JPS61226113A - Production of drawn tube with high dimensional accuracy - Google Patents

Abstract

PURPOSE:To produce the drawn tube of high dimensional accuracy by specifying the taper angle of a die and the radius of curvature of corner part and by specifying thickness processing degrees. CONSTITUTION:A metallic tube 2 is drawn from a die 1 with using of a core metal 4. In this case the approaching part A of the die is tapered at the angle in the range of 8-12.5 deg.. The part between from the terminal point of the tapered part upto the starting point of a bearing B is taken as 60-500mm radius of curvature and the die 1 to make radii coming in touch with the tapered part and its terminal point is used. The drawing is performed so that the thickness working degrees shown in the following equation become in the range of either 5-8% or 14-17%. Equation: Thickness working = (thickness t0 before drawing - thickness t1 after drawing) X 100/(thickness t0 before drawing).

Description

[Detailed description of the invention] January 31st from 11th The present invention relates to a method for manufacturing a drawn tube with high dimensional accuracy.

More specifically, the present invention relates to a method of drawing a metal tube with a die using a metal core, and a method of manufacturing a drawn tube with high dimensional accuracy.

BACKGROUND OF THE INVENTION The manufacture of tubes that require high dimensional accuracy is usually carried out by drawing the tubes using a die using a cored metal. However, in recent years, in the field of mechanical tubes, there has been an increasing demand for tubes with high dimensional accuracy, and for this reason, it has become necessary to clarify the dimensional behavior during die drawing using a metal core.

FIG. 2 schematically shows a drawing process using a core bar according to the prior art. In the axial vertical cross-section of this prior art die, the approach section tapers at an angle of 12.5 DEG and the bearing starting point forms an arc with a radius of 1 to 3 mm. In the figure, reference number 1 indicates a die, and the tube 2 is pulled out while being supported from inside by a core bar 4 attached to the tip of a mandrel 3.

However, in the case of such conventional techniques, the rate of dimensional change after drawing of the tube is large, and changes in external dimensions vary depending on the dimensions of the main tube and the degree of drawing.

Therefore, it has been difficult to manufacture drawn tubes with high dimensional accuracy using conventional drawing methods using such dies.

Problems to be Solved by the Invention The purpose of the present invention is to solve the above-mentioned problems of the prior art and to provide a drawn pipe with high dimensional accuracy in a pipe manufacturing method by die drawing using a metal core. be.

More specifically, the purpose of the present invention is to change the die shape and at the same time find optimal drawing conditions that provide high dimensional accuracy.
The object of the present invention is to provide a method for manufacturing a drawn tube with high dimensional accuracy by performing drawing within this range.

Means for Solving the Problems The present inventors have completed the present invention by experimentally observing the dimensional behavior during die drawing using a metal core and conducting theoretical analysis.

In other words, the present inventors have discovered that in order to obtain high dimensional accuracy, it is necessary to change the die shape and limit the drawing degree, that is, the degree of wall thickness. The present invention was completed based on this knowledge.

According to the present invention, in the method of drawing a metal tube using a die using a core metal, the axial cross section of the die is tapered at an angle in the range of 8 to 12.5'' at the approach part,
Using a die whose part between the end point of the tapered part and the bearing start point has a radius of curvature of 60 to 500 mm and forms an arc that touches the tapered part at its end point, the wall thickness machining rate shown by the following formula is 5 to 8%. and 14 to 17%.

Thickness processing rate= Before explaining the method of the present invention in detail, in order to simplify the explanation, the die shape used in the method of the present invention will be explained.

FIG. 1 is a schematic cross-sectional view taken along a vertical plane passing through the axis of the die in a state in which a metal tube is being drawn out by the die used in the method of the present invention.

The inner surface of the die 1 includes an approach part A that starts contact with the material and reduces the outer diameter of the material, a bearing part B that shapes the material, and a relief part on the exit side of the die where the material separates from the die surface. It is composed of C.

According to the invention, the approach portion Δ of the die includes a tapered portion with an angle α, and the cross section of the inner surface of the die between the end point F of this tapered portion and the bearing starting point S is formed by a circular arc with a radius R. This arc touches the tapered portions at their end points, has a center O on a vertical plane that is perpendicular to the die center axis and passes through the bearing starting point S.

As shown in FIG. 1, the metal tube 2 comes into contact with the tapered part of the approach part A of the die, and its outer diameter is reduced by the pulling force, and this reduction in outer diameter is continued by the circular arc part following the approach part A. will be carried out.

When the surface of the metal tube whose outer diameter has been reduced reaches the bearing fulcrum S of the die, the outer diameter of the metal tube is fixed at the bearing part, and the metal tube is separated from the die surface at the relief part C. In the figure, 3 is a mandrel, and 4 is a plug that is attached to the tip of the mandrel and supports the metal tube 2 from the inside with respect to the die to process the metal tube 2 for thinning.

Furthermore, the symbols in the figure indicate the following.

d: Inner diameter of die bearing part, D. = Outer diameter of the metal tube before being drawn, DI = Outer diameter of the metal tube after being drawn, to: Thickness of the metal tube before being drawn, tl: Thickness of the metal tube after being drawn. The reasons for limiting the die shape and wall thickness workability will be explained below.

In the method of the present invention, the die shape and the range of wall thickness processing are determined so that the outer diameter change rate is ±0.5% or less. Here, the outer diameter change rate is defined by the following equation.

(1) Effect of die taper angle α In order to investigate the effect of the angle α of the tapered part of the die on the rate of change in outer diameter, dies with various taper angles α satisfying the following conditions were manufactured and drawn. .

R=100mm.

D, = 90+++mφ, Do=100+n+nφ, Δt/1o=o, i5, where Δt”to t+ The obtained results are shown in Figure 3. As shown in Figure 3, the outer diameter changes depending on the taper angle α of the die. Although the rate varies, 8
In the range of ~12.5°, the fluctuation remains within ±0.5%. Therefore, in the present invention, the taper angle of the die is set to 8 to 1.
The range was set at 2.5°.

(2) How to influence the radius of curvature R of a part of the die corner In order to investigate the effect of the radius of curvature R of a part of the die corner on the rate of change in the outer diameter, various corner parts were tested while satisfying the following conditions. A die with a radius of curvature R was prepared and drawing was performed.

D1=90m+nφ, Do=lOOmmφ, α=lO' Δt/1o=0.15, The results obtained are shown in FIG.

As shown in Figure 4, the radius of curvature R of a part of the corner of the die
When d is small, the tube after being drawn has an outer diameter considerably smaller than the inner diameter d of the die bearing section, but as the radius of curvature increases, the outer diameter of the tube after drawing becomes larger and becomes larger than the inner diameter of the die bearing section. becomes. The radius of curvature R is 6
In the range of 0++oo to 500mm, the outer diameter change rate is ±
0.5% or less, and the method of the present invention also resulted in a die having a corner portion with a radius of curvature R within this range.

(3) Influence of drawing thickness (Δt/to) In addition, the taper angle α of the die is 10 @, the radius of curvature R of a part of the corner is 100 mm, and the inner diameter d of the die bearing part is 90 m.
A metal tube having an outer diameter Do of 100 mm was drawn to 90+t++n using a die of 100 mm. At this time, the outer diameter of the six cores 4 was varied, and the relationship between the degree of wall thickness processing and the rate of change in outer diameter is shown in FIG.

As is clear from the results shown in Figure 5, the outer diameter change rate is ±
To reduce the thickness to 0.5% or less, the wall thickness processing rate should be 5 to 8% and 1
It must be in the range of 4-17%.

EXAMPLE A metal tube was drawn using a die having the shape shown in FIG. 1 and under the conditions shown in Table 1 below, and a mandrel giving the wall thickness workability shown in Table 1.゛The rate of change in outer diameter was calculated from the outer diameter of the tube before and after drawing, and is shown in Table 1.

As is clear from the results shown in Table 1, within the scope of the present invention, the outer diameter change rate is ±0.5% or less, and the dimensional accuracy is extremely high.

On the other hand, in specimens Nα4 and Nα5 whose die shape and wall thickness workability are outside the range of the present invention, the outer diameter change rate is -1.5% and -2.0%, and the dimensional accuracy is poor.

Effects of the Invention The present invention has succeeded in manufacturing drawn pipes with high dimensional accuracy by improving the die shape and maintaining the wall thickness processing rate within an appropriate range in a method for drawing metal pipes using a metal core. It is something.

In the past, many studies have been conducted on the behavior of dimensional changes during dry drawing, but this invention is the first to study dimensional changes during drawing using a cored metal, and this is the first example in the field of mechanical tubes. It can fully meet the demands for high dimensional accuracy.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view taken along a vertical plane passing through the die axis in a state in which a metal tube is being drawn by the die used in the method of the present invention, and FIG. This is an axial vertical cross section of the die. FIG. 3 is a graph showing the influence of the angle α of the tapered portion of the die on the rate of change in outer diameter. FIG. 4 is a graph showing the influence of the radius of curvature of a part of the corner of the die on the rate of change in the outer diameter. FIG. 5 is a graph showing the relationship between the degree of wall thickness processing and the rate of change in outer diameter. (Main reference numbers) l...Dice, 2...Pipe, 3...Mandrel, 4...Core metal, A...Die approach part, B...Dice bearing part, C ...Relief part of the die, Patent applicant Sumitomo Metal Industries Co., Ltd. Agent Masahiko Arai, patent attorney Figure 1

Claims (1)

[Claims] (1) In the method of drawing a metal tube using a die using a core metal, the axial cross section of the die has an approach part of 8 to 1
Using a die that is tapered at an angle in the range of 2.5 degrees, the part between the end point of the tapered part and the bearing start point forms an arc with a radius of curvature of 60 to 500 mm and touches the tapered part at the end point, and the following is done. A method for producing a drawn pipe with high dimensional accuracy, characterized in that drawing is performed so that the degree of wall thickness work shown by the formula is in the range of either 5 to 8% or 14 to 17%. However, wall thickness processing rate = [wall thickness before drawing (t_0) - wall thickness after drawing (t_1) / wall thickness before drawing (t_0)] x 100