Free reference
Welding math
Not many formulas, but the ones there are turn up constantly — and they turn up under time pressure. Each page gives the formula, what every symbol means, and worked examples you can follow line by line.
Every number on these pages is tested
The worked examples are not typed out by hand and hoped for. Each one is checked against the calculator implementation in the test suite, so a transcription slip fails the build rather than teaching you the wrong answer.
Heat and energy
4 topicsHI = (V x I x 60) / (1000 x v)Heat InputHeat input packages volts, amps, and travel speed into one number that predicts how hot the joint gets and how slowly it will cool, which is why procedures control it rather than the three parameters separately.v = distance / time, or v = (V x I x 60) / (1000 x HI)Travel SpeedTravel speed is the one welding parameter set entirely by the welder's hand rather than the machine, and it is also the parameter that heat input is most sensitive to, which makes measuring it worth the stopwatch.HI_eff = f x (V x I x 60) / (1000 x v)Arc Energy and Arc EfficiencyNot all the energy an arc produces ends up in the steel, and the fraction that does depends heavily on the process, which is why the same gross heat input means different things under a flux blanket and under an open tungsten arc.T_preheat rises with thickness, carbon equivalent, hydrogen, and restraintPreheat and Interpass TemperaturePreheat slows the rate at which a weld cools through the transformation range, giving hydrogen time to diffuse out and giving the heat affected zone a chance to form something tougher than untempered martensite.
Weld geometry
5 topicst = leg x cos45 = leg x 0.7071, and leg = t / 0.7071Fillet Weld Leg and ThroatA fillet is specified by its leg but carries load across its throat, and the constant 0.7071 that converts between them is just the cosine of the forty-five degree angle an equal-leg fillet makes.A = leg^2 / 2, Vol = A x L, W = Vol x densityFillet Weld Area, Volume, and WeightEstimating filler metal starts with the area of a triangle: half the leg squared gives the cross-section, length turns it into volume, and density turns volume into the pounds a job will actually buy.A = (R x T) + (T - f)^2 x tan(angle / 2)Groove Weld Cross-Sectional AreaA single-V groove splits neatly into a rectangle at the root and two triangles above it, which turns a fabrication estimate into two pieces of secondary-school geometry.A_reinf = (2/3) x w x h, convexity% = 100 x h / wWeld Reinforcement and ConvexityThe crown on a weld face is close enough to a parabolic cap that two thirds of width times height gives its area, which turns an eyeballed hump into pounds of filler and a measurable convexity ratio.A_gap = R x T, A_extra = (R_actual - R_nominal) x TJoint Fit-Up and Root OpeningA root opening is a parallel-sided slot, so every extra thousandth of gap costs a full thickness of filler metal along every inch of joint, which is why fit-up is a cost control and not just a quality one.
Metallurgical parameters
3 topicsCE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15Carbon Equivalent (IIW)Carbon equivalent rolls a steel's whole alloy content into one carbon-like number so two very different chemistries can be compared for how hard their heat affected zones will get when a weld cools fast.Pcm = C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5BPcm Cracking ParameterPcm is a carbon equivalent tuned for modern low-carbon steels, where the older expression penalises manganese so heavily that a perfectly weldable plate can be flagged as difficult.Dilution% = 100 x (base metal melted / total weld pass)Dilution PercentageEvery weld pass is a mixture of filler metal and melted base metal, and dilution is the fraction that came from the base plate, which is what determines the composition the deposit actually ends up with.
Productivity
2 topicsDR = W_deposited / t_arc, or DR = melt-off rate x efficiencyDeposition RateDeposition rate measures how fast a process puts metal in the joint while the arc is actually burning, which is only half the productivity picture and often the less important half.OF% = 100 x (arc time / total time), W = DR x arc hoursOperating Factor and Arc TimeOperating factor is the fraction of a paid shift during which the arc is actually burning, and because it varies far more between shops than deposition rate does, it is usually where the real productivity difference lives.