Bolting and riveting are mechanical joining operations commonly used in aerospace, automotive, structural, and general mechanical applications where permanent or semi-permanent connections are required. The operations are best suited for assemblies with dissimilar materials or those requiring periodic disassembly (bolting).

Capabilities

Advantages: Suitable for all materials, good control of tolerance, and rapid lead times.

Disadvantages: Low shape complexity, may require several machines, heavy tool wear and cost, and a likelihood of excessive scrap.

Applications: Structural frames, engine mounts, brackets, enclosures.

Process Cycle

Bolting and riveting cycle time consists of:

• Hole preparation (drilling or punching): 30-60% of total cycle time
• Insertion of fasteners: Hand or automatic insertion uses 10-30%
• Deformation or torqueing: Rivet head forming or torque tightening may use 10-20%
• Inspection and quality check: Generally 5-15%

Cycle times vary from seconds (automatic riveting) to minutes (hand bolting). Fastening rate is largely a function of access to the joint as well as complexity of parts.

Equipment

Bolting Tools:

• Manual, pneumatic, electric torque wrenches
• Bolt feeders and automatic tightening machines
• Torque angle gauges

Riveting Tools:

• Electric, hydraulic, or pneumatic rivet guns
• Orbital/radial riveting machines
• Rivet delivery systems

Tooling

Principal Tools:

• Drills, punches (for making holes)
• Bolts, nuts, rivets (many head and shaft configurations)

Auxiliary Tools:

• Jigs and fixtures for aligning parts
• Torque testers and calipers
• Inspection gauges for head diameter, depth, and position

Materials

Fasteners are often made from steel, stainless steel, aluminum, titanium, and plastic (non-structural). Surface treatments like zinc plating or anodizing improve corrosion resistance.

Possible Defects

• Inadequate load distribution because of uneven holes
• Material cracking or thread stripping because of over-tightened fasteners
• Loosening of rivets because of insufficient deformation
• Material incompatibility or absence of surface finish and corrosion
• Fatigue failure in cyclical loads or due to vibration

Prevention of these defects is realized by using proper torque control, selecting appropriate materials, and monitoring the process.

Design Guidelines

• Always provide clearance holes for bolts and interference/tolerance holes for rivets
• Provide access space for tool insertion and torqueing
• Conform to standard head and shank size to simplify sourcing
• Employ symmetrical fastening to avoid warping
• Employ self-locking nuts or thread-locking compounds for vibration conditions

DFMA Compliance Tips:

• Design for single-sided access when feasible
• Minimize excess fastener variety
• Utilize modular hole patterns and standard sizes
• Verify thermal and galvanic compatibility of base material and fastener

Cost Drivers

Most significant cost drivers of riveting and bolting are:

• Fastener type and material: Specialty bolts/rivets more expensive
• Hole preparation: Precision drilling and tool life
• Access requirements: Safer, quicker assembly with increased access
• Assembly speed: Manual vs. automated operations
• Tooling and fixturing: Every setup, special jigs raise setup cost
• Inspection and rework requirements: Influenced by design tolerance and access

Reduction in joint number, fastener type, and tooling may lower the assembly cost by as much as 40% in mass production applications.