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Like any filler metal, the metal-cored wire has unique characteristics, benefits and limitations. When used in the correct applications, metal-cored wires will help improve quality, minimize costs and increase productivity. In this article, we will discuss the characteristics of the metal-cored wire and its most appropriate applications.
The Fundamentals of Metal-Cored Wire
Metal-cored wires are similar to flux-cored wires in that both types of filler metals have a tubular construction. However, metal-cored wires do not produce a slag that must be removed after each welding pass, resulting in a higher deposition efficiency and lesser post-weld cleaning as compared to flux-cored wires.
Metal-cored wires are filled with metallic powders, alloys and arc stabilizers. This composition can vary depending on the desired properties and characteristics such as lowering oxidation, achieving higher strengths and reducing silicon deposits on the weld metal.
Even though the technique for welding with metal-cored wire is comparable to that of solid wire, the metal-cored wire actually produces a different welding arc and weld profile characteristic. Because of its tubular construction, the welding current only passes through the outside metal sheath instead of through the entire cross-sectional area as with solid wire. Therefore, for the same welding current, the metal-cored wire will carry a higher current density. This gives metal-cored wires a wide penetration profile, as well as a higher deposition rate as compared to solid wire.
Metal-Cored Wires Versus Solid Wires
Firstly, metal-cored wires offer significantly higher deposition rates compared to solid wires in many applications. This means that the welder can weld at higher travel speeds and reduce distortion on critical components. For the welding operation, this leads to a higher throughput and lesser rework.
Secondly, because of the wide penetration profile, metal-cored wires are more tolerate of poor part fit-up and will bridge gaps more easily and accurately without burn-through.
Lastly, metal-cored wires present distinct productivity benefits in the pre-weld and post-weld phases of the welding operation. Metal-cored wires tend to be more tolerant of dirt, mill scale and rust, which are commonly found on the base material. Because the material doesn’t have to be as clean to produce high-quality welds, non-value-added activities such as cleaning and grinding prior to welding can either be reduced or eliminated. When metal-cored wires are used, the process tends to produce very little spatter and minimal weld defects such as porosity, lack of fusion and undercuts. This means that the post-weld activities such as grinding and chipping of spatter are usually not required, and there will also be a reduction in rejection rates.
The reduction or elimination of the pre-weld and post-weld activities can increase the flow of the completed parts to other stages of the production, and also free up labour that can then be reallocated to other sections of the welding operation to produce more parts. This will help improve the overall productivity of the facility.
Identify the Correct Applications for Metal-Cored Wires
Metal-cored wires are easily alloyed and available in many different chemistries. This makes them suitable for welding a wide variety of base materials including mild steel, low-alloy steel and stainless steel. Because of its ability to provide a wide bead profile and high travel speeds, the metal-cored wire is well suited for the automotive industry for the welding of the chassis and steel wheels. The metal-cored wire has also been used for welding heavy equipment and rail cars since it can easily weld through mill scale and rust and has a high deposition rate which is ideal for welding the thick plates found in these applications. Metal-cored wires have also been used for the welding of piping in the food and petrochemical industries, as well as other components that are prone to burn-through or those that require exceptional bead appearances.
Generally speaking, any existing application that uses solid wire for welding of welds that are 3 inches or longer, in the flat or horizontal position with spray transfer mode, can be converted to the metal-cored wire. For such a conversion, companies usually choose to increase the wire diameter of the metal-cored wire by one size over the solid wire, thereby eliminating the need for multiple different sizes of solid wire in the welding operations. Standardizing on one diameter of metal-cored wire helps to improve the logistics and minimize errors in production.
While metal-cored wires offer multiple benefits in many applications, it is not always the best product to use in every circumstance. Metal-cored wires have a higher initial investment cost as compared to solid wires. So, if the application involves many short welds with a lot of starts and stops, then the extra cost will not pay-off in welder efficiency or productivity. In addition, if the welding operation is not the bottleneck in the entire production process, then increasing the welder’s productivity by increasing the deposition rate will not result in any advantage to the overall productivity of the facility. Lastly, metal-cored wires are also not ideal for welding applications that involve plenty of vertical and overhead welding.
Make an Informed Decision
Selecting the best filler metal for the job shouldn’t be taken lightly. Using a metal-cored wire can help increase productivity, save money and reduce quality issues if it is used in the correct application. If you have any doubts, always contact your trusted filler metal supplier to have a discussion.