JPH07113183A - Production of ultra-thin hemisphere - Google Patents

Abstract

PURPOSE:To make the thickness of a rough hemisphere almost uniform and ultra-thin by controlling immersion time at the time of immersing the rough hemisphere formed by a superplastic molding method into an etching liquid. CONSTITUTION:The rough hemisphere is produced by subjecting a uniform plate material, such as titanium alloy, having high specific strength of the thickness of the pressurization threshold to superplastic molding. This rough hemisphere 1 is connected to a hoisting down machine 4 with a programming function through a hoisting down jig 3. The time when the rough hemisphere 1 is immersed into the etching liquid 2 is controlled by the operation of this hoisting down machine 4. The thick part of the coarse hemisphere 1 is immersed for long in the etching liquid and the thin part is immersed therein for short. A tank of the min. weight having a high safety factor is obtd. if the composite material tank of a spherical shape or tear drop shape is produced by this method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an ultra-thin hemisphere, and a fuel tank for a satellite attitude control device (reaction control system: RCS), which requires severe weight reduction, and a two-part type kick for a satellite. It can be advantageously applied to the production of spherical tanks or teardrop tanks such as motor tanks or flying tanks, especially when these tanks are made using composite materials such as carbon fiber reinforced plastic (CFRP). The present invention relates to a method which can be advantageously applied to the production of an ultrathin inner shell sphere required for

[0002]

2. Description of the Related Art In conventional satellites, the tank is not so large, so that a uniform wall thickness (t ₀ ) as shown in FIG.
The thin hemisphere 2 as shown in FIG. 3 (b) was formed by the superplastic forming method using the plate material 1. The higher this manner at the molding of the elongation of the sheet large, that is, as at deeper depths thickness becomes thinner (t _1> t ₂₎ for high-pressure gas at the thinnest portion corresponding to the apex of the thin hemisphere (t ₂₎ It had to be designed so as to satisfy the safety factor stipulated by the Control Law, and there was too much margin in the wall thickness, especially at a large depth and large diameter, which wasted weight.

FIG. 4 shows an example of the plate thickness distribution after forming from a uniform plate material (t ₀ = 1.4 mm). As shown in the figure, the thickness of the central portion is considerably smaller than the thickness of the peripheral portion. Figure 4
4A is a table showing the plate thickness distribution before superplastic forming, and FIG. 4B is a table showing the plate thickness distribution after superplastic forming. The horizontal axis of FIG. 4B connects the center of the hemisphere to the apex. Angle from position {Fig. 4
(See (c)), and the vertical axis indicates the wall thickness at the intersection of the angle and the circumference (see FIG. 4 (c)).

As one of the solutions to this problem, the thickness of a plate material portion which is a peripheral portion of a hemisphere is previously ground by grinding or the like so that the thickness after molding as already proposed by the present inventors becomes uniform. There is also a processing method for forming a uniform thin hemisphere by thinning and performing superplastic forming (Japanese Patent Laid-Open No. 63-56317), but in this method, the thickness after forming is 0.5 mm.
You can only do so. This is because, with this method, the thinnest part near the fixed part expands before the central thick part expands and breaks during molding in the following.

[0005]

Since the fuel tank of the attitude control device for a satellite is required to be lightly weighted, it is necessary to use a high-strength titanium alloy to make the fuel tank thinner and lighter. Both the spherical shape and the teardrop shape are often used as the shape of the fuel tank, and the thin-walled hemisphere and thin-walled cone of this tank are usually formed by a superplastic forming method using a uniform plate material.

As shown in FIG. 4, a product formed by using a uniform plate material has a larger wall thickness at a smaller depth and a larger diameter, resulting in loss of weight. The weight loss is not so noticeable for small tank size, but this weight loss is not allowed in the satellite that strictly controls the weight on the gram order. Especially, it is necessary to make the inner shell sphere of titanium alloy etc. used for the purpose of fuel compatibility and airtightness maintenance of CFRP tank etc. as thin as possible, but the required wall thickness is 0.1-0.3 mm. The thickness was so thin that it exceeded the limit of the thickness that could be processed by the method proposed by the present inventors. In view of the above-mentioned state of the art, the present invention aims to provide a method for producing a uniform ultrathin hemisphere.

[0007]

Means for Solving the Problems The present invention forms a rough hemisphere by a superplastic forming method using a uniform plate material having a high specific strength of a thickness at a pressure limit by the superplastic forming method, and It is a method for producing an ultra-thin hemisphere, characterized in that chemical corrosion is performed by controlling the time of immersing each part of the rough hemisphere in a corrosive solution so as to be uniform.

That is, the present invention uses a uniform plate material having a relatively high specific strength at a working limit thickness by the superplastic forming method,
Coarse hemispheres are formed by superplastic forming, and the chemical corrosion method is used to control the immersion time in a corrosive solution so that the thickness of the coarse hemispheres is uniform. It is something that is done.

[0009]

When the rough hemisphere is formed by the superplastic forming method, the wall thickness is uniform in the circumferential direction, but the wall thickness gradually changes toward the apex in the meridian direction. Further, in the chemical corrosion method, if the whole is immersed, the wall thickness can be uniformly reduced in the order of several microns per minute in proportion to the immersion time. Therefore, the thick portion of the coarse hemisphere is long, and the thin portion is short, and by controlling the immersion time in the corrosive liquid, the thickness of the coarse hemisphere can be made substantially uniform and ultra-thin.

[0010]

EXAMPLES An example of the present invention will be described below in terms of weight% of Al:
5.5-8.5, V: 3.5-4.5, Fe <0.2
5, O <0.20, C <0.08, N <0.05, H <
Titanium alloy with composition of 0.015 (Ti-6Al-4V)
The case of using will be described. This titanium alloy plate was heated at a temperature of 880 to 920 ° C. and a stress of 0.5 to 1.0 kg /
mm ² and strain rate: 10 ⁻⁴ to 10 ⁻³ sec ⁻¹ , the gas pressure pattern is adjusted to form a rough hemisphere by the superplastic forming method. The procedure up to this point is the same as the conventional method until the rough hemisphere is formed by the superplastic forming method.

Next, the coarse hemisphere 1 is set as shown in FIG. The coarse hemisphere 1 is connected to a hoist / unwinder 4 with a programming function through a hanging jig 3. By the operation of the hoisting / unwinding machine 4, the time for immersing the coarse hemisphere 1 in the corrosive liquid 2 is controlled.

The immersion time is controlled as shown in FIG. FIG. 2A shows an example of the wall thickness distribution of the rough hemisphere 1 formed by superplastic forming of a titanium alloy, and the hatched portion shows the wall thickness to be reduced in order to make the wall thickness uniform. In the case of titanium alloys, the rate of metal thinning in a corrosive liquid (for example, a mixed liquid of 10% nitric acid and 1% hydrofluoric acid) is about 4 microns per minute both inside and outside, so the dipping time is as shown in FIG. It is calculated from the quantity as shown in FIG. The horizontal axes of FIGS. 2A and 2B represent θ shown in FIG. 2C.

[0013]

According to the present invention, a uniform ultra-thin hemisphere can be manufactured. Therefore, a spherical or teardrop-shaped CFRP can be produced using this.
When a composite material tank such as is manufactured, a tank having the minimum weight that satisfies the safety factor specified in the High Pressure Gas Control Law can be obtained. Therefore,
It is very effective as a means for manufacturing satellite tanks where weight control is strictly performed on the gram order.

[Brief description of drawings]

FIG. 1 is an explanatory view of a part of the method for producing an ultrathin hemisphere of the present invention.

FIG. 2 is a table showing an example of a wall thickness distribution of a coarse hemisphere to be thinned when manufacturing an ultrathin hemisphere of the present invention, and a relationship of a dipping time to a corrosive solution corresponding to the wall thickness distribution.

FIG. 3 is an explanatory diagram of a hemispherical wall thickness distribution obtained by a conventional superplastic forming method.

FIG. 4 is a 1.4 mm thick titanium alloy (Ti-6Al-4).
Explanatory drawing of the wall thickness distribution of the hemisphere obtained by the superplastic forming method from the uniform plate material of V).

Claims (1)

[Claims] 1. A rough hemisphere is formed by a superplastic forming method using a uniform plate material having a high specific strength at a thickness of a pressing limit by the superplastic forming method, and the rough hemisphere is made to have a uniform wall thickness. A method for producing ultra-thin hemispheres, characterized by controlling the time of immersion in the corrosive liquid of each part of the hemisphere to perform chemical corrosion.