Verification the Numerical Simulation of the Strip Drawing Test by its Physical Model

Abstract

When numerically simulate the stamping processes, it is important to define the friction coefficients in different regions. These depend on the deformation processes due to various stress-strain states in each area. In the deep drawing process, the friction conditions in the blankholder-blank-die area and blank-die radius area differ. The analytical models for the friction coefficients determination by strip drawing test are presented in the paper. The equations have been used to calculate the friction coefficients based on a physical model of the strip drawing test and its numerical simulation. The physical and numerical experiments have been performed on Zn coated IF steel DX54D with thickness 0.78 mm. Hill48 yield law and Hollomon's hardening curve have been used as material characteristics when numerically simulated. The blank-holding forces 4 and 9 kN have been set during the experiment and numerical simulation. Good conformity of numerical simulation and the physical model have been found when friction coefficients were calculated from analytical models including the ratio of drawing forces measured with fixed and rotated cylinder. Additionally, the normal contact pressure under the blankholder and on the die radius was evaluated from the numerical simulations. The highest value has been found at the die radius start.

A Study of the Coefficient of Friction in Steel Sheets Forming

“…Experimental tests of the friction coefficient value only allow the determination of friction in selected areas of the drawpiece, which leads to the need to use multiple friction tests. In addition to many simulation tests used in the industry, numerical methods have been used to study the interactions in the sheet-tool interface [9][10][11].…”

Recent Developments and Trends in the Friction Testing for Conventional Sheet Metal Forming and Incremental Sheet Forming

“…The interaction between the two surfaces and the oxide and debris layers formed is constantly changing and strongly affected by the forming conditions [12]. It is well known [13,14] that friction changes as a result of plastic deformation of the material and the increased surface roughness. This leads to the transition from a hydrodynamic to a mixed friction regime, and the metal to metal contact increases.…”

“…In this test, a plane specimen of the tool material is pressed against a strip of sheet metal, which is drawn simultaneously [15]. The strip is drawn between non-rotating counter-samples, which are mostly flat [14] or have cylindrical shape [13,15] (Figure 4). The existence of frictional forces between the contact surfaces assists in achieving better accuracy of measurement of the COF.…”

“…Kim et al [22] used TCT to establish guidelines on how to select the optimum combinations of die materials, coatings, and lubricants for stamping of galvanized AHSS (DP600, TRIP780, and DP980) for automotive structural parts. Ball-on-disc tests were used to a large extent in describing the tribological behavior of materials in the contact region and to determine the COF [13,14]. It is important to note that these tests are quite similar to scratch tests and are different from ring compression tests and pin-on-disc tests.…”

“…For a very small dγ, one can assume that sin dγ 2 ≈ dγ 2 and dF << F. Thus, combining Equations (12) and (13) gives:…”