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Wear reducing coating systems with adapted lubrication for hot forming tools

 
: Paschke, H.; Bistron, M.

Tribologie und Schmierungstechnik 60 (2013), No.2, pp.13-17
ISSN: 0724-3472
ISSN: 0036-6218
English
Journal Article
Fraunhofer IST ()
Warmmassivumformung; Verschleißreduzierung; Rißbildung; Hartstoffschichtsystem; PACVD; Plasmanitrierung; Schmierung; hot forging; wear protection; cracks; hard coating systems; PECVD; plasma nitriding; lubrication

Abstract
Schmiedegesenke unterliegen hohen und komplexen Beanspruchungen, welche in Folge hohe abrasiv und adhäsiv bedingte Verschleißraten auf den Werkzeugoberflächen verursachen. Um den auftretenden Verschleiß zu reduzieren, wurden mittels PACVD-Technologie verschiedene 2..3 µm dicke Hartstoffschichten des Systems Ti-B-N entwickelt. Hauptaugenmerk lag hierbei auf dem jeweiligen Schichtdesign, das in Kombination mit einer angepassten Plasmanitrierung optimiert wurde. Die Einsatzfähigkeit für die Warmmassivumformung wurde in Verschleißuntersuchungen durch Serienschmiedeprozesse mit einer automatisierten Exzenterpresse sehr anwendungsnah qualifiziert. Dies erfolgte unter Berücksichtigung der Schmierumgebung, welche grafitbasierte sowie eine grafitfreie Schmiermittelvariante umfasste. Im Ergebnis der Untersuchung wurde ein erfolgreiches System aus Schichtlayout, Plasmanitrierung und Schmierung identifiziert.

 

Due to high process temperature conditions classical wear protection concepts are limited in the field of hot forming tools. The tribological properties are much different compared to room temperature conditions and the use of lubricants is lim ited. Additionally thermal shock conditions and the increase of sticking workpiece material are leading to severe wear. A recently developed new concept is using wear resistant coatings with adapted lubricants. Recent studies address the investigation in application near forging tests with forging tools under varied lubrication conditions. The obtained results show the high potential of the coatings developed on the base of ternary Ti-B-N systems in a special multilayer design. Additionally different lubrication formulas were tested in interaction with the optimized tool surfaces. Ti-B-N coatings are thermally stable, antiadhesive against workpiece material and wear resistant. Examples and charac terization results for these coatings in different layer designs obtained through plasma enhanced chemical vapor deposi tion (PECVD) will be presented. Coating variants with best qualified properties were applied to forging dies for experimental examination. As a result of the tests, wear can be reduced significantly by using thermally stable boron multilayer coatings. To receive wear values under production conditions, an automated forging process was used for testing. In these investigations lubricants with different water -graphite formulation, a graphite-free and a tool cooled only with water and no lubricant were examined. After 3000 forged parts, the coatings were investigated by tactile measurement, SEM and EDX analyses to characterize the occurring wear. Promising results show possibilities for a further adaptation of this concept in industrial forging processes.

: http://publica.fraunhofer.de/documents/N-268941.html