JP3215993B2 - Metal surface remelting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remelting treatment method for locally modifying a partial surface layer such as an aluminum alloy casting.

[0002]

2. Description of the Related Art A member having a complicated shape such as a cylinder head is usually formed by casting. However, cast products have internal defects such as porosity,
Since the structure is coarse, a product having high fatigue strength cannot be obtained as compared with a forged product or a press-formed product. In order to improve the fatigue strength of a cast product, it is only necessary to reduce internal defects and refine crystal grains. In order to refine the crystal grains, it is sufficient to increase the cooling rate during solidification. However, when the cooling rate is increased, not only does the flow of the molten metal, the formability of the casting such as the molten metal flow be hindered, but also the internal Defects may freeze and remain inside.

In the production of an aluminum alloy cylinder head, once formed by casting, a part requiring particularly high fatigue strength is irradiated with high-density heating energy such as a TIG arc, a laser beam, an electron beam or a plasma arc. A method for locally modifying the surface layer by re-melting and subsequently rapidly solidifying the solidified layer is disclosed in
It is proposed in 193733. This local surface modification method is called “remelting treatment” or “remelting treatment”.

Japanese Patent Application Laid-Open No. 64-218 discloses a method for preventing the occurrence of craters in the following "remelt treatment". The outline will be described with reference to FIG.
As shown in cross section in FIG. 6A, "remelting treatment" of the work
An abutment 11 is formed in advance at the processing end portion of the portion where the TIG is to be performed, and a TIG torch 1, for example, is used as a high-density heating device. Irradiate 2. The surface layer of the work heated by the arc 2 is melted to form a molten metal pool 4 indicated by a broken line, and the surface thereof forms the remelt treatment layer 3 while the molten metal is drawn from the surroundings to form the concave portions 5.

When the TIG torch 1 approaches the projection 11 at the processing end, the TIG torch 1 is raised in the arrow direction as shown in FIG. 6B so that the tip of the TIG torch 1 does not collide with the projection 11. 11 is irradiated with arc 2. At the processing end position T, the molten metal of the protrusion 11
Crater does not occur. After the remelt treatment, the remaining portion of the protrusion 11 is cut off by processing on the product dimensions shown by the two-dot chain line 10. FIG. 6C shows a cross section of the remelt processing layer 3 after processing on the product dimension surface indicated by the two-dot chain line 10.

[0006] Also, Japanese Patent Laid-Open No. 15866/1990 discloses that
Another method for preventing crater formation in remelting is described. The outline is described with reference to FIG. FIG.
As shown in the cross section in A, the remelt processing section is set in advance so that the processing end position T of the portion where the remelt processing of the workpiece is performed is the hole processing position 21 for hot plug or the like indicated by the dashed line. The surface of the workpiece is irradiated with the arc 2 while moving the TIG torch 1 in the direction of the arrow. Arc 2
The surface layer of the work heated by the above is melted to form a molten metal pool 4 indicated by a broken line, and the surface thereof forms the remelt treatment layer 3 while the molten metal is drawn from the surroundings to form the concave portion 5. At the processing end position T, as shown in FIG. 7B,
The molten metal immediately below the TIG torch 1 is drawn to generate craters 14. After the remelt treatment, processing is performed on a product dimension surface indicated by a two-dot chain line 10 to perform hole processing. FIG. 7C shows a cross section of the remelt processing layer 3 after processing. The craters 14 generated by the remelt treatment are removed from the product by processing the holes 20.

[0007]

In the above-described method described with reference to FIG. 6, it is necessary to form the cast product with projections in advance, and it is not only inconvenient to handle the work, but also after the remelt process. Residual portions of the protrusions must be removed. Further, the TIG torch 1 is raised at the processing end to prevent the tip of the TIG torch 1 from colliding with the projection. As shown in FIG. 6C, the effective remelt depth d at this portion is different from that of the other remelt processing layers 3. Smaller. FIG.
In the above-described method, it is necessary to perform drilling after the remelt process because casting cannot be performed in advance by providing a cast-out hole at a site such as a hot plug hole, and the processing end portion is not a hole processing scheduled position. Therefore, the remelt processing part is restricted.

[0008] The present invention solves the above-mentioned problems, and the portion to be subjected to the remelt treatment is not limited by the product shape.
It is another object of the present invention to provide a method for remelting a metal surface which can prevent the occurrence of craters in a remelt process without adding an extra processing step before and after the process.

[0009]

According to the present invention, there is provided a method for applying a high-density thermal energy to a metal surface while transferring the same to re-melt the surface layer and subsequently modifying the surface layer by rapid solidification. A remelting treatment method for a metal surface, which comprises injecting a wire of the same metal in a solid state into a molten pool at an end portion.

[0009]

By injecting a wire of the same metal into the molten metal pool at the end of the treatment, it is possible to prevent the molten metal pool from being heated by absorbing the heat of fusion and to supply the molten metal to the molten metal pool to prevent the occurrence of craters. .

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the remelting process of the present invention, and FIG.
FIG. 3 is an explanatory view of a TIG torch, and FIG. 3 is a plan view showing a part to be subjected to a remelting process. T as high density heating energy
IG is used. As shown in FIG. 2, a wire feeder 6 is attached to the TIG torch 1, and an aluminum alloy wire 7 of the same quality as the work base material is sent out to the molten metal pool 4 by variably adjusting a feeding speed by a feeding motor (not shown). . As shown in FIG. 3, a portion 3 between the inlet valve seat hole VI and the exit valve seat hole VE and between these and the hot plug hole P, which are the portions of the aluminum alloy cylinder head W where the heat load is highest, TIG
The torch 1 was supported by a six-axis robot, and the position and speed at which the remelting process was performed were controlled.

In FIG. 1, a surface of a workpiece W is irradiated with an arc 2 while moving a TIG torch 1 from a start position S in an arrow direction. The surface layer of the work heated by the arc 2 is melted to form a molten metal pool 4 immediately below the arc 2, and the portion where the arc 2 has passed solidifies sequentially. After the remelting process is performed to the final processing position T by the arc 2, the TIG torch 1 is stopped as shown in FIG. 1B, and as shown in FIG. An aluminum alloy wire 7 is injected. The aluminum alloy wire 7 is melted by the heat of the arc 2 and the molten metal in the molten metal pool 4 to form a bulge 8. Thereafter, when the irradiation of the arc 2 is stopped, the processing end portion T
The swelling 8 formed in the above becomes smaller due to coagulation shrinkage,
No craters are formed as shown in FIG. 1D.

Next, a specific embodiment will be described.
A cylinder head made of an aluminum alloy casting for a diesel engine obtained by molding a JIS, AC2B aluminum alloy by a low-pressure casting method is used as a work, and between the valve seats VI and VE, which are the portions having the highest heat load shown in FIG. The remelt treatment of the present invention was performed between the holes P.

First, the work W is fixed at room temperature to a jig connected to the ground, and then the TIG with the wire feeder 6 is fixed.
The torch 1 is supported by a robot arm, and the remelt processing unit 3 in FIG. 3 is continuously irradiated with the arc 2. When the maximum current at the time of the remelting treatment was 420 A, the maximum remelting depth H shown in FIG. 1D was about 11 to 12 mm. At the processing end position, the movement of the TIG torch 1 is stopped, and
-350-280-120A, and the injection speed of the aluminum alloy wire 7 was 0.5-1.0-2.
Gradually increase it to 5-5.0 m / min. As a result, the occurrence of craters was prevented, and the height h of the swelling 8 after solidification shrinkage shown in FIG. 1D was about 1 mm.

According to the above method, since the aluminum alloy wire 7 is directly injected into the molten metal pool 4, there is almost no variation in the amount of build-up in the concave portion 5, and the crater generation rate at the final processing position is almost 0%. Become. Also,
The swelling height due to the injection of the aluminum alloy wire 7 is constantly about 1 mm. This facilitates post-processing, and does not require a large processing allowance, thereby saving aluminum base material. In addition, TIG
When the torch 1 is stopped, the amount of heat input becomes too large, so that fine crystal grains may not be obtained. In the present invention, by injecting the wire, the molten metal pool 4 is prevented from being heated due to the absorption of the heat of fusion accompanying the melting of the wire. The resulting reformed layer covers the portion where thermal fatigue fracture occurs in the combustion chamber of the cylinder head, and the internal structure and mechanical properties are determined by the DAS value (the value of this value is determined by the distance between the secondary arms of the dendritic crystal grains. Represents the size of crystal grains.) = 6 to 7 μm and hardness (HB) = 80 or more.

Another application example of the present invention is shown in FIGS. According to the present invention, it is not necessary to provide a special projection or a processing hole at the processing end portion, so that the processing end point can be set freely.
By utilizing this characteristic, not only the linear remelting process but also a closed-loop remelting process can be performed. For example, in the cylinder head, as shown in FIG. 4, the remelt treatment layer 3 can be formed annularly around the valve seats VI and VE, and in the piston 9 shown in FIG. Can be formed in an annular shape.

[0016]

According to the present invention, it is possible to prevent the occurrence of craters at the end of the remelt treatment and to improve the thermal fatigue strength by setting the remelt treatment part without being restricted by the product shape.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a processing step of the present invention.

FIG. 2 is an explanatory diagram of a TIG torch used in the present invention.

FIG. 3 is a plan view of a processing target portion of the present invention.

FIG. 4 is a plan view of another processing unit of the present invention.

FIG. 5 is a perspective view of another processing target portion of the present invention.

FIG. 6 is an explanatory view of a conventional processing step.

FIG. 7 is an explanatory view of another conventional processing step.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 TIG torch 2 Arc 3 Remelt treatment layer 4 Molten pool 5 Depression 6 Wire feeder 7 Aluminum alloy wire

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuki Sugawara 3-1-2 Akanehama, Narashino-shi, Chiba Pref. Hitachi East Service Engineering Co., Ltd. (56) References JP-A-62-180046 (58) Field surveyed (Int.Cl. ⁷ , DB name) C23C 26/00 B23K 15 / 00,26 / 00 C22F 3/00 F02F 1/24

Claims (1)

(57) [Claims] 1. A method for applying a high-density thermal energy to a metal surface while moving the same to re-melt the surface layer and subsequently modify the surface layer by rapid solidification, wherein the homogeneous metal is added to the molten metal pool at the terminal end of the treatment. A method for remelting a metal surface, comprising: injecting a wire in a solid state.