Overview
ISO/TR 18491:2015 - Welding and allied processes - Guidelines for measurement of welding energies - provides practical guidance on how to measure the parameters needed to calculate arc energy and heat input for arc welding processes. The Technical Report explains measurement methods for traditional and modern, waveform‑controlled power sources, highlights common sources of error, and gives recommendations to ensure consistency between welding procedure qualification and production.
Key topics and requirements
- Arc energy vs heat input: The report distinguishes arc energy (product of arc voltage and current divided by travel speed) from heat input, which is arc energy adjusted by an arc efficiency factor. Measurement methods are the same for both.
- Three measurement methods:
- Method A: Calculate from arc voltage, welding current and travel speed.
- Method B: Calculate from instantaneous energy and run length.
- Method C: Calculate from instantaneous power and travel speed.
- Note: For waveform‑controlled welding (e.g., pulsed GMAW, synergic or microprocessor‑controlled sources) Methods B or C are recommended; Method A can introduce errors up to about 70%.
- Measurement parameters:
- Arc voltage: Measure as close to the arc as practical to avoid cable voltage drop; record connector positions in the WPQR/WPS.
- Welding current: Use a shunt or clamp meter on a straight cable section; include all return/earth conductors.
- Instantaneous energy/power: Use meters or power sources capable of true energy/power calculations with sampling rates sufficient to capture waveform changes (typical guideline: sampling ≥10× waveform frequency).
- Travel speed and run length: Determine by depositing a run, measuring time and length, or by built‑in mechanized welding meters.
- Calibration and validation: Calibrate or validate measuring instruments per ISO 17662.
Practical applications and users
ISO/TR 18491:2015 is used to:
- Verify and document Welding Procedure Specifications (WPS) and Welding Procedure Qualification Records (WPQR) consistent with ISO 15607 / ISO 15614 requirements.
- Support quality control during fabrication by welding engineers, inspectors, QA/QC personnel, and certification bodies.
- Guide suppliers of welding power sources and external meters on measurement capability for true power/energy and sampling requirements.
- Apply to manual, mechanized and multi‑arc welding operations; for multi‑arc systems measure each arc individually.
Related standards
- ISO 15607 / ISO 15614 - Welding procedure specification and qualification.
- ISO 17662 - Calibration, verification and validation of welding equipment and measuring devices.
- ISO/TR 17671 (all parts) - Recommendations for welding of metallic materials.
Keywords: ISO TR 18491:2015, welding energy measurement, arc energy, heat input, waveform-controlled welding, instantaneous power, welding calibration.
