Constructing virtual simulation platform to improv

2022-07-30
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Build a virtual simulation platform to improve the machining quality of impeller

as a key component of power machinery, the integral impeller is widely used in aerospace and other fields. The profile of impeller blade is very complex, which has a great impact on engine performance, long design and development cycle, and heavy manufacturing workload. Its processing technology has been regarded as an important topic in the manufacturing industry. The traditional processing technology adopts the split processing scheme, that is, the blade and the hub are made of different blanks, and many pieces of the factors that affect the plastic mechanical properties of the blade are welded on the hub. This scheme is not only time-consuming and laborious, but also difficult to ensure the performance indicators of the impeller

with the continuous development of high-speed milling technology, multi axis CNC machine tools, especially five axis CNC machine tools and CAM technology, the application of five axis linkage CNC machine tools for impeller machining can not only ensure that the ball head part of the tool can cut the workpiece accurately, but also use its rotating axis to work to avoid interference or over cutting between the tool body or tool bar part of the tool and other parts of the workpiece, which fully meets the requirements of impeller parts production

for the impeller machining program generated after cad/cam processing, the interference inspection of tool path and program trial cutting must be carried out before the formal machining of impeller. Its purpose is to test and verify the correctness of NC program, so the simulation technology of virtual reality technology is produced. It can fully and realistically reflect the real machining environment and machining process, such as workpiece clamping and positioning, machine tool adjustment, cutting parameter selection, and the comparison of machining results and design results; At the same time, the collision and interference in the processing process shall be warned in advance. Therefore, the practicability of field tools, clamps, cutters, etc. is reasonably evaluated, and the machinability of products, tooling, etc. and the rationality of process procedures can be evaluated, which is also required by process and programming personnel

impeller processing process analysis

the impeller structure can be divided into two parts: hub surface and blade surface. The blade includes coating surface, pressure surface and suction surface, as shown in Figure 1. The impeller hub surface is formed by rotating the blade neutral surface root curve and the blade neutral surface top curve around the Z axis; The design datum plane passing through the rotation axis Z is the meridian plane; The neutral surface is the surface between the pressure surface and the suction surface of the blade

from the structural characteristics of the integral impeller, it can be seen that there are many constraints for tool path planning when machining the integral impeller, and the space between adjacent blades is small. It is very easy to produce collision and interference during machining, and it is difficult to automatically generate interference free tool path

the machining difficulty of the integral impeller is as follows

(1) the impeller processing channel is narrowed, the blade is relatively long, and the stiffness is low. It is a thin-walled part, which is very easy to deform in the processing process

(2) the blade depth at the narrowest part of the flow channel is more than 9 times of the tool diameter, and the adjacent blade space is extremely narrow. The tool diameter is small during angle clearing, and the tool is easy to break. The control of cutting depth is also the key technology of machining

(3) the impeller surface is a free-form surface (including small blades and narrow channels), and the blades are distorted seriously, which is easy to interfere during machining

the subject adopts Mikron UCP 800duro five axis linkage machining center to finish machining the impeller

according to the process analysis results and the adopted five coordinate finishing equipment, the processing route of the selected case impeller in this subject is: blank →

turning the outer meridian surface → five coordinate finishing. For blades and fillets, the five coordinate equipment is used to process them at one time, which not only ensures the continuity of tool path cutting, but also ensures the accuracy of blades and fillets and the connection between blades and fillets. The five coordinate finishing process is divided into: rough machining of flow channel → rough machining of blades → semi finishing of blades → semi finishing of flow channel → finishing of blades → finishing of flow channel

this topic uses UG nx4.0 to plan the machining path of the integral impeller and compile the NC program

building a virtual simulation platform

one of the indicators of virtual simulation processing technology is that the virtual simulation environment and system can realistically reflect the real processing. Therefore, in the process of building the virtual machine tool environment, it is necessary to carefully collect the relevant technical data and appearance data of the physical machine tool, clarify the geometric motion relationship between the moving axes of the machine tool, and ensure that the built virtual machine tool environment is consistent with the physical machine tool environment

1 virtual simulation

VERICUT software is selected, and Cimcoedit software is used as the platform of process simulation system to conduct virtual simulation on the integral impeller

(1) VERICUT software

vericut is a CNC machine tool machining simulation and optimization software specially designed for manufacturing industry developed by CGTech company of the United States. Since its inception in 1988, the software has been widely used in the machining field of parts with complex structures and high-precision parts (such as turbine machinery parts). By preparing to simulate the whole machining process of the machine tool and verify the machining program, VERICUT avoids the collision and interference of the machine tool, realizes the optimization of the program, and improves the production efficiency and the surface quality of parts

(2) CIMCO edit software

in addition to the VERICUT software with powerful simulation function, a convenient program code code viewing software Cimcoedit is introduced at two different levels of programmers and operators. It has low requirements for computer hardware environment and is easy to operate and apply. It is suitable for application in manufacturing field. It has practical numerical control functions, intelligent comparison of files, three-dimensional simulation of tool path and program statistics

Fig. 3 before and after tool handle assembly

2 UC enables automatic unloading of experimental force

the establishment of process simulation system of P 800 five axis machining center simulation platform requires pre-defined or configured machine environment, fixture, tool, control system, etc. in order to obtain geometric motion model and relevant data of machine tool, it is necessary to analyze Measure the mechanical motion relationship and corresponding dimensions (such as the geometric motion relationship between the axes x, y, Z, a and C), the size of the workbench, the size and specification of the accessory head, and the initial height of the beam from the workbench

through the collection, collation and analysis of the relevant technical data of the machine tool, the 3D model of UCP 800 machine tool is built with the center of the C rotary table of the machine tool as the zero point by using the UG nx4.0 CAD software function, and the Mikron five coordinate machine tool model is completed, as shown in Figure 2

according to the geometric motion structure of the machine tool shown in Figure 2, open the "component tree" machine tool structure tree in the VERICUT software simulation environment, Po Chun Hsu, a member of the "base (0, 0, 0)" team, said: "After chemical treatment, modify the industrial polyethylene node. First, add five moving parts of the machine tool, namely x, y, Z, a and C, and then rearrange them by dragging according to the linkage relationship between the axes. In order to realize the authenticity of the machine tool simulation, output the 3D machine tool parts built in UG in STL format and add them to the relevant parts of the machine tool structure tree, and configure the UCP 800 machine tool structure tree.

for machine tools , the control system is the premise of correctly simulating the machining program and the interpretation and processing of the machining program instructions. Next, configure the control system for the impeller simulation environment. The CNC control system of Mikron UCP 800 coordinate machine tool is configured as Heidenhain itnc530 system, so l under the "library" directory of vericu software is selected

vericut software itself has the basic functions of the control system, but for each physical machine tool equipment, there will be some special instructions. For the special instructions that these control system files do not have, they must be redeveloped to achieve special customization through macro commands and subroutines

3 tool library environment

the establishment of tool library mainly includes the establishment of tools, tool handles and blades, as well as the definition of tools, tool driving points and clamping points. Taking the machining tool environment of integral impeller as an example, this paper constructs a relative tool library for workpiece. In order to ensure the authenticity of tool data, it is necessary to actually measure the tool handle of UCP 800 machine tool. According to the measured data, the tool handle contour is created with the help of UG CAD function

then open VERICUT's Tool Manager dialog box, right-click in the left area, pop up the shortcut menu related to "tool management", and create "mill milling cutter" according to the prompt. Set the creation "tool ID" to "No. 1" tool, and the tool used for machining the impeller is a taper tool, so select the subtype. In order to reflect the real state of the tool, it is necessary to assemble the tool with the previously created tool holder

first export the tool handle profile created by UG CAD in dwg/dxf format, and then create a new tool according to the above steps. It is named "4" tool here. The difference from creating "1" tool is that its component type is "holder tool handle". Next, assemble the tool handle for "1" tool. The "1" tool before and after assembly is shown in Figure 3. According to the above ideas, create "2" and "3" cutters, and finally complete the tool library file

after the tool library is created, in order to install the tool on the machine spindle according to the correct position, it is also necessary to adjust the "gage point" parameter of the tool. Here, with the help of VERICUT's "x-caliper" function, the "gage point" parameter of the tool is adjusted

4 fixture environment

in addition to the machine tool itself and tool library, the machine tool environment also includes machine tool fixtures, and the corresponding machine tool fixture library includes general fixtures, special fixtures and combined fixtures. A special fixture is designed for the machining of the impeller and the five coordinate machine tool, as shown in Figure 4

tool path and program verification

in the field processing, in order to facilitate the operator to browse the tool path visually and visually, Cimcoedit software is used to view it. Open the program file and select the configured ucp800 machine environment (including machine geometry and control system). Through the simulation of the virtual machine tool environment, the impeller processing program can be directly used to carry out the actual processing on the ucp800 five coordinate machine tool, eliminating the link of program trial cutting. The processed integral impeller is shown in Figure 5

conclusion

practice shows that using cad/cam technology, according to three-dimensional coordinate measurement or existing data, using UG software to carry out three-dimensional solid modeling and multi axis programming for the structural characteristics of complex parts such as impellers, the model of the integral impeller and the fixture design of the integral impeller are obtained

any load on the blade surface of the integral impeller will not cause the displacement sinking of the load sensor, which has always been a difficult point in machining. Through this design, after post-processing and application of the program code of the five coordinate NC machine tool, the accuracy of the machined blade basin surface can reach 0.1mm, and the machining allowance of 0.5mm on the back of the blade is completed by the subsequent polishing process

by building a virtual simulation platform and using the virtual simulation machine tool environment, the simulation and verification of the machining program of the impeller parts with large curvature change involved in this subject are completed, and the real simulation and process monitoring are achieved at the same time; Reduce or even avoid the waste products of impeller manufacturing, and improve the surface quality and surface roughness level; The application of virtual technology reduces the risk of manufacturing, effectively reduces the production cost and improves the efficiency. (end)

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