JP5120295B2 - Low pressure casting mold - Google Patents

Description

The present invention relates to a casting mold .

  FIG. 1 is a schematic view showing a low-pressure casting method. In a general low-pressure casting method, in the sealed container 11, the molten metal 13 in the crucible 14 is raised by pressurized air from below through a hot water pipe (Stoke) immersed in the molten metal, and sealed. Hot water is poured into the mold 10 above the container 11. Thereafter, when the pressurization is stopped at the time of completion of solidification of the pouring gate portion, the melt in a liquid state that has not solidified falls by gravity, and the molten metal in the hot water supply pipe is returned to the crucible 14. Thereafter, the casting in the mold 10 is taken out.

The defect which generate | occur | produces in such a low pressure casting method is demonstrated. FIG. 2 is an explanatory diagram of defects occurring in the low pressure casting method.
As shown in FIG. 2, the molten metal (aluminum) is filled from the lower side with pressurized air. Since the mold is deprived of heat during the filling process, the temperature is lower at the top when filling is completed. Naturally, the solidification basically proceeds from the top. Normally, when the upper mold 20 and the lower mold 30 are opened up and down in the mold after solidification, the product adheres to the upper mold 20. However, solidification has progressed from the schedule at that time, and if it has solidified to the lower part of the gate, the shape may not come off and the gate part may be broken or the product may remain in the lower mold 30. . The shape in which the product cannot be taken out when the mold is opened up and down is called “undercut”.

Also, since aluminum shrinks in the process of becoming liquid to solid, it is necessary to supply molten aluminum that has solidified and shrunk, but if it solidifies in order from the top as intended, it will flow from the bottom through the unsolidified part. Can be supplied (from the gate). (This is called the “push-up hot water effect”.) However, when the middle of the aluminum melt path from the gate or from the gate (part B in FIG. 2) solidifies first, the molten aluminum is added to the tip. It becomes impossible to supply. When solidified and contracted in such a state, the contents in the portion A in FIG. This is called the “shink nest”.
In order to continue supplying aluminum for the solidification shrinkage of the product part, it is necessary to continue pressurization at least until the product part solidifies, but if it is pressurized for too long, it solidifies to the lower part of the gate and undercuts. .

  To prevent these defects, conventional low pressure casting deals with the suppression of sink marks in the product by setting the position, shape and size of the gate and the pressurization pattern (filling pattern). It was dealt with by setting the pressure pattern. In this case, the optimum pressure pattern setting needs to be changed when there is a change in mold temperature due to fluctuations in the outside air temperature or cycle time. Therefore, for example, as disclosed in Patent Document 1, Patent Document 2, Patent Document 3, and the like, a method of setting an optimal pressurization pattern based on the molten metal temperature and the mold temperature at the start of filling is performed. It was.

  However, in the above method, when the mold temperature is greatly lowered, the gate is rapidly solidified, so the pressurization time has to be shortened to prevent undercut, and a predetermined optimum pressurization pattern is formed. Setting was difficult. When the pressurization time is shortened, the hot water pouring effect of the pouring gate is diminished, which causes a problem that it is difficult to suppress the occurrence of the sink nest in the product.

JP 2002-254154 A Japanese Patent Laid-Open No. 7-60429 JP-A-11-47908

  In view of the above problems, the present invention provides a low-pressure casting method and a casting mold in which undercutting is easily prevented and generation of a sink nest in a product is suppressed.

In order to solve the above-mentioned problems, the invention of claim 1 is a low-pressure casting mold for supplying a molten metal with a pressurized gas to perform low-pressure casting of a product part, and the mold is an upper mold (20). And the lower mold (30), and the lower mold (30) is divided into at least a gate upper mold (31) in the upper gate (2) and a lower gate mold (32) in the lower gate (3). A constricted shape portion (9) is formed at the boundary between the upper gate (2) and the lower gate (3). Further, the upper gate mold (31) and the lower gate mold (32) Each having a heater (4, 6) and a temperature sensor (5, 7), between the upper mold (20) and the upper gate mold (31), and between the upper gate mold (31) and the gate. A heat insulating material (8) is installed between the lower mold (32) and the upper mold (3 ) And the temperature of the lower mold (32) are set to different set temperatures so that the solidification time of the molten metal at the upper part (2) is slightly longer than the solidification time of the product part. The temperature of the upper gate mold (31) in the upper gate (2) is set .

Thereby, since the mold temperature at the upper and lower portions of the gate can be controlled to a target set value by the heater, even if there is a mold temperature change due to fluctuations in the outside air temperature or cycle time, a sufficient hot water effect can be obtained. Undercut prevention is also easy. In addition, by setting the mold temperature at the top of the sprue high, it is possible to delay the solidification of the sprue, making it possible to reduce the sprue. Even products with different shapes can be molded easily.
Moreover, by controlling the temperature of the gate, the quality can be stabilized and the position, shape and size of the gate can be freely controlled.
By installing the heat insulating material (8), the mold temperature at the top and bottom of the gate can be controlled independently by the heater, and the target set value can be controlled.
And because the heater can control the mold temperature at the upper and lower parts of the gate part to a target set value, even if there is a mold temperature change due to fluctuations in the outside air temperature and cycle time, a sufficient hot water effect can be obtained, Undercut prevention is also easy. In addition, by setting the mold temperature at the gate low, it is possible to delay the solidification of the gate, so it is possible to reduce the size of the gate. Even products with different shapes can be molded easily.

  In addition, the code | symbol attached | subjected above is an example which shows a corresponding relationship with the specific embodiment as described in embodiment mentioned later.

It is the schematic which shows a low pressure casting method. It is explanatory drawing of the defect which generate | occur | produces in a low pressure casting method. It is a figure which shows roughly the metal mold | die which divided the gate part into two. It is a figure explaining the gate of the cylinder of a single cylinder engine, (a) is a front view (upper) which shows a product shape, a top view (lower), (b) is a front view (upper) which shows an example of a gate. And (c) are a front view (top) and a plan view (bottom) showing another example of the gate.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. About each embodiment, the same code | symbol is attached | subjected to the part of the same structure, and the description is abbreviate | omitted. Similarly, with respect to the prior art, parts having the same configuration are denoted by the same reference numerals and description thereof is omitted.

An embodiment of the present invention when casting the product part 1 with a low pressure casting mold will be described.
FIG. 3 is a diagram schematically showing a mold obtained by dividing the gate portion into two parts. The upper mold 20 is also divided into several parts, but is omitted here. It is important not to cause a sink in the product part 1. In the case of FIG. 3, the lower mold 30 is divided into three parts, and the gate part of the lower mold 30 is further divided into two parts, an upper part 2 and a lower part 3. The lower mold 30 appropriately sets the number of divisions as necessary. A heater and a temperature sensor for controlling the heater are installed in the lower mold 32 and the upper mold 31 of the lower mold 30, respectively. In order to hold the pouring gate lower part 3 in an unsolidified state, the temperature of the pouring gate lower mold 32 is controlled by the second heater 6 and the second temperature sensor 7 for controlling it, and the pouring gate upper part 2 is solidified at a target time. In addition, the temperature of the gate top mold 31 is controlled by the first heater 4 and the first temperature sensor 5. In addition, a heat insulating plate 8 that prevents heat transfer between the gate upper mold 31 and the gate lower mold 32 is installed between the molds, so that independent temperature control is possible for each mold. ing.

  Here, the gate upper mold 31 and the gate lower mold 32 are divided into two, but it is not always necessary to divide into two if the gate shape is such that there is no problem in mold opening when taking out the product. In this case, the first heater 4 and the first temperature sensor 5 are provided in order to solidify the upper gate 2 at a target time, and the second heater 6 and the second heater 6 are coupled to hold the lower gate 3 unsolidified. A second temperature sensor 7 to be controlled is provided to control the temperature. The gate shape can be variously modified as is well known. Further, the temperature control can be performed in two or more stages according to the gate shape. The gate upper mold 31 and the gate lower mold 32 are divided into two parts, but may be divided into two or more parts.

  Conventionally, if the product part is larger than the spout (or if the spout is smaller than the product part), it takes time to solidify due to the large amount of heat even if the temperature at the completion of filling is lower in the product part. The spout will solidify first. If it becomes so, it will become impossible to supply the molten metal with respect to the solidification shrinkage | contraction of a product part, and it will arise that a sink nest generate | occur | produces in a product part. For this purpose, it is important to set the gate size according to the product. Since the gate can only be attached to the flat part, only the shape and size can be set according to the shape of the product. Depending on the shape of the product, only a small gate may be provided and the product shape must be changed. It was.

  According to this embodiment, such problems are solved, and the mold of the gate is divided into two or more, and the temperature setting of different systems is performed to control the solidification of the gate. Is. The heater can control the mold temperature at the gate to the target set value, so that even if there is a mold temperature change due to fluctuations in the outside air temperature or cycle time, a sufficient hot-water injection effect can be obtained and undercut prevention is also possible. It becomes easy. In addition, by setting the mold temperature at the gate low, it is possible to delay the solidification of the gate, so it is possible to reduce the size of the gate. Even products with different shapes can be molded easily.

Next, control of the mold temperature at the gate will be described.
The following viewpoints are important in controlling the mold temperature of the gate. That is, in low-pressure casting, the temperature of the gate is controlled, and the gate 9 in FIG. 3 is used as the final solidified portion to suppress the formation of sink nests inside the product, and below the constricted shape of the gate (below the gate 9). It is necessary to satisfy both of the points of preventing undercut due to progress of solidification to the lower part of the gate. For this purpose, the temperature is set separately for the part that solidifies at the target time (upper gate) and the part that remains unsolidified (lower gate), and the upper part of the gate is optimal from the shape and size of the product and the gate. The solidification timing is set, and the mold temperature for achieving the solidification timing is set.

As an example, for the lower part of the gate, the mold surface temperature is fixed at a temperature at which aluminum does not solidify (600 ° C.). Regarding the temperature setting at the top of the gate, it varies depending on the shape and size of the product and the gate, but the solidification time at the top of the gate is slightly longer than the solidification time of the product (longer by a predetermined time). Set the mold temperature at the top of the gate slightly higher (higher by a small predetermined temperature).
Regarding the setting of the mold temperature T at the top of the gate, heat transfer from the molten aluminum to the mold is considered by the following formula.

ΔQ = k (Ta−Td)
Where ΔQ is the amount of heat transfer from the molten aluminum to the mold per unit time and unit area
k: heat transfer coefficient,
Ta: molten aluminum temperature,
Td: mold temperature

The molten metal temperature and mold temperature at the completion of filling are calculated by molten metal flow analysis (CAE, Computor Aided Engineering). Based on these temperatures, the time t until the total ΔQ in the above equation reaches the amount of heat removal required for solidification is first calculated for the product part. The mold temperature T ₀ at the top of the gate is calculated so that the solidification at the top of the gate is the same as the time t, and the mold at the top of the gate is slightly higher than T ₀ so that it is slightly longer than the time t. Set the temperature T.
Regarding the pressurization pattern control, a method of measuring the temperature at the top of the gate and ending the pressurization at a time when the gate is considered to have solidified can be considered.

Next, as another embodiment, a cylinder of a single cylinder engine is considered as an example of the gate. 4A and 4B are diagrams illustrating a gate of a cylinder of a single cylinder engine. FIG. 4A is a front view showing the product shape (upper), a plan view (lower), and FIG. 4B is a front view showing an example of the gate. A figure (top), a top view (bottom), and (c) are a front view (top) and a plan view (bottom) showing another example of the gate.
From the product shape in Fig. 4 (a), there are two possible locations for the sprue to be installed, Fig. 4 (b) and (c), but Fig. 4 (b) shows that the sprue is too small for the product. Since the hot water effect cannot be expected, conventionally, FIG. 4 (c) has been employed. In this case, since the gate becomes larger, the cycle time becomes longer (productivity becomes worse), the weight of the gate relative to the product weight becomes larger, the waste (the portion to be discarded) becomes larger, and the material yield becomes worse. According to each embodiment of the present invention, by optimally setting the mold temperature of the gate, a sufficient hot-water effect can be expected even at the gate of FIG. 4B, and FIG. 4B can be adopted. became. Thereby, productivity improvement and material yield can be improved.

DESCRIPTION OF SYMBOLS 1 Product part 2 Upper gate 3 Lower gate 4 First heater 5 First temperature sensor 6 Second heater 7 Second temperature sensor 9 Gate 20 Upper mold 30 Lower mold 31 Upper gate mold 32 Lower gate mold

Claims (1)

A mold for low-pressure casting in which molten metal is supplied with pressurized gas to low-pressure cast the product part,
The mold comprises an upper mold (20) and a lower mold (30),
The lower mold (30) is divided into at least a gate upper mold (31) in the upper gate (2) and a lower gate mold (32) in the lower gate (3),
A constricted portion (9) is formed at the boundary between the upper gate (2) and the lower gate (3),
Further, the gate upper mold (31) and the gate lower mold (32) each include a heater (4, 6) and a temperature sensor (5, 7) ,
A heat insulating material (8) is installed between the upper mold (20) and the gate upper mold (31) and between the gate upper mold (31) and the gate lower mold (32), respectively. Has been
The temperature of the gate upper mold (31) and the temperature of the lower gate mold (32) are set to different set temperatures, and the solidification time of the melt in the upper gate (2) is determined by the solidification of the product part. The mold for low-pressure casting , wherein the temperature of the upper gate mold (31) in the upper gate (2) is set to be slightly longer than the time .

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