Method for testing the forming limit path of a tube and testing die therefor

Abstract

The application discloses a kind of test pipe material forming limit path loading method, first part will complete half tube be cut into specified shape and always under the action of hemispherical rigid punch drawing, it is measured that first, second principal strain direction of half tube test piece is all in tension-compression state, obtain the left half of strain forming limit;Second part changes rigid punch structure and keeps the shape of half tube test piece complete, it is measured that first, second principal strain direction of half tube test piece is all in tension-tension state, obtain the right half of strain forming limit.The application provides the obtaining method of pipe material strain forming limit diagram, makes up the vacancy that complete forming limit diagram is obtained by pipe material rigid hemispherical rigid punch method;The obtaining method is realized by replacing different shapes and sizes of half tube test piece and different shapes and sizes of rigid punch;The method has the advantages of convenient operation, test safety, few moulds, high efficiency, low cost and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for obtaining a strain forming limit curve of a pipe, in particular to a loading method for testing a forming limit path of a pipe and a testing die thereof. BACKGROUND

[0002] The test of the forming limit of a metal pipe is generally carried out by loading in the interior of the pipe, and the medium filled in the interior of the pipe is a low-pressure medium (liquid or gas), so that the pipe is deformed to necking or rupture in the die cavity, and then the forming limit curve is measured. This method is a common method for measuring the forming limit of a metal pipe. However, since the filled medium is a liquid or gas, the sealing requirement during the test is extremely strict, and the equipment requirement is high, thereby increasing the test cost.

[0003] The traditional hemispherical rigid punch method for testing the forming limit of a metal material generally requires a metal plate as a test piece. This method is the most common method for testing the forming limit of a metal material, which is loading in the normal direction of the surface of the plate. For the forming limit of a pipe, many people directly use the hemispherical rigid punch method to test the forming limit of a plate of the material as a basis for judging the rupture instability. However, this method cannot obtain a complete and accurate forming limit curve, that is, the forming limit of each part of a curved surface structure cannot be judged. SUMMARY

[0004] The present application aims to provide a loading method for testing a forming limit path of a pipe, which optimizes the shape of a test piece to make the processing more simple, and the installation and operation of the test more convenient and fast, and can obtain an accurate strain forming limit diagram. The present application also provides a testing die thereof.

[0005] Technical scheme: A loading method for testing a forming limit path of a pipe, comprising the following steps:

[0006] Step one: take a plurality of half-pipes to be tested, and cut them into a plurality of shapes;

[0007] Step two: place one of the half-pipes in a die, and place the half-pipe between the working parts of the upper die and the lower die of the die, so that the two side ends of the half-pipe are flush with the boundary of the groove of the lower die, the center of the half-pipe is aligned with the center of the groove of the lower die, and the upper die and the lower die are connected by bolts to fix the half-pipe therebetween;

[0008] Step three: coaxially connect the rigid punch and the punch base by the stud, and insert the rigid punch downward from the through hole of the upper die to the center of the half-pipe through the punch base;

[0009] Step four: complete the strain forming limit test by deep drawing the half-pipe downward through the rigid punch;

[0010] Step 5: Replace the half tubes one by one and reinstall them in the mold, and perform strain forming limit tests one by one to measure the strain forming limit on the left side.

[0011] Step 6: Take multiple test half tubes of the same shape again, install them in the mold in sequence, remove the original rigid punch, take multiple rigid punches of various shapes, install them in sequence on the punch base, and perform strain forming limit test on the test half tubes of the same shape, and measure the right part of the strain forming limit.

[0012] Step 7: Obtain all positive and negative portions of the second principal strain under linear loading by measuring half-tubes of different shapes and sizes and rigid punches of different shapes and sizes, thereby obtaining all complete tube forming limit diagrams.

[0013] In addition to metal tubing, this method is also applicable to obtaining the forming limits of sheet metal with curved surface features.

[0014] Furthermore, the tested pipe material is aluminum, copper, or steel, with a thickness of 0.5–5 mm.

[0015] Furthermore, when obtaining the left side of the strain forming limit, the shape of the half tube is variable, the middle part of the half tube is the test area, the two ends are the non-test areas, the center of the half tube has multiple widths, the non-test areas are hollow parts, and the corresponding rigid punch shape is hemispherical, so that the test area of ​​the half tube is in a tension-compression state.

[0016] Ideally, when obtaining the left side of the strain forming limit, the diameter of the half tube is 50-150 mm and the length is 60-160 mm. The corresponding rigid punch shape is a hemisphere with a radius of 25-30 mm, and the outer circumferential surfaces at both ends of the half tube are provided with arc-shaped hollow parts along the circumferential direction.

[0017] Optimal test area widths for the middle section of the half-tube are 20mm, 30mm, 40mm, 50mm, and 60mm, respectively, and hollow section radii are 50mm, 50.278mm, 51.25mm, 53.214mm, and 56.667mm, respectively.

[0018] Furthermore, when obtaining the right side of the strain forming limit, the shape of the rigid punch is variable. The rigid punch is an ellipsoid with multiple major and minor axis ratios, and the semi-tube structure is complete, so that the semi-tube test area is in a tension-tension state.

[0019] Ideally, when obtaining the right side of the strain forming limit, the major axis of the rigid punch is 50mm, and the minor axes are 30mm, 35mm, 40mm, 45mm, and 50mm respectively, corresponding to a half-tube width of 120mm.

[0020] Furthermore, during strain forming limit tests, the DIC three-dimensional full-field strain measurement and analysis system was used to monitor the deformation of the half-tube in real time and obtain the principal and secondary strains at the rupture location of half-tubes of different shapes and sizes.

[0021] A test mold for the above-mentioned loading method for testing the forming limit path of a pipe includes an upper mold, a lower mold, a punch base, a stud, and a rigid punch. The lower bottom surface of the upper mold has a semi-circular curved upper mold protrusion in the middle, and the upper surface of the lower mold has a semi-circular curved lower mold groove in the middle. The upper mold is placed on the lower mold and connected by bolts so that the upper mold protrusion and the lower mold groove cooperate. The half-pipe is placed between the two. The upper mold has an upper mold through hole in the middle that passes through the upper mold protrusion, and the lower mold has a lower mold through hole in the middle that passes through the lower mold groove. The upper mold through hole and the lower mold through hole are coaxially connected. The rigid punch and the bottom end of the punch base are coaxially connected by a stud. The punch base is inserted into the upper mold through hole so that the rigid punch abuts against the half-pipe.

[0022] Ideally, the upper die, lower die, and punch base should all be made of mold steel, the studs should be M10 fully threaded double-ended studs, and the punch base and rigid punch should each have corresponding internal thread grooves.

[0023] Beneficial effects: Compared with the prior art, the advantages of the present invention are: The present invention provides a method for obtaining the strain forming limit diagram of pipes or plates with curved surface features, filling the gap in obtaining a complete forming limit diagram using the rigid hemispherical rigid punch method for pipes; this method, while ensuring that the rigid punch is hemispherical, sets the half-tubes to different shapes to ensure that the half-tube specimen is in a tension-compression state under the action of the rigid punch, thus obtaining the left half of the strain forming limit; this method, by changing the shape of the rigid punch, puts the complete half-tube specimen in a tension-tension state, thus obtaining the right half of the strain forming limit; this method, by combining half-tube test specimens of different shapes and sizes with rigid punches, has the advantages of convenient operation, safe testing, fewer molds, high efficiency, and low cost. Attached Figure Description

[0024] Figure 1 This is a three-dimensional structural schematic diagram of the test mold of the present invention;

[0025] Figure 2 This is a cross-sectional structural schematic diagram of the test mold of the present invention;

[0026] Figure 3 This is a schematic diagram of the structure of the test piece of the present invention;

[0027] Figure 4 This is a schematic diagram of the rigid punch of the present invention;

[0028] Figure 5 This is a schematic diagram of fitting a complete curve in this invention. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] A loading method for testing the limit path of pipe forming includes the following steps:

[0031] Step 1: Take multiple test tubes 6 and cut them into various shapes.

[0032] Step 2: Place one of the half tubes 6 into the mold. The half tube 6 is pressed between the working parts of the upper mold 1 and the lower mold 2. The two ends of the half tube 6 are flush with the boundary of the groove of the lower mold. The center of the half tube 6 is aligned with the center of the groove of the lower mold. The upper mold 1 and the lower mold 2 are connected by bolts to fix the half tube 6 between them. The half tube 6 is positioned at the center of the lower mold 2 based on the baseline and serves as the test piece for the experiment.

[0033] Step 3: Connect the rigid punch 5 and the punch base 3 coaxially through the stud 4. Insert the rigid punch 5 downward through the upper die through the punch base 3 until the rigid punch 5 contacts the center of the half tube 6.

[0034] Step 4: The strain forming limit test is completed by drawing the half tube 6 downward through the rigid punch 5. The rigid punch draws the test piece to the point of fracture and instability.

[0035] Step 5: Replace half-tube 6 in sequence and reinstall it in the mold. Then, perform strain forming limit tests sequentially and measure the strain forming limit on the left side, such as... Figure 5 As shown.

[0036] Step Six: Take multiple test halves 6 of the same shape again, install them sequentially in the mold, and remove the original rigid punch 5. Take multiple rigid punches 5 of various shapes, install them sequentially on the punch base 3, and perform a strain forming limit test on the test halves 6 of the same shape. Measure the right side of the strain forming limit, such as... Figure 5 As shown.

[0037] During the strain forming limit test, the deformation of the test specimen was monitored in real time using the DIC three-dimensional full-field strain measurement and analysis system. The principal strain and secondary strain at the fracture location were obtained for test specimens of different shapes and sizes.

[0038] Step 7: By measuring the positive and negative parts of the second principal strain under linear loading using half-tubes 6 of different shapes and sizes and rigid punches 5 of different shapes and sizes, the strain forming limit curves of the tube under tension-tension and tension-compression states are fitted, thereby obtaining all complete tube forming limit diagrams.

[0039] The pipes being tested are made of aluminum, copper, or steel, with a thickness of 0.5–5 mm.

[0040] When obtaining the left portion of the strain forming limit, the shape of half-tube 6 is a variable, such as... Figure 3 As shown, the middle part of the half-tube 6 is the test area, and the two ends are non-test areas. The center of the half-tube 6 has various widths, and the non-test areas are hollow parts. The corresponding rigid punch 5 is hemispherical in shape, so that the test area of ​​the half-tube 6 is in a tension-compression state.

[0041] When the left side of the strain forming limit is obtained, the diameter of the half tube 6 is 50-150 mm and the length is 60-160 mm. The corresponding rigid punch 5 is a hemispherical shape with a radius of 25-30 mm. The outer circumferential surfaces of both ends of the half tube 6 are provided with arc-shaped hollow parts along the circumferential direction.

[0042] When obtaining the right-hand side of the strain forming limit, the shape of the rigid punch 5 is a variable, such as... Figure 4 As shown, the rigid punch 5 is an ellipsoid with various major and minor axis ratios, and the semi-tube 6 has a complete structure, so that the test area of ​​the semi-tube 6 is in a tension-tension state.

[0043] In one embodiment, the dimensional relationship between the test piece (half-tube 6) and the rigid punch is shown in Table 1, and the corresponding results are as follows: Figure 5 The graph shown.

[0044] Table 1

[0045]

[0046]

[0047] When obtaining the left part of the strain forming limit, the width H of the test area in the middle part of the half tube 6 is 20mm, 30mm, 40mm, 50mm, and 60mm, respectively, and the radius R of the hollow part is 50mm, 50.278mm, 51.25mm, 53.214mm, and 56.667mm, respectively. The corresponding rigid punch 5 is a hemisphere with a diameter (major axis T1) of 50mm.

[0048] When the right side of the strain forming limit is obtained, the major axis T1 of the rigid punch 5 is 50mm, and the minor axis T2 is 30mm, 35mm, 40mm, 45mm and 50mm respectively, and the width H of the corresponding half tube 6 is 120mm.

[0049] A test mold for the above-mentioned loading method for testing the forming limit path of the test tube, such as... Figure 1 , 2 As shown, it includes an upper mold 1, a lower mold 2, a punch base 3, a stud 4, and a rigid punch 5. The upper mold 1, the lower mold 2, and the punch base 3 are all made of mold steel.

[0050] The upper mold 1 has a semi-circular curved upper mold protrusion in the middle of its lower bottom surface, and the lower mold 2 has a semi-circular curved lower mold groove in the middle of its upper surface. The upper mold 1 is placed on the lower mold 2 and connected by bolts so that the upper mold protrusion and the lower mold groove fit together. The half tube 6 is placed between the two. The upper mold 1 has an upper mold through hole in the middle that passes through the upper mold protrusion, and the lower mold 2 has a lower mold through hole in the middle that passes through the lower mold groove. The upper mold through hole and the lower mold through hole are coaxially connected. The rigid punch 5 and the bottom end of the punch base 3 are coaxially connected by studs 4. The punch base 3 is inserted into the upper mold through hole so that the rigid punch 5 abuts against the half tube 6.

[0051] The stud 4 is an M10 fully threaded double-ended stud, and the punch base 3 and the rigid punch 5 are respectively provided with corresponding internal thread grooves.

[0052] This invention provides a method for testing the forming limit path loading of pipes based on semi-tube structural components. The method includes a set of molds, a series of rigid punches with different structures, and a series of semi-tube test pieces of specific shapes. The forming limit test is completed by drawing the semi-tube test pieces with rigid punches. Semi-tube test pieces of different shapes are placed tightly into the lower mold; the semi-tubes undergo the forming limit test process by drawing them with rigid punches; the semi-tube test pieces are drawn using rigid punches of different structures to ensure they reach a state of instability and fracture. Then, the left half of the strain forming limit is obtained by measuring the semi-tube test pieces of different shapes with hemispherical rigid punches, and the right half of the strain forming limit is obtained by measuring the fully drawn semi-tube test pieces with rigid punches of different structures, thus obtaining a complete forming limit diagram. This invention provides a method for obtaining the strain forming limit diagram of pipes, filling the gap in obtaining a complete forming limit diagram using the rigid hemispherical rigid punch method. This method is achieved by changing semi-tube test pieces and rigid punches of different shapes and sizes; the method has advantages such as convenient operation, safe testing, fewer molds, high efficiency, and low cost.

Claims

1. A loading method for testing the limit path of pipe forming, characterized in that... Includes the following steps: Step 1: Take multiple test half tubes (6) and cut them into various shapes; Step 2: Place one of the half tubes (6) into the mold. The half tube (6) is pressed between the working parts of the upper mold (1) and the lower mold (2). The two ends of the half tube (6) are flush with the edge of the groove of the lower mold. The center of the half tube (6) is aligned with the center of the groove of the lower mold. The upper mold (1) and the lower mold (2) are connected by bolts to fix the half tube (6) between the two. Step 3: Connect the rigid punch (5) and the punch base (3) coaxially through the stud (4), and insert the rigid punch (5) downward through the upper die through hole until the rigid punch (5) contacts the center of the half tube (6); Step 4: The strain forming limit test is completed by drawing the half tube (6) downward through the rigid punch (5); Step 5: Replace the half tubes (6) one by one and reinstall them in the mold. Then perform strain forming limit tests one by one and measure the strain forming limit on the left side. Step 6: Take multiple test half tubes (6) of the same shape again, install them in the mold in sequence, and remove the original rigid punch (5). Take multiple rigid punches (5) of various shapes, install them in sequence on the punch base (3) and perform strain forming limit test on the test half tubes (6) of the same shape. Measure the right part of the strain forming limit. Step 7: Obtain all positive and negative portions of the second principal strain under linear loading by measuring half-tubes (6) of different shapes and sizes and rigid punches (5) of different shapes and sizes, thereby obtaining all complete tube forming limit diagrams.

2. The loading method for testing the limit path of pipe forming according to claim 1, characterized in that: The pipes being tested are made of aluminum, copper, or steel, with a thickness of 0.5–5 mm.

3. The loading method for testing the limit path of pipe forming according to claim 1, characterized in that: When the left side of the strain forming limit is obtained, the shape of the half tube (6) is variable, the middle part of the half tube (6) is the test area, the two ends are the non-test areas, the center of the half tube (6) takes multiple widths, the non-test area is a hollow part, and the corresponding rigid punch (5) is hemispherical, so that the test area of ​​the half tube (6) is in a tension-compression state.

4. The loading method for testing the limit path of pipe forming according to claim 3, characterized in that: When the left side of the strain forming limit is obtained, the diameter of the half tube (6) is 50-150 mm and the length is 60-160 mm. The corresponding rigid punch (5) is a hemispherical shape with a radius of 25-30 mm. The outer circumferential surfaces of both ends of the half tube (6) are provided with arc-shaped hollow parts along the circumferential direction.

5. The loading method for testing the limit path of pipe forming according to claim 4, characterized in that: The widths of the test areas in the middle part of the half tube (6) are 20mm, 30mm, 40mm, 50mm, and 60mm, respectively, and the radii of the hollow parts are 50mm, 50.278mm, 51.25mm, 53.214mm, and 56.667mm, respectively.

6. The loading method for testing the limit path of pipe forming according to claim 1, characterized in that: When the right side of the strain forming limit is obtained, the shape of the rigid punch (5) is variable. The rigid punch (5) is an ellipsoid with multiple major and minor axis ratios. The half tube (6) has a complete structure, so that the test area of ​​the half tube (6) is in a tension-tension state.

7. The loading method for testing the limit path of pipe forming according to claim 6, characterized in that: When the right side of the strain forming limit is obtained, the major axis of the rigid punch (5) is 50mm, and the minor axis is 30mm, 35mm, 40mm, 45mm and 50mm respectively, and the width of the corresponding half tube (6) is 120mm.

8. The loading method for testing the limit path of pipe forming according to claim 1, characterized in that: During the strain forming limit test, the deformation of the half tube (6) was monitored in real time using the DIC three-dimensional full-field strain measurement and analysis system to obtain the principal strain and secondary strain at the rupture location of the half tube (6) of different shapes and sizes.

9. A test mold for a loading method for testing the limit path of pipe forming as described in any one of claims 1 to 8, characterized in that: The upper mold (1), lower mold (2), punch base (3), stud (4), and rigid punch (5) are included. The lower bottom surface of the upper mold (1) is provided with a semi-circular curved upper mold protrusion in the middle. The upper surface of the lower mold (2) is provided with a semi-circular curved lower mold groove in the middle. The upper mold (1) is placed on the lower mold (2) and connected by bolts so that the upper mold protrusion and the lower mold groove are matched. The half tube (6) is placed between the two. The upper mold (1) is provided with an upper mold through hole that passes through the upper mold protrusion in the middle. The lower mold (2) is provided with a lower mold through hole that passes through the lower mold groove in the middle. The upper mold through hole and the lower mold through hole are coaxially connected. The rigid punch (5) and the bottom end of the punch base (3) are coaxially connected by stud (4). The punch base (3) is inserted into the upper mold through hole so that the rigid punch (5) and the half tube (6) abut against each other.

10. A test mold according to claim 8, characterized in that: The upper die (1), lower die (2), and punch base (3) are all made of mold steel. The stud (4) is an M10 fully threaded double-ended stud. The punch base (3) and the rigid punch (5) are respectively provided with corresponding internal thread grooves.

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