ASTM E2492-07
(Test Method)Standard Test Method for Evaluating Springback of Sheet Metal Using the Demeri Split Ring Test
Standard Test Method for Evaluating Springback of Sheet Metal Using the Demeri Split Ring Test
SCOPE
1.1 This test method provides a means of evaluating the springback behavior of metals in a test that simulates a stretch-draw forming process. The test method can also be used to calibrate computer simulation codes by selecting appropriate control parameters to achieve satisfactory correlation between simulation and test results.
1.2 The values stated in SI units are standard.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E2492–07
Standard Test Method for
Evaluating Springback of Sheet Metal Using the Demeri
Split Ring Test
This standard is issued under the fixed designation E2492; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope rework much more likely and complicated. This can add
months and great costs to the achievement of successful dies.
1.1 This test method provides a means of evaluating the
While dealing with springback in traditional metals is largely
springback behavior of metals in a test that simulates a
overcome by experience, new metals often have so much
stretch-drawformingprocess.Thetestmethodcanalsobeused
springback that they can only be used after much trial and
tocalibratecomputersimulationcodesbyselectingappropriate
error. The quantification and prediction of the tendency of
control parameters to achieve satisfactory correlation between
metals to springback is addressed by this test method.
simulation and test results.
4.2 The magnitude of the springback is a convolution of the
1.2 The values stated in SI units are standard.
elastic modulus, the flow stress of the metal of interest, the
1.3 This standard does not purport to address all of the
sheet metal thickness and the amount and type of cold work
safety concerns, if any, associated with its use. It is the
introduced by the forming process. Since the cup forming
responsibility of the user of this standard to establish appro-
process contains features of many forming operations, the
priate safety and health practices and determine the applica-
amount of springback measured by the Demeri split ring test is
bility of regulatory limitations prior to use.
indicative of the behavior of the metal in many stamping
2. Terminology
operations.
4.3 The amount of springback that occurs in this test is very
2.1 Definitions:
large compared to other approaches. This improves measure-
2.1.1 springback—the difference between the final shape of
ment accuracy and reduces experimental error in all types of
a part and the shape of the forming die.
formable metals.
2.1.2 Demeri Split Ring Test—a test that measures the
4.4 This test does not require measurement fixtures or any
springback behavior of sheet metal by comparing the diameter
sophisticated profiling equipment for accurate measurement of
of a ring extracted from the wall of a flat bottom cup and the
springback. Conventional length measuring instruments are all
diameter of the same ring split to release residual stresses.
that is needed to perform the required measurements.
3. Summary of Test Method
4.5 Thistestcanbeusedtorankmaterialsaccordingtotheir
tendency to springback after a forming operation (see Refs
3.1 The test method consists of four steps: (1) deep draw a
1-3). Since springback depends on the sheet thickness, metals
cylindrical cup from a circular blank with a constant clamp or
should be compared at the same thickness. Experience has
blankholder force, (2) cut a circular ring from the mid-section
shown that the test can also be used in conjunction with an
of the drawn cup, (3) split the ring along a certain direction to
appropriate analysis to predict quantitatively the amount of
release residual stresses caused by the stretch-draw operation,
springback occurring after a forming operation (see Refs 2-9).
and (4) measure the opening of the ring (springback).
4.6 This test provides a method to compare springback
4. Significance and Use
predictions by various numerical simulation codes.Test results
canbeusedtocalibratecomputersimulationcodesbyselecting
4.1 The formability of materials is affected by springback,
proper control parameters and appropriate material models to
the difference between the final shape of a part and the shape
achieve satisfactory correlation between simulation and test
of the die that formed it. Materials having a large amount of
results. Test data can be used to evaluate and improve current
springback create difficulties for the die designer and make die
forming and simulation capabilities.
4.7 The experimental setup and test procedure are simple,
This test method is under the jurisdiction of ASTM Committee E28 on
and test results are highly repeatable.
Mechanical Testing and is the direct responsibility of Subcommittee E28.02 on
Ductility and Flexure Testing.
Current edition approved June 1, 2007. Published June 2007. DOI: 10.1520/ The boldface numbers in parentheses refer to the list of references at the end of
E2492-07. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2492–07
FIG. 1 Cross Section Through the Experimental Setup Used for Cup Drawing
5. Apparatus 6. Hazards
5.1 Cup Forming Apparatus—A die set and punch are 6.1 Forming equipment can be dangerous. Care must be
needed to form the cup from circular sheet metal blanks for taken to keep hands away when forming the cups.
subsequent testing. The die set consists of upper and lower 6.2 Cutting and slicing equipment can also cause injury if
tools with centrally located circular holes. The sheet is held care is not taken in their use.
between these and formed into a cup by the action of a punch 6.3 Sheet metal generally has sharp edges and burrs. Pre-
that fits through the hole in the upper and lower dies. This cautions, such as gloves and safety glasses should be worn.
arrangement is shown in Fig. 1. The apparatus can be part of a When the ring is split open, it is required to be restrained in
double acting press where the clamp force on the upper tool of some way to avoid artifacts due to sudden springback. If it is
the die is generated hydraulically, followed by movement of not restrained, harm to the person splitting the ring may result.
the punch to make the cup.Alternatively, the upper tool can be
7. Sampling, Test Specimens, and Test Units
held down by a combination of bolts and Belleville spring
washerstoachieveaconstantforce.Inthiscase,thecupcanbe 7.1 Samples for testing shall be from the same lot or heat as
formed in a universal or compression testing machine. the material of interest except where the measurement of
5.2 Ring Slicing Apparatus—The cutting equipment, used springback is being made to rank different types of materials
to slice the ring from the cup and split it, must not change the for future reference. In this latter case, it will suffice to use
worked state of the ring, as this will affect the result. Good material typical of the specification.
results have been obtained with laser cutting equipment, 7.2 Test units shall be in SI units.
electro discharge machining (EDM), and slow speed diamond
8. Procedure
wheels. Shears have been shown to badly distort the ring and
leave burrs that affect the result. Other methods are acceptable 8.1 The dimensions used in this section are defined here for
if they can be shown to agree with one of the successful convenience. The depth of the drawn cup is d (see Fig. 2). The
methods. height of the ring extracted from the cup is h (see Fig. 2). The
5.3 Dimensional Measurement Apparatus—Methods of wall thickness of the cup is t . The diameter of the unsplit ring
w
measuring the location of the ring to be extracted from the cup is D , measured to the midthickness (see Fig. 3). D is equal to
o o
(h ) (see Fig. 2), the initial ring diameter (D ), the ring height the average of the outside and inside diameters (OD/2 + ID/2)
o o
(h), the ring wall thickness (t ) and the final diameter of the ortheoutsidediameterminusthewallthickness(OD–t ).The
w
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split open ring (D) are required. Most methods having the diameter of the split ring at midthickness is D (see Fig. 3) and
f f
required accuracy and precision are acceptable for the first may be determined in the same way as for the unsplit ring.The
threemeasurements.Onlyanon-contactingmethod,suchasan chord length measured between the midthickness tips of the
optical micrometer, traveling microscope, or comparator, split ring is C (see Fig. 3). The length of the section of the
should be used for measuring the final diameter as this is very circumference removed by the splitting operation is X (see Fig.
sensitive to the presence of additional forces. 3).
E2492–07
FIG. 2 Ring Location in a Drawn Cylindrical Cup
FIG. 3 Steps in Splitting a Test Ring
8.2 The initial step in obtaining samples for this test is to 8.3 Rings from the formed cups shall be cut (20 6 1) mm
form cylindrical cups from (200 6 2) mm diameter, drawing from the bottom of the cup as shown in Fig. 2. The rings shall
oil-lubricated, circular blanks to a maximum depth, d,of55 be (25 6 1) mm high (h) and have an external diameter OD of
mm. Cups of this depth have been routinely made from (110 6 1) mm. The wall thickness (t ) shall be measured in
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formable aluminum and steel sheet. To minimize friction, a three positions (top, middle, and bottom) in two locations
sheet of solid lubricant is applied to the die side of the blank. (rolling and transverse) to an accuracy of 0.02 mm, and
The tooling used for this test is shown in Fig. 1. Sheet metal averaged. The diameter D shall be measured in the same
o
blanks are to be centered in the die to an accuracy of 62 mm. positions and to an accuracy of 0.1 mm, and averaged. The
The punch and die radii shall be both (12.0 6 0.1) mm and the diameter D shall be measured from the midthickness (that is,
o
die gap (5.0 6 0.1) mm. Due to the die gap requirement, this neutral axis) of the ring. The height of the ring, h, shall be
method is only
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