Influence of Tool Finishing on the Wear Development in Strip Drawing Tests with High Strength Steels

Abstract

With the increasing usage of high-strength steel, tool wear becomes a major challenge in sheet metal forming. As tribological properties are in consequence of the system characteristics, wear prediction is extremely difficult. The wear resistance characteristic curve is introduced in a former publication of the authors to predict wear in sheet metal forming. With the help of this curve, the evaluation of the tool life spans in strip drawing tests under different contact pressures is possible. However, other influencing factors on tool wear should also be taken into account. In this paper, two types of tools made from cold working steel and cast iron are used to investigate the influence of the tool characteristics hardness and surface roughness on the wear behavior and the life span in strip drawing tests with high strength steels. Moreover, the dominating wear mechanisms with respect to different tool properties are also discussed. As a consequence, the wear resistance characteristic curves are derived and new values to characterize the wear resistance in terms of hardness and surface roughness are presented. With the results, more knowledge about the influencing factors on wear is given and the life spans of different tribological systems can be quantitatively predicted. Finally, the wear behavior of the tools after rework is also discussed.

Influence of the sheet metal Seebeck coefficient on wear detection based on thermoelectric measurement

“…Compared to the measured Seebeck coefficient shown in Figure 5, the boundary value of the current is approximately proportional to the development of the combined Seebeck coefficient. According to the estimated temperature rise at the end of the steady-state based on equation ( 4) and (5) shown in Figure 8b, the temperature increase of the H630LA is higher than that of aluminum alloy and stainless steel. For low alloy steel H630LA, it can be concluded that the risk of severe wear increases if the contact temperature rises by 10°C.…”

“…In comparison, the development of the thermoelectric current remains just above 0 μA in the low range and shows a linear increase up to the 14 th stroke with a value of 7.36μA. Assuming that the sheet metal roughness of the lower side remains constant, resulting in an unchanged temperature on the die (ΔT2=0), since the combined Seebeck coefficient SBH+S, the measured current Ith and the resistance are known, it is possible to calculate the temperature increase ΔT1 by equation ( 4) and (5). In this case, ΔT1 is calculated as 7.98°C.…”

“…In the authors' previous study, an inline method for wear detection through the measurement of thermoelectric current based on the Seebeck Effect was proposed [4] and applied in strip drawing test with different tool geometries [5].…”

Strain Induced Surface Change in Sheet Metal Forming: Numerical Prediction, Influence on Friction and Tool Wear

“…Besides the frictional behavior, wear also of high interest especially due to the increasing use of the high-strength-steels in sheet metal forming. In a study carried out by the authors of this paper, the influence of the surface finishing and the hardness of the forming tools on the wear development as well as the tool life is investigated [22]. The characteristic value, the specific wear force F V , is used for the prediction of the life span [22,23] (see Equation ( 1)),…”

“…with σ N the contact stress, z the penetration of the roughness asperities, H S the sheet metal hardness and the H T the tool hardness [22]. The parameter z is determined by the surface roughness of the tools and workpiece used in the sheet metal forming process [24].…”