Test methods for sheet metal forming
Good ductility properties are especially in great demand for thin sheet. In forming technology sheets are treated in various manufacturing processes such as rolling, open die forging, impact extrusion, extrusion molding, deep drawing or bending. It is used to turn a flat sheet metal blank into its final shape.
Sheet metal testing machines from ZwickRoell test the required properties for sheet metal processing with tensile forces of up to 1,000 kN. Test methods for sheet metal forming provide characteristic values for metalworking and metal processing include tests such as cupping tests, earing tests and hole expansion tests.
Innovation is largely driven by transport technology, particularly the automotive industry. Increasing demands on sheet metal materials under the general heading of lightweight construction have led to the development of high-strength and ultra high-strength steel materials, although their reduced ductility and higher elastic recovery are setting new challenges for forming technology and process control.
Cupping tests Earing tests Hole expansion tests Other test methodsRequest a consultation
Typical Test Methods for Sheet Metal Forming
Typical sheet metal forming test methods include the classical cupping test to Erichsen (ISO 20482) and Olsen (ISO 20482), the earing test for determination of earing tendency (ISO 11531 / EN 1669) and hole-expansion tests to ISO 16630, which are seeing increasing use with high strength steel materials.
Particular importance is given to determination of forming limit curve (FLC) to ISO 12004, which is used in a two-stage experiment to generate critical deformations in tests, which are then compared with existing deformations on real components and evaluated. Once the forming limit curve (FLC) has been determined, it is used during the component design stage to help optimize sheet metal forming, thereby speeding up the development process.
Additional Test Methods for Sheet Metal Forming:
To ensure that materials have the required characteristics and that the forming processes run correctly, not only special sheet meta testing are used, but also standard test methods such as tensile tests or flexure tests.
Tensile test Biaxial tensile test Draw bead tests 3-point flexure test Small plate bending test U-bend test
Tensile tests including r and n-value determination
Thin sheets are frequently required to possess good ductility combined with high strength. The r- and n-values are determined in the tensile test in order to characterize the sheet metal forming properties.
The r-value describes the vertical anisotropy. For the r-value, thetransverse strain on the tensile specimen is additionally measured.
The n-value describes the hardening (increase in strain) during plastic deformation up to uniform elongation and is determined from the tensile stress data and strain values.
ZwickRoell offers a wide range of standard testing systems up to 2,500 kN for determining characteristic values from tensile tests; these systems also provide high-precision testing under high loads.
Tensile test ISO 6892-1 Tensile test ASTM E8 r-value determination n-value determination
Biaxial tensile test
A distinctive feature is the two-axis tensile test, which is used to determine the deformation properties of the material. It is primarily employed in research and development, as it allows defined stress values to be set and investigated at the intersection point of the specimen.
ZwickRoell produces these biaxial testing machines to customer requirements. In most cases, strain is measured optically. There are two different solutions available from ZwickRoell. ZwickRoell works together with partners to create solutions for measuring high resolution strain distribution.
Draw bead test
This test is designed to determine the coefficients of friction between a steel sheet and a deep drawing tool in order to determine the ideal lubricant for this forming process, thereby enabling cracks and creases to be avoided and ensuring an optimum deep drawing process.
The draw bead fixture can be easily installed in a standard testing machine. For the test, a sheet metal strip with typical dimensions (300 mm x 30 mm x 2 mm) is axially gripped in the upper standard specimen grip and the draw bead tool is closed. The strip is then drawn through the draw bead tool. This procedure can be repeated automatically, with a variable number of repetitions.
The digitally controlled clamping force of the draw bead tool guarantees accurate and reproducible test results. The tool die can be quickly interchanged to meet different testing specifications.
Flexure testing
The 3-point flexure test serves to not only determine the characteristics of the flexural properties but also visually evaluates the flexural edge. In particular, the behavior of the weld seams are visually examined during the flexure test. ZwickRoell’s range of flexure test kit options combined with adaptations to existing specimen holders provide an ideal solution.
Small Plate Bending Test
The small plate bending test determines the bending angle of vehicle body panel sheets determine the deformation behavior and the susceptibility to metal materials failing during forming processes with dominant bending elements (e.g. hemming operations) or during crash loading.
These tests can be performed with special test kits in 3- or 4-point flexure tests in all AllroundLine materials testing machines.
U-bend test
The U-bend test is used to test finishes and coatings on fine sheet metals. It is performed with a BUP sheet metal testing machine.
Hot forming
- In the last few years, press hardening has become an increasingly important production method in hot forming in order to meet specific requirements for a lower overall weight with higher crash safety.
- This method's objective is to achieve equal or higher stiffness of profile sheet metal parts than would be achievable with conventional forming technology, while using a reduced amount of material.
- Numerous automobile manufacturers use these processes to produce structural parts of the chassis, such as A and B columns, transmission tunnels, carriers of front and rear bumpers, door sills, door reinforcements, side members, roof racks, and roof frames.
- Compared to conventional forming, hot forming is naturally more complex and allows you to produce components with high //strength, great geometric complexity, and minimized //springback effects in a short amount of time. The specimens are removed from the end product and the strength is determined not only in a classic hardness test but also in a tensile and flexure test.
