JP7125906B2 - Holding power evaluation method and shrinkage evaluation method - Google Patents

Description

The present invention provides a method for evaluating the holding force of a casting obtained by solidifying a molten metal made of a metal material with respect to a mold forming a cavity, and the amount of shrinkage from the molten metal filled in the cavity. It relates to a shrinkage amount evaluation method for evaluating.

Casting is a well-known method of filling a cavity formed by contacting a plurality of molds with molten metal and solidifying the molten metal to obtain a casting (molded product), and is widely practiced. has reached Here, in order to take out the casting obtained in the cavity, first, the molds are separated from each other. At this time, the casting adheres to one die (usually a fixed die that is positioned and fixed). For this reason, the casting apparatus is provided with a plurality of ejector pins for ejecting the casting from the mold.

That is, the ejector pin slides against the mold and exposes its tip so as to protrude from the mold. As a result of this exposure, the casting is pressed by the ejector pin, and as a result, the casting is released from the mold. The ejector pin is designed to have sufficient rigidity against this pressure, for example, by setting its diameter sufficiently large.

However, the holding force of the cast product against the mold increases contrary to predictions (evaluations), and as a result, a large reaction force may act on some of the ejector pins. In such a case, it becomes difficult to separate the casting from the mold. Conversely, if the holding force is excessively smaller than the evaluation, a large-sized driving device that imparts a large amount of energy is required to operate the ejector pin whose diameter is set excessively large, which is uneconomical. . From such a point of view, it is required to predict the holding force of the casting to the mold.

An analysis method described in Patent Document 1 is known as a technique for analyzing the strain and stress of castings.

JP 2015-132564 A

According to the diligent studies of the present inventors, even if the analysis method described in Patent Document 1 is carried out, the holding power is still highly evaluated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides a method for evaluating a holding force capable of properly evaluating the holding force, and a method for properly evaluating the amount of shrinkage of a cast product from molten metal. An object of the present invention is to provide a method for evaluating the amount of shrinkage.

In order to achieve the above object, according to one embodiment of the present invention, a cast product obtained by solidifying a molten metal made of a metal material in a cavity of a casting apparatus is held against a mold forming the cavity. A holding force evaluation method for evaluating applied force,
A linear expansion coefficient acquisition step of filling a cavity of a measuring device with molten metal and measuring the amount of shrinkage when the molten metal solidifies, and obtaining the linear expansion coefficient of the metal material based on the measured amount of shrinkage;
A shrinkage amount acquisition step of obtaining a shrinkage amount when the molten metal changes into the cast product based on the linear expansion coefficient;
A holding force evaluation step of obtaining a stress using a material model as the amount of shrinkage as a strain and evaluating the stress as a holding force;
A hugging force evaluation method is provided.

It is also possible to evaluate the amount of shrinkage of the casting according to the above. That is, according to another embodiment of the present invention, a shrinkage amount evaluation method for evaluating the amount of shrinkage from the molten metal of a casting obtained by solidifying the molten metal made of a metal material in the cavity of a casting apparatus. There is
A linear expansion coefficient acquisition step of filling a cavity of a measuring device with molten metal and measuring the amount of shrinkage when the molten metal solidifies, and obtaining the linear expansion coefficient of the metal material based on the measured amount of shrinkage;
A shrinkage amount acquisition step of obtaining a shrinkage amount when the molten metal changes into the cast product based on the linear expansion coefficient;
A method for evaluating the amount of shrinkage is provided.

According to the present invention, since the coefficient of linear expansion is obtained by actual measurement, it is possible to accurately evaluate the amount of shrinkage before and after the molten metal solidifies. This shrinkage amount is used as the strain of the stress-strain curve to obtain the stress, and the stress is evaluated as the holding force against the mold. Since the contraction amount is evaluated with high precision, the holding force is also evaluated with high precision.

Based on the evaluated gripping force, when designing the casting apparatus, it is possible to accurately determine what degree of rigidity the ejector pin should be provided. Therefore, it is possible to provide an ejector pin that allows the casting to be easily removed from the mold. Moreover, since it is possible to select a drive device having an appropriate size for driving the ejector pin, it is possible to avoid an increase in size of the casting apparatus by providing a large drive device. Cost reduction can be achieved.

1 is a schematic flow of a hugging force evaluation method according to an embodiment of the present invention; It is a schematic side cross-sectional view of a measuring device for obtaining a coefficient of linear expansion. Fig. 3 is a stress-strain curve at 25°C for the Ohno-Wang model; 2 is the stress-strain curve at 200° C. of the Ohno-Wang model; 2 is the stress-strain curve at 250° C. of the Ohno-Wang model; 3 is the stress-strain curve at 300° C. of the Ohno-Wang model; 3 is the stress-strain curve at 350° C. of the Ohno-Wang model; 4 is the stress-strain curve at 400° C. of the Ohno-Wang model; 4 is the stress-strain curve at 450° C. of the Ohno-Wang model;

Hereinafter, the contraction amount evaluation method according to the present invention will be described in detail with reference to the attached drawings, citing preferred embodiments in relation to the hugging force evaluation method.

FIG. 1 is a schematic flow of a hugging force evaluation method according to this embodiment. This hugging force evaluation method includes a linear expansion coefficient obtaining step S1, a contraction amount obtaining step S2, and a hugging force evaluation step S3. The shrinkage amount evaluation method according to the present embodiment is a part of the hugging force evaluation method, and can be implemented by performing the linear expansion coefficient obtaining step S1 and the shrinkage amount obtaining step S2.

Conventionally, when designing a casting apparatus, it is assumed that the coefficient of linear expansion of the same kind of metal material is constant. The present inventors speculated that this premise contributes to the overestimation or underestimation of the holding force. Therefore, in the linear expansion coefficient acquisition step S1, the linear expansion coefficient of the metal material is actually measured.

In the linear expansion coefficient obtaining step S1, the linear expansion coefficient is obtained when the molten metal made of the metal material solidifies. FIG. 2 shows a measuring device 10 for that purpose. The measuring device 10 has a base 12 and a substantially rectangular parallelepiped lower mold 14 and upper mold 16 (both molds), and a cavity 18 is formed by these lower mold 14 and upper mold 16 . The material of the lower mold 14 and the upper mold 16 and the surface roughness of the part facing the cavity 18 are matched to the material of the mold of the casting apparatus for industrially producing the casting and the surface roughness of the part facing the cavity 18. is preferred. Examples of materials for the lower die 14 and the upper die 16 include alloy tool steel.

Thermocouples 20 are installed at a plurality of locations on the lower die 14 . The tip of the thermocouple 20 faces the cavity 18, so that the temperature of the molten metal M inside the cavity 18 can be measured at all times. One upper mold 16 is formed with a sprue 22 and a runner 24 for pouring the molten metal M into the cavity 18 .

Support plates 26a and 26b are erected at positions of the base 12 facing the longitudinal ends of the lower mold 14 and the upper mold 16, respectively. A pedestal 28b is provided. A first laser transmitter/receiver 30a is positioned and fixed to the first pedestal 28a, and a second laser transmitter/receiver 30b is similarly positioned and fixed to the second pedestal 28b. A first displacement rod 32a and a second displacement rod 32b are displaceably supported by the support plates 26a and 26b. The first displacement rod 32a and the second displacement rod 32b are made of quartz glass, and a first reflecting plate 34a and a second reflecting plate 34b are provided at respective ends facing the first laser transmitter/receiver 30a and the second laser transmitter/receiver 30b. be provided. The first laser transmitter/receiver 30a and the first reflector 34a, and the second laser transmitter/receiver 30b and the second reflector 34b are covered with a resin cover 36, respectively.

The other ends of the first displacement rod 32 a and the second displacement rod 32 b are inserted into the cavity 18 . Therefore, the other ends of the first displacement rod 32a and the second displacement rod 32b are covered with the molten metal M filled in the cavity 18, and when the molten metal M solidifies thereafter, they are embedded in the solidified product, which is a cast product. be done.

In the above configuration, the thermocouple 20, the first laser transmitter/receiver 30a, and the second laser transmitter/receiver 30b are electrically connected to a personal computer (PC) 38 that serves both as an arithmetic circuit and a control circuit.

The linear expansion coefficient acquisition step S1 is performed as follows using the measuring device 10 configured as described above.

First, the first laser transmitter/receiver 30a and the second laser transmitter/receiver 30b are activated, and laser light B is transmitted from each. The laser light B is reflected by the first reflecting plate 34a and the second reflecting plate 34b, and returns to the first laser transmitter/receiver 30a and the second laser transmitter/receiver 30b. The first laser transmitter/receiver 30a and the second laser transmitter/receiver 30b receive the laser light B that has returned. The PC 38 individually calculates the distance from the first laser transmitter/receiver 30a to the first reflector 34a and the distance from the second laser transmitter/receiver 30b to the second reflector 34b based on the elapsed time from the start of transmission to the start of light reception. calculate.

In this state, a molten metal M made of, for example, a metal material such as an aluminum alloy is poured from the sprue 22 . The molten metal M reaches the cavity 18 via the runner 24 and is accumulated. In other words, the molten metal M is filled into the cavity 18 . By this filling, the molten metal M covers the other ends of the first displacement rod 32a and the second displacement rod 32b. The amount of molten metal to be poured may be such that the liquid level of the molten metal M reaches the middle of the runner 24 . Also, the temperature of the molten metal M is constantly detected by a plurality of thermocouples 20 and transmitted to the PC 38 as information.

After pouring, the molten metal M is naturally cooled. Along with this cooling, the molten metal M solidifies, and the other ends of the first displacement rod 32a and the second displacement rod 32b are embedded inside the solidified product.

The molten metal M undergoes volumetric contraction while being solidified and changed into a solidified product. Therefore, at the longitudinal ends of the cavity 18, the first displacement rod 32a and the second displacement rod 32b are pulled by the shrinking molten metal M, and are straightened in the direction away from the first laser transmitter/receiver 30a and the second laser transmitter/receiver 30b. physically displaced. Therefore, in the first laser transmitter/receiver 30a and the second laser transmitter/receiver 30b, the elapsed time from the start of transmission to the start of light reception becomes longer than before pouring.

Here, quartz glass has a small coefficient of thermal expansion. Therefore, the amount of shrinkage of the first displacement rod 32a and the second displacement rod 32b is negligibly small compared to the amount of shrinkage when the molten metal M solidifies. Therefore, the amount of displacement of the first displacement rod 32a and the second displacement rod 32b can be evaluated as the amount of contraction of the molten metal M.

When the volume contraction ends, the displacement of the first displacement rod 32a and the second displacement rod 32b also ends. As a result, in the first laser transmitter/receiver 30a and the second laser transmitter/receiver 30b, the elapsed time from the start of transmission to the start of light reception becomes constant. The PC 38 obtains the temperature change and elapsed time of the molten metal M (solidified product) up to this point, and the displacement distances of the first displacement rod 32a and the second displacement rod 32b. Then, the temperature drop rate is calculated based on the temperature change amount (temperature drop amount) and the elapsed time, and the linear expansion coefficient is calculated based on the distance before solidification and the displacement distance before and after solidification. As described above, the temperature drop rate and the coefficient of linear expansion are acquired for each portion where the thermocouple 20 is provided.

If necessary, the lower mold 14 and the upper mold 16 are made of different materials or have different surface roughnesses on the surfaces facing the cavity 18, and the linear expansion coefficient acquisition step S1 is performed. For example, at least one of the lower mold 14 and the upper mold 16 may be changed to a heat insulating material. In this case, it is possible to evaluate the coefficient of linear expansion at the thick portion of the casting produced by the casting apparatus. When both the lower die 14 and the upper die 16 are made of alloy tool steel, the coefficient of linear expansion is evaluated at the thin-walled portion of the casting produced by the casting apparatus.

Next, the contraction amount acquisition step S2 is performed. That is, the PC 38 calculates the amount of shrinkage in the solidified product based on the temperature distribution of the solidified product and the calculated coefficient of linear expansion. Also, the mold is opened, the solidified product is taken out, and the actual shrinkage amount is measured. As a result, the calculated amount of shrinkage substantially matched the actual amount of shrinkage, with an error of 1% or less. On the other hand, the amount of shrinkage calculated using a known coefficient of linear expansion was approximately three times the amount of actual shrinkage, and the error was 166%.

By performing the steps up to this shrinkage amount acquisition step S2, the shrinkage amount of the cast product obtained by the casting apparatus can be evaluated for each temperature. Since the amount of shrinkage is evaluated based on the coefficient of linear expansion obtained by actual measurement, there is an advantage that the evaluation result regarding the amount of shrinkage is accurate. In addition, when the lower mold 14 and the upper mold 16 are changed to different materials, it is possible to evaluate the amount of shrinkage of the parts having different thicknesses in the casting.

Next, the holding force evaluation step S3 is performed. In this case, a material model is used. As a material model, an elastic model, an elasto-plastic model, an elasto-plastic creep model, etc. are known, but it is preferable to use the Ohno-Wang model. This is because in this case, an evaluation result with a small error from the actual measurement value can be obtained.

In the Ohno-Wang model, simulations provide stress-strain curves at arbitrary temperatures for each strain rate. As an example, the stress when the strain rate is 10 ⁻² /sec, 10 ⁻³ /sec, 10 ⁻⁴ /sec at 25 ° C., 200 ° C., 250 ° C., 300 ° C., 350 ° C., 400 ° C., 450 ° C.- The strain curves are shown in FIGS. 3 to 9, respectively, together with the actual measurement results obtained by the tensile test. However, FIG. 3 shows only when the strain rate is 10 ⁻³ /sec. The dashed line is the stress-strain curve obtained by simulation using the Ohno-Wang model, and the solid line is the stress-strain curve obtained by actual measurement.

From these FIGS. 3 to 9, the stress-strain curve obtained by simulation by the Ohno-Wang model was obtained by actual measurement in a wide temperature range of 25° C. to 450° C. (especially 200° C. to 400° C.). It can be seen that the stress-strain curve is in good agreement with the curve.

The shrinkage evaluated in the shrinkage acquisition step S2 corresponds to the strain in the stress-strain curve. Also, the cooling rate can approximate the strain rate. Therefore, the holding force at a given temperature can be evaluated as follows. That is, for example, when evaluating the hugging force at 25° C., first, the amount of shrinkage at 25° C. is plotted on the X-axis of the graph shown in FIG. 3 as strain.

A perpendicular L1 is then drawn from this plot point to the stress-strain curve at a strain rate close to the cooling rate. Further, a horizontal line L2 is drawn from the intersection point P of this perpendicular line L1 and the stress-strain curve toward the Y-axis of the graph. The Y-axis coordinate value of L2 is the stress, and this stress can be evaluated as the holding force of the molten metal M at the temperature. Therefore, the stress-strain curve at room temperature of the Ohno-Wang model can be used to obtain the holding force of a casting that has been cooled down to room temperature.

As described above, the stress-strain curve determined by the Ohno-Wang model accurately approximates the stress-strain curve obtained by actual measurement. Therefore, the holding force can be evaluated with high accuracy. Further, when the lower mold 14 and the upper mold 16 are changed to different materials and the coefficient of linear expansion is obtained, it is possible to evaluate the holding force of the parts having different thicknesses in the casting.

Based on the holding force evaluated in this way, when designing the casting apparatus, it is possible to determine what degree of rigidity the ejector pin should have for each part. Therefore, it is possible to provide an ejector pin that allows the casting to be easily removed from the mold. Moreover, it becomes easy to select a device having an appropriate size as a drive device for driving the ejector pin. Therefore, by providing a large-sized drive device, it is possible to avoid an increase in the size of the casting apparatus and to reduce the cost.

The present invention is not particularly limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention.

For example, a material model other than the Ohno-Wang model may be used.

DESCRIPTION OF SYMBOLS 10... Measuring apparatus 14... Lower mold 16... Upper mold 18... Cavity 20... Thermocouple 30a, 30b... Laser transceiver 32a, 32b... Displacement bar 34a, 34b... Reflector 38... Personal computer M... Molten metal

Claims (5)

A holding force evaluation method for evaluating the holding force of a casting obtained by solidifying a molten metal made of a metal material in a cavity of a casting apparatus against a mold forming the cavity,
The surface condition of the mold in the measuring device is adjusted to the surface condition of the mold in the casting device, and the cavity formed by the mold in the measuring device is filled with molten metal to measure the amount of shrinkage when the molten metal solidifies. a linear expansion coefficient acquisition step of measuring and obtaining the linear expansion coefficient of the metal material based on the measured shrinkage amount;
A shrinkage amount acquisition step of obtaining a shrinkage amount when the molten metal changes into the cast product based on the linear expansion coefficient;
A holding force evaluation step of obtaining a stress using a material model as the amount of shrinkage as a strain and evaluating the stress as a holding force;
A holding power evaluation method having 2. The evaluation method according to claim 1, wherein an Ohno-Wang model is used as said material model. 3. The evaluation method according to claim 1, wherein the material or surface roughness of said mold of said measuring device is changed, and the coefficient of linear expansion of said metal material is measured for each. A shrinkage amount evaluation method for evaluating the amount of shrinkage of a casting obtained by solidifying a molten metal made of a metal material in a cavity of a casting apparatus, from the molten metal,
A linear expansion coefficient acquisition step of filling a cavity of a measuring device with molten metal and measuring the amount of shrinkage when the molten metal solidifies, and obtaining the linear expansion coefficient of the metal material based on the measured amount of shrinkage;
A shrinkage amount acquisition step of obtaining a shrinkage amount when the molten metal changes into the cast product based on the linear expansion coefficient;
Shrinkage amount evaluation method having. 5. A shrinkage amount evaluation method according to claim 4, wherein the material of the mold of said measuring device is changed and the coefficient of linear expansion of said metal material is measured for each material.

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