Investigation of the influence of process parameters on adhesive wear under hot stamping conditions

Abstract

Abstract. Current challenges like increasing safety standards and reducing fuel consumption motivate lightweight construction in modern car bodies. Besides using lightweight workpiece materials like aluminum, hot stamping has been established as a key technology for producing safety relevant components. Producing hot stamped parts out of ultra-high strength steels offers the possibility to improve the crash performance. At the same time the weight of car structure is reduced by using thinner sheet thicknesses. In order to avoid oxide scale formation and ensure corrosion protection, AlSi coatings are commonly deposited on the sheet surfaces used for direct hot stamping. This workpiece coating has a critical impact on the tribological conditions within the forming process and, as a consequence, influences the quality of hot stamped parts as well as tool wear. AlSi coatings have been identified as major reason for adhesive wear, which represents the main wear mechanism in hot stamping. Within this study, the influence of the process parameters on adhesive wear are investigated in dependency of workpiece and tool temperatures, drawing velocities and contact pressures. The tribological behavior is analyzed based on strip drawing experiments under direct hot stamping conditions. The experiments are performed with AlSi coated 22MnB5 in contact with the hot working tool steel 1.2367. For analyzing the amount of adhesion on the friction jaws, the surfaces are characterized by optical measurements. The experiments indicate that higher workpiece temperatures cause severe adhesive wear on the tool surface, while an increase of drawing velocity or contact pressure led to reduced adhesion. The measured friction coefficients decreased with rising amount of adhesion and remained at a constant level after a certain adhesive layer was built up on the tool surface.

Experimental Evaluation of Galling Under Press Hardening Conditions

“…However, the transfer layer continued to grow at the leading edge at a rapid rate, thus resulting in early failure due to severe galling (about 250 mm total sliding). This has also been discussed by Schwingenschlögl et al [22]; more adhesion occurred at a higher load in conjunction with the enhanced sintering effect at higher temperatures. It is important to note that the coefficient of friction reported in this figure corresponds to the most stable part of the friction curves and the curve for 15 MPa contact pressure was relatively stable only for about 2 mm of sliding distance.…”

Die Material Selection Criteria for Aluminum Hot Stamping

“…In consequence, the automotive sector, which is the industrial application where hot stamping is most implanted, uses extensively hot work tool steels. Hot stamping die related friction and wear have been studied extensively employing hot work tool steels, with 1.2343 [12][13][14][15][16], 1.2344 [17][18][19][20][21][22][23], and 1.2367 [18,24] as the most frequent choices. Some have been also employed for aluminum coated steel hot stamping [20], together with proprietary steels such as Toolox ® 44 from SSAB [21], QRO90 ® Supreme from Uddeholm [2,25], or W300 ® from Böhler [4].…”

“…• reciprocating pin-on-disk [2,3,26,27], • reciprocating ball-on-disk [20], • regular ball-on-disk [13][14][15]18,21,27], • block-on-ring [17], • hot strip drawing [4,16,[22][23][24][25], • cross cylinder [19], • block-on-cylinder [13], • and top hat drawing test [27].…”

Tribological interactions and modelling of friction in hot stamping

“…Merklein et al (Merklein, Wieland and Fell 2014) and Schwingenschlögl et al (Schwingenschlögl, Weldi and Merklein 2017) observed the opposite: a decrease in wear height for increasing contact pressure. This effect is contradictory to Archard's formula and expectations.…”

“…Wieland et al (Wieland and Merklein 2015) observed a marginal influence of the blank temperature. Schwingenschlögl et al (Schwingenschlögl, Weldi and Merklein 2017) observed an increased material transfer at higher temperatures and relate this to an increased diffusion rate.…”