Verification of blade CNC machining program

The blade is one of the main components of the steam turbine, especially its steam channel part, which determines the power generation power of the steam turbine and directly affects the quality of the steam turbine product. With the continuous development of my country’s steam turbine industry, the design level of blades is also constantly improving. They are mainly twisted blades with variable cross-sections. The profile line of the blade steam channel is a three-dimensional coordinate data point in space. The processing accuracy is very high and the processing is very difficult. In order to improve the power generation efficiency of the steam turbine and reduce heat consumption, Harbin Steam Turbine Co., Ltd. conducted a joint design with Sanwei Company. The inlet and outlet edges of the blade steam passage are thin, and the tip and root fillets are small. From processing to inspection, full-line projection perspective is required, and the types vary. Multi-axis CNC machine tools are required for processing, and equipment and processes are required. The technical level is very high. Therefore, verifying the correctness of the CNC machining program before CNC machining is carried out has become a very important link in the CNC machining process.

1. Characteristics of CNC machining programs for blade ducts and blade tip and blade root fillets

The blade duct profile is very complex and requires a spatial three-dimensional design. First, we use the B-Spline surface to fit the blade profile data points. The constructed surface passes through the given profile value points. Then, we comprehensively process the belt width and tool step length. , tool radius and other factors, interpolate and encrypt its profile from the horizontal and vertical directions respectively, determine the data points passed by the CNC machining program, and then compile the CNC machining program. When compiling the CNC machining program, in line with the principle of unifying the benchmark and reducing the number of tool passes, the CNC machining programs for the blade duct profile, blade top and root fillets, and inlet and outlet edge fillets are compiled together, so that For medium-length blades, the number of procedures can reach tens of thousands. The characteristics of its program are: long program segments, large spans in program coordinate points, cumbersome four-coordinate or five-coordinate program data, and more opportunities for errors.

2. Analysis of common errors in blade CNC machining programs

As the blade duct design is becoming more and more complex and the accuracy requirements are getting higher and higher, the CNC machining procedures are becoming more and more complex, and the probability of errors is also increasing. Normally, if the processing program is not compiled properly, the following problems may occur:

·Interference or collision occurs between the tool and the workpiece; ·The tool radius is selected too large, and the parts are incompletely processed, resulting in large residues; ·The tool radius is selected too small, and the cutting efficiency is low; ·The feed speed or cooling state of the machine tool is inappropriate ;·The processing plan is unreasonable, affecting the processing efficiency;·The control system of the machine tool does not accept the processing program;·The shape or size of the part is wrong;·The zero point selection is inappropriate and the tool setting point cannot be found.

The emergence of these problems often causes a lot of troubles in the actual processing of parts, such as rewriting the processing program, grinding parts after processing, repairing parts or tooling, scrapping parts, delaying product delivery, etc. This will fundamentally weaken the reliability of CNC machining technology and affect its promotion and application. Therefore, studying the verification technology of CNC machining programs not only has important theoretical significance, but also has important practical significance.

3. Commonly used CNC machining program verification methods

1. Manual inspection method

The manual inspection method is characterized by its convenience and flexibility. Usually the inspector reads the machining program, or checks the tool path during machining with the help of graph paper and other drawing tools and finds some errors. Due to the tedious and complex processing procedures of the blade steam passage, the manual inspection method not only consumes a lot of time, but is also prone to errors, so this method has been gradually eliminated.

2. Experimental processing method

The test processing method is a method of processing blade test pieces or other material (mostly non-metallic materials) parts. Since experimental machining intuitively and truly reflects the machining process, this method basically meets the needs of program verification. Although the experimental processing method is an effective method to verify the processing program, it also has many shortcomings, mainly including:

·Long processing time;

·The processing accuracy is not high;

·Occupy the machine tool and affect the surrounding environment;

·The processing parameters cannot be verified;

·The processing cost is huge.

Although there are many shortcomings in using the experimental processing method to verify the processing program, this method is still used because it can more accurately reflect the entire processing process, and the overall level of blade CNC processing in my country is still in the development stage.

3. Computer simulation verification method

With the rapid development of computer software and hardware, computer simulation methods have been used to verify the correctness of blade profile CNC machining programs. This method mainly displays the blade model, tool path, tool shape, etc. during the machining process on a computer graphics display. This method is used to simulate the machining process of the part and check whether the tool position calculation is correct and whether the machining process occurs. Overcutting, whether the selected tool, tool path, and the way of advancing and retracting the tool are reasonable, whether there is interference or collision between the tool and the profile, etc.

4. Display verification

With the rapid development of computer simulation technology, there are currently many methods used for computer simulation verification of machining programs. Although the one-time investment cost of using computer simulation to verify is relatively high, it has been increasingly widely used because it can greatly reduce experimental processing costs and bring long-term benefits.

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