Explain the classification of rapid prototyping process with neat flow chart?
Rapid prototyping (RP) is a term for a group of technologies used to quickly fabricate a scale model of a physical part or assembly using three-dimensional computer-aided design (CAD) data. While the most popular forms of rapid prototyping are a subset of additive manufacturing, the classification of RP processes can be broader, encompassing different methods based on how the final object is created.
The most common and widely accepted classification scheme for rapid prototyping processes is based on the state of the raw material and the method used to form the part. This often leads to three main categories: additive, subtractive, and formative.
1. Additive Processes
Additive processes, also known as additive manufacturing or 3D printing, are the most prominent and widely used methods for rapid prototyping. These processes build a part layer by layer, directly from a digital model. They are crucial for creating complex geometries and internal features that are impossible to achieve with other methods.
Vat Photopolymerization: Uses a liquid photopolymer resin and a light source (e.g., UV laser) to selectively cure and solidify each layer. Examples include Stereolithography (SLA) and Digital Light Processing (DLP).
Material Extrusion: A heated nozzle extrudes a thermoplastic filament layer by layer to build the part. Fused Deposition Modeling (FDM) is the most well-known example.
Powder Bed Fusion: A thermal energy source, like a laser or electron beam, selectively fuses powdered material in a build chamber. Examples include Selective Laser Sintering (SLS) for polymers and Selective Laser Melting (SLM) for metals.
Material Jetting: Similar to an inkjet printer, this process deposits droplets of material (e.g., photopolymer) and cures them with UV light. It is known for high resolution and multi-material capabilities.
Binder Jetting: A liquid binder is selectively jetted onto a powder bed, which then hardens to form the part. Post-processing like sintering is often required.
Sheet Lamination: Sheets of material (paper, metal, or plastic) are bonded together and then cut to shape, typically with a laser, to form the object.
Directed Energy Deposition: A high-energy source (laser or electron beam) melts and fuses material as it's deposited from a nozzle. This method is often used for repairing or adding to existing parts.
2. Subtractive Processes
Subtractive rapid prototyping involves starting with a solid block of material and removing unwanted material to create the final object. These methods are typically faster for simple geometries and can use a wider range of materials, especially for functional prototypes.
CNC Machining: This is the most common subtractive method, using Computer Numerical Control (CNC) to automate the movement of cutting tools to shape the part. This can include milling, turning, drilling, and grinding. CNC prototyping is excellent for producing high-precision, functional prototypes from a variety of engineering-grade materials like metals and durable plastics.
3. Formative Processes
Formative processes create a part by shaping a material that is in a semi-solid or liquid state. The material is formed into the desired shape before it solidifies. These methods are often used for creating low-volume prototypes and for materials that are difficult to work with using additive or subtractive methods.
Casting: Molten material (metal, plastic) is poured into a mold. While traditional casting can be a slow process, rapid tooling—creating a mold quickly with other RP methods—makes it a viable rapid prototyping technique.
Molding: This includes processes like injection molding and vacuum casting. In injection molding, molten material is injected into a mold cavity. For rapid prototyping, a mold can be quickly made from a soft material like silicone to produce a few dozen or a few hundred parts for testing.
Compressive Sintering: Similar to Powder Bed Fusion, but the powder is compacted and then sintered to form the object, often at a higher pressure.