In Part 1 of this report (see WD&F, September/October 2009, p. 9), we used a version of dimensional analysis that I learned from my grandfather to derive a basic equation that can be used to estimate welding costs. In Part 2, we'll put that equation to work, and in the process, learn how to reduce welding costs.

Previously, we determined that welding costs are generated from four general categories, as follows:

• Labor and Overhead Cost
• Filler Metal Cost
• Shielding Gas Cost (where applicable)
• Electrical Cost

As an illustration of representative welding data, the Table is reproduced here, and will be used in the following computations.

We also show Step 6 - Total Cost per Pound again here.

With this data, it is a simple process to insert the values into the equation shown in Step 6, leading us to the Cost Calculation.

The pie chart illustrates how these four cost components contribute to the total cost.

By far, the biggest cost of welding is the skilled labor and overhead that goes into making the weld — in this case, 83 percent. To reduce this component of the total cost, the labor and overhead cost must go down, the deposition rate must go up, or the operating factor will have to increase. Reducing labor and overhead costs is usually impractical, so efforts to reduce welding costs typically rely on achieving higher welding deposition rates.

Instead of welding at, say, 10 pounds per hour, let's assume a weld of comparable quality could be made at 12 pounds per hour. We can quickly plug 12 pounds per hour into the equation above, and find that the labor component goes from $16.67/lb. to $13.89/lb., saving $2.78/lb. This is a 14 percent decrease in the overall cost per pound.

But, you may say… “To get the increased deposition rate, the welding current will go up. How will this affect electrical costs?”

Good point. Once again, the derived equations are helpful. To keep things simple, let's assume that the 20 percent increase in deposition rate requires a 20 percent increase in current, so instead of 335 amps, 400 amps are needed. However, notice that the cost per pound of weld deposit doesn't change, because this higher value for amperage is divided by the deposition rate. In other words, the two increases cancel each other out.

If there is no need to increase the shielding-gas flow rate, the increase in deposit rate will reduce the cost of shielding gas per pound of weld deposited. This contributes an additional 11 cents per pound to the savings. When combined with the labor savings, this takes the total savings to $2.89/lb.

Let's return to the labor and overhead component of cost. Another way to decrease this cost is to increase the operating factor, the amount of time the arc is actually lit. Increasing the arc time can reduce welding costs substantially, but this area of opportunity is often overlooked.

For example, consider the time wasted (and the corresponding reduction in operating factor) due to these activities:

• Frequent changing of 30-lb. wire spools where bulk packaging is feasible
• Time lost waiting for a crane to arrive to rotate a part, vs. the use of a welding positioner
• Looking for misplaced tools
• Downtime due to clogged gas cups, plugged liners, etc.
• Weld repairs (removal of faulty weld, then rewelding the same part)

If eliminating one or more of these activities can result in an operating factor increase from 30 percent to 35 percent, the overall cost decreases by 12 percent, or $2.38/lb.

Let's next look at filler metals, which account for 13 percent of overall costs. A change in filler metal supplier might be able to reduce the purchase cost by, say, 10 percent, resulting in a direct savings of 10 percent per pound of filler metal purchased, but this is only 26 cents/lb. of deposited weld. If the lower cost filler metal caused any production problems, such savings would be quickly eroded.

For shielding gas costs, we will consider the effect of a reduction in flow rates of 5 cubic feet per hour. Such a reduction would reduce overall costs per pound by 7.5 cents. Again, if such a reduction resulted in quality problems, costs will actually increase.

Finally, let's analyze electrical costs. In our example, a power source electrical efficiency of 80 percent was assumed. What if a 90 percent efficient machine was used instead? This will result in an 11 percent savings in electricity, or 1.7 cents per pound of weld deposited.

All of the above examples are simple illustrations, and to be clear, perhaps none of them are possible: you need to determine your current welding costs and then determine the impact of any potential changes you might make to reduce your costs.

As the bar chart shows, we found that, for the specific conditions studied:

1. A 20 percent increase in deposit rate reduced overall costs by $2.89/lb.

2. A 5 percent increase in operating factor reduced overall costs by $2.38/lb.

3. A 10 percent reduction in the filler metal cost reduced overall costs by $0.26/lb.

4. A 5 cubic foot per hour reduction in gas flow rate results in a $0.075/lb. reduction.

5. A 10 percent increase in the power source efficiency reduced overall costs by $0.017/lb.

The above numbers speak for themselves: if you really want to reduce your welding costs, you need to devote time and attention to reducing the labor and overhead cost. And dimensional analysis, as my grandfather taught me, is a great tool for deriving the equations that will lead us to the correct conclusion.

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Omer W. Blodgett, Sc.D., P.E., senior design consultant with The Lincoln Electric Co., struck his first arc on his grandfather's welder at the age of ten. He is the author of Design of Welded Structures and Design of Weldments, and an internationally recognized expert in the field of weld design. In 1999, Blodgett was named one of the “Top 125 People of the Past 125 Years” by Engineering News Record. Blodgett may be reached at (216) 383-2225.