Figure 4 - uploaded by Andreas Mark
Content may be subject to copyright.
Source publication
The jet printing of a dense mixed non-Newtonian suspension is based on the rapid displacement of fluid through a nozzle, the forming of a droplet and eventually the break-off of the filament. The ability to model this process would facilitate the development of future jetting devices. The purpose of this study is to propose a novel simulation frame...
Similar publications
![Figure 1. Geometry of the numerical model [8].](profile/Raphael-Comminal-2/publication/326271012/figure/fig1/AS:753791901110274@1556729402844/Geometry-of-the-numerical-model-8_Q320.jpg)
This paper investigates the influence of shear-rate dependent viscosity on the strand deposition flow during Extrusion-Based Additive Manufacturing. Extrusion-Based Additive Manufacturing, also known as Fused Deposition Modeling (FDM), is a manufacturing method in which material is joined layer by layer into a 3D object. A solid filament is heated...
Citations
... In other words, the flow of the solder paste, or other functional fluids, is intermittent, and as such, the volume flux will depend on the time-dependent rheological behaviour of the fluid. A number of studies have used shear thinning models like the Carreau-Yasuda model and crossviscosity model to portray the thixotropic behaviour of these pastes (Durairaj et al., 2002, Svensson et al., 2016, Vachaparambil, 2016. Use of these simple viscosity models for numerical simulations of jet printing has shown substantial deviations from experimental observations, especially when comparing droplet morphology (Svensson et al., 2016, Vachaparambil, 2016. ...
... A number of studies have used shear thinning models like the Carreau-Yasuda model and crossviscosity model to portray the thixotropic behaviour of these pastes (Durairaj et al., 2002, Svensson et al., 2016, Vachaparambil, 2016. Use of these simple viscosity models for numerical simulations of jet printing has shown substantial deviations from experimental observations, especially when comparing droplet morphology (Svensson et al., 2016, Vachaparambil, 2016. In Mark et al.'s (2013) study, the Carreau-Yasuda model is used to describe the shear thinning behaviour of the solder paste along with a two-fluid model for assessing the granular suspension. ...
... In Figure 3, the measured viscosity is shown exhibiting a dependence on flow history, which is not predicted by the Carreau-Yasuda model. The parameters of the Carreau-Yasuda model used for comparison, in Figure 3, are based on the rheological model used by Svensson et al. (2016). As measurements of viscosity at zero shear rate cannot be performed on a plate-plate rheometer, the initial shear rate is chosen to be 1 s -1 and the sample is given time to reach a steady viscosity value at the steady shear rate, which affects the initial structural parameter z t=0 . ...
Purpose
The purpose of the paper is to develop a methodology to characterize the rheological behaviour of macroscopic non-Brownian suspensions, like solder paste, based on microstructural evolution.
Design/methodology/approach
A structure-based kinetics model, whose parameters are derived analytically based on assumptions valid for any macroscopic suspension, is developed to describe the rheological behaviour of a given fluid. The values of the parameters are then determined based on experiments conducted at a constant shear rate. The parameter values, obtained from the model, are then adjusted using an optimization algorithm using the mean deviation from experiments as the cost function to replicate the measured rheology. A commercially available solder paste is used as the test fluid for the proposed method.
Findings
The initial parameter values obtained through the analytical model indicates a structural breakdown that is much slower than observations. But optimizing the parameter values, especially the ones associated with the structural breakdown, replicates the thixotropic behaviour of the solder paste reasonably well, but it fails to capture the structure build-up during the three interval thixotropy test.
Research limitations/implications
The structural kinetics model tends to under-predict the structure build-up rate.
Practical implications
This study details a more realistic prediction of the rheological behaviour of macroscopic suspensions like solder paste, thermal interface materials and other functional materials. The proposed model can be used to characterize different solder pastes and other functional fluids based on the structure build-up and breakdown rates. The model can also be used as the viscosity definitions in numerical simulations instead of simpler models like Carreau–Yasuda and cross-viscosity models.
Originality/value
The rheological description of the solder paste is critical in determining its validity for a given application. The methodology described in the paper provides a better description of thixotropy without relying on the existing rheological measurements or the behaviour predicted by a standard power-law model. The proposed model can also provide transient viscosity predictions when shear rates vary in time.
