Multi-axis NC machining programming technology for sculptured curved mixed-flow blades Abstract: Runner blades are the key components of energy conversion of hydraulic turbines and the most difficult parts to machine. At present, multi-axis NC machining is the most effective machining method to solve this kind of large sculpture curved parts. Multi-axis NC machining programming is the most important link to realize its high precision and high efficiency machining. This paper introduces the key technologies involved in five-axis NC machining programming of large sculptured surfaces of Francis turbine blades, such as three-dimensional modeling of runner blades, tool path calculation, cutting simulation, machine tool collision simulation and post-transformation. Through the link and research of these technologies, the multi-axis linkage machining of large blades is developed and realized.

Keywords: numerical control programming

introduce

Hydraulic turbine is the motive force of hydropower generation. The manufacture of turbine runner blades and the quality of runner have great influence on the safe, reliable and economical operation of hydropower units. Turbine runner blades are very complex sculptural surfaces. In the manufacturing process of large and medium-sized units, the long-term manufacturing process of "sand casting-grinding wheel shovel grinding-three-dimensional template detection" can not effectively ensure the accuracy and manufacturing quality of blade profile. At present, five-axis NC machining technology is a cutting-edge high-tech in the field of machining. The NC machining programming of large complex curved surface parts is the most important technical basis to realize its digital manufacturing, and its NC programming technology is a process of digital simulation evaluation and optimization. Its key technologies include: three-dimensional modeling and positioning of complex parts, five-axis linkage tool path planning and calculation, tool axis control technology for machining sculpture surfaces, cutting simulation and interference inspection, and post-processing technology. The multi-axis NC programming technology of large-scale complex surfaces makes it possible to machine the multi-axis NC machining of sculptured surface runner blades, which will greatly promote me.

The development and progress of turbine industry in China laid a foundation for the development of hydropower equipment manufacturing industry in China to advanced manufacturing technology.

Programming process of multi-axis NC machining for large Francis turbine blades. Five-axis NC programming of large complex curved parts is much more complicated than ordinary parts. According to the characteristics of Francis turbine blade with large volume and large curvature change, the process design is carried out by analyzing the machining requirements, and the machining scheme is determined. The appropriate machine tools, tools and fixtures are selected to determine the reasonable tool path and cutting parameters. The geometric model of the blade is established, and the movement trajectory of the cutter relative to the blade during machining is calculated. Then the cutting simulation of the blade and the movement simulation of the machine tool are carried out, and the machining parameters, cutter parameters and cutter axis control scheme are repeatedly modified until the simulation results do not interfere with the collision e-commerce database "-5 *1%) 5:/1$)" 3, and then it is carried out according to the acceptable program format of the numerical control system of the machine tool. The specific programming process is shown in Figure-.

Figure-Programming process of five-axis NC machining for large Francis blades! "! Three-dimensional geometric modeling of Francis turbine blades This complex sculptural surface of Francis turbine blades consists of a front face, a back face, a belt-shaped revolving surface connected with the upper crown, a belt-shaped revolving surface connected with the lower ring,

If it is big, you can write a. */0 program to read these three-dimensional coordinate points, and then use bicubic multi-patch patches to shape the surface through curves with free-form characteristics, as shown in figure 1. The blank shape of the blade can be offset calculated from the design data points, or "234$" surface modeling can be determined from the point aggregation method obtained from three-dimensional measurement, and each surface of the blade can be stitched into a solid.

! "# Blade Machining Process Planning

The selection of machining scheme and parameters determines the efficiency and quality of NC machining. According to the structure and characteristics of the blade to be machined, a large gantry mobile five-axis CNC milling and boring machine can be selected. According to the principle of three-point positioning, after a lot of research and analysis, it is decided to adopt the universal adjustable bracket with balls on the back, position the blade with the positioning pin welded by the blade, weld the necessary process blocks on the blade and clamp it with some universal tensioners. When processing the front side, put the back side of the blade into the clamping fixture with the same clamping fixture as the back side when processing the back side, adjust and align it with the welding process block, and still clamp it with the universal tension and compression device. Because the blade is composed of multiple curved surfaces, in order to solve the collision problem in the machining process, we use tools to machine the front and rear surfaces of the blade in different areas along the streamline.

Different curvatures are processed by different cutter diameters and different cutter axis control formulas. Generally, each surface is divided into multiple rough milling and one finish milling. Under the condition that the lathe bed does not collide and interfere with the workpiece and fixture, the large-diameter curved surface milling cutter should be used as much as possible to improve the machining efficiency. On the front and back of the blade, we choose the tool diameter! Rough milling of -56 curved surface milling cutter! -16 surface milling cutter finish milling, the cutter head adopts curved surface! 76 curved surface milling cutter processing, water! Five-axis side milling of 76 spiral corn end mill. According to the follow-up simulation, the tool position is edited repeatedly to find a reasonable machining scheme. Meet the processing requirements

Requirements, the machine tool runs normally and keeps a certain tool life as much as possible &; N bsp to improve processing efficiency. ! Tool path generation in five-axis machining of blades According to the characteristics of various curved surfaces of large Francis blades, reasonable tool path planning and calculation are the key to make the generated tool path non-interference, collision-free, stable and efficient. Because the cutter position and cutter axis direction of five-axis machining change, five-axis machining is composed of cutter position vector and cutter axis direction vector in workpiece coordinate system, and the cutter axis can be controlled by rake angle and inclination angle, so we can calculate the cutter position vector and cutter axis vector according to the local coordinates of the surface at the cutting point. From the point of view of processing efficiency,

Surface quality and cutting performance, selection

Parameters of modeling along the blade

Line as milling process

The direction is divided into multiple rough milling and summation.

A fine milling, and then arranged.

Sub-processing zones, defining

Parameters related to machine tools,

According to the blade selected above

Keywords machined parts, clamping diagram,

Tool path generation of Francis blade

Positioning formula, lathe, cutter, cutting parameters and allowance distribution divide the blade into multiple combined surfaces.

Separate treatment. Through the analysis of the curvature distribution of the surface, different face milling cutters are used for different areas. Roughing gives the allowance for each machining, and finishing uses milling cutters with the same diameter. Given the residual height according to the roughness requirement, the cutting type, cutting parameters, cutter axis direction, cutter advance and retreat mode and other parameters are selected according to the specific situation, and the generated tool path is shown in the figure. However, for sculptural curved parts with large and uneven curvature changes like blades, we need to do a lot of tool position editing according to the situation, and further do interference collision inspection and modification through cutting simulation.

Edit the tool path. ! Simulation of Five-axis NC Machining of "# Blade"

Numerical control machining simulation is based on machining environment, tool path

Check and optimize the machining process with material removal process. on the computer

Simulation verifies the tool path of multi-axis linkage machining and assists in machining tools.

Use interference inspection and collision inspection between machine tool and blade instead of trial cutting or

Trial processing technology can greatly reduce the manufacturing cost and shorten the development cycle.

Period, avoid the collision between processing equipment and blades and fixtures, and ensure the processing.

Security of the process. Machining parts "! The code is being put into practical processing.

It is usually necessary to try cutting before, and turbine blades are very complicated sculptures.

The development and utilization of simulation technology for NC machining of curved surfaces is the fifth of its successful adoption.

The key of axis linkage NC machining. Here, we first enter the e-commerce database 324&; %'; & 6: 6) (Technology Department of Line 2)

Unified analysis, clear machine tools! "! System model, machine tool structure and ruler

English system, machine tool motion principle and machine tool coordinate system. Use three dimensions! ,-Software architecture

The solid geometric models of moving parts and fixed parts of vertical machine tools are reformed.

Convert it into a format that can be used by simulation software, and then establish a tool library and put it into simulation software.

Create a new user file in the file and set it to use! "! Establishment of system and machine tool.

The dynamic model, namely the component tree, adds the geometric model of each component, which is accurate.

Positioning, and finally setting machine parameters. Next, convert the blade model to

The tool path is calculated from the machining position, and then the blade is cut through this path.

Three-dimensional dynamic simulation of process, tool path and machine tool motion. In this way,

You can clearly monitor the over-cutting, under-cutting and cutting during blade machining.

Rod and connecting system and blade, moving parts of machine tool and blade and fixture.

Interference and collision between, so as to ensure the quality of numerical control programming, reduce

The workload and labor intensity of trial cutting improve the one-time success rate of programming.

Shorten product design and processing cycle and greatly improve production efficiency. such as

The popularization in NC machining industry can produce great economic and social benefits.

Benefit. The cutting simulation of the blade is shown in the figure. Machining blades with a machine tool is similar to machining them with a lathe.

As shown in figure/

Figure. Mixed-flow blade cutting simulation diagram/

Machining Simulation of Francis Blade with Machine Tool

! Post-processing of blade tool path

Post-processing is an important content of NC programming, which will make us go back and forth.

Tool path data generated by surface is converted into data suitable for a specific machine tool. reprocess

The two basic elements are tool path data and post-processor. We should first

First of all, understand the structure of gantry mobile five-axis CNC milling and boring machine, the auxiliary equipment equipped with the machine tool, the function of the machine tool, the way to realize the function and the machine tool.

Equipped with numerical control system, familiar with the system "! Programming includes functional codes.

The composition and meaning of. Then apply the general template root for post-processor.

According to the above knowledge, develop a customized special post-processor. And then put

We have obtained the source files of tool positions for input and conversion into files that can be controlled by machine tools.

"! Code.

% conclusion

Multi-axis NC programming of complex surfaces is a problem involving many fields.

The complex process of knowledge is a process of digital simulation and optimization. This article introduces

Shao's multi-axis linkage programming technology for large turbine blades has been applied in engineering.

In the actual NC programming of large blades, five functions of large runner blades are realized.

Tool path calculation and machining simulation of axis linkage NC machining provide a guarantee for post-processing.

Continuing the quality and efficiency of NC machining, it has been used as the five axes of large turbine blades.

The programming tool of linkage NC machining has been applied in practical production.