## Introduction

Arc Energy calculation is specified in ISO/TR 18491 for most ISO welding standards.

There are 3 equations quoted for calculating arc energy:

Where the symbols are:

Abbreviations and symbols |
Term |
Unit |

I | Arc welding current | A |

L | Length of run | mm |

U | Arc voltage | V |

v | Travel speed | mm/s |

E | Arc Energy | kJ/mm |

IE | Instantaneous energy | J |

IP | Instantaneous Power | J/s |

*Table **1** Symbols of Terms used (ISO/TR 18491:2015(E))*

ISO/TR 18491 specifies the arc energy calculation. To change arc energy to heat input the arc energy is multiplied by the process efficiency.

The equations 2 and 3 are essentially the same and are measuring instantaneous power. Equation 1 is more of the traditional approach and is using average value of voltage and current.

According to ISO/TR 18491 all 3 equations are permitted for power sources that do not employ direct electronic control of the waveform, noted as “non-waveform controlled” power sources. If the welding process is a controlled waveform power source equations 2 or 3 must be used. This means using a meter capable of monitoring voltage and current simultaneously to determine the instantaneous energy or power.

A waveform controlled power sources is defined as:

“All pulsed welding processes, for example, pulsed gas metal arc welding, are waveform-controlled welding processes. Power sources that are sold as synergic, programmable, or microprocessor-controlled are generally capable of waveform-controlled welding.”

The differences can be very high between the calculation methodologies. These are some examples.

## TIG power source Arc Energy Calculation

### DC TIG

DC TIG is probably the simplest waveform to deal with electronically. This is a typical 0.1 second sample.

*Figure **1** DC TIG Waveform (0.1 second)*

Not surprisingly both calculation methods give the same result.

*Method 1. *

Average current: 115.6 A

Average voltage: 10.2 V

Say the welding is performed at 120 mm/min (2mm/s). Equation 1 is:

E = 0.590 kJ/mm

*Method 2 and 3. *

Instantaneous power is the average of every measurement of U x every measurement of I.

Taking the first few data points:

Voltage (V) | Current (I) | Energy (UxI) (J) | |

10.12 | 115.66 | 1170.96 | |

10.07 | 115.79 | 1166.26 | |

10.07 | 115.79 | 1166.26 | |

10.03 | 115.66 | 1160.44 | |

10.05 | 115.79 | 1163.25 | |

10.05 | 115.66 | 1161.95 | |

10.05 | 115.66 | 1161.95 | |

10.05 | 115.66 | 1161.95 | |

10.06 | 115.92 | 1166.05 | |

10.03 | 115.92 | 1163.04 | |

10.02 | 115.92 | 1161.54 | |

10.05 | 115.92 | 1164.55 |

Then averaging the Energy column gives the average instantaneous power J/s. In this case 1184.67 J/s. Hence equation 3 becomes:

E = 0.592 kJ/mm

Both methods give the same answer within 1%.

### Pulse TIG

Under ISO/TR 18491 it could be argues that pulse TIG is a controlled waveform power source.

*Figure **2** Pulse TIG Waveform (0.7 second)*

The waveform is still very clean, and the voltage only changes slightly as the current pulse comes on and off.

*Method 1. *

Average current: 111.7 A

Average voltage: 10.8 V

Say the welding is performed at 120 mm/min (2mm/s). Equation 1 is:

E = 0.603 kJ/mm

*Method 2 and 3. *

*PI = 1210.73*

E = 0.605 kJ/mm

Difference less than 1% in this case.

## MIG Power Source Arc Energy Calculation

### Spray transfer MIG welding

Spray transfer MIG is closest to DC TIG, but not such a clean waveform.

*Figure **3** SPRAY transfer MIG 0.1 second*

*Method 1. *

Average current: 199.0 A

Average voltage: 29.7 V

Say the welding is performed at 120 mm/min (2mm/s). Equation 1 is:

E = 2.955 kJ/mm

*Method 2 and 3. *

*PI = 5899.77*

E = 2.949 kJ/mm

Difference less than 1%

### DIP transfer MIG welding

*Figure **4** DIP transfer MIG 0.1 second*

*Method 1. *

Average current: 97.2 A (averages based on 0.5 seconds of data)

Average voltage: 17.5 V

Say the welding is performed at 120 mm/min (2mm/s). Equation 1 is:

E = 0.851 kJ/mm

*Method 2 and 3. *

*PI = 1699.1*

E = 0.850 kJ/mm

Again, less than 1% difference.

### Pulse MIG Welding

Pulse MIG welding is considered a controlled waveform power source.

*Figure **5**Pulse MIG 01. Second*

*Method 1. *

Average current: 147.8 A (averages based on 0.5 seconds of data)

Average voltage: 24.8 V

Say the welding is performed at 120 mm/min (2mm/s). Equation 1 is:

E = 1.833 kJ/mm

*Method 2 and 3. *

*PI = 4375.3*

E = 2.188 kJ/mm

Method 2 and 3 produces an arc energy 20% higher than Method 1.

Controlled DIP transfer

This is waveform that is controlled by the power source to minimise spatter and improve the welding process stability.

*Figure **6** Controlled DIP transfer 0.1 second*

*Method 1. *

Average current: 180.8 A (averages based on 0.5 seconds of data)

Average voltage: 18.9 V

Say the welding is performed at 120 mm/min (2mm/s). Equation 1 is:

E = 1.709 kJ/mm

*Method 2 and 3. *

*PI = 3764.6*

E = 1.882 kJ/mm

Method 2 and 3 produces an arc energy 10% higher than Method 1.

## Summarising Arc Energy Calculation

### Comparing the results

Process |
Method 1 |
Method 2 &3 |
Difference |

DC TIG | 0.590 | 0.592 | 0.4% |

Pulse TIG | 0.603 | 0.605 | 0.3% |

Spray MIG | 2.955 | 2.949 | 0.2% |

DIP MIG | 0.851 | 0.850 | 0.1% |

Pulse MIG |
1.833 |
2.188 |
19.4% |

Controlled DIP |
1.709 |
1.882 |
10.1% |

For pulse MIG and controlled DIP it is important to use a monitor capable of recording instantaneous power. All our welding monitors are capable of providing arc energy calcluations based on instantaneous power.