The key technology and application prospect of com

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The key technology and application prospect of turn milling machining

machining efficiency and accuracy are the eternal goals in the field of metal processing. With the continuous development of numerical control technology, computer technology, machine tool technology and processing technology, the traditional processing concept can no longer meet people's requirements for processing speed, efficiency and accuracy. In this context, composite machining technology came into being. Generally speaking, compound processing refers to the general term of processing technology that can complete different processes or different process methods on one processing equipment. At present, there are two different types of composite processing technology. One is the combination of different processing methods based on energy or motion mode; The other is based on the principle of process concentration and mainly based on mechanical processing technology. Turning milling composite processing is one of the most rapidly developing processing methods in this field in recent years

at present, aviation product parts are characterized by multiple varieties, small batches, complex process, and extensive use of integral thin-walled structures and difficult to machine materials. Therefore, bottlenecks such as long manufacturing cycle, large amount of material removal, low processing efficiency and serious processing deformation are common in the manufacturing process. In order to improve the processing efficiency and accuracy of complex aviation products, technicians have been looking for more efficient and precise processing methods. The emergence of turning milling compound processing equipment provides an effective solution to improve the processing accuracy and efficiency of aviation parts. Some Chinese plastic materials and products export enterprises may be frowning

compared with the conventional NC machining process, the outstanding advantages of compound machining are mainly shown in the following aspects

(1) shorten the product manufacturing process chain and improve production efficiency

turning milling combined processing can achieve one-time card loading to complete all or most of the processing procedures, thus greatly shortening the product manufacturing process chain. In this way, on the one hand, the production assistance time caused by the change of clamping is reduced, and at the same time, the manufacturing cycle and waiting time of tooling and fixtures are reduced, which can significantly improve the production efficiency

(2) reduce clamping times and improve machining accuracy

the reduction of card loading times avoids the error accumulation caused by the transformation of positioning reference. At the same time, most of the current turning milling compound processing equipment have the function of detection, which can realize the in-situ detection and accuracy control of key data in the manufacturing process, so as to improve the processing accuracy of products

(3) reduce the floor area and production cost

although the single price of turning milling composite processing equipment is relatively high, due to the shortening of manufacturing process chain, the reduction of equipment required for products, as well as the reduction of the number of fixtures, workshop floor area and equipment maintenance costs, it can effectively reduce the investment, production operation and management costs of the overall fixed assets

key technology of composite machining

although composite machining has incomparable advantages over conventional single machining, the utilization rate of turning milling composite machining has not been fully brought into play in the field of aviation manufacturing at present. The key reason is that the application time of turn milling compound machining in the field of aviation manufacturing is still relatively short, and the turn milling compound machining technology, NC programming technology, post-processing and simulation technology suitable for the structural process characteristics of aviation parts are still in the exploratory stage. In order to give full play to the efficiency of turning milling compound processing equipment and improve the processing efficiency and accuracy of products, we must comprehensively overcome and solve the above key foundations and realize integrated application

1 process technology of turning milling composite machining

different from conventional processing equipment, a turning milling composite machining center is actually equivalent to a production line. How to formulate a reasonable process route, clamping method and select a reasonable tool according to the process characteristics of parts and the process characteristics of turn milling compound machining is the key to achieve efficient and precision machining

process concentration is the most distinctive process feature of composite processing. Therefore, a scientific and reasonable process route is the key factor to improve the efficiency and accuracy of turn milling compound machining. Take the s192f milling and turning compound machining center of Swiss Baume company shown in Figure 1, which does not coincide with the main needle, as an example. The machine tool has the functions of five axis milling, turning, boring, drilling, sawing and automatic feeding. It adopts FANUC 31I numerical control system and has the functions of tool vector smoothing, super forward-looking, high-speed interpolation and so on. It is especially suitable for high-speed and precision machining of shaft, rotary and other parts. The machining center has outstanding advantages in the machining of aviation impeller. When the bar material is used as the impeller blank, the conventional impeller processing route first uses the numerical control lathe to turn the outer contour of the impeller, and then the finish machining benchmark; On this basis, the five axis CNC machining center is used for slotting, rough machining, semi finishing, and finishing of profile and wheel hub; Finally, hole machining is carried out on the five axis machining center or drilling equipment. The s192f milling machining center can not only complete all the processing of the above processes through one-time clamping, but also realize the batch processing of the impeller through the functions of sawing and automatic feeding when the bar is used for processing. The whole process can be completed automatically without manual intervention. The process route can be set in the following ways: bar loading on the main shaft → rough turning of the external contour of the impeller → fine turning of the external contour → five axis milling and slotting → rough machining of the channel → semi finishing of the channel → finishing of the channel → drilling → clamping on the back of the main shaft → turning the bottom plane of the impeller → drilling. It can be seen that one-time clamping can complete all impeller processing procedures, and the processing efficiency and accuracy can be greatly improved

for turning and milling machining centers with double tool holders (as shown in Figure 2, WFL turning and milling compound machining center in Austria), the equipment of double tool towers has a dual channel control system, the upper and lower tool holders can be controlled separately, and synchronous machining can be realized through the synchronous statement in the code. In order to give full play to the processing capacity of the equipment, multiple processes of parts can be processed at the same time through the synchronous operation of double tool holders on the premise of processing conditions. Through the synchronous setting of the upper and lower tool holders, the rough boring of the inner hole can be completed at the same time of rough turning the shape, so as to further improve the processing efficiency. Through the synchronous movement of the upper and lower tool holders, the machining of a series of holes is completed, which not only improves the efficiency of machining, but also reduces the influence of workpiece deformation by offsetting the axial force of drilling. In order to realize this function, it is necessary to make a systematic and in-depth study of the process plan in the early process design, determine the serial and parallel sequence of the process route, and realize the above functions through the reasonable combination of processing programs

2 NC programming technology of turning and milling complex machining

the development of turning and milling complex machining technology also puts forward higher requirements for NC programming technology, which is also a bottleneck that restricts the application of turning and milling complex machining equipment in actual production. Due to the short application time of turning milling compound processing into actual production, in the absence of professional compound processing solutions, it is usually to use general cam software to plan some processing programs, and then the process personnel manually integrate the programs to meet the requirements of compound processing machine tools for processing programs. This solution has very high requirements for process personnel. Compared with the traditional NC programming technology, the programming difficulties of turning milling compound machining are mainly reflected in the following aspects

(1) there are many kinds of processes. For technologists, they should not only master the programming methods of NC turning, multi axis milling, drilling and other processing methods, but also accurately define the connection between processes and the way of advance and retreat. Therefore, during NC programming, it is necessary to have an intuitive understanding of the process model and the distribution of machining allowance after the completion of the current process, so as to facilitate the programming of the next process and the setting of advance and retreat tools

(2) the serial parallel sequence in the programming process must be determined in strict accordance with the process route. When many parts are processed on the turning milling compound machining center, the complete processing from raw materials to finished products can be realized, so the preparation result of the processing program must be consistent with the process route. At the same time, multi-channel parallel machining also needs to be comprehensively considered in the process of NC machining programming. It can be seen that in order to realize efficient compound machining, we should develop a process solution integrating process programming simulation

(3) for some functions of turning milling compound machining, the current general cam software does not support it. Compared with conventional single equipment processing, the machine tool motion and processing functions of turn milling combined processing are much more complex. The current general cam software is not enough to fully support the programming of these advanced functions, such as measurement, sawing, automatic feeding, tailstock control, etc. Therefore, the program compiled by the general cam software still needs a lot of manual or interactive ways to be applied to the automatic turn milling compound machining

(4) integration of processing procedures. At present, the NC programs after the general cam software is compiled are independent of each other. In order to realize the complex automatic and complete machining such as turning and milling, these independent machining programs need to be integrated and integrated. When used as materials, high molecular polymers are required to have necessary mechanical properties. This integration must be guided by the process route of the parts. First, determine which programs are parallel, then determine the processing sequence of different process methods, and give accurate tool change, card replacement, benchmark conversion, forward and backward tool instructions, etc

it can be seen that it is very difficult to program NC programs for turning and milling compound machining, and there are still many defects and deficiencies in the current general cam software for turning and milling compound machining. In order to make up for these shortcomings, it is a more realistic solution to develop a special programming system suitable for product technology and composite processing equipment on the basis of the existing general cad/cam software. On the one hand, it reduces the repeated investment in software purchase, and at the same time, it can avoid the defects of non reuse of process knowledge and complex staffing caused by the non-uniform programming platform

3 the post-processing technology of turn milling composite machining

corresponds to the NC programming technology. Due to the complex process method and many moving parts, the turn milling composite machining puts forward higher requirements for the current post-processing software and technology. Compared with conventional CNC equipment, the difficulties of post-processing are mainly reflected in the following aspects

(1) the connection movement between different processes requires strict accuracy. Because there are many kinds of machining processes carried out on the turning and milling compound equipment, the automatic switching of machining mode, cutting tools and moving parts must be completed timely and accurately after the completion of the current process, so as to ensure the correctness and safety of the machining process. In order to achieve this goal, on the one hand, it is required to set a reasonable tool advance and retreat mode and the timing of automatic tool change and coolant start and stop. On the other hand, it is more important to set the position of other non moving parts during the current process. In this way, the collision between moving parts and non moving parts of the machine tool can be avoided during tool change and machining, and the safety and stability of the machining process can be ensured

(2) it is necessary to automatically determine the process sequence and NC program. Due to the relatively long process route in composite machining, relying on manual organization and integration of the post finished NC code is not only inefficient, but also prone to errors. ideal

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