Metal Cored Welding Wires Their Advantages and Disadvantages

Manufacturers nowadays possess a broad selection of options in selecting the best welding approach and consumable to use for a certain application. The various considerations needed for deciding on this involve welder expertise, apparatus, availability of consumables, environmental challenges and economics of the procedure. One of the increasing approach for welding steel is the usage of metal cored wires for welding. better duty cycles, low fumes, faster travel speeds and cost efficiency are some of the key factors for their usage. The benefits and drawbacks of the metal cored welding wires can best establish if the approach can maximize efficiency and profitability.

Development of Metal Cored Wires

The carbon arc process to join two pieces of metal has gone through constant enhancement including the first coated electrode, the initial inert gas welding process (GTAW) as well as the initial submerged arc welding (SAW). The key purpose in every improvement is to increase the integrity of the weld, to make it swifter, more preliable, and more cost efficient via better work productivity. The solid wire process extended the usage of continuous solid wire applications to vertical and overhead welding which in turn are not conveniently adaptable to the SAW process.

Considering this, there have been many ground breaking designs for continuous welding that offer better deposition rates. However, a majority possessed problems and were not commercially possible till flux cored wire process was launched. Original large diameter flux cored wires offered improved metal penetration, smoother arc transfers, lower spatter levels and were less complicated to use than solid MIG wires, but they were constrained to flat and horizontal positions and the apparatus were heavy and complicated. As flux cored wires developed, smaller sized diameters came up leading to the potential to weld in all positions. Enhancements in equipment also made welding using flux cored wires more comfortable. These offered high deposition rates in the vertical and overhead placements. Acid or rutile slag methods provided high welder appeal, excellent mechanical properties and lent themselves to many purposes previously welded with the MIG or SAW procedure.

The final challenge to attain both high deposition rates or the quantity of weld metal deposited per hour and high deposition efficiencies that flux cored wires could not deliver was how much of the welding consumable could essentially become part of the weld deposit. The high efficiency level of flux cored wires retaining the high deposition efficiencies of the solid MIG wire method was needed. This emerged in the form of a fabricated composite cored wire recognized as the metal cored wire.

Metal Cored Welding Wires

Metal cored wires are classified under the American Welding Society specification with solid MIG wires - AWS A 5.18-93 for mild steel, AWS A5.28-98 for low alloy and AWS A5.9-93 for stainless steel. Metal cored wires have the same basic classification for strength level and chemical composition as solid MIG wire but are denoted by a “C” for composite wire. For example, a 70 KSI metal cored wire having a chemical composition and mechanical properties equivalent to an E70S-6 solid wire will be classified as an E70C-6 composite wire. Considered to have some characteristics equivalent to flux cored wires and additional characteristics similar to solid wire, metal cored wires do share a comparable structure to flux cored wires and overall performance similar to solid MIG wires.

The external metallic sheath of a cored wire conducts the electrical current for welding. Because of the fabricated, composite characteristics of cored wires, their current carrying density is increased, which enhances deposition rates at equivalent current levels when compared to solid MIG wires.

The internal parts of a metal cored wire are made up chiefly of the alloys, manganese, silicon, and in some situations, nickel, chromium and molybdenum as well as very small quantities of arc stabilisers such as sodium and potassium, with the balance being iron powder. Metal cored wires are able to have alloy compositions developed for specific applications in smaller batches as compared to the typical large heats of solid wire. several alloy compositions utilising chromium, nickel and molybdenum are available including austenitic and ferritic stainless steel alloys. Metal cored wires have minor to no slag creating ingredients in the internal fill of the wire. similar to solid MIG wire, welds produced with a metal cored wire just have small silicon islands from the deoxidising products that appear on the exterior of the weld. This makes it possible for multiple pass welding without deslagging.

Metal cored wires fit into specific welding use and certain factors require to be considered in selecting a metal cored wire. Metal cored wires deliver much advantage over flux cored wires or solid MIG wires for specific applications. To select if that specific application is appropriate take into take into consideration both the benefits and possible negatives of making use of metal cored wires.

High Deposition Efficiency

Whenever a weld is produced, a percentage of the welding consumable is shed to slag, spatter and fume. Deposition efficiency pertains to the quantity of a consumable that turns into deposited weld metal. The better the deposition efficiency of a consumable, the lower the quantity of that consumable is wasted by not becoming part of the deposited weld metal. Because of the properties of a flux-cored wire with slag covering the molten weld puddle, they possess an efficiency in the range of 84-89% depending upon the diameter and slag volume of the specific wire design. Solid MIG wires are remarkably efficient based on almost non-existent slag. Solid MIG wires will ordinarily demonstrate efficiencies in the range of 95-98% based upon the mode of the transfer used. 

Deposition Efficiency

A genuine “spray” transfer under high Argon shielding gas mixtures will yield the highest deposition efficiency. Metal cored wires have arc characteristics equivalent to solid MIG wires and possess very low spatter level as well as low slag volume, in addition exhibit deposition efficiencies in the 92-98% range along with the selection of spray transfer mode and high Argon shielding gas mixtures. When solid wires are utilised in the “short arc” transfer mode or with higher CO² content shielding gas, some deposition efficiency is lost due to increased spatter level. This the same as with flux cored and metal cored wires. variations in transfer mode and shielding gas impact on the deposition efficiency. In high-speed applications, solid MIG wires are utilised at lower voltages to prevent a large spray column. Using a solid MIG wire at voltages that generate a high spray column can generate undercut, underfill and can prevent the high travel speeds essential for productivity. This generates a higher level of fine spatter which in turn reduces the deposition efficiency of the wire. When the similar procedure is used with metal cored wires, the degree of fine spatter is drastically decreased. together with superior deposition efficiency, routine maintenance costs for tooling and equipment are lower.

Deposition Rates

The deposition rate of a welding consumable is the measurement of exactly how much weld metal is deposited in a given time period. Deposition rates together with deposition efficiency are the primary determinants of the cost efficiency of a consumable. typically expressed as Kg/hr, flux cored and metal cored wires have some of the maximum deposition rates of all of the welding consumables. Flux cored and metal cored wires are capable of obtaining deposition rates as large as 5.4-6.4 Kg/hr for a 1.2 mm diameter wire. This even comes close to a solid MIG wire in the same diameter of 3.6-4.5 Kg/hr. The high deposition rates coupled with high deposition efficiencies and reduced slag volume can permit the metal cored wire to be utilised at higher travel speeds resulting in enhanced work productivity. A standard guideline is that whenever a deposition rate of 4 kg/hr or higher is attained with a metal cored wire compared to a solid MIG wire, the economics of the weld will certainly demonstrate a cost benefits in favour of the metal cored wire.

High Duty Cycles, High Travel Speeds

Any continuous welding process innately has a higher duty cycle or continuous arc time. The SMAW method of stick electrodes necessitates the welder to halt in small intervals of the weld to de-slag and switch electrodes. The duty cycle for SMAW electrodes is regarded to be in the range of 20%. This converts to merely 12 short minutes of welding each hour an arc is generated. With a continuous process like cored wire or solid MIG wire, the duty cycle enhances to approximately 50% of the time or 30 minutes per hour for arc generation. This aspect makes the utilization of automatic or robotic welding appealing, the capability to use a continuous process. coupled with the boost in duty cycle occurs the advantage of faster travel speeds. Automated welding is only restricted to the supply of components to the weld station and the travel speed of the process. Solid MIG and flux cored wires lead to the increased duty cycles, but only metal cored wires possess the capabilities of merging high duty cycles with high travel speeds to take advantage of these aspects without compromising bead appearance, penetration and weld integrity. Increases in travel speed of 35-40% are not impracticable when switching from a solid MIG wire to a metal cored wire. enhanced duty cycles and higher travel speed can drastically decrease the cost of welding. 

Low Slag Volume, Low Spatter Levels

combined with increase duty cycle of a consumable is the decrease in the removal of slag from the weld. This is one of the most significant benefits solid MIG wires possess over flux cored wires. Because of the compositional characteristics of the metal cored wires, they in addition possess extremely low slag volume like solid MIG wires. The advantages of metal cored wires occurs in reduced spatter levels that requires cleaning from the parent material ahead of finishing. The little silicon islands produced on the weld are conveniently removed. Metal cored wires calibrated to the appropriate welding parameters and making use of high Argon mixes for shielding gas at the same time reduce the quantity of spatter.

This is in particular, an edge in continuous operations where the part moves from an assembly or welding operation immediately into a cleaning and painting operation. Cleaning of weld spatter from a fabricated piece can cost considerably in post weld clean up. Metal cored wires possess the benefit of possessing arc stabilisers in both the internal components and also applied to the exterior of the wire. The arc stabilisers greatly enhance the arc characteristics and also reduce the spatter levels.

Economics of Metal Cored Wires

The actual benefit for any change in process or welding consumable occurs with the economics of the change. How can we do it much better, but at a significantly less cost per unit. Obtaining the incumbent filler metal at a reduced price is a misnomer since the real cost of the filler metal for welding is a tiny percentage of the total and therefore optimum savings are not accomplished. When breaking down the real cost per kg for a deposited weld, the cost of the filler metal merely contributes roughly 15% of the overall cost. Other variables such as labour and overhead, equipment, electrical cost, deposition efficiency and deposition rates of the filler metal have a much bigger influence.

Consider an application using 1.4 mm E70S-6 MIG wire welded under pulse conditions modified to metal cored wire welded and at the exact same wire feed speed, voltage and travel speed. Because of the advantages of the metal cored wire, the travel speed could very well be enhanced upto 20%. Not only has the travel speed enhanced, boosting the throughput, the number of essential maintenance tasks decreases along with the time to make the repairs by 10%. Because the line time cost is computed in dollars per minute, a substantial saving is actualised through even small advancements in productivity enhancement. The cost per kg for metal cored wire is a lot more than the cost per kg for solid MIG wire, but the actualised savings more than balance out any supplemental cost for the metal cored wire.

In an additional application, a 1.0 mm ER409Cb solid MIG wire welded under pulse conditions for a thin wall tube is modified to a 1.2 mm EC409Cb metal cored wire welded under pulse conditions with faster travel feed speed. Not only will the travel speeds increase, but an supplemental benefit is the capability of the metal cored wire to bridge gaps due to poor fit up. This leads to to reduced defect rate and the necessity to rework parts off line. The benefits are on an average a 40% increase in production, reduced consumable cost per kg of weld metal and reduced maintenance cost.

Disadvantages of Metal Cored Wires

To attain the optimum benefit from using metal cored wires, an automated or robotic setup is essential. Expecting the optimum prospective boost in travel speed to be met and continuously maintained in a handheld functioning is anticipating a lot from a welder. Automated systems are dependable and do not tire neither do they require breaks. provided that a continuous supply of parts are provided, an automated system continues on working. If a existing application is being managed only by handheld welding stations, a capital investment is required to an automated system. Repetitiveness of an application is required to reduce set up and jig costs. expertise in programming a robot is required on account of an raise in weld puddle fluidity. Such could be the scenario in welding a small diameter tube where the placement of the torch to the part is more sensitive with a metal cored wire. The expense of the automated system has to be planned for also in addition to the potential to deliver a realistic payback on the investment.

In order to attain a spray transfer, which is the best mode to deliver outstanding wetting in of the bead and to reduce spatter, high Argon gas mixtures are essential. Although high proportions of Argon in the shielding gas decrease fumes generation these types of shielding gases also produce more heat and increased levels of radiant light. Water-cooled welding guns together with safeguard from the arc and reflected light are vital for a safe work environment. This is an additional factor automated systems assist in maximising the rewards of metal cored wires. They are not as susceptible as a welder to the consequences of the additional heat and radiant light produced.

To gain all placement capability with a metal cored wire either a short arc transfer mode or pulse mode is needed. Short arc would be eliminated on account of the considerable drop in deposition rate, deposition efficiency and increase in spatter. Most pulse machines do not incorporate a program specifically for metal cored wires. Although not completely essential, the development of a synergistic curve and pulse parameters does indeed greatly enhance the general performance of a metal cored wire. If current equipment is not capable to pulse or does not have a pulse program specifically for metal cored wires and the need to improve the arc and interoperability is there, the equipment manufacturer must make alterations and program customization to the power source. Depending on the machine manufacturer, these types of adjustments may possibly be able to be made to the existing power sources.

A substantial boost in productivity and throughput in one station are going to be negated if the succeeding stations down the line are unable to cope with the additional parts. It wouldn't be an advantage to enhance productivity by 30-40% in a weld station if the station is merely operated 50-60% of the time as a result of parts backing up. Payback on the investment would be extended to the point of being unappealing to the majority. When taking into consideration the increase in parts per hour that can be attained from switching to the increased productivity metal cored process, the stations down the line from the operation also need to be considered as far as their potential of coping with the increase from efficiency increases.

Metal cored wires can be an advantage irrespective of whether they are utilised in a handheld operation or in an automated weld station. From handheld to simple automation to a complete multi-process robot, metal cored wires can and do deliver gains over other choices in consumables.