CNC machining refers to a process method for processing parts on CNC machine tools. The process procedures of CNC Machining and traditional machine tool processing are generally the same, but there have also been obvious changes. A machining method that uses digital information to control part and tool displacement. It is an effective way to solve the problems of variable varieties of parts, precision cnc machining, complex shapes, and high precision, and to achieve efficient and automated processing.
History Of CNC Machining
CNC technology originated from the needs of the aviation industry. In the late 1940s, an American helicopter company proposed the initial idea of CNC machine tools. In 1952, the Massachusetts Institute of Technology in the United States developed a three-coordinate CNC milling machine. In the mid-1950s, this CNC milling machine was used to process aircraft parts. In the 1960s, CNC systems and programming work became increasingly mature and perfect. CNC machine tools have been used in various industrial sectors, but the aerospace industry has always been the largest user of CNC machine tools. Some large aviation factories are equipped with hundreds of CNC machine tools, mainly cutting machine tools. The parts processed by CNC include the integral wall panels, beams, skins, partitions, propellers of aircraft and rockets, as well as the mold cavities of the casings, shafts, disks, and blades of aeroengines, and the special cavity surfaces of the combustion chambers of liquid rocket engines. . In the early days of the development of CNC machine tools, CNC machine tools with continuous trajectory were mainly used. Continuous trajectory control, also known as contour control, requires the tool to move along a prescribed trajectory relative to the part. Later, we vigorously developed point control CNC machine tools. Point control means that the tool moves from one point to another as long as it reaches the target accurately regardless of the movement route.
Application Of CNC Machining
From the beginning, CNC machine tools selected aircraft parts with complex profiles as processing objects to solve the key problems that are difficult to solve with ordinary processing methods. The biggest feature of CNC machining is the use of perforated tape (or tape) to control the machine tool for automatic processing. Because aircraft, rockets and engine parts each have different characteristics: aircraft and rocket parts and components are large in size and complex in shape; engine parts and components are small in size and high in precision. Therefore, the CNC machine tools used in aircraft, rocket manufacturing departments and engine manufacturing departments are different. In aircraft and rocket manufacturing, large-scale CNC milling machines with continuous control are mainly used, while in engine manufacturing, both continuously controlled CNC machine tools and point-controlled CNC machine tools (such as CNC drilling machines, CNC boring machines, machining centers, etc.) are used. .
Advantages and Disadvantages Of CNC Machining
CNC machining has the following advantages:
- ① The number of tooling is greatly reduced, and complex tooling is not required for processing parts with complex shapes. If you want to change the shape and size of parts, you only need to modify the part processing program, which is suitable for new product development and modification.
- ② The processing quality is stable, the processing precision is high, and the repeatability is high, adapting to the processing requirements of aircraft.
- ③ The production efficiency is high in the case of multi-variety and small batch production, which can reduce the time of production preparation, machine tool adjustment and process inspection, and the cutting time is reduced due to the use of the optimal cutting amount.
- ④ It can process complex surfaces that are difficult to process with conventional methods, and can even process some processing parts that cannot be observed.
The disadvantage of CNC machining is that machine tools and equipment are expensive and require high-level maintenance personnel.
In order to improve the degree of 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. For example, computer numerical control uses a small or microcomputer to replace the controller in the numerical control system, and uses software stored in the computer to perform calculation and control functions. This soft-connected computer numerical control system is gradually replacing the initial state of the numerical control system. Direct CNC uses one computer to directly control multiple CNC machine tools, which is very suitable for small batch and short-cycle production of aircraft. The ideal control system is an adaptive control system that can continuously change processing parameters. Although the system itself is complex and expensive, it can improve processing efficiency and quality. In addition to the improvement of CNC systems and machine tools in terms of hardware, another important aspect of the development of CNC is the development of software. Computer-aided programming (also called automatic programming) means that after the programmer writes the program in CNC language, it is input into the computer for translation, and finally the computer automatically outputs punched tape or magnetic tape. The more widely used CNC language is APT language. It is broadly divided into main processor and post-processor. The former translates the program written by the programmer and calculates the tool trajectory; the latter compiles the tool trajectory into the part processing program of the CNC machine tool.
The Process Of CNC Machining
CNC machining generally refers to the process of processing parts on CNC machine tools. CNC machine tool is a machine tool controlled by a computer. The computer used to control the machine tool, whether it is a special computer or a general-purpose computer, is collectively called a CNC system. The motion and auxiliary actions of CNC machine tools are controlled by instructions issued by the CNC system. The instructions of the CNC system are compiled by the programmer according to the material of the workpiece, processing requirements, characteristics of the machine tool and the instruction format (CNC language or symbols) specified by the system. The CNC system sends run or stop information to servo devices and other functional components according to program instructions to control various movements of the machine tool. When the part processing program ends, the machine tool will automatically stop. Any CNC machine tool cannot work if there are no program instructions input into its CNC system.
The controlled actions of the machine tool generally include the starting and stopping of the machine tool; the starting and stopping of the spindle, the change of rotation direction and speed; the direction, speed and mode of the feed motion; the selection, length and radius compensation of the tool; the replacement and cooling of the tool Opening and closing of liquid, etc.
CNC machining programming methods can be divided into manual (artificial) programming and automatic programming. Manual programming, all the contents of the program are written manually according to the instruction format specified by the CNC system. Automatic programming is computer programming, which can be divided into automatic programming methods based on language and painting. However, no matter what automatic programming method is used, corresponding supporting hardware and software are required.
It can be seen that realizing CNC machining programming is the key. But programming alone is not enough. CNC machining also includes a series of preparatory work that must be done before programming and the aftermath of programming. Generally speaking, China CNC machining technology mainly includes the following contents:
- (1) Select and determine the parts and content for CNC processing;
- (2) Process analysis of CNC machining of part drawings;
- (3) Process design of CNC machining;
- (4) Mathematical processing of part drawings;
- (5) Write processing program sheet;
- (6) Make control media according to the program sheet;
- (7) Program verification and modification;
- (8) First piece trial processing and on-site problem handling;
- (9) Finalization and archiving of CNC machining process documents.
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