Lec 25: Powder-Feed Additive Manufacturing (Part 1)

Summary

The lecture introduces powder-feed additive manufacturing, focusing on processes that deliver metal powder into a localized melt pool to build or add material.

Core Process

• A focused energy source—most prominently a laser—creates a small melt pool on a substrate or existing part.
• Powder is conveyed through a nozzle into the pool. The powder melts and solidifies as the nozzle and workpiece move relative to one another, forming a deposited track or layer.
• Repeating this motion builds features or parts. The process can also add material to existing components, such as for repair or surface modification.
• The lecture refers to this family of techniques by names including direct metal deposition, laser deposition, and Laser Engineered Net Shaping (LENS).

Process Planning and Workflow

The lecture describes a general workflow:

1. Prepare the model and plan the build. A CAD model is converted into a build plan, including slicing and decisions about the deposition path and orientation.
2. Consider geometric access and support. The direction in which material can be deposited affects how a feature should be planned. Some deposition arrangements can produce overhanging features without conventional support structures.
3. Deposit the material. The energy source forms the melt pool while a synchronized powder-delivery system feeds material into it.
4. Post-process the part. Deposited parts may need finishing or machining to achieve the required final form.

Powder-Delivery Systems

The lecture distinguishes between mechanical and gas-assisted powder metering and transport methods:

• Screw-based systems: A motor-driven screw meters powder and moves it toward the delivery point. Screw speed helps control the powder feed rate. Some arrangements can combine powders from separate reservoirs, for example when feeding more than one material.
• Vibratory systems: Mechanical vibration moves powder from a reservoir toward the outlet. Vibration settings affect how quickly powder is transported.
• Gravity-fed systems: Powder falls through a hopper or column under gravity. These systems depend on the setup and on the powder’s ability to flow reliably.
• Rotating or indexing mechanisms: Rotating plates, hoppers, or chambers regulate how much powder is picked up and transferred to the delivery line.
• Electrostatic conveying: Electrical effects can influence powder movement through a tube. The subtitles provide limited detail about this method.
• Gas-assisted delivery: A carrier gas transports powder through the delivery system and toward the nozzle. Inert gas is also used around the melt pool to help protect it during deposition.

Nozzle and Deposition Considerations

• The nozzle must direct powder into the melt pool rather than allowing it to disperse away from the deposition zone.
• Coaxial or multi-directional powder delivery can help maintain powder delivery as the deposition direction changes.
• A side-fed arrangement may restrict the direction from which material can be deposited.
• Nozzle design, powder-flow control, and shielding-gas delivery are important for forming a stable deposit.

Speakers and Sources

• Lecturer: Prof. Sajan Kapil, Department of Mechanical Engineering, Indian Institute of Technology Guwahati, as identified in the course metadata.
• Source/channel: NPTEL IIT Guwahati.