1、Designation: E 2492 07Standard Test Method forEvaluating Springback of Sheet Metal Using the DemeriSplit Ring Test1This standard is issued under the fixed designation E 2492; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 simulates astretc
3、h-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 standard.1.3 This standard does not purport to addres
4、s 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 regulatory limitations prior to use.2. Terminology2.1 Definitions:2.1.1 springbackthe differenc
5、e 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 wall of a flat bottom cup and thediameter of the same ring split to release residual stress
6、es.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-sectionof the drawn cup, (3) split the ring along a certain direction torelease residual stress
7、es 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 shape of a part and the shapeof the die that formed it. Materials having a large amount ofsp
8、ringback 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 traditional metals is largelyovercome by experience, new metals often have so muchspringbac
9、k 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 convolution of theelastic modulus, the flow stress of the metal of interest, thesheet metal thick
10、ness 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 test isindicative of the behavior of the metal in many stampingoperations.4.3 The amount of
11、 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 measurement fixtures or anysophisticated profiling equipment for accurate measurement ofspr
12、ingback. 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 forming operation (see Refs1-3).2Since springback depends on the sheet thickness, metalsshould be
13、 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 operation (see Refs 2-9).4.6 This test provides a method to compare springbackpredictions by vari
14、ous numerical simulation codes. Test resultscan be used to calibrate computer simulation codes by selectingproper control parameters and appropriate material models toachieve satisfactory correlation between simulation and testresults. Test data can be used to evaluate and improve currentforming and
15、 simulation capabilities.1This test method is under the jurisdiction of ASTM Committee E28 onMechanical Testing and is the direct responsibility of Subcommittee E28.02 onDuctility and Flexure Testing.Current edition approved June 1, 2007. Published June 2007.2The boldface numbers in parentheses refe
16、r to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.7 The experimental setup and test procedure are simple,and test results are highly repeatable.5. Apparatus5.1 Cup Forming Appara
17、tusA 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 action of a punchthat fits through the hole in the
18、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, the upper tool can beheld down by a combination o
19、f 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, usedto slice the ring from the cup and split it, must not change theworked state of the ring, as this wi
20、ll 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 are acceptableif they can be shown to agree with on
21、e 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 final diameter of thesplit open ring (Df) are required.
22、 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 as this is verysensitive to the presence of addition
23、al 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 and burrs. Pre-cautions, such as gloves and safety
24、 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 Units7.1 Samples for testing shall be from the s
25、ame 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 units shall be in SI units.8. Procedure8.1 The dimens
26、ions 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, measured to the midthickness (see Fig. 3). Dois equal to
27、the average of the outside and inside diameters (OD/2 + ID/2)or the outside diameter minus the wall thickness (ODtw). Thediameter of the split ring at midthickness is Df(see Fig. 3) andmay be determined in the same way as for the unsplit ring. Thechord length measured between the midthickness tips o
28、f theFIG. 1 Cross Section Through the Experimental Setup Used for Cup DrawingE2492072split 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 obtaining samples for this test is toform cylindrical cups from
29、 (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 die side of the blank.The tooling used for this test is sh
30、own 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 metal having a maximumthickness of 3 mm. Since the lubric
31、ation 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 typical of good practice(0.8 m). Punch speed shall be kept con
32、stant 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 sheetmetals. The clamp (or blankholder) force is about one-thi
33、rd 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) shall be measured inthree positions (top, middle, and bott
34、om) 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 is,neutral axis) of the ring. The height of the ring, h,
35、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.8.4 The prepared rings shall then be split along the rollingdirection to allow t
36、hem 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 measure of the releasedresidual stress and the resulting springback.FIG. 2 Ring Location in a Drawn Cylindrical CupFIG. 3 Steps in Splitting a Test RingE24920
37、738.5 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 rings during the splittingprocess to avoid dynamic effects on the
38、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 measure of theresulting springback. It is uniquely related to the di
39、fference 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 diameter, Df, and chordlength, C, shall be measured from the midth
40、ickness (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 Do1 2Dfarcsin C X! / Df! (1)where:Dfand Do= average diameters of the split and
41、 unsplitrings, respectively,C = chord length of the split ring, andX = length of circumference removed by the cut-ting process that split the ring.NOTE 1This equation can be solved implicitly to any degree ofaccuracy desired.9.2 Alternatively, the following approximate expression canbe used to calcu
42、late Dffrom C to an accuracy of better than1%:Df5 Do0.0635A3 0.0475A21 0.3416A 1 0.9983! (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 originalsheet and the diameter of the circular blank.10.2 The
43、 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 may include changes in wall thickness along the wall andan
44、y 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.10.4 The means of splitting the ring and the final diameter,Df, and/or chord length, C, shall be report
45、ed. 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 diameterdifference (Df Do), or the true chord length (C + X).FIG. 4 Traces of Split Rings for Three Sheet MetalsE249207411. Pr
46、ecision and Bias311.1 The precision of this test method is based on aninterlaboratory study of E 2492 Test Method for EvaluatingSpringback of Sheet Metal Using the Demeri Split Ring Test,conducted in 2004. One laboratory tested six different materi-als. Four test results, or replicates, were produce
47、d 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 onelaboratory shall be judged not equivalent if they differ by morethan the “
48、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
49、 % probability of being correct.11.1.2 ReproducibilityThe interval representing the dif-ference between two test results for the same material, obtainedby different operators using different equipment in differentlaboratories. The reproducibility is being determined and willbe available within five years (November 2012).11.2 BiasAt the time of the study, there was no acceptedreference material suitable for determining the bias for this testmethod, therefore no statement on bias is being made.11.3 The precision statement was determined through sta-tistical examinatio
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