Numerical Control Machining

Tool selection:
1. Principles for selecting CNC tools Tool life is closely related to cutting parameters. When formulating cutting parameters, you should first choose a reasonable tool life, and a reasonable tool life should be determined according to the optimization goal. Generally, there are two types of tool life: the highest productivity tool life and the lowest cost tool life. The former is determined according to the goal of the least single-piece working hours, and the latter is determined according to the goal of the lowest process cost. When selecting tool life, you can consider the following points: choose according to the complexity of the tool, manufacturing and sharpening costs. The tool life of complex and high-precision tools should be selected higher than that of single-edged tools. For machine-clamped indexable tools, due to the short tool change time, in order to give full play to its cutting performance and improve production efficiency, the tool life can be selected lower, generally 15-30 minutes. For multi-tool machine tools, combined machine tools and automated processing tools that are relatively complex in tool installation, tool change and tool adjustment, the tool life should be selected higher, especially to ensure tool reliability. When the productivity of a certain process in the workshop limits the productivity of the entire workshop, the tool life of the process should be selected to be lower. When the total factory expenditure per unit time of a certain process is large, the tool life should also be selected to be lower. When finishing large parts, in order to ensure that at least one tool pass is completed and to avoid tool change during cutting, the tool life should be determined according to the part accuracy and surface roughness. Compared with ordinary machine tool processing methods, CNC machining places higher requirements on tools. It not only requires good quality and high precision, but also requires stable size, high durability, and good performance of breaking and rowing. At the same time, it requires easy installation and adjustment to meet the high efficiency requirements of CNC machine tools. The tools selected on CNC machine tools often use tool materials suitable for high-speed cutting (such as high-speed steel, ultra-fine-grained cemented carbide) and use indexable inserts.

2. Select tools for CNC turning CNC turning tools are generally divided into three categories: forming turning tools, pointed turning tools, and arc-shaped turning tools. Forming turning tools are also called model turning tools. The contour shape of the machined parts is completely determined by the shape and size of the turning tool blade. In CNC turning, common forming turning tools include small radius arc turning tools, non-rectangular groove turning tools and threading tools. In CNC machining, forming turning tools should be used as little as possible or not at all. Pointed turning tools are turning tools characterized by straight cutting edges. The tip of this type of turning tool is composed of straight main and secondary cutting edges, such as 900 internal and external circle turning tools, left and right end turning tools, grooving (cutting) turning tools and various external circle and internal hole turning tools with very small tip chamfers. The selection method of the geometric parameters (mainly geometric angles) of the pointed turning tool is basically the same as that of ordinary turning, but it should be comprehensively considered in combination with the characteristics of CNC machining (such as machining routes, machining interference, etc.), and the strength of the tool tip itself should be taken into account. The second is the arc turning tool. The arc turning tool is a turning tool characterized by an arc cutting edge with a very small roundness or linear profile error. Each point of the arc edge of the turning tool is the tip of the arc turning tool. Therefore, the tool position is not on the arc, but on the center of the arc. The arc turning tool can be used for turning internal and external surfaces, and is particularly suitable for turning various smooth connection (concave) forming surfaces. When selecting the arc radius of the turning tool, the arc radius of the two-point turning tool cutting edge should be less than or equal to the minimum curvature radius on the concave contour of the part to avoid machining shallowness. The radius should not be too small, otherwise it will not only be difficult to manufacture, but also cause damage to the turning tool due to weak tip strength or poor heat dissipation of the tool body.

3. Selecting tools for CNC milling In CNC machining, flat-bottomed end mills are commonly used for milling the inner and outer contours of planar parts and milling planes. The empirical data of the relevant parameters of this tool are as follows: First, the milling cutter radius RD should be less than the minimum curvature radius Rmin of the inner contour surface of the part, generally taking RD=(0.8-0.9)Rmin. Second, the processing height H of the part < (1/4-1/6)RD to ensure that the tool has sufficient rigidity. Third, when using a flat-bottom end mill to mill the bottom of the inner groove, because the two passes of the groove bottom need to overlap, and the radius of the tool bottom edge Re=R-r, that is, the diameter is d=2Re=2(R-r), the tool radius is Re=0.95 (Rr) when programming. For the processing of some three-dimensional surfaces and variable angle contours, spherical milling cutters, annular milling cutters, drum milling cutters, conical milling cutters and disc milling cutters are commonly used. Most CNC machine tools use serialized and standardized tools. There are national standards and serialized models for the tool holders and tool heads of indexable machine-clamped external cylindrical turning tools, end turning tools, etc. For machining centers and machine tools with automatic tool changing devices, there are serialized and standardized regulations for tool holders. For example, the standard code for the tapered shank tool system is TSG-JT, and the standard code for the straight shank tool system is DSG-JZ. In addition, for the selected tools, the tool dimensions must be strictly measured before use to obtain accurate data, and the operator enters these data into the data system, and the processing process is completed through program call, thereby processing qualified workpieces.