Process Description

In spray forming in the Osprey mode, a source of molten metal is converted into a spray of droplets by gas atomization. The droplets are collected on a substrate where they aggregate to form a high density preform (Ref 5, 9), as shown in Fig. 1. The preform can be used in the as-sprayed condition or after conventional working operations. The production of billets, strip, and tubing by spray forming is illustrated schematically in Fig. 2.

Fig. 1 A schematic of spray forming in the Osprey mode

Fig. 2 A schematic of the production of billet, strip, and tubing by spray forming

For commercial viability in spray forming in the Osprey mode, close tolerances in shape and dimensions, consistency in microstructure, and a high product yield are essential. This viability requires an understanding of and control over the effects of several independent process parameters: melt superheat, metal flow rate, gas pressure, spray motion, spray height (distance between the gas nozzles and the substrate), and substrate motion (substrate rotation speed, withdrawal rate, and tilt angle). Several parameters can be selected prior to, but not during, the process, such as the diameter of the metal delivery nozzle, the atomizer design, and the substrate material.

Primary process parameters that can be changed during the operation (i.e. on-line) are listed in Table 1. Advantages and disadvantages of the Osprey process are cited as follows:

Advantages

• Densities >98% of theoretical

• Fine equiaxed grains

• No macroscopic segregation

• Absence of prior particle boundaries

• Enhanced mechanical properties

• Material/alloying flexibility

Limitations

Overall yield Shape control

• Compositional control in microalloying

Table 1 Representative on-line parameters in Osprey spray forming

Melt superheat, °C

10-200

Melt flow rate, m /s

10-5-10-3

Atomizing gas

N2, Ar, He, or mixed gases

Gas pressure, MPa

0.5-1.0

Scanning frequency, Hz

0-10

Spray height, mm

■350

0 0

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