Z

Deposition Nozzle

Re-Solidified Titanium Alloy

Prior Passes

Process Coordinate System

Deposition Nozzle

Re-Solidified Titanium Alloy

Prior Passes

Pre-Alloyed or Mixed Elemental Powders

Powder-Laser Interaction

Molten Titanium Alloy Puddle

Direction of Part Motion

Pre-Alloyed or Mixed Elemental Powders

Powder-Laser Interaction

Molten Titanium Alloy Puddle

Direction of Part Motion

Fig. 4.13. Laser Deposition Process Source: Aeromet

savings in materials, machining costs, and cycle times over conventional forged or machined parts.

Laser forming is conducted in a chamber that is constantly being purged with high purity argon to prevent atmospheric contamination, such as the one shown in Fig. 4.14. CAD files are used to generate the desired trajectory paths. The trajectory paths are then transmitted as machine instructions to the system which contains a high power CO2 laser heating source. The laser beam traces out the desired part by moving the titanium substrate plate beneath the beam in the appropriate x-y trajectories. Titanium pre-alloyed powder is introduced into the molten metal puddle, and provides for build-up of the desired shape, as the laser is traversed over the target plate. A 3-D preform is fabricated by repeating

Fig. 4.14. Laser Deposition System Source: Aeromet

the pattern, layer-by-layer, over the desired geometry and indexing the focal point up one layer for each repeat pattern. Preforms generally are deposited with 0.030-0.20 in. of excess material which is removed by final machining. The process is capable of depositing between two and ten pounds of material per hour, depending on part complexity.17 Preforms have been laser formed from a number of titanium alloys, including Ti-6Al-4V, Ti-5-2.5, Ti-6242S, Ti-6-22-22S, and CP Ti. Depending on the exact process used, the static properties will be 0-5 ksi lower than equivalent wrought properties. The fatigue properties are essentially equivalent to wrought material; however, some processes require HIP after forming to obtain equivalence by closing internal pores.

Potential savings with this technology include much better material utilization. While the buy-to-fly ratio for forgings is in the range of 5 to 1 for simple shapes and 20 to 1 for complex shapes,18 the ratio for laser forming is about 3 to 1 which includes the substrate that forms 2/3 of the as-deposited part. Machining times are reduced by as much as 30%. In addition, there are no expensive dies or tools required. Finally, the part lead times are much shorter; 12-18 months for forgings versus only several months for laser formed preforms. This process can also be used to conduct local repairs on damaged or worn parts. Some of the part features that can be achieved are shown in Fig. 4.15, and a typical rib section is shown in Fig. 4.16.

Substrate Material

0.25 in. Thick Plate Shown. Bar, Forging, Casting Also Possible Generally is Web of Finished Part

Fig. 4.15. Laser Deposited Part Features

Substrate Material

0.25 in. Thick Plate Shown. Bar, Forging, Casting Also Possible Generally is Web of Finished Part

Fig. 4.15. Laser Deposited Part Features

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