JPS6338256B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention is used in the field of casting male and female molds for steel sheet presses or synthetic resin injection molding, and relates to a method for suppressing warping and deformation in casting large molds. Conventional technology Conventionally, when precision casting a large mold for steel plate press molding or synthetic resin injection molding, the alignment accuracy of the male and female molds must be 0.2 mm or less, so the inner bottom surface of the core mold is The method used was to use a ceramic mold with a ceramic layer laid over it to precisely cast every detail. However, if the shape of the casting, that is, the mold, is complex, the casting will linearly contract during the cooling process after solidification, compressing the core-shaped mold, but when the mold strength is high, the mold will shrink while destroying the mold. Since this is not possible, it is transformed as shown by the dotted line. That is, since the casting is formed by the restraint of the mold, free shrinkage is inhibited, and warping deformation inevitably occurs, it has been difficult to perform casting with a tolerance within ±0.2 mm/m upon completion of casting. For example, if a mold is made using the ceramic molding method, which allows for high-precision casting, and precision cast with zinc alloy, a relative warpage of 10 to 13 mm will occur at 2 meters, making it unusable. It was not possible to obtain a usable mold unless we took measures against friction through excellent machining and die spotting. Problems to be Solved by the Invention The causes of deformation of the final finished product, that is, the mold, by the conventional method are (1) the unevenness of the thickness of the casting, which causes differences in the cooling rate of each part; (2) Molten metal is cast into a core mold and attempts to contract during solidification, but free contraction is inhibited by the resistance of the core mold.The problems described in (1) and (2) above result in warping and deformation. In order to eliminate the conventional problems, the present invention aims to ensure that when pouring molten metal into a mold, the mold has sufficient strength.
Once the solidification of the cast metal material is completed and the shape of the cast is frozen, the strength of the mold is released to allow each part of the cast to contract freely, allowing the cast to contract naturally and preventing abnormal deformation. This invention aims to cast high-precision cast products. Means for Solving the Problems The present invention provides a width of 10 mm along the side wall 1a of the core mold 1 or the part of the ceramic mold (hereinafter simply referred to as the mold) that receives the shrinkage force generated when the casting material I solidifies. Form a gap hole 2 of 20 mm to 20 mm, fill the coagulation hole 2 with dry sand 3, remove the dry sand 3 immediately after reaching the solidification temperature of the casting material A, and reduce the lateral pressure strength of the core mold 1 or mold. The mold is cast by lowering the temperature. Operation According to the method of the present invention, immediately after the casting material A reaches the solidification temperature, the core mold 1 or the dry sand 3 formed in the mold is removed from the gap hole 2 with a width of 10 mm to 20 mm. The strength of the child mold 1 or mold is eliminated, and the shrinkage force generated when the casting material A solidifies is absorbed by the gap hole 2 from which the dry sand 3 with a thickness of 10 mm to 20 mm has been extracted. Example An example of the present method will be described with respect to a U-shaped casting made of zinc alloy and shown in Fig. 2.
1 is an upper mold, 1 is a core mold made by airtightly polymerizing the upper mold 4,
5 is a ceramic layer. A sprue 4a is bored in the side of the upper mold 4. Inside the core mold 1, a side wall 1 is provided with a small distance 1 from the side walls 1a, 1a.
a, 1a, that is, along the side that receives the shrinkage force generated when the casting material A solidifies, with a width of 10 mm to
20mm gap holes 2, 2 are drilled and these gap holes 2,
2 is filled with dry sand 3,3. A temperature sensor (CA wire) 6 for detecting the solidification temperature is buried inside the casting material A, and exhaust pipes 7, 7 communicating with the gap holes 2, 2 are bored in the bottom part 1b, and the exhaust pipes 7, 7
is connected to an external vacuum device 8. When casting according to the embodiment, the upper mold 4 is superposed on the core mold 1, and the interstitial holes 2, 2 are filled with dry sands 3, 3, respectively. Further, the core mold 1 is filled with the casting material I by pouring molten metal from the sprue 4a, and a temperature sensor 6 connected to a computer 9 is embedded inside the casting material I. A riser water is injected into the upper mold 4 located above the casting material A. Then, the temperature sensor 6 detects the solidification completion temperature of the casting material A, and inputs the electric signal to the computer 9 connected to the temperature sensor 6. The vacuum device 8 is activated by the command from the computer 9, and the drying process is performed. Sand 3, 3 is discharged from pipe 7,
When the liquid is sucked out through the hole 7, the gap holes 2, 2 become voids. On the other hand, the shrinkage force toward the center of the casting material A that is being cooled is
It is absorbed by pressing a, 1a and crushing the gap holes 2, 2. The experimental details of this example are as follows. The chemical composition of the zinc alloy as a prototype casting is:

[Table] The shape is U-shaped, and the dimensions of each part are as shown in FIG. The reason for the U-shaped cross section is that the shape is simple in order to reduce the factors that cause deformation and to reliably identify the cause of warp deformation.
The reason why the length was made relatively long at 600 mm was because the amount of shrinkage is expressed as a function of length, so the amount of deformation is noticeable and can be read visually even when measured on a scale of mm. The reason for increasing the thickness of the lower surface is to make the casting sufficiently thick to eliminate temperature unevenness on the lower surface, prevent thermal stress from occurring, and prevent deformation. The reason why the rising length was set to 150 mm was to increase the length of the sides that make up the deformation angle, so that the mold resistance deformation during shrinkage would appear. Furthermore, in order to make molds with high precision, we created a mold model.
In order to make the ceramic mold model in the next process with an accuracy of within 0.05mm, there will be no deformation during mold release.
It was created by faithfully inverting it using silicone rubber. Ceramic slurry was poured onto the surface of the mold to create a highly accurate mold. Figure 4 shows a cross section of a hollow mold developed to suppress deformation due to prototype mold resistance. Since the casting weight is considered to be several tons, the pressure strength of the mold is required to be 30 to 50 kg/cm ² . Therefore, if the metal is poured into a mold with the hollow layer still in place, the mold will collapse, which is dangerous. As a countermeasure, it was decided to fill the hollow layer of the mold with dry sand to ensure the above-mentioned pressure resistance, and in order to guarantee the strength, a simple test device shown in FIG. 6 was used. This simple test device fixes support frames B and C on the left and right sides of a base plate A with a gap between them, and a hydraulic jack E equipped with a 100 kg load cell D that retracts toward one support frame B is attached to the other support frame. C, and the dry sand 3 is sandwiched between the support frame B and the load cell D to conduct a pressure test. The constant correction of k was performed using the theoretical formula of soil mechanics and the results of the dry sand pressure test, and the pressure resistance theoretical curve shown in Figure 5 was obtained (the points represent experimental values). This can be expressed as a theoretical formula based on sand mechanical considerations as follows. W′=e ^h′ −h′−1 h′=4k/dh W=3bρgd ² /16k ² W′ Curve when k is 0.7 b=100 h=90 W: Pressure resistance b: Width ρ: Sand Specific gravity g: Gravitational acceleration d: Thickness of sand h: Height of sand k: Constant representing friction unique to sand From the curve in Figure 5, the thickness of sand to ensure pressure resistance of dry sand is 10~ At 20mm, it is recognized that it can be adopted as a practical value. In order to verify whether the hollow mold method is effective in suppressing deformation, we investigated (1) open casting (a structure in which there is no upper mold, and the metal is poured directly from above), and (2) general casting (a structure in which the entire circumference of the casting is poured into the mold). (3) Hollow mold construction method (a gap hole is provided in the inner wall of (2) above, the gap hole is filled with dry sand, and the metal is poured into the core mold. After solidifying the casting material, the sand is removed after the shape has stabilized.) We conducted casting experiments using the three types of casting methods mentioned above, measured the inside of the prototype castings, and compared them to determine the deformation prevention effect. I judged it. After casting, let it cool naturally for 48 hours until the casting temperature reaches 70℃.
After confirming that it had descended below, the mold was dismantled.
Measure the distance between the inner walls of the U-shaped prototype casting,
The seventh figure expresses the difference with the physical property value as the amount of deformation.
It is a diagram. The distance from the center of the prototype casting material A to the root R is 300 mm, and the amount of shrinkage is calculated from physical property values to be 2.73 mm. Each casting method results in a different amount of shrinkage, and the shrinkage amount for the hollow mold method in Figure 7 is closest to the physical property calculation value, 0.8 mm.
It is thought that precision casting was possible to the target dimensions. In the case of the hollow mold method, shrinkage is more free than in the general casting method, and the seventh point is that it approaches the physical property value.
This can be seen from the values in the figure. In addition, at the root region, the material is shrunk to a value that is almost close to the physical property value. Effects According to the present invention, the thickness of the dry sand filled in the interstitial holes is set to 10 mm to 20 mm, so it has high pressure resistance, and when the cast material completes solidification, the dry sand that is formed in the cast material is Since a gap is created inside along the side wall of the mold where the contraction force acts, the strength of the mold is released, and the contraction force of the casting material acts toward the center, crushing the side wall of the mold toward the gap, and the contraction force is released. As a result, the casting material contracts obediently and warping is suppressed, making it possible to cast a high-precision mold with extremely little warping.

[Brief explanation of drawings]

The figures show examples of the present invention, in which Fig. 1 is a cross-sectional view of a mold for casting a press mold, Fig. 2 is a perspective view of a test casting, and Fig. 3 is a cross-section of the mold in a state of resistance deformation. Figure 4 is a sectional view of a hollow mold, Figure 5 is a pressure resistance curve of dry sand, and the dots represent experimental values.
FIG. 6 is a side view of the dry sand compressive strength testing apparatus, and FIG. 7 is a side wall shrinkage deformation diagram of the U-shaped experimental casting. Code; 1... Core mold, 1a... Side wall, 1b...
... Bottom, 2 ... Interstitial hole, 3 ... Dry sand, 4 ... Upper mold, 4a ... Sprue, 5 ... Ceramic layer, 6 ...
Temperature sensor, 7... Discharge pipe, 8... Vacuum device, 9... Computer, l... Interval, i...
...Casting material, B...root, C...boiling water, W...
Pressure load, b...width, ρ...specific gravity of sand, g...gravitational acceleration, d...thickness of sand, h...height of sand, k
...Constant representing the friction unique to sand, A...Bedplate,
B, C...Support frame, D...Load cell.

Claims (1)

[Claims] 1. Gap holes 2 with a width of 10 mm to 20 mm are formed inside the core mold 1 along the side wall 1a with a small distance 1 from the side wall 1a, and these gap holes 2 are filled with dry sand 3. A method for suppressing warping and deformation in large mold casting, characterized by removing dry sand 3 immediately after a casting material A poured into a child mold 1 reaches a solidification temperature.