L17 Processing

What are typical casting defects?

Cavities; undersize; cold shuts; inclusions; stress cracks; gas porosity; warpage.

Name processes suited for the manufacturing of fiber‐reinforced polymers.

Resin Transfer Molding (RTM) and compression/injection molding of fiber‐reinforced composites (preform → resin injection → curing).

Name the process steps for injection molding.

Mold closing → plasticization (melting & homogenizing granulate) → injection of melt into the cavity → holding/topping-up → cooling → mold opening and part ejection.

What are the main differences between Injection Molding & Extrusion?

Injection molding produces complex 3D parts with high detail but requires expensive molds and large production runs; extrusion creates continuous profiles of constant cross-section (2D complexity), also high precision but limited geometry, and is only economical for long lengths.

Right or wrong? Extrusion is suited for manufacturing parts with complex geometries in all three spatial directions. Why?

Wrong: extrusion only produces parts with a constant cross-section along their length (complexity in two dimensions), so it cannot create fully 3D geometries.

What are advantages and drawbacks for Additive Manufacturing?

Advantages: enables highly complex, lightweight, and functionally integrated parts; supports mass customization at low volumes. Drawbacks: high equipment and material cost, slow for large batches, requires extensive pre- and post-processing, and lacks industry standards.

When does it make sense to use additive manufacturing as a production process?

When producing low-volume or highly customized parts with complex internal features or functional integration where traditional tooling would be too costly or impossible.

Name Additive Manufacturing processes used for aerospace industry. Describe their basic process principle.

Selective Laser Melting (SLM): a laser selectively fuses powder layer by layer in a powder bed; Electron Beam Melting (EBM): an electron beam in vacuum melts metal powder layer by layer.

What are the main differences between EBM and SLM? How does this affect the production process?

EBM uses an electron beam in a vacuum environment, providing faster build rates and less residual stress but lower surface finish; SLM uses a laser in an inert-gas atmosphere, yielding finer resolution and surface quality but generally slower builds.