Conversion and Calculations
Conversion and Calculations tests the handful of formulas that govern robotic arc welding, plus the unit discipline that keeps them right. Most items take one or two steps, and most errors come from mixing units.
Core formulas
- Heat input in kJ/in: (volts x amps x 60) divided by (1000 x travel speed in in/min).
- Heat input in kJ/mm: divide the kJ/in value by 25.4, or work directly in mm/min.
- Deposition rate in lb/h: 13.3 x wire diameter squared in inches x wire feed speed in in/min, then multiply by deposition efficiency.
- Wire feed speed: in/min x 25.4 = mm/min; in/min x 0.4233 = mm/s.
- Gas flow: cfh x 0.472 = liters per minute.
Unit discipline
Amperage and voltage must be arc values, not machine readings taken under different conditions. Travel speed must be actual TCP speed along the joint, including coordinated positioner motion. With a weave, instantaneous speed differs from programmed speed, and heat input calculations use programmed travel speed with the weave accounted for separately.
Worked example
A procedure runs 26 V, 220 A, and 12 in/min. Heat input = (26 x 220 x 60) / (1000 x 12) = 343,200 / 12,000 = 28.6 kJ/in, which is 28.6 / 25.4 = 1.13 kJ/mm. The WPS maximum is 1.5 kJ/mm. Production raises travel speed to 16 in/min for cycle time: (26 x 220 x 60) / (1000 x 16) = 21.5 kJ/in, or 0.84 kJ/mm, under the maximum. The reasoning matters: faster travel lowers heat input but also lowers penetration and invites lack of fusion, so the change still needs validation even though the heat input limit is met.
Second example
0.045 in wire at 350 in/min: 13.3 x 0.002025 x 350 = 9.4 lb/h at full efficiency, or about 8.7 lb/h at 92 percent deposition efficiency.
Traps
Dropping the 60; using wire feed speed where travel speed belongs; multiplying instead of dividing when converting kJ/in to kJ/mm; treating duty cycle and deposition efficiency as the same percentage.