Sheet Metal Forming in Automotive Engineering

Sheet metal must have good forming properties. Typical forming processes, such as deep drawing and stretch forming are regulated by standard testing methods. Zwick's BUP sheet metal testing machines test these properties with drawing forces up to 1,000 kN. Another important but complex test is the determination of the forming limit curve, from which engineers can derive limit strains which should not be exceeded during forming processes. Zwick works in close collaboration with highly specialized partners to develop the optical measurement technology required for recording strains during the drawing process.

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.

Tensile tests

Tensile tests

Simple Tensile Test

Zwick 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.

r- and n-value determination

Tensile test with 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 forming properties. The n-value describes the hardening (increase in strain) during plastic deformation up to uniform elongation, while the r-value describes the vertical anisotropism. The n-value is determined from the tensile stress data and strain values; for the r-value the transverse strain on the tensile specimen is also measured.

Biaxial tensile test

Biaxial Tensile Test

A distinctive feature is the two-axis tensile test, which is used to determine the deformation properties of the material. The test is primarily employed in research and development since it allows defined stress values to be set and examined at the intersection point of the specimen. Zwick produces these testing machines to customer requirements. In most cases, strain is measured optically. There are two different solutions available from Zwick. Zwick works together with partners to create solutions for measuring high resolution strain distribution.

Fracture Toughness Testing

Fracture toughness testing KIc is an important characteristic for metal materials in safety-related applications such as aircraft construction, power plant construction, and even automotive engineering. Fracture toughness is determined using a specimen in which an artificial crack has been introduced. The specimen is subjected to load until it breaks. Fracture toughness can be determined from the load-deformation curve and the length of the crack.
Fracture toughness testing

Flexure Test

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. Zwick’s range of flexure test kits combined with adapters for existing specimen holders provide an ideal solution.
215_Flexure test

Draw Bead Test

This test is designed to determine the coefficient 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 unit can easily be 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.
216_Draw bead

High-Speed Tensile Test

Material behavior at high strain rates is critical for applications in the automotive industry. Accidents involve material deformation at high speeds and this must be taken into account in the automobile design phase. The necessary material properties are determined using high-speed tensile testing machines from Zwick's HTM series. These servo-hydraulic testing machines achieve deformation speeds of up to 20 m/s on specimens at forces up to 160 kN.
217_High speed tensile

Disk flexure test

The disk flexure 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. You can perform these tests with special test kits in 3- or 4-point flexure tests. 
218_Paper flexure