In which design process do parts exist independently before assembly?

The bottom-up design process is characterized by developing parts or components independently before they are assembled into a complete system. This approach involves creating individual modules or elements, which can be designed and refined separately, allowing for flexibility and innovation in the design of each piece. Once these components are finished, they are brought together in the assembly phase to form the final product. Each part can be optimized based on its specific function without being constrained by the overall system during the initial design stages.

In contrast, top-down design typically starts with a complete system in mind, breaking it down into smaller components, which may limit the independence of each part during their development. Prototyping focuses on creating a working model of the design, which is often intended to test concepts rather than develop parts as independent entities. Stereolithography, a form of 3D printing, is a manufacturing process rather than a design methodology and is used to create objects layer by layer, rather than emphasizing the independent creation of parts. Thus, bottom-up design is the most fitting choice as it emphasizes the independent nature of parts before assembly.