Height Dependent Laser Metal Deposition Process Modeling

Abstract

Laser metal deposition (LMD) is used to construct functional parts in a layer-by-layer fashion. The heat transfer from the melt region to the solid region plays a critical role in the resulting material properties and part geometry. The heat transfer dynamics can change significantly as the number of layers increase, depending on the geometry of the sub layers. However, this effect is not taken into account in previous analytical models, which are only valid for a single layer. This paper develops a layer dependent model of the LMD process for the purpose of designing advanced layer-to-layer controllers. A lumped-parameter model of the melt pool is introduced and then extended to include elements that capture height dependent effects on the melt pool dimensions and temperature. The model dynamically relates the process inputs (laser power, material mass flow rate, and scan speed) to the melt pool dimensions and temperature. A finite element analysis (FEA) is then conducted to determine the effect of scan speed and part height on the solid region temperature gradient at the melt pool solidification boundary. Finally, experimental results demonstrate that the model successfully predicts multilayer phenomenon for two deposits on two different substrates.

Effect of stress relaxation on distortion in additive manufacturing process modeling

“…Modeling of AM has primarily focused on predicting thermal response [2][3][4][5][6][7], predicting distortion and residual stress, [8][9][10][11][12], and developing distortion mitigation techniques [13,14].…”

Iterative learning control of bead morphology in Laser Metal Deposition processes

“…In previous work, a model describing the interaction between track height, i.e. layer number, and melt pool morphology was developed [8]. The model describing the LMD process can be written as a set of nonlinear, ordinary differential equations.…”

“…The model developed in [8] consists of a mass balance, an energy balance, a momentum balance across the melt pool boundary, an equation describing the rate of change of the solidification boundary of the melt pool, and static equations relating the melt pool volume and cross-sectional area to melt pool width and length. These equations can be rearranged into a set of three ordinary differential equations and three output equations describing the LMD process.…”

“…In addition to the issues associated with the type of control algorithm used, the plant models used for feedback-type control only account for the dynamics associated with single-layer depositions or require that the model be identified for each layer [1,7]. In previous work, it has been shown that the dynamics and melt pool morphology of the LMD process are height-dependent [8]. Taking these issues into account, a natural choice for a control algorithm is an adaptive-type controller that changes with each fabricated layer.…”

“…Yet, only recently has there been some effort to use ILC to control additive manufacturing processes [12]. Therefore, this paper aims to use the model developed in [8], which incorporates the dependency of the melt pool morphology on part height, to design an iterative process controller, by using existing optimal control methods, to track an iteration varying reference.…”