High Quality Rivets for Precision CNC Machining(define stiffness Frank)

  • Time:
  • Click:13
  • source:ZIEG CNC Machining
Rivets are a critical component in many manufacturing and engineering applications. As parts become more complex and machines more precise, having high quality rivets is essential for proper function and durability. For computer numerically controlled (CNC) machining, choosing the right rivets can impact the quality and precision of the finished product. Here’s an overview of how to select optimal rivets for CNC applications.
Rivet Material
The material used for rivets directly affects their strength, corrosion resistance, and compatibility with the application. Common rivet materials include:
- Aluminum: Lightweight yet strong, aluminum rivets offer high shear and tensile strength. They have good corrosion resistance and electrically and thermally conductive. Aluminum is easy to machine and suitable for aircraft and other transportation applications.
- Steel: Known for its high strength, steel rivets are available in various grades with different levels of hardness, ductility, and corrosion resistance. Carbon steels and stainless steels are commonly used. Steel rivets are popular for industrial machinery, construction, and marine applications.
- Copper: With excellent conductivity and corrosion resistance, copper rivets are primarily used in electrical applications. They are softer than steel and aluminum.
- Titanium: Extremely strong but lightweight, titanium rivets provide strength comparable to steel at 40% the weight. They withstand high temperatures and corrosion. Aerospace and motorsports rely on titanium rivets.
- Plastics: For less demanding applications, plastic rivets provide an affordable option. Thermosets and thermoplastics like nylon are common. Plastic rivets have low strength but high chemical and electrical resistance.
The choice depends on factors like strength needs, environment, weight, and cost. Aluminum, steel, and titanium are commonly used in CNC machined parts.
Rivet Strength
A rivet’s strength comes from its head size, shank diameter, material grade, and processing method. This determines how much force the rivet can withstand before failing. Key measures of rivet strength:
- Shear strength: Resistance against lateral or shearing forces. This is the primary force experienced by rivets.
- Tensile strength: Resistance to forces trying to pull the rivet apart.
- Fatigue strength: Ability to withstand cyclical shearing forces over time.
Higher grades of rivet materials generally have higher strength capabilities. Processing methods like heat treating can also improve strength. Stronger rivets allow for tighter fit-up of CNC machined parts under tension or vibration.
Shank Style
The shank is the main body of the rivet which gets inserted into the hole. Shank style impacts fit, installation, and strength. Common types include:
- Solid shank: Simple and versatile full-body shank suitable for most applications. Provides good shear strength.
- Semi-tubular: Partial hollow shank with a smaller diameter than head. Offers weight savings while still providing good grip and shear strength.
- Tubular: Fully hollow shank for maximum weight reduction and flexibility. Ideal for lightweight parts. Lower shear strength than solid shank.
- Grooved: Parallel grooves along the shank improves vibration resistance and fatigue strength. Common in high-stress aerospace applications.
- Stepped: Shank has sections of different diameters. Allows rivet to expand and fill different size holes.
The shank style should suit the design loads and assembly method. CNC machined parts often use solid or semi-tubular rivets.
Head Styles
Rivet heads are flattened or rounded on one end to create a wide clamping surface. Head shape and size factor into installation process and joint strength. Typical head options are:
- Dome head: Rounded convex shape makes this head style easy to install. Good for automatic riveting. Low-profile head is unobtrusive.
- Countersunk head: Flat circular head designed to sit flush within a countersunk hole. Provides a smooth finished surface.
- Modified countersunk head: Combination of domed and countersunk head for eased installation and a flush exterior surface.
- Flat head: Straight cylindrical head with flat top surface. Offers highest shear strength for its diameter.
- Universal head: Dome head with a flat bearing surface to provide high clamp force. Withstands vibration well.
For CNC parts, dome, countersunk, and universal head rivets allow for automated installation. Flat heads offer the greatest strength in tight spaces.
Rivet Finishes
Rivet shanks and heads receive different finishes to facilitate installation, resist corrosion, and improve appearance:
- Natural finish: No additional processing after heat treatment. Provides optimal shear strength.
- Anodized: Electrolytic oxide layer enhances corrosion and weather resistance. Common for aluminum rivets. Varying colors available.
- Plated: Electroplated metal coatings like zinc, cadmium, or tin improve corrosion resistance. Common for steel rivets.
- Passivated: Chemical treatment to form protective oxide layer on stainless steel rivets. Enhances corrosion resistance.
- Painted: Colored polymer coatings add decoration and further corrosion protection.
CNC machined parts involve close-tolerance holes and often require stronger natural finish or anodized rivets. Plating offers both strength and corrosion resistance.
Installation Method
Rivets get installed in different ways, each putting unique demands on the rivet. Common techniques include:
- Hammering: Rivets hammered by hand or machine. Requires malleable dome head that mushrooms outward.
- Pulling: Jaws of a rivet gun grip and pull the shank, expanding the rivet. Needs a ductile shank.
- Rolling: Compresses rivet between a roller and anvil, spreading the shank. Requires soft malleable material.
- Screwing: Screw-like threads draw rivet tight. Allows for removal and vibration resistance.
- Impact: Explosive force flares rivet shank. Used for remote high-strength fastening.
CNC machinery typically utilizes pulling or rolling techniques suitable for common head styles and materials. Impact fastening sees niche applications.
Usage Environment
The operating conditions that rivets are exposed to affect material and finish requirements:
- Temperature: Withstand fluctuations and extremes like weather, engine heat, or cryogenic liquids.
- Exposure: Resist corrosion from water, chemicals, salt spray, fuels, UV radiation, and air pollutants.
- Loads: Handle tension, vibration, impact, and cyclic forces over time.
- Electrical: Conduct or insulate current as needed.
- Weight limits: Strength-to-weight ratio impacts performance in vehicles and aircraft.
CNC parts see a wide range of mechanical, chemical, electrical, and environmental conditions. Select rivets accordingly.
By considering these factors - material, strength, shank, head, finish, installation, and environment - manufacturers can select optimized rivets for their CNC machined components. With sound engineering principles and thorough testing, high quality rivets ensure precision assembly and reliable long-term performance. CNC Milling CNC Machining