More than 50% of total production time is spent on assembly or fastening. However, mechanical fastening usually represents less than 5% of the total in-place or assembled cost of a product.
When automatic assembly is used, the fastener or fastening method must not only meet product requirements but must be compatible with the assembly machinery.
Successful automatic applications are characterized by:
- Dimensional consistency of all components and fasteners. Automatic assembly may require more precise tolerances than the product.
- Stable design that is not changed frequently, or family designs which can be easily programmed.
- Volume production, which one estimate suggests should be at least 300 units/hr, or a million units/yr.
- Simple components that can be handled automatically, such as shafts or rods. Such parts are more easily fed and do not require complex feed mechanisms to orient them correctly.
In selecting fasteners for automatic assembly, the designer should try to standardize fastener size as much as possible. Standardization means fewer assembly stations and lower tooling and retooling costs. Installation components are widely available for standard fasteners.
In all cases, feeding and reliable orientation are generally the most difficult parts of the assembly process. If a fastener can be fed properly, it can be installed.