided into integral and mosaic according to the structure. The mosaic type includes a welded type and a machine clamp type. Tools can be divided into special forms, high-speed steel tools, carbide tools, diamond tools, cubic boron nitride tools, ceramic tools. The machining process is divided into drilling tools, milling tools, and boring tools. According to the shape of the tool, it is divided into a flat bottom knife, a ball end knife, a taper knife, a T-shaped knife, a barrel knife, and a special-shaped knife.

(2) Selection of CNC machining tools 1. Selection of tools When performing free-form surface (mold) processing, since the cutting speed of the end of the ball-end tool is zero, in order to ensure the machining accuracy, the cutting distance is generally the tip-tight distance. Therefore, the ball head is often used for the finishing of curved surfaces. Flat-end cutters are superior to ball-end knives in terms of surface quality and cutting efficiency. Therefore, as long as the roughing or finishing of the surface is guaranteed, the flat-blade knives should be preferred. In addition, the durability and accuracy of the tool are highly dependent on the tool price. It must be noted that in most cases, the choice of a good tool increases the tool cost, but the resulting processing quality and processing efficiency increase. , can make the entire processing cost greatly reduced. In the machining center, various tools are mounted on the tool magazine, and the tool selection and tool change operations are performed at any time according to the program. Therefore, a standard tool holder must be used in order to quickly and accurately load the standard tool for drilling, expanding, reaming, boring, milling, etc. onto the machine tool spindle or tool magazine. The programmer should be aware of the structural dimensions, adjustment methods, and adjustment range of the tool holder used on the machine to determine the radial and axial dimensions of the tool during programming. 2, the relationship between tool cutting life and cutting amount When formulating the cutting amount, the tool life should be considered first. The principle of selecting the tool according to the tool life is: according to the tool complexity, manufacturing, and grinding cost. Complex and high precision tool life should be chosen to be higher than single-edged tools. For the machine clamp indexable tool, due to the short tool change time, in order to give full play to the cutting performance and improve the production efficiency, the tool life can be selected to be lower, generally 15 - 30min. For multi-tool machines, combination beds and automated machining tools with complicated tools, tool changes and tool adjustments, the tool life should be higher, especially for tool reliability. In the case of large-scale finishing, in order to ensure that at least one pass is completed and the tool is changed midway during cutting, the tool life should be determined according to the part accuracy and surface roughness. 3. Selection of tool materials The tool selected should have a high enough hardness to adapt to high pressure, high temperature and severe friction. Under normal circumstances, the hardness of the tool material should be at least 60HRC above the hardness of the workpiece material; The wear resistance, better wear resistance can reduce the wear of the tool, thus prolonging the service life of the tool; to have higher toughness, only with sufficient toughness to withstand the cutting force, impact and vibration of the process system; In order to ensure that the hardness, wear resistance and toughness of the tool do not occur or only produce small changes at high temperatures, the high temperature resistance of the tool material is required to be good; the good processability of the tool material is also an important aspect, which is beneficial to the tool. Repair and manufacturing.

Second, the choice of cutting amount Milling processing cutting amount includes cutting speed, feed rate, backing knife amount, side knife amount. The amount of cutting mainly affects cutting force, cutting power, tool wear, machining quality and processing cost. The selection of cutting amount should follow the following principles: Under the premise of ensuring the machining accuracy and surface roughness of the parts, the cutting performance and the durability of the tool should be fully utilized, and the performance of the machine tool should be fully utilized. Different processing methods should be used. The amount of cutting, programmers should determine the amount of cutting per process when programming, which can maximize production efficiency and reduce processing costs.

(1) The choice of the amount of back-feeding knife ap Turning processing can be divided into rough, semi-finish and fine. For roughing (Ra 50 - 12.5μm), the total machining allowance is cut off as much as possible during one pass. On medium power machines, the backfeed can be taken as 8 - 10mm. For a semi-finished car (Ra is 6.3 - 3.2 μm), the amount of back knife can be taken as 0. 5 - 2mm. When finishing the car (Ra is 1. 6 - 0. 8μm), the amount of backing knife can be taken as 0. 1 - 0. 4mm. In the following situations, the rough car is generally divided into several passes. First of all, when the machining allowance left by the workpiece is too large, the cutting force will be too large in one pass, and the machine power shortage or the tool strength may be insufficient. Secondly, the rigidity of the process system is not enough, or the machining allowance of the workpiece is very uneven, which causes a large vibration during the turning process. Third, in interrupted cutting, the tool is hit by a large impact. In the above situation, if you need to take the knife twice, then the amount of the back knife for the first pass should be as large as possible, and the amount of the back knife for the second pass should be as small as possible. In order to ensure a long tool life, high machining accuracy and low surface roughness of the finished tool. When the second pass is taken, the amount of back-feeding knife can take 1/3 of the machining allowance - about 1/4. (II) Determination of feed speed f In CNC turning, when roughing, there is generally no too high workpiece surface roughness requirement. At this time, the cutting force is generally large, so a reasonable feed rate f is equal to the process. The maximum amount of feed the system can withstand. This feed rate is limited by the following factors: the strength and rigidity of the turning tool holder, the strength of the lathe feed mechanism, the strength of the insert, and the rigidity of the workpiece. The feed rate includes the feed rate (fυ) and the feed per tooth. The instantaneous velocity of the selected point on the cutting edge relative to the feed of the workpiece is referred to as the feed rate. The amount of displacement of the tool relative to the workpiece in the direction of feed motion is called the feed amount in mm/r. The main purpose of semi-finishing and finishing is to improve the surface quality and machining accuracy of the parts. It is not possible to blindly increase the depth of cut. According to the remaining allowance during roughing, the cutting depth is reduced by knife to make the machining accuracy and surface quality. Gradually improve. The excessive selection of the feed rate reduces the machining accuracy and surface quality. In the semi-finishing and finishing, generally 20 - 50mm / min is a reasonable choice range. (3) Determination of cutting speed vc 1) Relationship between cutting speed vC and built-up height Hb. Because the top of the built-up edge is particularly unstable, it is easy to break, and some broken pieces may stick to the surface that has already been driven; the built-up edge increases the cutting depth of the tool by Δh, and the built-up edge will be generated periodically. , growth, shedding, resulting in Δh also periodically increase and decrease, its changes may cause vibration, so in the finishing car should choose a reasonable cutting speed to avoid the most easily generated turning speed area of ​​built-up edge. In the low-speed turning area I does not produce built-up edge; in the II area, the height of the built-up edge increases to the maximum with the increase of the cutting speed; the height of the built-up edge in the III area decreases with the increase of the turning speed; The internal built-up edge is no longer produced. Therefore, in actual production and processing, the cutting speed should avoid the medium speed zone as much as possible.

Third, with the development of CNC machining center machine tools, the processing technology requirements continue to improve, CNC machining methods are also more diverse, from simple manual programming to complex surface software programming, while the requirements for cutting tools are more accurate, Diverse. In some processing links, the realization of the processing technology requirements is the completion of tasks, while some processing and production tasks are about quality, efficiency, and efficiency. Only a reasonable selection of cutting tools and cutting quantities can ensure the smooth completion of the task and maximize the benefits.