JPH11290962A - Tension bending method of material to be formed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control variance in machining precision by constantly ensuring a stable spring back quantity in the tension bending of an aluminum alloy material to be formed, regardless of the mechanical characteristic of individual base material and the variance of cross-sectional shapes during mass production. SOLUTION: A prescribed tension strain ε is applied to a base material in a manner that a tensile stress not less than a proof stress is added in the longitudinal direction before tension bending, and after a tension t1 is measured when reaching the proof stress, the tension bending is performed by setting a tension t2 to be applied during the machining in accordance with t1. The tension t2 is set such that a tension t2', when a target shape is obtained in the tension bending of the material, is preliminarily determined, as is a tension t1' when the material reaches the proof stress, and that the tension t2 to be applied during the tension bending is set so that it becomes t2'/t1'=t2/t1 in accordance with the tension t1 measured for each material. The tension t1 and t1' may be represented by a tension reaching such a prescribed tension strain ε as a tensile stress not less than the proof stress is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to bending of a profiled material, which suppresses dimensional errors caused by springback after bending during mass production, and performs tensile bending with high profiled material accuracy. It is.

[0002]

2. Description of the Related Art A variety of processing apparatuses are used for bending, and among them, tension bending, which has high processing accuracy, has attracted attention. FIG. 1 shows a schematic diagram of the tensile bending process. In the bending process, since the shape changes due to the springback after the process, a predetermined product shape cannot be obtained, and it may be difficult to perform subsequent joining, assembling, or the like. For this reason, it is necessary to set a mold and processing conditions in anticipation of the springback amount. However, especially with extruded profiles, there is a large variation in the cross-sectional shape and dimensions of the material due to die wear, etc., and there are large variations in the mechanical properties of the material. Accuracy variation occurs.

For this reason, in the case of press-through bending,
As seen in Japanese Patent Application Laid-Open No. 9-10852, the amount of movement of the movable mold is changed according to the 0.2% proof stress during the tensile test,
There is also a method of adjusting the amount of springback by changing the bending moment. However, this method cannot compensate for the deterioration of the processing accuracy due to the variation between the same billets. In order to compensate for this drawback, Japanese Patent Application Laid-Open
As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 141339, there is a method in which the hardness of an individual workpiece is measured by press-through bending, and this is converted into the proof stress of the material to determine the processing conditions. However, this method has a problem that it can cope with variations in mechanical properties of individual materials, but cannot cope with variations in cross-sectional shapes of the materials.

[0004] In the case of tensile bending, since the bending is performed by pressing a profile into a mold, the springback cannot be corrected by the above method.
For this reason, in the tension bending process, the amount of springback itself is reduced by setting the tension excessively, and the error is reduced. However, in the case of an aluminum profile, for example, increasing the tension causes an increase in the amount of cross-sectional deformation or a problem of breakage.

[0005]

DISCLOSURE OF THE INVENTION The present invention relates to a method for tensile bending of a profile material, which is to improve the mechanical properties of individual materials being mass-produced.
It is an object of the present invention to provide a bending method capable of suppressing a variation in processing accuracy and ensuring mass production by always guaranteeing a stable springback amount regardless of a variation in cross-sectional shape.

[0006]

According to the present invention, when a section is subjected to tensile bending, a predetermined tensile strain ε such that a tensile stress greater than the proof stress is applied in the longitudinal direction before the section is bent, and After measuring the tension t1 when the tension reaches t1, the tension t2 to be applied during the processing is set according to t1, and the tensile bending is performed. More specifically, in the initial condition setting, the tension t2 'applied during the bending when a predetermined shape is obtained in the tensile bending of the profile, and the tension when the profile reaches the proof stress Find t1 'in advance,
The tension t2 to be applied during the tension bending is set so that t2 '/ t1' = t2 / t1 according to t1 measured for each section. In the practice of the present invention, it is desirable that the tensile strain ε applied before bending be kept at a level slightly exceeding the proof stress. Also, tensions t1, t
1 ′ can be easily obtained by measuring the rate of increase in tension with respect to the amount of movement of the chuck portion, and can be represented by the tension when a predetermined tensile strain ε occurs.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a schematic view of a tension bending method according to the present invention. Springback occurs due to the flow stress difference between the inside and the outside with respect to the bending neutral axis. This stress difference is determined by the relative relationship between the stress generated in the bending and the tensile stress caused by the tension applied during the bending. In particular, in the case of a material having a small work hardening rate in the plastic region, such as an aluminum alloy profile subjected to T5 treatment, the flow stress can be represented by a 0.2% proof stress in general.
It can be said that the amount of springback is determined by the ratio between the 0.2% proof stress and the tensile stress caused by the tension. In addition, even when the working ratio due to bending is not so large, the flow stress is approximately 0.2%.
% Proof stress can be represented. That is, by determining the tension t2 to be applied during bending according to the equation (1), it is possible to perform high-precision bending with a constant springback amount. t2 / t1 = X (Const) (1) Here, t1 is the tension when the member reaches the proof stress in the tension step before bending. X is a constant that is a reference value, using a tension t2 ′ applied during bending when a predetermined shape is obtained in the initial condition setting, and a tension t1 ′ when the member reaches the proof stress, X = t2 '/ t1'.

[0008] By determining the tension t2 during bending in accordance with the equation (1), not only the proof stress of the material but also the proof stress is always kept within the cross section even when the cross-sectional area such as the thickness of the member changes. Since a constant ratio of tensile stress is applied, a highly accurate bent product can be obtained irrespective of variations in the mechanical properties and cross-sectional dimensions of the material. Note that t1 can be easily obtained by moving the clamp portion so that a plastic strain of 0.2% or more is applied according to the distance L between the material clamps before bending. Further, t1 and t1 'can be represented by the tension when a predetermined strain amount is reached such that a tensile stress higher than the proof stress is generated.

For mass production, t1 is measured using a sensor capable of measuring the amount of displacement of the chuck portion, a load cell or a hydraulic gauge capable of measuring the tension generated in the chuck portion, and setting conditions before mass production is started. By making a simple feedback device that compares the value with the set reference value and calculates t2, it is possible to easily automate the feedback device. Further, in the method of the present invention, by applying a tension higher than the proof stress value before molding, it is possible to correct distortion in the longitudinal direction of the material, and a secondary effect of improving material shape accuracy can be expected.

It is desirable that the amount of tensile strain applied before molding be kept at a level slightly exceeding the proof stress in order to suppress a decrease in elongation at break of the material. For example, in the case of an extruded aluminum material, the proof stress value is usually about 10 to 40 kgf / mm ² or less and the elastic modulus is about 7000 kgf / mm ² ,
Since tensile strain is negligible work hardening as long as slightly exceeding the yield strength (addition, work hardening rate is low if T5 tempered material), _0.2 yield strength _sigma, if the elastic modulus and E, tensile The strain ε can be approximately expressed as follows: ε = 0.2 + (σ _0.2 / E) × 100 (2) If the above numerical values are applied to this, the tensile strain ε Is approximately 0.3 to 0.8%. Therefore, in the case of an extruded aluminum material, it is desirable to set the tensile strain ε before molding within a range of 0.3 to 0.8%. Further, in the case of a 6000 series aluminum alloy T5 tempered material used in various directions as an extruded aluminum material, since σ _0.2 is approximately 20 to 25 kgf / mm ² , the tensile strain ε before forming is 0.5 It is desirable to set within the range of 0.6.

[0011]

EXAMPLE An extruded aluminum material (□ -shaped material) was bent to produce a product having a bending angle of 10.5 degrees at an inner radius of 1000R. The test material is a 20 × 20 mm (plate thickness 1.5 mm) square cross section, 6N01-T5 material. FIG. 3 shows the cross-sectional shape and processing conditions of the test material. First, preliminary processing is performed to obtain the basic processing conditions, and the target product shape is obtained when performing the tensile bending processing with the tension t2 '= 1.5 ton and the bending set angle θ = 12.8 °. Was confirmed. At the same time, this test material is 0.5%
It was measured that a tensile force (t1 ') of 2.5 tons was generated when a tensile strain (ε) was applied. Therefore, t2 '/ t1' = 3/5 as a reference value.

As a conventional example, both ends of the profile are clamped and the tension is made constant (1.5 ton) to carry out a tensile bending process.
As an example of the present invention, both ends of the profile are clamped and a tensile strain of 0.5% is applied in the length direction, and the tension (t1) generated at that time is measured so that t2 / t1 = 3/5. Tensile bending was performed with the tension t2 set. The number of tests is 10 in each case. The extruded material was alternately sampled from the tip of the extruded material for the conventional example and for the example of the present invention so as not to be affected by the variation in the material, and 10 samples were assigned to each. After the tensile bending test, the return angle △ θ due to the springback was measured, and △ θ / θ representing the springback was calculated. The results are shown in FIGS. 4 and 5. The horizontal axis in the figure is the test material N
o. Is shown. The solid line in the figure is a target value as a product.

As shown in FIGS. 4 and 5, it can be seen that the variation of the springback (△ θ / θ) is significantly reduced in the example of the present invention. The difference between the maximum value and the minimum value of 本 θ / θ for each of the ten lines is 0.02 in the example of the present invention, but is 0.08 in the conventional example, and the range of the variation of the springback angle is in the example of the present invention. In comparison with the conventional method, it is reduced to about 1/4, and it can be said that the processing accuracy is remarkably improved by the tensile bending method of the present invention.

[0014]

According to the present invention, variations in machining accuracy can be suppressed by always guaranteeing a stable amount of springback regardless of variations in mechanical properties and cross-sectional shapes of individual materials during mass production. .

[Brief description of the drawings]

FIG. 1 is a schematic view of a tension bending process.

FIG. 2 is a schematic view illustrating a process of a tensile bending process according to the present invention.

FIG. 3A is a cross-sectional view of a profile used in an example, and FIG. 3B is an explanatory view of test conditions.

FIG. 4 is a graph showing a springback amount of a conventional example.

FIG. 5 is a graph showing the amount of springback of the example of the present invention.

Claims (4)

[Claims] When a section is subjected to tensile bending, a predetermined tensile strain ε is applied before the bending so that a tensile stress greater than the proof stress is applied in the longitudinal direction of the section, and the tension t1 when the proof stress is reached is obtained. After the measurement, the tension t2 applied during bending is t
A tensile bending method for a shaped material, wherein the tensile bending is performed by setting according to (1). 2. A tension t2 'applied during the bending when a predetermined shape is obtained in the tensile bending of the profile,
The tension t1 'at the time when the section reaches the proof stress is determined in advance, and the tension t2 applied during the bending process according to claim 1 is calculated as t2' / t1 '= according to the tension t1 measured for each section.
A tensile bending method for a shaped material, wherein the method is set to be t2 / t1. 3. The method according to claim 1, wherein the tensions t1 and t1 'are represented by a tension at a time when a predetermined tensile strain .epsilon. Is generated such that a tensile stress higher than a proof stress is generated. Tension bending method for profile. 4. An extruded aluminum material having a tensile strain ε
Is set to 0.3 to 0.8%.
3. The method for tensile bending a section according to any one of the above items 3.