Method for estimating the properties of thin-walled parts of castings

Abstract

To provide a method for estimating characteristics of a thin part of a casted product which can estimate the characteristics of the thin part by locally vibrating the thin part without generating a defect in the thin part of the casted product.SOLUTION: Local parts a to e of a wing body 12 are vibrated by locally blowing pulse-like air to the wing body 12 of a turbine wheel 1, the natural frequency of the local parts a to e of the wing body 12 is detected by detecting a vibration of the local parts a to e and performing Fourier transform on the vibration, and the characteristics of the local parts a to e are estimated from the detected natural frequency.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for estimating characteristics such as thickness, composition, and defects of thin-walled portions of castings, and more particularly to a method for measuring the local natural frequency of a thin-walled portion and estimating the characteristics. [Background technology]

[0002] A commonly used method for estimating the characteristics of a casting is to strike the casting with an impact hammer or the like, measure the striking sound with a microphone, or measure the shock waves with a vibrometer, and then determine the natural frequency from the frequency characteristics.

[0003] Patent Document 1 discloses a method of blowing pulsed air onto a stretched tape to vibrate it, and measuring the vibration with a displacement meter to detect the natural frequency. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2002-148139 Summary of the Invention [Problem to be solved by the invention]

[0005] However, it is difficult to locally detect the natural frequency of a casting, especially in its thin-walled parts, when striking with a conventional impact hammer or the like, and even if the shape of the impact hammer or the like is devised so that it can strike the thin-walled parts, problems such as damage to the thin-walled parts can occur due to the impact.

[0006] The present invention is intended to solve these problems, and aims to provide a method for estimating the characteristics of a thin-walled portion of a casting, which is capable of vibrating only a localized portion of the thin-walled portion and estimating its characteristics without causing any damage to the thin-walled portion of the casting. [Means for solving the problem]

[0007] In order to achieve the above object, in the first invention, pulsed air is blown locally onto a thin-walled portion (12) of a casting (1) to vibrate local portions (a to e) of the thin-walled portion (12), the vibrations of the local portions (a to e) are detected and Fourier transformed to detect the natural frequencies of the local portions (a to e) of the thin-walled portion (12), and the characteristics of the local portions (a to e) are estimated from the detected natural frequencies.

[0008] In the first invention, the natural frequency of a local thin-walled portion accurately reflects the characteristics of that local portion, and detecting the natural frequency allows for the optimization of the design of a casting mold for molding that local portion and the optimization of casting conditions. When vibration is excited with continuous air, natural vibrations due to vibration modes transmitted from other than the excited local portion may be detected, but by exciting vibration with pulsed air, particularly with a narrow pulse width, it is possible to eliminate natural vibrations due to other vibration modes.

[0009] In the second invention, the characteristic is the thickness of the local portions (a to e).

[0010] In the third aspect of the present invention, the casting is a turbine wheel (1), and the thin-walled portion is a blade (12) of the turbine wheel (1).

[0011] In the fourth invention, at least one of the edge tip (a), edge middle (b), edge root (c), blade surface center (d) and blade lower edge (e) of the blade body (12) is selected as the local thin-walled portion.

[0012] The symbols in parentheses above indicate, for reference, the correspondence with specific means described in the embodiments to be described later. [Effects of the Invention]

[0013] As described above, according to the method of estimating the characteristics of a thin-walled portion of a casting of the present invention, it is possible to estimate the characteristics of the thin-walled portion by vibrating only a localized portion of the thin-walled portion without causing any damage to the thin-walled portion of the casting. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing an equipment configuration for carrying out the method of the present invention. [Figure 2] 1 is a side view of a turbine wheel to which the method of the present invention is applied; DETAILED DESCRIPTION OF THE INVENTION

[0015] The embodiments described below are merely examples, and various design improvements made by those skilled in the art without departing from the gist of the present invention are also included in the scope of the present invention.

[0016] Figure 1 shows a turbine wheel 1 of a turbocharger. The turbine wheel 1 is a cast product, and a plurality of blades 12 (ten in this embodiment) are formed around a rotating shaft 11, and these blades 12 correspond to the thin-walled portion whose characteristics are estimated by the method of the present invention. In Figure 1, the turbine wheel 1 is placed on a silicone rubber plate 2 serving as an insulator, and each blade 12 is in an upright position. The tip of an air blow nozzle 3 with a diameter of 1 to 2 mm is positioned close to the blade surface of one of the blades 12 from the side, at a distance of about 1 to 15 mm.

[0017] The base end of the air blow nozzle 3 is connected to a pulse solenoid valve 4, through which it communicates with a 0.2 MPa compressed air source 5. The pulse solenoid valve then periodically injects pulsed air, for example at 1 Hz and with a duty ratio of 10%, into the local area on the blade surface of the blade body 12 that faces the tip of the air blow nozzle 3, and the pressure of the jet excites the local area. The vibration of the local area of ​​the blade body 12 is measured by a laser Doppler vibrometer 6, A / D converted at a sampling frequency of 50 kHz, and input to a computing device 7. The signal is then fast Fourier transformed and peak-held in the computing device 7, and 10 peak-held values ​​are detected as the natural frequency of the local area, the average of which is calculated.

[0018] In this embodiment, five locations were selected as local portions of the blade body 12, namely, a (edge ​​tip), b (edge ​​middle), c (edge ​​root), d (blade surface center), and e (blade lower edge), as shown in Figure 2, and the tip of the air blow nozzle 3 was brought close to each of them to detect the natural frequencies of each of the local portions a to e. These are shown in Table 1. Table 1 shows the maximum, minimum, average, and variation (difference between the maximum and minimum) of the natural frequencies of the above local portions a to e measured for each of the 10 blade bodies 12 of the same turbine wheel 1.

[0019] [Table 1]

[0020] As is clear from Table 1, among the ten blade bodies 12 of the same turbine wheel 1 at each local portion a to e, the variation in the natural frequency at the edge end a, edge middle b, edge root c, and blade surface center d was about 1 kHz (5% of the absolute value of the natural frequency), and the variation in the natural frequency at the blade lower edge e was even smaller, at about 0.7 kHz (3% of the absolute value of the natural frequency).

[0021] Table 2 shows the results of detecting and averaging the natural frequencies at each local point a to e of each blade body 12 for three 10-blade turbine wheels A-1 to A-3 of the same type, and then calculating the individual average value for each turbine wheel A-1 to A-3. As is clear from Table 2, for turbine wheels A-1 to A-3 of the same type, the 3σ variation in the individual average values ​​was about 1.0 kHz (5% of the absolute value of the natural frequency).

[0022] [Table 2]

[0023] Table 3 shows the results of detecting and averaging the natural frequencies at local points a to e of each blade 12 for three other 10-blade turbine wheels B-1 to B-3 of the same type, and then calculating the individual average values ​​for each turbine wheel B-1 to B-3. As is clear from Table 3, the 3σ variation in the individual average values ​​for turbine wheels B-1 to B-3 of the same type was about 0.9 kHz (5% of the absolute value of the natural frequency).

[0024] [Table 3]

[0025] As described above, according to this embodiment, the natural frequencies of the local portions a to e of each blade body 12, which are the thin-walled portions of the turbine wheel 1 as a cast product, can be measured accurately within a certain error by bringing the air blow nozzle 3 close to the blade body 12. Therefore, if the composition is clear, the thickness of the local portions a to e can be estimated, and conversely, if the thickness is clear, the composition of the local portions a to e can be estimated. In other words, the local characteristics of the thin-walled portions can be estimated, and these characteristics can be fed back into the design of the casting mold.

[0026] Furthermore, from the natural frequencies of each local portion a to e of the multiple blade bodies 12, the average natural frequency of each blade body 12, the average natural frequency of the entire turbine wheel 1, or the average natural frequency of each lot of turbine wheel 1 can be obtained, and by statistically processing these, the design of the casting mold and the optimization of the casting conditions can be performed based on the characteristics estimated from the statistical processing. In the above embodiment, the turbine wheel is used as the casting and the blade body is used as the thin-walled portion, but the present invention is not limited to this. [Explanation of symbols]

[0027] 1...turbine wheel (cast product), 12...wing body (thin section), 3...air blow nozzle, 4...pulse solenoid valve, 5...compressed air source, 6...laser Doppler vibrometer, 7...calculating device, a...edge tip (local), b...edge middle (local), c...edge root (local), d...wing surface center (local), e...wing lower edge (local).

Claims

1. A method for estimating characteristics of a thin-walled portion of a casting, comprising blowing pulsed air locally onto a thin-walled portion of the casting to excite the local vibration of the thin-walled portion, detecting the local vibration and performing a Fourier transform to detect the local natural frequency of the thin-walled portion, and estimating the characteristics of the local portion from the detected natural frequency.

2. The method for estimating characteristics of a thin-walled portion of a casting according to claim 1, wherein the characteristic is a thickness of the local portion.

3. 3. The method for estimating characteristics of a thin-walled portion of a casting according to claim 1, wherein the casting is a turbine wheel, and the thin-walled portion is a blade of the turbine wheel.

4. 4. The method for estimating the characteristics of a thin-walled portion of a casting according to claim 3, wherein at least one of an edge tip, an intermediate edge, an edge root, a center of a surface, and a lower edge of the blade body is selected as the local thin-walled portion.

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