The blade is one of the main components of the steam turbine, and its steam section in particular determines the power generated by the steam turbine and directly affects the quality of the turbine product. With the continuous development of China's steam turbine industry, the design level of the blades is also constantly improving, mainly for the variable section twisted blades. The air path section line of the blade is a spatial coordinate data point, which requires high processing precision and is difficult to process. Harbin Turbine Co., Ltd. has jointly designed with the 3D company to improve the power generation efficiency and reduce heat consumption of steam turbines. The inlet and outlet steam fins of the blade steam path are relatively thin, and the top of the blade and the root of the blade have small round corners. From the processing to the inspection, a full line projection perspective is required, and the types vary, requiring a multi-axis CNC machine tool to process the equipment and process. The technical level is very demanding. Therefore, verifying the correctness of the NC machining program before CNC machining becomes a very important part of the NC machining process.
1 Characteristics of the NC Machining Program for Blade Air Passage, Top Blade and Root Round Corners
The blade-vapour line is very complicated for space three-dimensional design. First, we use B-Spline surfaces to fit the data points of the blade type. The surface thus constructed passes the given value points, and then the width of the comprehensive processing band and the step length of the tool are used. The factors such as tool radius, etc., are interpolated and encrypted from the horizontal and vertical sides of the model, and the data points passed by the NC machining program are determined, thus the NC machining program is prepared. In the preparation of NC machining programs, in accordance with the principle of unity and reduction of the number of passes, the blade steam guide surface; the top of the blade, the fillet of the blade root, and the NC machining program of the inlet and outlet flanges are prepared together. There are tens of thousands of procedures for medium-length blades. The features of the program are: long program segments, large program coordinate point spans, tedious four-axis or five-axis program data, and many opportunities for errors.
2 Analysis of Common Mistakes in Blade NC Machining Programs
As the current design of blade air passages is becoming more and more complex and the accuracy requirements are getting higher and higher, the numerical control machining programs are also becoming more and more complicated, and the probability of errors has also increased. In general, if the processing program is not properly prepared, the following problems may occur:
Interference or collision between tool and workpiece;
The tool radius is too large, parts are incomplete, and large residues appear.
Tool radius selection is too small, cutting efficiency is low;
Unsuitable machine feed or cooling conditions;
The processing scheme is irrational and affects the processing efficiency.
The control system of the machine tool does not accept the machining program;
Parts of the wrong shape or size;
The zero point selection is not appropriate and no tool point can be found.
The appearance of these problems often causes a lot of troubles for the processing of the actual parts, such as reprogramming the machining program, grinding the parts after machining, repairing the parts or tooling, scrapping the parts, and delaying the product delivery. This will fundamentally weaken the reliability of CNC machining technology and affect its application. Therefore, the verification technology of NC machining program not only has important theoretical significance, but also has important practical significance.
3 commonly used numerical control program verification method
Manual inspection
Manual inspection method is more convenient and flexible. Usually the examiner reads the machining program, or uses the coordinate paper and some other drawing tools to check the tool path during machining and finds some errors. Due to the cumbersome and complicated process of blade steam path processing, the manual inspection method not only takes a lot of time, but also easily leads to errors again. Therefore, this method has gradually been eliminated.
Test processing method
The test processing method is a method of processing parts using blade test pieces or other materials (mostly non-metallic materials). Because the test process intuitively and truly reflects the process, this method basically meets the need for program verification.
Although the experimental processing method is an effective method to verify the processing procedure, it also has many shortcomings. The main ones are:
Longer processing time;
The processing accuracy is not high;
Occupy the machine and affect the surrounding environment;
Processing parameters cannot be verified;
Processing costs are huge.
Although the use of experimental processing methods to verify the processing program has many shortcomings, but because it can more accurately reflect the entire process, and the overall level of China's blade CNC machining is still in the development stage, so this method is still used.
Computer Simulation Verification
With the rapid development of computer software and hardware, the use of computer simulation method to verify the correctness of the blade surface NC machining program has been adopted. This method is mainly used to display the blade model, tool path, tool shape, etc. on the computer graphic display in the process of machining. This method is used to simulate the machining process of the part, check whether the tool position calculation is correct and whether the processing process occurs. Overcutting, whether the selected tool, the path of the knife, the way of entering and retracting the knife is reasonable, and whether the tool and the model face interference or collision.
4 show verification
With the rapid development of computer simulation technology, there are many methods for computer simulation verification of machining programs. Although the use of computer simulations validates that one-time investment costs are higher, it has been increasingly used because it can greatly reduce experimental processing costs and can bring long-term benefits.
There are many methods for computer simulation verification. The most commonly used verification method for blade machining programs is the display trajectory verification method. That is, the wireframe of tool location data (spindle center coordinate and tool axis vector) is displayed, and whether the tool position trajectory is continuous is checked. The tool position calculation is correct. Then the tool position data is displayed together with the wire frame of the surface being machined, so as to judge whether the tool position path is correct or not, and whether the path of the tool path or the way of retracting the tool is reasonable. The basic idea is to remove all machining surfaces and related profiles from the surface modeling results, take out the tool path information from the tool position calculation results (tool location file), and then combine them to display, or in the selected tool. The tool model is placed on the site, and then the tool model is moved along the path of the tool to determine the location of the center of the tool on the tool path, the tool axis vector, the relative position of the tool and the machined surface, and whether the advance/retract mode is reasonable.
1 Characteristics of the NC Machining Program for Blade Air Passage, Top Blade and Root Round Corners
The blade-vapour line is very complicated for space three-dimensional design. First, we use B-Spline surfaces to fit the data points of the blade type. The surface thus constructed passes the given value points, and then the width of the comprehensive processing band and the step length of the tool are used. The factors such as tool radius, etc., are interpolated and encrypted from the horizontal and vertical sides of the model, and the data points passed by the NC machining program are determined, thus the NC machining program is prepared. In the preparation of NC machining programs, in accordance with the principle of unity and reduction of the number of passes, the blade steam guide surface; the top of the blade, the fillet of the blade root, and the NC machining program of the inlet and outlet flanges are prepared together. There are tens of thousands of procedures for medium-length blades. The features of the program are: long program segments, large program coordinate point spans, tedious four-axis or five-axis program data, and many opportunities for errors.
2 Analysis of Common Mistakes in Blade NC Machining Programs
As the current design of blade air passages is becoming more and more complex and the accuracy requirements are getting higher and higher, the numerical control machining programs are also becoming more and more complicated, and the probability of errors has also increased. In general, if the processing program is not properly prepared, the following problems may occur:
Interference or collision between tool and workpiece;
The tool radius is too large, parts are incomplete, and large residues appear.
Tool radius selection is too small, cutting efficiency is low;
Unsuitable machine feed or cooling conditions;
The processing scheme is irrational and affects the processing efficiency.
The control system of the machine tool does not accept the machining program;
Parts of the wrong shape or size;
The zero point selection is not appropriate and no tool point can be found.
The appearance of these problems often causes a lot of troubles for the processing of the actual parts, such as reprogramming the machining program, grinding the parts after machining, repairing the parts or tooling, scrapping the parts, and delaying the product delivery. This will fundamentally weaken the reliability of CNC machining technology and affect its application. Therefore, the verification technology of NC machining program not only has important theoretical significance, but also has important practical significance.
3 commonly used numerical control program verification method
Manual inspection
Manual inspection method is more convenient and flexible. Usually the examiner reads the machining program, or uses the coordinate paper and some other drawing tools to check the tool path during machining and finds some errors. Due to the cumbersome and complicated process of blade steam path processing, the manual inspection method not only takes a lot of time, but also easily leads to errors again. Therefore, this method has gradually been eliminated.
Test processing method
The test processing method is a method of processing parts using blade test pieces or other materials (mostly non-metallic materials). Because the test process intuitively and truly reflects the process, this method basically meets the need for program verification.
Although the experimental processing method is an effective method to verify the processing procedure, it also has many shortcomings. The main ones are:
Longer processing time;
The processing accuracy is not high;
Occupy the machine and affect the surrounding environment;
Processing parameters cannot be verified;
Processing costs are huge.
Although the use of experimental processing methods to verify the processing program has many shortcomings, but because it can more accurately reflect the entire process, and the overall level of China's blade CNC machining is still in the development stage, so this method is still used.
Computer Simulation Verification
With the rapid development of computer software and hardware, the use of computer simulation method to verify the correctness of the blade surface NC machining program has been adopted. This method is mainly used to display the blade model, tool path, tool shape, etc. on the computer graphic display in the process of machining. This method is used to simulate the machining process of the part, check whether the tool position calculation is correct and whether the processing process occurs. Overcutting, whether the selected tool, the path of the knife, the way of entering and retracting the knife is reasonable, and whether the tool and the model face interference or collision.
4 show verification
With the rapid development of computer simulation technology, there are many methods for computer simulation verification of machining programs. Although the use of computer simulations validates that one-time investment costs are higher, it has been increasingly used because it can greatly reduce experimental processing costs and can bring long-term benefits.
There are many methods for computer simulation verification. The most commonly used verification method for blade machining programs is the display trajectory verification method. That is, the wireframe of tool location data (spindle center coordinate and tool axis vector) is displayed, and whether the tool position trajectory is continuous is checked. The tool position calculation is correct. Then the tool position data is displayed together with the wire frame of the surface being machined, so as to judge whether the tool position path is correct or not, and whether the path of the tool path or the way of retracting the tool is reasonable. The basic idea is to remove all machining surfaces and related profiles from the surface modeling results, take out the tool path information from the tool position calculation results (tool location file), and then combine them to display, or in the selected tool. The tool model is placed on the site, and then the tool model is moved along the path of the tool to determine the location of the center of the tool on the tool path, the tool axis vector, the relative position of the tool and the machined surface, and whether the advance/retract mode is reasonable.
1. Adopt CNC technology, servo motor feeding, with high efficiency, stable workpiece precision.
2. Important functional components adopt modular assembly, easy to repair it.
3. Easy programming, can read CAD drawing and also can use the program generated by lofting software. It can read TEKLA lofting software files, such as NC1 format.
4. With self-diagnosis failures function.
5. X, Y axis are driven by servo motor + ball screw + linear guide, the precision is better.
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Shandong Sunrise CNC Machine Co., Ltd , https://www.scmcnc.com