JP4548995B2 - Strengthening the aluminum wheel mounting surface - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for reinforcing a mounting surface of a light alloy wheel for a vehicle on an axle, and particularly to a method for reinforcing an aluminum wheel mounting surface for a truck or a bus.
[0002]
[Prior art]
The wheel for trucks and buses is generally a steel-steel welded structure. However, forged or cast aluminum wheels have come to be adopted in terms of weight reduction, heat dissipation of tires and brakes, and design.
[0003]
On the other hand, when replacing a steel wheel with aluminum, it is necessary to increase the thickness of the wheel hub compared to the case of steel because of the difference in material strength between steel and aluminum. At this time, when the vehicle width of a truck or the like is determined, there is a problem that the hub thickness of the aluminum wheel cannot be increased to a thickness that meets the strength standard of cast aluminum. Further, increasing the thickness of the hub is contrary to the purpose of reducing the weight of the wheel.
[0004]
Japanese Patent Application Laid-Open Nos. 9-122893 and 10-225825 disclose prior art that solves the above problems. Japanese Patent Application Laid-Open No. 9-122893 discloses a manufacturing method for improving the fatigue strength of cast aluminum wheels for trucks and buses. In other words, "cast aluminum products for trucks and buses are cast aluminum by performing all three types of strengthening processing, including forging between bolt holes, burnishing of nut seats and shot blasting of mounting surfaces in any order. "A manufacturing method for strengthening a mounting bolt hole portion of a wheel" is described.
[0005]
Japanese Patent Application No. 10-225825 discloses a method for imparting sufficient fatigue strength and rigidity to the entire surface of a light alloy wheel and improving the gloss and brightness of the wheel surface. That is, “Light alloy wheels are made of steel or stainless steel balls with relatively large specific gravity and / or irregularly shaped media with rounded corners placed in the barrel, giving strong vibrations and beating the media on the wheel surface. By doing so, a hardened layer is formed and a smooth glossy skin close to a mirror surface is obtained ”.
[0006]
However, the prior art described above also has the following problems. That is, in the technique described in Japanese Patent Application Laid-Open No. 9-122893, it is necessary to perform all three kinds of strengthening processes, and the number of strengthening steps is increased, resulting in a decrease in production efficiency. Further, it is described that the wheel is mounted on the axle without machining the nut seat and the mounting surface after the three types of strengthening, and the nut is tightened. The surface condition of the shot peening skin is also rough, and if it is mounted in this state, there is a risk of serious accidents such as protrusions on the tightening surface becoming slack or loosening of the mounting bolts while the truck or bus is running. . There has been no disclosure of the technique of shot peening in which the mounting bolt does not loosen even on shot peening skin.
On the other hand, the technique described in Japanese Patent Application No. 10-225825 is excellent in giving radiance to the entire wheel. On the other hand, since beating is carried out by vibration in the barrel, it was not possible to give sufficient compressive residual stress to the necessary part of the wheel surface and the level of production efficiency of the wheel was not satisfactory.
[0007]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems. In an aluminum wheel for trucks and buses, an aluminum wheel mounting surface and a method for strengthening a mounting bolt hole and a nut seat surface that achieve the object of weight reduction and high production efficiency. Is to provide.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems in the present invention, in the first invention, in the aluminum wheel for trucks and buses, the center hole of the aluminum wheel which has completed the casting and heat treatment process and the axle of the aluminum wheel to the axle are provided. Shot peening is performed after the mounting surface, mounting bolt hole and nut seat surface are cut, and then the necessary parts excluding the mounting surface to the axle of the aluminum wheel and the mounting bolt hole and nut seat surface are cut according to the center hole reference. It was decided to.
In the second invention, the shot peening in the first invention is performed with a steel ball having a particle size of 0.3 to 0.6 mm.
[0009]
In the conventional method for producing an aluminum wheel, shot peening is performed on the entire aluminum wheel that has been cast and heat-treated. The purpose of this shot peening was to strengthen the portion where the cast skin portion such as the window portion of the wheel remains in the final product and to improve the surface skin on the appearance.
[0010]
In other words, for the mounting surface of the wheel axle, the mounting bolt hole, and the nut seat surface, which are the problems this time, the surface roughness (arithmetic mean roughness display) 1.6 μm by machining after the shot peening process. Finished to the extent. For this reason, since the compressive residual stress layer formed on the mounting surface, the mounting bolt hole, and the surface of the nut seat surface is removed by machining, an improvement in fatigue strength cannot be expected.
The reason why the shot skin is removed by machining is that the surface roughness of the shot skin is not good. That is, the surface roughness (in arithmetic mean roughness display) of the shot skin is about 12 μm, and it was considered that the surface roughness of the mounting surface and the seating surface is too rough. This is because if the surface roughness of the mounting surface or seating surface is rough, there is a concern that the bolts may loosen due to various projecting loads when the vehicle travels and the protrusions (parts with a rough surface roughness) sag.
The present invention changes the mounting timing of the shot peening process, which has been conventionally performed, without providing a special (extra) processing step, and the mounting surface of the aluminum wheel for trucks and buses, the mounting bolt hole, and the nut seat The strength of the surface can be increased.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a manufacturing process of a truck or bus aluminum wheel according to an embodiment of the present invention will be described. 1 is a cross-sectional view of an aluminum wheel for trucks according to an embodiment of the present invention, FIG. 2 is a side view seen from the direction A in FIG. 1, FIG. 3 is a side view seen from the direction B in FIG. 1 is an enlarged cross-sectional view of the mounting bolt hole in FIG. 1, and FIG. 5 is an enlarged view of a portion P in FIG.
For the aluminum wheel that has been cast and heat-treated, first, the center hole 7 of the wheel 100, the mounting bolt hole 3, the nut seat surface 4 and / or the mounting surface 2 of the wheel on the axle are in a finished product state (normally finished state) ) And then shot peening is performed on the entire wheel. After shot peening is complete, the rim and valve holes are cut. As a result, the mounting bolt hole 3, the nut seat surface 4, the mounting surface 2, the center hole 7, and the cast skin portion remain as shot skin, and the other portions become cut skin.
[0012]
Here, an important point is the surface roughness of the shot peening skin. That is, the essence of the present invention is that not only the execution time of the shot peening process is changed, but also the mounting surface, the mounting bolt hole and the nut seat surface can be mounted on the vehicle in a state of shot peening skin (without machining). is there. Therefore, it is necessary to specify a shot peening method that enables this.
The steel ball used for this shot peening is made of stainless steel or steel, and the diameter of the steel ball is generally 0.3 to 1.0 mm, more preferably in the range of 0.3 to 0.6 mm. The surface roughness is about 8.0 μm (arithmetic average roughness). If the diameter of the steel ball is smaller than 0.3 mm, the mass of the steel ball itself becomes small, so that a sufficient compressive residual stress cannot be applied to a necessary portion. On the other hand, when the thickness is larger than 0.6 mm, the surface roughness of the shot peening skin becomes rough, which is not preferable. As a supplementary explanation, a conventional shot peening uses a steel ball having a diameter of 0.8 mm, and the surface roughness at this time is about 12 μm (arithmetic mean roughness).
The shape of the steel ball includes a spherical shape and a cylindrical shape (cut wire shape), but a spherical shape is suitable for maintaining good surface roughness.
[0013]
Next, cracks occurring in the fatigue test of aluminum wheels for trucks and buses will be described. As shown in FIGS. 2 and 5, many cracks are found near the contact surface boundary line (axle side outer peripheral line) 5 with the wheel mounting surface 7 and the nut seat surface 4. A hair crack 8 is generated from the contact surface boundary line 5 of the wheel mounting surface 2 toward the outside, and the hair crack 8 progresses when the fatigue test is continued. Further, the hair crack 1 generated on the nut seat surface 4 shown in FIG. 5 also progresses when the fatigue test is continued.
To prevent this cracking, compressive residual stress is applied to the mounting bolt hole and nut seat surface by shot peening, and a shot skin part is left about several mm outside the boundary line (contact surface) of the wheel mounting surface (shot skin). This is solved by the boundary line 6). Note that the present invention need not be limited to the spherical seat shown in FIG.
[0014]
【Example】
The aluminum wheel for a 17-inch truck shown in FIGS. 1 to 3 was cast while being pressurized with an acicular pin in a rigid die casting machine. Next, in order to improve strength and elongation, heat treatment was performed for solution and aging.
Next, the center hole 7, the mounting hole (bolt hole 3 and nut seat surface 4), and the mounting surface to the axle were cut as necessary. The surface roughness at this time was 1.6 μm in terms of arithmetic average roughness. In addition, in order to ensure machining accuracy, the center hole was also machined in the first machining process, and machining was performed based on the center hole 7 in the second machining.
Next, shot peening was performed using a 0.4 mm stainless steel ball under the condition of a shot speed of 40 to 50 m / sec, and then other necessary parts were cut based on the center hole. When the endurance test is performed on the aluminum wheel manufactured in this way under the specified conditions, and the mounting surface, the mounting bolt hole and the nut seat surface are cut skin, the rejected surface is shot skin Passed.
[0015]
Here, the contents of the durability test will be described. Each endurance test has its own method, and there is no common test. The endurance fatigue test mainly consists of a rotating bending test and a drum test. This drum test is a test in which the drum is rotated while pressing the drum against the tire with a constant force while the tire is mounted on the wheel. As a result, the tire (wheel) is driven and rotated, which corresponds to a running test. As described above, in this embodiment, a comparative test of a conventional wheel and a wheel based on the present invention was performed according to the test regulations of M company.
[0016]
【The invention's effect】
By carrying out shot peening on the mounting surfaces of aluminum wheels for trucks and buses to the axle, the same mounting bolt holes and nut seats, and mounting these surfaces on the axles without machining, The fatigue strength is increased by the compressive residual stress applied to the shot skin surface, and cracks generated on the wheel mounting surface, the mounting bolt hole, and the nut seat surface can be eliminated. Also, the mounting surface of the wheel to the axle and the minimum necessary parts of the mounting bolt hole and nut seat surface are left as it is, and other parts, that is, the outer surface and the rim part are cut by machining. It has a radiant skin, and the appearance of aluminum can be recognized. Therefore, it is possible to increase the fatigue strength of the mounting surface, the same mounting bolt hole, and the nut seat surface while ensuring the design characteristics as an aluminum wheel, thereby improving the merchantability.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a truck aluminum wheel according to an embodiment of the present invention.
FIG. 2 is a side view seen from the direction A in FIG.
FIG. 3 is a side view as seen from the direction B in FIG. 1;
4 is an enlarged cross-sectional view of a mounting bolt hole in FIG. 1. FIG.
FIG. 5 is an enlarged view of a P portion in FIG. 3;
[Explanation of symbols]
1 Hair crack of nut seat surface 2 Mounting surface of aluminum wheel to axle 3 Mounting bolt hole 4 Nut seat surface (spherical seat)
5 Contact surface boundary line with axle side of mounting surface (Axle-side outer peripheral line)
6 Shot skin boundary 7 Center hole 8 Hair crack 100 on mounting surface Aluminum wheel

Claims (1)

In an aluminum wheel for trucks and buses, the center hole of the aluminum wheel that has completed the casting and heat treatment process, the mounting surface of the aluminum wheel on the axle, the mounting bolt hole, and the nut seat surface are cut, and then the entire aluminum wheel Shot peening is performed with a steel ball with a particle size of 0.3 to 0.6 mm , and then the necessary parts excluding the mounting surface of the aluminum wheel on the axle, the mounting bolt hole and the nut seat surface are cut according to the center hole standard. A method for strengthening an aluminum wheel mounting surface.

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