Batch Processing in Preassembled Die Sets—A New Process Design for Isothermal Forging of Titanium Aluminides

Abstract

Titanium aluminide (TiAl) turbine blades produced by isothermal forging have recently been implemented in the low-pressure part of commercial aircraft jet engines. However, the slow speed of isothermal forging, costly molybdenum-based dies and the required protective forging atmosphere makes the process rather expensive. Currently, industrial forging is done by closed-die isothermal forging processes with stationary dies. Idle time occurs when single parts are inserted and extracted from the dies. As an interesting alternative for forging small parts, a new set-up is devised and explored in this work, i.e., batch processing. Using a die set which allow for off-line preassembly and preheating, multiple parts can be forged in one stroke. The design of the batch process was based on a new material model, which was implemented into a finite element system to identify the forging parameters. The setup of the press transport system for batch processing, as well as the results of the simulations and forging experiments are presented. A cost comparison between the new process and conventional forging with stationary dies concludes that for smaller parts such as compressor blades, batch processing offers advantages regarding productivity and cost.

Additive Manufacturing of Hot-Forming Dies Using Laser Powder Bed Fusion and Wire Arc Direct Energy Deposition Technologies

“…Most researchers are trying to utilize traditional die steels for additive die manufacturing [20,25,26], using various technical solutions such as the use of preheated substrate to prevent defects like hot cracks. A method for the hybrid production of dies has also been proposed wherein only individual elements of the die working surfaces are produced using additive manufacturing [30,31]. In this case, by reducing the volume of deposited metal, residual stresses and, consequently, the risk of defects, are reduced.…”

Gefügeeinstellung mittels Schmieden im Mehrfachhub/Microstructure adjustment by forging in multiple strokes - Increasing the degree of freedom during hot forming enables individual component properties

“…Die gewünschte Gefügeumwandlung des Gussgefüges in ein globulares Gefüge wird durch hohe Umformgrade beim Gesenkschmieden erreicht, da vor allem kritische Werkstückbereiche den hohen Anforderungen genügen müssen und ein Mindestglobularisierungsgrad von 70 % erforderlich ist. Die nötigen hohen Umformgrade korrelieren mit einem geringen Materialausnutzungsgrad beim isothermen Gesenkschmieden [2]. Das Verhältnis zwischen eingesetztem Volumen des Ausgangsgusswerkstoffs und dem finalen Bauteilvolumen wird als Materialausnutzungsgrad bezeichnet.…”

Model Predictive Control of the Punch Speed for Damage Reduction in Isothermal Hot Forming

“…The forging process of a turbine blade currently takes ~4-5 minutes for the production of the preform and for the final-forging each (cf. [7]). TiAl materials initially show a steep increase in yield stress during hot forming, but even at low degrees of deformation they reach a pronounced yield stress maximum and then show a steep yield stress drop.…”