ASTM E2492 - 07(2012) Standard Test Method for Evaluating Springback of Sheet Metal Using the Demeri Split Ring Test (Withdrawn 2017).pdf

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1、Designation: E2492 07 (Reapproved 2012)Standard Test Method forEvaluating Springback of Sheet Metal Using the DemeriSplit Ring Test1This standard is issued under the fixed designation E2492; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re

2、vision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method provides a means of evaluating thespringback behavior of metals in a test that si

3、mulates astretch-draw forming process. The test method can also be usedto calibrate computer simulation codes by selecting appropriatecontrol parameters to achieve satisfactory correlation betweensimulation and test results.1.2 The values stated in SI units are to be regarded asstandard. No other un

4、its of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of reg

5、ulatory limitations prior to use.2. Terminology2.1 Definitions:2.1.1 springbackthe difference between the final shape ofa part and the shape of the forming die.2.1.2 Demeri Split Ring Testa test that measures thespringback behavior of sheet metal by comparing the diameterof a ring extracted from the

6、 wall of a flat bottom cup and thediameter of the same ring split to release residual stresses.3. Summary of Test Method3.1 The test method consists of four steps: (1) deep draw acylindrical cup from a circular blank with a constant clamp orblankholder force, (2) cut a circular ring from the mid-sec

7、tionof the drawn cup, (3) split the ring along a certain direction torelease residual stresses caused by the stretch-draw operation,and (4) measure the opening of the ring (springback).4. Significance and Use4.1 The formability of materials is affected by springback,the difference between the final

8、shape of a part and the shapeof the die that formed it. Materials having a large amount ofspringback create difficulties for the die designer and make dierework much more likely and complicated. This can addmonths and great costs to the achievement of successful dies.While dealing with springback in

9、 traditional metals is largelyovercome by experience, new metals often have so muchspringback that they can only be used after much trial anderror. The quantification and prediction of the tendency ofmetals to springback is addressed by this test method.4.2 The magnitude of the springback is a convo

10、lution of theelastic modulus, the flow stress of the metal of interest, thesheet metal thickness and the amount and type of cold workintroduced by the forming process. Since the cup formingprocess contains features of many forming operations, theamount of springback measured by the Demeri split ring

11、 test isindicative of the behavior of the metal in many stampingoperations.4.3 The amount of springback that occurs in this test is verylarge compared to other approaches. This improves measure-ment accuracy and reduces experimental error in all types offormable metals.4.4 This test does not require

12、 measurement fixtures or anysophisticated profiling equipment for accurate measurement ofspringback. Conventional length measuring instruments are allthat is needed to perform the required measurements.4.5 This test can be used to rank materials according to theirtendency to springback after a formi

13、ng operation (see Refs1-3).2Since springback depends on the sheet thickness, metalsshould be compared at the same thickness. Experience hasshown that the test can also be used in conjunction with anappropriate analysis to predict quantitatively the amount ofspringback occurring after a forming opera

14、tion (see Refs 2-9).4.6 This test provides a method to compare springbackpredictions by various numerical simulation codes. Test resultscan be used to calibrate computer simulation codes by selectingproper control parameters and appropriate material models toachieve satisfactory correlation between

15、simulation and test1This test method is under the jurisdiction of ASTM Committee E28 onMechanical Testing and is the direct responsibility of Subcommittee E28.02 onDuctility and Formability.Current edition approved April 1, 2012. Published May 2012. Originallyapproved in 2007. Last previous edition

16、approved in 2007 as E249207. DOI:10.1520/E2492-07R12.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesNOTICE: This standard has either been

17、superseded and replaced by a new version or withdrawn.Contact ASTM International (www.astm.org) for the latest information1results. Test data can be used to evaluate and improve currentforming and simulation capabilities.4.7 The experimental setup and test procedure are simple,and test results are h

18、ighly repeatable.5. Apparatus5.1 Cup Forming ApparatusA die set and punch areneeded to form the cup from circular sheet metal blanks forsubsequent testing. The die set consists of upper and lowertools with centrally located circular holes. The sheet is heldbetween these and formed into a cup by the

19、action of a punchthat fits through the hole in the upper and lower dies. Thisarrangement is shown in Fig. 1. The apparatus can be part of adouble acting press where the clamp force on the upper tool ofthe die is generated hydraulically, followed by movement ofthe punch to make the cup. Alternatively

20、, the upper tool can beheld down by a combination of bolts and Belleville springwashers to achieve a constant force. In this case, the cup can beformed in a universal or compression testing machine.5.2 Ring Slicing ApparatusThe cutting equipment, used toslice the ring from the cup and split it, must

21、 not change theworked state of the ring, as this will affect the result. Goodresults have been obtained with laser cutting equipment,electro discharge machining (EDM), and slow speed diamondwheels. Shears have been shown to badly distort the ring andleave burrs that affect the result. Other methods

22、are acceptableif they can be shown to agree with one of the successfulmethods.5.3 Dimensional Measurement ApparatusMethods ofmeasuring the location of the ring to be extracted from the cup(ho) (see Fig. 2), the initial ring diameter (Do), the ring height(h), the ring wall thickness (tw) and the fina

23、l diameter of thesplit open ring (Df) are required. Most methods having therequired accuracy and precision are acceptable for the firstthree measurements. Only a non-contacting method, such as anoptical micrometer, traveling microscope, or comparator,should be used for measuring the final diameter a

24、s this is verysensitive to the presence of additional forces.6. Hazards6.1 Forming equipment can be dangerous. Care must betaken to keep hands away when forming the cups.6.2 Cutting and slicing equipment can also cause injury ifcare is not taken in their use.6.3 Sheet metal generally has sharp edges

25、 and burrs.Precautions, such as gloves and safety glasses should be worn.When the ring is split open, it is required to be restrained insome way to avoid artifacts due to sudden springback. If it isnot restrained, harm to the person splitting the ring may result.7. Sampling, Test Specimens, and Test

26、 Units7.1 Samples for testing shall be from the same lot or heat asthe material of interest except where the measurement ofspringback is being made to rank different types of materialsfor future reference. In this latter case, it will suffice to usematerial typical of the specification.7.2 Test unit

27、s shall be in SI units.8. Procedure8.1 The dimensions used in this section are defined here forconvenience. The depth of the drawn cup is d (see Fig. 2). Theheight of the ring extracted from the cup is h (see Fig. 2). Thewall thickness of the cup is tw. The diameter of the unsplit ringis Do, measure

28、d to the midthickness (see Fig. 3). Dois equal tothe average of the outside and inside diameters (OD/2 + ID/2)FIG. 1 Cross Section Through the Experimental Setup Used for Cup DrawingE2492 07 (2012)2or the outside diameter minus the wall thickness (ODtw). Thediameter of the split ring at midthickness

29、 is Df(see Fig. 3) andmay be determined in the same way as for the unsplit ring. Thechord length measured between the midthickness tips of thesplit ring is C (see Fig. 3). The length of the section of thecircumference removed by the splitting operation is X (see Fig.3).8.2 The initial step in obtain

30、ing samples for this test is toform cylindrical cups from (200 6 2) mm diameter, drawingoil-lubricated, circular blanks to a maximum depth, d,of55mm. Cups of this depth have been routinely made fromformable aluminum and steel sheet. To minimize friction, asheet of solid lubricant is applied to the d

31、ie side of the blank.The tooling used for this test is shown in Fig. 1. Sheet metalblanks are to be centered in the die to an accuracy of 62 mm.The punch and die radii shall be both (12.0 6 0.1) mm and thedie gap (5.0 6 0.1) mm. Due to the die gap requirement, thismethod is only applicable to sheet

32、metal having a maximumthickness of 3 mm. Since the lubrication and surface finish ofthe dies, punch, and sheet metal can affect the springback,these details must be known and reported (see Section 10) evenif they conform to conventional forming practice. Surfaceroughness of the tools should be typic

33、al of good practice(0.8 m). Punch speed shall be kept constant at (5 6 1)mm/second. Clamp (or blankholder) force shall be kept con-stant at a known value to produce wrinkle and split free cups.Aclamp force of 88 kN has produced successful cups from DS,A6022-T4, BH210, HSLA50, DP600 and TRIP600 sheet

34、metals. The clamp (or blankholder) force is about one-third thepunch (drawing) force.8.3 Rings from the formed cups shall be cut (20 6 1) mmfrom the bottom of the cup as shown in Fig. 2. The rings shallbe (25 6 1) mm high (h) and have an external diameter OD of(110 6 1) mm. The wall thickness (tw) s

35、hall be measured inthree positions (top, middle, and bottom) in two locations(rolling and transverse) to an accuracy of 0.02 mm, andaveraged. The diameter Doshall be measured in the samepositions and to an accuracy of 0.1 mm, and averaged. Thediameter Doshall be measured from the midthickness (that

36、is,neutral axis) of the ring. The height of the ring, h, shall bemeasured at (0, 90, 180, and 270) degrees around the ringwhere (0 and 180) degrees coincide with the rolling direction.The ring height, h, shall be measured to an accuracy of 0.02mm at each location and averaged.FIG. 2 Ring Location in

37、 a Drawn Cylindrical CupFIG. 3 Steps in Splitting a Test RingE2492 07 (2012)38.4 The prepared rings shall then be split along the rollingdirection to allow them to open up and to springback as shownin Fig. 3. The amount by which the diameter of a ring changesfrom its original unsplit diameter is a m

38、easure of the releasedresidual stress and the resulting springback.8.5 Examples of the diameter of the rings before and aftersplitting are shown in Fig. 4 for three sheet metals: drawingquality steel (DS), bake hardenable steel (BH33) and alumi-num alloy (A6022).8.6 It is necessary to restrain the r

39、ings during the splittingprocess to avoid dynamic effects on the springback. Aftersplitting, the restraint must be removed gradually. The chordlength of the open ring shall be measured at three locations(top, center, and bottom) to an accuracy of 0.1 mm andaveraged. The average chord length is a mea

40、sure of theresulting springback. It is uniquely related to the difference indiameters of the unsplit and split rings as shown in Section 9.Alternatively, the diameter of the split ring may be measured atthree locations (top, center, and bottom) to an accuracy of 0.1mm and averaged. Measurements of d

41、iameter, Df, and chordlength, C, shall be measured from the midthickness (or neutralaxis) of the ring.9. Calculation or Interpretation of Results9.1 Assuming that the open ring is circular, the finaldiameter and chord of the split ring are related exactly by thefollowing expression:Df5 Do12DfarcsinC

42、 2 X!/Df! (1)where:Dfand Do= average diameters of the split and unsplit rings,respectively,C = chord length of the split ring, andX = length of circumference removed by the cuttingprocess that split the ring.NOTE 1This equation can be solved implicitly to any degree ofaccuracy desired.9.2 Alternativ

43、ely, the following approximate expression canbe used to calculate Dffrom C to an accuracy of better than1%:Df5 Do0.0635A32 0.0475A210.3416A10.9983! (2)where:A =(C X)/Do.10. Report10.1 The report shall contain a description or identificationof the material tested together with the thickness of the or

44、iginalsheet and the diameter of the circular blank.10.2 The report shall include all relevant details of cupforming, such as the binder force, the punch speed, lubrication,surface finish of dies, punch, and sheet metal, and the geometryof the die and punch. Additional information on the resultingcup

45、 may include changes in wall thickness along the wall andany evidence of asymmetry in forming, wrinkling or tearing.10.3 The location of the ring in the cup, ho, its diameter, Do,wall thickness, tw, height, h, and the method of extraction shallbe included.FIG. 4 Traces of Split Rings for Three Sheet

46、 MetalsE2492 07 (2012)410.4 The means of splitting the ring and the final diameter,Df, and/or chord length, C, shall be reported. If only the chordlength is reported, the amount of material removed by thesplitting operation, X, must also be reported.10.5 The springback may be reported as either the

47、diameterdifference (Df Do), or the true chord length (C + X).11. Precision and Bias311.1 The precision of this test method is based on aninterlaboratory study of E2492 Test Method for EvaluatingSpringback of Sheet Metal Using the Demeri Split Ring Test,conducted in 2004. One laboratory tested six di

48、fferent materi-als. Four test results, or replicates, were produced for five ofthe materials, and seven test results were measured for the sixthmaterial (DS). Each test result reported was the result of asingle analytical determination.11.1.1 RepeatabilityTwo test results obtained within onelaborato

49、ry shall be judged not equivalent if they differ by morethan the “r” value for that material; “r” is the intervalrepresenting the critical difference between two test results forthe same material, obtained by the same operator using thesame equipment on the same day in the same laboratory.11.1.1.1 Any judgment in accordance with this statementhas an approximate 95 % probability of being correct.11.1.2 ReproducibilityThe interval representing the differ-ence between two test results for the same material, obtainedby different operators using diff