The use of CNC machine tools for metal cutting is not only the main metal cutting method in the aerospace manufacturing industry, but also dominates the entire industrial production. In the transformation of CNC cutting methods, production quality management has also undergone great changes. Traditional manual machine tool processing parts, the processing quality of individual processes depends on the skills of workers. In CNC machining, the craftsman not only needs to be responsible for the process formulation, but also the NC machining program preparation, CNC tool selection and process parameter formulation. Therefore, CNC machining efficiency and machining quality are significantly affected by CNC tools.
The processing method of aerospace manufacturing industry is mainly based on small-volume and multi-variety mixed-line processing. Compared with the mass-produced automobile manufacturing industry, in the machining of parts, due to the difficult processing of parts and the difficult processing characteristics of the part structure, Not only has an urgent need for high-performance CNC knives, but also suitable tool management technology has important significance and application value for the improvement of CNC production quality.
The tool management technology in the narrow sense only involves the logistics management of the tool. Tool management techniques used in mass production such as automotive engines include not only tool logistics management, but also tool definition, cutting parameters, cutting data, tool adjustment and tool grinding, CAM interface, and tool usage prediction. Through the application of tool management technology, the tools in mass production can be separated and managed by a professional tool management service team to realize tool distribution at the production site and reduce production costs. This tool management technology has many problems for the special production methods of the aerospace manufacturing industry. Today's aerospace companies have established relatively complete information management systems such as CAPP, ERP and PDM, and tool-related logistics management functions are already in place. However, the tool has its particularity. In the process development, it is necessary to know not only the shape and size of the tool, but also the choice of materials and cutting parameters that the tool is suitable for.
Cutting is a multivariable complex time-varying system including machine tools, tools, parts, fixtures, and processes. The cutting state corresponding to the cutting parameters and the machining results obtained are affected by various links and many parameters of the cutting system. It is difficult to establish standard uniform cutting. Process system models to describe and optimize process parameters. As the main provider of tools, tool manufacturers often use trade-offs to recommend available cutting parameters or approximate machining cases for the tools and objects to be processed. It does not provide tool life and machining effect prediction, and relies on actual machining. The results were roughly evaluated.
The cutting database is mainly used to provide machine tools and tool selection when formulating specific process plans for process personnel.
Choose solutions and optimize feasible processing parameters. Since the micro-milling process system involves all aspects of machining such as machine tools, tools, workpieces, fixtures, lubrication and cooling, and due to the dynamic time-varying characteristics of the machining process, the optimal process parameters are often difficult to determine. This is also the main factor that makes the existing metal cutting database difficult to put into practical use.
For the particularity of aerospace manufacturing, the management technology of high-performance CNC tools should include tool performance evaluation, tool field application, and tool logistics.
Tool performance evaluation method
With the increasing complexity of aerospace structural components, more and more difficult-to-machine feature structures are covered. In the past, the tools selected by basic cutting tests often showed significant performance differences for different structural features. That is to say, the same tool often exhibits a large difference in cutting performance when cutting different structural features.
In order to reasonably evaluate the performance of aerospace titanium alloy structural parts milling tools and to find milling tools suitable for aerospace titanium alloy structural parts, it is necessary to judge the performance of cutting tools based on the understanding and familiarity with the structural characteristics of aerospace titanium alloy complex structural parts.
In order to optimize the titanium milling tool and optimize the cutting parameters, a variety of titanium alloy test pieces were designed. Figure 1 is a reference sample designed to refer to the S-shaped part of the machine tool performance test. By defining a uniform cutting path, not only can the cutting performance of the tool be compared, but also the performance of the machine can be tested, which provides a personalized evaluation of the cutting parameters. A reference method.
For example, tool life and metal removal rate are used as roughing evaluation indicators to construct a comprehensive evaluation model of tool performance. Through actual cutting tests, four types of PVD alumina coatings of WSM35, WSM35S, WSP45 and WSP45S are compared and evaluated. The fuzzy membership degree of the data is evaluated. The performance of cutting the S-shaped area is WSM35S, WSP45, WSP45S, WSM35, and the performance of cutting the reverse cavity is WSM35S, WSM35, WSP45, WSP45S.
Tool performance evaluation using benchmarks, a number of comparative tests have shown that more reasonable cutting parameters can be provided for process development.
Tool field application
Tool field application refers to the tool selection, cutting parameters, life prediction, wear management, tool adjustment and tool change from the process planning.
The basic process of tool selection is to obtain the relevant tool, tool holder, and recommended cutting parameters based on the structure and material of the part being machined through the tool sample. The advantages and disadvantages of tool selection have a decisive influence on the processing quality, processing efficiency and processing cost, and also affect the preparation of CNC machining programs. In particular, difficult-to-machine materials such as titanium alloys and high-temperature alloys commonly used in the aerospace industry are sensitive to tool materials, insert geometry and cutting parameters. Any mismatching can lead to increased tool wear or reduced efficiency. Since tool selection relies on “knowledge”, Walter first provided TEC-CCS tool management assistant software to provide users with tool advice for overall milling and hole machining; Kennametal also introduced NOVOTM tool management software, which utilizes a variety of The way the parameters are constrained provides the user with tool recommendations. The above software also provides cutting force and cutting torque and power calculation functions.
Taking full advantage of the performance of high-performance cutting tools requires not only selecting the right tool for the machining object, but also arranging reasonable cutting parameters for the tool during the process. Since the machining of the part on the machine tool is a multivariable complex time-varying process, it is necessary to adjust the cutting parameters recommended by the tool according to the machine state, the part clamping method, and the machining allowance.
Since titanium alloys and superalloys are easy to work harden, proper feed and depth of cut should be used to keep the cutting under the hardened layer. In the application of ceramic tool cutting high-temperature alloy, the cutting speed usually needs to exceed 80m/min during turning to make full use of the hardness difference between ceramic and high-temperature alloy for efficient cutting; in milling, the cutting line speed needs to exceed 600m/min to achieve similar At the same time, due to the brittleness of the ceramic tool, when the coolant or the micro-lubrication is applied, the expansion of the liquid in the micro-crack on the surface of the tool will increase the crack expansion speed and accelerate the damage of the tool. The air-cooling or dry cutting method should be adopted as much as possible.
In the actual machining process, the feedback of tool cutting effect is an important basis for tool, cutting parameter improvement and tool cost control. In the existing workshop production management system, the actual tool cutting life and the dynamics of the machining process are mostly oral reports of the on-site operators. If relevant data statistics are performed, the on-site management workload will increase sharply. How to obtain the relevant tool application results in an efficient, timely and comprehensive manner in production remains to be further explored.
According to the survey of the quality of CNC cutting parts in the domestic aerospace manufacturing industry, most quality problems are caused by simple errors. For example, in the process of machining large-scale parts of CNC machine tools, due to factors such as cutting fluid injection and on-site noise, it is especially common for operators to neglect problems such as incorrect tool call, tool length error, and excessive tool wear. The application of technical means for such error-proof processing has a good effect, such as establishing a tool distribution system in the workshop, providing a tool list according to the daily task of each machine tool, and the tool is confirmed by the special personnel on the tool presetter, and then distributed. To the corresponding tool magazine, the tool change prompt is performed according to the expected tool life in the program.