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Research Papers: Heat Transfer in Manufacturing

# Heat Transfer During Deposition of Molten Aluminum Alloy Droplets to Build Vertical Columns

[+] Author and Article Information
M. Fang, S. Chandra, C. B. Park

Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON, M5S 3G8, Canada

J. Heat Transfer 131(11), 112101 (Aug 19, 2009) (7 pages) doi:10.1115/1.3156782 History: Received July 23, 2007; Revised April 23, 2009; Published August 19, 2009

## Abstract

To create functional metal parts by depositing molten metal droplets on top of each other, we have to obtain good metallurgical bonding between droplets. To investigate conditions under which such bonds are achieved, experiments were conducted in which vertical columns were formed by depositing molten aluminum alloy (A380) droplets on top of each other. A pneumatic droplet generator was used to create uniform, 0.8 mm diameter, molten aluminum droplets. The droplet generator was mounted on a stepper motor and moved constantly so as to maintain a fixed distance between the generator nozzle and the tip of the column being formed. The primary parameters varied in experiments were those found to have the strongest effect on bonding between droplets: substrate temperature $(250–450°C)$ and deposition rate (1–8 Hz). Droplet temperature was constant at $620°C$. To achieve metallurgical bonding between droplets, the tip temperature of the column should be maintained slightly below the melting temperature of the alloy to ensure remelting under an impacting drop and good bonding. The temperature cannot exceed the melting point of the metal; otherwise the column tip melts down. The temperature at the bottom of a column was measured while droplets were being deposited. An analytical one-dimensional heat conduction model was developed to obtain the transient temperature profile of the column, assuming the column and the substrate to be a semi-infinite body exposed to a periodic heat flux. From the model, the droplet deposition frequency required to maintain the tip temperature at the melting point of the metal was calculated.

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## Figures

Figure 8

Variation of Tdrp with Ttip, assuming that Tint equals the solidus temperature

Figure 9

Predicted variation of tip temperatures during growth of columns at substrate temperatures of 250°C, 350°C, and 450°C. The deposition rate was 1 Hz for all cases.

Figure 10

Predicted variation of tip temperatures during growth of columns at substrate temperatures of 250°C, 350°C, and 450°C, respectively. The deposition rate was 2 Hz for all cases.

Figure 11

Predicted variation of tip temperatures during growth of columns at droplet deposition rates of 1 Hz, 2 Hz, 4 Hz, and 8 Hz, respectively. The substrate temperature was 450°C for all cases.

Figure 1

Schematic diagram of the experimental apparatus

Figure 2

A column built with 50 droplets deposited at a rate of 2 Hz on a substrate at 200°C. Scale markings are 0.5 mm apart.

Figure 3

Columns built by depositing 20 droplets. Substrate temperature and deposition rates were varied. Scale markings are 0.5 mm apart.

Figure 4

Temperature variation at base of columns being built by depositing 20 droplets. Substrate temperatures were 250°C, 350°C, and 450°C, respectively, and the deposition rate was 4 Hz for all cases.

Figure 5

Temperature variation at the base of columns being built by depositing 20 droplets. The deposition rates were 2 Hz, 4 Hz, and 8 Hz, respectively, and the substrate temperature was 350°C for all cases.

Figure 6

Geometry of heat conduction model

Figure 7

Comparison of the measured and predicted base temperatures during fabrication of the column on a substrate of 450°C and at 8 Hz deposition rate

## Errata

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