JP5482628B2 - Casting inspection method - Google Patents

Description

  The present invention relates to a method for inspecting a cast product. In particular, the present invention relates to a technique for identifying an abnormality inside a cast product.

  Patent Document 1 discloses a technique for identifying a defect in a cast product by generating an eddy current in the cast product and detecting the distribution and change of the eddy current. The “defect” here is typically a portion where the strength of the cast product is insufficient.

JP 2005-91288 A

  The flow of the eddy current changes depending on the temperature of the casting. For this reason, with the technique of patent document 1, the defect of the casting in a high temperature state cannot be pinpointed correctly. Moreover, in the technique of patent document 1, it is necessary to attach a probe to a casting in order to detect an eddy current. It is usually not possible to attach the probe to a casting that is in a high temperature state. For the above reasons, the technique disclosed in Patent Literature 1 cannot inspect a cast product in a high temperature state. Therefore, in the technique of Patent Document 1, the cast product can be inspected only after the cast product taken out from the mold is cooled. If the cooling time for the inspection can be omitted, the production efficiency of the cast product can be improved. That is, if inspection of a cast product in a high temperature state can be performed, improvement in manufacturing efficiency can be expected. The “cast product in a high temperature state” is typically a cast product immediately after casting.

  The present specification provides a method for inspecting a cast product capable of inspecting a cast product in a high temperature state.

  The technology disclosed in this specification provides a technology for inspecting a cast product using infrared intensity emitted from the surface of the cast product. Although this technology will be described in detail later, there is also a finding that there is a correlation between the quality of the cast product and the roughness of the cast product surface, and between the roughness of the cast product surface and the infrared intensity emitted from the surface. It was created based on the knowledge that there is a correlation.

  The method for inspecting a cast product disclosed in the present specification detects an infrared intensity of a high radiation region having a thermal radiation infrared ray ratio higher than a reference value on the surface of the cast product, and an inspection region defined as an inspection object on the surface of the cast product. Detecting the infrared intensity of the light source, and calculating the ratio between the infrared intensity of the inspection area and the infrared intensity of the high radiation area. The “infrared intensity of the region” means the intensity of infrared rays generated on the surface of the casting in the region. Typically, the “infrared intensity of the region” corresponds to the infrared intensity measured in the region when the surface of the casting is photographed with a thermography device.

  In the step of detecting the infrared intensity of the high emission area and the inspection area, the infrared intensity of other areas may be detected in addition to the infrared intensity of these areas. For example, typically, after measuring an infrared intensity distribution in a wide range on the surface of a cast product with a thermography apparatus, the infrared intensity of those areas may be specified for a high radiation area and an inspection area included in the measurement range. A plurality of inspection areas may exist.

  Infrared rays observed on the surface of the cast product include infrared rays generated by thermal radiation from the cast product and infrared rays reflected on the surface of the cast product. The above-mentioned “thermal radiation infrared ray ratio” means the proportion of infrared rays generated by thermal radiation among infrared rays generated on the surface of the casting. Therefore, the above “high radiation region” means a portion where the ratio of infrared rays generated by thermal radiation is high. Since it is difficult for infrared rays to reach the inside of the concave portion formed in the cast product from the outside, the infrared rays due to reflection are reduced. Therefore, such a portion has a high thermal radiation infrared ray ratio and can be used as a high radiation region. The high radiation area for detecting the infrared intensity may be determined in advance or may be specified every time inspection is performed. It is preferable that the thermal radiation infrared ray ratio in the high radiation region is as high as possible. For example, the reference value can be set to a value close to 100% such as 95%. In this case, a high radiation region can be selected from regions where the thermal radiation infrared ray ratio is 95% or more. The reference value can also be determined relatively. For example, a region having a relatively high thermal radiation infrared ratio than the surrounding region may be a high radiation region, or a region having the largest thermal radiation infrared ratio in the infrared intensity observation range on the casting surface may be a high radiation region. It is good.

  In this inspection method, the infrared intensity of the inspection region and the high radiation region of the surface of the cast product taken out from the mold is detected. Next, a ratio between the infrared intensity of the inspection area and the infrared intensity of the high radiation area (hereinafter referred to as an intensity ratio) is calculated. Most of infrared rays observed in the high radiation region are infrared rays caused by thermal radiation. Moreover, the temperature of the cast product taken out from the mold is distributed substantially uniformly throughout the cast product. For this reason, the intensity | strength of the infrared rays which have arisen by the thermal radiation from each part of a casting is substantially equal to the infrared intensity of a high radiation area | region. Therefore, the intensity ratio is a value corresponding to the thermal radiation infrared ratio in the inspection area. The thermal radiation infrared ray ratio is low in a portion having a rough surface (high surface roughness) and high in a portion having a smooth surface (low surface roughness). Therefore, the surface roughness of the inspection area can be specified from the intensity ratio. On the other hand, the structural characteristics (particularly the structural characteristics related to strength) of the rough material (the cast product just taken out of the mold and before cutting) are roughened on the surface of the rough material (cast product). It is known to correlate with degree. Therefore, by specifying the surface roughness of the inspection area, it is possible to specify the abnormality of the rough material in the inspection area. Here, “abnormality of the coarse material” means that the strength of the coarse material is lower than the assumed strength, or that “galling” (described later) is generated on the surface of the coarse material. Moreover, the measurement of infrared intensity can be easily performed on a cast product in a high temperature state. That is, this inspection method is suitable for inspecting a cast product in a high temperature state taken out from a mold.

  It is preferable that the inspection method described above further includes a step of detecting a frequency of sound generated by hitting the inspection region. Moreover, it is preferable that the inspection method described above further includes a step of detecting an attenuation rate of sound generated by hitting the inspection region.

  The frequency of the sound generated by hitting the cast product changes according to the structural characteristics of the rough material of the hit part. When the crystal grain size of the coarse material is small, the frequency of the sound generated by hitting becomes high. Therefore, by detecting the frequency of the sound generated by hitting the inspection area, it is possible to specify the abnormality of the rough material in the inspection area. Further, the sound generated by hitting a cast product attenuates quickly if there is a defect such as a crack in the hit portion. Therefore, by detecting the attenuation rate of the sound generated by hitting the inspection area, it is possible to specify the abnormality of the rough material in the inspection area. The inspection for hitting the casting can also be performed when the casting is hot. By using a combination of the inspection by these sounds and the inspection by the thermal radiation infrared ratio described above, a more precise inspection can be performed.

  The inspection method described above preferably further includes a step of classifying the quality of the inspection region by comparing the calculated ratio (that is, the intensity ratio) with a reference intensity ratio prepared in advance. The reference strength ratio is a strength ratio determined in advance by experiments or the like, and corresponds to a strength ratio uniquely corresponding to a specific quality (typically strength) of a cast product. For example, the reference strength ratio is determined by experiment as a strength ratio corresponding to the strength required for the cast product.

  In this inspection method, whether the surface roughness in the inspection area is close to the normal surface roughness by comparing the intensity ratio with a reference intensity ratio prepared in advance (for example, an intensity ratio obtained at normal time). It can be determined whether or not. When an intensity ratio that is significantly different from the reference intensity ratio is calculated, it is understood that there is some abnormality in the inspection area. As an example, if the strength ratio obtained in the inspection is larger than the reference strength ratio, the cast product is classified as passing the quality, and if the strength ratio obtained in the inspection is smaller than the reference strength ratio, the cast product is inferior in quality. being classified.

The typical sectional view showing the internal structure of the coarse material of coarse structure. The typical sectional view showing the internal structure of the coarse material of dense structure. The typical sectional view showing the internal structure of the coarse material of two-layer structure. The flowchart which shows the inspection method of an Example. Explanatory drawing of infrared rays A1 by thermal radiation and infrared rays A2 by reflection. The table | surface which shows the master thermal radiation infrared rays ratio of each test | inspection area | region.

The characteristics of the inspection method according to the example are listed below.
(Feature 1) The embodiment relates to a method of inspecting a die-cast product cast using a cavity surface coated with fibrous carbon.
(Feature 2) A plurality of inspection areas are defined on the surface of the die-cast product.
(Feature 3) Infrared intensity is detected for each inspection region, and an intensity ratio is calculated for each inspection region.
(Characteristic 4) A normal thermal radiation infrared ray ratio is determined for each inspection region. The “thermal radiation infrared ratio at normal time” means the thermal radiation infrared ratio of a casting that has passed a predetermined quality standard.
(Feature 5) For each inspection region, the detected intensity ratio is compared with the normal thermal radiation infrared ratio.

  In the inspection method of the embodiment, a die-cast product is inspected. First, the die cast product to be inspected will be described. The die-cast product to be inspected by the inspection method of the example is manufactured by pouring a molten metal of Al (aluminum) added with a small amount of other metals (Cu, Si, Mg, etc.) into a mold and solidifying the molten metal. Is done. When the molten metal solidifies, first, primary crystals are precipitated in the molten metal. As the temperature of the molten metal decreases, the number of primary crystals increases and the particle size of each primary crystal increases. When the temperature further decreases, the molten metal around the primary crystal solidifies to become a eutectic. Therefore, a large number of primary crystals exist inside the rough material of the die cast product. The particle size of the primary crystal varies greatly depending on the cooling rate when the molten metal is cooled. Generally, the faster the melt is cooled, the smaller the primary crystal grain size. The smaller the primary crystal grain size, the higher the strength of the rough material of the die-cast product.

  The die-cast product to be inspected by the inspection method of this embodiment is manufactured using a mold in which fibrous carbon (carbon nanofiber, carbon nanotube, etc.) is applied to the cavity surface. For details of the aluminum die casting method using fibrous carbon, refer to Japanese Patent Publication No. 2010-131651. Fibrous carbon is applied only to a part of the cavity surface. The cavity surface to which the fibrous carbon is applied is a surface on which a portion requiring particularly high strength is formed in the die cast product. In addition, there is a surface on which the fibrous carbon is not applied on the cavity surface. The surface not coated with fibrous carbon includes a surface covered with a heat insulating material and a surface not covered with any of the fibrous carbon and the heat insulating material. The molten metal cooling process varies depending on the type of cavity surface. Below, the cooling process of a molten metal is demonstrated for every kind of cavity surface.

  First, the cavity surface covered with the heat insulating material will be described. The cavity surface near the gate is covered with a heat insulating material. For this reason, in this region, it is difficult to transfer heat from the molten metal to the mold. That is, the molten metal is difficult to be cooled. Therefore, the molten metal can easily flow in the vicinity of the gate, and the molten metal can be spread over the entire cavity. In the stage of cooling the molten metal after filling the cavity with the molten metal, the molten metal is slowly cooled in this region. Therefore, in the coarse material solidified in this region, as shown in FIG. In this case, the primary crystal grain size is 12 μm or more. Hereinafter, the structure of a coarse material having a large primary crystal grain size as shown in FIG. 1 is referred to as a coarse structure. A coarse material having a coarse structure has low strength. Therefore, the position of the gate of the mold is taken into consideration so that only a portion of the die-cast product where the strength is not so required has a coarse structure. As described above, normally, only a portion of the die-cast product that does not require so much strength has a coarse structure, but if an abnormality occurs during casting, the other portion may have a coarse structure. When the particle size of the primary crystal is large, the surface of the coarse material naturally becomes rough. That is, the surface of the coarse material having a coarse structure becomes rough (the surface roughness becomes high).

  Next, the cavity surface covered with fibrous carbon will be described. While the molten metal is flowing into the cavity, the thermal conductivity of the fibrous carbon on the cavity surface is low. For this reason, heat is not easily transmitted from the molten metal to the mold, and the molten metal flows easily. When the cavity is filled with the molten metal, high pressure is applied to the fibrous carbon on the cavity surface, and the thermal conductivity of the fibrous carbon increases. As a result, heat is removed from the molten metal and the molten metal is solidified. Thus, in the region near the cavity surface covered with the fibrous carbon, the entire molten metal in this region is rapidly cooled from the timing when the cavity is filled with the molten metal. Therefore, the coarse material solidified in this region has a smaller particle size of the primary crystal 100 as shown in FIG. In this case, the primary crystal grain size is less than 5 μm in the region on the surface side, and the primary crystal grain size increases toward the inner side, but the primary crystal grain size is also less than 12 μm in the innermost region. Hereinafter, the structure in which the grain size of the primary crystal 100 is small as shown in FIG. 2 is referred to as a dense structure. A coarse material having a dense structure has high strength. Since the coarse material having a dense structure is formed of fibrous carbon having a rough surface, the surface of the coarse material having a dense structure becomes rough (the surface roughness increases).

  Next, the cavity surface not covered with fibrous carbon or heat insulating material will be described. Since the cavity surface is not covered with a heat insulating member, heat is easily transmitted from the molten metal to the mold in this region. For this reason, when the molten metal starts to flow into the cavity, the molten metal is cooled and solidified on the cavity surface. Thereafter, when the cavity is filled with the molten metal, heat is gradually taken away from the molten metal at a position away from the cavity surface, and the entire molten metal is solidified. Thus, in this region, the molten metal is rapidly cooled on the cavity surface, and the molten metal is slowly cooled at a position away from the cavity surface. Therefore, as shown in FIG. 3, the coarse material solidified in this region has a small particle size of the primary crystal 100 in the region 102 on the surface side, but a large particle size of the primary crystal 100 in the region 104 inside. In this case, the grain size of the primary crystal is less than 5 μm in the region 102 on the surface side, but is 12 μm or more in the region 104 on the inner side. Hereinafter, a structure in which the grain size of the primary crystal is extremely larger in the region on the inner side than the region on the surface side as shown in FIG. 3 is referred to as a two-layer structure. A coarse material having a two-layer structure has lower strength than a coarse material having a dense structure. In the coarse material having the two-layer structure, the grain size of the primary crystal in the region on the surface side is small, so that the surface of the coarse material having the two-layer structure becomes smooth (the surface roughness becomes low).

  Next, the inspection method of the embodiment will be described. The inspection area that is the target for performing the inspection method of the embodiment is determined in advance. A plurality of inspection areas are predetermined on the surface of the die-cast product. In the following description, it is assumed that there are three inspection regions B1 to B3. In this inspection method, each process is performed according to the flowchart shown in FIG.

  In step S2, a die-cast product that is still hot immediately after being taken out of the mold is photographed by a thermography device. As shown in FIG. 5, the thermography device 120 detects infrared rays from the die cast product 110. Thereby, the thermography device 120 outputs an image showing the infrared intensity distribution on the surface of the die-cast product 110. In this embodiment, a general-purpose thermography apparatus is used. For this reason, the thermography device outputs an image indicating a temperature distribution obtained by converting the detected infrared intensity into a temperature. However, as will be described later, infrared rays detected by the thermographic apparatus include infrared rays A1 (infrared rays caused by thermal radiation of die-cast products) correlated with the temperature of the die-cast product, and infrared rays A2 (infrared rays caused by reflection) that have no correlation with the temperature. )It is included. Therefore, it can be said that the data output by the thermography apparatus indicates the infrared intensity distribution in arbitrary units rather than the temperature distribution. The infrared intensity distribution detected in step S2 includes the infrared intensity of the inspection regions B1 to B3 and the infrared intensity of a pseudo black body portion described later.

  In step S4, the infrared intensity of the pseudo black body is specified from the infrared intensity distribution detected in step S2. The “pseudo black body part” is a name given to a part of the surface of the die cast product having a high thermal radiation infrared ray ratio. The pseudo black body portion will be described below. As shown in FIG. 5, infrared rays from the die-cast product 110 (that is, infrared rays detected by the thermography device 120) include infrared rays A1 generated by thermal radiation from the die-cast product 110 and infrared rays that reach the die-cast product 110 from the outside. Infrared rays A2 generated when A3 is reflected from the surface of the die-cast product 110 are included. The ratio of infrared radiation A1 due to thermal radiation in the infrared radiation from the die-cast product 110 is the thermal radiation infrared radiation ratio. Infrared rays A3 from the outside hardly reach the recess 112 formed in the die cast product 110. Therefore, almost no infrared rays A2 are generated from the inside of the recess 112 due to reflection. For this reason, the thermal radiation infrared ray ratio in the recessed part 112 is about 100%. A substance having a thermal radiation infrared ray ratio of 100% is generally called a black body. Since the thermal radiation infrared ray ratio in the recess 112 is approximately 100%, it is referred to herein as a pseudo black body portion. The pseudo black body part for detecting the infrared intensity in step S4 is determined in advance. In the present embodiment, the region having the highest thermal radiation infrared ray ratio in the photographing range by the thermography device 120 is predetermined as the pseudo black body portion.

  In step S6, a thermal radiation infrared ratio distribution on the surface of the die-cast product is calculated from the infrared intensity distribution detected in step S2 and the infrared intensity of the pseudo black body part specified in step S4. That is, as described above, almost all of the infrared rays emitted from the pseudo black body portion are infrared rays caused by thermal radiation. On the other hand, infrared rays emitted from the surface of the die-cast product other than the pseudo black body portion include infrared rays caused by thermal radiation and infrared rays caused by reflection. Moreover, in the die-cast product immediately after taking out from a metal mold | die, temperature is distributed substantially uniformly. Therefore, the intensity of infrared rays emitted by thermal radiation from the surface of the die cast product other than the pseudo black body part is substantially equal to the infrared intensity of the pseudo black body part. For this reason, by dividing the infrared intensity of the pseudo black body portion by the infrared intensity of a predetermined region, the thermal radiation infrared ratio of the region can be calculated. By calculating the thermal radiation infrared ray ratio at each part of the casting product surface, the thermal radiation infrared ray ratio distribution on the surface of the die cast product can be obtained. That is, the infrared intensity of the pseudo black body part is divided by the infrared intensity at each position of the infrared intensity distribution, and the newly generated distribution is the thermal radiation infrared ratio distribution.

  The infrared emissivity of the surface of the die-cast product varies depending on the surface state. The “infrared emissivity” as used herein means the amount of energy radiated from the surface of a substance at a certain temperature and the energy radiated from a black body (a virtual object that absorbs 100% of the energy given by radiation) at the same temperature. The ratio with the quantity. Of the surface of the die-cast product, the infrared emissivity is low at a portion having a smooth surface (low surface roughness). In the portion where the infrared emissivity is low (the portion where the surface is smooth), since the infrared ray is easily reflected on the surface, the ratio of the infrared ray due to reflection increases and the thermal radiation infrared ray ratio becomes low. Therefore, the thermal radiation infrared ray ratio becomes low on the surface of the above-described two-layer structure portion of the surface of the die cast product. On the other hand, the thermal radiation infrared ray ratio becomes high on the surfaces of the dense structure and the coarse structure described above. Therefore, it is possible to determine whether each part of the die-cast product has a two-layer structure from the thermal radiation infrared ray ratio.

  In step S8, the thermal radiation infrared ratio in the inspection regions B1 to B3 is specified from the thermal radiation infrared ratio distribution calculated in step S6. And the thermal radiation infrared rays ratio of test area | region B1-B3 is compared with a master thermal radiation infrared rays ratio. In addition, the master thermal radiation infrared ray ratio defines the normal thermal radiation infrared ray ratio of the inspection region. The “thermal radiation infrared ratio at normal time” means the thermal radiation infrared ratio of a casting that has passed a predetermined quality standard. As shown in FIG. 6, the master thermal radiation infrared ray ratio is determined for each inspection region. The master thermal radiation infrared ray ratio of each inspection area is determined in advance based on the past results. The inspection region B1 is a portion that usually has a two-layer structure. Therefore, the master thermal radiation infrared ray ratio is low. The inspection area B2 is usually a portion having a dense structure. Therefore, the master thermal radiation infrared ray ratio is high. The inspection region B3 is a portion that usually has a two-layer structure. However, since the inspection region B3 is surrounded by ribs, it is difficult for infrared rays due to reflection to occur (the state is close to a pseudo black body portion), and thus the master thermal radiation infrared ray ratio is high.

  For example, when the fibrous carbon peels from the cavity surface in the die casting process, the coarse material solidified in the vicinity of the peeled region has a two-layer structure, and the strength is lower than that of the dense structure. The place that should be a dense structure is a place where strength is required. Therefore, if the portion that should be a dense structure has a two-layer structure, the strength may be insufficient. As described above, the thermal radiation infrared ratio of the two-layered coarse material is lower than the thermal radiation infrared ratio of the denser coarse material. Therefore, it can be seen that if the thermal radiation infrared ratio of the inspection area B2 is lower than the master thermal radiation infrared ratio, it is highly likely that a part of the inspection area B2 has a two-layer structure. As a result, it is possible to detect a defect whose strength does not satisfy a predetermined required specification.

  In addition, a part of the surface of the die cast product may burn into the mold and peel off from the die cast product. Then, the surface of the peeled part becomes rough. Such a defect is called “scissors”. When galling occurs, the thermal radiation infrared ray ratio in that portion increases. Also, when other defects such as hot water wrinkles occur, the surface becomes rough and the thermal radiation infrared ray ratio increases. Therefore, when the thermal radiation infrared rays ratio of inspection area | region B1-B3 is higher than the master thermal radiation infrared radiation ratio, it turns out that defects, such as galling and hot water wrinkles, exist in the inspection area | region.

  As described above, in step S8, the presence / absence of abnormality in each inspection area is determined by comparing the thermal radiation infrared ratio of each inspection area B1 to B3 with the master thermal radiation infrared ratio. Note that a series of processing in steps S4 to S8 is executed by an arithmetic device (not shown) connected to the thermography device.

  In step S10, each inspection area B1 to B3 is hit with a hitting means such as an iron ball, and the sound generated by this is detected by a sound collecting microphone. Further, the frequency of the waveform detected by the microphone is analyzed by an arithmetic device connected to the microphone. Thereby, the natural frequency of the die-cast product is detected. Furthermore, the sound attenuation rate is detected. Further, the arithmetic device determines pass / fail of each inspection region based on the detected natural frequency and attenuation rate.

  When frequency analysis is performed on the sound waveform generated by hitting a die-cast product, peaks (maximum values) are usually obtained at several frequencies. In the case of the present embodiment, maximum values are obtained in a low frequency region of about 100 Hz, a medium frequency region of about 1 kHz, and a high frequency region of about 10 kHz. These frequencies are unique frequencies for each die-cast product. The natural frequency in the low frequency region varies depending on the shape of the die cast product. Therefore, the difference between the natural frequency in the low frequency region and a predetermined frequency (the natural frequency in the low frequency region obtained with a non-defective product) is calculated, and the die-cast product has the shape as designed based on the difference. It can be determined whether or not. The natural frequency in the middle frequency region varies depending on the thickness of the hit region. Calculate the difference between the natural frequency in the middle frequency range and the frequency determined in advance (the natural frequency in the middle frequency range obtained with a non-defective product), and based on the difference, the hit area is as designed. It can be determined whether or not. In addition, the natural frequency in the medium frequency region may change when the coarse material has a two-layer structure or when there is a cast hole in the coarse material. Therefore, the presence or absence of these can also be inspected based on the natural frequency in the middle frequency range. The natural frequency in the high frequency region varies depending on the grain size of the primary crystal inside the rough material in the struck region. If the particle size of the primary crystal is large, the natural frequency in the high frequency region is low, and if the particle size of the primary crystal is small, the natural frequency in the high frequency region is high. For this reason, if the hit region is a dense structure or a two-layer structure, the natural frequency in the high frequency region is high, and if the hit region is a coarse structure, the natural frequency in the high frequency region is low. That is, the difference between the natural frequency in the high frequency region and a predetermined frequency (the natural frequency in the high frequency region obtained with a non-defective product) is calculated, and based on the difference, whether the hit region has a coarse structure It can be determined whether or not. In the inspection by the thermal radiation infrared ratio described above, it is possible to determine whether or not it has a two-layer structure. Therefore, by combining the inspection by the thermal radiation infrared ratio and the inspection by the natural frequency in the high frequency region, It is possible to accurately specify whether each part has a dense structure, a coarse structure, or a two-layer structure.

  Further, the attenuation rate of the sound generated by hitting varies depending on the presence or absence of cracks in the hit area. If any abnormality occurs in the die casting process, minute cracks may occur on the surface of the die cast product or in the vicinity of the surface. When a crack is generated, the attenuation rate is increased. When no crack is generated, the attenuation rate is decreased. Therefore, the presence or absence of a crack in the vicinity of the inspection region can be determined by detecting the attenuation rate.

  In addition, when the determination is made based on the natural frequency and the sound attenuation rate, the sound pressure does not affect the determination result. Therefore, even if the strength when hitting the die-cast product varies, it is possible to make an accurate determination.

  Step S10 is performed from when the die-cast product is taken out of the mold until it is cooled to room temperature (that is, still in a high temperature state). For this reason, the temperature of the die-cast product at the time of executing step S10 varies depending on the cooling rate of the die-cast product, the time from when the die-cast product is taken out until the step S10 is executed, and the like. The above-described natural frequency and damping rate also change depending on the temperature of the die cast product. That is, a large error occurs in the natural frequency and damping rate detected in step S10 depending on the temperature of the die cast product. However, this temperature error can be corrected if the temperature of the die-cast product is known. In the inspection method of this embodiment, in step 4, the infrared intensity of the pseudo black body is specified. As described above, the infrared intensity of the pseudo black body portion represents the temperature of the die cast product. Therefore, in step S10, it is possible to accurately inspect the natural frequency and the damping rate by correcting the error due to temperature.

  As described above, according to the inspection method of the present embodiment, it is possible to accurately specify whether each inspection region of the die-cast product has a dense structure, a two-layer structure, or a coarse structure. it can. Further, according to this inspection method, it is possible to inspect whether or not each inspection region of the die-cast product has defects such as cracks, galling, hot water wrinkles, and cast holes. Further, this inspection method can inspect a high-temperature die-cast product immediately after being taken out from the mold. There is no need to wait for the die-cast product to cool to room temperature. Therefore, a die-cast product can be efficiently manufactured by applying this inspection method to a die-cast product manufacturing line.

  Further, according to the thermography apparatus, a wide range of infrared intensity distribution can be detected in a short time. Moreover, according to the thermography apparatus, the infrared intensity distribution of the die-cast product can be detected in a non-contact manner. That is, it is not necessary to install equipment on the die cast product for inspection. Therefore, the die cast product can be inspected in a short time.

  In the above-described embodiment, the sound frequency and attenuation rate are detected in step S10. However, the sound speed in the die-cast product may be detected. The speed of sound in a die-cast product varies depending on the internal structure of the die-cast product. Therefore, it is possible to inspect whether there is an abnormality in the internal structure of the die-cast product depending on the speed of the detected sound.

  Further, in the above-described embodiment, the pseudo black body part for detecting the infrared intensity in step S4 is determined in advance. This pseudo black body portion can be determined as follows. First, a die-cast product manufactured on the manufacturing line is prepared, and a thermocouple is attached to a concave portion (a portion that can be used as a pseudo black body portion) of the die-cast product. Next, the die-cast product is placed in a thermostatic bath and heated for a predetermined time. Next, the die-cast product is taken out from the thermostat, and the infrared intensity distribution on the surface of the die-cast product is detected by a thermography device. As described above, according to the thermography apparatus, the infrared intensity is output as a value converted into temperature. Next, a location where the difference between the temperature detected by the thermocouple and the temperature output by the thermography device is small is specified. Thus, the region where the difference between the temperature detected by the thermocouple (actual temperature) and the temperature output by the thermographic device (temperature converted from the infrared intensity) is small is used as the pseudo black body portion in step S4. be able to.

  In the above-described embodiment, the pseudo black body part for specifying the infrared intensity in step S4 is determined in advance. However, the pseudo black body part for detecting the infrared intensity in step S4 is determined according to the detection result in step S2. It may be changed.

  In the inspection method of the embodiment, the thermal radiation infrared ratio distribution on the surface of the die-cast product is calculated from the infrared intensity distribution detected in step S2 and the infrared intensity of the pseudo black body part specified in step S4. Specifically, the infrared radiation intensity of the inspection area is calculated by dividing the infrared intensity of the pseudo black body part by the infrared intensity of the inspection area. A value obtained by dividing the infrared intensity of the pseudo black body portion by the infrared intensity of the inspection area corresponds to an intensity ratio (ratio of the infrared intensity of the inspection area to the infrared intensity of the high radiation area).

  In the inspection method of the embodiment, the region having the highest thermal radiation infrared ray ratio in the measurement range of the infrared intensity by the thermography device is specified as the pseudo black body part, and the intensity ratio is as described above using the infrared intensity of the pseudo black body part. Was calculated. When multiple areas that can be used as a pseudo black body part are assumed, an area having a thermal radiation infrared ray ratio higher than a predetermined reference value (reference thermal radiation infrared ray ratio) is specified as a pseudo black body part. May be. That is, the inspection method of the embodiment detects the infrared intensity of the high radiation area (pseudo black body portion) whose thermal radiation infrared ray ratio is higher than the reference value on the casting product surface, and the infrared intensity of the inspection area on the casting product surface. Then, the ratio (intensity ratio) between the infrared intensity of the inspection area and the infrared intensity of the high emission area is calculated.

  In the inspection method of the embodiment, the quality of the cast product is determined using the obtained strength ratio as an index. Specifically, pass / fail is determined by comparing the obtained intensity ratio with the master thermal radiation infrared ray ratio. The “master thermal radiation infrared ray ratio” corresponds to the intensity ratio of the inspection region in the cast product determined to be non-defective. That is, the “master thermal radiation infrared ray ratio” corresponds to the “reference intensity ratio”.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

100: Primary crystal 110: Die-cast product 112: Recess 120: Thermography device

Claims (4)

A method for inspecting a cast product,
Detecting the infrared intensity of the high radiation area where the ratio of thermal radiation infrared radiation is higher than the reference value on the casting surface, and detecting the infrared intensity of the inspection area defined as the inspection target on the casting surface;
Calculating the ratio between the infrared intensity of the examination area and the infrared intensity of the high radiation area;
The inspection method characterized by having.   The inspection method according to claim 1, further comprising a step of detecting a frequency of a sound generated by hitting the inspection area.   The inspection method according to claim 1, further comprising a step of detecting an attenuation rate of sound generated by hitting the inspection area.   The inspection method according to claim 1, further comprising a step of classifying the quality of the inspection region by comparing the calculated ratio with a reference intensity ratio prepared in advance.

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