Research on NC programming of engine integral impe

Research on NC programming of engine integral impeller based on UG

1 preface

integral impeller, as a key component of turbine machinery, is widely used in aviation, aerospace and other fields. The quality of its pin disk friction and wear experimental machine directly affects its aerodynamic performance and mechanical efficiency. Therefore, its processing technology has always been an important topic in the turbine manufacturing industry. At present, foreign countries generally use five coordinate machining special software for integral impeller [1], mainly including max-5 and max-ab impeller machining special software of nrec company in the United States, integral impeller machining module of starrag NC machine tool in Switzerland, and special impeller machining software such as hyperMILL. In addition, some general software such as UG, CATIA and Pro/E can also be used for integral impeller machining. At present, only a few domestic enterprises (such as colleges and universities such as Northwest University of technology and some engine professional factories and professional institutes of aerospace system) can process the integral impeller, and the process level is still far from the international advanced level. On the whole, there is still a big gap between the research and application in the field of impeller processing in China and developed countries. The software and hardware of many enterprises depend on imports. The software with independent copyright has not been popularized and applied in production. It has not passed the standard in the manufacturing technology of high-performance impeller such as narrow channel and small wheel hub ratio. Therefore, it is imperative to study the processing technology of high-performance impeller

2 CAD/CAM system structure diagram of integral impeller

integral milling impeller processing refers to that the blank adopts forged parts, and then turns into the basic shape of blade wheel rotation. The hub and blade are processed in one blank on the five axis NC machining center. It can meet the strength requirements of compressor impeller products, with small surface error and less mass removal during dynamic balance. Therefore, it is an ideal processing method. With the maturity of five axis NC machining technology, this kind of parts that originally need manual manufacturing can be manufactured through overall processing. The CAD/CAM system structure diagram [2] of machining integral impeller by NC machining method is shown in Figure 1

3 structural characteristics and processing difficulties of micro compressor rotor

most integral impellers in China are imitated according to the scale of foreign impellers, and the impeller studied in this paper is the compressor rotor on the micro aeroengine independently developed by Beihang Institute of energy and power engineering. The outlet diameter of the compressor rotor is 81mm, including 8 primary blades and 8 secondary blades. The height of the outlet blade is 3mm, the diameter of the impeller inlet is 44.3mm, the height of the inlet blade is 17.15mm, the thinnest part of the blade is 0.4mm, and the minimum spacing between adjacent blades is 3.1mm, as shown in Figure 2

in order to make the aerodynamic design reach the international advanced level, the compressor rotor adopts structures such as large torsion angle and variable fillet at the root, which puts forward high requirements for processing. The machining difficulty of rotor is as follows:

1. The integral impeller with the same diameter of 81mm in the world usually has 12 blades or 14 blades, while this rotor has 16 blades and its secondary blades are also longer, which further narrows the machining channel and further increases the machining difficulty

2. When the tool diameter is 2.5mm, the rigidity is poor and it is easy to break. Controlling the cutting depth is also the key

3. The surface of the impeller is free-form surface, the flow channel is narrow, the blade is seriously distorted, and has the trend of backward tilt. It is very easy to interfere during processing, and the processing is very difficult. Sometimes, in order to avoid interference, some surfaces need to be machined in sections, so it is difficult to ensure the consistency of the machined surface

4. The curvature radius of the leading edge fillet changes greatly, the angle of the machine tool changes greatly during the machining process, and it is difficult to process the surrounding blade

5. Due to the need of impeller strength, variable fillet is also used between hub and blade. Because the channel is narrow and the blade is high, the machining of variable fillet is also a difficulty

in short, the narrow channel, large torsion angle and variable fillet of this impeller have brought great difficulties to the processing, and there is no such difficult integral impeller in China

4 processing scheme of compressor rotor

the overall processing of impeller adopts the forming processing of hub and blade on one blank, rather than the process method of welding the blade on the hub after processing and forming. The processing scheme is as follows []:

1. In order to improve the strength of the integral impeller, the blank is generally forged parts, and then the datum plane is turned to process the basic shape of the impeller. The blank of compressor rotor is shown in Figure 3

2. Slotting processing of impeller air flow channel

the position of slotting processing slot should be selected in the middle of the air flow channel. The flat bottom taper shank rod milling cutter should be used to run parallel to the air flow channel, and ensure that there is a certain machining allowance between the groove bottom and the wheel hub surface, as shown in Figure 4

among them, the flat bottom taper shank bar milling cutter is a cemented carbide tool, and its specification is: the diameter of the flat bottom part is 3mm, the half cone angle is 2 °, the diameter of the tool shank is 6mm, and the length of the tapered part is 20mm

the spindle speed selected in this step is 10000r/min and the feed speed is 800mm/min. The control panel of the NC machine tool is generally equipped with the spindle speed and feed speed adjustment (magnification) switch, which can adjust the spindle speed and feed speed according to the actual processing situation in the processing process

3. Slot expansion processing of impeller air flow channel and rough processing of blades

slot expansion processing adopts spherical taper shank rod milling cutter. Starting from the slotting position, expand the slot from the center to the outer edge to both sides of the blade. The slot expansion processing should ensure that a certain finish machining allowance is reserved for the blade shape. Usually, the groove expanding processing and finish milling of the wheel hub surface are completed at one time. Because the impeller channel is narrow, the blade is high, and the distortion is serious, and the cutting area needs to be determined according to the driving surface in UG NC machining programming, the slot expansion machining needs to be processed in two parts

Part I: select the driving surface as the hub surface and expand the groove. At this time, it cannot be processed to the wheel hub surface, and further groove expansion processing is required

Part II: further groove expansion and blade rough machining. Select the driving surface as the offset surface of the blade surface, and further expand the groove while rough machining the blade

among them, the rod milling cutter with spherical taper shank is a cemented carbide tool, and its specification is: the diameter of the ball head part is 3mm, the half cone angle is 2 °, the diameter of the tool shank is 6mm, and the length of the tapered part is 20mm. The spindle speed selected in this step is 20000r/min and the feed speed is 3000mm/min

4. Finish machining of blade and wheel hub

the finish machining under uniform allowance ensures good surface machining quality. The ball end milling cutter is used for finish machining, because the minimum spacing between adjacent blades is 3.1mm and the deepest part of the blade is 17.15mm. Considering the interference, the rotor finishing cutter adopts the ball end bar milling cutter with a diameter of 2.5 from fraisa company of Switzerland, and the space avoidance of the cutter is 20mm. The spindle speed during processing is 260000r/min and the feed speed is 5000mm/min

5. Variable fillet finishing

the left side of the large and small blades is variable fillet, and the fillet radius varies linearly from 1.25mm to 2.2mm to 1.25mm from the leading edge to the trailing edge of the blade. The maximum fillet occurs at 22% near the trailing edge. The right side of the blade is a constant fillet of 1.25mm. The variable fillet can be completed by one-time cutting. At this time, the radius of the tool ball head is greater than the minimum radius of the variable fillet. The speed of the spindle and the feed speed of the blade are the same as those of the hub

the above procedures shall be indexed and rotated, and the next procedure shall be executed after processing all hubs or blades to ensure uniform stress release and reduce machining deformation error

5 NC programming of compressor rotor

5.1 flow chart of machining compressor rotor with UG

when NC programming of rotor with UG, it is usually guided by the flow chart shown in Figure 5 to create the tool path of each operation and run through the whole process of machining [2]

5.2 NC programming

5.2.1 establish the parent node group

1. Under the tool node, add all the tools used in processing and set their tool parameters

2. Under the geometry node, select the blank, set the machining coordinate system, and select the avoidance geometry as the rotor entity

3. Under the method node, set the display color of spindle speed, feed rate and tool path during rough, semi-fine and finish machining

5.2.2 according to the power, it is divided into hydraulic horizontal tensile testing machine and electronic horizontal tensile testing machine. The slotting processing of impeller air flow channel

extract the flow channel surface, and the U and V parameter lines are shown in Fig. 6 (a). Because the processing of the impeller channel needs to be along the air flow direction, rearrange the U and V parameter lines of the channel to make the U parameter or V parameter line along the air flow direction. Because of the particularity of this runner surface, after readjusting the U and V parameters, the runner surface is divided into three surfaces. The rearranged V parameter line is shown in Fig. 6 (b), which is along the air flow direction

1. The machining of the front surface of the flow channel (as shown in Fig. 6 (b))

adopts variable contour milling. The deeper the machining depth is, the more serious the interference is. One tool axis control method is not necessarily appropriate, so it is divided into two tool axis control methods. One is: normal to drive (for upper half layer processing) and the other is: toward point (for lower half layer processing)

process the upper half layer, and the parameter settings of the program are as follows:

1) the drive method adopts surface area

2) the front surface of the flow channel is selected as the driving geometry, that is, side 1 in Fig. 6 (b)

3) establish avoidance geometry, taking the whole part as the avoidance geometry. If there is interference, the tool will be retracted automatically. Generally, automatic tool retraction is selected during rough machining to avoid interference

4) rough machining, with tolerance = 0.1mm for row spacing

5) tool axis control mode: normal to drive

6) the start step and end step of surface% in the cutting area are set to: 50, which means cutting a knife in the middle of the machining surface

7) set non cutting, i.e. non cutting movement, and select the forward and backward tool along the tool axis

8) under cutting, set stock margin: 7mm; Set multiple passes, and the cutting depth of each layer is 0.5mm

process the lower half layer, and the parameter settings of the program are as follows:

1) the tool axis control mode is: ward point

2) under cutting, set stock margin: 0.2mm; Set multiple passes, and the cutting depth of each layer is 0.5mm

3) other parameter settings are the same as the procedure for processing the upper half layer

because the key of variable axis surface contour milling is to select the tool axis control mode, the subsequent processing only describes the tool axis control mode

2. The machining of the left end surface of the flow channel (as shown in Figure 6 (b))

adopts variable axis surface contour milling to process this surface. One tool axis control mode is normal to drive (for the machining of the upper part) and the other is relative to drive (for the machining of the lower part)

(3) machining of the right end surface of the flow channel (as shown in Figure 6 (b))

the curvature of this surface changes very gently, and the included angle between the normal direction of each point on the surface and the blade surface is close to 0. Therefore, the tool axis control mode selected for machining this surface is normal to drive. The generated machining tool path is shown in Figure 7

5.2.3 slot expanding processing of impeller air flow channel

slot expanding processing tool path is similar to slotting processing, except that the start step of surface% in the cutting area is set to 0 and end step: 100, which means cutting the whole channel surface and generating tool path, as shown in Figure 8

5.2.4 further groove expansion and rough machining of blades

after groove expansion, most of the allowance of the flow channel has been processed to ensure precision黑龙江大姨妈量少持续时间长怎么回事
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