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Introduction
Fasteners are essential components in product assembly, although they often do not directly contribute to product functionality. Their primary role is to join parts together. However, fasteners can increase production complexity, time, and cost—especially when bolts and nuts are involved. Therefore, minimizing the number and variety of fasteners is a key strategy in DFMA (Design for Manufacturing and Assembly).
1. Use Fasteners of the Same Kind
In an optimized design, reducing fastener variety enhances standardization and simplifies inventory and assembly. For example, a design initially using four types of bolts (differing in length, head shape, and thread) was improved by switching to a single standard bolt—M3x6—for all applications
2. Use Snap Joint Assemblies or Edge Folds Instead of Fasteners
Snap joints offer a faster, more cost-effective, and environmentally friendly alternative to traditional fasteners. As shown in Figure 1-2, two plastic parts are connected using snap joints.
Similarly, in sheet metal components, compressed edge folds can be utilized to reduce the number of fasteners. Figure 1-3 illustrates how a design using four bolts was optimized to use only two bolts with the addition of a folded edge.
3. Avoid Disconnected Fastener Designs
Reducing the number of separate parts helps eliminate unnecessary fasteners. Integrating components into a single part decreases assembly time and increases efficiency. Figure 1-4 demonstrates this concept.
4. Use Tapping Screws Instead of Machine Screws
Tapping screws eliminate the need for threaded holes or embedded nuts, thereby reducing production steps and component costs. This is effective for both metal and plastic components, provided the product doesn’t require frequent disassembly or high fastening strength.
5. Use Bolts and Nuts as a Last Resort
Among fastening methods, bolts and nuts are the least efficient and most expensive. They should only be used when the design requires extremely high precision or when no other fastening method is viable.