Patent Application
20170266722
The present invention relates to a light alloy wheel formed of a light alloy such as an aluminum alloy, a method for manufacturing the same and a device for manufacturing the same.
As light-alloy vehicle wheels attached to automobiles (passenger cars, etc.), aluminum wheels which are entirely formed of an aluminum alloy by a low-pressure casting method etc. are used for reducing the vehicle mass.
In manufacturing the light alloy wheels by the casting method, it is required to reduce a casting detect such as a shrinkage cavity. PTL 1 discloses an example of such manufacturing method.
JP-A-2008-155235 (paragraph 0044 and FIGS. 1 and 3)
In the prior art casting method exemplarily disclosed in PTL 1, the prevention of the shrinkage cavities on the rim part is sometimes insufficient. The shrinkage cavities formed on the rim part are likely to cause air leakage from the rim part. Therefore, a method of manufacturing a light alloy wheel is demanded in which the shrinkage cavities on the rim part are reduced as compared to the prior art technology so as to prevent the air leakage.
Thus, it is an object of the invention to provide a light alloy wheel that allows the manufacture of a light alloy wheel in which the casting defect such as the shrinkage cavities on the rim part is reduced so as to prevent the air leakage as compared to the prior art manufacturing method, as well as a method and a device for manufacturing the light alloy wheel.
According to the first invention, a method for manufacturing a light alloy wheel that comprises a substantially annular rim part and a disc part that is joined to one edge of the rim part on an inner side and is to be attached to an axle comprises: a molten metal pouring step for pouring a light alloy molten metal from a sprue opened into a mold cavity formed into a shape of the rim part; and a forced cooling step for, after the molten metal pouring step, forcibly cooling the light alloy molten metal poured into the mold cavity formed into the shape of the rim part such that one predetermined cooling means of a plurality of cooling means provided along an entire circumference on an outer side or an inner side of the mold cavity formed into the shape of the rim part is first operated and an other cooling means thereof is then operated.
In the first invention, the forced cooling step may be performed such that one cooling means located farthest from the sprue of the plurality of cooling means is first operated and the other cooling means is then operated in sequence toward the sprue.
In the first invention, the forced cooling step may be performed by forcibly cooling the light alloy molten metal poured into the mold cavity formed into the shape of the rim part such that relative to a cooling power of the one cooling means, a cooling power of the other cooling means decreases toward the sprue.
In the first invention, an operation time of the cooling means may gradually decrease from a position farthest from the sprue toward the sprue.
In the first invention, the cooling means may comprise a coolant path, and a coolant flow rate of the cooling means may be gradually reduced from the position farthest from the sprue toward the sprue.
In the first invention, it is preferable that the light alloy molten metal poured into the mold cavity formed into the shape of the rim part in the molten metal pouring step is directionally solidified from a position farthest from the sprue toward the sprue in the forced cooling step.
In the first invention, it is preferable that the upper mold comprises a plurality of inside spaces in which the cooling means are enclosed, and at least the one cooling means is enclosed by one of the inside spaces different from the other cooling means, and it is more preferable that the cooling means are each independently enclosed by one of the inside spaces.
In the first invention, it is preferable that the rim part is cooled in the forced cooling step such that a relation of A<B is satisfied, where A is a secondary dendrite arm spacing (DAS II) by the secondary arm method of α-Al of the light alloy molten metal solidified at the position farthest from the sprue in the mold cavity formed into the shape of the rim part, and B is a DAS II in the light alloy molten metal solidified in front of the sprue.
In the first invention, it is preferable that the rim part is forcibly cooled such that A, B and C satisfy a formula (1) below, where C is DAS II in the light alloy molten metal solidified at an intermediate portion between the sprue and the position farthest from the sprue in the mold cavity formed into the shape of the rim part.
A+(B−A)×0.1<C<B−(B−A)×0.1 (1)
In the first invention, it is preferable that the rim part comprises a crossing portion with the disc part, and the plurality of cooling means are disposed along the entire circumference on the outer side or the inner side of the mold cavity formed into a shape of the crossing portion.
According to the second invention, a light alloy wheel comprises a substantially annular rim part; and a disc part that is joined to the rim part and is to be attached to an axle, wherein A, B and C satisfy a formula (2) below, where A is DAS II at a position circumferentially farthest from a position with a maximum DAS II in a cross section of the rim part orthogonal to the wheel, B is a maximum DAS II and C is DAS II at an intermediate portion between the position with the maximum DAS II and a position circumferentially farthest therefrom.
A+(B−A)×0.1<C<B−(B−A)×0.1 (2)
In the second invention, it is preferable that the rim part comprises a crossing portion with the disc part, and an average porosity of the crossing portion is not more than 1%.
According to the third invention, a device for manufacturing a light alloy wheel that comprises a substantially annular rim part and a disc part that is joined to one edge of the rim part on an inner side and is to be attached to an axle comprises: a mold comprising a cavity formed into a shape of the light alloy wheel; a sprue opened into a cavity formed into a shape of the rim part of the cavity formed into the shape of the light alloy wheel; a plurality of cooling means attached to the outer side or inner side of the mold cavity formed into the shape of the rim part along a circumferential direction; and a control means that operates such that, after the light alloy molten metal is poured from the sprue opened into the cavity formed into the shape of the rim part, of the plurality of cooling means, one cooling means located farthest from the sprue is first operated and an other cooling means thereof is then operated in sequence toward the sprue.
In the third invention, it is preferable that the cooling means comprise a cooling block with a cooling pipe and are attached to the outer side of the cavity formed into the shape of the rim part.
In addition, it is preferable that the upper mold comprises an inside space formed in a circumferential direction along the cavity formed into the shape of the rim part, and the cooling means comprise a cooling pipe arranged in the inside space, and it is more preferable that the one cooling means and the other cooling means are arranged in different ones of the inside space.
In addition, it is desirable that the control means operates such that, after the light alloy molten metal is poured from the sprue opened into the cavity formed into the shape of the rim part, of the plurality of cooling means, one cooling means located farthest from the sprue is first operated and the other cooling means thereof is then operated in sequence toward the sprue, and the control means controls an operation time or a cooling pressure of the cooling means such that relative to a cooling power of the one cooling means, a cooling power of the other cooling means decreases in sequence toward the sprue.
According to the inventions, it is possible to provide a high-strength light alloy wheel that allows the manufacture of a light alloy wheel in which the casting defect such as the shrinkage cavities on the rim part is reduced so as to prevent the air leakage as compared to the prior art manufacturing method, as well as a method and a device for manufacturing the light alloy wheel.
Based on the specific embodiments, the inventions will be described in reference to the drawing. The invention, however, is not intended to be limited to the embodiments and Examples described below, and can be appropriately modified and implemented within the same scope as long as the functions and effects of the invention can be obtained.
As a result of intense study on the casting method to achieve the above-described objects, the present inventors made the present invention based on the finding that it is possible to achieve such objects when after pouring a molten metal into a cavity, plural cooling means provided on a mold to cool a rim part are operated at different timings varied according to a distance from a sprue (hereinafter, sometimes referred to as “side gate”) opened into a mold cavity having the shape of the rim part and/or according to variation in volume of the rim part in a circumferential direction.
That is, a rim-part cavity 1 to be filled with a light alloy molten metal has a small-volume rim-part cavity 1a facing an aperture portion 2 and a large-volume rim-part cavity 1b facing a spoke-portion cavity 3 as shown in
The method for manufacturing a light alloy wheel of the invention is provided to solve such problems and is for manufacturing a light alloy wheel having a substantially annular rim part and a disc part which is joined to one edge of the rim part on the inner side and is to be attached to an axle. The method includes a molten metal pouring step for pouring a light alloy molten metal from a sprue opened into a mold cavity formed into the shape of the rim part, and a forced cooling step performed after the molten metal pouring step to forcibly cool the light alloy molten metal poured into the mold cavity formed into the shape of the rim part so that one predetermined cooling means out of plural cooling means provided along the entire circumference on the outer side or inner side of the mold cavity formed into the shape of the rim part is operated first, and thereafter, the other cooling means are operated.
In the invention using such configuration, when a portion of the rim part cot located around a sprue (side gate) opened into the mold cavity having the shape of rim part, i.e., a portion of the rim cooled at a slower rate than surrounding areas and likely to remain as a localized high-temperature portion (hereinafter, sometimes referred to as “hot spot”), is cooled to a certain temperature by the one cooling means, it is possible to achieve directional solidification along the circumferential direction of the rim (hereinafter, sometimes referred to as “circumferential directional solidification”) without forming extra thickness portions. As a result, a riser effect acts on the entire rim part from the side gate and casting defects such as shrinkage cavities occurring in the rim part can be reduced as compared to the conventional manufacturing method.
In more detail, when a light alloy wheel is formed by a casting method in which a light alloy molten metal is poured from a sprue (hereinafter, sometimes referred to as “side gate”) 19 opened into a cavity 100b which has the shape of the rim part and is defined by an upper mold 13 and a pair of movable split molds 14 as shown in
Next, the invention will be specifically described based on the first and second embodiments. Firstly, a configuration of a light alloy wheel manufactured in the both embodiments and constituent elements of the commonly used manufacturing device and mold will be described.
A light alloy wheel manufactured in each embodiment of the invention will be described in reference to
An example of a device for manufacturing the wheel having such configuration will be described in reference to
As shown in
The configuration of the manufacturing device provided with the mold 100 will be described. As shown in
When using the manufacturing device 80 having such configuration, clamping of the mold 100 composed of the lower mold 12, the upper mold 13 and the pair of movable split molds 14 is completed in a predetermined period of time after the start of casting. After completion of the clamping, the pressurizing means starts to pressurize the holding furnace in accordance with a preset pressurizing pattern. The molten metal 80h in the holding furnace 80b is pushed up by the pressure and is then supplied into the cavity of the mold 100 from the center gate 18 and the side gates 19 through the stalks 18a and 19a. Once the molten metal 80h reaches an inner flange portion cavity 25a and the cavity is completely filled with the molten metal 80h, pressure applied by the pressurizing means is increased for a predetermined period of time to supply more molten metal 80h so that the volume reduced by shrinkage due to solidification is refilled. After the predetermined period of time, pressure applied to the holding furnace 80b by the pressurizing means is released and the molten metal 80h remaining in the stalks 18a and 19a returns to the holding furnace 80b, thereby completing casting of the wheel.
The method and device for manufacturing the light alloy wheel in the first embodiment of the invention will be described in reference to
The mold 100 of the first aspect has plural chillers 15 as an example of plural cooling means which are provided in the movable split molds 14 on the outer side of the cavity (crossing portion-forming cavity) having the shape of the coupling (crossing) portion between the rim part and the disc part and are arranged along the entire circumference. In detail, each chiller 15 in the present aspect is constructed from a cooling block 15b with a cooling pipe 15a and has a circumferential length substantially equal to a width of a base joint of each spoke (design portion) 9g. Such chiller 15 is configured that a coolant such as cooling air or cooling water is circulated in arrow directions through the cooling pipe 15a to cool the cooling block 15b. The cooling block 15b is preferably formed of a material which has a higher thermal conductivity than a material constituting the mold and does not contaminate an aluminum alloy molten metal even when in contact with the molten metal.
The arrangement of the chillers 15 configured as described above will be described in reference to
The rim part 9a is coupled to the spokes 9g on the disc part 9e side and the crossing portions 26 are thereby formed, as described previously. The crossing portion 26 is thicker than the non-crossing portion 27 and is thus likely to be a hot spot. In addition to the crossing portions, uneven thickness portions which are likely to be hot spots are sometimes formed for a design reason. In the present invention, the crossing portions and the uneven thickness portions are called “thick portions”.
The above-described chillers as cooling means are arranged on the outer side of the rim part cavity 100b but may be arranged on the inner side, and also may be provided on any of the lower mold 12, the upper mold 13 and the movable split molds 14 as long as they are located at positions allowing preferably the thick portions of the rim part to be cooled. In this regard, however, cooling means do not necessarily need to be provided for all thick portions, and the cooling means may not be provided at the positions corresponding to the thick portions close to the side gates 19. However, among the lower mold 12, the upper mold 13 and the movable split molds 14, the area facing the thick portions and the space for installing the cooling means are largest in the movable split molds 14 and it is thus preferable to provide cooling means on the movable split molds 14.
Also, in combination with cooling from the outer side of the rim part-forming cavity using the cooling means provided on the movable split molds as described above, it is sometimes necessary to cool from the inner side of the rim part-forming cavity in order to adequately solidify the molten metal filled in the rim part-forming cavity. The cooling from inner side of the rim part-forming cavity can be adjusted by appropriately selecting a material constituting the mold and the structure of the mold. In detail, the chillers as described above may be arranged on the upper mold, or, a cooling pipe which is a cooling means in the second embodiment described later may be arranged in an inside space provided in the upper mold.
The manufacturing device in the first embodiment has plural cooling means (chillers) as described above and is also provided with a control means for controlling the plural cooling means so that, after a light alloy molten metal is poured from the side gate 19 opened to the rim part cavity 100b, one cooling means located farthest from the side gate 19 is operated first, and the other cooling means are then operated in sequence toward the side gate 19. The control means is realized by, e.g., CPU which executes a program. Alternatively, the control means may be partially or entirely constructed from a hardware circuit such as reconfigurable circuit (Field Programmable Gate Array: FPGA) or application specific integrated circuit (ASIC).
In detail, the cooling means can be controlled by a program stored in the control means, in which, e.g., wait time, circulation duration and pressure of the coolant flowing through the cooling pipe 15a in the cooling block 15b are set for each cooling means. The coolant wait time is a period from completion of filling of the molten metal into the cavity to start of coolant circulation through the cooling pipe 15a, the circulation duration is a period from start to end of the coolant circulation, and the coolant pressure is pressure of circulating coolant. In order to operate the plural cooling means at different timings, the coolant wait time is differently programmed for each cooling means. The coolant wait time for the one cooling means to be operated first is set to the shortest, and the coolant wait time for the other cooling means is set to be longer. The coolant wait time is preferably set to the shortest for the cooling means located farther from the side gate and is increased for the other cooling means as a distance from the side gate decreases. The cooling condition setting is adjusted such that when, for example, it is considered that a thick portion is not sufficiently cooled, cooling power of the corresponding cooling means is increased by reducing the coolant wait time, increasing the circulation duration or increasing the coolant pressure, or a combination of two or more thereof. The setting can be such that cooling power of the one cooling means to be operated first is the highest and cooling power of the other cooling means to be subsequently operated decreases toward the sprue. In this case, cooling power of the other cooling means may decrease with a gradient towards the sprue.
Next, a method for manufacturing a light alloy wheel using the mold 100 shown in
After making sure that the molten metal is filled up to the upper end of the cavity in the molten metal pouring step, the plural chillers 15 are operated such that the chiller 151 as the one cooling means located farthest from the side gate is operated first and the chillers 152 and 153 as the other cooling means are operated in this order, thereby forcibly cooling the light alloy molten metal poured into the mold cavity having the shape of the rim part. “Operation” of the cooling means is to make the coolant circulate through the cooling pipe 15a. As a result, the rim main body cavity 23a including the crossing portions 26 is cooled and the aluminum alloy molten metal is directionally solidified toward the side gate 19.
When it is difficult to achieve circumferential directional solidification only by operating the plural cooling means at different timings, forced cooling of the light alloy molten metal poured into the mold cavity having the shape of the rim part is desirably performed with such conditions that cooling power of the one cooling means is the highest and cooling power of the other cooling means decreases toward the side gate. It is thereby possible to achieve circumferential directional solidification more preferably.
Since cooling power of the cooling means can be adjusted by changing operation time (circulation duration), it is more desirable to gradually decrease operation time of cooling means from the position farthest from the side gate toward the side gate.
Since cooling power of the cooling means can be adjusted also by changing the coolant flow rate (coolant pressure), it is further desirable that the coolant flow rate in the cooling means with a coolant path be gradually reduced from the position farthest from the side gate toward the side gate.
After completing the forced cooling step, the molten metal is returned to the holding furnace by releasing the pressure in the holding furnace and the completely solidified wheel material is demolded.
The method and device for manufacturing the light alloy wheel in the second embodiment of the invention will be described in detail in reference to
As shown in
The cooling pipes 13a-1 (the one cooling means) and 13b-1 (the other cooling mean 1) provided in the first inside space 131a inject the cooling air supplied through an air supply means 130 in the first inside space 131a. The cooling pipe 13a-1 is located at the center of the first inside space 131a in the circumferential direction, i.e., at the position farthest from the side gate 19 in the circumferential direction. Meanwhile, the cooling pipe 13b-1 is located on a side of the cooling pipe 13a-1, i.e., on the side gate 19 side of the cooling pipe 13a-1 in the circumferential direction. The axial position of the cooling pipes 13a-1 and 13b-1 in the first inside space 131a corresponds to the position of the inner flange portion cavity 25a as shown in
Now, referring to
As shown in
In the second embodiment, the inside space formed inside the upper mold 13 is divided into the first inside space 131a and the second inside space 132a, and the cooling pipes (the one cooling means) 13a-1 present at the position farthest from the side gate 19 is arranged in the first inside space 131a and is separated at least from the cooling pipe 13c-1 (the other cooling means 2) which is arranged in the second inside space 132a, and such configuration has the following advantageous technical significance. That is, if the cooling pipes 13a-1 to 13c-1 are arranged in the same inside space, the cooling air injected from the firstly-operated cooling pipe 13a-1 causes substantially simultaneous cooling of the entire upper mold 13, not pinpoint cooling of the peripheral wall of the upper mold 13 at the position farthest from the side gate 19. If the entire upper mold 13 is cooled substantially simultaneously, it is difficult to achieve desired circumferential directional solidification. In contrast, when the inside space is divided into the first inside space 131a and the second inside space 132a so that the cooling pipes 13a-1 and 13b-1 are provided in the first inside space 131a and the cooling pipe 13c-1 in the second inside space 132b as is in the second embodiment, the cooling air injected from the cooling pipes 13a-1 and 13b-1 stay inside the first inside space 131a and preferentially cools the peripheral wall of the upper mold 13 at which the first inside space 131a is present. Thus, the portion of the peripheral wall of the upper mold 13 facing the side gate 19 is prevented from being cooled at the same time and is cooled by the cooling air injected from the cooling pipe 13c-1 arranged inside the second inside space 132b. Such configuration, in which the cooling pipes 13a-1 as the one cooling means and the cooling pipe 13c-1 as the other cooling means arranged at a position corresponding to the side gate are provided in separate inside spaces, is preferable since circumferential directional solidification is achieved more easily.
To adequately solidify the molten metal filled in the rim part-forming cavity, it is sometimes necessary to cool from the outer side of the rim part-forming cavity in combination with the cooling from the inner side of the rim part-forming cavity using the cooling means (cooling pipe) provided on the upper mold as described above. The cooling from the outer side of the rim part-forming cavity can be adjusted by appropriately selecting a material constituting the mold and the structure of the mold, and the mold 100 of the second embodiment is configured that the plural chillers 15 are provided in the movable split molds 14 on the outer side of the crossing portion-forming cavity so as to be arranged along the entire circumference. In detail, each chiller 15 in the present aspect is constructed from the cooling block 15b with the cooling pipe 15a and has a circumferential length substantially equal to a width of a base joint of each spoke (design portion) 9g. Such chiller 15 is configured that a coolant such as cooling air or cooling water is circulated in arrow directions through the cooling pipe 15a to cool the cooling block 15b. The cooling block 15b is preferably formed of a material which has a higher thermal conductivity than a material constituting the mold and does not contaminate an aluminum alloy molten metal even when in contact with the molten metal.
In a 90° section from the side gate portion in the circumferential direction, the chillers 15 configured as described above are arranged as shown in
Various conditions of coolant (cooling air) injected from the cooling pipes 13a-1 to 13c-1, e.g., the cooling conditions such as wait time until injection of the cooling air (hereinafter, sometimes referred as “injection wait time”), injection duration of the cooling air and pressure of the cooling air are independently set for each of the cooling pipes 13a-1 to 13c-1 and controlled by a program. The injection wait time is a period from completion of filling of the molten metal into the cavity to start of air injection and is indicated by T1 to T3 in
The manufacturing device in the second embodiment having the cooling means as described above is also provided with a control means which controls the plural cooling means so that, after a light alloy molten metal is poured from the side gate 19 opened to the rim part cavity 100b, one cooling means located farthest from the side gate 19 is operated first and the other cooling means are then operated in sequence toward the side gate 19, and the control means also controls operation time or cooling pressure of the cooling means so that cooling power of the one cooling means is the highest and cooling power of the other cooling means decreases in sequence toward the side gate 19. The control means is realized by, e.g., CPU which executes a program. Alternatively, the control means may be partially or entirely constructed from a hardware circuit such as FPGA or ASIC.
The method for manufacturing a light alloy wheel in the second embodiment of the invention includes a molten metal pouring step in which, from the side gate (sprue) 19 opened to the cavity 100b having the shape of the rim part and defined by the upper mold 13 and the pair of movable split mold 14, a light alloy molten metal is poured into the cavity 11 which has the shape of the light alloy wheel and is formed in the mold 100 having the upper mold 13, the lower mold 12 and the pair of movable split molds 14 as shown in
In detail, firstly, the lower mold 12, the upper mold 13 and the pair of movable split molds 14 in
After the molten metal is filled up to the inner flange portion cavity 25a in the molten metal pouring step, the forced cooling step is performed by operating the cooling pipes (cooling means) 13a-1 to 13c-1 so that the cooling air is circulated through and injected from the cooling pipes 13a-1 to 13c-1. The forced cooling step here may be performed such that the cooling pipes 13b-1 are firstly operated as the one cooling means as shown in
Circumferential directional solidification of the molten metal filled in the rim-part cavity 100b which is achieved by the above-described manufacturing method will be described in reference to
In the mold 100 having the cooling pipes 13a to 13c configured as described above, solidification of the molten metal 80h filled in the rim part cavity 100b through the side gates 19 progresses as described below. That is, the solidification of the molten metal 80h filled in the rim part cavity 100b starts at the position farthest from the side gates 19 when cooled by the cooling pipe (the one cooling means) 13a-1 which is operated first. In the second embodiment, the solidification of the molten metal 80h starts at a point Q which a circumferentially middle portion between a pair of side gates 19 as well as an axial position corresponding to the inner flange portion cavity 25a arranged at an upper end. The molten metal 80h started to solidify at the point Q of the upper portion then gradually solidifies when cooled by the cooling pipe 13b-1 (the other cooling means 1) and the cooling pipe 13c-1 (the other cooling means 2) while orienting from the inner flange portion cavity 25a down to the side gates 19 from the line R1 toward the line R7 as indicated by the arrows P1 to P3. As such, in the manufacturing method in the embodiments of the invention, it is possible to achieve desired circumferential directional solidification which progresses from the position farthest from the side gate 19 towards the side gate 19.
In order to operate the cooling pipes 13a-1 to 13c-1 at different timings, the program is made so that, for example, injection wait times T1 to T3 for the cooling pipes 13a-1 to 13c-1 are different from each other as shown in
In order to achieve circumferential directional solidification more effectively, it is desirable to set so that cooling power of the cooling pipe 13a-1 is the highest and cooling power of the cooling pipes 13b-1 and 13c-1 decreases toward the side gate 19. In detail, it is possible to realize it when injection durations t1 to t3 of the cooling air injected from the cooling pipes 13a-1 to 13c-1 gradually decrease (preferably in a gradient manner) in this order or when the air pressures F1 to F3 gradually decrease (preferably in a gradient manner) in this order.
After completing the forced cooling step, the molten metal 80h is returned to the holding furnace 80b by releasing the pressure in the holding furnace 80b, the completely solidified wheel material is taken out of the mold 100 and, if required, is appropriately treated by, e.g., processing or painting, etc. A desired wheel is thereby obtained.
The light alloy wheel of the invention has a substantially annular rim part and a disc part joined to one edge of the rim part on the inner side and to be attached to an axle, and is characterized in that A, B and C satisfy the formula (2): A+(B−A)×0.1<C<B−(B−A)×0.1, where A is DAS II at a position circumferentially farthest from a position with the maximum DAS II on the cross section of the rim part taken orthogonal to the wheel, B is the maximum DAS II and C is DAS II at an intermediate portion between the position with the maximum DAS II and a position circumferentially farthest therefrom. Since the values of DAS II in the respective sections of the rim part have such specific relation, the light alloy wheel of the invention has fewer casting defects such as shrinkage cavities occurring in the rim part, has higher strength and causes less air leakage than the conventional light alloy wheels. The light alloy wheel which is more advantageous in terms of strength and air leakage can be obtained when porosity of the crossing portion is not more than 1%.
Next, Examples 1 to 5 which correspond to the first embodiment will be described in comparison with Comparative Example 1. Light alloy wheels were made through the molten metal pouring step in which a casting aluminum alloy molten metal equivalent to AC4CH defined by JIS H 5202 is poured as a light alloy molten metal from the side gate 19 opened into the mold cavity shown in
The obtained light alloy wheels were subjected to measurements of secondary dendrite arm spacing (hereinafter, sometimes referred to as DAS II) in α-Al of the rim part (measurement of secondary arm spacing), average porosity of the crossing portion and air leakage rate. The measurement methods will be described in reference to
In the light alloy wheels in Examples 1 to 5, circumferential directional solidification in the rim part was achieved as understood from the DAS II values, and casting defects such as shrinkage cavities occurring in the rim part were less than the light alloy wheel in Comparative Example 1 manufactured by the conventional method as understood from the average porosity. It was found that the air leakage rate of the light alloy wheel was improved in all of Examples 1 to 5 as compared to Comparative Example 1. In the light alloy wheel in Comparative Example 1, circumferential directional solidification of the rim part was imperfect and the average porosity was slightly higher than Examples 1 to 5. The air leakage rate of the light alloy wheel in Comparative Example 1 was not sufficiently small in view of productivity.
It was found that it is preferable to forcibly cool the molten metal poured into the rim part cavity 100b by performing the forced cooling step so that a relation A<B is satisfied, where A is DAS II in the molten metal solidified in the position PA farthest from the side gate 19 in the rim part cavity 100b and B is DAS II in the molten metal solidified in the position PB in front of the side gate.
Furthermore, it was also found that it is preferable to forcibly cool the molten metal poured into the rim part cavity 100b by performing the forced cooling step so that A, B and C satisfy the formula (1) below, where C is DAS II in the light alloy molten metal solidified in the intermediate portion between the side gate 19 and the position farthest from the side gate 19 in the rim part cavity 100b.
A+(B−A)×0.1<C<B−(B−A)×0.1 (1)
In addition, it was found that the light alloy wheel is preferably configured so that A, B and C satisfy the formula (2) below, where A is DAS II at a position circumferentially farthest from a position with the maximum DAS II on the cross section of the rim part taken orthogonal to the wheel, B is the maximum DAS II and C is DAS II at an intermediate portion between the position with the maximum DAS II and a position circumferentially farthest therefrom.
A+(B−A)×0.1<C<B−(B−A)×0.1 (2)
Next, Examples 6 to 9 which correspond to the second embodiment will be described in comparison with Comparative Example 2. Light alloy wheels were made through the molten metal pouring step in which a casting aluminum alloy molten metal equivalent to AC4CH defined by JIS H 5202 is poured as a light alloy molten metal from the side gate 19 opened into the mold cavity shown in
The obtained light alloy wheels were subjected to measurements of DAS II in the rim part, average porosity of the crossing portion and air leakage rate. Table 2 shows the manufacturing conditions and DAS II, average porosity and air leakage rate of the obtained light alloy wheels.
In the light alloy wheels in Examples 6 to 9, circumferential directional solidification in the rim part was achieved as understood from the DAS II values, and casting defects such as shrinkage cavities occurring in the rim part were less than the light alloy wheel in Comparative Example 2 manufactured by the conventional method. It was found that the air leakage rate of the light alloy wheel was improved in all of Examples 6 to 9 as compared to Comparative Example 2. In Comparative Example 2, circumferential directional solidification of the rim part was imperfect and the light alloy wheel had somewhat more casting defects such as shrinkage cavities in the rim part than the light alloy wheels made by the manufacturing methods used in Examples 6 to 9.
It was found that it is preferable to forcibly cool the molten metal poured into the rim part cavity 100b by performing the forced cooling step so that a relation A<B is satisfied, where A is DAS II in the light alloy molten metal solidified in the position farthest from the side gate 19 in the rim part cavity 100b and B is DAS II in the light alloy molten metal solidified in front of the side gate 19.
Furthermore, it was also found that it is preferable to forcibly cool the molten metal poured into the rim part cavity 100b by performing the forced cooling step so that A, B and C satisfy the formula (1) below, where C is DAS II in the light alloy molten metal solidified in the intermediate portion between the side gate 19 and the position farthest from the side gate 19 in the rim part cavity 100b.
A+(B−A)×0.1<C<B−(B−A)×0.1 (1)
In addition, it was found that the light alloy wheel is preferably configured so that A, B and C satisfy the formula (2) below, where A is DAS II at a position circumferentially farthest from a position with the maximum DAS II on the cross section of the rim part taken orthogonal to the wheel, B is the maximum DAS II and C is DAS II at an intermediate portion between the position with the maximum DAS II and a position circumferentially farthest therefrom.
A+(B−A)×0.1<C<B−(B−A)×0.1 (2)
Next, Examples 10 to 13 using the preferred mold 200 in the second embodiment will be described in comparison with Comparative Example 3. Wheels were made through the molten metal pouring step in which a casting aluminum alloy molten metal equivalent to AC4CH defined by JIS H 5202 is poured as a molten metal from the side gate 19 opened into the cavity of the mold 200 shown in
The obtained light alloy wheels were subjected to measurements of DAS II in the rim part, average porosity of the crossing portion and air leakage rate. Table 3 shows the manufacturing conditions and DAS II, average porosity and air leakage rate of the obtained light alloy wheels.
In the light alloy wheels in Examples 10 to 13, circumferential directional solidification in the rim part 9a was achieved as understood from the DAS II values, and casting defects such as shrinkage cavities occurring in the rim part 9a were less than the light alloy wheel in Comparative Example manufactured by the conventional method. It was found that the air leakage rate of the light alloy wheel was improved in all of Examples 10 to 13 as compared to Comparative Example 3. In Comparative Example 3, circumferential directional solidification of the rim part was imperfect and the light alloy wheel had somewhat more casting defects such as shrinkage cavities in the rim part than the light alloy wheels made by the manufacturing methods used in Examples.
It was found that it is preferable to forcibly cool the molten metal poured into the rim part cavity 100b by performing the forced cooling step so that a relation A<B is satisfied, where A is DAS II in the molten metal solidified in the position PA farthest from the side gate 19 in the rim part cavity 100b and B is DAS II in the molten metal solidified in the position PB in front of the side gate.
Furthermore, it was also found that it is further preferable to forcibly cool the molten metal poured into the rim part-forming cavity by performing the forced cooling step so that A, B and C satisfy the formula (1) below, where C is DAS II in the molten metal solidified in the intermediate position Pc between the position PB of the side gate 19 and the position PA farthest from the side gate 19 in the rim part cavity 100b.
A+(B−A)×0.1<C<B−(B−A)×0.1 (1)
In addition, it was found that the light alloy wheel is preferably configured so that A, B and C satisfy the formula (2) below, where A is DAS II at a position circumferentially farthest from a position with the maximum DAS II on the cross section of the rim part taken orthogonal to the wheel, B is the maximum DAS II and C is DAS II at an intermediate portion between the position with the maximum DAS II and a position circumferentially farthest therefrom.
A+(B−A)×0.1<C<B−(B−A)×0.1 (2)
The invention is applicable to a light-alloy vehicle wheel which is formed of a light alloy such as aluminum alloy or magnesium alloy and is to be installed on an automobile such as passenger car.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-186012 | Sep 2014 | JP | national |
| 2014-210459 | Oct 2014 | JP | national |
| 2014-256886 | Dec 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/076073 | 9/14/2015 | WO | 00 |
