The selection of cutting tools and the determination of cutting amount are important contents in the CNC machining process. It not only affects the processing efficiency of CNC machine tools (attribute: automatic machine tools), but also directly affects the processing quality. CNC machining generally CNC machining usually refers to computer digitally controlled precision machining, CNC machining lathe, CNC machining milling machine, CNC machining boring and milling machine, etc. The feed route for finishing is basically carried out along the contour of its parts. Therefore, the work of determining the feed route is to determine the feed route for rough machining and empty stroke. The development of CAD / CAM technology makes it possible to directly use CAD design data in CNC machining, especially the connection between microcomputer and CNC machine tool, so that the entire process of design, process planning and programming is completed on the computer, generally no output is required Special craft documents.
At present, many CAD / CAM software packages provide automatic programming functions. These software generally prompt related problems of process planning in the programming interface, such as tool selection, machining path planning, cutting amount setting, etc., as long as the programmer sets the relevant The parameters (parameter), you can automatically generate an NC program (procedure) and transfer to the CNC machine tool to complete the processing. Therefore, the tool selection and cutting amount determination in CNC machining are completed in the state of human-machine interaction, which is in sharp contrast to ordinary machine tool processing, and also requires programmers to master the basic principles of tool selection and cutting amount determination. Fully consider the characteristics of CNC machining when programming. This article discusses the problems of tool selection and cutting amount determination that must be faced in CNC programming, gives some principles and suggestions, and discusses the issues that should be paid attention to.
1. The types and characteristics of commonly used tools for CNC machining
CNC machining tools must be adapted to the characteristics of high-speed, high-efficiency and high degree of automation of CNC machine tools (attribute: automated machine tools). Generally, they should include general-purpose tools, universal connection tool holders (bǐng) and a small number of special tool holders. The tool holder is connected to the tool and mounted on the power head of the machine tool, so it has been gradually standardized and serialized. There are many ways to classify CNC tools. According to the cutter structure, it can be divided into:
- ①integral type;
- ②embedded (xiāng) embedded type, which is connected by welding or machine clamp type, and machine clamp type can be divided into two types: non-indexable and indexable;
- ③special type, such as compound Tool, shock-absorbing tool, etc.
According to the materials used to make tools, it can be divided into:
- ① HSS tools;
- ② carbide tools;
- ③ diamond tools;
- ④ tools of other materials, such as cubic boron nitride (B) tools, ceramic (raw materials: non-metallic minerals) tools, etc. .
From the cutting process, it can be divided into:
- ① turning tools, divided into outer circles, inner holes, threads, cutting tools, etc .;
- ② drilling tools, including drill bits, reamers, taps, etc .;
- ③ boring tools;
- ④ milling tools .
In order to meet the requirements of CNC machine tools for the durability and stability of the tools (interpretation: stable and stable; no changes), easy adjustment, and interchangeability, machine-clamped indexable tools have been widely used in recent years, reaching the entire CNC tool in number. 30% ～ 40%, the amount of metal removal accounts for 80% ～ 90% of the total.
Compared with the tools used on ordinary machine tools, CNC tools have many different requirements, mainly with the following characteristics:
- ⑴Good rigidity (especially rough machining tools), high precision (accuracy), low vibration resistance and thermal deformation;
- ⑵ Good interchangeability, convenient for quick tool change;
- ⑶High life, stable cutting performance (explanation: stable and stable; no change), reliable;
- ⑷The size of the tool is easy to adjust to reduce the time for tool change adjustment;
- ⑸The tool should be able to break or curl chips reliably to facilitate the removal of chips (Remove);
- ⑹ Serialization and standardization to facilitate programming and tool management. In numerical control processing, the control system sends out instructions to make the cutter perform various movements that meet the requirements, and expresses the processing of technical requirements and processing requirements such as the shape and size of the workpiece in the form of numbers and letters.
It generally refers to the process of processing parts on CNC machine tools. In order to improve production automation, shorten programming time and reduce CNC machining costs, a series of advanced CNC machining technologies have also been developed and used in the aerospace industry.
2.The choice of CNC machining tools
The selection of tools is carried out in the state of human-machine interaction of NC programming. The tools and tool holders should be correctly selected according to the processing capacity of the machine tool, the performance of the workpiece material, the processing procedure, the cutting amount and other relevant factors. Tool selection The general principle is: easy installation and adjustment, good rigidity, high durability and precision. Under 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 size of the tool should be adapted to the surface size of the workpiece to be processed. In production, end mills are often used to process the peripheral contours of flat parts; when milling planes, carbide insert mills should be selected; when machining bosses and grooves, high-speed steel end mills should be selected; and rough surface processing Or rough machining holes, you can choose corn milling cutters with xiāng carbide inserts; for the processing of some three-dimensional profiles and varying bevel contour shapes, ball head milling cutters, ring milling cutters, and cone milling cutters are often used. And disc milling cutter.
In free-form surface machining, because the cutting speed of the end of the ball head tool is zero, in order to ensure the machining accuracy (accuracy), the cutting line spacing is generally very dense, so the ball head is often used for finishing of the curved surface. CNC machining CNC is also known as computer gong, CNCCH or CNC machine tool. It is actually a name from Hong Kong, which greatly reduces the number of tooling. CNC machining of parts with complex shapes does not require complicated tooling. CNC machining is a new type of processing technology and the main work It is to compile the processing program, that is, to convert the original manual to computer programming. If you want to change the shape and size of the part, you only need to modify the part processing program, which is suitable for new product development and modification. Flat-faced cutters are superior to ball-end cutters in terms of surface machining quality and efficiency. Therefore, flat-faced cutters should be preferred as long as they are not roughened or finished on the premise of undercutting. In addition, the durability and accuracy of the tool have a great relationship with the price of the tool. It must be noted that in most cases, although the choice of a good tool increases the cost of the tool, the resulting improvement in processing quality and processing efficiency , You can greatly reduce the entire processing cost.
On the machining center, various tools are installed on the tool magazine, and the tool selection and tool change are performed at any time according to the program. Therefore, a standard tool holder must be used so that the standard tools used in drilling, boring, expanding, milling and other processes can be quickly and accurately installed on the machine tool spindle or tool magazine. The programmer should understand the structure size, adjustment method and adjustment range of the tool holder used on the machine tool, so as to determine the radial and axial dimensions of the tool during programming. At present, the machining center in China adopts the TSG tool system. Its tool handles are of two types: straight shank (three specifications) and tapered shank (four specifications), including a total of 16 different types of tool shanks.