JP2008260048A - Casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a casting method capable of preventing the generation of a shrinkage nest or controlling the generation position of the shrinkage nest.
When a material with low thermal conductivity (equivalent to SKD61) is used, the shrinkage nest 3 is located at the surface layer portion, but when a nesting 2 made of a material with high thermal conductivity is used. It turns out that it is moving toward the center part of thickness from a surface layer part.
This is because the portion in contact with the insert 2 made of a material having a high thermal conductivity is cooled earlier than the other portions.
[Selection] Figure 2

Description

  The present invention relates to a casting method suitable for pressure casting a molten metal such as an aluminum alloy.

  In order to reduce the burden on the environment, weight reduction is required for engines and the like, and the application of aluminum alloys is expanding. Moreover, the casting time by pressure casting is shortened from the request | requirement of productivity improvement.

However, casting has a problem of shrinkage cavity, and proposals for solving this problem have been proposed in Patent Documents 1 to 3, for example.
In Patent Document 1, each of an upper mold, a lower mold and a sliding mold is made of materials having different thermal conductivities, and a member having a low thermal conductivity is arranged for a mold corresponding to a thin portion of a cast product. It has been proposed to cause sexual coagulation.

  Patent Document 2 discloses a technique for preventing the occurrence of shrinkage cavities and the like by inserting a cooling pipe through which cooling water flows into a mold and controlling the flow rate of the cooling water.

  Patent Document 3 is provided with a cooling metal that can adjust the amount of protrusion from the molding surface of the mold for removing the thickness of the bearing holder, and performs directional solidification that controls the solidification rate of the molten metal in the thick portion of the bearing holder. Thus, a casting method has been proposed in which casting defects are less likely to occur.

Japanese Patent Laid-Open No. 1-237067 JP-A-1-228660 JP-A-6-126411

  In the method disclosed in Patent Document 1 described above, the overall thermal conductivity of the upper mold, the lower mold, or the sliding mold is the same, so that it is impossible to finely control the directional solidification. In addition, since a mold made of a material having a low thermal conductivity is arranged in the thin wall portion of the cast product, it can only deal with products having a simple cross-sectional shape such as a wheel.

  In Patent Document 2 and Patent Document 3, directional solidification cannot be performed at a location where a cooling pipe cannot be inserted, and in a cast product having a complicated structure, the surface layer portion is made dense. Therefore, the problem of shrinkage cavities in the surface layer cannot be completely solved.

  In order to solve the above problems, the casting method according to the present invention is a casting method in which a cavity defined in a mold is filled with molten metal and solidified, and is required to have a dense structure and no shrinkage. Directional solidification is performed using a material having a higher thermal conductivity than the mold material of the other part as the mold material of the part facing the casting surface layer.

  If a material having a higher thermal conductivity than that of the other part of the mold material is attached to a part of the mold in the form of a nest or a pin, it can be applied to a cast product having a complicated structure.

  Also, in the directional solidification, since it solidifies from the surface layer portion that is in contact with the material having high thermal conductivity, even if shrinkage occurs, it is in a place moved toward the center of the casting from the originally generated portion. Arise.

  According to the casting method of the present invention, even a cast product having a complicated structure can be directional solidified to the finest detail, so that it is necessary to increase the density of the structure of the surface layer portion where it is required. As a result, it is possible to prevent the formation of shrinkage cavities in the surface layer portion of the portion to be obtained, so that a cast product having excellent functionality can be obtained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a casting apparatus for carrying out a casting method according to the present invention. In the embodiment, the casting apparatus is used for casting a cylinder block.

  The casting apparatus includes a mold 1 made of a material having a low thermal conductivity (equivalent to JIS: SKD61) and a nesting 2 made of a material having a high thermal conductivity. The mold 1 is divided into a movable mold and a fixed mold. Further, instead of the insert 2, a pin made of a material having high thermal conductivity may be used.

As the above-described material having high thermal conductivity, for example, materials having the following compositions are preferable.
In terms of mass content, 0.15% or more and 0.35% or less of C, 0.05% or more and less than 0.20% of Si, 0.05% or more and 1.50% or less of Mn, and 0.020 % P, 0.013% S or less, 0.10% or less Cu, 0.20% or less Ni, 0.20% or more and 2.50% or less Cr, 0.50% or less, % To 3.00% Mo, together with 0.05% to 0.30% V and Nb, 0.020% to 0.040% Al and 0.003% O Further, a composition containing 0.010% or more and 0.020% or less of N and the balance being substantially made of Fe and having a Rockwell hardness of 30 HRC or more and 40 HRC or less is preferable.

  Further, 0.0002% to 0.0020% B, 0.0005% to 0.0100% Ca, 0.01% to 0.15% Se, 0.01% to 0% It is more preferable to contain Te of 15% or less and Zr of 0.003% to 0.20%.

  FIG. 2 (a) is a diagram showing the position of the shrinkage nest when a nesting made of a material with high thermal conductivity is used, and FIG. 2 (b) is the shrinkage nest when a material with low thermal conductivity (equivalent to SKD61) is used. It is a figure which shows a position.

The casting conditions are as follows.
In a 3,500 ton die-casting machine, the pressure is increased to 0.3 ± 0.1 m / s for low speed injection, 3 ± 0.1 m / s for high speed injection, and 860 ± 50 kgf / cm ^{2 for} maximum pressure. The curing time was 25 ± 3 sec.

  As is apparent from FIG. 2, when a material with low thermal conductivity (equivalent to SKD61) is used, the shrinkage nest 3 is located at the surface layer portion, but a nesting 2 made of a material with high thermal conductivity is used. In this case, it can be seen that the film moves from the surface layer portion toward the central portion of the wall thickness.

  This is because the portion in contact with the insert 2 made of a material having a high thermal conductivity is cooled earlier than the other portions, so that there is no shrinkage in this portion. It becomes a place moved toward the center. When the shrinkage nest appears in the surface layer portion, it becomes a casting defect, which is eliminated.

  FIG. 3A is a photomicrograph showing the structure of the surface layer portion in contact with the insert made of a material having high thermal conductivity, and FIG. 3B is the surface layer portion in contact with a material having low thermal conductivity (equivalent to SKD61). As is apparent from this photograph, the molten metal that contacts the portion made of the material having a high thermal conductivity is cooled more rapidly than the molten metal in the other portion, so that the structure becomes small and dense.

  Incidentally, it is disclosed in Spear et Modern castings 43 (1963) that the solidification structure becomes dense as the cooling rate increases.

  The casting method according to the present invention is suitable for an aluminum alloy pressure casting method, but can also be applied to other casting methods.

Sectional drawing of the casting apparatus which enforces the casting method which concerns on this invention (A) is a diagram showing the position of the shrinkage nest when a nesting made of a material with high thermal conductivity is used, and (b) is the position of the shrinkage nest when a material with low thermal conductivity (equivalent to SKD61) is used. Illustration (A) is a photomicrograph showing the structure of the surface layer part that is in contact with the insert made of a material having high thermal conductivity, and (b) is the structure of the surface layer part that is in contact with a material having low thermal conductivity (equivalent to SKD61). Photomicrograph showing

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Mold which consists of material with low thermal conductivity (equivalent to SKD61), 2 ... Nest which consists of material with high thermal conductivity, 3 ... Shrinkage nest.

Claims (3)

A casting method in which a cavity defined in a mold is filled with a molten metal and solidified, and as a mold material of a portion facing a casting surface layer portion that is required to have a dense structure and no shrinkage cavity, A casting method characterized in that directional solidification is performed using a material having a higher thermal conductivity than a mold material in another part. 2. The casting method according to claim 1, wherein the material having a higher thermal conductivity than the mold material of the other part is attached to a part of the mold in the form of a nest or a pin. The casting method according to claim 1, wherein the shrinkage cavity is moved from the surface layer portion toward the casting center portion by the directional solidification.

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