JP4136543B2 - Method for forming film on cast product surface, method for producing film cast product, pre-treatment method for film formation, and film cast product - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a film forming method on a cast product surface for forming a coating film or a plating film on the surface of the cast product, a method for producing the film cast product, a pretreatment method for film formation, and a film cast product. .
[0002]
[Prior art]
For cast products such as tire wheels, a coating film is formed on the surface of the cast product in order to improve its design (for example, mirror finishing) or to improve the durability of the product. It has been broken. Usually, film formation on the surface of a cast product is performed by machining the surface of the cast product 1 (see FIG. 1A) using a cutting tool 2, as shown in FIGS. After cutting or polishing by (see FIG. 1 (b)), the coating 3 is formed on the surface of the cut or polished casting 1 (see FIG. 1 (c)).
[0003]
However, when the film is formed on the surface of the cast product by the above method, there are the following problems. That is, as shown in FIG. 1 (b), when the surface of the cast product 1 is polished by machining using the cutting tool 2, there are a lot of casting defect holes 1 a existing in the cast product 1. It will be exposed on the surface. Accordingly, when the coating film 3 is formed on the surface of the casting 1 as shown in FIG. 1C, the air in the pores 1a is baked as shown in FIG. Swells up and pushes up the coating film 3 to cause a blister defect 4, which impairs the appearance of the product. In particular, in the case of a clear coating, which is a transparent coating, among the coatings, the blistering defect 4 is more likely to occur than the colored coating due to the nature of the coating. Since the portion acts as a lens and the defect becomes more conspicuous, there is a problem in that the appearance of the product is remarkably impaired.
[0004]
For the above problems, a step of performing shot blasting on the design surface of the cast aluminum wheel, and a step of mechanically smoothing the shot blasted design surface (the same as polishing by cutting in the above method) And an aluminum wheel surface treatment method (for example, the same process as the coating film formation in the above method) is disclosed (for example, the surface treatment for giving a smooth surface to the smooth design surface) (for example, Patent Document 1). According to this surface treatment method, holes near the surface of the cast product are crushed and disappeared by shot blasting, and blistering defects can be prevented.
[0005]
[Patent Document 1]
JP-A-6-293993 [0006]
[Problems to be solved by the invention]
However, in practice, the effect of preventing blistering defects by the above surface treatment method is still insufficient. That is, a film forming method on the surface of a casting that can effectively prevent blistering defects has not yet been found, and development of such a film forming method has been desired.
[0007]
The present invention has been made in view of such problems of the prior art, and the object of the present invention is a casting that can effectively prevent blistering defects and does not impair the appearance of the product. An object of the present invention is to provide a film forming method on the surface, particularly a film forming method on a cast product surface that can be suitably used for forming a clear coating film.
[0008]
[Means for Solving the Problems]
As a result of earnest research to solve the above-mentioned problems, the present inventor achieved the above object by previously removing the cast skin of the cast product by cutting to expose the inner layer when performing the shot peening treatment. The present invention has been completed. That is, the present invention provides the following film forming method, method for producing a film casting, a pretreatment method for film forming, and a film casting.
[0009]
[1] A film-forming method on a cast product surface in which a coating film or a plating film is formed on the surface of the cast product, wherein the cast skin of the cast product is removed by cutting to expose the inner layer, and the exposure The inner layer is subjected to shot peening treatment to form holes that are casting defects to form a sealing layer, and the surface of the sealing layer is cut or polished by machining, and the cutting or polishing is performed. A film forming method on the surface of a cast product, characterized in that a coating film or a plating film is formed on the surface of the sealing layer.
[0010]
[2] A method for producing a film-cast product in which a coating film or a plating film is formed on the surface of the cast product, wherein the cast skin of the cast product is removed by cutting to expose an inner layer, By subjecting the exposed inner layer to shot peening treatment, holes that are casting defects are sealed to form a sealing layer, and the surface of the sealing layer is cut or polished by machining. A method for producing a film-casting product, comprising forming a coating film or a plating film on the surface of a polished sealing layer.
[0011]
[3] A pretreatment method for forming a coating film or a plating film on the surface of a cast product, wherein the cast skin of the cast product is removed by cutting to expose an internal layer, and the exposed internal layer A film is formed by performing a shot peening treatment on the surface to form pores that are casting defects and forming a sealing layer, and cutting or polishing the surface of the sealing layer by machining. Pre-processing method for.
[0012]
[4] A film-formed cast product in which a coating film or a plating film is formed on the surface of the cast product, wherein a layer having a depth of 0 to 50 μm on the basis of the surface of the cast product in the cast product is an A layer, in the case where a layer of depth 1000~1050μm the basis of the casting surface is defined as B layer, the number of holes is casting defects, 0-2 per unit cross-sectional area of the a layer / mm ^2, wherein 10 to 50 pieces / mm ² per unit cross-sectional area of the B layer, and a coating film or a plating film is formed on the surface of the A layer.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
When developing the film forming method of the present invention, the present inventor firstly shot blasting (synonymous with shot peening processing; hereinafter referred to as “shot peening processing”) as disclosed in JP-A-6-293993. The reason why the effect of preventing blistering defects is insufficient despite the fact that it has been applied. As a result, when the shot peening process is performed directly on the surface of the cast product (in this case, the casting surface of the cast product) as in the method described in JP-A-6-293993, the metal structure is deformed by the shot peening process. It has been found that since the amount is very small, the sealing effect of the shot peening process is not fully exhibited, and the voids of casting defects existing in the cast product remain.
[0014]
More specifically, even if shot peening treatment is performed on the casting surface, the energy of the projection material (steel ball, cut wire, etc.) is not transmitted to the inside of the cast product, but exists in the cast product. It does not reach the sealing effect of crushing voids of casting defects. Therefore, when polishing by cutting is performed after the shot peening treatment, the voids of casting defects existing inside the casting are exposed on the surface of the casting. When a coating film is formed on the surface of the casting product with the voids exposed on the surface in this way, when the coating film is baked, the air in the pores expands and pushes up the coating film, resulting in blistering defects. It is.
[0015]
Therefore, in the present invention, when the shot peening treatment is performed, the cast surface of the cast product is previously removed by cutting to expose the inner layer. By doing so, the energy of the projection material is sufficiently transmitted to the inside of the cast product, so that it is possible to reliably crush the voids of the casting defects existing inside the cast product and obtain a sufficient sealing effect. Can do. Therefore, even after polishing by shot processing after shot peening treatment, voids of casting defects are not exposed on the surface of the cast product. Can be effectively prevented.
[0016]
Hereinafter, embodiments of the film forming method of the present invention will be specifically described with reference to the drawings. In the present specification, “cross-sectional area” means a cross-sectional area of a cross section perpendicular to the surface of the cast product.
[0017]
(1) 1st process (removal of cast skin)
As shown in FIGS. 2A to 2B, the first step in the film forming method of the present invention is a step of removing the casting surface 21b of the cast product 21 by cutting to expose the inner layer 21c. As described above, when the shot peening process is performed, the casting surface 21b is removed in advance by the cutting tool 22 of the cutting machine or the like, so that the energy of the projection material is sufficiently transmitted to the inside of the casting 21. The void 21a of the casting defect existing inside can be reliably crushed, and a sufficient sealing effect can be obtained.
[0018]
As long as the cast product used in the present invention is manufactured through a normal casting process, the material, shape, etc. are not particularly limited. For example, when the cast product is a vehicle wheel, an alloy made of an Al alloy such as AC4C (JIS) or AC4CH (JIS) can be suitably used. Further, heat treatment such as solution treatment and aging treatment may be performed after casting.
[0019]
The cast surface means the surface of the cast product as cast, that is, the surface where the cast product is in contact with the mold at the time of casting, and an oxide film called black skin is formed on this portion. In the present invention, at least the oxide film portion may be removed by cutting. Usually, if the cutting allowance is set to about 1.5 mm (cutting a portion having a depth of 1.5 mm on the basis of the cast product surface), the oxide film portion can be sufficiently removed. The cutting method is not particularly limited, and the cutting may be performed using a general-purpose cutting machine (for example, a lathe, a milling machine, or the like).
[0020]
In the present specification, the term “inner layer” means a portion other than the cast skin of the cast product. The inner layer has an advantage that it can fully enjoy the sealing effect of the shot peening process. Further, the inner layer of untreated castings not subjected to shot peening process to be described later is vacancy number per unit cross-sectional area of 10 to 50 / mm ² is casting defects.
[0021]
The number of holes per unit cross-sectional area in the present invention is the number of holes existing in an area of about 60 mm ² by mirror-polishing the cross section of the cast product and taking a photograph at a magnification of 100 using a microscope. It means a value obtained by counting and converting to the number of holes per unit cross-sectional area.
[0022]
(2) Second step (shot peening process)
As shown in FIGS. 3A to 3B, the second step in the film forming method of the present invention is a step of subjecting the exposed inner layer 21c to shot peening to form a sealing layer 21d. .
[0023]
The shot peening treatment is a treatment in which a projection material 25 (steel ball, cut wire, etc.) having a diameter of about 1 mm is sprayed onto the surface of the object to be treated (in the present invention, the cast product 21), and usually the fatigue strength of the object to be treated. It is often performed for the purpose of improving the surface hardness, improving the surface hardness, or cleaning the surface. However, in the present invention, it is used as a process for sealing the vacant hole 21 of the casting defect (the reference numeral 21a ′ in FIG. 3B indicates a crushed hole).
[0024]
The method of the shot peening treatment is not particularly limited as long as the projection material is sprayed onto the surface of the object to be processed. For example, a turntable for placing and rotating the object to be processed, and the projection material to be processed Method of performing shot peening treatment by using a device equipped with a wide-angle rotor (impeller) for spraying on the surface, and spraying the projection material onto the surface of the workpiece by the wide-angle rotor while rotating the workpiece by the turntable Etc.
[0025]
In the present specification, the term “sealing layer” means a portion of the cast product in which the number of pores that are casting defects is 0 to 2 / mm ² per unit cross-sectional area. The inner layer of an untreated cast product that is not subjected to shot peening treatment has 10 to 50 holes / mm ² per unit cross-sectional area of the casting defect, whereas the sealing layer subjected to shot peening treatment Has extremely few holes. A blistering defect can be effectively prevented by forming a coating film on the surface of the sealing layer having an extremely small number of pores.
[0026]
Although depending on the conditions of the shot peening treatment, when the shot peening treatment is performed on the inner layer, the sealing effect usually reaches a portion having a depth of about 300 μm based on the surface of the inner layer. That is, by performing the shot peening treatment, a portion having a thickness of about 300 μm from the surface of the inner layer becomes a sealing layer.
[0027]
(3) Third step (surface cutting / polishing)
The 3rd process in the film-forming method of this invention is a process of cutting or grind | polishing the surface of the sealing layer 21d by machining, as shown to Fig.4 (a)-(b).
[0028]
This cutting / polishing is a process performed for mirror-finishing the surface of the casting 21 from a design requirement.
[0029]
In the third step, it is necessary to cut or polish the “surface of the sealing layer” by machining with the cutting tool 26 of the cutting machine. Thus, if the machining allowance for cutting / polishing is set within the range of the thickness of the sealing layer 21d (as described above, the thickness of the sealing layer 21d is about 300 μm, so it is set to about 200 μm), Since the sealing layer 21d having an extremely small number of holes is exposed on the surface, the holes 21a having casting defects are not exposed on the surface of the casting 21. On the other hand, if the machining allowance for cutting and polishing is set beyond the range of the thickness of the sealing layer 21d (the thickness of the sealing layer 21d is set to be more than 300 μm), the sealing effect of the shot peening process is not achieved. The inner layer 21c (the portion where the number of holes 21a which are casting defects is 10 to 50 / mm ² per unit cross-sectional area) is exposed on the surface of the casting 21 and causes blistering defects, which is not preferable. .
[0030]
The cutting / polishing method in the third step is not particularly limited, and the cutting may be performed using a general-purpose cutting machine (for example, a lathe or a milling machine) or a dedicated mirror surface processing machine.
[0031]
(4) Fourth step (film formation)
The 4th process in the film-forming method of this invention is a process of forming the coating film 23 or a plating film on the surface of the sealing layer 21d cut or polished, as shown to Fig.5 (a)-(b). Yes (reference numeral 28 in FIG. 5 (b) indicates a film-cast product). By performing such film formation, it is possible to improve the designability or the durability of the product.
[0032]
The coating film 23 is formed by coating and spraying the coating material 27 on the surface of the casting 21 to form the coating film 23 and then baking it by heating at a high temperature. Examples of the coating film 23 include a clear coating film in addition to a colored coating film. The film forming method of the present invention is a clear coating in which, due to the nature of the coating film 23, blistering defects are likely to occur compared to a colored coating film, and the blistering defect part acts as a lens, making the defects more noticeable. It can be particularly suitably used for film formation.
[0033]
The plating film is formed by a conventionally known plating method such as electroplating, chemical plating, hot dipping, or vapor phase plating. In the formation of the plating film, no blistering defect is generated as in the case of coating film formation, but if the voids of the casting defect are exposed on the surface of the casting, the plating film is dented into its shape. End up (dental defect). The film forming method of the present invention can effectively prevent such dent defects.
[0034]
In addition, the film-forming method of this invention can also be considered as the manufacturing method of a film-forming cast product from a different viewpoint. That is, by performing the first step to the fourth step, it is possible to manufacture a film-cast product in which a coating film or a plating film is formed on the surface of the cast product.
[0035]
According to the film-forming method of the present invention or the method for producing a film-cast product, a layer having a depth of 0 to 50 μm based on the surface of the cast product in the cast product is a layer A, and a depth of 1000 to 1000 based on the surface of the cast product. When the 1050 μm layer is defined as the B layer, the number of holes as casting defects is 0 to 2 / mm ² per unit cross-sectional area of the A layer, and 10 to 50 / mm ² per unit cross-sectional area of the B layer. ^{In addition} , a film-forming cast product in which a coating film or a plating film is formed on the surface of the A layer can be obtained. Such a film-casting product has a coating film or a plating film formed on the surface of the layer A having a very small number of pores, and therefore has few blister defects or dent defects and is excellent in the appearance of the product.
[0036]
Further, the first to third steps in the film forming method of the present invention can be considered as a pretreatment method for forming a coating film or a plating film on the surface of the cast product. The cast product subjected to such pretreatment can effectively prevent blister defects or dent defects during film formation, and does not impair the appearance of the product.
[0037]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples.
[0038]
In the following Example 1 and Comparative Example 1, a vehicle wheel having an outer diameter of 14 inches made of an Al alloy AC4CH (JIS) was used as a cast product. The vehicle wheel is heat-treated (solution treatment, aging treatment) after casting.
[0039]
In Example 1 and Comparative Example 1, the surface of the vehicle wheel was mirror-finished to form a clear coating film. As an evaluation method, the ten vehicle wheels were subjected to the film formation method of the present invention (Example 1) and the conventional film formation method (Comparative Example 1), and each vehicle wheel was baked after the clear coating film was baked. The design surface was evaluated as having an effect of preventing blistering defects by rejecting those having two or more blistering defects with a diameter of 1 mm or more as failing and one or less.
[0040]
(Example 1)
First, the cast surface (black skin, oxide film) of the cast product was removed by cutting to expose the inner layer. Specifically, the cutting allowance was set to 1.5 mm (cutting up to a depth of 1.5 mm with reference to the cast product surface), and cutting was performed using a general-purpose cutting machine (lathe). . When the number of vacancies as casting defects in the inner layer exposed by this cutting was determined, it was 20 to 30 / mm ² (average value of 10 vehicle wheels) per unit cross-sectional area.
[0041]
Next, the exposed inner layer was subjected to shot peening treatment to form a sealing layer. Specifically, a device having a turntable for placing and rotating a cast product and a wide-angle rotor (impeller) for injecting a projection material onto the surface of the cast product is used. While rotating, the projection material was sprayed onto the surface of the cast product with a wide-angle rotor to perform a shot peening process.
[0042]
As conditions for the shot peening treatment, as a projection material, a stainless steel cut wire having a length of 0.6 mm and a diameter of 0.6 mm is used, the projection amount is 300 kg / min, the projection speed is 60 m / sec, and the projection time is 100 seconds. It was.
[0043]
By applying the shot peening of the, sealing layer of pores numbers 0-2 per unit sectional area of / mm ² (average of ten vehicle wheel) is formed is a casting defects. The thickness of the sealing layer was about 300 μm (average value of 10 vehicle wheels) on the basis of the surface of the tire wheel.
[0044]
Further, the surface of the sealing layer (the surface of the tire wheel) was mirror-finished by machining. At this time, the machining allowance for mirror finishing is set within the range of the thickness of the sealing layer (as described above, the sealing layer thickness is about 300 μm, so it is set to about 200 μm). The mirror surface processing was performed using.
[0045]
Finally, a clear coating film was formed on the surface of the mirror-sealed sealing layer. Specifically, after a clear paint made of an acrylic resin was sprayed on the surface of the tire wheel to form a coating film, this was heated and baked at a high temperature. As a result, 2 of the 10 vehicle wheels were rejected because there were 2 or more blister defects with a diameter of 1 mm or more on the design surface, but 8 had a blister defect with a diameter of 1 mm or more on the design surface. It was less than 1 and passed.
[0046]
(Comparative Example 1)
First, shot peening treatment was performed directly on the cast skin (black skin, oxide film) of the cast product. The method for performing the shot peening process and the conditions for the shot peening process were the same as in Example 1.
[0047]
Next, the surface of the vehicle wheel subjected to the shot peening treatment was mirror-finished by machining. At this time, the machining allowance for the mirror finishing was set to 0.25 mm, and the mirror finishing was performed using a dedicated mirror finishing machine.
[0048]
Finally, a clear coating film was formed on the mirror-finished vehicle wheel surface. Specifically, after a clear paint made of an acrylic resin was sprayed on the surface of the tire wheel to form a coating film, this was heated and baked at a high temperature. As a result, of the 10 vehicle wheels, 2 were 1 or less blister defects with a diameter of 1 mm or more present on the design surface, but 8 were 1 mm or more with a diameter present on the design surface. There were two or more blister defects, and it was rejected.
[0049]
(Discussion)
As is apparent from the evaluation results in Example 1 and Comparative Example 1, according to the film forming method of the present invention (Example 1), 80% of the vehicle wheel can be accepted, and excellent blistering defects are achieved. The prevention effect was shown. That is, the occurrence of blister defects can be significantly suppressed as compared with the conventional film formation method (Comparative Example 1).
[0050]
【The invention's effect】
As described above, in the film forming method of the present invention, when the shot peening process is performed, the casting surface of the cast product is removed in advance by cutting to expose the inner layer. Defects can be effectively prevented, the appearance of the product is not impaired, and in particular, it can be suitably used for forming a clear coating film.
[Brief description of the drawings]
FIG. 1 is a process diagram (a) to (d) showing a conventional film forming method.
2A to 2B are process diagrams (a) to (b) showing a film forming method of the present invention.
3A to 3B are process diagrams (a) to (b) showing a film forming method of the present invention.
4A to 4B are process diagrams (a) to (b) showing a film forming method of the present invention.
5A to 5B are process diagrams (a) to (b) showing a film forming method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Cast article, 1a ... Hole, 2 ... Cutting tool, 3 ... Paint film, 4 ... Blister defect, 21 ... Cast article, 21a ... Hole, 21a '... Collapsed hole, 21b ... Cast surface, 21c ... inner layer, 21d ... sealing layer, 22 ... cutting tool, 23 ... coating film, 25 ... projection material, 26 ... cutting tool, 27 ... paint, 28 ... film-forming casting product.

Claims (4)

A method of forming a film on a casting product surface by forming a coating film or a plating film on the surface of the casting product,
Removing the cast skin of the cast product by cutting to expose the inner layer;
By performing shot peening treatment on the exposed inner layer, holes that are casting defects are sealed to form a sealing layer,
Cutting or polishing the surface of the sealing layer by machining,
A film forming method on the surface of a cast product, wherein a coating film or a plating film is formed on the surface of the sealed or polished sealing layer. A method for producing a film-cast product in which a coating film or a plating film is formed on the surface of the cast product,
Removing the cast skin of the cast product by cutting to expose the inner layer;
By performing shot peening treatment on the exposed inner layer, holes that are casting defects are sealed to form a sealing layer,
Cutting or polishing the surface of the sealing layer by machining,
A method for producing a film-casting product, comprising forming a coating film or a plating film on the surface of the sealed or polished sealing layer. A pretreatment method for forming a coating film or a plating film on the surface of a casting,
Removing the cast skin of the cast product by cutting to expose the inner layer;
By performing shot peening treatment on the exposed inner layer, holes that are casting defects are sealed to form a sealing layer,
A pretreatment method for film formation, wherein the surface of the sealing layer is cut or polished by machining. A film-cast product in which a coating film or a plating film is formed on the surface of the cast product,
In the cast product, a layer having a depth of 0 to 50 μm based on the surface of the cast product is defined as A layer, and a layer having a depth of 1000 to 1050 μm based on the surface of the cast product is defined as a B layer, which is a casting defect. The number of holes is 0 to 2 / mm ² per unit cross-sectional area of the A layer, and 10 to 50 / mm ² per unit cross-sectional area of the B layer,
A film-cast product comprising a coating film or a plating film formed on the surface of the A layer.

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