Riveting in Sheet Metal Fabrication(titanium harder than steel Trista)
- source:YESCOM CNC Machining
What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - a smooth cylindrical shaft and a head. The rivet shaft is inserted through holes in the materials being joined. The excess shaft is then flattened into another head with a hammer or rivet gun, creating a permanent joint. The rivet head and sheet material are clamped together between the two rivet heads through pressure and friction. This tight joint is capable of withstanding significant shear and tensile loads.
Rivets come in a wide variety of head shapes, shaft lengths, and materials. Some common types include:
- Solid rivets - made entirely from one material like steel, aluminum, copper, or Monel
- Blind rivets - hollow and installed with only access to one side
- Drive rivets - have a pre-formed head and are installed simply by driving the tail end
- Structural rivets - used for critical structural joints in aircraft, bridges, etc.
Benefits of Riveting
There are several important benefits that make riveting a popular choice for joining sheet metal:
Permanent - Once installed, the rivets constitute a permanent, non-reversible joint. The materials cannot come apart without destroying the rivet. This is advantageous for critical or structural applications.
Strong - Rivet joints have high shear and tensile strength. The joint strength depends on factors like material, rivet diameter, grip length, and hole preparation. Properly installed rivets are more than adequate for most general fabrication work.
Vibration resistant - Rivet joints tend to resist vibration and shock loads better than many other fasteners. The joint flexibility helps prevent loosening over time. This makes rivets well-suited for equipment housings and vehicle bodies.
Weight - Rivets add very little weight to an assembly. Steel rivets weigh just a fraction of comparable bolts or screws. This makes them ideal for weight-sensitive applications like aircraft.
No damage to materials - Unlike welding, riveting does not affect the metallurgical properties of the base materials being joined. The high heat of welding can alter material strength. Riveting allows different metals to be joined with no compromise to their individual characteristics.
Corrosion resistant - Properly installed and spaced rivets do not interfere with protective coatings on the joint materials. This resistance to corrosion makes them well-suited to equipment exposed to weather.
No torque requirements - Rivets function with consistent clamping force not precise torque like bolts. This simplifies installation and makes for more uniform joints.
Appearance - The smooth surface and consistent installation of rivets makes for an attractive assembly with neat lines. This aesthetically pleases some designers and manufacturers.
Lower cost - While riveting requires some specialized tools, it is generally faster and less expensive than welding or machining other fasteners. The simplicity of installation also reduces labor.
Disadvantages of Rivets
Rivets do have some disadvantages that must be considered:
Permanent - Rivets cannot be removed without destroying them. This makes repairs or disassembly impossible. Maintenance may require drilling out old rivets.
Hole alignment - The holes in each material must be precisely aligned for rivet insertion. Misalignment can lead to leaks, joint weakness, and an uneven surface appearance.
Surface damage - Hammering the rivets and compressing the joint can damage protective coatings and deform thin materials. Care must be taken to avoid these problems.
Specialty tools - Riveting requires access to both sides, precise hole sizing and alignment, and specialty tools like rivet guns, bucking bars, and sets. This equipment represents an additional investment.
Vibration loosening - While resistant, very high levels of vibration over time can still loosen rivets. Additional fasteners may be required for critical applications prone to extreme vibration.
Skill - Proper rivet spacing, hole sizing, material preparation, and installation technique require training and practice to perfect. Poor riveting work will lead to weak joints.
Rivet Joint Design Considerations
Using rivets effectively requires attention to certain design factors:
- Rivet diameter - This determines joint strength. It must match hole size and sheet material thickness.
- Material matching - Rivet material should match the base material to avoid galvanic corrosion.
- Grip length - The uninstalled rivet length must be sufficient to span the joined materials with enough excess to form the second head.
- Edge distance - Rivets along sheet edges require increased spacing to avoid edge tearing.
- Spacing - Rivets must be spaced based on joint strength needs, with larger spacing in non-critical areas.
- Rivet pattern - Staggering rows of rivets evenly distributes load. Some patterns resist vibration better.
- Hole fit - Hole diameter should match the rivet shaft with allowance for expansion during installation.
- Material preparation - Joint materials may need degreasing, descaling, or abrasion to optimize rivet adhesion.
Proper design must distribute load across enough appropriately sized and spaced rivets to create a joint stronger than the base materials. Consulting rivet manufacturer specifications and load tables provides guidance to engineers.
There are several installation techniques used to join sheet metal with rivets:
Hand Riveting - A basic riveting tool set consists of a bucking bar, rivet sets, pop rivet pliers, and a hammer. Access is needed to both sides of the material. One set holds the rivet in place while the other hammers the tail to form the second head. Rows of rivets are progressively installed. Hand riveting requires skill and practice to achieve quality, consistent joints.
Pneumatic Riveting - These rivet guns use compressed air to quickly upset the rivet tail. Guns come in squeezer and impact models. Squeezers use pressure to deform the tail while impacts strike and form it. This automation speeds the riveting process compared to hand work.
Hydrolic Riveting - Hydraulic power provides more controlled force to install rivets. Computerized systems closely regulate the pressure, providing precision upset force. This creates uniform high-strength joints. Hydraulics excel at large or difficult rivets in thick stacks of material.
Self-Pierce Riveting (SPR) - This cold forming process uses special semi-tubular rivets that do not require drilled holes. The rivet pierces the top sheet and spreads in the bottom layer without cracking it. SPR simplifies automation and joining dissimilar metals.
Blind Riveting - Blind rivets allow installation from only one side. The pull mandrel is joined to the rivet body and used to draw the tail into the second head after insertion. The mandrel snaps off after installation. Blind rivets excel where backside access is limited.
Rivet Nut Inserts - These internally threaded inserts provide strong thread reinforcement in sheet materials too thin for tapping. They install like rivets but provide reusable, wear resistant threads for bolts.
Rivets play an important role in countless sheet metal fabrication projects across every industry. By understanding their strengths, weaknesses, and best practices, manufacturers can effectively incorporate riveting to produce robust and reliable assemblies. With the right joint design and controlled installation process, rivets will continue providing permanent and versatile sheet metal joints. CNC Milling CNC Machining