Contact rivets in electrical engineering

Classification and importance of contact rivets

Contact rivets are among the most established electrical contact parts in the low-voltage range. They are used wherever electrical currents must be switched or carried reliably and a permanent mechanical connection between contact material and carrier material is required.

As a dedicated product category, contact rivets are standard in relays, installation switches, circuit protection devices, thermostats and many electromechanical assemblies.

In industrial practice, contact rivets have remained relevant despite alternative solutions such as contact tips or contact profiles. Key reasons are process stability, good suitability for automation and a clearly defined contact geometry.

From an engineering perspective, contact rivets are not a simple commodity part but a functionally critical component. Performance results from the interaction of material, geometry, manufacturing quality and the assembly process. Design errors often become visible only in the field, for example through increased contact resistance, contact welding or reduced service life.

What is a contact rivet?

A contact rivet is an electrical contact part with a rivet function. It permanently connects the electrically active contact surface to a metallic carrier, typically a stamped strip or contact band made of copper or copper alloys. The joint is created by plastic deformation of the rivet shank during riveting.

Structurally, a contact rivet consists of two functional areas:

• the contact head forming the switching/contact surface
• the rivet shank providing mechanical fixation in the carrier material

After setting, the result is a form-fit connection that ensures both electrical conductivity and mechanical stability. An additional metallurgical joint such as welding or brazing is not required.

Distinction from other contact parts

Contact rivets compete directly with other contact solutions such as contact tips, wire contacts or contact profiles. Each option has specific strengths and design constraints.

Compared with welded contacts, contact rivets often provide advantages in:

• reproducible contact geometry
• low thermal impact on the carrier material
• stable process behavior at high volumes

Compared with contact profiles, contact rivets can be simpler to integrate, but typically require more precious metal per contact point. For clearly defined contact positions and limited installation space, they are often the more economical solution.

Design and geometry of contact rivets

Basic geometry and function

The geometric design of a contact rivet strongly influences electrical and mechanical behavior. Key parameters are not only the diameter and height of the contact head but also the head-to-shank diameter ratio and the shank length.

A shank that is too short can reduce mechanical retention, while an overly long shank can destabilize the riveting process or deform the carrier material.

Head shapes and contact surfaces

In practice, clearly defined common head shapes are used. Typical are flat, round or spherical contact heads. Selection depends on contact force, available space and the required contact behavior.

Flat heads provide a defined contact area and are often used with stable contact forces. Round and spherical heads promote point-like force transfer and can support self-cleaning effects and contact stability at lower contact forces.

Dimensional tolerances

Contact rivets require tight dimensional and form tolerances. Deviations in the tenth-millimeter range can already affect:

• contact force
• contact resistance
• switching behavior
• service life

Achievable tolerances depend on the material, the forming degree and the manufacturing process.

Materials for contact rivets

Material selection is the main lever to adapt a contact rivet to its application. It largely determines erosion behavior, tendency to weld, contact resistance and service life.

Silver-based materials as a principle

Due to its very high electrical conductivity, silver is the base material for most contact rivets. Pure silver has limitations, especially at higher switching loads or in DC applications.

Alloying and/or combining with metal oxides allows targeted adjustment of properties.

Typical silver materials for contact rivets

AgNi (silver-nickel)

AgNi materials are widely used in relays and switches. They provide a balanced combination of conductivity, erosion resistance and mechanical stability. The nickel content influences hardness and wear behavior and is adapted to the application.

AgSnO₂ (silver-tin oxide)

AgSnO₂ is preferred for inductive loads and higher inrush currents. It is characterized by high resistance to welding and stable switching performance. Lower ductility must be considered during forming.

AgCu (silver-copper)

AgCu alloys offer increased mechanical strength. With rising copper content, electrical conductivity decreases. They are often used for moderate switching loads.

AgZnO (silver-zinc oxide)

AgZnO can be an alternative to AgSnO₂ in certain applications. Suitability is strongly application-dependent and should be evaluated technically.

Powder-metallurgical contact materials

Powder-metallurgical silver metal-oxide materials feature a fine, homogeneous distribution of oxide particles in the silver matrix. This supports stable switching behavior and high erosion resistance.

At the same time, these materials are less ductile than melt-metallurgical alloys, which can limit forming options for contact rivets.

Cadmium-containing materials

Silver-cadmium oxide materials were historically used for high switching loads. Their current use depends on application, market and the regulatory framework. In some cases, valid exemptions may exist. Blanket statements about usability are not appropriate.

Contact rivets as solid, bimetal and trimetal versions

Solid contact rivet

Solid contact rivets consist entirely of the contact material. They are generally well formable and can be produced with high process reliability, but require comparatively higher precious metal usage.

Bimetal contact rivet

Bimetal contact rivets combine a contact head made of silver material with a shank made of copper or a copper alloy. This reduces precious metal usage without fundamentally impairing the electrical function of the contact surface.

Trimetal contact rivet

Trimetal contact rivets consist of multiple metallurgically bonded layers. They enable targeted adaptation to electrical and mechanical requirements, but require more complex manufacturing and tight process control.

Manufacturing of contact rivets

Wire as starting material

Manufacturing typically starts from wire. Wire quality directly affects dimensional stability, microstructure and surface condition of the finished rivet.

Depending on design, solid, composite or multilayer wires are used and adapted to the subsequent forming process in terms of material combination, diameter and microstructural condition.

Forming processes

Forming is typically carried out on multi-stage machines. Wire sections are cut and the contact head is produced by cold forming. Depending on the material, intermediate annealing may be required to ensure defined formability.

Process stability

Stable production requires:

• homogeneous microstructure
• clean surfaces
• defined hardness condition

Deviations directly influence the downstream riveting process.

Assembly: setting contact rivets

Setting is typically integrated inline into stamping or assembly operations. The shank is plastically deformed and forms a closing head on the backside of the carrier.

Key influencing factors include:

• hole diameter and hole quality
• setting force and tool geometry
• material combination of rivet and carrier

A properly designed setting process is essential for a gas-tight joint with low contact resistance.

Typical applications of contact rivets

Contact rivets are used in a wide range of electromechanical systems, particularly in electrical engineering and installation technology.

Typical fields of use include:

• relays and auxiliary contactors
• lighting and installation switches
• thermostats and temperature sensors
• motor protection and circuit protection devices
• electromechanical contact assemblies

Contact rivets are also used in the automotive sector, for example in relay and switching assemblies, where higher requirements for material selection and process stability typically apply.

Practical design criteria

For functional reliability, several parameters must be considered together:

• current type (AC or DC)
• switching and continuous current
• load type (resistive, inductive, capacitive)
• switching frequency
• contact force and contact geometry

Optimizing individual parameters in isolation often leads to issues in practice.

Quality assurance and testing

Contact rivets are typically checked for:

• dimensions and form
• surface condition
• microstructure and hardness
• bond strength for composite designs

In addition, electrical tests are often performed in the assembled state.

Selection criteria for engineering and purchasing

In industrial practice, both engineering and purchasing are involved. While engineering focuses on function, service life and process reliability, purchasing emphasizes cost stability, availability and consistent quality. A robust selection concept must cover both perspectives.

Engineering perspective

Key criteria include electrical load, current type, load type, required switching life, contact force and environmental conditions. Contact rivets must be considered as part of the overall system together with carrier, counter-contact and mechanical design.

Purchasing perspective

Typical criteria include precious metal content, options for bimetal/trimetal designs, batch sizes, consistent quality over time, and traceability/quality documentation. Technical support helps avoid overdesign and cost.

Shared decision basis

Close coordination between engineering and purchasing has proven effective. Technically sound design reduces later field issues and change effort, while economically optimized design keeps piece costs stable.

Economic considerations

At high volumes, contact rivets are a very stable and economical solution. Precious metal usage is cost-relevant, so composite designs are widely established in many applications.

FAQ about contact rivets

When are contact rivets preferable to welded contacts?

For high volumes with clearly defined contact positions and automated processes, contact rivets often provide high process stability without thermally stressing the carrier.

Which silver materials are commonly used?

AgNi and AgSnO₂ are commonly used. Selection is always application-dependent.

Are contact rivets suitable for DC switching?

Generally yes. However, DC requires particularly careful material selection due to erosion and material transfer effects.

Are cadmium-containing contact rivets ruled out?

Use depends on application and the regulatory framework. In some cases, valid exemptions may exist.

What does the service life of a contact rivet depend on?

On material, contact force, switching load, switching frequency and environmental conditions.

Which information should purchasing provide when requesting contact rivets?

For a technically robust and economically sensible design, not only quantities should be provided. In practice, the following information is essential:

• intended application (e.g., relay, installation switch, thermostat)
• current type (AC or DC) and approximate switching/continuous currents
• load type (resistive, inductive, capacitive), if known
• desired or previously used contact material
• contact rivet version (solid, bimetal, trimetal) and available installation dimensions
• requirements for service life, quality assurance or traceability

Incomplete information often leads to follow-up questions or to conservative overdesign. A coordinated specification between engineering and purchasing supports reproducible production and stable series supply.

 

Note: Further technical information on contact parts, materials and applications can be found in the knowledge section of AX-METALS GmbH. For technical questions or project-related coordination, please contact us.