JPH01197020A - Manufacture of formed product having required wall thickness by superplastic blow forming method - Google Patents

Abstract

PURPOSE:To adjust local wall thicknesses of a formed product by preforming a stock to be worked to bring local wall thicknesses to be a prescribed value after superplastic blow forming and then performing superplastic working. CONSTITUTION:An upper cup-shaped die 2 contains a pressurizing room 4 having a special shaped inside wall and a stock 1 to be worked pinched by upper and lower cup-shaped dies is pushed onto the inside wall of a pressurizing room 4 by a gas pressure from a forming room 5 at first. Then, the room 5 is released from the pressure and then the stock 1 is crept by application of a gas pressure from the pressurizing room 4 and is formed into a formed stock 1b. By addition of a preforming stage to make a preformed stock 1a, the wall thickness of a formed product is uniformized. Thus, local wall thicknesses of a formed product are adjustable and material strength of the formed product is increased by addition of a simple stage preforming a stock to be worked.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application: The present invention relates to superplastic blow moldability, in which blow molding is performed by heating a workpiece to a temperature at which the material exhibits superplasticity.

BACKGROUND TECHNOLOGY: Superplasticity is the property of certain materials, such as aluminum and its alloys, copper and its alloys, stainless steel, titanium and its alloys, in a certain temperature range below its inherent melting point (aluminum: 400-600°C). °C, titanium and its alloys: approx. 850 °C, stainless steel = 90
0-1050°C) with very high elongation (400-6
000%) without being damaged. Utilizing this property to form products with complex shapes, deep-drawn products, etc. in a single operation is called superplastic processing, in which gas (e.g. argon) pressure is applied from one side of the workpiece. The method of forming by pressing the other side against the female mold is called superplastic blow molding.

Superplastic blow moldability is currently measured by well-known methods, for example, U.S. Pat.
No. 0, 4181000 specifications, JP-A-58-28
No. 520, Japanese Unexamined Patent Publication No. 58-173031, and the like are disclosed.

Problems of the present invention: The biggest problem with superplastic blow moldability is that it is difficult to make the wall thickness of the product uniform. Since this problem is very important and serious, we will specifically explain a typical example of shape change during superplastic blowing of a superplastic material shown in Fig. 3 in the case of a hollow cylinder with a bottom. As the shape becomes more complex, the degree of non-uniformity in wall thickness increases.)

In the figure (a), the workpiece (ordinary plate) is the upper bowl-shaped mold 2.
It shows a state where it is airtightly held by the lower bowl-shaped mold 8 (
Bowl-shaped broadly refers to an open box shape with an eight-dimensional recess, and includes recesses in the shape of a sphere, an ellipsoid, etc.). When the gas pressure in the pressurized chamber 4 built into the upper bowl-shaped mold 2 is applied, the workpiece 1 assumes the shape of a hollow sphere (arc-shaped cross section) due to its surface tension (ignoring gravity). (b) Figure). When one end of the workpiece contacts the molding chamber 5 of the lower bowl-shaped mold 8, surface tension-dependent creep that maintains a three-dimensional arc is suppressed on the contact surface, and the inner wall of the molding chamber 5 and the workpiece l Since the friction between the two is large, creep in the direction parallel to the wall surface is also suppressed, and thinning of the workpiece l hardly occurs. This phenomenon occurs sequentially from the part closest to the center (chamber A) of the workpiece l, and as shown in Figure (c), the wall thickness of the bottom corner of the molding chamber 5, which is farthest from point A, For example, the wall thickness at the center of the bottom is large.

This phenomenon can be said to be an essential defect of conventional superplastic blow molding.

Solution: As a solution to the above problem, in the present invention, based on the preferable wall thickness distribution of a molded article (product) produced by performing superplastic blow processing, a method that is likely to provide the wall thickness distribution as a result of blow processing is provided. , a preformed body with different wall thicknesses is made at different locations, and this is subjected to superplastic blow processing.

That is, the present invention provides a method of forming a workpiece and an upper bowl-shaped die, which are in mutual engagement with each other to airtightly hold the outer edge of the workpiece in a superplastic state. In superplastic blow molding, pressurized gas is supplied to a pressurized chamber in which the workpiece is molded by pressing it against the inner surface of the lower bowl-shaped inner molding chamber having a desired shape. In advance, when superplastic blow molding is performed, the wall thickness is preformed with variations so that each part has the desired thickness; It is a manufacturing method.

It goes without saying that methods other than superplastic blow formability can be used for preforming.

Effect: When an internal pressure P is applied to a thin cylinder or a thin sphere with an average radius R1 and a wall thickness t, the force (stress) acting on a unit area in the tangential direction is (For example, Chemical Engineers'
Handbqok 3rd Edition, Perr
y, page 1238, formula (1). ) Equation (1) is the simplest equation that expresses the relationship between pressure and stress, but due to changes in the geometrical shape, the equation changes to υ (for example, the stress in the axial direction of a thin-walled cylinder is expressed by Equation (1)). It becomes 1/2 of the right side.Although a hollow cylinder may have cracks in the axial direction,
It is well known that circumferential cracks do not occur. ).

Pressure is a force acting perpendicular to a surface, and stress is a force acting parallel to a surface.
Even if the pressure is constant, as can be seen from the top,
The stress values vary.

Note that a thin plastic body subjected to internal pressure tends to become spherical due to surface tension.

In addition, in superplastic blowing, the stress is 0.0% of the elongation rate.
8~. It is proportional to the first power, but preferably 0.5 to the first power.0 When a superplastic material is placed in a low-temperature atmosphere, the thin-walled part cools first and its plasticity decreases, while the thick-walled part maintains a high temperature. , and the creep continues. Select the cooling temperature appropriately, and
If it changes over time, it will no longer be spherical, but the wall thickness can be kept almost constant. For example, U.S. Pat.
No. 181000 proposes a method of controlling wall thickness by controlling a constant temperature according to a mathematical formula, but it is extremely difficult to maintain a constant temperature inside the cavity of a superplastic blow molding machine. When temperature is added as a manipulated variable, it becomes 4-dimensional (2-dimensional position, 1-dimensional temperature, 1-dimensional time) or 5-dimensional (8-dimensional position, 1-dimensional temperature, 1-dimensional time). Mathematical control is extremely uneconomical. become.

In the method of the present invention, a workpiece (also referred to as a blank) is pre-processed according to each molded article (product) so that the wall thickness is finally constant (desired value in a broad sense). This makes it extremely easy to obtain a desired molded product.

It should be noted that the effect of surface tension on a superplastic material is to minimize its surface area (and therefore its surface energy).

Example: For the sake of simplicity, a case of a bottomed hollow cylindrical molded product (product) that is symmetrical about the cylinder axis (two axes) will be described. For other complex shapes, further geometrical considerations are required, but are not relevant to the point of the invention.

In FIG. 1, the workpiece preform 1a has a thickness that depends on the line φ when the origin is point A (the midpoint when the workpiece is assumed to be a flat plate). These thicknesses are determined by their respective solid angles (solid angles determined by a specific range within the line and a specific range within the meridian. In the case of FIG. 1, there is no need to consider the inward direction since it is symmetrical about the z-axis. ) is determined by numerical calculations to match the total amount of molded products included. For example, the solid angle surrounded by φ1 and φ2 includes the bottom corner of the product, so the wall thickness is a dog, and φ
In the solid angle surrounded by 8 and φ4, only a small part of the cylinder wall is included, so if the wall thickness is small, calculation of the wall thickness at each solid angle can be done by analysis once the three-dimensional shape of the product is determined. It can be very easily determined visually or numerically, and the accuracy of the calculated value can be improved by finely stratifying the inner line φ and the inner line θ.

It is generally advantageous to make the shape of a preformed workpiece approximate to a part of a sphere (3D arc), but when mass producing products with the same shape, the optimal shape can be determined by trial and error. (Reason: Local temperature affects plastic working.)

The substantial part of the operation for superplastically forming a preformed workpiece is the same as in the conventional method.

However, if there is a risk that the workpiece at the superplastic temperature may deform, pressurized gas is introduced not only into the pressurizing chamber 4 but also into the forming chamber 5 in the early stage of processing to reduce the pressure difference between the two chambers. It may be desirable to make it smaller.

Note that the stratification within the line and within the warp does not have to be equiangular, but must be changed according to the shape of the product.

Regarding the preforming of the workpiece, it goes without saying that not only the superplastic blowing method but also processing methods such as hot forging, cold forging, cutting, and grinding can be used.

However, when the shape of the molded product is simple, for example, in the case of the above-mentioned hollow cylinder with a bottom, it is not possible to adjust the thickness distribution of the molded product using only superplastic blow processing, as shown in Figure 2. can.

In this case, the upper bowl-shaped die 2 has a built-in pressurizing chamber 4 having a special-shaped inner wall as shown in the figure, and the workpiece is held between the upper and lower arm-shaped dies as shown in figure 0). The object 1 is first pressed against the inner wall of the pressurizing chamber 4 by gas pressure from the molding chamber 5 side, as shown in FIG. Next, the pressure is released from the molding chamber 5 side, and gas pressure is applied from the pressurized chamber 4 side to cause creep as shown in Fig.
By adding the preforming process as shown in the figure, the thickness of the molded product becomes uniform. The reason why this phenomenon occurs is not clear at present, but it is an extremely economical method.

Effects of the Invention The present invention makes it possible to adjust the local wall thickness of a molded article (product) by adding an extremely simple and easy step of preforming the workpiece to superplastic blow moldability.
It goes without saying that this can increase the mechanical strength of the molded product.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a method for determining the extreme wall thickness of a workpiece when preforming the workpiece in the present invention (please note that the molded product is shown by a solid line). . FIG. 2 is an explanatory diagram of the process of an embodiment in which the inside of the pressurized chamber of the upper bowl-shaped chamber is used for preforming, and the thickness of the molded product is made uniform by only superplastic blow processing. FIG. 3 is a diagram illustrating that the thickness of a molded product is not constant in conventional superplastic blow processing. l...i workpiece, la...workpiece preform, l
b...Workpiece molded product, 2...Upper bowl-shaped mold, 3...
・Lower bowl-shaped mold, 4...pressurizing chamber, 5...molding chamber Figure 2 J (d)

Claims (1)

[Claims] 1. An upper bowl-shaped mold and a lower bowl-shaped mold that engage with each other to airtightly sandwich the outer edge of the workpiece in a superplastic state, by the workpiece and the upper bowl-shaped mold. In superplastic blow molding, a pressurized gas is supplied to the pressurized chamber to be formed, and the workpiece is pressed against the inner surface of the lower bowl-shaped mold to form the desired shape. After molding and superplastic blow molding, the local wall thickness of the molded product is made to a desired value, and then superplastic blow processing is performed; Molding to a desired wall thickness by superplastic blow moldability. method of manufacturing the product. 2. The inner surface of the pressure chamber in the upper bowl-shaped mold forms a female mold of the preform, and the workpiece is pressed against the inner surface of the pressure chamber by pressurizing the lower bowl-shaped chamber with gas, 2. The manufacturing method according to claim 1, wherein a preform is formed, and then gas pressure is applied to the pressurizing chamber to perform superplastic blow processing. 3 If the preformed workpiece is in the shape of a three-dimensional arc, the center of the first workpiece is the origin (A), the creep direction passing through the origin (A) and the center of the three-dimensional arc is taken as the Z axis, and the latitude angle is The wall thickness of the preform was changed so that the preformed workpiece contained the amount of the final product contained in each solid angle element produced by stratifying the solid angle into m arc minutes and long angle into n arc minutes. The manufacturing method according to claim 1, wherein the manufacturing method is: 4. The pressure in the molding chamber formed by the workpiece and the lower bowl-shaped die is maintained slightly higher than the pressure in the pressurizing chamber to prevent initial deformation of the preform, or The manufacturing method according to item 3.