Abstract
In this article, a mathematical model is formulated to predict the evolution and final geometry of an axisymmetric billet (i.e., round) obtained using an off-axis spray arrangement. The model is formulated by calculating the shape change of a profile curve of a billet surface, based on an axisymmetric surface. On the basis of this model, a methodology to determine the “shadowing effect” coefficient is presented. The modeling results suggest that there are three distinct regions in a spray-formed billet: a base transition region, a uniform diameter region, and an upper transition region. The effects of several important processing parameters, such as the withdrawal velocity of substrate, maximum deposition rate, spray distribution coefficient, initial eccentric distance, and rotational velocity of substrate, on the shape factors (e.g., the diameter size of the uniform region and the geometry of the transition regions) are investigated. The mechanisms responsible for the formation of the three distinct regions are discussed. Finally, the model is then implemented and a methodology is formulated to establish optimal processing parameters during spray forming, paying particular attention to deposition efficiency.
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Abbreviations
- \(\dot H\) :
-
deposition rate per unit area (mm3/mm2 · s)
- Δh :
-
normal growth distance of a point during a time interval (mm)
- Δt :
-
deposition time interval (s)
- d s :
-
reference distance, i.e., distance between the atomizer and a reference plane perpendicular to the spray axis (mm)
- d p :
-
distance between the atomizer and any plane perpendicular to the spray axis (mm)
- d r :
-
the distance between the atomizer and the rotation axis (mm)
- a s :
-
maximum deposition rate at reference distance (mm/s)
- b s :
-
spray distribution coefficient at reference distance (mm−2)
- a :
-
maximum deposition rate (mm/s)
- b :
-
spray distribution coefficient (mm−2)
- s :
-
the shortest distance between a deposited point and the spray axis (mm)
- ξ :
-
shadowing effect coefficient
- x p, yp, zp :
-
Cartesian coordinates of a point P in billet surface
- x 1 y 1, z 1 and x 2, y 2, z 2 :
-
Cartesian coordinates of any two neighboring points in a profile curve
- a t :
-
position vector of the atomizer
- p :
-
position vectors of point P in billet surface
- p′ :
-
position vector of a point P′ very near P in the element curve
- e n :
-
unit normal vector of a point P
- e s :
-
unit vector of spray axis
- e f :
-
unit vector of flight direction from the atomizer to a point P
- n :
-
tangential vector of a point P
- m :
-
normal vector of a plane determined by Y-axis and a profile curve
- ‖V‖:
-
Euclidean norm of a vector V
- β :
-
angle between the positive direction of X-axis and the plane determined by a profile curve and Y-axis (°)
- ω :
-
rotational velocity of substrate (°/s)
- ν :
-
withdrawal velocity of substrate (mm/s)
- ν cri :
-
critical withdrawal velocity of substrate to spray form round billets (mm/s)
- l e :
-
initial eccentric distance of the spray axis (mm)
- l em :
-
maximum initial eccentric distance to spray form billets (mm)
- φ :
-
inclined angle of the spray axis to the rotation axis (°)
- Y :
-
deposition efficiency in stable growth stage
- D :
-
diameter of uniform region (mm)
- R p :
-
required billet diameter in industrial production (mm)
- O :
-
the center of substrate
- V :
-
vertex of a round billet
- T :
-
intersection point between the spray axis and the profile curve in XOY plane (X>0)
- A 0 :
-
initial position of the atomizer
- A t :
-
atomizer position during spray forming
- S 0 :
-
intersection point between the initial spray axis and the substrate
- S :
-
intersection point between the spray axis and billet surface at any moment
- P, Q, P 1, P 2, P j, Pn :
-
points in billet surface
- Σ :
-
a profile curve
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Lin, Y.J., Lavernia, E.J., Bobrow, J.E. et al. Modeling of spray-formed materials: Geometrical considerations. Metall Mater Trans A 31, 2917–2929 (2000). https://doi.org/10.1007/BF02830347
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DOI: https://doi.org/10.1007/BF02830347