Manufacturing time estimator based on kinematic and thermal considerations: application to WAAM process

Abstract

Metal additive manufacturing has been pointed as the answer to reduce manufacturing time and cost for aeronautic parts with a high buy to fly ratio. The manufacturability of a part by additive manufacturing depends on important indicators that would allow it to be cost effective. One key indicator is the manufacturing time, which is highly dependent on an important factor: the interlayer time. The interlayer time is the time needed by the material to cool down to a chosen temperature, called interlayer temperature, that allows a new deposition of molten material. The interlayer temperature is defined by using time-temperature-transformation (TTT) diagrams, the final goal being to avoid the appearance of detrimental phases that could lead to a decrease in the material’s mechanical properties. The interlayer temperature is intimately correlated with the cooling curve. The difficulty of predicting the cooling time is due to the influence of the part geometry, the deposition strategy, and the dimensions of the substrate. Their correlation needs to be understood in order to minimize the deposition time (Dt) while ensuring an acceptable material quality. This paper presents a methodology to estimate manufacturing time that combines kinematic and thermal criteria for Wire and Arc Additive Manufacturing (WAAM) process. Application is performed for stainless steel 316L. In this first step toward an advanced manufacturing time estimator, only the first layer attached to the building plate is analyzed from a thermal point of view. The thermal analysis is based on an analytical model enabling the evaluation of the preheating temperature (PhT) in a first approach and providing an adequate framework for the evaluation of cooling curves in a second time. The model includes an accurate description of robot kinematics through the consideration of a realistic travel speed variation along the toolpath. It is used to evaluate an indicator that quantifies the thermal influence of a given deposition strategy. The results show the dependency relationship between manufacturing strategy and inherent thermal gradient and its implications on part production time.