Aspects of Wear Prediction in Precision Forging

Abstract

Precision forging is a rather new special hot forming technology with a high economic potential. The lifetime of a forging tool is one of the most decisive factors during the economical evaluation of a forging and is therefore the subject of intensive investigation and research work. This paper shows results obtained in experimental work and theoretical analysis for the determination of tool wear. Observations have shown that the temperature of the raw material is of major importance for tool wear because of damaging effects on crystalline structure and in consequence mechanical properties of boundary layers of the forging tool. The example of temperature calculation which is strongly connected with heat exchange inside the tribological system explains the complex problems of the theoretical analysis. Additionally the heat transfer itself influences the geometry of the finished forged part, which is in the industrial case of major importance. The heat transfer during the different manufacturing stages has been analysed using the finite element method, which has been further developed to automatically determine the heat-transfer coefficient. Finally, a new method to calculate wear amounts at critical areas of forging tools is presented.

Advanced Wear Simulation for Bulk Metal Forming Processes

“…Doege et al [8] have used Archard´s equation in a commercial finite element code for the analysis of die wear in a precision hot forging process, taking pressure dependent heat transfer into account. Due to complexity of the occurring microstructural and tribological effects, not all process-specific factors have been taken into account.…”

New starting points for the prediction of tool wear in hot forging

“…To be more precise, because of the simultaneous action of such loads and their complex interactive effects, the surface layer takes on a very non-homogeneous structure (becomes damaged). Wear decisively influences tool endurance in approximately 72% of cases (on tool arbor radius only wear is decisive), mechanical cracks in approximately 25%, thermal cracks in approximately 2% and plastic deformations in approximately 1% of cases [1][2][3][4][5]. These loads and the properties of the elements of a given tribological system are expressed by a number of parameters, which are mutually dependent, so that we cannot treat them separately.…”

“…Scale thickness with its mix of oxides is the dominant index in establishing predictive relations between the surface shear and contact pressure, temperature gradients and modes of lubrication. The model of a constant friction factor, as is commonly used in most finite element method (FEM) codes, for instance in the modelling of the metal forming processes, however, is in this regard deficient [2][3][4][5][6][7][8][9][10]33].…”

“…The majority of the above mentioned parameters influence the tool surface temperature, which due to the effect of surface softening (tempering) of the tool, has a decisive influence on the tool wear [3,4,6]. The spatial influence of other more important influential parameters, for instance the contact pressure and the relative speed of slippage, is less known.…”

Simulação numérica do campo de tensões na microestrutura do aço ferramenta AISI H13 durante o forjamento a quente.

“…Do ponto de vista econômico, Doege et al (1994) apud Deshpande (2011) descrevem que a relevância do estudo dos mecanismos de dano da parte ferramental empregada no forjamento, bem como a otimização dos seus materiais, consiste no fato de que:…”