Definition of CNC machining
Use the computer to control the processing program of the parts on the CNC milling machine or machining center, and the program automatically completes the processing of the parts. This process is called “CNC (Computer-Numerical Control)”, that is, computer digital control. It is a new type of machine tool formed by adding a set of numerical control device to the ordinary milling machine. Its function is to realize the functions of digital program control, automatic programming and auxiliary design and manufacture. At present, this technology has been used in many fields in the world, such as automobile, aviation, aerospace, machinery and other industrial sectors.
Features of CNC machining
1. CNC milling is a processing method that uses a computer-controlled machine tool to automatically cut through a program. It has the advantages of high production efficiency, good working conditions, fewer operators, stable and reliable quality and continuous production. In the rough machining of metal parts, due to the multi-axis linkage method for high-speed cutting, its efficiency is several to dozens of times higher than that of traditional manual or semi-automatic equipment; at the same time, due to the small tool radius (generally less than 5mm), the Chips are not easy to stick to the knife; in addition, because the machine tool itself is equipped with a coolant system, the life of the tool is greatly extended. But its main disadvantage is that it can only realize single-piece small-batch production and it is not suitable for manufacturing parts with complex shapes.
2. CNC turning is a process method of mechanical turning process using a computer-controlled lathe. It automatically controls the relative motion trajectory between the tool and the workpiece to complete the finishing process of the parts. This method can meet the requirements of mass production and has high precision. But the disadvantage of this method is that it cannot be assembled at one time for complex shapes. Clamp positioning and automatic size measurement. Therefore, specialized technical workers are required to complete this work and corresponding detection devices are required to check the surface quality and dimensional accuracy of the workpiece.
Types of CNC Machining Operations
In actual production, CNC operations are generally divided into two categories: one is programming; the other is the input of processing programs. When programming, it is usually necessary to use some auxiliary tool software, such as automatic programming machine, automatic tool change system (ATE), etc. These tool software can greatly improve the efficiency and accuracy of programming.
Overview of CNC machining parts processing procedure
When performing CAM programming, it is first necessary to determine the processing method of the part, and then select the appropriate programming language (such as FANUC, SIEMENS, Huazhong CNC, etc.) according to different processing methods, and formulate the specific process route and operation steps. Since the machine models of each manufacturer are different and their functions are not exactly the same, it is necessary to write corresponding processing programs for different equipment to ensure the correct execution of the programs. For example, various tools and fixtures are used in turning; various types of milling machines and various tools are used in milling; and many types of grinding wheels are used in the grinding process. These situations will affect the writing work of CAM program. Therefore, we must understand the basic situation of the type of equipment used and its functional characteristics before programming.
What principles should be followed in the arrangement of CNC processing sequence?
1. From simple to complex. Due to the different structure, shape and material of parts, the processing routes on CNC machine tools are also different. Generally, the plane contour is processed first, and then the inner cavity, outer cavity and boss are gradually finished. For more complex parts, the entire processing process can be completed in multiple times. 2. From coarse to fine. For the same type of parts, the rough and finish processing routes are basically the same; but for different types of parts, this is not the case: for example, the rough and finish processing routes of shaft parts are very different (see Figure 1). 3. Reasonably arrange the time allocation between processes according to the production plan. Generally speaking, under the premise of ensuring product performance, it is better to reduce the average time between processes as much as possible (see Table 1), which is conducive to improving production efficiency and shortening the manufacturing cycle of products. The contradiction between workers’ operation skills often encounters such a problem in actual production: when a certain work step requires more cutting amount (such as hole drilling or tapping), but the equipment capacity required for this process is not enough. What to do when there are restrictions?
The difference between CNC machining and traditional machining
1. In traditional mechanical processing, due to the size limitation of the machine tool, the diameter and length of the tool are limited to a certain extent. The CNC system can automatically program, automatically set the tool, automatically measure the workpiece and display the tool path according to the requirements of the part drawing, so as to complete the entire processing process automatically.
2. In traditional mechanical processing, due to the complex and changeable shape and size of the workpiece (such as cavity parts or inner cavity surface), it is necessary to continuously adjust the position of the tool according to the actual situation to meet the cutting requirements of workpieces of different shapes and sizes; In the CNC system, various types of tool path selection and corresponding tool path selection can be realized only by setting program parameters.
3. For some large and complex parts or workpieces that are difficult to guarantee tolerance requirements (such as box parts), the traditional processing technology cannot guarantee the accuracy requirements; and the CNC system can eliminate the influence of these errors through software compensation technology.
The pros of CNC machining
1. It can process parts with complex shapes, such as small holes, blind holes, deep grooves, etc.
2. It can process various parts with high precision requirements, such as high-precision shaft parts or high-precision spline shafts, etc.
3. It can complete the processing of various processes in one clamping and positioning, which improves production efficiency and saves man-hours.
The cons of CNC machining
1. Due to the high-speed cutting tool, there is relative motion between the tool and the workpiece, which will generate a large cutting force; at the same time, cutting force will also be generated due to tool wear and installation errors. These factors lead to reduced tool durability and increased machine tool spindle power. In addition, tool breakage is also prone to occur during high-speed machining (that is, chips leave the tool without being cut off).
2. When burrs appear on the machined surface, it is difficult to remove the burrs by ordinary turning; but it is easy to realize the automatic deburring function by using CAM programming.
3. Since CAM programming is a continuous production process that uses program control for automatic circulation, its production efficiency is much lower than that of manual operation (generally, the efficiency of manual operation is about 10 times that of manipulator or copy milling machine).
How to monitor and adjust during CNC processing?
When using CAM software, because the operator is not familiar with the program, it is often impossible to control the machining process well. In order to ensure the dimensional tolerance requirements of parts, it is necessary to carry out necessary monitoring and adjustment according to actual needs.
What should I prepare before CNC programming?
1. First of all, you must be familiar with the C language. Because a lot of software is based on C language, such as some mobile phone programs, games, etc., and some embedded systems, etc.; secondly, you must be familiar with the MFC (Windows MFC) development environment. This may be a bit difficult for beginners, but it can still be learned as long as you study hard; again, you need to understand some commonly used data structures and algorithms. The last is to master some basic data processing knowledge. This knowledge should be accumulated and summarized in the usual study.
What are the types of CNC machining support software?
CAM (Computer Aided Machining) refers to computer-aided manufacturing, that is, computer technology that uses digital means to design, analyze, manufacture and assemble products. It is a method of digitizing various elements in the machining process or part processing program and expressing them numerically. It has the characteristics of fast calculation speed, high efficiency and easy automation, and is one of the main ways to improve labor productivity. It is the most widely used CNC machining method in the manufacturing industry, including turning, milling and grinding.
CAE (Computer Aided Excellence) is Computer Aided Science Experiment (CAT). It is a general term for a mathematical model system and its corresponding tool software package aimed at research and development; its purpose is to help people effectively solve various practical problems or provide a basis for decision-making; its content involves a variety of disciplines from qualitative to quantitative fields and their intersection and penetration; its scope of application has been developed from pure scientific research to all walks of life for national economic construction and national defense construction.
CAPP(Computer Aided Process Planning) is the general term for computer programs and methods used to plan enterprise resource planning (ERP) systems. Personnel fully grasp and use modern information technology to engage in effective means and tool systems for various business management.
PDM (Product Data Management) is a technology used to manage all product-related information (including part information, configuration, documents, CAD files, structures, authority information, etc.) and all product-related processes (including process definition and management) . Through the implementation of PDM, the production efficiency can be improved, which is beneficial to the management of the whole life cycle of the product, the efficient use of documents, drawings and data can be strengthened, and the workflow can be standardized.
Extensive functionality offered by CNC machining technology
In the processing of CNC machine tools, CNC system provides many functions to help users in production, including automatic programming, automatic tool setting, tool compensation, spindle speed control and various auxiliary functions. For example: in terms of automatic programming, it can complete the linkage programming of multi-coordinate points and the interpolation program generation of compound trajectory; in terms of auxiliary functions, it includes various measuring tools (such as three-coordinate measuring machines), tool length compensation and position compensation, et