JPS5927660B2 - Tube forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the manufacture of tubular pieces of ductile material, and more particularly to extruding the tubular pieces through an inclined die so that one part of the circumference of the tube is freer than the other part. The present invention relates to a method of changing tube wall eccentricity or forming a bend by providing a large diameter reduction.

A number of tube bending methods have been developed, but generally speaking, most of these methods involve modifications of some basic process.

There is no single method that can be effectively applied to all of the various bend formation situations in which variations in tubular section size, diameter to wall thickness ratio, material, or bend angle are considered. For example, pressing methods in which the tube is placed across a plurality of wiper dies and subjected to pressure exerted by post-forming dies are useful where slight flattening of the tube can be tolerated. The roll bending method uses three or more rolls arranged in a triangular shape, the center of which is adjustable in position. The workpiece is fed between a fixed driven roll and an adjustable roll to form a bend. The draw method bends the tube by locking it to a rotating form and pulling the tube through a pressure die. All of these methods result in thinning of the tube wall, especially in its outer ring, and loss of roundness of the cross-sectional circumference. These problems become more severe as the tube walls become thinner and/or the degree of bending increases. In an attempt to eliminate the loss of cross-sectional roundness, various types of mandrels or other internal support means have been used with some degree of success.

In some cases, the use of internal tools has complicated the process and introduced new problems such as damage to internal walls or uneven thinning. U.S. Patent No. 3,354,68
No. 1 discloses a method and apparatus for bending and forming an elbow from a tubular piece by extrusion through a forming die. Part of this device consists of a tapered land that attracts bending by a difference in frictional forces, the frictional forces being greater on the inside of the bent tube than on the outside. . Incidentally, this is a concept opposite to that of the present invention, as will be described later. Another problem that is widely known in the tube industry is that of tube wall eccentricity.

Eccentricity is simply defined as the distance between the center of a tube cross-section with respect to its inner diameter and its center with respect to its outer diameter. When these centers do not coincide, the member is said to be eccentric. Modifying eccentricity involves reducing differences in wall thickness. U.S. Pat. No. 3,095,083 discloses a method and apparatus for correcting eccentricity by pulling a member through a tilted die without internal tooling. However, it has been found that following this method not only limits the amount of eccentricity correction that can be obtained, but also causes the die to create wall thickening in some cases and thinning in others. It was done. This same technique for providing eccentricity correction is also used in US Pat. No. 3,131,803, where a tilted die is used in conjunction with an internal mandrel. Other approaches to eccentricity correction include U.S. Pat. No. 3,167,176 using a swivel mandrel.
Techniques exist, such as those found in U.S. Pat. No. 3,698,229, which remove metal from thicker portions of tubes. The method of the present invention overcomes many of the problems associated with prior art methods in connection with tube bending and eccentricity correction.

In aspects of the invention relating to bending, a tube of ductile material is extruded through an angled die defined as having an axis in an angular relationship to its longitudinal axis. The tilting die used here has bilateral symmetry (Bilateraly) with respect to the axis of the incoming tube.
mmetry). That is, a unique plane of symmetry includes the axis of the incoming tube. When the tube-shaped member is extruded through the die, it is subjected to different swaging effects in different parts and at the same time is subjected to a displacement of forces acting at right angles to the tube axis, resulting in bending. Unlike prior art practical methods, the tube undergoes wall thickening over its entire circumference. A second aspect of the invention involves forcing the tubular member through the tilting die to effect eccentricity correction by properly orienting the initially eccentric tube with respect to the tilt angle of the die.

The application of angled dies in composite dies for forming tubular fittings such as elbows is disclosed in the same application.

The present invention can be used to bend an already formed tube-like member to produce a high quality bend, to correct an undesired eccentricity of the tube, or to create a desired eccentricity characteristic. The present invention is directed to a method for selectively changing various dimensional aspects of.

The present invention is applicable to tubular members made from flowable (ductile) materials such as ferrous and non-ferrous metals and plastics and related flowable materials. Bending the Tube Referring to FIG. 1, a tube-like member 10, the outer surface of which may be suitably treated with an industrial lubricant, is positioned in the entry compartment of an inclined die 12.

An introduction guide compartment (not shown) may be desired. dice 12
is placed on or firmly attached to the support fixture 14. A press platen 16 is in releasable contact with or otherwise affixed to the free end of the tubular member 10 and is in and out of the die 12.
to push through. The tube does not necessarily have to be pushed at its end; the tube can be pushed using a gripper that clamps it in front of the die entrance.
The pushing force may be provided by a press or other pushing device. Fixture 14 carries forming die 12 and provides an exit path for formed tubular member 26 through opening 18. Referring to FIG. 2, the inclined die 12
The combination of this and the tube-like member 10 pushed into it is
It is characterized under certain geometrical considerations involved.

The part 10 also starts with an initial outer diameter 0Ds. It should be noted that for convenience of illustration, FIG. 2 shows a particular configuration of a symmetrical die (i.e., a tilted die) consisting of two conical sections. For illustrative purposes, the centerline of the tube 10 as it enters the die 12 is shown as a horizontal dotted line.
The inclined die 12 has an entrance conical section 20 and a relief.
It can be conceived as a shape consisting of conical sections 22.
Conical section 20 is a first truncated hollow conical section and conical section 22 is a second truncated hollow conical section. These compartments do not necessarily have to be conical, although cones are used for most practical processes. Conical sections 20 and 22 meet at truncated surfaces, commonly referred to as lands or throats 24, so that when unbent tubular member 10 is forced through conical section 20, the tubular member bends across the land. It passes into the compartment 22 as a tube 26 . The tubular member 10, which initially starts with an outer diameter of 0 Ds, is transformed by passing through a die into a shaped tubular member 26 exhibiting an outer diameter of 0 Df. The inlet conical section 20 may be further defined in relation to the starting member 10 and the formed member 26 by the following symbols: In FIG. 2, an angled die is shown where the die exit face 27 is perpendicular to the die or cone centerline.

This exit face 27 does not necessarily have to be perpendicular to the die centerline, although this is desired for most practical processes. Alternatively, the outlet face 27 can be tilted to either side from this orthogonal orientation and, of course, still provide a tube bending effect. It will be seen that Ix and 11 define oppositely located steep and shallow sections of the inlet section 20 with respect to the centerline of the member 10.

As the member 10 is forced through the die 12, its circumferential portion, which is the steepest part of the die, experiences a greater swage (reduction in diameter) than the opposite part, so that the maximum swage is achieved at the conical part associated with the maximum entrance angle 1x. and associated swage deer occur. Established metal forming principles specify the maximum practical angle that can be used without resulting in over-machining that creates high pressure forces that are likely to cause buckling or irregular bending of the tube. The inventors have determined that Ix has an upper critical limit of about 40 degrees;
It has been found that the angle of inclination has a critical upper limit of 20° and should be greater than or equal to 0° and equal to or less than the cone angle. The critical limit value of Ix varies somewhat depending on the 0Ds/t ratio (t is the initial tube wall thickness), the degree of diameter reduction, and the friction properties. When these limits are exceeded,
The incoming tube is prone to bending, and the part exiting the die is prone to unpredictable, irregular bends and non-uniform radii of curvature. In other words, these limits define transition zones and, when not exceeded, result in a predictable range of uniform bending of the tube with a uniform radius of curvature.
Beyond this transition zone, the part exiting the die exhibits unpredictable behavior, with a surprising reduction in bending and disturbances in the radius of curvature. The swaging action that acts differentially in different parts brings about a proportional flow of material, which causes a large elongation in the part of the tube-like member that receives a large swage, and the different elongation in different parts causes bending. is generated.

During extrusion of the tubular member 10 through the die 12,
The portion of the member circumference closest to the 11 element 25 of the inlet conical section contacts the die before its opposite portion contacts the Ix element 23 of the conical section. This deviation of the initial contact at the inlet section 20 results in a perpendicular dicer misalignment of the tube 10, thus creating a force couple, which eventually promotes further bending of the tube. Even in the extreme case of no reduction in diameter, a tube forced through a tilting die encounters this die force deviation and thus bends.
This phenomenon can be proven geometrically. As long as the angle of inclination is large enough to cause some finite amount of plastic deformation of the tube, permanent bending will occur. It has been found that the above method results in a generally tubular cross section that remains substantially circular and results in wall thickening along the entire cross section.

When properly carried out, the method virtually eliminates the risk of tube wall collapse that inhibited so many prior art bending methods, yet does not require the use of mandrels or other types of internal supports. do not need. The method of the present invention also exhibits highly desirable coverage in terms of 0 Ds/t ratios compared to prior art methods without the need for internal support equipment, with minor changes in specific materials. Bending well in excess of 180° is commonly practiced, the only restriction being removal of the bending tube from the equipment.

The method can be applied to any malleable or ductile material.
By providing support on either the outer or inner surface of the straight tube 10, buckling can be suppressed. By carrying out the entire process under a sufficiently high hydrostatic pressure environment (eg, in a high pressure chamber), normally brittle materials (without breaking or being difficult to deform) can be bent. The tube can be formed cold, warm or hot. Table 1 below summarizes test results obtained when certain carbon steel tubes were bent under a 5.3% reduction in outside diameter.

As a result of a comprehensive review of many tests, the inventor has determined that the radius of curvature of a bent tube is strongly influenced by the angle of inclination and, to a lesser extent, by the reduction in the outer diameter and the initial diameter vs. It was also found that the thickness ratio is also affected.

The required pressing force on the tube within the die is strongly influenced by the degree of reduction in the outer diameter and is also significantly influenced by the slope angle, cone angle, and initial diameter-to-thickness ratio. The inventors have also found that maximum bending occurs when the slope angle approaches 18 and the cone angle is minimally on the order of 2 degrees beyond the slope angle. The test results further indicate that maximum bending occurs when the percent reduction in the outside diameter of the tube is equal to about 1/2 of the initial diameter-to-thickness ratio value. Correcting Tube Eccentricity Pushing the tube-like member through the angled die 12 creates a force that results in a material flow that is proportional to the swaging angle at which a particular portion of the tube is encountered.

In all cases, pressing the member 10 through the die 12 results in an increasing wall thickness along the entire circumference. The maximum thickness increase occurs in the portion of the tube that meets the maximum nuage (at Ix) and the minimum thickness increase corresponds to the minimum swage (at Ii). FIG. 3 shows a cross section of the tubular member 10 before being introduced into the inclined die 12.

A minimum wall thickness 28, a maximum wall thickness 30, and an inner diameter 32 are shown. Eccentricity is exaggerated.
Ne

[Brief explanation of the drawing]

Bamboo 4 fields - 4 - Shidori +, Do≠ Yumisaki one tot area, h
←The country muft tube-like member 10 is forced through the die 12 according to the process previously described. However, when threaded for the purpose of correcting eccentricity, the orientation of the member is extremely important. Because pushing a part through the die always results in an increase in wall thickness along the perimeter of the part, the minimum wall thickness section 28 is the maximum swage section 2 of the die.
It must be made to meet 0. The maximum swage angle may be selected based on the amount of eccentricity correction required. Of course, bending will occur with correction of eccentricity, and therefore a straightening operation of the tube will be required depending on the application. FIG. 4 shows a cross-section of the member 26 after it exits the relief cone section 22 of the die. The member is shown as having a wall 34 of uniform cross-section over its entire circumference. Inner diameter 36 is the initial inner diameter 32
The outer diameter 0Df is also reduced from the initial outer diameter 0Ds. The table shows the % eccentricity (
This is to compare the changes (after straightening). As can be easily seen, a significant increase in the change in % eccentricity characterizes the method. In some cases, it may be desirable to change the eccentricity rather than correct it. In these cases, the incoming tube is properly oriented relative to the die to effect the desired variation in wall thickness along the circumference of the tube according to the principles previously described. A general view of a suitable device is shown.

Claims (1)

Claims: 1. A die with a frusto-conical passage terminating in a throat, formed with a steeply sloped portion and a gently sloped portion just opposite it, and having a maximum die entrance angle Ix.
is not more than about 40° and the die inclination angle is not more than about 20° and greater than 0° and less than or equal to the cone angle C, where Ix is equal to C+T and T is in the die centerline. is the angle between the center line of the tube and
C is the angle between the conical surface and the die centerline) A method of bending the tube in the die by pushing the tube through the die passage to bend the tube in the die where the tube meets the area of maximum slope. The tube is placed under an orbital swage force that varies from a maximum value to a minimum value where the tube meets the gently sloped section, and at the same time is placed under a deviation of the force within the die that creates a couple or moment, and the tube is restrained beyond the throat. A tube bending method that consists of bending without bending. 2. The die has an inclination angle of 18 degrees and a cone angle of 18 to 20 degrees with respect to the maximum bending of the tube.
The method described in section. 3. The method according to claim 1, wherein the tube is bent while undergoing reduction and contraction of its outer diameter. 4. The method of claim 1, wherein the entire wall cross-section of the tube increases in thickness upon passing through the die. 5 The wall of the initial tube changes thickness and the tube is increased in thickness by a greater amount than other wall portions which undergo a lesser degree of swaging, such that the wall of the tube undergoes the greatest swaging and has a greater thickness than other wall portions which undergo a lesser degree of swaging. 4. The method of claim 3, wherein the method is forced through a die. 6. The method of claim 5, wherein the least thick portion of the tube is not subjected to the greatest swage.