The choice of cutting tool and the determination of the cutting amount are important contents in the numerical control processing technology. It not only affects the machining efficiency of the numerical control machine tool, but also directly affects the processing quality. The development of CAD/CAM technology makes it possible to use CAD design data directly in NC machining. Especially the connection between the microcomputer and the CNC machine tool makes it possible to complete the entire process of design, process planning and programming on the computer.

 

Nowadays, many CAD/CAM softwares include automatic programming functions. These softwares usually indicate the relevant problems of process planning in the programming interface, such as tool selection, machining path, cutting amount setting, etc. The programmer only needs to set relevant parameters. , you can automatically generate NC program and transfer to the CNC machine to complete the processing. Therefore, the tool selection and cutting amount determination in the numerical control machining are completed under the human-machine interaction state, which is in stark contrast with the ordinary machine tool processing. At the same time, the programmer is required to master the basic principles of tool selection and cutting amount determination. Take full account of the characteristics of CNC machining when programming. This paper analyzes the problem of tool selection and cutting amount determination that must be faced in numerical control programming.

 

First, the types and performance of commonly used tools for CNC machining

 

CNC machining tools must adapt to the characteristics of high-speed, high-efficiency and high-degree of automation of CNC machine tools, and generally include general-purpose tools and universal connection tool holders. The tool holder is connected to the tool and mounted on the power head of the machine, so it has been gradually standardized and serialized. There are several ways to classify CNC tools. According to the tool structure can be divided into: 1 monolithic; 2 mosaic. According to the materials used to manufacture the tool can be divided into: 1 high-speed steel tools; 2 carbide cutting tools; 3 diamond tools; 4 ceramic tools. From the cutting process can be divided into: 1 milling tools; 2 drilling tools; 3 boring tools; 4 turning tools.

 

Tool material should have the performance:

 

(1) The hardness of the high hardness tool material should be higher than the hardness of the workpiece

 

(2) Adequate toughness to withstand cutting forces, vibrations and shocks;

 

(3) High wear resistance Abrasion resistance is the ability of the material to resist wear;

 

(4) The ability of high heat-resistant tool materials to maintain hardness, wear resistance, strength, and toughness at high temperatures;

 

(5) Good processability

 

Second, the choice of CNC machining tools

 

The choice of tools should be based on the machine tool's processing ability, the performance of the workpiece material, processing procedures, cutting amount and other relevant factors for the correct choice of tool and handle. The general principle of tool selection is: easy installation and adjustment, good rigidity, high durability and high precision. In the premise of meeting the processing requirements, try to choose a shorter tool holder to improve the rigidity of the tool processing.

 

When selecting a tool, the dimensions of the tool must be adapted to the surface dimensions of the workpiece being machined. In production, the processing of plane contours often uses end mills; when milling planes, carbide insert face milling cutters are selected; when machining rough surfaces or rough machining holes, milling cutters equipped with hard alloy inserts can be selected; Some three-dimensional profile and variable bevel profile shape processing, often using ball-end cutters, circular cutters, tapered cutters and trapezoidal milling cutters. When performing surface machining, ball-nose tools should be used, and the radius of the ball head tool should be less than the minimum radius of curvature of the surface. Because the tip cutting speed of the ball head tool is zero, the cutting pitch is generally very dense to ensure machining accuracy, and the flat head cutter is superior to the ball nose cutter in both surface machining quality and cutting efficiency. Therefore, as long as the accuracy is guaranteed Under the premise of the premise, whether it is rough surface machining or finishing, priority should be selected flat knife.

 

In the numerical control processing, since the sharpening, measurement, and replacement of the tool are mostly performed manually, and the occupation time for the tool is longer, therefore, the arrangement order of the tools must be reasonably arranged. Generally should follow the following principles: 1 Minimize the number of tools; 2 After a tool is clamped, it should complete all the machining parts it can perform; 3 The rough finish tool should be used separately, even the same size of the tool; 4 After the first hole; 5 first finish the surface finish, after the two-dimensional contour finishing; 6 where possible, should use the automatic tool change function of CNC machine tools to improve production efficiency.