JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year ADDITIVE MANUFACTURING Previous Question Paper (March - 2021 - R16)

Rapid Prototyping (RP) is a group of additive manufacturing techniques used to quickly fabricate a physical model of a part or assembly using three-dimensional computer-aided design (CAD) data. It allows for the iterative design and validation of complex geometries without the need for traditional tooling or machining.

RP systems are generally classified based on the state of the starting material:

1. Liquid-based systems: Utilize photopolymer resins that cure upon exposure to light (e.g., Stereolithography (SLA), Solid Ground Curing (SGC)).
2. Solid-based systems: Utilize materials in solid form such as wires, laminates, or powders (e.g., Fused Deposition Modeling (FDM), Laminated Object Manufacturing (LOM)).
3. Powder-based systems: Utilize materials in powder form, often fused by lasers or binders (e.g., Selective Laser Sintering (SLS), Selective Laser Melting (SLM), Three-Dimensional Printing (3DP)).

Data preparation in Stereolithography (SLA) is the critical process of converting a 3D CAD model into a format suitable for the machine to build the part layer by layer. The process involves:

1. CAD Modeling: Creating the initial 3D design in a CAD software package.
2. Conversion to STL: The CAD model is converted into an STL (Stereolithography) file. This format approximates the surfaces of the model using a mesh of triangles. The accuracy of the model depends on the chord height and angular tolerance settings during export.
3. Repair and Validation: The STL file must be 'watertight' (manifold), meaning there are no holes, overlapping triangles, or inverted normals. Software tools are used to check and repair these geometric errors.
4. Slicing: The repaired STL file is oriented and sliced into thin horizontal cross-sections. This generates a series of 2D layers that define the toolpath for the laser.

The primary data file format is the STL file, which stores the geometry as a list of triangular facets defined by their vertices and a surface normal vector. While simple and universal, STL files do not contain information about units, color, or material properties, necessitating the use of secondary formats like SLC (Stereolithography Contour) or CLI (Common Layer Interface) for more precise layer-by-layer data transmission.