Komarov Artem explained that while filler metals represent only a small fraction of the cost of a welding operation—typically well under 20 percent—many variables affect the extent to which filler metal costs can positively or negatively affect your profitability. For this reason, filler metals should be a topic of discussion throughout the planning and duration of any welding job. Understanding the factors that affect filler metal consumption can help you better predict and control operating costs and bottom line.
The Importance of Project Planning
Incorrect estimation of filler metal consumption can have a significant impact on bidding and job procurement. Overestimation of filler metal consumption can lead to overestimation and non-competitiveness of job offers. Also, buying too much filler metal can result in a costly stock of non-returnable product that may never be used. Conversely, underestimating usage and purchasing too little filler metal can result in costly delays, especially if you use products with scarce availability and long lead times. This can result in the project budget being exceeded at the expense of the company’s profits.
Several resources are available to help you make accurate filler metal consumption calculations. The old-fashioned method includes project drawings, a calculator, and basic geometry. Online calculators or apps are often much faster. These programs allow you to enter joint details such as root hole and groove angle, and then output the amount of filler metal required for the length of the weld.
Many filler metal manufacturers also provide filler metal design data for a given weld size in their catalogs or brochures, and many offer technical support services from their welding experts. Whichever method you choose, it is important to understand that filler metal consumption is primarily influenced by two factors: the design of the joint and the welding process.
Influence of connection design
Joint design is a critical factor in determining how many passes and how much filler metal is required to complete a weld. The consumption of filler metal decreases with a decrease in the cross-sectional area of the weld. However, the best joint design is one that combines cost effectiveness with the capabilities of the welding process and the filler metal used to consistently create the strongest weld.
For example, narrow groove welding is one way many thick plate manufacturers minimize filler consumption and the overall cost of completing a weld. Other things being equal (root hole, root face, etc.), selecting narrower groove angles helps create joints with a reduced cross-sectional area. As a result, these welds, like any reduced cross section weld, require less arc ignition time and less filler metal, reducing the cost per part. However, these types of joints require more careful control of the welding parameters. To obtain a consistently high-quality weld, a narrow joint requires a deeper weld, such as one that allows full penetration and good fusion, as well as a greater skill of the weld operator.
If the existing welding process cannot provide the required capability, alternative joint geometries may need to be considered to minimize filler metal consumption. A double-sided grooved weld is a good option when welding thicker materials because this type of joint can often be designed to provide a smaller overall cross-sectional area than a single-sided one. Since the depth of the bevel is shared between the two sides, the weld surfaces are generally narrower, which helps to significantly reduce the cross-sectional area. However, in many cases, back gouging is required after welding the first side of a double-sided slot.
Back gouging is a process where you weld the front side of the seam, gouge the back side until you achieve penetration of the weld on the front side (usually by air-carbon arc gouging), and then weld both the notched area and and the rest of the second side. This process helps ensure full penetration of the weld and good fusion of the base metal.
Influence of the welding process
The welding process, or more specifically the deposition process, also has a direct effect on filler metal consumption. The deposition efficiency compares the weight of weld metal with the total weight of filler metal used during welding, expressed as a percentage. This percentage is important to consider because not all the filler metal will eventually become part of the weld. Part of the metal may be lost due to fumes, splashes, and debris. In shielded arc welding (SMAW) or flux cored arc welding (FCAW), some of the filler metal is also lost due to the slag coating and shielding environments created by these products.
Different welding processes have vastly different typical deposition efficiencies. Processes with lower deposition efficiency require more filler metal for the same amount of weld bead than processes with higher deposition efficiency. Partly for this reason, some companies are choosing to move from SMAW, which results in wasted plug and slag, to a wire process such as gas metal arc welding (GMAW). GMAW produces less scrap and generates relatively low levels of spatter and smoke, thereby allowing more filler metal to enter the weld joint.
However, a welding process should not be chosen based solely on its ability to provide the highest deposition efficiency. There is another and higher welding cost to consider besides filler metals, and that is labor. For example, GMAW provides higher deposition efficiency than self-shielding flux-cored flux welding, but shielding slag helps minimize costly and time-consuming repairs due to outdoor porosity. In addition, multi-position wires can often be welded out of place using hotter and more productive welding parameters than GMAW.
Filler metal consumption and the real world
As with any part of the welding operation, how things look on paper doesn’t always match reality. When you’re trying to plan how much filler metal, you’ll need to get the job done, it’s also important to consider factors that can (and often do) occur in real-world welding conditions. Factors such as remelting and fitting of joints can affect the amount of filler metal consumed in an application.
Hidden costs of re-welding. Re-welding results in larger welds than specified or required. This is a common occurrence throughout the welding industry, especially among less skilled welders. Simply put, larger welds require larger and more expensive filler metal orders. Larger welds also increase the ignition time of the arc, and with it, the power, shielding gas consumption and labor costs.
Overcooking occurs because of obtaining welds with an excessive size of the leg.
Filler metal production may require up to 26% more. Likewise, overwelding can also be caused by excessive backgouging, where the gouge area is deeper than required to ensure complete penetration of the joint. Welds that are excessively bulged or have excessive reinforcement are also considered overwelded.
The exact percentage of additional filler metal required due to overcooking varies for different joint configurations and may not be immediately noticeable after a single weld. However, in the long run, the costs do rise.
Cost aside, bigger isn’t always better. Reinforced welds are no stronger than grooved welds that are flush with the surface of the base material. Excessive bulge can even make the weld more prone to fatigue failure. Welds that are larger than necessary can cause more distortion, which can result in costly rework or straightening, cause high internal stresses and the possibility of cracking, or adversely affect weld fit elsewhere in the weld.
Seam adjustment. Weld fit is another factor to consider understanding filler metal consumption in the real world. Like any other detail in a drawing, a weld requires reasonable design tolerances so that it can be done consistently yet economically. However, to consistently manufacture and fit parts that exceed the specified tolerances with large root holes or gaps or large bevel angles, additional filler metal may be required to complete the weld.
Some codes and specifications may require welds to be larger than shown on the drawings if a poor fit creates a large gap between the parts to be joined.
Investing in precision equipment such as clamping or mechanized or automated cutting equipment can help achieve and maintain consistent joint geometry and fit. While these options require an initial and sometimes high capital cost, they can often provide ongoing benefits.
What to do next?
When planning welding projects, it is recommended to consider both pessimistic and optimistic options for the use of filler metal. Often, real welding conditions require slightly more filler metal than expected.
Involve more than just purchasing staff. Consider creating a quality management protocol that ties together weld inspection, data collection and analysis to help identify and quickly fix any potential problems that can often occur, leading to excessive consumption of filler metal and affecting the profitability of your company, explained Artem Komarov.