Experimental Evaluation of Galling Under Press Hardening Conditions

Abstract

Severe adhesion, also referred to as galling, is a critical problem in press hardening, especially in stamping tools used for hot forming of Al-Si-coated ultra-high strength steel. Galling is known to develop rapidly on the tool surface and it negatively affects the quality of the formed products. Earlier research on this topic has focused on the galling initiation. However, studies on the galling development during extended sliding and the corresponding quantitative measurement still lack depth. In the present study, a tribological test is established to study the galling development under press hardening conditions. The tribological test setup aims to simulate extended sliding between the Al-Si-coated boron steels and the tool die material. The contact conditions in the interface are studied by a numerical model of the tribological test. The friction coefficients and material transfer are discussed taking into account the variation of the different test conditions. Using the results from the tribological tests, the galling simulation is performed in the numerical model. A geometry-updated sample based on the galling (transferred material build-up) height is simulated and the consequent pressure fluctuation is obtained in the numerical model. This contributes to the explanation of the severe transferred material accumulation during the test.

Die Material Selection Criteria for Aluminum Hot Stamping

“…The frequency has been chosen to resemble the average sliding speed between a die radius and a hot stamped sheet in a contact radius of an omega profile of a servomechanical press 100 mm/s. Although it is several orders of magnitude over the value employed in some references [26,27], this value fits with most works in the checked literature 25-100 mm/s [2,3,15,16,20,21,25].…”

“…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].…”

A review of recent advances in tribology

“…Deng et al [538] employed a specially designed tribological test for galling evaluation in press hardening conditions at elevated temperature and developed a numerical model of the test in order to understand galling behaviour in terms of the contact conditions at the tool-workpiece interface. The test temperature has been found to be an important factor in terms of the galling severity.…”

Galling phenomena in metal forming

“…Simulations that take into consideration changes in the tool shape due to wear have been conducted [84]. A simulation example for a case in which a newly designed tool is simulated by considering the galling height has been performed [85].…”