Overview
EN ISO 18594:2007 (ISO 18594:2007) defines a standardized method to measure the transition resistance in resistance welding processes - specifically resistance spot-, projection- and seam-welding - for aluminium and steel sheet(s). The standard describes the experimental set‑up, measurement procedure and reporting requirements for single sheets or two overlapping sheets, with or without surface treatment or coating. It is intended for consistent, comparable assessment of electrical contact behavior in the weld zone.
Key topics and technical requirements
- Concepts and definitions: contact resistance, bulk resistance, total resistance, set‑up resistance and transition resistance (transition resistance = total − set‑up resistance).
- Measuring set‑up: electrodes, sensing clamps, d.c. power source and voltmeter configuration to measure voltage drop between sensing clamps while current flows through specimen.
- Measurement procedure:
- Prepare specimens (recommended size example 50×100 mm) and record surface condition (oiled, phosphated, conversion coated, etc.).
- Measure set‑up resistance (electrodes in direct contact) before and after each test series; use the mean as the set‑up resistance for the series.
- For each specimen perform a minimum of seven total-resistance measurements at locations ≥15 mm from centre/edge; record voltage after (15 ± 1) s under nominal electrode force.
- Use at least five test pieces from different locations to calculate mean, standard deviation and coefficient of variation.
- Equipment and limits (examples from Table 1):
- Electrode material: CuCrZr or CuCr; recommended diameters ~20 mm (aluminium) and ~16 mm (steel).
- Electrode force: 5–7.5 kN (aluminium), 3.5 kN (steel) with ±5% accuracy.
- d.c. set‑up current e.g. 10 A (up to <100 A), digital voltmeter sensitivity ~1 µV.
- Mechanical requirements: high stiffness to avoid electrode sliding; electrode axis eccentricity ≤ 0.1 mm; sensing clamp distance > 15 mm from current introduction.
