JP2009208094A - Die casting for vehicle steering gear housing, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a die casting for a vehicle steering gear housing having high strength and suitable as a column housing and a rack housing in a vehicle steering gear. <P>SOLUTION: Disclosed is a die casting for a vehicle steering gear housing produced by a nonporous die casting process using an aluminum alloy as the material. The amount of occluded gas at the inside of the casting is controlled to ≤5 cc/100 g-Al, and also, the Rockwell hardness at the surface and inside thereof is controlled to ≥55 HRB. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a die casting for a vehicle steering device housing used as a column housing or a rack housing of a vehicle steering device, and more particularly to a die casting for a vehicle steering device housing obtained by die casting an aluminum alloy and a method for manufacturing the same.

  Aluminum alloy die-casting is obtained by injecting molten aluminum alloy into a mold at high pressure, and is used in a wide range of fields such as transportation, electricity, aviation, and construction because of its high shape accuracy and low cost. Has been. In particular, in a vehicle steering apparatus that is required to be light in terms of energy saving and low fuel consumption, it is possible to reduce the thickness and weight of parts and obtain a clean casting surface even if the shape is complicated. For this reason, column housings and rack housings are manufactured by die casting an aluminum alloy.

By the way, recent vehicle steering devices have been improved in functions such as higher torque and higher output, and a larger load than conventional ones has been applied to column housings, rack housings, and the like. There is also a need for a rack housing (hereinafter referred to as a die casting for housing).
Currently, die castings for housings are often manufactured by the ordinary die casting method, but the ordinary die casting method is likely to cause internal defects due to entrainment of oxides and air, and heat treatment and welding at high temperatures due to internal defects. There is a problem that it is difficult. For this reason, it is conceivable to improve the strength by changing the cooling conditions and casting conditions of the ordinary die casting method, but it is difficult to obtain a die casting for housing with a stable strength.

Thus, as a die-casting method in which oxides and air are less involved and heat treatment and welding are possible, for example, as shown in Patent Documents 1 and 2, a non-porous die-casting method is known.
JP 50-21143 A Japanese Patent Laid-Open No. 2-200364

However, the non-porous die casting methods described in Patent Documents 1 and 2 have not been sufficiently studied regarding the amount of occluded gas in the castings to be produced and the strength inside the castings. There is a problem that a suitable casting strength cannot be obtained.
That is, when the amount of gas contained in the manufactured casting increases, mechanical strength such as casting specific gravity and tensile strength decreases. Moreover, even if the surface layer of the manufactured casting is hard, the required strength may not be obtained if the inside of the casting is soft.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a high-strength die casting for a vehicle steering device housing suitable as a column housing or a rack housing of a vehicle steering device and a method for manufacturing the same. is there.

In order to solve the above-described problems, a die-casting for a vehicle steering device housing according to claim 1 according to the present invention is manufactured by a non-porous die-casting method using an aluminum alloy as a material, and the occluded gas amount inside the casting is 5 cc / This is a die cast casting for a vehicle steering apparatus housing having a surface and internal Rockwell hardness of HRB55 or more, and 100 g-Al or less.
According to a second aspect of the present invention, in the die cast casting for a vehicle steering device housing according to the first aspect, the aluminum alloy is an Al—Si—Cu based aluminum alloy ADC12 of JIS H5302.

  On the other hand, in the method for manufacturing a die cast casting for a vehicle steering device housing according to claim 3, the molten aluminum alloy fed at a high temperature and high pressure into the closed mold passes through the gate having a reduced gate area, and This is a method in which the jetting speed is increased and sprayed into the cavity to increase the reaction area between the sprayed aluminum alloy melt and the oxygen gas present in the mold.

  Furthermore, in the method for manufacturing a die cast casting for a vehicle steering device housing according to claim 4, a mold release agent made of water-soluble graphite is provided on the mold surface in contact with the molten aluminum alloy in the mold. A lubricant was applied.

According to the die-casting for a vehicle steering device housing according to the present invention, a die-casting for a housing having high specific gravity, excellent structure and high strength can be produced.
Further, according to the method for manufacturing a die-casting for a vehicle steering device housing according to the present invention, the reaction area between the oxygen gas and the aluminum alloy melt existing in the mold is increased, so that the efficiency of the oxidation reaction is improved. High quality die castings for housing can be produced.

A method for manufacturing a die cast casting for a vehicle steering device housing according to the present invention (hereinafter referred to as a housing die casting) and its characteristics will be described below with reference to the drawings.
The die casting for housing of this embodiment is manufactured by a non-porous die casting method using JIS H5302 Al—Si—Cu based aluminum alloy ADC12 as a material.

  A method for producing a die-casting for a housing is such that an oxygen gas (active) is injected into a mold before injecting a molten metal (ADC 12) made of an aluminum alloy (ADC12) into a closed mold (not shown). The air in the cavity, gate, and runner is replaced with oxygen gas by blowing in gas, and then high temperature and high pressure aluminum alloy molten metal is injected into the mold, and the molten metal is cooled and solidified for die casting for housing. Manufacture castings.

Oxygen gas sent into the mold is blown out from the mold joints and gates, so that outside air is prevented from entering the cavity from the mold joints and gates. The oxygen gas fed into the mold reacts with the molten aluminum alloy to become fine Al ₂ O ₃ of 1 μm or less and is dispersed in the die casting for housing. As a result, the oxygen gas in the mold disappears, the cavity is in a vacuum state, and the molding of the die casting for housing is completed. Thus, this embodiment can manufacture the casting product which does not generate | occur | produce a gas and does not produce an internal defect by manufacturing the die-casting for housings by the non-porous die-casting casting method.

  By the way, when performing non-porous die casting, if the oxygen gas in the mold (cavity, gate, runner) is insufficiently substituted, the die concentration for the housing manufactured by reducing the oxygen concentration in the mold The gas content in the casting may increase (gas entrainment increases). When the amount of gas contained in the die casting for housing increases, the mechanical strength such as the specific gravity and tensile strength of the die casting for housing decreases. For this reason, as is clear from the test results of the gas content and strength described later, the occluded gas amount of the manufactured die casting for housing was set to 7 cc / 100 g-Al or less.

  In order to improve the oxidation reaction between the oxygen gas fed into the mold and the molten aluminum alloy when performing the non-porous die casting method, the reaction area between the oxygen gas and the molten aluminum alloy should be increased. Good. Therefore, in the present embodiment, the gate area of the mold is reduced, and the molten aluminum alloy that has been fed into the mold at a high temperature and high pressure increases the ejection speed at the gate and is injected into the cavity in the form of a spray. . Thereby, since the reaction area of the sprayed aluminum alloy molten metal and oxygen gas is increased, the efficiency of the oxidation reaction can be improved.

  Further, a mold release agent and a lubricant are applied to the mold surfaces forming the cavities, gates, and runners in the mold. If this release agent / lubricant is oily, gas is generated by contact with the molten aluminum alloy, and there is a possibility that it will exist as an internal defect of the die casting for housing without causing an oxidation reaction with the molten aluminum alloy. Therefore, in the present embodiment, water-soluble graphite that generates a small amount of gas is used as a release agent / lubricant to prevent internal defects of the housing die casting.

  Here, in order to examine the optimal occlusion gas amount of the die casting for housing, the present inventors die cast Al—Si—Cu-based aluminum alloy ADC12 having different occlusion gas amounts by a non-porous die casting method, A test piece having the shape shown in FIG. 1 (total length L1: 230 mm, central portion parallel length L2: 60 mm, gauge distance L3: 50.0 ± 0.1 mm, central portion parallel width w: 6.4 ± 0.1 mm, Nine (thickness t: 4 mm) were produced. Next, each prepared test piece is set in a universal testing machine manufactured by Instron, and a tensile strength test is performed under a test condition of a crosshead moving speed: 0.5 mm / min. The distortion of each test piece is measured with a video extensometer. It was measured. And the stress-strain curve was created from the tensile stress loaded on the test piece and the measured value of the video extensometer, and the tensile strength (breaking strength) σ of each test piece was obtained from the obtained stress-strain curve.

  Table 1 shows the amount of stored gas and tensile strength of each test piece, and FIG. 2 shows the correlation between the amount of stored gas and tensile strength as a curve.

  As apparent from FIG. 2, when the occluded gas amount of the die cast casting for housing is 8 cc / 100 g-Al or more, the tensile strength σB rapidly decreases. Therefore, in order to ensure a sufficient tensile strength σB, the amount of occluded gas in the die casting for housing is set to 7 cc / 100 g-Al or less. And in order to set it as the die-casting for housings suitable for heat processing and welding, it is preferable to make occluded gas amount into 5 cc / 100g-Al or less.

  By the way, since HRB hardness (Rockwell hardness) has a load larger than Vickers hardness, the plastic region is wide, and the hardness value including not only the surface but also internal information can be known. In this case, information on specific gravity, internal structure, defects, surface chill layer, and the like is also included. Therefore, in order to ensure an appropriate HRB hardness, it is desirable that the structure has few nest defects, high specific gravity, and excellent structure.

  Therefore, Table 2 shows the HRB hardness and tensile strength σB of the grip portion after the tensile test of each test piece described above, and FIG. 3 shows a correlation between the HRB hardness and the tensile strength σB in a curve.

  As can be seen from FIG. 3, when the HRB hardness is manufactured at 55 or more, sufficient tensile strength σB can be ensured, high density die castings for housing with few nest defects, high specific gravity and excellent structure can be obtained. Can do.

  From the above, this embodiment can manufacture a high-quality die casting for housing that does not cause gas entrainment and does not cause internal defects by the non-porous die casting method in which oxygen gas is blown into the mold. . Also, because the amount of occluded gas is set to 7cc / 100g-Al or less and the HRB hardness is 55 or more, the die casting for housing is manufactured. Therefore, the high quality die casting for housing with high specific gravity, excellent structure and high strength. Castings can be produced.

Further, in the present embodiment, JIS H5302 Al-Si-Cu-based aluminum alloy ADC12 is used as a casting material, and the mechanical tensile strength is higher than that of Al-Mg-based alloy. Die castings for housings can be manufactured.
In addition, in this embodiment, when performing the non-porous die casting method, the gate area of the mold is reduced, and the molten aluminum alloy that has been fed into the mold at high temperature and pressure increases the ejection speed at the gate. In addition, since the sprayed aluminum alloy is injected into the cavity and the reaction area of the sprayed aluminum alloy melt and oxygen gas is increased, the efficiency of the oxidation reaction can be improved.

  In addition, water-soluble graphite that generates a small amount of gas is applied as a mold release agent / lubricant to the mold surfaces that form the cavities, gates, and runners in the mold. Can be prevented.

[Example]
In order to confirm the effect of the present invention, the present inventors die cast 18 column housings 1 of the automobile steering system shown in FIG. 4 using JIS H5302 Al—Si—Cu based aluminum alloy ADC12. Then, a test piece (total length L1: 230 mm, central portion parallel length L2: 60 mm, gauge distance L3: 50. A test piece having the same shape and the same dimensions as 0 ± 0.1 mm, central parallel width w: 6.4 ± 0.1 mm, and thickness t: 4 mm was cut out. Further, the amount of occluded gas and mechanical properties (HRB hardness, tensile strength) were measured for each test piece. Table 3 shows the amount of occluded gas and mechanical properties (HRB hardness, tensile strength) of each test piece described above, and FIG. 5 shows the correlation between the HRB hardness and tensile strength of each test piece. It is a thing.

  In Table 3, Examples 1 to 9 were produced by a non-porous die casting method in which the occluded gas amount was changed within the range of 1.5 to 10.5 cc / 100 g-Al. Moreover, in Table 3, Comparative Examples 1-6 changed the occlusion gas amount in the range of 3.0-14.0cc / 100g-Al, and manufactured it by the nonporous die-casting method. Further, in Table 3, Comparative Examples 7 to 9 were produced by ordinary die casting.

As apparent from Table 3 and FIG. 5, when the amount of occluded gas is 7.0 cc / 100 g-Al or less and the HRB hardness is 55 or more (Examples 1, 3, 4, 6, 7), sufficient The column housing 1 can be manufactured while ensuring the tensile strength.
Further, as in Comparative Examples 1 to 3, it can be seen that the tensile strength of the column housing 1 cannot be secured unless the HRB hardness is 55 or more even when the occluded gas amount is 7.0 cc / 100 g-Al or less. Further, as in Comparative Examples 7 to 9, the amount of occluded gas in the column housing 1 manufactured by the ordinary die casting method exceeds 15.0 cc / 100 g-Al, and the specific gravity and hardness decrease, so the strength decreases. I understand that.

It is a figure which shows the test piece used for the intensity | strength test of an aluminum alloy die-casting. It is a figure which shows the relationship between the amount of occluded gas of a test piece, and tensile strength. It is a figure which shows the relationship between the HRB hardness (Rockwell hardness) of a test piece, and tensile strength. It is a figure which shows the column housing of the motor vehicle steering device manufactured by the nonporous die-casting casting method using the aluminum alloy ADC12. It is a figure which shows the relationship between the HRB hardness (Rockwell hardness) and tensile strength of the test piece cut out from the column housing shown in FIG.

Explanation of symbols

    1 ... Column housing, σB ... Tensile strength

Claims (4)

  It is manufactured by a non-porous die-casting method using an aluminum alloy as a material, the amount of occluded gas inside the casting is 5 cc / 100 g-Al or less, and the surface and interior Rockwell hardness is HRB 55 or more. Die casting for vehicle steering device housing.   The die cast casting for a vehicle steering apparatus housing according to claim 1, wherein the aluminum alloy is an Al-Si-Cu aluminum alloy ADC12 of JIS H5302.   The molten aluminum alloy fed into the closed mold at high temperature and high pressure passes through the gate with a small gate area, and is sprayed into the cavity in a spray form at a high spray speed. A method for producing a die cast casting for a vehicle steering device housing, wherein a reaction area between the molten aluminum alloy and the oxygen gas existing in the mold is increased.   4. The die cast casting for a vehicle steering device housing according to claim 3, wherein a mold release agent / lubricant made of water-soluble graphite is applied to a mold surface in contact with the molten aluminum alloy in the mold. Method.

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