In the manufacturing of relays, contactors, and high-performance switches, automated high-speed riveting using stamping equipment is the standard method for joining contact rivets to spring leaves. As the electrical industry advances, precision requirements for contact riveting have increased significantly. However, quality control teams frequently encounter persistent assembly defects during high-speed production—such as micro-cracks at the silver-copper interface, head cracking on AgSnO₂ contacts, surface impressions, and gaps or deformation between the contact and spring leaf.

When these issues arise, the contact rivet itself is often assumed to be defective. However, comprehensive failure analyses reveal that most riveting defects stem directly from dimensional mismatches between the contact head profile and the riveting die cavity.

As a specialized supplier of precision electrical contact solutions, SHZHJ provides an in-depth analysis of how die-to-contact matching impacts riveting quality and how precision tooling parameters eliminate assembly defects.

1. Impact of Die-to-Contact Mismatch on Riveting Quality

When the geometry of the riveting die cavity does not match the contact head, severe mechanical defects occur post-riveting. These mismatches include undersized or oversized cavity diameters, incorrect cavity depths, improper draft angles, improper spherical radii (SR), and incorrect transition radii (R).

1.1 Interface Micro-Cracks at the Silver-Copper Joint

• Riveting Conditions: Tests were conducted using bimetal rivets () on automatic stamping equipment with pressure using a V-shaped conical riveting tool. Quality requirements specify a tail expansion of, zero cracking at the silver-copper interface, zero gap between contact and leaf, and a smooth surface finish.
• Defect Analysis: Microscopic observation and cross-sectional testing revealed dark lines and micro-cracks were detected along the silver-copper bonding edge.
• Root Cause: Conical riveting decomposes forces into axial and radial vectors, improving shank expansion but delivering high instantaneous impact to the contact head. If the contact head does not fit tightly against the bottom of the die cavity (especially near the transition radius ), instantaneous shock deforms the head. Because the bonding edge of the bimetal joint is mechanically the most vulnerable zone, cracks form under impact easily.
• Contributing Die Mismatches: Undersized/oversized die cavity diameters, undersized/oversized draft angles, oversized spherical radii (SR), or undersized transition radii (R).

1.2 Surface Cracking on AgSnO₂ Contacts

When riveting Silver Tin Oxide (AgSnO2) contacts, radial cracking frequently occurs along the outer edge of the contact head. The primary cause is an oversized die cavity, which allows the contact head to undergo excessive secondary expansion during compression, accelerating head cracking.

• Contributing Die Mismatches: Oversized die cavity diameter, undersized draft angle, or oversized spherical radius (SR).

1.3 Surface Impressions and Flaking

Impressions on the contact working face are primarily caused by an undersized die cavity. During entry, the side of the contact head forcefully scrapes against the cavity wall, generating fine metallic debris. These loose particles stick to the inside of the die and press into subsequent contact faces during stamping.

• Contributing Die Mismatches: Undersized die cavity diameter, oversized draft angle, or undersized transition radius (R).

1.4 Gaps and Component Distortion

• Gaps Between Contact and Leaf: Occur when the die cavity volume is larger than the contact head volume, preventing the head material from filling the cavity.
• Spring-Leaf Deformation: Occurs when the die cavity volume is smaller than the contact head volume. Excess contact material overflows and distorts the copper leaf (causing indentations or downward bowing). Additionally, undersized draft angles or rough cavity sidewalls prevent smooth ejection, leading to leaf deformation.
• Contributing Die Mismatches: Undersized/oversized cavity diameters, incorrect cavity depths, or undersized draft angles.

2. Precision Tooling Parameters for Optimum Matching

To ensure a tight fit during riveting, eliminate gap clearances, and prevent edge cracking, die cavity dimensions must be calibrated against actual scanned contact head dimensions:

1. Dimensional Scanning: Contact head T-thickness is measured with a micrometer. The head diameter (D), draft angle (θ), spherical radius (SR), and transition radius (r) are scanned using optical projection point-cloud alignment and converted to CAD geometry.

2. Calibrated Cavity Dimensions:

• Cavity Diameter: Set to the maximum measured contact head diameter (6.120mm).
• Cavity Depth: Set to the minimum measured contact head thickness minus 03mm (1.520mm).
• Draft Angle: Set slightly larger than the maximum contact draft angle by  5°(17.5°).
• Spherical Radius (SR): Set slightly smaller than the minimum contact spherical radius by 5 mm (16.0 mm).
• Transition Radius (R): Set slightly larger than the maximum contact transition radius by 05mm (0.5mm).

3. Entrance Relief Chamfer: When maximum contact thickness (1.586mm) exceeds cavity depth (1.520mm), excess material has no expansion space, intensifying impact forces on the contact base. Adding a rounded entrance chamfer at the mouth of the die cavity provides a designated buffer zone for excess material, reducing base impact and preventing die sticking.

Validation Results: Testing across 3 separate batches ( 100 units each) and subsequent continuous mass-production runs of 50000 units achieved zero interface cracking, zero gap clearances, and full compliance with all technical requirements.

Technical Cooperation with SHZHJ

Achieving consistent, zero-defect contact assembly requires precise coordination between contact dimensions and riveting tooling parameters. SHZHJ supports global switchgear, relay, and contactor manufacturers through:

• Precision Contact Rivets: High-consistency bimetal contact rivets tailored for high-speed automated stamping equipment.
• Tooling Alignment & Technical Guidance: Engineering review of your contact drawings and die cavity parameters to eliminate assembly defects prior to mass production.
• Pre-Assembled Riveting Solutions: Fully riveted and stamped contact leaf assemblies tested for zero-gap bonding and defect-free surface finish.

Meet Our Engineering Team at InnoTrans 2026

Are you looking to optimize contact assembly yields or resolve riveting defects on your production lines? Meet the SHZHJ technical team at InnoTrans 2026 in Berlin to review your drawings and specifications.

📍 Venue: Messe Berlin, Germany

🏛️ Location: Hall 11.1, Stand 115

📩 Technical Inquiries: Contact us at info@shzhj.com or visit www.shzhj.com to request sample proposals and engineering evaluations.