JPH02258401A - Fretting damage prevention for automotive wheel - Google Patents

Abstract

PURPOSE:To improve the durability of a wheel with simplicity and low cost by applying graphite to the hum attachment datum surface of an automotive wheel and radiating laser to it to establish its surface hardness within a particular range. CONSTITUTION:By applying graphite to the hub attachment datum surface of an automotive wheel and radiating laser to it, the hardness of the hub attachment datum surface is established to HV 300 - 700. Namely, only to the hub attachment datum surface which is a necessary section for the automotive wheel, first, graphite is applied and dried. Next, a laser beam is radiated to the section. As a result, applied carbon is immersed into the wheel material from the surface in form of solid solution, and a relevant portion is tempered by self-cooling after laser radiation. Since the hardness of the surface becomes HV 300 - 700, it is possible to prevent fretting damage effectively, thus improving the durability of the wheel with simplicity and low cost.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for effectively preventing fretting damage to a reference surface of an automobile wheel and improving its durability when attached to a hub disk. It is.

<Prior Art and its Problems> In general, the most important characteristics required for automobile wheels that are fixed to hub discs with bolts, regardless of whether they are passenger cars, trucks, buses, etc., are strength and durability. However, when an automobile is used under harsh conditions for a long period of time, fatigue cracks may occur in the wheels, and measures to prevent this have been intensively studied for safety reasons.

The location where fatigue cracks occur in automobile wheels varies depending on the shape, material, and load applied to the wheel, but the typical location is the air vent area of the wheel.

The hat and hub are attached at three locations on the reference surface.

Since the fatigue cracks that occurred in the air holes and the hat were caused by stress concentration, countermeasures were taken in terms of material, shape, molding method, etc., and some results were obtained. On the other hand, fatigue cracks on the reference surface of hub installations are caused by "fretting damage due to repeated contact with the hub disc", which occurs because the hub disc and wheel are fastened with bolts. However, no effective countermeasure has been found.

However, many proposals have been made for the prevention of fretting damage to general steel materials, such as a) reduction of contact surface pressure.

b) Reduction of relative slip amount.

C) Reduction of coefficient of friction.

d) Increase in surface hardness.

e) Application of compressive residual stress.

It is known that the following measures are effective.

However, due to its function, it is difficult to adopt the measures shown in items a) and b) above when attaching a hub to a car wheel relative to a reference surface.From the perspective of item C) above, however, [Measures to apply fluororesin seals] are also considered as "measures to apply sit-beaning" from the perspective of item e) above.
There are examples where these have been adopted, but with fluororesin seals, there are problems with the durability of the seal itself and changes in force when tightening to the hub disk, and with sit-beaning, it is difficult to control residual stress. There were problems such as problems with the surface and roughness of the surface, so none of them could be said to be practical.

Considering these problems, the most effective and stable measure to prevent frent damage to the reference surface when mounting an automobile wheel hub is one that simultaneously satisfies the requirements shown in items d) and e) above. "Induction hardening", "Carburizing"
Alternatively, the conclusion was that a surface hardening method such as "nitriding" would be used. However, in order for induction hardening to be effective, the material steel must have at least 0.2% by weight of solid solute carbon. Induction hardening cannot be applied to steel. Furthermore, since carburizing and nitriding are atmospheric treatments using gas or liquid, these treatments generally harden the entire part and significantly impair toughness, so they cannot be applied to automobile wheels.

However, although there is a method of carburizing and nitriding only the necessary parts of the part (hub mounting reference surface), it is not economical because it takes a lot of time and effort to prevent carburizing and nitriding of unnecessary parts. Therefore, it could not be called a practical method.

Therefore, an object of the present invention is to provide an economical and simple method for attaching an automobile wheel hub to effectively suppress fretting damage on the reference surface and improve the durability of the wheel. placed.

Means for Solving the Problems> The present invention was completed as a result of numerous experiments and studies conducted from various viewpoints in order to achieve the above object. After applying graphite to the reference surface, laser irradiation is performed, and by this, the surface hardness of the reference surface is set to H series 300 to 700. It is characterized by the fact that it can effectively prevent damage caused by

In other words, in the present invention, graphite is first applied and dried only on the necessary parts of an automobile wheel (the reference surface for hub attachment), and then when this part is irradiated with a laser beam, the applied carbon is removed from the surface of the wheel. In addition to penetrating into the material and becoming a solid solution,
This method takes advantage of the phenomenon that self-cooling after laser beam irradiation hardens the area, resulting in a surface hardness of H 300 to 700, effectively preventing fretting damage. The present invention will be explained in more detail along with its operation.

Now, in order to prevent fretting fatigue damage, it is necessary to suppress the occurrence and growth of fretting fatigue cracks. The presence of surface compressive residual stress is effective.

There are mechanical, chemical, and thermal methods to generate a surface hardening layer, but mechanical or thermal hardening methods are not recommended for low carbon steel materials with low yield points such as wheel materials. Have difficulty.

On the other hand, a chemical surface hardening method can be applied, but as already explained, attaching the wheel material to the hub requires a great deal of cost and man-hours if only the reference surface is partially treated.

However, when a graphite material such as graphite paint, which is extremely easy to handle, is applied to the reference surface for attaching the hub of the wheel material as an auxiliary agent, and this area is irradiated with a laser, the graphite infiltrates and dissolves only in that area. Only the necessary portions are modified to be heat-processable, and the modified portions are transformed into martensitic material by subsequent self-cooling to form a hardened layer. Since the portion where martensitic transformation has occurred undergoes volumetric expansion, the formed hardened layer inevitably becomes a compressive residual stress layer. As a result, it is extremely effective and easy to achieve partial surface hardening and imparting compressive residual stress to automotive wheel materials, which was impossible or impractical in terms of quality and man-hours using normal means. I can,
When attaching a hub to an automobile wheel, it becomes possible to properly prevent fretting damage on the reference surface.

Furthermore, based on experimental results regarding laser processing, we have
It has been reported that the graphite applied to improve the absorption efficiency of laser light dissolves in the molten part of the surface of the workpiece, causing cracks, which is an inconvenient phenomenon.'' Conference Lecture Summary, Volume 35 ('84-
10), pp. 76-77], there has never been any suggestion made in the past that the above-mentioned solid solution phenomenon of graphite could be appropriately suppressed and utilized for engineering purposes.

By the way, in the method of the present invention, there is no particular restriction on the "graphite" applied to the reference surface for wheel hub mounting, and either graphite or graphite-containing substances may be applied, but depending on availability, workability, etc. From this point of view, it can be said that the above-mentioned "graphite paint" is suitable.

In addition, as mentioned above, a hardened layer due to martensitic transformation inevitably becomes a compressive residual stress field, and a tensile residual stress field is formed in the vicinity, but in order to effectively utilize these phenomena, it is necessary to limit the degree of stress. need to be controlled. This is the reason why the surface hardness of the hardened layer is specified in the method of the present invention. In other words, when attaching a hardened wheel to a hub, the surface hardness of the reference surface is Hν<300, which means that the amount of carbon dissolved in solid solution or the cooling rate is insufficient, resulting in a hardened surface layer due to martensitic transformation and a compressive residual stress layer. Both of these are small, leading to an insufficient effect in preventing fretting fatigue damage.On the other hand, the surface hardness of Hν>700 means that the amount of dissolved carbon or the cooling rate is too high, causing cracks during cooling. This means that "the surface hardness of the reference surface for mounting hardened wheels on the hub" is based on II series 30.
It was decided that the value should be adjusted to be between 0 and 700. In order to satisfy this condition, it is necessary to set laser beam irradiation processing conditions in which the laser output, focus, and operation speed are appropriately adjusted according to the base material carbon concentration and plate thickness. For example, when processing a wheel material with a thickness of 3 mm by irradiating a CO2 laser beam with an output of 5 kW with a focal point distance of 3 fi, the base material carbon concentration is 0.15% by weight or more and the scanning speed is 1.0%.
When the carbon concentration is less than 0.15% by weight and the scanning speed is 5.0 m/min or more, the surface hardness is only about 11ν280 and the desired performance is not exhibited.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

<Example> First, a JiSSAPH381n plate (hot rolled steel plate for automobile structures) with a thickness of 3.5 m was prepared, and three types of test pieces were cut from it. Paint containing 25% by weight of graphite is applied to the area (slightly wider than the area that contacts the shoe) to a dry film thickness of 20I.
After coating and drying to give xm, the portion was irradiated with laser light to form a hard layer.

The laser beam irradiation was carried out using a 5 kW CO□ laser emitting device with Ar seal gas at a focal point distance of 3 cranes or more, but the scanning speed was 3 m/min for one type and 3 m/min for the remaining one. was set at 1.5 m/min.

Next, for the three types of test materials mentioned above, the "carbon concentration in the depth direction from the surface" at the contact area with the shoe was determined by E.
In addition to measuring with PMA, hardness was also measured at the same site.
Furthermore, a plane bending fatigue test (fretting fatigue test) was conducted, and the three types of test materials are summarized as follows.

Test material A: untreated steel plate (comparison material).

Sample material B: processed at a scanning speed of 3 m 1 minute (processed material equivalent to the present invention).

Sample material C: processed at a scanning speed of 1.5 m/min (processed material equivalent to the present invention).

Here, plane bending fatigue test (fretting fatigue test)
As shown in Fig. 1, a test material (wheel material) 2 whose one end is fixed with a bolt and nut 1 is tightened at an intermediate position with a bolt and nut 4 through a shoe 3 made of the same material as the hub disc. A method was used to investigate the occurrence of fatigue cracks by repeatedly applying bending moments to the free end. In addition, the code|symbol 5 in the figure shows the mount of a test machine, and 6 shows the base.

The carbon concentration measurement results thus obtained are shown in FIG. 2, the hardness measurement results are shown in FIG. 3, and the results of the plane bending fatigue test (fretting fatigue test) are shown in FIG.

From the results shown in FIGS. 2 and 3, it is clear that the treatment according to the present invention caused the surface of specific parts of the wheel material to have a carbon concentration of 0.
．． It can be seen that the hardness increases by 11 to 0.14% by weight, and the hardness increases by Hva 60 to 430, respectively.

And plane bending fatigue test (fretting fatigue test)
From FIG. 4 showing the results, the critical stress amplitude for fatigue failure was 11 kgf/- for sample material A (comparative material), whereas it was 17 kgf/- for sample material B, which had the measures taken according to the present invention.
It can be confirmed that remarkable fretting fatigue strength improvement effects of 55% and 82%, respectively, can be secured with kgf/- and 20 kgf/- in the case of sample C.

<Summary of Effects> As explained above, this method is an extremely simple method for the conventional general automobile wheel manufacturing process (hub installation involves applying graphite paint, etc. to the reference surface and irradiating it with laser light). According to the method of the present invention, which simply adds
Industrially extremely useful effects are brought about.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of a fretting fatigue test method. FIG. 2 is a graph showing the results of an investigation of the carbon concentration distribution in the sample material. FIG. 3 is a graph showing the results of a circular survey of the hardness distribution in the sample material. FIG. 4 is a graph showing the results of the fretting fatigue test of the sample materials. In the drawings: 1.4... Bolts and nuts. 2... Test material (material equivalent to wheel material). 3...Shoe (material equivalent to hub disc). 5...8 units, 6...base. Figure 1 Figure 2

Claims (1)

[Claims] Fretting of a hub mounting reference surface for an automobile wheel, characterized in that the surface hardness of the hub mounting reference surface is set to Hv300-700 by coating graphite on the hub mounting reference surface of an automobile wheel and performing laser irradiation. Damage Prevention Law.