JP5732826B2 - 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 estimating whether there is an abnormality in 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. It is known that the strength of a cast product depends on the presence of a cast hole or a crack or the size of the particle size.

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 taken out from the mold is cooled and the cast product cannot be inspected until the temperature is stabilized. If the cooling time for the inspection can be shortened, the production efficiency of the cast product can be improved. In other words, if inspection of a cast product in a high temperature state can be performed quickly, 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 an inspection method capable of quickly inspecting a cast product in a high temperature state.

The casting inspection method disclosed in the present specification includes a cooling step of cooling the casting and detecting a temperature decrease amount of an inspection region defined as an inspection target on the surface of the casting.
In the method for inspecting a cast product according to the present invention, the cast product is formed by a first region formed by a cavity surface covered with fibrous carbon and a cavity surface not covered by the fibrous carbon and the heat insulating material. It has the 2nd field. The inspection method includes a cooling step for cooling the cast product, detecting a temperature drop amount of the test region defined as an inspection target in each of the first region and the second region on the surface of the cast product, and the temperature of the first region. Comparing the amount of decrease with the first reference temperature decrease amount and comparing the temperature decrease amount of the second region with the second reference temperature decrease amount. The first reference temperature decrease amount is larger than the second reference temperature decrease amount.

  A region where defects are generated in a cast product generally has high heat insulation (low thermal conductivity). For this reason, when the cast product is cooled, there is a difference in the amount of temperature drop during cooling between a region where defects are present and a region where defects are not present. In the region where the defect exists, the heat conduction is hindered by the defect, so that the heat inside the casting is hardly dissipated. On the other hand, in the area where no defect exists, the inside of the cast product is well cooled. For this reason, even if the entire cast product is uniformly cooled, when viewed locally, the region where the defect exists has more residual heat than the region where the defect does not exist. In other words, the temperature of the surface of the region where the defect exists is less likely to decrease the temperature than the surface of the region where the defect does not exist, and the temperature decrease amount is small. In this inspection method, the casting is cooled and the temperature drop in the inspection region is detected. Therefore, the presence or absence of a defect in the inspection region can be specified based on the detected temperature decrease amount. Further, the temperature of the inspection region (that is, the cast product surface) can be detected in a non-contact manner by a thermography device or the like. That is, the amount of temperature decrease can be detected without contact. In this inspection method, it is necessary to cool the cast product, but it is sufficient that the cast product is cooled to some extent, and it is not necessary to cool the cast product until the temperature of the cast product is stabilized as in the conventional inspection method. Therefore, according to this inspection method, a cast product in a high temperature state can be inspected quickly. Note that the temperature decrease amount may be calculated by detecting the temperature of the inspection region before and after cooling. Further, when the temperature of the inspection area before cooling is known, it is possible to detect the temperature decrease amount by detecting only the temperature of the inspection area after cooling.

  It is preferable that the inspection method described above further includes a local heating step of locally heating the inspection region and detecting a temperature rise rate of the inspection region after the cooling step.

  When the casting surface is locally heated, the temperature of the casting surface increases. At this time, there is a difference in the amount of temperature rise during heating between a region where defects are present and a region where defects are not present. In areas where defects are present, after the pre-cooling step, more heat remains in the casting compared to areas where no defects exist (ie, the interior of the casting is maintained at a high temperature). ). For this reason, on the surface of the cast product in which defects are present, the amount of temperature increase during local heating increases. On the other hand, the surface of the cast product having no defects inside is cooled to the inside of the cast product in a cooling step performed in advance. Therefore, on the surface of the cast product in a region where no defect exists, the amount of temperature increase is small during local heating. In the inspection method described above, after the cooling step, the inspection region is locally heated and the temperature rise in the inspection region is detected. A defect in the inspection region can be identified from the detected temperature rise amount. In this inspection method, the inspection region is locally heated. According to the local heating, the temperature of the inspection region can be changed more rapidly than the cooling in the cooling step. In this way, it is possible to specify the defect more accurately by changing the temperature of the inspection region more rapidly and specifying the temperature change amount.

  In the inspection method described above, it is preferable to cool the casting by submerging the casting in the cooling step. According to such a configuration, the cast product can be easily cooled.

  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, the abnormality (defect) of the rough material in the inspection region can be specified by detecting the frequency of the sound generated by hitting the inspection region. 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. By using a combination of the inspection based on these sounds and the above-described inspection based on the temperature drop amount, a more precise inspection can be performed.

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 typical sectional view showing the internal structure of the rough material which has crack-like defect 108. FIG. FIG. 3 is a schematic cross-sectional view showing an internal structure of a coarse material having a cast hole 110. The flowchart which shows the inspection method of an Example. The flowchart which shows the inspection method of an Example (continuation of FIG. 6). Explanatory drawing of infrared rays A1 by thermal radiation and infrared rays A2 by reflection. The table | surface which shows temperature T0 of each area | region, temperature difference (DELTA) T, and master temperature difference (DELTA) TM.

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 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.
(Characteristic 3) A normal amount of temperature drop during cooling is determined for each inspection region. The “normal temperature drop” means the temperature drop of a casting that has passed a predetermined quality standard.
(Feature 4) The amount of temperature drop during cooling is detected for each inspection region. Then, the detected temperature decrease amount is compared with the normal temperature decrease amount for each inspection region.
(Feature 5) In the cooling step, the die-cast product is cooled for a predetermined time. Since the cooling time is determined, the above-described temperature decrease amount is equivalent to the temperature decrease rate.
(Characteristic 6) A normal temperature increase amount during local heating is defined for each inspection region. The “normal temperature rise” means the temperature rise of a casting that has passed a predetermined quality standard.
(Characteristic 7) The temperature rise amount at the time of local heating is detected for each inspection region. Then, the detected temperature increase amount is compared with the normal temperature increase amount for each inspection region.
(Feature 8) In the local heating step, the examination region is heated for a predetermined time. Since the heating time is determined, the above-described temperature increase amount is equivalent to the temperature increase rate.

  In the inspection method of the embodiment, a die-cast product is inspected. First, a die cast product to be inspected will be described. The die-cast product to be inspected by the inspection method of the embodiment is manufactured by pouring a molten alloy of Al (aluminum) with a small amount of other metals (Cu, Si, Mg, etc.) into the 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 in the die cast coarse material. The particle diameter of the primary crystal varies 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 die cast crude material.

  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 molded out of 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 the 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 where the strength is not so required has a coarse structure, but if an abnormality occurs during casting, the other portion may have a coarse structure. A coarse material having a coarse structure has a high thermal conductivity as long as there are no defects such as cracks and cast holes inside. Therefore, when a coarse material having a coarse structure is heated or cooled from the surface side, the temperature easily changes to the inside of the coarse material.

  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. A coarse material having a dense structure has a high thermal conductivity as long as there are no defects such as cracks and cast holes inside. Accordingly, when a coarse material having a dense structure is heated or cooled from the surface side, the temperature easily changes to the inside of the coarse material.

  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 a coarse material having a dense structure, the grain size of the primary crystal changes extremely at the boundary 106 between the surface region 102 and the inner region 104, and this boundary 106 becomes a heat insulating layer. Therefore, when the two-layered coarse material is heated or cooled from the surface side, the heat conduction is hindered by the boundary 106, and therefore, the temperature inside the coarse material (that is, the region 104 on the inner side) hardly changes.

  In addition, various defects may occur inside the die cast product. As shown in FIG. 4, there may be a crack-like defect 108 extending in a layer form in the very vicinity of the surface of the die-cast product. The crack-like defect 108 becomes a heat insulating layer. Therefore, when the coarse material at the location where the crack-like defect 108 exists is heated or cooled from the surface side, the heat conduction is hindered by the defect 108, so that the temperature inside the coarse material is difficult to change.

  Further, as indicated by reference numeral 110 in FIG. 5, a cavity defect called a cast hole may be formed inside the die-cast product. The cast hole 110 becomes a heat insulating layer. Accordingly, when the rough material at the location where the cast hole 110 is present is heated or cooled from the surface side, the heat conduction is inhibited by the cast hole 110, and therefore, the interior of the rough material (that is, the inner side of the cast hole 110). Area) is hard to change in temperature. However, the cast hole is often small in size. A small cast hole has little effect on the temperature change of the coarse material.

  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 flowcharts shown in FIGS.

  In step S2, a die-cast product that is still hot immediately after being taken out from the mold is photographed by the thermography device. The die-cast product is taken out from the mold at a stage where the temperature is distributed within a range of about 200 to 300 ° C. after being cooled inside the mold. After the die-cast product is taken out from the mold, heat conduction occurs inside the die-cast product, and the temperature distribution in the die-cast product becomes more uniform. The temperature of the die-cast product at this time is about 200 to 250 ° C. That is, in the die-cast product immediately after being taken out from the mold, the temperature is substantially uniformly distributed within a range of about 200 to 250 ° C. As shown in FIG. 8, the thermography device 120 detects infrared rays from the die-cast product 111. As a result, the thermography device 120 outputs an image showing the infrared intensity distribution on the surface of the die-cast product 111. 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, the infrared rays detected by the thermographic apparatus include infrared rays A2 (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. 8, infrared rays from the die-cast product 111 (that is, infrared rays detected by the thermography device 120) include infrared rays A1 generated by thermal radiation from the die-cast product 111 and infrared rays that reach the die-cast product 111 from the outside. Infrared rays A2 generated when A3 is reflected from the surface of the die-cast product 111 are included. The ratio of infrared rays A1 due to thermal radiation in the infrared rays from the die-cast product 111 is the thermal radiation infrared ray ratio. Infrared rays A3 from the outside hardly reach the recess 112 formed in the die-cast product 111. 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. And the thermal radiation infrared ray ratio of test | inspection area | region B1-B3 is specified from the calculated thermal radiation infrared ray ratio distribution. Here, as described above, substantially 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 distributes substantially uniformly in the range of 200-250 degreeC. 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 in 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 obtained thermal radiation infrared ray ratio distribution includes the thermal radiation infrared ray ratios of the inspection regions B1 to B3. Therefore, the thermal radiation infrared ray ratio of the inspection regions B1 to B3 can be specified from the thermal radiation infrared ray ratio distribution.

  The series of processing in steps S4 to S6 described above is executed by an arithmetic device (not shown) connected to the thermography device. The calculation using the detection value of the thermography apparatus described later is also executed by this calculation apparatus.

  In step S8, the die-cast product is submerged. The die-cast product is submerged in the water stored in the container. As a result, the die-cast product is cooled. When a predetermined time elapses while the die-cast product is submerged, the die-cast product is pulled up from the water. Then, water droplets on the surface of the die cast product are removed.

  In step S10, the die-cast product is photographed by the thermography device 120 in the same manner as in step S2. Thereby, the infrared intensity distribution on the surface of the die-cast product is detected. The infrared intensity distribution detected in step S10 includes the infrared intensity of the inspection regions B1 to B3 and the infrared intensity of the pseudo black body portion.

  In step S12, the temperature of the pseudo black body portion and each of the inspection regions B1 to B3 is calculated. The temperature of the pseudo black body part is calculated by converting the infrared intensity of the pseudo black body part detected in step S10 into a temperature. Since the pseudo black body portion has a thermal radiation infrared ray ratio of approximately 100%, the infrared intensity detected in step S10 can be directly converted into a temperature. In the case of the present embodiment, the pseudo black body portion has any temperature within a range of 200 to 250 ° C., and is a representative point of the temperature of the die cast product. On the other hand, the temperatures of the inspection regions B1 to B3 are calculated as follows. First, the infrared intensity of each inspection region B1 to B3 detected in step S10 is multiplied by the thermal radiation infrared ratio of each inspection region B1 to B3 calculated in step S6. Thereby, the infrared intensity due to the heat radiation generated in each of the inspection regions B1 to B3 after cooling (when executing step S10) is calculated. Next, the calculated infrared intensity by thermal radiation is converted into temperature. Thereby, the temperature after cooling of each inspection area | region B1-B3 is calculated correctly. As described above, the temperature of the die-cast product before cooling (immediately after taking out from the mold) is substantially uniformly distributed within a range of 200 to 250 ° C. (that is, the temperature before cooling of each inspection region is known). Is). Therefore, calculating the temperatures of the inspection regions B1 to B3 after cooling is equivalent to calculating the amount of temperature decrease in the cooling process of these regions. FIG. 9 illustrates the temperature T0 of each region obtained in step S12. The inspection region B1 is a portion that should have a two-layer structure, and the inspection regions B2 and B3 are portions that should have a dense structure. As shown in FIG. 9, in the inspection region B1 that should have a two-layer structure, the temperature T0 after cooling is usually higher than the inspection regions B2 and B3 that should have a dense structure (that is, the amount of temperature decrease is small). ).

  In step S14, as shown in FIG. 9, a temperature difference ΔT between each of the inspection regions B1 to B3 and the pseudo black body portion is calculated.

  In step S16, the temperature difference ΔT calculated for each of the inspection regions B1 to B3 in step S14 is compared with the master temperature difference ΔTM. The master temperature difference ΔTM is predetermined for each inspection region. The master temperature difference ΔTM in each inspection area is shown in FIG. The master temperature difference ΔTM defines a normal temperature difference ΔT between the inspection regions B1 to B3. The normal temperature difference ΔT means a temperature difference ΔT obtained with a die-cast product that passes a predetermined quality standard. Naturally, when measuring the temperature difference of a die-cast product that has passed a predetermined quality standard, the temperature difference is the same as when measuring the temperature difference of the die-cast product to be inspected (temperature before cooling or cooling conditions). Measure.

  If the temperature difference ΔT is smaller than the master temperature difference ΔTM, it means that the inspection region is colder than usual, and if the temperature difference ΔT is larger than the master temperature difference ΔTM, the inspection region is smaller than usual. It means not cold. When the temperature difference ΔT of the inspection region B1 that should have a two-layer structure is extremely larger than the master temperature difference ΔTM (when it is not cooler than usual), the boundary portion of the two-layer structure (in the inspection region B1) It is considered that a defect (for example, a crack-like defect or a cast hole) having a greater heat insulation than the boundary 106) in FIG. 3 exists. In addition, when the temperature difference ΔT between the inspection regions B2 and B3 to be a dense structure is extremely larger than the master temperature difference ΔTM (when it is not cooled more than usual), the coarse materials in the inspection regions B2 and B3 are two layers. It is considered that there is a structure or there is a defect with high heat insulation inside the inspection regions B2 and B3. Since the inspection regions B2 and B3 that should have a dense structure are places where strength is required, if the inspection regions B2 and B3 have a two-layer structure, the strength may be insufficient. Thus, it can be considered that one of the defects is that the region to be a dense structure has a two-layer structure. In step S16, the presence or absence of a defect in each inspection region is determined by comparing the temperature difference ΔT in each inspection region with the master temperature difference ΔTM. For example, in the example of FIG. 9, when the difference between the temperature difference ΔT and the master temperature difference ΔTM is 10 ° C. or more, it is determined that there is an abnormality (the inspection area has a defect). In the inspection areas B1 and B3, the temperature difference ΔT is close to the master temperature difference ΔTM. Therefore, it is determined that the inspection areas B1 and B3 are not abnormal. On the other hand, in the inspection region B2, the temperature difference ΔT is 26 ° C. higher than the master temperature difference ΔTM. For this reason, it is determined that the inspection area B2 is abnormal.

  In step S16, the presence or absence of a defect is determined based on the temperature difference ΔT calculated in step S14, not the temperature (degrees Celsius) calculated in step S12. The temperature difference ΔT indicates the relative temperature of the inspection region with respect to the pseudo black body portion. In this way, the reason why the defect is specified based on the temperature difference ΔT is that the temperature of the entire die-cast product may increase or decrease due to variations in the conditions of each process. By using the temperature difference ΔT, it is possible to specify the defect by eliminating the influence of the temperature variation of the entire die cast product. However, when the inspection is performed in an environment where the temperature variation of the entire die-cast product does not occur so much, the inspection may be performed using the temperature T0 instead of the temperature difference ΔT.

  Further, it is necessary to remove water droplets and the like after the die-cast product is lifted from the water in step S8 until the die-cast product is photographed by the thermography device in step S10. For this reason, the time interval from when the die-cast product is lifted out of the water to when the image is taken by the thermography device is increased to some extent. For this reason, the temperature distribution on the surface of the die-cast product is homogenized during this time, and the temperature difference due to the defect may disappear. For this reason, in step S16, a relatively large defect can be identified, but it is difficult to identify a small defect. Therefore, in this inspection method, the process after step S18 is implemented following step S16 (FIG. 7).

  In step S <b> 18, the inspection regions B <b> 1 to B <b> 3 are locally heated by a halogen heater or the like while photographing with the thermography device 120. Local heating is performed for a predetermined time. And the thermography apparatus 120 detects the variation | change_quantity of the infrared intensity before and behind local heating of each test | inspection area | region B1-B3. Step S18 is performed for each of the inspection areas B1 to B3. Next, in step S20, from the amount of change in the infrared intensity of each inspection region B1 to B3 detected in step S18 and the thermal radiation infrared ratio of each inspection region B1 to B3 calculated in step S6, local heating in step S18 is performed. The temperature rise amount of each inspection area | region B1-B3 before and behind is calculated.

  In step S22, the temperature increase amount of each of the inspection regions B1 to B3 calculated in step S20 is compared with the master temperature increase amount. The master temperature increase amount is predetermined for each inspection region. The master temperature rise amount defines the temperature rise amount that is normally obtained in step S20 in each of the inspection regions B1 to B3. The normal temperature rise means the temperature rise obtained with a die-cast product that passes a predetermined quality standard.

  A temperature rise amount smaller than the master temperature rise amount means that the inspection region has not risen more than usual, and a temperature rise amount larger than the master temperature rise amount means that the inspection region is normal. It means that the temperature is rising. In a coarse material having a two-layer structure and a coarse material having a heat insulation defect, the inside of the coarse material is maintained at a high temperature at the start of the local heating step because the inside is difficult to be cooled in the cooling step. Therefore, the surface area of such a rough material is heated from both the front side and the inner side in the local heating in step S18. For this reason, the temperature of the surface of the coarse material rises rapidly. Therefore, such a rough material has a large temperature rise. By comparing the temperature increase amount of each inspection region with the master temperature increase amount, it is possible to determine the presence or absence of a defect in each inspection region.

  As described above, the inspection region where the temperature drop is smaller than usual in step S16 is a region having a two-layer structure, a region where a crack-like defect is present, or a region where a cast hole is present. If the inspection area where the temperature drop is smaller than normal in step S16 and the temperature rise is larger than normal in step S22, the inspection area is a two-layer structure area or an area where crack-like defects exist. It is believed that there is. In addition, when the inspection region in which the temperature drop is smaller than normal in step S16 rises to normal and the identification degree in step S22, this inspection region is considered to be a region where a cast hole exists. As described above, the difference in temperature rise between the two-layer structure and crack-like defects and the cast hole is because the two-layer structure and crack-like defects spread in the form of a plane, so the influence of heat insulation is affected over a wide range. On the other hand, since the casting hole is a point-like defect, heat is easily conducted between the surface side and the inner side of the coarse material through the periphery of the casting hole. In addition, when there is a cast hole in the inspection area, a circular pattern may be seen in the output image of the thermography apparatus. As described above, in the region where it is determined that there is a defect in step S16, it can be determined in step S22 whether the defect is a cast hole or another defect.

  In addition, the inspection region where the temperature drop is about the same as normal in step S16 is a dense structure region or a coarse structure region. However, even in the region of the two-layer structure, if the difference in the primary crystal grain size is small between the front side and the inner side, it may be determined in step S16 that the temperature drop is about the same as usual. Therefore, the inspection region where the temperature drop is about the same as that in step S16 may include a two-layer structure region. If the inspection region in which the temperature drop is about the same in step S16 is higher than normal in step S22, the inspection region is considered to be a two-layer structure region. If the temperature rises to the same extent as usual in step S22, the inspection region is considered to be a region from a dense structure to a coarse structure. As described above, the inspection region that cannot be specified as the two-layer structure in Step S16 can be specified as the two-layer structure in Step S22 because the temperature in the local heating in Step S18 changes more rapidly than the cooling in Step S8. In this way, by rapidly heating the inspection region by local heating, it is possible to more accurately detect the difference in temperature rise caused by the difference in heat insulation, and to identify the two-layer structure more accurately. .

  As described above, the defect can be identified with a considerably high accuracy by the processing up to step S22. However, in the process up to step S22, it cannot be determined whether the inspection area has a dense structure or a coarse structure. Further, in the processing up to step S22, it is not possible to determine whether the inspection region is a two-layer structure or a region where a crack-like defect exists. Therefore, in the inspection method of the present embodiment, the following steps are further executed.

  In step S24, each inspection area 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. Thus, 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 frequency and attenuation rate.

  When frequency analysis is performed on the sound waveform generated by hitting, normally peaks (maximum values) are obtained at three 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 frequencies unique to 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 the 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 crystals inside the coarse material in the struck region. If the grain size of the crystal inside the coarse material is large, the natural frequency in the high frequency region becomes low, and if the grain size of the crystal inside the coarse material is small, the natural frequency in the high frequency region becomes 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 based on the temperature change described above, it is not possible to determine whether the structure is a dense structure or a coarse structure, but this can be determined in step S24.

  Further, the attenuation rate of the sound generated by hitting varies depending on the presence or absence of cracks in the hit area. 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 the inspection based on the temperature change described above, it cannot be determined whether the defect has a two-layer structure or a crack, but this can be determined in step S24.

  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 S24 is performed before the die-cast product is completely cooled (before the temperature is stabilized). For this reason, the temperature of the die-cast product when executing step S24 varies depending on the cooling rate of the die-cast product, the timing of executing step S24, 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 S24 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, the temperature of each inspection region is measured in step 18. Therefore, in step S24, 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 part of the die-cast product has a dense structure, a two-layer structure, or a coarse structure. Furthermore, according to this inspection method, it is possible to inspect each part of the die-cast product for the presence of defects such as cracks and cast holes. Further, this inspection method can be executed without waiting until the die-cast product taken out from the mold is cooled and the temperature is stabilized. Therefore, even if this inspection method is applied to a production line for die-cast products, the die-cast products can be produced efficiently.

  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, a die-cast product can be inspected without contact. That is, it is not necessary to install a device on a die-cast product for inspection. Therefore, the die-cast product can be inspected in a short time.

  Points to note about the inspection method of the embodiment will be described. In the examples, the casting was cooled from a state where the temperature of the casting was distributed within a range of about 200 to 250 ° C. The temperature of the cast product before cooling is not limited to 200 to 250 ° C., but it is preferable that the temperature of the cast product before cooling is 150 ° C. or higher in order to determine defects based on the amount of temperature decrease before and after cooling. That is, in the cooling step, it is preferable to cool a cast product having a temperature of 150 ° C. or higher after being taken out from the mold.

  Moreover, in the inspection method of an Example, it cooled from the state in which the temperature of a casting is distributed at about 200-250 degreeC. When the temperature before cooling cannot be controlled, it is also preferable to provide a step of measuring the temperature of the inspection region defined as the inspection target on the surface of the casting prior to the cooling step. In this case, the cooling step is performed after measuring the temperature of the inspection region, and then the temperature of the inspection region after cooling is measured. Thus, the amount of temperature decrease in the inspection area before and after cooling is calculated.

  In the case of FIG. 9, assuming that the temperature before cooling is 200 ° C. in any inspection region, the amount of temperature decrease in the region B1 is 200 ° C.-145 ° C. = 65 ° C. The amount of temperature decrease in the region B2 is 200 ° C.-73 ° C. = 127 ° C. The amount of temperature decrease in the region B3 is 200 ° C.-75 ° C. = 125 ° C. Thus, in the embodiment, since the temperature of each inspection region before cooling is known, the temperature of each inspection region after cooling becomes a value corresponding to the amount of temperature decrease in each inspection region. Further, in the example, the quality of the inspection area was determined by comparing the difference ΔT between the cooling temperature of each inspection area and the cooling temperature of the black body portion with the master temperature difference ΔTM. The temperature difference ΔT corresponds to the amount of temperature decrease in the inspection region relative to the black body portion. Therefore, the inspection method of the embodiment also determines pass / fail (that is, whether there is a defect) based on the amount of temperature decrease before and after cooling of each inspection region. The master temperature difference ΔTM is determined based on a temperature decrease amount (reference temperature decrease amount) obtained with a die-cast product that has passed a predetermined quality standard. Therefore, the quality of each inspection region can be accurately determined by comparing the temperature difference ΔT of each inspection region with the master temperature difference ΔT.

  In the above-described embodiment, the sound frequency and attenuation rate are detected in step S10. However, the sound speed in the rough material may be detected. The speed of sound in the coarse material varies depending on the internal structure of the coarse material. Therefore, it is possible to inspect whether there is any abnormality in the internal structure of the coarse material 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 a manufacturing line is prepared, and a thermocouple is attached in 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 Celsius temperature of each inspection region is calculated from the infrared intensity of the inspection region and the infrared intensity of the pseudo black body portion. However, the temperature of each inspection area may be expressed using other arbitrary units. For example, when imaging with a thermography device can be performed in an environment with few error factors, the variation in the thermal radiation infrared ratio in the inspection region is reduced, so the infrared detected by the thermography device without considering the thermal radiation infrared ratio The intensity itself may be used as a value indicating temperature. Even such a value can be inspected for the presence or absence of a defect in the inspection region by comparing with a normal value (master value).

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 108: Defect 110: Cast hole 111: Die-cast product 112: Recess 120: Thermography apparatus

Claims (5)

A method for inspecting a cast product,
The casting has a first region formed by a cavity surface covered with fibrous carbon, and a second region formed by a cavity surface not covered with fibrous carbon and heat insulating material,
A cooling step for cooling the casting, and detecting a temperature drop amount of the inspection area defined as an inspection object in each of the first area and the second area on the surface of the casting;
Comparing the temperature decrease amount of the first region with the first reference temperature decrease amount, and comparing the temperature decrease amount of the second region with the second reference temperature decrease amount;
Have
An inspection method, wherein the first reference temperature decrease amount is larger than the second reference temperature decrease amount . After the cooling step, the local heating step for locally heating the inspection region and detecting the amount of temperature increase in the inspection region;
The inspection method according to claim 1, further comprising:   The inspection method according to claim 1 or 2, wherein, in the cooling step, the cast product is cooled by submerging the cast product.   The inspection method according to claim 1, further comprising a step of detecting a frequency of sound generated by hitting the inspection region.   The inspection method according to claim 1, further comprising a step of detecting an attenuation rate of sound generated by hitting the inspection area.

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