Ensuring High Quality Rivets for CNC Machining(alloy steel vs stainless steel Andy)
- source:YESCOM CNC Machining
What Makes a Quality Rivet?
A quality rivet needs to meet certain standards in terms of materials, dimensions, head shape, and strength. Here are the key factors that determine rivet quality:
Materials - Aircraft grade aluminum is the most common material for CNC rivets. Stainless steel, copper, and monel are also options for specialized applications. The material must be durable, corrosion resistant, and suitable for the expected lifespan of the finished product.
Dimensions - The rivet shank diameter, head height, grip length, and other dimensions must conform to specified tolerances, usually +/- .002 inches. This ensures consistency and proper fit.
Head Shape - Common rivet head shapes include round, flat, countersunk, and brazier. The head needs to seat properly against the workpiece when set.
Strength - Shear and tensile strength ratings will indicate the rivet's load capacity for joining materials together. This must align with design specifications.
Certifications - Many industries require rivets to be certified to certain manufacturing standards like NASM, AN, and MS. This validates their quality level.
Choosing the Right Rivets
CNC machinists need to select the optimal rivet type, size, and specs based on these factors:
- Base Materials - What metals or alloys are being joined? Different materials require rivets made of compatible metals.
- Joint Design - The joint configuration impacts rivet length, grip, and head shape. flush rivets are common for smooth surfaces.
- Fastening Requirements - Consider the shear and tensile loads. This determines the rivet's required diameter and strength rating.
- Environmental Conditions - Will the rivets be exposed to heat, moisture, chemicals? Specialized coatings or materials may be needed.
- Industry Standards - Certain certifications and specs may be mandated for aerospace, defense, automotive, or medical applications.
- Cost - More exotic rivet materials and tighter tolerances increase cost. Balance performance needs with budget constraints.
Proper Handling and Storage
To maintain quality, rivets must be properly handled, stored, and prepared prior to use:
- Store rivets in a clean, dry environment to prevent corrosion. Seal any unused portions.
- Inspect rivets before use. Discard any with damaged heads, shanks, or distorted dimensions.
- Keep different sizes and types of rivets clearly separated to avoid mix-ups.
- Organize rivets by job or work cell for easy access. Consider rack systems or bin storage.
- Clean rivets with solvents to remove any oils, dirt, or coatings prior to use.
- Pre-set and heat rivets if needed to ease insertion and improve heading. Follow all equipment safety procedures.
Automated Riveting Techniques
CNC machined parts are often assembled using automated riveting systems for quality and efficiency. Here are some common methods:
- Robotic Riveting - Articulated robots are programmed to handle riveting guns and bucking bars to precisely drive rivets.
- Specialized Riveting Heads - These advanced heads integrate feeding, insertion, clinching, and other functions for touchless riveting.
- Line Riveting - Riveting stations or cells are set up to allow just-in-time riveting as parts transfer through.
- Impact Riveting - Powerful electromagnetic, pneumatic, or servo impact tools hammer-set rivets at up to several thousand blows per minute.
- Self-Piercing Rivets - These special rivets pierce and interlock thin sheets of material without pre-drilled holes.
- Blind Rivets - Rivets that can be installed from one side without access to the back are ideal for tight spaces.
Inspection and Quality Control
Meticulous inspection validates the riveting process quality and proper seating of every rivet:
- Confirm all rivets match the specified type, material, size, certification, etc. for that application.
- Visually inspect each rivet head for good form, tight fit, concentricity, and no cracks.
- Ensure rivets penetrate both workpieces fully and grip length is sufficient.
- Check for proper clamping force between riveted materials. No gaps, bending, or distortion.
- Verify full-form or flush rivet heads as dictated by the joint design needs.
- Conduct tap or vibration tests to identify any loose rivets. These must be replaced.
- Sample destructive testing to check rivet adhesion and that shear/tensile strength meets requirements.
By dialing in quality at every step - material selection, storage, handling, automation, and inspection - CNC machinists can produce riveted products that meet even the most demanding application requirements. Investing in high-performance rivets is a small price to pay to avoid failures, rework, hazards, or damage to your reputation. The quality is worth it. CNC Milling CNC Machining