What are the main technologies and future uses of the turn-mill machining center?

Machining efficiency and precision are the eternal goals pursued in metal processing. With the continuous development of CNC technology, computer technology, machine tool technology, and machining technology, the traditional machining concept can not meet the requirements of people on processing speed, efficiency, and precision. In this context, composite machining technology came into being. Generally speaking, composite processing refers to processing equipment that completes different processes or different methods of processing technology.

The current composite machining technology is mainly manifested in two different types: one is based on energy or movement of different composite processing methods; another is based on the principle of process centralization, based on machining process-based composite. Milling and turning composite machining has been one of the most rapid developments in the field of processing methods in recent years.

The current aviation product parts are highlighted as a multi-species small batch, complex process, and widely used in the overall thin-walled structure and difficult to process materials, so the manufacturing process generally exists in the manufacturing cycle is long, the amount of material removal, processing efficiency is low, and the processing of deformation and other serious bottlenecks.

To improve the machining efficiency and machining accuracy of aviation complex products, technicians have been seeking more efficient and precise machining process methods. The emergence of mill-turn composite machining equipment to improve the machining accuracy and efficiency of aviation parts provides an effective solution.

Mainly advantages

Compared with conventional CNC machining process, composite machining has outstanding advantages mainly in the following aspects.

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

Turning and milling composite machining can be realized once the card is loaded to complete all or most of the machining process, thus greatly shortening the product manufacturing process chain. This on the one hand reduces the production of auxiliary time due to changes in card loading, but also reduces the manufacturing cycle of fixtures and fixtures and waiting time, which can significantly improve production efficiency.

(2) Reduce the number of clamping, and improve machining accuracy.

The reduction of the number of mounting to avoid the accumulation of errors caused by the transformation of the positioning reference. At the same time, most of the current mill-turn compound machining equipment has the function of online detection, which can realize the manufacturing process of key data in the detection and precision control, thus improving the machining accuracy of the product.

(3) Reduce floor space and production costs.

How to develop a reasonable process route, mounting methods, and selection of reasonable tools according to the characteristics of the parts process and mill-turn composite machining process is to realize the key to efficient precision machining.

Process concentration is the most distinctive process characteristic of composite machining. Therefore, a scientific and reasonable process route is the key factor in improving the efficiency and precision of mill-turn machining.

Take the S192F milling and turning composite machining center of Swiss Baomei Company shown in Figure 1 as an example, the machine tool has five-axis milling, turning, boring, drilling, sawing automatic feeding, etc. It adopts the FANUC31i numerical control system, which has the functions of tool vector smoothing, super prospective, high-speed interpolation, etc., and it is especially suitable for high-speed and precision machining of parts such as shafts and rotary parts.

In aviation impeller processing, this machining center has outstanding advantages. When using bar stock as impeller blanks, the conventional impeller machining process route first utilizes a CNC lathe to turn the external contour of the impeller, and then fine-turns the machining reference;

On this basis, the use of five-axis CNC machining centers for grooving, roughing, semi-finishing, and finishing of the profile and hub; and finally in the five-axis machining center or drilling equipment for hole processing.

The use of S192F milling and turning machining centers can not only complete all the processing of the above process by a single loading, but also when the bar material for processing can be sawed, automatic feeding, and other functions to achieve batch processing of impellers, the entire process can be completed automatically without human intervention.

The process route can be set up as follows: spindle loading bar material → rough turning impeller external profile → fine turning external profile → five-axis milling slotting → runner rough machining → runner semi-finishing → runner finishing → drilling → back spindle loading → turning impeller bottom plane → drilling. It can be seen that a loading card to complete all the impeller machining process, machining efficiency, and accuracy can be greatly improved.

For turning and milling machining centers with dual tool holders (such as Austria’s WFL turning and milling machining centers shown in Figure 2), dual-turret equipment has a dual-channel control system, the upper and lower tool holders can be controlled individually, and synchronous machining can be achieved through synchronous statements in the code. To give full play to the processing capacity of the equipment, can be in the processing conditions allow the premise of synchronous operation through the dual tool holder to achieve the parts of multiple processes at the same time processing.

Through the synchronized setting of the upper and lower tool holders, the rough boring of the bore can be completed at the same time as the rough turning of the shape, thus further improving the machining efficiency. The synchronized movement of the upper and lower tool holders to complete a series of holes not only improves the machining efficiency but also reduces the impact of workpiece deformation through the mutual offset of the axial force of drilling.

To achieve this function, it is necessary to carry out a systematic and in-depth study of the process program during the preliminary process design, determine the serial and parallel order of the process route, and realize the above functions through a reasonable combination of machining procedures.

CNC programming technology

The development of mill-turn machining, but also of the CNC programming technology puts forward higher requirements, which also restricts the mill-turn machining equipment in the actual production application of a bottleneck link.

Due to the mill-turn composite machining into the actual production of the application of a shorter period, in the absence of professional solutions for composite machining, usually the use of general-purpose CAM software to plan out part of the machining program, and craftspeople and then manually integrate the program to meet the composite machining machine tool on the requirements of the machining program.

This solution is very demanding on the craftsmen. Compared with the traditional CNC programming technology, the programming difficulties of mill-turn compound machining are mainly reflected in the following aspects.

(1) The variety of processes is complicated.

For craftsmen, not only to be able to master CNC turning, multi-axis milling, drilling, and other processing methods of programming methods but also for the articulation between the process and the way in and out of the tool needs to be accurately defined. Therefore, in CNC programming, you need to complete the current process model and the distribution of machining allowances to have an intuitive understanding of the next process of programming and setup in and out of the tool.

(2) The programming process of string parallel order must be determined in strict accordance with the process route.

Many parts in the mill-turn machining center processing can be achieved from the raw material to the finished product of the complete processing, so the results of the machining program must be consistent with the process route. At the same time, multi-channel parallel processing also needs to be in the process of CNC machining program preparation for comprehensive consideration. It can be seen that to achieve efficient composite machining should be developed process-programming-simulation integrated process solutions.

(3) For certain functions of mill-turn machining, the current general-purpose CAM software does not yet support it.

Compared with conventional single-device processing, mill-turn compound processing with machine movement and processing functions is more complex, the current general-purpose CAM software is not yet sufficient to fully support the programming of these advanced features, such as online measurement, sawing, automatic feeding, tailstock control, etc.. Therefore, the use of general-purpose CAM software compiled out of the program still requires a lot of manual or interactive way to be applied to automated mill-turn compound machining.

(4) The integration of machining programs.

At present, the general CAM software compiled after the completion of the NC program is independent of each other, to realize the mill-turn compound such a complex automated complete processing, the need for these independent machining programs integration and integration. This integration must be guided by the process route of the part, first, determine which programs are parallel, and then determine the machining sequence of different process methods, and give the exact tool change, mounting card replacement, datum conversion, as well as in and out of the tool instructions.

As can be seen, mill-turn machining CNC programming is very difficult, and the current general-purpose CAM software for mill-turn machining there are still many defects and deficiencies.

To make up for these shortcomings, the existing general CAD / CAM software based on the development of product technology and composite machining equipment for the development of specialized programming systems is a more realistic solution. This on the one hand reduces the duplication of investment in the acquisition of software but also avoids the process knowledge that can not be reused due to the programming platform is not uniform, complex staffing, and other defects.

Post-processing technology

Mill-turn composite processing post-processing technology and CNC programming technology correspond to the mill-turn composite processing due to the complexity of the process method, moving parts, and other reasons, which puts forward higher requirements for the current post-processing software and technology. Compared with conventional CNC equipment, the difficulties of its post-processing are mainly reflected in the following aspects.

(1) The articulation movement between different processes requires strict accuracy.

As a result of a variety of machining processes on the mill-turn equipment, so after the completion of the current process must be timely and accurately completed the automatic switching of the processing mode, tools, and moving parts to ensure that the machining process is correct and safe.

To achieve this purpose, on the one hand, the requirements of setting a reasonable way into and out of the tool and automatic tool change, coolant on and off timing, and more importantly, in the current process need to be set in the current process of processing the position of other non-moving parts. To avoid the machine tool in the tool change and processing of moving parts and non-moving parts between the collision, to ensure the safety and stability of the machining process.

(2) The need for automatic determination of the process sequence and CNC program.

Due to the relatively long process route in composite machining, relying on manually to completion of the NC code after the rear of the organization and integration is not only inefficient but also easily leads to errors.

The ideal solution is to automatically determine the machining sequence and the process method embedded in the tool position file during post-processing and to automatically maintain it in the NC code after post-processing is completed.

To this end, CNC programming is completed after the tool position file information needs to contain not only the corresponding process method, tool position information but also needs to contain the corresponding machining sequence, the type and number of tools used, so that in the post-processing process to achieve the sequence of technology, technology and tool methods and tools for automatic determination.

(3) Post-processing technology for different machining methods.

The post-processing program of mill-turn compound processing not only requires the realization of multi-axis CNC milling, turning and drilling post-processing, but also the realization of sawing, automatic feeding, tailstock control, and program cycle calling, etc. The post-processing algorithms of mill-turn compound processing include the post-processing of all existing CNC machining process types, and also the realization of seamless integration and motion articulation between different machining modes. Integration and motion articulation between different machining methods.

(4) The full utilization of the advanced functions of the control system.

Currently used for mill-turn machining center CNC systems are very advanced control systems, such as the Baomei S192FT FANUC31i system, the WFL150 SINUMERIK840D system.

Most of these advanced control systems are equipped with advanced functions such as automatic feed optimization, tool vector smoothing, super forward-looking, and high-speed, high-precision interpolation. Therefore, it is necessary to reflect the functions of these advanced CNC systems in the appropriate position in the machining code completed at the post-processing stage to realize the full utilization of the effectiveness of the mill-turn machining equipment.

(5) Non-cutting function processing and call.

Composite processing machine tools in addition to turning, milling, drilling, boring and other cutting functions, but also in the transition between the various processes required for non-cutting functions, such as automatic feeding, unloading, spindle docking, tailstock control and so on.

In the post-processing needs to be these functions as a common module for the program to call, call the order and timing needs to be determined according to the process route. These functions of the current post-processing software is not yet available.

Mill-turn machining simulation technology

Turn-mill complex machining due to more moving parts, complex functions, programming is completed after the processing simulation is particularly important.

To improve the application level and programming efficiency of mill-turn complex machining, it is necessary to vigorously promote the application of simulation technology. Currently used for mill-turn machining simulation software mainly TopSolid, Gibbs and so on. The realization of mill-turn machining simulation can also rely on the current general-purpose CNC machining simulation software (such as Vericut, NCSimul, etc.), according to the structure of the mill-turn machining equipment, movement characteristics, special features and CNC systems, through customization and macro function development to achieve the machining process of motion simulation.

The use of general CNC machining simulation software to realize the simulation of mill-turn machining needs to first build a relatively real machine tool environment in the simulation system, focusing on the relative motion relationship between the moving parts of the machine tool and the establishment of geometric positional relationships.

On this basis, the establishment of the tool library used in the machining process and the corresponding tool number.

Then configure the CNC system of the machine tool and CNC program machining benchmarks, and the post-completion of the NC code loaded into the simulation system, you can perform the simulation of the machining process.

Unlike conventional CNC machining, some functions (such as multi-channel machining, tailstock control, etc.) also need to be completed through the development and customization of macro functions.

Application prospects of mill-turn composite machining technology and development proposals

Generally speaking, mill-turn composite machining centers are processing more complex products, such as such as aviation products. The main problems faced by the manufacturing process of traditional processing are highlighted as long process routes, complex processes, low processing efficiency, processing deformation is serious, and high processing costs, but instead of mill-turn composite machining, both in the field of aircraft manufacturing or engine manufacturing has an extremely broad space for development.

The traditional practice is such as the aircraft fuselage frame milling processing usually through the material / blank preparation, benchmark machining, roughing inside shape, roughing shape, finishing benchmark, semi-finishing and finishing inside shape, semi-finishing and finishing shape, hole machining, clamping trimming, testing and other dozens of processes, many times over the folder to complete.

The current aviation engine field of the whole leaf disk processing is also used as a whole forging blank, after turning and milling, milling, polishing, surface treatment and strengthening, testing, and flaw detection, there are dozens of processes to complete.

These parts often have a long manufacturing cycle, occupying the machine time usually reaches hundreds of hours, and the machining process requires the use of many different types of CNC machine tools and a large number of fixtures, cutting tools, measuring tools, and so on.

In addition, the repeated replacement of the mounting card not only causes a long waiting time in the manufacturing process of the parts, affecting the production cycle but also causes the accumulation of mounting errors, thus affecting the dimensional accuracy of the parts and machining results.

Turn-mill composite machining can realize the processing of all or most of the above typical aerospace parts through one-time loading, thus providing a new way for efficient and precise processing of complex aerospace parts. Its application advantages are mainly reflected in the following aspects:

(1) The number of card loading is significantly reduced, improving machining efficiency while eliminating errors caused by changes in machine tools and card loading methods.

(2) The process is more centralized, can significantly shorten the machining process chain, and reduce waiting time and machine non-working time.

(3) Without changing the positioning state under the premise of turning, milling, drilling, and other machining methods to realize the machining process, reduce the number of fixtures to ensure the consistency of dimensional accuracy.

(4) Most of the current mill-turn machining has the function of online measurement, which can be used to measure the machining results in the process and between the processes in situ, to achieve the accuracy control of the entire machining process.

It can be seen, that milling and turning composite machining equipment has these advantages can effectively make up for the current aviation complex parts manufacturing process deficiencies, and can significantly improve the processing accuracy and efficiency of the product.

To give full play to the processing efficiency of advanced composite machining equipment, and further improve the manufacturing efficiency and quality of aviation products, there is an urgent need to carry out the following aspects of work.

(1) Combined with the process characteristics of aviation product parts, an in-depth study of the composite machining process, including the development of process routes, loading mode, tooling, cooling, and cutting parameters, such as the reasonable selection.

(2) According to the motion structure of the composite machining equipment and the process characteristics of the product, develop and customize the corresponding CNC programming, post-processing, cutting simulation, and other systems, to form an integrated solution of process-programming-post-processing-simulation, and reduce the requirements of composite machining on the craftsmen.

(3) Form process specifications.

Combined with the simulation, test cutting, and the process experience accumulated in the actual production, the formation of solidified process specifications for mill-turn composite machining, to guide the subsequent processing of other parts.

(4) Focus on the cultivation of talents.

Composite machining equipment is representative of the current cutting-edge technology in the field of machining, both process preparation and operation and maintenance are more complex than conventional equipment, a high-level R & D team is to realize the health of the equipment, the key to efficient operation.

Conclusion

The current composite machining equipment is moving towards a greater range of processes, higher efficiency, and large-scale and modular direction. The aviation product manufacturing field has been an important stage for advanced manufacturing technology, with the increasing speed of aviation product replacement, process dispersed processing equipment will be gradually replaced by process centralized flexible automation equipment, which provides a broader development and application space for composite processing technology.