Riveting in Sheet Metal Fabrication(acetal Gladys)
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- source:MAJA CNC Machining
What is a Rivet?
A rivet is a mechanical fastener consisting of a cylindrical shaft and head. During installation, the rivet is placed in a hole drilled through the materials being joined. The tail end is then upset, usually using a riveting hammer or rivet gun. This causes the rivet shank to expand, securing the rivet in place. The rivet head and upset tail clamp the joined materials together tightly.
Rivets for Sheet Metal
Several factors determine the optimal rivet type for sheet metal fabrication:
- Material - Aluminum, steel, stainless steel each require rivets made of compatible alloys. Most rivets have an aluminum alloy body and steel mandrel.
- Strength - The rivet must withstand expected loads without failing. Tensile and shear strength ratings are available for each rivet type and size.
- Sheet thickness - Thicker materials require longer rivets. Standard rivets suit 0.5-3 mm sheets. Extra long rivets are available for thicker stacks.
- Grip length - This is the maximum material thickness the rivet can clamp. It depends on rivet length and the diameter of the drilled hole.
- Head style - Common options include round, countersunk, and flush heads. Countersunk heads provide a flat surface finish.
- Installation method - Hand set, hammer set, and pneumatic rivet guns each impart different forces when upsetting the rivet.
Common Rivet Types
- Solid/Round Head Rivets – General purpose rivets with a domed head. They suit most hand or hammer setting applications.
- Countersunk Head Rivets – The flat, conical head is flush with the material surface for a smooth finish. They require an angled countersunk hole.
- Structural Rivets – Made from high strength steel alloys. Important for structural joints subjected to vibrations.
- Blind Rivets – Tubular rivets designed for fastening sheet metal where access is only available from one side.
- Self-Piercing Rivets – Combine piercing and riveting in a single operation. No pre-drilled hole is needed.
- Drive Rivets – Also called screw rivets. They combine threads with high clamping force.
Rivet Joint Design
Proper design is crucial for rivets to perform as intended. Factors to consider include:
- Spacing – Rivets should be spaced at 3-4 times the sheet thickness along a joint. Edge margins should equal 1.5 times the rivet spacing.
- Edge margins – Sufficient material must exist between the rivet holes and sheet edges to prevent tear-out.
- Pitch – This is the center-to-center distance between rivet holes along a joint. Consistent pitch prevents distortion.
- Rows – Multiple parallel rows of rivets evenly distribute stresses across wide joints. Row spacing is usually 2-3 times the sheet thickness.
- Materials – Riveting dissimilar metals can accelerate galvanic corrosion. Isolate materials like aluminum from steel.
- Hole fit – Holes should be 0.05-0.1 mm larger than the rivet shank diameter for proper installation.
Riveting Process
Correct technique is critical during riveting to produce quality joints:
1. Drilling – Holes must be round within 0.1 mm and sized according to rivet diameter. Use sharp drill bits, low speeds, and gentle feed rates.
2. Deburring – Remove all burrs and shavings from holes to prevent cracking under rivet pressure.
3. Aligning – Clamp or tack materials to keep everything aligned during riveting.
4. Inserting – Place the correct rivet length in each hole with the head against the accessible sheet surface.
5. Setting – Use the recommended force, number of hits, and hammer for each rivet type. Set symmetrically.
6. Forming – Ensure the rivet forms a full head that clamps materials securely. Avoid shallow or off-center heads.
7. Inspecting – Check for cracked holes, lifted heads, or incomplete forming. Replace defective rivets.
8. Finishing – Grind flush any uneven or oversized rivet heads.
Riveting Equipment
- Drill press – For drilling precision, accurately aligned holes. Use drill guides to control position.
- Hole punch – Quick alternative to drilling for high production rates. Limited to standard hole sizes.
- Riveting hammer – Weighted hammer with a large, domed striking face to flare rivet tails.
- Pneumatic rivet gun – Uses compressed air to upset rivets consistently with proper force. Requires less operator skill.
- Rivet sets and bucking bars – Shape and support the rivet tail during hammer setting. Correct sets must match rivet type and size.
- Rivet spacer – A simple footed tool for checking aligned spacing between drilled holes.
- Dyes – Used to flare hollow rivet tails to the required diameter for optimum strength.
- Micrometer and go/no-go gauges – Essential for quality control checks of rivet lengths and hole sizes.
Riveting Tips
- Use the recommended grip range – Under or over sizing leads to joint failure.
- Set rivets starting from the middle and moving outwards.
- Apply masking tape to easily mark hole locations.
- Set each rivet with multiple light hits rather than fewer heavy blows.
- Use standard length rivets whenever possible for cost and availability.
- Keep rivet mandrels from jamming in guns by spraying with dry lubricant.
- Blind rivets can replace many solid rivets for simplified installation.
- Always consult rivet manufacturer specifications for proper usage.
Riveting remains an efficient, reliable method for fastening sheet metal components. With attention to joint design, material selection, and installation techniques, rivets produce robust structures across numerous industries. CNC Milling CNC Machining