Riveting in Sheet Metal Fabrication(diseño de un molde de inyeccion Jessie)
- source:MAJA 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 shaft is inserted into pre-drilled holes in the materials being joined. The excess material at the tail end is then upset, or mushroomed outward, to form the second head. This process is called riveting.
The resulting rivet holds the materials together through clamping force and friction. The rivet heads grip the materials on both sides to prevent the joint from separating. Rivets are available in a wide variety of styles, sizes, and materials to accommodate different fabrication requirements.
Benefits of Riveting
There are several advantages that make riveting a popular joining technique in sheet metalworking:
- Permanent Fastening - Unlike screws or bolts, rivets form a permanent connection that will not loosen over time. This makes them suitable for critical structures and assemblies.
- Vibration Resistant - The tight clamping force creates excellent vibration and shock resistance. Riveted joints are less prone to fatigue failure.
- Weight Savings - Rivets allow thinner and lighter material gauges to be used, an important consideration in industries like aerospace.
- No Access to Backside Needed - Rivets can be installed from one side only, unlike bolts. This simplifies assembly in cases with limited access to the back of the joint.
- Speed and Ease of Automation - Riveting tools and machines allow very rapid installation compared to other fastener types. The process is easy to automate.
- Material Flexibility - Rivets can join dissimilar or non-weldable materials like plastics. Special rivet materials are available for high strength or corrosion resistant connections.
Some common materials used for rivets include:
- Aluminum - Lightweight and conductive, aluminum rivets are ideal for aircraft and other transportation applications.
- Steel - Low cost and very strong, steel rivets provide high shear and tensile strength. May be prone to corrosion if not properly protected.
- Stainless Steel - Addition of chromium and nickel alloys make stainless rivets highly corrosion resistant. Used in harsh environments.
- Copper - Soft and easily deformed, copper rivets conform well to irregular joint surfaces. Used for non-critical connections.
- Monel - A nickel-copper alloy with strength, ductility and corrosion resistance superior to steel rivets. Common in marine applications.
- Titanium - Extremely strong but lightweight titanium alloy rivets offer high strength-to-weight ratio. Mainly used in aerospace assemblies.
Installing rivets requires specialized tools to accurately drill holes, insert the rivet, and deform the tail to form the second head. Common riveting tools include:
- Pneumatic Rivet Guns - Rivet guns use compressed air to quickly insert the rivet and upset the tail. Allows one-handed operation for easy maneuverability.
- Hydraulic Riveting Tools - More powerful hydraulic versions are used for larger rivets in heavy fabrication. Provide the force needed for very tight joints.
- Hammer Sets - For manual riveting, hammer sets are matched to the rivet head size to form the second head. Requires some skill.
- Autofeeding Rivet Machines - For production environments, autofeed riveters automatically insert and set rivets from a feeder tube at very high speeds.
- Robotic Riveting Systems - Programmable robots with specialized riveting end effectors provide fully automated high-speed riveting with precision and repeatability.
Rivet Joint Design
Proper design of the joint is critical to achieve a secure connection with rivets. Key factors include:
- Hole Diameter - Precision drill bits matched to the rivet diameter ensure a tight fit and prevent hole elongation.
- Material Thickness - Rivet length should be 3-4 times the combined thickness of the materials being joined.
- Spacing and Pitch - Rivets should be spaced at 3-4 diameters apart for rows and columns. Closer spacing increases joint strength.
- Edge Distance - Allow at least 2 rivet diameters from joint edges to prevent tear-out.
- Washer Requirements - Washers may be needed to prevent sheet deformation if riveting very thin or soft materials.
Good technique is needed to produce quality riveted joints:
- Hole Alignment - Mate parts together and clamp securely before drilling holes to ensure accurate alignment.
- Rivet Insertion - Use tooling that matches rivet size. Insert the rivet straight and completely flush with material surface.
- Set the Tail - Slowly form the second head to flatten and flare the rivet tail without cracking it.
- Work Hardening - Peen the shop head with a hammer to work harden and increase joint strength.
- Check Final Result - Inspect rivet height and shape of both heads to confirm proper setting.
Riveting plays an indispensable role in sheet metal fabrication across countless industries and products. Correct selection of rivet type and size along with proper joint design, preparation, tooling, and installation technique will produce robust, reliable and permanent riveted connections. CNC Milling CNC Machining