US20140306091A1

US20140306091A1 - Casting member and method for manufacturing same

Info

Publication number: US20140306091A1
Application number: US14/362,772
Authority: US
Inventors: Takashi Tomita; Yuichi Furukawa; Shuji Sotozaki; Takehiro Ito
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2011-12-07
Filing date: 2011-12-07
Publication date: 2014-10-16
Also published as: JP5776790B2; WO2013084323A1; CN103958090A; JPWO2013084323A1

Abstract

Disclosed are an inexpensive casting member on which a film with high peel strength is formed, and a method for manufacturing the casting member. A surface-treated mold (1) includes a metal mold (10) having the molding surface including a plurality of protrusions (11) each having an inverse-slope shape, and a carbon film (20) formed on the molding surface of the metal mold (10). The surface-treated mold (1) is manufactured through a step (S1) including a modeling step (S10) for producing the metal mold (10), by means of selective laser sintering, which has the molding surface including the plurality of protrusions (11) each having the inverse-slope shape, and a film-forming step (S20) for forming the carbon film (20) on the molding surface of the metal mold (10) produced in the modeling step (S10).

Description

TECHNICAL FIELD

The present invention relates to a casting member such as a metal mold, and to a method for manufacturing the casting member.

BACKGROUND ART

Conventionally, widely known is a technique on a casting member such as a metal mold, by which a film such as a carbon film including nanocarbons is formed on a part of the surface of the casting member (e.g. on the molding surface of the casting member) in order to accomplish decrease of mold-release resistance and the like.
Moreover, publicly known is a technique for making a part, on which the film is to be formed, of the surface of a casting member bumpy by means of shot blasting or the like to increase surface area of the part, thereby inhibiting the film from peeling from the part (for example, see Patent Literature 1).
However, if the surface of the casting member is worked by means of the shot blasting or the like, the surface area of the worked part is not sufficiently increased. Therefore, it is expected that peel strength of the film is further increased.
Moreover, the surface processing such as the shot blasting needs to be additionally performed when the casting member as mentioned above is manufactured, which causes problems that cost required for manufacturing the casting member is increased for example.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2011-156549 A

SUMMARY OF INVENTION

Problem to be Solved by the Invention

The objective of the present invention is to provide an inexpensive casting member on which a film with high peel strength is formed, and a method for manufacturing the casting member.

Means for Solving the Problem

A first aspect of the invention is a casting member used for casting, which includes a base material manufactured by means of selective laser sintering, which has a surface including a plurality of minute irregularities each having an inverse-slope shape, and a film formed on the surface of the base material.
Preferably, the base material is a metal mold having a molding surface, and the film is formed on the molding surface of the base material.
A second aspect of the invention is a method for manufacturing a casting member used for casting, which includes a modeling step for producing a base material, by means of selective laser sintering, which has a surface including a plurality of minute irregularities each having an inverse-slope shape, and a film-forming step for forming a film on the surface of the base material.
Preferably, the film is a carbon film including at least one kind of nanocarbon, and in the film-forming step, the carbon film is formed on the surface of the base material by heating the base material while supplying a reactive gas used to make the carbon film.
More preferably, a temperature and a time for heating the base material in the film-forming step are set to a temperature and a time for performing an aging treatment for hardening the base material, respectively.

EFFECTS OF THE INVENTION

The present invention makes it possible to inexpensively inhibit a film from peeling off.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a surface-treated mold according to an embodiment of the present invention.

FIG. 2 shows a step for manufacturing the surface-treated mold.

FIG. 3 is a timing chart showing a film-forming step.

FIG. 4 is a timing chart showing an aging treatment of a conventional metal mold.

FIG. 5 is a timing chart showing a step for forming a carbon film on the molding surface of the conventional metal mold.

DESCRIPTION OF EMBODIMENTS

With reference to FIG. 1, described below is a surface-treated mold 1 as an embodiment of a casting member according to the present invention.
As shown in FIG. 1, the surface-treated mold 1 includes a metal mold 10 as a base material, and a carbon film 20 formed on the molding surface of the metal mold 10.
The metal mold 10 is used for die casting or the like, and has a surface (upper surface in FIG. 1) formed as the molding surface. The metal mold 10 is produced by means of selective laser sintering, the surface thereof is rough owing to a plurality of minute irregularities.
The selective laser sintering is a technique for, while laminating layers consisting of predetermined metal powder (e.g. maraging steel powder), melting a predetermined part of each of the layers with a laser so as to model a product with a desired shape. The selective laser sintering is known as a type of rapid prototyping.
Through the selective laser sintering, the metal powder melts and solidifies. Therefore, the plurality of minute irregularities is formed on the surface of the metal mold 10, which makes the surface of the metal mold 10 rough.
The plurality of minute irregularities formed on the surface of the metal mold 10 produced by means of the selective laser sintering consists of a plurality of protrusions 11.
For convenience, described below is only the plurality of protrusions 11 on the molding surface of the metal mold 10 which forms a part of the surface of the metal mold 10.
The protrusion 11 protrudes from the molding surface of the metal mold 10 toward the outside (upper side in FIG. 1), and has an inverse-slope shape (what is called an undercut shape). Specifically, the protrusion 11 is formed to gradually increase in width (dimension in the right-left direction in FIG. 1) from the base end (bottom end in FIG. 1) to the protruding end (top end in FIG. 1) thereof. In other words, the distance between the adjoining protrusions 11 gradually decreases toward the outside (upper side in FIG. 1) of the metal mold 10.
Thus, the molding surface of the metal mold 10 is formed as a bumpy surface consisting of the plurality of protrusions 11. In other words, the molding surface of the metal mold 10 includes the plurality of minute irregularities each having the inverse-slope shape (what is called the undercut shape).
The carbon film 20 is a dense film for reducing mold-release resistance of the molding surface of the metal mold 10, for preventing the molding surface of the metal mold 10 from melting, and the like. In the present embodiment, the carbon film 20 includes at least one kind of nanocarbon.
In the present invention, the nanocarbon is a microscopic fibrous nanocarbon such as carbon nanofiber, carbon nanotube, carbon nanocoil, or carbon nanofilament.
For example, the carbon film 20 may consist of a plurality of carbon nanofibers formed on the molding surface of the metal mold 10, or may consist of a plurality of carbon nanotubes formed on the molding surface of the metal mold 10. In addition, substantially spherical fullerenes each consisting of a plurality of carbon atoms may be applied to the fibrous nanocarbons such as carbon nanofibers.
The carbon film 20 covers the plurality of protrusions 11 on the molding surface of the metal mold 10, and fills every space between the adjoining protrusions 11.
Thereby, anchor effect is produced between the carbon film 20 and the plurality of protrusions 11.
Specifically, the plurality of protrusions 11 upward protrudes from the molding surface of the metal mold 10, thereby restraining the carbon film 20 from moving in a direction (right-left direction in FIG. 1) parallel to the molding surface of the metal mold 10. In addition, since the protrusion 11 has the inverse-slope shape (what is called the undercut shape), the plurality of protrusions 11 restrains the carbon film 20 from moving in a direction (top-bottom direction in FIG. 1) perpendicular to the molding surface of the metal mold 10.
Therefore, the anchor effect produced between the carbon film 20 and the plurality of protrusions 11 inhibits the carbon film 20 from peeling from the molding surface of the metal mold 10.
As mentioned above, in the surface-treated mold 1, the molding surface of the metal mold 10 is formed as a bumpy surface consisting of the plurality of protrusions 11 each having the inverse-slope shape (what is called the undercut shape), and the carbon film 20 is formed on the molding surface of the metal mold 10.
This makes it possible to make the area of the molding surface of the metal mold 10 larger than that of the molding surface (e.g. molding surface worked by means of shot blasting) of a conventional metal mold, and to form more nanocarbons on the molding surface of the metal mold 10.
Therefore, it is possible to strongly combine the carbon film 20 with the molding surface of the metal mold 10, and to inhibit the carbon film 20 from peeling from the molding surface of the metal mold 10.
Moreover, more nanocarbons are formed on the molding surface of the metal mold 10, thus enabling to form the carbon film 20 with larger thickness (vertical dimension in FIG. 1).
Therefore, it is possible to improve adiabaticity of the molding surface of the metal mold 10, and consequently to suitably flow molten metal thereon during casting. In addition, the carbon film 20 suitably holds a release agent, thus enabling to improve oil-retentivity of the molding surface of the metal mold 10.
In the present embodiment, the carbon film 20 including at least one kind of nanocarbon is used as a film according to the present invention, but the film is not limited thereto.
For example, a dense film such as hard chromium plating, or black rust may be used as the film according to the present invention.
With reference to FIGS. 2 to 5, described below is a step S1 for manufacturing the surface-treated mold 1 as an embodiment of a step for manufacturing a casting member according to the present invention.
As shown in FIG. 2, the step S1 includes a modeling step S10 and a film-forming step S20.
The modeling step S10 is a step for producing, by means of the selective laser sintering, the metal mold 10 having the molding surface which includes the plurality of minute irregularities each having the inverse-slope shape (what is called the undercut shape).
In the modeling step S10, the metal mold 10 having the molding surface on which the plurality of protrusions 11 is formed is made from metal powder such as maraging steel powder by means of the selective laser sintering.
The film-forming step S20 is a step for forming the carbon film 20 on the molding surface of the metal mold 10.
In the film-forming step S20, the metal mold 10 is heated while supplying reactive gas used to make the carbon film 20, such as acetylene gas, to the metal mold 10 under an atmosphere of inert gas such as nitrogen in an atmosphere furnace, thereby forming the carbon film 20 on the molding surface of the metal mold 10.
It is preferable that an aging treatment for hardening the metal mold 10 is performed while forming the carbon film 20 on the molding surface of the metal mold 10 in the atmosphere furnace.
Specifically, as shown in FIG. 3, after changing an atmosphere in the atmosphere furnace into an atmosphere of nitrogen (N₂), the atmosphere is heated to 570° C. while supplying acetylene (C₂H₂) and ammonia (NH₃) to the inside of the atmosphere furnace. Then, the metal mold 10 is heated for 4 hours while maintaining the temperature.
Consequently, the carbon film 20 is formed on the molding surface of the metal mold 10, and the aging treatment is applied to the metal mold 10.
As shown in FIG. 4, in a conventional aging treatment, a metal mold is heated at 570° C. for 4 hours.
In the film-forming step S20 according to the present embodiment, the metal mold 10 is heated at the same temperature and for the same time as the conventional aging treatment.
Therefore, through the film-forming step S20, the aging treatment is applied to the metal mold 10.
As shown in FIG. 5, conventionally, a carbon film is formed on the molding surface of a metal mold at a temperature (480° C.) lower than that at which the aging treatment is performed. In other words, the temperature at which the carbon film is formed on the molding surface of the metal mold is different from the temperature at which the aging treatment is performed.
However, the carbon film formed on the molding surface of the metal mold does not deteriorate by oxidation if the temperature of the carbon film is not over 600° C. Therefore, the carbon film may be formed on the molding surface of the metal mold at the temperature (570° C.) at which the aging treatment is performed.
In the present embodiment, the metal mold 10 is heated at 570° C. in the film-forming step S20, but the temperature at which the metal mold 10 is heated is not limited thereto.
The temperature at which the carbon film 20 is formed on the molding surface of the metal mold 10 is preferably 400° C. (temperature at which nanocarbons can form) or more, and the temperature at which the aging treatment of the metal mold 10 is performed is preferably 350° C. or more. Therefore, the temperature at which the metal mold 10 is heated in the film-forming step S20 is preferably 400° C. or more.
Additionally, as mentioned previously, since the carbon film 20 may deteriorate by oxidation at a temperature higher than 600° C., the temperature at which the metal mold 10 is heated in the film-forming step S20 is preferably 600° C. or less.
Therefore, it is preferable that the temperature at which the metal mold 10 is heated in the film-forming step S20 is 400 through 600° C.
In the case of forming the carbon film on the molding surface of the metal mold at the same temperature and for the same time as the aging treatment of the metal mold, if a quantity of reactive gas such as acetylene gas supplied to the metal mold is reduced by approximately 20% of a conventional quantity (quantity of the reactive gas supplied to the metal mold in the case of forming the carbon film at a temperature lower than that at which the aging treatment of the metal mold is performed), the quality of the carbon film hardly varies. Therefore, the quantity of the reactive gas such as acetylene gas supplied thereto may be changed (reduced) depending on conditions of the aging treatment of the metal mold. In the present embodiment, the time for supplying ammonia (NH₃) is reduced in order to make the supply of the ammonia (NH₃) smaller than a conventional supply thereof (see the hatched areas in FIGS. 3 and 5). Note that the supply of nitrogen (N₂) is increased instead of reducing the supply of the ammonia (NH₃).
Moreover, depending on the conditions of the aging treatment of the metal mold, the time for heating the metal mold may be changed so that the quality of the carbon film hardly varies.
Thus, the temperature and the time for forming the carbon film 20 are changed so that the quality of the carbon film 20 hardly varies, and are equalized to those for performing the aging treatment of the metal mold 10. This makes it possible to concurrently performing, in the film-forming step S20, the formation of the carbon film 20 on the molding surface of the metal mold 10, and the aging treatment of the metal mold 10.
Therefore, it is possible to reduce the time and the cost required for manufacturing the surface-treated mold 1 without additionally performing the aging treatment of the metal mold 10.
Generally, after the aging treatment of the metal mold is performed, a step for forming a carbon film on the molding surface of the metal mold. The metal mold hardened through the aging treatment is heated again when the carbon film is formed on the molding surface of the metal mold, and thereby the effect of the aging treatment is weakened. However, in the present invention, the formation of the carbon film 20 on the molding surface of the metal mold 10, and the aging treatment of the metal mold 10 are performed at the same time in the film-forming step S20. This makes it possible to make the metal mold 10 desired hardness without the effect of the aging treatment weakening.
As mentioned above, in the step S1, the surface-treated mold 1 is manufactured by performing the modeling step S10 and the film-forming step S20 in this order.
The molding surface of the metal mold 10 produced in the modeling step S10 is rough owing to the plurality of protrusions 11. However, since the dense carbon film 20 is formed on the molding surface of the metal mold 10 in the film-forming step S20, the molding surface of the surface-treated mold 1 is dense.
Conventionally, rough processing for forming the shape of the metal mold, and finishing processing for smoothing the surface thereof are performed in this order, and thereby the metal mold is produced. After that, the surface of the metal mold is worked into the bumpy surface by means of shot blasting or the like, and the film such as the carbon film is formed on the bumpy surface.
On the other hand, in the present invention, the metal mold 10 having the rough surface is produced in the modeling step S10, and then the dense carbon film 20 is formed on the molding surface of the metal mold 10 in the film-forming step S20, thereby manufacturing the surface-treated mold 1. Therefore, the surface processing such as the finishing processing and the shot blasting does not need to be performed.
This makes it possible to reduce the time and the cost required for manufacturing the surface-treated mold 1.
Moreover, in the modeling step S10, the metal powder is melted with a laser, and solidifies, thereby producing the metal mold 10. Therefore, the surface of the metal mold 10 is activated, namely, the newly-formed surface of the metal mold 10 is exposed.
In particular, in the step S1, the film-forming step S20 is performed without performing the surface processing such as the finishing processing and the shot blasting after the modeling step S10. This makes it possible to keep the molding surface of the metal mold 10 activated without an oxide film forming on the molding surface of the metal mold 10 even when the carbon film 20 is formed on the molding surface of the metal mold 10.
Therefore, in the film-forming step S20, a reaction between the molding surface of the metal mold 10 and reactive gas such as acetylene gas is promoted, thus enabling to form the firm carbon film 20 in a short time.
Not only a metal mold such as the surface-treated mold 1 but also a sliding member such as a plunger tip may be used as a casting member according to the present invention.
For example, in the case where a plunger tip is used as a casting member according to the present invention, a film similar to the carbon film 20 is preferably formed on the outer circumferential surface (sliding surface) of the plunger tip.

INDUSTRIAL APPLICABILITY

The present invention is applied to a casting member such as a metal mold, and to a method for manufacturing the casting member.

REFERENCE SIGNS LIST

1: surface-treated mold (casting member)
10: metal mold (base material)
11: protrusion
20: carbon film

Claims

1. A casting member used for casting, comprising:

a base material manufactured by means of selective laser sintering, which has a surface including a plurality of minute irregularities each having an inverse-slope shape; and

a film formed on the surface of the base material.

2. The casting member according to claim 1, wherein

the base material is a metal mold having a molding surface, and

the film is formed on the molding surface of the metal mold.

3. A method for manufacturing a casting member used for casting, comprising:

a modeling step for producing a base material, by means of selective laser sintering, which has a surface including a plurality of minute irregularities each having an inverse-slope shape; and

a film-forming step for forming a film on the surface of the base material produced in the modeling step.

4. The method according to claim 3, wherein

the film is a carbon film including at least one kind of nanocarbon, and

in the film-forming step, the carbon film is formed on the surface of the base material by heating the base material while supplying a reactive gas used to make the carbon film.

5. The method according to claim 4, wherein

a temperature and a time for heating the base material in the film-forming step are set to a temperature and a time for performing an aging treatment for hardening the base material, respectively.