ISO 18278-2:2016

Overview

ISO 18278-2:2016 - Resistance welding - Weldability - Part 2: Evaluation procedures for weldability in spot welding specifies laboratory test procedures to determine the acceptable welding current range and electrode life for resistance spot welding. It applies to assemblies of uncoated and coated sheets with individual thicknesses from 0.4 mm to 6.0 mm and is intended to characterize the effects of electrode design, material, cooling and welding equipment on spot weld quality.

Key topics and technical requirements

• Scope and purpose: Defines procedures to evaluate weldability in spot welding by measuring welding current range and electrode life.
• Welding equipment & electrodes:
  • Electrodes shall be of type A 2/2 material (see ISO 5182) and have geometry defined per ISO 5821.
  • Electrode conditioning: electrodes shall not be conditioned before tests.
• Welding current and control:
  • Specify AC or DC; use constant current control.
  • For AC equipment, welding current shall be at least 30% of RMS value at full conduction angle.
• Mechanical settings:
  • Limit electrode impact (recommend approach speed 0.15 m/s and/or peak force < 150% of nominal).
  • Squeeze time must allow electrode force to build before current initiation.
• Electrode cooling:
  • Inlet water 20 °C (max 30 °C); separate water supply per electrode; minimum 4 l/min per electrode. Cooling passages and dimensions must comply with referenced ISO requirements.
• Measurements & detection:
  • Welding current and force per ISO 18278‑1.
  • Weld diameter measured after destructive testing (see ISO 17677‑1).
  • Expulsion detection via visual inspection or monitoring of electrode displacement, welding voltage or electrode force signals.
• Test procedures:
  • Use three specimens per current setting (two for destructive testing, one reserved).
  • Start below bonding current and increase current in 200 A steps, never decreasing. Continue until 10% above the current at which splashing (expulsion) first occurred.
• Alignment tolerances:
  • Electrode eccentricity < 0.5 mm; angular deflection ≤ 5° (methods in Annex A).

Practical applications and users

This standard is used by:

• Welding engineers and R&D teams evaluating material and coating weldability
• Process qualification and quality assurance teams in automotive, aerospace and metal fabrication
• Resistance welding equipment and electrode manufacturers
• Test laboratories performing spot weld characterization and electrode life testing

Benefits include standardized, repeatable methods to define safe welding current ranges, optimize electrode design/cooling and predict electrode life to reduce scrap and improve production consistency.

Related standards

Normative references include: ISO 669, ISO 5182, ISO 5821, ISO 10447, ISO 14270, ISO 14272, ISO 14273, ISO 14373, ISO 15609‑5, ISO 17653, ISO 17677‑1, ISO 18278‑1 - all relevant for implementing and interpreting ISO 18278-2 test procedures.