Aero-engine hollow blade wax mold ultrasonic thickness measuring method

Abstract

The invention discloses an aero-engine hollow blade wax mold ultrasonic thickness measuring method, which adopts the parameters that the pulse rising time of a pulse generator is 10 nanoseconds, the frequency is 10 MHz, and the bandwidth range of a pulse receiver is 2.5-20 MHz, so that the pulse generator has certain penetrating power to a wax mold, at least can clearly display a first bottom wave, and meets the requirement of resolution; the enough signal-to-noise ratio in the whole detection range is ensured, and the effective measurement of the wall thickness of the hollow blade wax mold is met. Meanwhile, the water distance of the water immersion probe is further controlled to be one time of focal length, the resolution and penetrating power are improved, clutters are reduced, the accuracy of ultrasonic wave for detecting the thickness of the wax mold is improved, and the problems that when the ultrasonic wave is propagated in a wax mold material, attenuation is large, the penetrating power is poor, and high-precision measurement of the hollow blade wax mold is difficult are solved.

Description

Technical Field

[0001] The invention relates to the technical field of non-destructive ultrasonic thickness measurement, and more specifically to a method for ultrasonic thickness measurement of a hollow blade wax mold of an aero-engine. Background Art

[0002] Hollow blade wax molds can improve the yield of cast blades. The quality of the blade wax mold determines the quality of the cast blade. Among them, wall thickness is an important geometric dimension indicator of the hollow blade wax mold, which directly affects the safety and life of the aircraft engine. Therefore, during the wax mold production process, it is necessary to monitor the stability of the wall thickness dimensions of the concerned area of ​​the hollow blade wax mold in order to timely detect manufacturing deviations and adjust the process to correct them.

[0003] At present, thickness detection mainly includes CT imaging method, optical measurement method and ultrasonic detection method. Among them, although the CT imaging method has high accuracy, it takes a long time to measure and has high cost, and is not suitable for batch detection of hollow blade wax molds. The optical measurement method has low cost and can be used as a means of batch detection. For example, CN 102230786 A discloses a method for detecting the wall thickness of hollow turbine blade wax molds based on optical measurement, which uses optical scanning to accurately measure the alignment of the ceramic core and the wax mold, and then calculates the wall thickness at each position through the cross-sectional line of the layer. This method requires multiple measurements of the data of the ceramic core and the wax mold, which is complicated to operate and reduces efficiency. The ultrasonic detection method can quickly detect the thickness, and the method is simple and efficient, but it is limited by the material and is prone to large errors.

[0004] The ultrasonic detection method is based on the pulse reflection principle. The ultrasonic wave is transmitted into the material to be tested and the material thickness is calculated based on the propagation time of the ultrasonic wave in the material. The probe excites the ultrasonic wave. When the ultrasonic wave reaches the upper surface of the test piece, a part of the ultrasonic wave enters the test piece, and most of it is reflected back and received by the probe to form an interface wave. The part of the ultrasonic wave that enters the test piece continues to propagate to the bottom surface of the test piece at the longitudinal wave speed in the test piece, and most of it is reflected back and passes through the upper surface of the test piece to be received by the probe to form a bottom surface echo. For a given material, its longitudinal wave velocity is constant. If the upper and lower surfaces of the test piece are parallel, the thickness of the test piece can be calculated based on the time difference between the interface wave and the bottom surface echo arriving at the probe (the propagation time of the ultrasonic wave in the material once). For example, CN102927935B uses ultrasonic wave to detect the wall thickness of single crystal hollow blades. This method has high detection accuracy and detection efficiency for single crystal metal blades. However, the wax mold material of the blade has the characteristics of large ultrasonic attenuation and poor penetration ability. The wall thickness of the hollow blade of an aircraft engine is relatively thin. In theory, a probe with a higher frequency should be used to ensure sufficient resolution. However, in actual experiments, it was found that the thickness measurement of the hollow blade wax mold is different from the thickness measurement of the metal casting hollow blade. When the frequency is too high, the amplitude of the first bottom wave of the inspected part is very low or even non-existent, making it impossible to measure the wall thickness. Summary of the invention

[0005] The main technical problem to be solved by the present invention is to provide an ultrasonic thickness measurement method for a hollow blade wax mold of an aero-engine in view of the shortcomings of the prior art that ultrasonic waves have large attenuation and poor penetration when propagating in the wax mold material, making it difficult to perform high-precision measurement of the hollow blade wax mold.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for ultrasonic thickness measurement of a hollow blade wax mold of an aircraft engine is provided. The method is based on an ultrasonic thickness gauge, which includes a probe, a pulse generator, a pulse receiver and a display screen. The steps include:

[0008] S1. Place the probe of the ultrasonic thickness gauge on the surface of the wax model, and the pulse generator emits ultrasonic waves into the wax model;

[0009] S2. When the ultrasonic wave reaches the upper surface of the wax model, part of the ultrasonic wave enters the wax model, and part of the ultrasonic wave is reflected back and received by the pulse generator to form an interface wave;

[0010] S3. Part of the ultrasonic wave that enters the wax model continues to propagate to the bottom surface of the wax model at the speed of longitudinal waves, and part of the ultrasonic wave is reflected back and passes through the upper surface of the wax model, and is received by the pulse generator to form a bottom surface echo;

[0011] S4. The receiving waveform and the time of each return point are displayed on the display screen, and the thickness of each dielectric layer is calculated according to the thickness calculation formula;

[0012] The pulse generator has a pulse rise time of 10 nanoseconds, a frequency of 10MHz, and a pulse receiver bandwidth range of 2.5 to 20MHz. When the frequency is too low, the longitudinal resolution is insufficient, resulting in the inability to separate the interface wave between the air and the wax model and the reflected wave between the wax model and the ceramic core, making it impossible to measure the thickness; when the frequency is too high, the ultrasonic wave attenuates too much in the wax model material, and the higher the frequency, the more obvious the attenuation, resulting in the first bottom wave amplitude of the wax model being tested being very low or even absent, resulting in no wave being detected during thickness measurement, and the thickness cannot be measured.

[0013] Furthermore, the probe of the ultrasonic thickness gauge is a probe with a delay function. The probe with a delay function can improve the surface resolution by utilizing the time delay between the probe wafer and the workpiece surface.

[0014] Furthermore, the probe of the ultrasonic thickness gauge is an immersion probe, which can delay the starting position of the interface wave, avoid the blind area caused by blockage, and have better resolution.

[0015] Furthermore, the water distance of the immersion probe is 1 times the focal length, that is, when the focus of the immersion probe is located on the surface of the inspected object, the water distance is equal to the focal length, the resolution is the best, the clutter is the smallest, and the penetration is the strongest.

[0016] Furthermore, the ultrasonic waveform displayed by the oscilloscope of the display screen is in a non-detection mode.

[0017] Furthermore, it also includes debugging and calibration of the ultrasonic thickness gauge.

[0018] Furthermore, the debugging and calibration includes: firstly using the material in the same state as the wax model blade to make calibration blocks with different thicknesses and parallel upper and lower surfaces, and then performing ultrasonic thickness measurement calibration on the calibration blocks.

[0019] Furthermore, the minimum thickness value of the calibration test block should be smaller than the minimum thickness value to be measured, the maximum thickness value of the calibration test block should be larger than the maximum thickness value to be measured, and the thickness of other calibration test blocks should be within the range.

[0020] Furthermore, the surface roughness of the calibration block is not greater than 0.8 μm, and the parallelism of the calibration block is not greater than 0.02 mm.

[0021] Compared with the prior art, the beneficial effects are:

[0022] According to the characteristics of the wax model material that the ultrasonic wave attenuation is large and the penetration ability is poor, the present invention strictly controls the pulse parameters, adopts the pulse generator pulse rise time of 10 nanoseconds, the frequency of 10MHz, and the pulse receiver bandwidth range of 2.5-20MHz parameters, so that it has a certain penetration ability, can at least clearly display the first bottom wave, and meet the requirements of resolution, ensure sufficient signal-to-noise ratio in the entire detection range, and meet the effective measurement of the wall thickness of the hollow blade wax model. At the same time, the water distance of the immersion probe is further controlled to be equal to the focal length, so as to improve the resolution and penetration, reduce clutter, and improve the accuracy of ultrasonic detection of wax model thickness. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the schematic diagram of ultrasonic thickness detection.

[0024] Figure 2 This is the waveform diagram when the frequency is 10MHz.

[0025] Figure 3 This is the waveform diagram when the frequency is 25MHz.

[0026] Figure 4 This is a physical picture of the calibration test block. DETAILED DESCRIPTION

[0027] The present invention will be further explained and illustrated below in conjunction with the embodiments, but the specific embodiments do not limit the present invention in any form.

[0028] Example 1

[0029] This embodiment provides an ultrasonic thickness measurement method for a hollow blade wax model of an aircraft engine, which uses an ultrasonic thickness gauge for measurement. The ultrasonic thickness gauge includes a probe, a pulse generator, a pulse receiver, and a display screen. The rise time of the pulse generator is 10 nanoseconds and the frequency is 10 MHz, which ensures sufficient longitudinal resolution and can meet the blade thickness measurement requirements.

[0030] The frequency bandwidth of the pulse receiver must match the frequency bandwidth of the probe. To ensure that the waveform is not distorted, the frequency bandwidth of the pulse receiver is required to cover the frequency bandwidth of the probe, which is 2.5-20MHz.

[0031] The display screen should include a thickness indicator and an oscilloscope. The thickness indicator is used to display the thickness value of the test piece, and the oscilloscope can display the ultrasonic waveform and other information to determine whether the thickness measurement is accurate. Since the ultrasonic wave attenuates greatly when propagating in the wax model material, generally only the time between the interface wave and the first bottom wave can be measured. In order to make the measurement value accurate, the leading edge of the gate must be aligned with the leading edge of the interface wave peak, and the trailing edge of the gate must be aligned with the leading edge of the first bottom wave. The non-detection (radio frequency) display form contains phase information because the waveform has not been detected, and the non-detection (radio frequency) method uses the interface wave and the first bottom wave as the measurement wave, so the operation is simplest and most accurate.

[0032] like Figure 1 , the probe 1 of the ultrasonic thickness gauge is attached to the surface of the wax model, and the pulse generator emits ultrasonic waves into the wax model. The pulse receiver and the pulse generator are in the same plane. When the ultrasonic wave reaches the upper surface 2 of the wax model, part of the ultrasonic wave enters the wax model 3, and part of it is reflected back and received by the pulse generator to form an interface wave 4. Part of the ultrasonic wave entering the wax model 3 continues to propagate to the bottom surface 6 of the wax model at the longitudinal wave speed in the wax model 3, and part of it is reflected back and passes through the upper surface of the wax model to be received by the pulse generator to form a bottom surface echo 5. The receiving waveform and the time of each return point are displayed on the display screen, and the thickness of each dielectric layer itself is calculated according to the thickness calculation formula.

[0033] like Figure 2 As shown, when the rise time of the pulse generator is 10 nanoseconds and the frequency is 10 MHz, the bandwidth range of the pulse receiver is 2.5 to 20 MHz. The first bottom wave in the A-scan imaging image is clearly visible, and the wall thickness of the hollow blade wax mold can be effectively measured.

[0034] Comparative Example 1

[0035] This comparative example provides an ultrasonic thickness measurement method for a hollow blade wax model of an aircraft engine, which is measured by an ultrasonic thickness gauge, which includes a probe, a pulse generator, a pulse receiver and a display screen. The frequency of the pulse generator is 5MHz. The bandwidth of the pulse receiver is 2.5-20MHz. The obtained waveform has insufficient longitudinal resolution, resulting in the inseparability of the interface wave between the air and the wax model and the reflected wave between the wax model and the ceramic core, making it impossible to measure the thickness.

[0036] Comparative Example 2

[0037] This comparative example provides an ultrasonic thickness measurement method for a hollow blade wax model of an aircraft engine, which is measured by an ultrasonic thickness gauge, which includes a probe, a pulse generator, a pulse receiver and a display screen. The frequency of the pulse generator is 15 MHz. The bandwidth of the pulse receiver is 2.5-20 MHz. The sensitivity obtained is not enough, and the amplitude of the first bottom wave in the A-scan imaging image is very low, so the thickness cannot be measured.

[0038] Comparative Example 3

[0039] This comparative example provides a method for ultrasonic thickness measurement of a hollow blade wax mold of an aircraft engine, which is measured by an ultrasonic thickness gauge, which includes a probe, a pulse generator, a pulse receiver and a display screen. The frequency of the pulse generator is 25MHz. The bandwidth of the pulse receiver is 2.5-20MHz. Figure 3 As shown in the figure, when the frequency is 25MHz, the waveform in the A-scan image is severely attenuated, the first bottom wave is not obvious, and the thickness cannot be measured.

[0040] Example 2

[0041] This embodiment provides an ultrasonic thickness measurement method for a hollow blade wax model of an aircraft engine. The high-frequency probe has high damping, so the pulse width is narrow and the near-surface resolution is good. However, the high-frequency probe has large attenuation and poor penetration. Therefore, when the wax model material has sufficient penetration, ultrasonic thickness measurement uses a high-frequency probe with a higher resolution as much as possible. When measuring thinner workpieces, this embodiment uses a probe with a delay function. The probe with a delay function can use the time delay between the probe wafer and the workpiece surface to improve the surface resolution for high-precision measurement of thinner workpieces.

[0042] Since the wall thickness of the hollow blade wax mold is relatively thin, the probe used should have a delay function. Among them, the immersion probe can delay the starting position of the interface wave, avoid the blind area caused by blockage, have better resolution, and is more suitable for measuring thin workpieces.

[0043] When the focus of the immersion probe is on the surface of the test piece (i.e. the water distance is equal to the focal length), the acoustic energy is concentrated in this area, the sensitivity is high, the signal-to-noise ratio is high, and the resolution is good. However, outside this area, the detection sensitivity decreases rapidly. In order to ensure sufficient sensitivity during thickness measurement, the gain needs to be increased, but this will result in excessive clutter, reduced resolution, and affect the thickness measurement results.

[0044] Example 3

[0045] This embodiment provides the debugging and calibration of the ultrasonic thickness gauge. The calibration block material used in the test is F28-44B. The ultrasonic calibration block is made of the same material and in the same state as the hollow blade wax model to ensure that its acoustic properties (such as sound velocity, attenuation coefficient, etc.) are consistent with the material of the inspected part. The ultrasonic thickness measurement test verification is carried out on a plane wax model calibration block with parallel upper and lower surfaces.

[0046] According to the thickness range of the parts to be tested, multiple calibration blocks are designed and manufactured. The minimum thickness value of the calibration block should be less than the minimum thickness value to be tested, and the maximum thickness value of the calibration block should be greater than the maximum thickness value to be tested. The thickness of other calibration blocks is taken in this range, and a point is selected on each calibration block as the reference point of the calibration instrument. Specifically, Figure 4The thicknesses are 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm and 1.6mm respectively. The surface roughness of the calibration block is not greater than 0.8μm, and the parallelism of the calibration block should be greater than 0.02mm.

[0047] This embodiment uses the minimum and maximum thickness flat wax model calibration test blocks to calibrate and debug the instrument, and then performs thickness measurement tests on four intermediate thickness flat wax model calibration test blocks. The measurement results are shown in Table 1 below:

[0048] Table 1

[0049]

[0050] It can be seen from Table 1 that when the thickness of the flat wax model calibration block is measured, the measurement accuracy is high, the maximum error is 0.02mm, and it has high accuracy.

[0051] Example 4

[0052] This embodiment conducts an ultrasonic thickness measurement application test on a curved hollow blade wax model. Since the wax model is a non-metallic material with a low melting point, it is not possible to perform wire cutting, and it is not suitable to use a caliper to measure the wall thickness of the hollow blade wax model after sectioning. In the present invention, the value of the wax model wall thickness measured by the blue light method is used as the true value. First, the ceramic core is scanned for the first time with blue light, and then the hollow blade wax model is scanned for the second time with blue light. The thickness difference between the two scans is the blue light measurement value of the hollow blade wax model wall thickness.

[0053] In order to verify the accuracy of the ultrasonic measurement results, the blade wax mold wall thickness detection point template was used to mark the measurement points of a type of hollow blade wax mold, and the blue light method and ultrasonic thickness measurement method were used to measure the thickness of the measurement points specified in the design drawing of the type of hollow blade wax mold numbered 1#, 2#, 3# and 4#. The results of the two methods for measuring 40 measurement points in 10 locations of 4 blades and the difference between the two methods are shown in Table 2 below:

[0054] Table 2

[0055]

[0056]

[0057]

[0058] As can be seen from Table 2, the ultrasonic measurement values ​​are close to the blue light scanning measurement values. Among the blade wax mold points with a thickness of 0.5mm≤t≤0.75mm, the maximum error point is point 5, with an error value of 0.05mm; among the blade wax mold points with a thickness of 0.75mm<t≤1.5mm, the maximum error point is point 7, with an error value of 0.11mm. Since the diameter of the ultrasonic thickness gauge probe is about 5mm, the hollow blade wax mold has a certain curvature, and the curvatures of different measurement points are also different. The variable curvature of the detection surface has a certain influence on the coupling performance of the ultrasonic probe, resulting in deviations in the data measured by blue light scanning and ultrasonic waves.

[0059] The analysis of the blue light scanning and ultrasonic measurement data shows that although there are deviations in the measurement values ​​of some points, they can all meet the requirements for measuring the wall thickness of the hollow blade wax mold. Therefore, the results of ultrasonic measurement are correct and effective.

[0060] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for ultrasonic thickness measurement of a hollow blade wax mold of an aircraft engine, characterized in that: The measurement is performed based on an ultrasonic thickness gauge, which includes a probe, a pulse generator, a pulse receiver and a display screen. The pulse generator has a pulse rise time of 10 nanoseconds and a frequency of 10 MHz. The bandwidth range of the pulse receiver is 2.5 to 20 MHz. The steps include: S1. Place the probe of the ultrasonic thickness gauge on the surface of the wax model, and the pulse generator emits ultrasonic waves into the wax model; S2. When the ultrasonic wave reaches the upper surface of the wax model, part of the ultrasonic wave enters the wax model, and part of the ultrasonic wave is reflected back and received by the pulse generator to form an interface wave; S3. Part of the ultrasonic wave that enters the wax model continues to propagate to the bottom surface of the wax model at the speed of longitudinal waves, and part of the ultrasonic wave is reflected back and passes through the upper surface of the wax model, and is received by the pulse generator to form a bottom surface echo; S4. The receiving waveform and the time of each return point are displayed on the display screen, and the thickness of each dielectric layer is calculated according to the thickness calculation formula.

2. The method for ultrasonic thickness measurement of a hollow blade wax pattern of an aircraft engine according to claim 1, characterized in that: The probe of the ultrasonic thickness gauge is a probe with a delay function.

3. The method for ultrasonic thickness measurement of aeroengine hollow blade wax mold according to claim 1, characterized in that: The probe of the ultrasonic thickness gauge is a water immersion probe.

4. The method for ultrasonic thickness measurement of a hollow blade wax pattern of an aircraft engine according to claim 3, characterized in that: The water distance of the immersion probe is 1 times the focal length.

5. The method for ultrasonic thickness measurement of aeroengine hollow blade wax mold according to claim 1, characterized in that: The ultrasonic wave form displayed by the oscilloscope of the display screen is in a non-detection mode.

6. The method for ultrasonic thickness measurement of aeroengine hollow blade wax mold according to claim 1, characterized in that: It also includes the commissioning and calibration of ultrasonic thickness gauges.

7. The method for ultrasonic thickness measurement of a hollow blade wax pattern of an aircraft engine according to claim 6, characterized in that: The debugging and calibration comprises: firstly using the material in the same state as the wax model blade to make calibration test blocks with different thicknesses and parallel upper and lower surfaces, and then performing ultrasonic thickness measurement calibration on the calibration test blocks.

8. The method for ultrasonic thickness measurement of aeroengine hollow blade wax mold according to claim 7, characterized in that: The minimum thickness value of the calibration test block should be less than the minimum thickness value to be measured, the maximum thickness value of the calibration test block should be greater than the maximum thickness value to be measured, and the thickness of other calibration test blocks should be within the range.

9. The method for ultrasonic thickness measurement of aeroengine hollow blade wax mold according to claim 7, characterized in that: The surface roughness of the calibration test block is no greater than 0.8 μm.

10. The method for ultrasonic thickness measurement of aeroengine hollow blade wax mold according to claim 7, characterized in that: The parallelism of the calibration test block is not greater than 0.02 mm.

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