The Importance of Quality Rivets in CNC Machining(diecast aluminum Pamela)
- source:GAENOR CNC Machining
What are Rivets?
A rivet is a mechanical fastener that consists of two main parts - a smooth cylindrical shaft and a head. The rivet is inserted into pre-drilled holes in the materials being joined, and the tail end is upset, or bucked, to form the second head. This creates a permanent joint.
Rivets come in a variety of styles, sizes, and materials. Some common types include:
- Solid rivets - made entirely of one material like steel, aluminum, copper, or Monel
- Semi-tubular rivets - hollow with a small hole in the center
- Blind rivets - rivets that can be installed without access to the backside
- Pop rivets - designed to be quickly installed by hand
Key Properties of Quality Rivets
For CNC machined parts and assemblies, the rivets used must have specific mechanical, dimensional, and material properties. Here are some of the key qualities that determine rivet quality:
- Shear and tensile strength - rivets must withstand shearing and tensile stresses without failing at the designed load capacity
- Ductility - allows rivets to be bucked and flattened to form the second head
- Dimensional consistency - precisely uniform shaft diameter and consistent head shape/size
- Concentricity - the rivet head and shaft must be perfectly centered to avoid failure
- Surface defects - no cracks, seams, or voids that could lead to rivet failure
- Materials match - rivet material should match or be compatible with the materials being joined
- Corrosion resistance - rivets should resist corrosion in the application environment
Rivet Strength Grade Requirements
Engineers select rivets with adequate strength for the intended application. Key measures of rivet strength include:
- Shear strength - resistance to lateral forces trying to slide the joined materials
- Tensile strength - resistance to forces pulling the joint apart
- Yield strength - stress level causing permanent deformation
Standard rivet strength grades designate the minimum shear and tensile strength values. Common designations include Grade 2, Grade 5, Grade 8, and AN470. Higher grades have greater strength capable of supporting more load.
Manufacturing Quality Rivets
Producing consistently high-quality rivets requires advanced manufacturing techniques and quality control checks. Here is an overview of how quality rivets are made:
- Materials - aircraft-grade aluminum, steel, titanium, copper alloys, and other metals are used, depending on the strength, corrosion resistance, and weight requirements.
- Forming - rivet shafts and heads are precisely formed to spec using techniques like cold heading, upset forging, precision machining, and hot forming. This ensures dimensional uniformity.
- Heat treating - some rivets are heat treated to enhance strength, hardness, and stress relief properties. Precise temperature controls and timing is critical.
- Surface finishing - processes like anodizing improve corrosion and wear resistance. The surface must be free of cracks or seams.
- Dimensional inspection - sample rivets from each batch are verified to meet dimensional tolerances using precision measuring tools like optical comparators.
- Mechanical testing - tensile, shear, pressure, and other tests confirm rivet strength meets or exceeds the rated grade minimums.
- Defect analysis - microscopic examination identifies any material or manufacturing defects before rivets are approved.
By following rigorous quality procedures throughout all stages of manufacturing, rivet suppliers can guarantee their products meet the tight specifications and consistency required in CNC machining applications.
Inspecting and Qualifying Rivets
For critical aerospace, defense, transportation, and industrial equipment projects involving CNC machining, buyers do not simply take the rivet supplier’s word when it comes to quality. Rigorous incoming inspections and qualification processes are applied:
- Certificate of Conformance (C of C) - suppliers provide documentation confirming all quality, testing, and traceability requirements are met.
- Dimensional inspection - sample rivets from the batch are measured to verify diameter, head shape, length, and other dimensional specs are within tolerance.
- Destructive testing - rivets are tested to failure to verify shear and tensile ratings match the specification grade.
- Process audits - the buyer may audit the supplier’s facilities and manufacturing processes to verify quality systems are in place.
- First Article Inspection - the first batch of rivets go through exhaustive inspections before production runs continue.
- Batch traceability - each batch receives a heat code or unique lot number to trace back to the raw material, production date, equipment used, and inspection data.
By qualifying rivet suppliers and verifying rivet quality, CNC machinists can feel confident that the rivets going into their finished products will perform reliably for the life of the assembly.
Installing Rivets in CNC Machined Components
The first step is having properly designed, precision-machined rivet holes in the components to be joined. CNC machining allows the holes to be located with tight tolerances of +/- 0.005 in. or better. Drilling, boring, punching, laser cutting, and other methods create hole sizes matched to the rivet diameter.
Cleanliness is also critical - any burrs, chips, or shavings must be removed from the holes and components to avoid contaminating the joint. Careful hole edge finishing prevents cracks or fractures when the rivet is expanded into place.
Pneumatic, hydraulic, or manual riveting systems then upset the rivet tails with a bucking bar to flair out the second head. Shank rotation helps evenly fill the hole and increase joint strength. Proper rivet gun settings and operator technique prevents applying excess force that could crush or deform the materials.
Quality inspections check the set rivets for proper head shape, good shank filling, and no cracks or seams. Once installed following best practices, high-quality CNC rivets deliver consistent, reliable performance and are integral to creating durable, precision-machined products.
Key Takeaways on Quality Rivets for CNC
- With consistent dimensions, material strength, and reliable performance, quality rivets are essential in CNC machined assemblies.
- Advanced manufacturing techniques like precision forming and heat treating allow rivet suppliers to achieve the tight tolerances and material properties needed for quality rivets.
- Buyers must qualify suppliers and aggressively inspect incoming rivets to ensure specifications are met prior to use in machining operations.
- Proper CNC hole preparation, cleanliness, and rivet installation practices enable quality rivets to provide maximum joint integrity and service life.
The right rivets make a crucial difference in the safety, strength, and longevity of CNC machined products. By understanding rivet properties and following proven quality assurance processes, manufacturers can feel confident in the reliability of the rivets used in their assemblies. The result is finished products that meet design expectations and deliver outstanding performance. CNC Milling CNC Machining