TABLE OF CONTENTS The design requirements to be met in choosing a joining process differ from those for choosing a shaping process. Even material compatibility is more involved than for shaping, in that joints are often to be made between dissimilar materials.
Processes for joining metals, polymers, ceramics and glasses differ. Adhesives will bond to some materials but not to others; methods for welding polymers differ from those for welding metals; and specific metals often require specific types of welds. The material-process matrix (Figure 18.2) includes four classes of joining process.
When the joint is between dissimilar materials, further considerations arise, both in manufacture and in service. The process must obviously be compatible with both materials. Adhesives and fasteners generally allow joints between different materials; many welding processes do not. Practicality in service is a different issue. If two materials are joined in such a way that they are in electrical contact, a corrosion couple appears if close to water or a conducting solution. This can be avoided by inserting an insulating interlayer between the surfaces. Thermal-expansion mismatch gives internal stresses in the joint if the temperature changes, with risk of damage. Identifying good practice in joining dissimilar materials is part of the documentation step.
Important joining-specific considerations are the geometry of the joint, the thickness of material they can handle and the way the joint will be loaded. Figures 18.13 and 18.14 illustrate standard joint geometries and modes...
