Overview
ISO 18594:2007 specifies a standardized laboratory method to determine the transition resistance in resistance spot-, projection- and seam-welding for aluminium and steel. The standard defines the experimental set‑up, measurement procedure and reporting requirements for single sheets or two overlapping sheets - with or without surface treatment or coating - to quantify electrical contact and bulk resistances relevant to resistance-welding quality and process development.
Key topics and technical requirements
- Measurement principle: Total resistance is measured between sensing clamps and converted to resistance by Ohm’s law (R = U / I). Transition resistance Rt = total resistance − set‑up resistance.
- Set‑up resistance: Measured with electrodes in direct contact (no specimen). Mean of measurements before and after each test series compensates for pick‑up on electrode faces.
- Test specimens and sampling: Minimum seven measurements per specimen location; recommended at least five specimens from different positions to capture variability. Measurement points must be ≥15 mm from centre-to-centre and from specimen edges.
- Timing & sequence: Apply electrode force, energize d.c. current and measure voltage drop after (15 ± 1) s.
- Equipment and tolerances:
- Electrode stiffness with axis eccentricity ≤ 0.1 mm and electrode speed at contact ≤ 15 mm/s.
- Sensing clamps located >15 mm from current introduction; if electrode caps used, attach clamps to electrodes.
- Typical force ranges given: Aluminium 5–7.5 kN, Steel ~3.5 kN (max error ±5%).
- Electrode materials: CuCrZr or CuCr; example diameters W 20 mm (Al) and W 16 mm (steel); working-face radii specified.
- d.c. power source and voltmeter specifications and resolution requirements (micro‑ohm sensitivity).
- Statistics & calculations: Mean Rt, standard deviation and coefficient of variation calculated per Clause 6 using results from the test series.
- Reporting: Test report shall include results, test date, reference to ISO 18594:2007 and examiner’s name/signature. Annex A provides a sample report layout.
Applications and who uses it
- Welding engineers and quality control laboratories assessing resistance welding process consistency, weldability and electrical contact performance for aluminium and steel components.
- R&D teams developing electrode designs, coatings or surface treatments where contact resistance influences heat generation and weld quality.
- Automotive, aerospace and manufacturing QA departments performing comparative testing of materials/coatings, validating process parameters for spot, projection or seam welding.
Related standards
- ISO 5821 - Resistance spot welding electrode caps (referenced in the bibliography of ISO 18594:2007).
Keywords: ISO 18594, resistance welding, transition resistance, spot welding, seam welding, projection welding, aluminium, steel, measurement procedure, contact resistance, welding quality, test report.
Open preview (PDF)Resistance spot-, projection- and seam-welding — Method for determining the transition resistance on aluminium and steel material
