CNC machining impeller

At the same time, this design is the design and processing procedure of the impeller manufacturing process, to introduce the details of impeller manufacturing, to use UG to solve the problems of the manufacturing industry and to prepare the impeller processing program. The concept of how to manufacture an impeller is introduced. The indirect purpose is to make Cnc Machining more famous so that more people can understand the benefits and scope of CNC machining.

Keywords: CNC machining, UG, tool path, machining simulation, 3D solid modeling, process, impeller

1.1 Product description

The integrated impeller is an important component of power machinery and is widely used in fields such as aerospace. Its processing technology has always been an important issue in the manufacturing industry. When machining the entire impeller, it can be seen from the shape and process of the entire impeller that there are more limitations in machining trajectory planning. The space between adjacent blades is small and collisions can easily occur during processing. It is difficult to automatically generate a machining trajectory that does not interfere. Therefore, in the process of machining the impeller, not only is it guaranteed that the machining trajectory of the blade surface can meet the requirements of geometric accuracy, but also because the thickness of the blade is limited, it is actually In machining, track planning must be taken into account in order to maintain the quality of machining.

1.2 Selection of processing method

Integral impeller machining has always been a problem for machining engineers and technicians. Many solutions have been proposed to handle qualified impellers. From the first casting light repair, after paraffin casting, there are methods like EDM. Among them, some manufacturers use 3D copy milling. However, these methods have low processing efficiency, are inferior in accuracy and mechanical properties, and have been fundamentally solved until the numerical control processing technology is applied to impeller processing.

The complexity of impeller machining is mainly due to the fact that the blades are complex curved surfaces. The ability to accurately machine complex shaped impellers is an important measure of the performance of CNC machines. Because CNC machines have 4-axis or 5-axis linkage

When used for impeller machining, the ball head of the tool is guaranteed to cut the workpiece accurately. You can also use the axis of rotation to keep the tool body or toolbar part away from the rest of the workpiece to avoid interference and excessive cutting.

Chapter 2 3D solid modeling of the entire impeller

  • 2.1 Overview of modeling method
  • 2.1.1 General modeling method

There are three types of surface modeling.

  • (1) Create a surface model from the original product design and sketches.
  • (2) A two-dimensional map based on surface modeling, so-called drawing modeling.
  • (3) Reverse engineering, that is, point mapping modeling.This time, I will introduce the general implementation procedure of the second type.

The drawing process is divided into two phases.In the first stage, modeling analysis is performed to determine the correct modeling concept and method. Included:

  • (1) Disassemble the photo into a single surface or quilt based on the correct identification information of the product.
  • (2) Determining the type and method of production of each surface, such as regular surfaces, draft surfaces or sweep surfaces;
  • (3) Determine the relationship between the joint surface (chamfer, cutting, etc.) and the connection order.

The second stage implements the following modeling:

  • (1) According to the drawing, draw the 2D view outline required for CAD / CAM software and convert each view to the actual spatial position.
  • (2) For each surface type, use the outline of each view to complete modeling of each surface.
  • (3) Chamfering, cutting, etc. according to the connection relationship between the surfaces.
  • (4) Complete modeling of product structure (entity).

2.1.2 Impeller modeling method

The three-dimensional shape of the integral impeller mainly consists of two parts, the blade and the hub. The curved surface of the blade is a free surface with high demands for smoothness and continuity. The shape of the blade is difficult to model because the section line is a complex free curve. It is now common to create a section line and then simulate the surface of the blade through the section line. Hub production is relatively easy. Create a hatch string in sketch mode. Use the stretch command to stretch the hatch string to create a hub. You can also use the rotate command to simulate the hub. It can be seen that the key to the shape of the entire impeller is the shape of the blade body. The three-dimensional shape of the blade is an important part of the entire impeller modeling process. Its design requirements are high and its surface shape is more complex.

3.1 Material selection

The impeller material should have good comprehensive mechanical properties, room temperature and high temperature strength, plasticity and toughness. Therefore, the impeller must meet sufficient requirements:

  • (1) Appropriate room temperature, high temperature mechanical properties;
  • (2) Has high damping capacity.
  • (3) High organizational stability.
  • (4) Good corrosion and corrosion resistance;
  • (5) Good process performance.

Since the impeller is one of the key components of an aircraft engine, it is necessary to ensure the strength of the component while minimizing the weight of the part. The LD5 aluminum alloy grade is selected for the availability and manufacturability of the parts.

The integrated impeller is a centrally symmetric part and the impeller must be accurately positioned during machining. Select a positioning reference. The hole + surface and the short surface at the exit end are used as the axial positioning reference, and the center hole of the impeller is used as the axial positioning reference. When the integrated impeller is machined, the impeller jig material is mounted on the mandrel and then pressed against the top and bottom edges.

3.2 Develop process root

Considering the actual operation of the entire impeller, the entire surface of the impeller generally has high precision, high speed rotation, and high dynamic balance requirements during operation. Combined with the analysis of impeller shape, structural properties and processing properties of the material impeller,

  • (1) The impeller has many blades. The blade depends on the diameter of the hub. The blade has a length, the blade is curved, and has a high degree of deformation and elevation. The choice of cutting direction for the tool is especially important because the relative motion of the tool during the machining process easily interferes with adjacent blades. In addition, the surface needs to be divided and care must be taken to ensure the consistency of the machined surface.
  • (2) It is difficult to use a large-diameter tool with good strength and rigidity because the flow path between blades is narrow and the processing space is small.
  • (3) The radius of curvature of the inlet and outlet edges of the blade changes significantly, and the angle between the tool and the fixture changes significantly.
  • (4) In order to meet the strength requirements, the transition between the impeller hub and the blades is smoothed and care must be taken in the tool selection.
  • (5) The blade is a thin-walled part with a complicated structure and low processing rigidity. The process configuration needs to repeat multiple steps to process the blade profile to prevent deformation due to machining residual stress.
  • (6) The material of the entire impeller is generally an aluminum alloy, stainless steel, titanium alloy, or the like.

Therefore, in order to improve the overall impeller strength, the blank generally refers to a forged product and then a flat lathe to machine the basic shape of the impeller gyrator.

Place the toolpath as follows:

  • 1, coil cylindrical;
  • 2. Mill the end face.
  • 3, drill the center hole.
  • 4, excavation;
  • 5, insert and remove the keyway.
  • 6, roughen the impeller profile.
  • 7, rough cutting blade.
  • 8, rough processing;
  • 9, complete the blade.
  • 10, finish flow surface.
  • 11, deburring processing.

4.2 Creating a processing environment

UG is general machining, multi-axis machining, multi-axis machining with 3 or more axes,

Therefore, the impeller machining cannot be satisfied by the usual machining method, and the machining environment for variable contour milling is determined as shown in Fig. 4-2 and Fig. 4-3.

4.4 Parameter setting processing and disconnection path generation

4.4.1 Tool trajectory planning method

The purpose of tool path planning is to generate a set of tool positions for the parts to be machined in order to achieve the highest machining efficiency while ensuring machining accuracy. For 2-axis and 3-axis CNC machining tool path planning, the planning process can be thought of as the process of determining the X and Y axis coordinates of the tool position. At the same time, the initial value of the Z-axis coordinates can be determined. Then, the subsequent interference processing completes the calculation without interference of the Z-axis coordinates. In 5-axis surface machining tool path planning, the initial position of the tool axis vector is parallel to the normal vector of the tool position points. The planning process also involves determining the maximum principal curvature at the tool position, i.e. the rotation angle of the tool axis vector around the heel angle. The angle of rotation around the vector direction, that is, the lateral slip angle, both determine the spatial orientation of the tool.

Toolpath planning tasks can be summarized as follows:

  • (1) Determine the shape of the tool trajectory.
  • (2) Determine the connection order and connection method of the tool trajectory.
  • (3) Obtain the density of the tool locus line and the density of the tool position on the tool locus.
  • (4) In tool path planning for 5-axis CNC machining, it is also necessary to determine the tool space orientation of each tool position.

Generating a multi-axis CNC toolpath is the basis and key to NC programming. There are many different calculation methods for different processing targets. As long as the optimum channel orientation can be determined, part of the work surface can be completed in a single pass. Some require multiple paths to complete, resulting in multiple toolpaths.

4.4.3 Process simulation

After setting all the cutting paths, run a 3D simulation to perform post-processing. Select 4-axis machining for post-processing.
The simulation results are shown in Figures 4-20, 42-1 and 4-22.

4.5 Post-processing

NC programming post-processing involves generating a machining toolpath file and generating a machine tool NC code instruction set. The postprocessor reads the system-generated toolpath file, extracts relevant processing information from it, and analyzes, determines, and processes the specified Cnc Machine tool according to its characteristics and NC program format requirements. Finally, generate an NC program that the CNC machine can directly recognize.
It is a post-processing of Cnc Processing. It directly affects the use of CAD / CAM software and the quality of parts. Select 5-axis machining and export the NC program as shown in Figure 4-23.

4.6 Machine simulation

The machine uses a 5-axis vertical milling machine and the control system is Sinumerk. If the selected machine model and control system is not available in the UG post-processing module, you must select the post-processing constructor of the processing tool from the UG Start menu. The post-processing constructor generates a post-processing file by setting the processing parameters of the selected machine tool and the detailed parameters of the control system.

Then, via the UG processing module, select the appropriate program and select post-processing to display the post-processing dialog box.

The dialog has a default post-processing file. You can also select the post-processing file you created and choose a location and organization to save it to.

The UG can be processed directly from the blocks generated by the simulation module. The simulation interface allows you to see the speed, feed rate, and coolant status of the machine. You can also monitor the coordinates of the tool in real time. In the NC program area, you can check the current processing stage of the program code.

The main work of this design is digital control of the impeller and simulation of machine tools. From the selection of parts to the final simulation of the virtual machine, many failures have occurred. After improvement, the design is finally completed. 5-axis CNC machining is one of the best solutions for obtaining curves and surfaces that are described by complex surfaces and irregular parts, especially numerical formulas and require sufficient accuracy. For example, the entire impeller blade, at the same time, the development and application of coordinate processing technology is closely related to CAD / CAM technology. This design mainly takes the single-chip impeller of an aero engine as an example to analyze geometric models, tool position calculations, tool path planning, and CNC machining techniques.

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