A manufactured assembly can connect parts by very different physical mechanisms. The main joining families include:

• mechanical fastening, using features such as bolts, screws, rivets or interference;
• fusion welding, where base material locally melts and resolidifies;
• solid-state welding, where bonding occurs without bulk melting;
• brazing and soldering, where a lower-melting filler flows between solid base parts;
• adhesive bonding, where a polymeric or reactive layer transfers load across an interface.

Selecting a joining process is not merely choosing the strongest joint. Important requirements include:

• material compatibility and thickness;
• joint accessibility;
• sensitivity to heating or distortion;
• whether loads are steady, repeated or impact-like;
• sealing or electrical requirements;
• production rate and automation;
• inspectability, repair and disassembly.

Joint geometry also changes how loads are transferred. A lap joint can spread load over an area, while an offset or edge-loaded joint can create strong local opening effects even when the overall applied force is modest.

For example, a removable machine cover may favor bolts because service access is essential. A thin automotive body panel may favor high-rate spot welding. A temperature-sensitive composite may favor adhesive bonding because melting the base material would damage it.

Joining is therefore a design decision that couples load path, materials, process physics, inspection and lifecycle requirements.