CN112547838A - Method for testing edge forming limit of metal plate - Google Patents
Method for testing edge forming limit of metal plate Download PDFInfo
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- CN112547838A CN112547838A CN201910850955.9A CN201910850955A CN112547838A CN 112547838 A CN112547838 A CN 112547838A CN 201910850955 A CN201910850955 A CN 201910850955A CN 112547838 A CN112547838 A CN 112547838A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C51/00—Measuring, gauging, indicating, counting, or marking devices specially adapted for use in the production or manipulation of material in accordance with subclasses B21B - B21F
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Abstract
The invention discloses a method for testing the edge forming limit of a metal sheet, which comprises the steps of establishing a spherical male die bulging test device comprising a blank holder, a male die and a female die and a sheet central positioning mechanism; preparing a thin plate sample with a circular arc notch in the middle of one side, and processing different edge qualities of the edge of the sample according to requirements; and placing the sample on one side of the spherical male die bulging die, aligning the arc center of the sample with the center of the spherical male die, and initiating cracking of the edge part at the arc center position under the action of tensile expansion and lateral force in the rising process of the male die. Testing a sample with good edge quality and a material with poor edge quality or the same edge quality and different structures, and measuring the displacement change and the main strain change of a cracking position by a digital image measuring system; by comparing the displacement or principal strain, the edge forming limit of the material at a particular edge condition is determined, as well as the sensitivity of the material to edge quality. The invention can accurately evaluate the edge forming limit and the edge quality sensitivity.
Description
Technical Field
The invention relates to the technical field of cold forming performance of metal plates, in particular to a method for testing the edge forming limit of a metal plate.
Background
The material proportion of the advanced high-strength steel in the automobile body is gradually increased due to the requirement of light weight of the automobile, and the forming performance is greatly different from that of the common mild steel due to the fact that the advanced high-strength steel is mostly strengthened by adopting a structure or phase change, the phase structure is complex, and the deformation process involves phase change. Because the strength is increased, the plasticity is reduced, the difference of the strength of each structure is large, the part is easy to generate local forming cracking on the edge, and the part which can be formed by using the mild steel can crack when using the high-strength steel, so the edge forming limit of the high-strength steel in the local forming process needs to be established as the evaluation index of the punching failure.
At present, the formability of the metal sheet is widely evaluated by a Forming Limit Curve (FLC), the fracture position of a sample measured based on a forming limit test starts from the inside of the sample, a crack appears in the center of the sample, and the edge part does not crack. Therefore, although the sheet material is well predicted to be subjected to necking or cracking in the single-pulling and double-pulling stress states, the situation that the sheet material is not subjected to FLC and cracks in the part edge forming process is difficult to evaluate, and the sheet material has certain limitations.
The edge formability is evaluated by measuring the change in the hole diameter before and after hole expansion using a standard hole expansion test (GBT 15825.4-2008) to obtain the hole expansion ratio as an evaluation index. When 60-degree conical reaming is adopted, for example, the edge failure strain is measured, a speckle spraying mode is adopted, after the edge of a sample is flanged, compared with the plane of an original plate, the flanging angle is changed violently, and a Digital Image measurement System (DIC) device cannot effectively obtain the edge strain value during fracture; when the cylindrical die is used for reaming, sometimes, reaming does not occur at the edge of the hole, but cracks are generated in the hole at a certain distance from the edge, and the cracking position is uncertain.
In the prior patent application, for example, the application number 201680025732.3 patent proposes an evaluation method for whether the sheared edge can be formed, and describes an evaluation technology for whether the edge of a material sheared after pre-forming can be formed, the evaluation method adopts a conical hole expanding test and a cylindrical punch hole expanding test on a pre-formed plate, the hole expanding rate is used as an evaluation index, and the local forming limit is not reflected. Meanwhile, the pre-forming changes the initial stress-strain state of the material and has obvious influence on the material structure.
For example, the application No. 201410468843.4 patent provides a method for evaluating the edge crack sensitivity of a high-strength thin steel plate, a steel ball die is adopted to carry out an expansion test to test the gaps of different trimming dies, the test sample is a one-way tensile strain state test sample, the stress state of the test sample is a one-way tensile state, the method is similar to the traditional tensile test, the blanking quality at different positions of the edge part after blanking is different, and the cracking position is not fixed; and the sample has no lateral force during stretching, so that the cracking condition of the part edge part during local forming in the actual stamping process cannot be truly reflected.
At present, for actual edge cracking under the condition of simultaneously bearing lateral force during the stretch-expansion forming, the conventional test method and the patent test method cannot accurately test or accurately feed back the forming limit under the real stress condition. The limit of the edge forming is related to the structure of the material, the shearing quality of the edge and the like, and the invention aims to provide a more applicable and higher-precision limit testing and evaluating technology for the edge forming of part edges.
Disclosure of Invention
In view of the above-mentioned defects in the prior art, the present invention aims to provide a method for testing the edge forming limit of a metal plate, which can accurately evaluate the edge forming limit and the edge quality sensitivity.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for testing the forming limit of the edge of a metal plate comprises the following steps:
1) a set of spherical male die test die is established, a punch (male die) is in a ball head shape with a certain diameter, the diameter of a female die is larger than that of the punch and ensures that a single-side gap of about 2mm is provided, meanwhile, the fillet radius of the female die in contact with a plate (sample) needs smooth transition, the diameter of a fillet is ensured to be larger than 5mm, and cracking caused by stress concentration at the fillet is avoided.
2) The sample preparation, open an arc opening in the intermediate position of sample one side straight flange, the arc can be the shape that other arc sections such as circular, ellipse constitute, guarantees that the sample fracture position is located the arc central authorities. The width of the sample needs to be more than half of the diameter of the ball head, the blank holder can be guaranteed to be capable of pressing the plate materials tightly, the materials do not flow at the position of the draw bead in the process of the sample, the length of the sample is at least 20mm larger than the diameter of the draw bead, the blank holder is guaranteed to be capable of pressing the plate materials tightly, the materials do not flow at the position of the draw bead in the whole test process, positioning pins or other positioning devices are arranged on two sides of the blank holder, and the arc center is guaranteed to correspond to the highest point. In the test process, the arc center is aligned with the center of the spherical male die, namely the plate material occupies half of the ball-end male die. According to the test condition, the states of the edge parts of the test sample can be different in modes of blanking, edge milling, linear cutting and the like, so that different edge quality can be obtained, including the change of the burr orientation.
3) Before the test is started, after speckles are sprayed on a sample, a plate is placed on one side of the ball head male die in the test process according to the method, a blank holder force is applied to compress the sample, meanwhile, digital image equipment is used for observing the test process and recording data, and the test is stopped until the sample is observed to be broken.
4) After the test is finished, the test sample is measured and subjected to data processing, the whole deformation process of the test sample can be recorded through a digital image device for measurement, the maximum height offset dH when the cracking position of the test sample is deformed from the bottom to the edge and cracks is measured, and the main strain before the fracture is measured, wherein the value of the main strain is formed by averaging the strains of at least 3 points in a small area of the fracture. The height maximum offset dH can also be measured by a vernier caliper or a straight edge.
5) And (4) processing test data, recording the magnitude of the maximum offset dH value of the sample, and if the dH1 value of the sample 1 is larger than the dH2 value of the sample 2, or the main strain of the sample 1 before fracture is larger than the main strain of the sample 2 before fracture, indicating that the edge forming limit of the sample 1 is higher than that of the sample 2. When the dH1 value of the edge state 1 is significantly larger than the dH2 value of the edge state 2, the samples are greatly influenced by the edge quality.
The sample with the edge completely removed from the burr influence is used as the sample with the best edge quality, and the maximum main strain epsilon of the sample before cracking is measured0And simultaneously measuring the maximum main strain epsilon of the material before cracking of quality samples at other edgessWherein s is the sample number, and both are epsilon0And epsilonsThe values are all greater than 0 and less than 1.
Definition of
The edge quality sensitivity coefficient is that the phi value is more than 0 and less than or equal to 1, and the closer to 1, the edge limit of the sample material is less obvious to the edge quality, and the more obvious the edge limit is.
When the test sample is tested, if the arc opening area of the test sample is not cracked or the cracking frequency is low, the forming limit of the material of the test sample is good, and the influence of the edge quality is small.
According to the method for testing the edge forming limit of the metal plate, the sample is placed on one side of the spherical male die for testing, the edge simulates a local forming state that the edge of a part has stretch-bulge forming and lateral force in the actual production process, namely the edge is not obviously thinned and cracks, and the method has practical significance. Meanwhile, the method has better operability and accuracy, can conveniently determine the edge forming limit of the plate, and solves the problem that the forming performance of the stamping edge of the existing plate has no accurate failure criterion.
Drawings
FIG. 1 is a schematic view of a spherical male test mold used in the test method of the present invention;
FIG. 2 is a schematic representation of a sample used in the test method of the present invention;
FIG. 3 is a graph illustrating the offset of the edge condition of two different materials according to an embodiment of the testing method of the present invention.
Detailed Description
The technical scheme of the invention is further explained by combining the drawings and the embodiment.
Referring to fig. 1 to 3, a method for testing an edge forming limit of a metal plate provided by the present invention includes the following steps:
1) a set of spherical male die test die is arranged on a forming tester, the diameter of a selected 100-ball head of the male die is 100mm, the diameter of a selected female die is 105mm, the round corner of the female die is R8, and a draw bead of a blank holder 300 is circular.
2) Material a and material B of sample 400 were two advanced high strength steels with thicknesses of 1.4mm and 2.2mm, respectively. For convenience, the sample 400 is selected to be rectangular, with a width of 100mm and a length of 200mm, and a central half-hole (as shown in fig. 2) with a diameter of 10mm is formed to ensure that the sample 400 can be compacted throughout the test.
3) The edge state comprises blanking and line cutting, the cutting edge is along the rolling direction, the burr side deviates from the upper surface of the male die 100 and is placed and sprayed with speckles, and digital image equipment can conveniently record data.
4) The sample 400 was placed on one side of the spherical punch 100 such that the center of the 10mm half hole of the sample 400 was aligned with the center of the spherical punch 100, and then the forming was started. Recording and analyzing the maximum height offset dH at the cracking position by digital image equipment, measuring the maximum main strain before the cracking position, taking the linear cutting edge as the better edge quality, taking the blanking edge as the worse edge quality, and measuring the epsilon corresponding to the linear cutting0Epsilon corresponding to punched edgesAnd calculating the edge quality sensitivity coefficient
The specific results are as follows:
as can be seen from fig. 3 and tables 1 and 2, when the edge quality of the material a is wire-cut, the dH value is higher and significantly higher than that of the punched edge sample. And the edge quality of the material B is that the dH values in the wire cutting and blanking are not different. Meanwhile, the edge quality sensitivity coefficients of the two materials are greatly different, namely the material A is 0.617, the material B is 0.894, and the edge limit of the material B is not obvious to the edge quality.
TABLE 1 offset comparison (mm) of different edge states of two materials
TABLE 2 principal strain at break for different edge states of two materials
Material A: epsilon0＝0.413，εs＝0.255，
Material B: epsilon0＝0.406，εs＝0.363，
It should be understood by those skilled in the art that the above embodiments are only for illustrating the present invention and are not to be used as a limitation of the present invention, and that changes and modifications to the above described embodiments are within the scope of the claims of the present invention as long as they are within the spirit and scope of the present invention.
Claims (7)
1. A method for testing the edge forming limit of a metal plate is characterized by comprising the following steps: the method comprises the following steps:
1) establishing a set of spherical male die test die;
2) preparing a sample, namely opening an arc-shaped opening in the middle of a straight edge on one side of the sample;
3) before the test is started, after speckles are sprayed on a sample, the sample is placed on a spherical male die test die, a blank holder force is applied to compress the sample, meanwhile, a digital image device is used for observing the test process and recording data, and the test is stopped until the sample is observed to be broken;
4) processing the obtained data, recording and comparing the maximum offset dH values of different samples, taking the sample with the edge completely removed from burr influence as the sample with the best edge quality, and measuring the maximum main strain value before cracking of the sample as epsilon0While measuring the material atMaximum principal strain value epsilon before cracking of other samples with different edge qualitysWherein s is the sample number, and both are epsilon0And epsilonsThe values are all greater than 0 and less than 1;
definition of
The edge quality sensitivity coefficient is that the phi value is more than 0 and less than or equal to 1, and the closer to 1, the edge limit of the sample material is less obvious to the edge quality, and the more obvious the edge limit is.
2. The method for testing the edge forming limit of a metal plate according to claim 1, wherein: the spherical male die test die comprises a spherical male die and a matched spherical female die, and the female die is also provided with a blank holder.
3. A method for testing the forming limit of the edge of the metal plate as claimed in claim 2, wherein: the draw beads are arranged on the blank holder, and the shape of each draw bead is a circular bead, a triangular bead or a double-circular bead.
4. A method for testing the forming limit of the edge of the metal plate as claimed in claim 2, wherein: the width of the sample is more than half of the diameter of a ball head on the male die, and the length of the sample is more than the diameter of the draw bead.
5. A method for testing the forming limit of the edge of the metal plate as claimed in claim 2, wherein: and positioning devices are arranged on two sides of the blank holder.
6. A method for testing the forming limit of the edge of the metal plate as claimed in claim 2, wherein: the center of the arc-shaped opening on the sample is aligned with the center of the male die.
7. The method for testing the edge forming limit of a metal plate according to claim 1, wherein: in the step 4), when the test sample is tested, if the arc-shaped opening area of the test sample is not cracked or the cracking frequency is low, the forming limit of the material of the test sample is good, and the influence of the edge quality is small.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113588421A (en) * | 2021-08-04 | 2021-11-02 | 唐山钢铁集团有限责任公司 | Method for evaluating forming performance of sheared edge of metal plate |
| CN113865954A (en) * | 2021-08-26 | 2021-12-31 | 唐山钢铁集团有限责任公司 | Construction method of non-contact forming limit diagram |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113588421A (en) * | 2021-08-04 | 2021-11-02 | 唐山钢铁集团有限责任公司 | Method for evaluating forming performance of sheared edge of metal plate |
| CN113865954A (en) * | 2021-08-26 | 2021-12-31 | 唐山钢铁集团有限责任公司 | Construction method of non-contact forming limit diagram |
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