JP2808496B2 - Superplastic forming method for metallic composite materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for superplastic forming a metal composite material applied to particles, whiskers, and short-fiber metal composite materials, which are remarkably defective due to deformation and have poor ductility.

[0002]

2. Description of the Related Art In a conventional superplastic forming method, as shown in FIG. 5, a plate 1 to be formed is set between a lower die 4 having a part shape on an inner surface and an upper die 3 having a fluid pressure inlet 3a. Then, after being heated to a predetermined temperature, a predetermined fluid pressure is applied to the plate 1 to be formed and stretched and formed.
It is used as a low-cost integral molding method for materials having superplastic deformation characteristics such as stainless steel.

[0003] Metal-based composite materials are not ductile at low temperatures and cannot be formed at room temperature, but they have superplastic deformation characteristics at high temperatures, so the above superplastic forming method can be applied. It is considered to be the only method of forming a plate of the composite material.

However, the metal-based composite material has a remarkable generation of internal defects (cavities) due to superplastic deformation in a tensile stress field. Further, since no plate material has been manufactured, the metal-based composite material has a relatively small thickness. There are few examples of the superplastic forming method, and the processing method for the present material is currently limited to forging and extrusion.

[0005]

In a conventional superplastic forming method, a tensile stress σ is applied to a plate to be formed by a fluid pressure P.
Occurs, which causes the plate to be stretched. Therefore, in the case of a metal-based composite material in which cavities are easily generated by tensile deformation, many cavities are generated with a low workability as shown in FIG. In addition, in many cases, a metal-based composite material has a defect (internal peeling) inside the material, and a crack propagates from the edge of the peeling to the plate surface (especially the outer surface) during forming, and cracks. Occurs. For this reason, in superplastic forming of a metal-based composite material plate, there is a problem that, since the processing limit is small, an applicable part shape is extremely restricted, and the formed part has many defects therein. .

SUMMARY OF THE INVENTION It is an object of the present invention to solve these problems in applying a superplastic forming method to a metal-based composite material and to provide a new superplastic forming method capable of improving a processing limit and a quality of a processed product.

[0007]

Superplastic forming method of the metal-based composite material of the present invention, in order to solve the problem] is made of a material having high illustrated and deformation stress superplasticity in the same processing conditions and the molded plate made of a metal-based composite material After disposing the hard plate on the lower mold and stacking the above-mentioned molded plate on the hard plate, disposing an upper mold having a fluid pressure inlet thereon, The method is characterized in that a fluid pressure is applied to a surface of a forming plate and the forming plate is superplastically formed together with the hard plate.

[0008]

In the above, since the elongation characteristics of the superplastic material greatly depend on the strain rate, in superplastic forming, the equivalent strain rate ε _{e of the} plate to be formed is always an appropriate constant value. equivalent stress sigma _e always control the molding pressure P to a constant value (σ _e = K · _{ε e} is to the constant epsilon _e from the relationship of ^m sigma _e is a constant which is generated in the plate (Where K and m are constants).

The above-mentioned equivalent stress σ _e is the main tensile and compressive stress σ ₁ , generated on the plate to be formed by the forming pressure P,
According to σ ₂ , σ ₃ (σ ₁ , σ ₂ > 0, σ ₃ <0), σ _e = ((σ ₁ −σ ₂ ) ² + (σ ₂ −σ ₃ ) ² + (σ ₃
- [sigma] ₁₎ ²⁾ since expressed ^1/2 / 2 ^1/2, increasing the absolute value of compressive stress sigma ₃ in the thickness direction, the tensile stress sigma _1, sigma ₂ is unless the above equation change The terms (σ ₂ −σ ₃ ) ² and (σ ₃ −σ ₁ ) ² increase, the equivalent stress σ _e increases, and the appropriate equivalent strain rate ε _e cannot be maintained.

Therefore, when the absolute value of the compressive stress σ _{3 in} the thickness direction is increased, the tensile stress σ ₁ , σ ₂
Must correspond stress sigma _e to a predetermined constant value by controlling the molding pressure P so decreases.

From the above, the load of the compressive stress in the plate thickness direction due to the forming of the plate to be formed on the hard plate acts to reduce the tensile stress in the plate surface.

As described above, a compressive stress is applied in the thickness direction of the plate to be formed, so that the tensile stress in the plate surface can be reduced. It is possible to do.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG.
In the present embodiment shown in FIG. 1, a hard plate 2 made of 7475AL and having a thickness t = 1.5 mm is disposed on a lower mold 4 having a hemispherical concave portion having a radius of 30 mm on the upper surface. It is made of 27% SiC whisker / 7075AL and has a thickness t =
After stacking the 1.5 mm shaped plate 1, the upper die 3 having the fluid pressure inlet 3a is disposed thereon, and the fluid pressure inlet 3a
Further, a fluid pressure is applied to the surface of the plate 1 to form the plate 1 together with the hard plate 2.

In the above description, since the elongation characteristic of the superplastic material greatly depends on the strain rate, in superplastic forming, the equivalent strain rate ε _{e of the} plate 1 to be formed is always an appropriate constant value, that is, Equivalent stress σ _e generated in formed plate 1
(Used to compare stresses that contribute to deformation)
There is always to the epsilon _e constant from the relationship of constant value and controlling the molding pressure P such that _{(σ e = K · ε e} m is required to be sigma _e is constant. Here K, m is a constant).

[0015] The equivalent stress sigma _e, when forming the shape of the molded plate 1 is hemispherical, the main stress of tension along the plate surface generated in the molded plate 1 by a molding pressure P as shown in FIG. 3 sigma ₁ and σ ₂ and the principal stress σ ₃ of compression perpendicular to the plate surface are expressed by the following equation. σ _e = ((σ ₁ −σ ₂ ) ² + (σ ₂ −σ ₃ ) ² + (σ ₃
In ^{_{-σ 1) 2) 1/2 / 2}} 1/2 above equation, increasing the absolute value of compressive stress sigma ₃ in the thickness direction, the tensile stress sigma _1, sigma ₂ is changed unless the above formula (sigma The terms ₂₋ σ ₃ ) ² and (σ ₃ −σ ₁ ) ² become large, the equivalent stress σ _e increases, and the appropriate equivalent strain rate ε _e cannot be maintained. Therefore, when the absolute value of the compressive stress σ _{3 in} the plate thickness direction is increased, the forming stress P is controlled so that the tensile stresses σ ₁ and σ ₂ in the plate surface are reduced, and the equivalent stress σ _e is set to a predetermined constant value. And must be.

From the above, the load of the compressive stress in the plate thickness direction due to the molding of the plate to be formed 1 on the hard plate 2 acts to reduce the tensile stress in the plate surface, and thereby the cavity is formed. It is possible to prevent the generation and the growth of cracks from the peeling portion which is internally pressed to the material.

In this embodiment, 27% SiC whisker /
For the molding plate 1 made of 7075AL, the proper molding conditions are a temperature of 500 ° C. and a strain rate of 1.0 × 10 ^−1.
sec ⁻¹ and the deformation stress under this condition is σ _e = 1
kgf / mm ^2, also deforming stress at the same conditions of the hard plate (7475AL) 2 is a σ _e = 3kgf / mm ^2.

Here, the forming pressure and stress state when the laminated plate is formed until the radius of curvature R becomes 50 mm will be considered as an example (for the sake of simplicity, the reduction in thickness is ignored).

In the formation of a hemisphere, the principal stress σ
_{Since 1} and σ ₂ are equivalent, the equivalent stress σ _e is σ _e = ((σ ₁ −σ ₂ ) ² + (σ ₂ −σ ₃ ) ² + (σ _{3
^{-Σ 1) 2) 1/2 / 2}} 1/2 = | σ 1 -σ 3 | = σ 1 -σ
₃ (∵σ ₁ > 0, σ ₃ <0).

The pressure required for forming the laminated plate is P _FROM , of which the pressure required for forming the hard plate 2 is P ₁ ,
Assuming that the pressure required for the molding of P2 is P ₂ (P ₁ + P ₂ = P _FROM ), in the hard plate 2, σ ₁ = RP ₁ / 2t = 50 P ₁ /2×1.5=50 P _{1
/ 3, σ 3 = -P 1} /2, σ e = 50P 1/3 + P 1 /
2 and P ₁ = 0.175 from σ _e = 3 kgf / mm ²
kgf / mm ² .

Further, in the molded plate _{1, σ 1 = 50P 2/} 3, σ 3 = - (P FROM + P 1) / 2 =
_{- (P 2/2 + P} 1) = - (P 2 /2+0.175),
_{σ e = 50P 2/3 +} P 2 /2+0.175 next, σ _e = 1kgf / mm ² from P ₂ = 0.048
kgf / mm ² .

Therefore, the pressure required for forming the laminate is P
_{FROM = P 1 + P 2 =} 0.223kgf / mm 2 , and the
At this time, the stress acting on the plate 1 is σ ₁ = σ ₂ =
0.8 kgf / mm ² , σ ₃ = −0.2 kgf / mm ²
Becomes

On the other hand, in the case where only the conventional plate 1 shown in FIG. 5 is formed, σ ₁ = 50P _FROM / 3, σ ₃ = −P _FROM / 2, σ _e = 5
0P _FROM / 3 + P _FROM / 2, P _FROM = 0.05 from σ _e = 1 kgf / mm ²
8 kgf / mm ² , σ ₁ = σ ₂ = 0.97 kgf / mm
² , σ ₃ = −0.029 kgf / mm ² .

Therefore, in the present embodiment, the maximum principal stress generated in the plane of the plate 1 to be formed is reduced by about 20% by being formed by overlapping the hard material 2. The effect of suppressing the growth of cracks originating from cavity formation and delamination due to the reduction of the maximum principal stress by 20% is very large,
As shown in FIG. 2, a hemisphere can be formed, and no cavity is formed at the vertex.

As described above, since the tensile stress generated in the surface of the plate to be formed can be reduced, it is possible to suppress the generation of cavities in the plate to be formed and the growth of cracks originating from the peeled portion. Was.

In the case of hemispherical molding with a working ratio of about 200%, it is possible to form without forming a cavity by reducing the maximum principal stress by about 20% as in this embodiment. The required maximum principal stress reduction amount varies depending on the shape and the working degree, and accordingly, the material and the thickness of the hard material are properly used in accordance with this.

A second embodiment of the present invention will be described below. In the second embodiment, the materials of the plate 1 and the hard plate 2 are the same as those of the first embodiment, but the plate 1 has a width of 60 mm.
It is formed into a corrugated shape having a depth of 60 mm and a depth of 60 mm. Since the formed shapes are different, the thickness ratio of the plate 1 to be formed and the hard plate 2 is changed.

In the above description, the principal tensile stress σ shown in FIG.
_1, for the sigma ₂ the principal compressive stress _{σ 3, σ 1 = RP /} t, σ 2 = σ 1/2, a σ ₃ = -P / 2, the maximum tensile principal stress sigma ₁ and the equivalent stress sigma _e The relationship is (Since the compressive principal stress σ ₃ generated on the cylindrical surface is sufficiently smaller than the tensile principal stresses σ ₁ and σ ₂ , the relationship is simplified to σ ₃ =
Σ ₁ = σ in hemispherical molding (considering 0)
_e , σ ₁ = 2σ _e / in corrugated molding (plane strain)
It is ^31/2 , and for a certain equivalent stress, the corrugated molding has a larger maximum tensile principal stress. The pressure P required for molding is P = 2tσ ₁ / R = 2tσ in hemispherical molding.
_e / R, P = tσ ₁ / R = 2tσ _{e for} corrugated molding
/ 3 ^1/2 R, and the corrugate is molded at a lower pressure, and the compressive stress in the thickness direction is also reduced.

Therefore, in the corrugated forming, the maximum tensile principal stress σ ₁ is larger than in the hemispherical forming, and the compressive stress σ _{3 in the} plate thickness direction is smaller, so that the thickness of the hard plate 2 relative to the plate 1 Unless the ratio is increased, the same cavity reduction effect cannot be obtained.

Also in this embodiment, the same operation and effect as those of the first embodiment were obtained by performing molding under the above conditions.

A third embodiment of the present invention will be described below. In the third embodiment, the material and the basic molding shape of the plate 1 and the hard plate 2 are the same as those of the second embodiment, but the width of the corrugate is 50 mm, the depth is 25 mm, and the forming degree ( Since the depth / width ratio of the corrugate is small,
And the thickness t of the hard plate 2 are 1.3 mm and 1.4 mm, respectively.
The thickness ratio is changed. This is because, when the degree of processing is small, the amount of generated cavities is also small, so that even if the thickness of the hard plate 2 is reduced, cavities can be prevented.

In this embodiment, the same operation and effect as those of the first and second embodiments were obtained by performing molding under the above conditions.

In the above-described second and third embodiments, the same cavity prevention effect was obtained by changing the thickness ratio of the hard plate 2 to the plate 1 with respect to changes in the forming shape and the degree of processing. The same effect can be obtained by changing the material of the hard plate 2.

As described above, by optimizing the material and thickness of the hard plate in accordance with the material, thickness and forming shape (including the degree of processing) of the plate to be molded, various shapes of metal composite materials of various materials can be obtained. It can be applied to superplastic forming.

The combination of the plate to be formed and the hard plate is 18
2% SiC Whisker / 2024AL
001AL (Spral) hard plate combination, 2
A combination of a molded plate made of 0% SiC whisker / 6061AL and a hard plate made of 8090AL, a molded plate made of 23% SiC whisker / 2014AL and 2090AL
There are many possible combinations of hard plates.

[0036]

The method for superplastic forming of a metal-based composite material according to the present invention is characterized in that a plate to be formed of a metal-based composite material is superplastically formed by superimposing it on a hard material made of a plate material having a higher deformation stress. Compressive stress can be applied in the thickness direction of the plate to be formed, thereby reducing the tensile stress (maximum principal stress) generated in the plate surface. It is possible to suppress the growth of the crack originating from the generation and separation parts.

If the formation of the cavity and the growth of the cracks are suppressed, the processing limit is improved, the shape of the part applicable to superplastic forming is expanded, and the defect of the formed part under the internal pressure is greatly reduced.

Therefore, the present invention has an effect of enabling superplastic forming of a metal-based composite material plate, and further greatly improving the processing limit and the quality of the processed product.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is a photograph of a metal structure of a plate formed according to the first embodiment.

FIG. 3 is an explanatory diagram of stress generated in a plate to be formed formed by the first embodiment.

FIG. 4 is an explanatory diagram of stress generated in a plate to be formed formed according to a second embodiment of the present invention.

FIG. 5 is an explanatory view of a conventional molding method.

FIG. 6 is a photograph of a metal structure of a plate formed by the conventional forming method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molded plate 2 Hard plate 3 Upper die 3a Fluid pressure inlet 4 Lower die

Claims (1)

(57) [Claims] 1. A hard plate made of a material exhibiting superplasticity and having a high deformation stress under the same processing conditions as a plate made of a metal-based composite material is disposed on a lower mold, and the hard plate is made on the hard plate. Suffered
An upper mold with a fluid pressure inlet on it after stacking the forming plates
From the fluid pressure inlet to the surface of the plate to be molded.
Superplastic forming method of the metal-based composite material of the same the molded plate was loaded, characterized in that superplastic forming with the hard plate.