When should you use flux-cored or metal-cored welding wire?

In addition to massive steel welding wire such as SG2 and SG3 there are also filled MIG/MAG-welding wires. The two main groups are:

• Gas-filled/flux-cored wire
• Metal powder filled / metal-cored wire

Both have a metal outer shell with a filled core, but that core is composed differently and therefore also differs from arc characteristics, slag formation, deposition rate and scope.

You can remember very rudely:

Flux-cored → strong in heavy structural fabrication, positional welding and deep penetration. Metal-cored → strong in high productivity, speed and low post-processing.

What is flux-cored welding wire?

The term flux-cored wire is widely used, but is technically a bit misleading.

The wire is not literally filled with gas.

The metal cloak contains a core containing among others:

• Flux
• Minerals
• Alloy elements
• Slug-forming substances
• Deoxidation agents

During welding, this core affects the weld pool, the arc and the protection of the weld metal.

What does flux-core mean?

Flux-cored literally means that the wire has a flux-filled core.

Therefore this wire is often abbreviated as:

FCAW. Flux Cored Arc Welding

Does flux-cored always need shielding gas?

No.

There are two main main groups:

• Gas protected flux-cored wire
• Self-protective flux-cored wire

What is gas-shielded flux-cored wire?

This wire is used together with an external shielding gas.

This may depend on the wire for example:

• Argon/CO2 blend gas
• CO2
• Other gas prescribed by the manufacturer

This wire is widely used in professional steel construction and structural fabrication.

What is self-protective flux-cored wire?

Self-protective flux-cored wire does not require an external gas bottle.

The core produces sufficient gaseous and slag forming protection during welding to shield the welding bath.

This is particularly interesting for:

• Outdoor work
• Assembly
• On-site repair
• Wind-sensitive conditions
• Work where a gas bottle is impractical

Is gasless welding wire the same as flux-cored wire?

Self-protective flux-cored wire is often commercially sold as gasless welding wire.

Technically, that's still a flux-cored wire.

Gasless only means that no external shielding-gas cylinder is required.

What is metal-cored welding wire?

metal-cored wire also has a metal cloak, but the core largely consists of metal powders and alloy elements.

This technique is referred to as:

MCAW Metal Cored Arc Welding

The wire is usually used with external shielding gas.

Does metal-cored wire also form slag?

Much less than traditional flux-cored wire.

Metal-cored wire was developed precisely for a combination of:

• High deposition rate
• High welding speed
• Good arc stability
• Little slag
• Less post-processing

There may be silicates and small deposits on the weld, but usually no thick classic slag layer as with many flux-cored wires.

What is the main difference between flux-cored and metal-cored?

Why do you use flux-cored wire?

Flux-cored wire is chosen especially when solid wire does not offer the optimal combination of:

• deposition rate
• penetration
• Position loadability
• Mechanical properties
• Productivity

For thick structural steel flux-cored can be a very efficient process.

What is flux-cored used for?

• Heavy steel construction
• Shipbuilding
• Bridge construction
• Mechanical engineering
• Offshore
• Heavy repair work
• Position welding
• Thick plate
• Long welds

What are the benefits of flux-cored wire?

• High deposition rate Possible
• Good penetration
• Strong in thick material
• Many wires suitable for positional welding
• Good mechanical properties possible
• Self-protective variants available
• Less prone to wind when self-protective
• Very suitable for productive structural fabrication

What are the disadvantages of flux-cored wire?

• More smoke
• More slag
• slag should be removed frequently
• More post-processing
• Higher wire price
• Settings More Critical
• Often less comfortable with very low welding currents
• Not ideal for thin sheet metal work
• Higher heat input possible
• More chance of welding errors when the process is set too cold

Why does flux-core often work less pleasantly on low current levels?

This is an important point that is regularly overlooked in sales demos and online movies.

A flux-cored wire can make an arc on relatively low current, but that doesn't mean that the wire performs optimally.

Many flux-cored wires have a practical process window in which sufficient power and arc energy are required to:

• Melt the metal cloak well
• Get the filling to react completely
• The slag to form correctly
• Get enough penetration
• Keep the weld pool well liquid

What happens if you load flux-cored too cold?

When the welding current and arc energy are too low, the process can become less stable.

Possible consequences:

• Unsatisfied arc
• Grove dropper transition
• Lots of splashes
• Poor humidification
• Bolle las
• Insufficient penetration
• Bad Merge
• Slack seals
• slag that hard to release

Why can the weld look good?

Because appearance is not the same as technical weld quality.

A flux-cored weld may look neat on the outside while insufficient fusion is present between the weld metal and the base material.

This risk increases when:

• welding current is too low
• The voltage is too low
• The welding speed is wrong
• The wire is too thick for the application
• The machine has insufficient power

Why do you often see flux-core online on small machines?

Because self-protective flux-cored wire is popular on compact hobby welding machines.

The sales argument is attractive:

Not required.

For occasional outdoor work, that can indeed be practical.

But there is an important difference between:

can lay a weld

and

Use a process in its optimum working area.

A small machine can get a 0.8 or 0.9 mm flux-cored wire melting, but at very low current the combination is not automatically ideal for thin sheet metal work.

Why isn't flux-core the best wire for very thin sheet metal work?

Flux-cored wire generally requires a relatively energy-rich process.

For thin material, this quickly creates a difficult compromise.

You want enough energy for:

• Stable Arc
• Good slag formation
• Good fusion

But not so much heat that you burn through the thin sheet material.

That process window could be small.

Is flux-core bad for a 200 A hobby machine?

Not automatically.

For suitable material and a suitable wire it can work fine.

But do not expect flux-core at 40 or 50 A to automatically produce the same fine behavior as a small solid wire with shielding gas.

For thin body paneling, solid wire with shielding gas is often much more pleasant to regulate.

Which wire diameter makes a big difference?

Especially with flux-cored wire.

A thicker wire needs a higher minimum practical range.

For example, with a small machine, over-cored wire can mean that the power source works almost continuously in a too low parameter zone.

Therefore, always check the manufacturer's details of:

• Wire type
• wire diameter
• Water catchment area
• Tension
• shielding gas
• Polarity

Why is a cored wire different from solid wire at the same diameter?

A cored wire has a metal cloak with a hollow core.

The electrical current essentially passes through the metal outer shell.

This makes the current density in the conductive metal different from a fully solid wire of the same external diameter.

This contributes to the characteristic melting and arc characteristics of cored wire.

Why can flux-core melt down quickly?

Because the current passes through a relatively smaller metal cross section area, the current density can be high.

This allows a cored wire to achieve high melting speed and deposition rate at suitable parameters.

That is one of the great advantages of production work.

What's the difference with metal-cored at low current?

Metal-cored wire also has a hollow wire construction, but the process is more focused on high productivity with little slag.

Also metal-cored is usually best served when sufficient power and wire speed are available.

For very low current thin sheetwork, solid wire is therefore often simpler and more economical.

Why do you use metal-cored wire?

Metal-cored becomes especially interesting when productivity is important.

The process can bring a high amount of metal into the weld per unit of time, while slag removal is largely avoided.

What is metal-cored used for?

• Production welding
• robotic welding
• Motor vehicle
• Mechanical engineering
• Long welds
• Heavy construction
• Mechanical welding
• Work where high welding speed is important

What are the advantages of metal-cored?

• High deposition rate
• High welding speed Possible
• Very little slag
• Less post-processing
• Good arc stability
• Good humidification
• Suitable for mechanisation
• Very suitable for robotic welding
• High productivity

What are the disadvantages of metal-cored?

• Higher wire price
• shielding gas required
• Not always economically at small quantities
• High wire speeds may require a powerful feeder
• Machine must have sufficient power
• Not automatically suitable for any position or application

Why can metal-cored be faster than solid wire?

Due to the construction of the wire, relatively much material can be fused at high wire speed.

In addition, the process can give a wide arc and good humidification.

In a production environment, this may mean:

• More welding meters per hour
• Less stops
• Cut less
• Remove less slag
• Higher robot productivity

Is metal-core the same as flux-core without slag?

No.

That's too simple a description.

Both are cored wires, but the core is different and the process is optimized for other purposes.

Metal-cored is mainly focused on metal transfer and productivity, while flux-cored also largely uses flux components for slag formation, protection and metallurgical properties.

Choose Flux-cored or massive SG2?

Choose Flux-cored or metal-cored?

Massive wire or metal-cored?

For smaller workshops and variable work, solid wire is often the simplest and most economical solution.

Metal-cored becomes interesting when time starts to become more important than the price per kilo of wire.

When does metal-cored earn itself back?

Especially when the saving is in working time.

Remember:

• Many welding meters
• High production series
• Robots
• Long straight welding
• Lots of post-processing with a different process
• High hourly costs

A roller wire can be more expensive while the complete welded product ultimately becomes cheaper.

When does flux-core earn itself back?

Flux-cored may become interesting when:

• Much thick material is welded
• Position welding required
• High deposition rate is important
• Mechanical requirements are high
• Working outside
• Less welding required

Which wire do you use for outdoor work?

For outdoor work, self-protective flux-cored wire is particularly interesting.

A conventional MIG/MAG process with external shielding gas can lose its gas protection due to wind.

Self-protective flux-cored wire is less dependent on that.

This does not mean that it can be used indefinitely in hard winds. Always follow the technical prescription.

Is self-protective flux-core better than stick welding outside?

Not by definition.

Both processes have strengths.

Flux-core offers continuous wire feed and can be very productive.

On the other hand, stick welding is extremely simple in terms of equipment and often very robust on location.

Which wire do you use for thin sheet metal work?

For thin steel, a solid wire with shielding gas is usually the first choice.

Examples include:

• 0,6 mm solid wire
• 0.8 mm solid wire

This generally allows the heat input to be finer than with a relatively coarser flux-cored application.

Which wire do you use for heavy construction steel?

With heavy construction steel both flux-cored and metal-cored can be interesting.

Please choose:

• Flux-cored when position, penetration and mechanical properties are important
• Metal-cored when high production speed and low post-processing are important

Which wire is suitable for vertical welding?

A lot of rutile flux-cored wires have been developed for very good position-weldability.

The slag helps support the weld pool.

This allows flux-cored to be particularly strong at:

• Vertically On
• Upper Hand
• Horizontal Hoses

However, check the welding positions for which the exact wire has been approved.

Is metal-cored good for vertical welding?

Some wires and procedures can do that, but metal-cored is much more often chosen for productive welding in favorable positions.

Flux-cored often has a stronger advantage when much needs to be welded out of position.

What is rutile flux-cored wire?

Rutiel flux-cored wire uses a rutile snail composition.

This wire is often known for:

• Soft bow
• Beautiful weld
• Good position loadability
• slag that lets go relatively easily
• High productivity

What is basic flux-cored wire?

Basic flux-cored wires are more focused on certain high mechanical and toughness requirements.

For example, they can be interesting in:

• Low temperature
• High shearing requirements
• Heavy structural fabrication
• Specific certified applications

The processing may be different from that of rutile wire.

What polarity do you use in flux-core?

That depends on the exact wire.

Many gas protected flux-cored wires are used with:

DCEP hindered electrode positive

Many self-protective wires use correctly:

DCEN hindered electrode

But this is not a universal rule.

Always use the polarity on the data sheet or packaging.

What happens to the wrong polarity?

The wire can still give an arc, but the welding characteristics can deteriorate significantly.

Possible problems:

• Lots of splashes
• Bad penetration
• Unstable Arc
• Bad slag formation
• Bad welding form
• Wrong mechanical performance

Which shielding gas do you use in flux-cored?

This varies greatly per wire.

Common features are:

• 100% CO2
• Argon/CO2 blend gas

The wire manufacturer shall indicate which gas is permitted.

Which shielding gas do you use in metal-cored?

Metal-cored wire is usually used with an argon-rich MAG blend gas.

The exact composition depends on the wire and the desired arc characteristic.

Can I use the same program as SG2?

Not automatically.

A synergistic program for massive SG2-wire is not necessarily correct for flux-cored or metal-cored wire.

If available, use a specific programme for:

• Flux Core
• FCAW
• Metal Core
• MCAW
• Cored Wire

Why does the welding machine need enough power?

Filled wire is especially effective when sufficient wire speed and arc energy are available.

A machine operating continuously against its maximum current can:

• Becoming thermally limited
• Insufficient voltage supply
• Have a small process window
• Do not get stable high deposition rate

Therefore, it is important to choose cored wire not only based on the maximum current rating on the front plate.

Is a four-roll wire feed important?

In professional use, yes.

Filled wire is often used in larger diameters and with high wire speeds.

A good four-roll feeder gives more grip and more stable wire transport.

Does flux-cored need a special drive roller?

Often a serrated or specially cored wire is used, depending on wire and manufacturer.

The pressure must be correct.

Too much pressure can distort the tubular wire.

Which MIG/MAG-torch do you need?

Due to the often higher average current and wire speed, the torch is more heavily loaded.

For heavy-cored wire applications can therefore be interesting:

• Heavy air-cooled torch
• water-cooled 401 Class
• water-cooled 501 class
• Heavy-duty industrial torch

The exact choice depends on welding current, switching load and wire diameter.

Why does flux-cored produce more smoke?

The filled core contains components that react and evaporate during welding.

As a result, smoke development can be significantly higher than with solid wire.

Good source extraction is therefore particularly important.

Why is smoke extraction at flux-core so important?

Because the welder can produce a lot of welding smoke at long production welding.

Use where possible:

• Source extraction
• Torch extraction
• General ventilation
• Appropriate respiratory protection according to risk analysis

Why should slag be removed completely?

With multi-layer flux-cored welding, the slag should be removed well between the layers.

Remaining slag can lead to slacken seals in the next welding layer.

How do you know if you need flux-core?

Ask yourself:

• Is the material relatively thick?
• Did I read a lot out of position?
• Do I need high deposition rate?
• Do I work outside?
• Are high mechanical demands important?
• Is snail removal acceptable?

When multiple answers are yes, flux-cored becomes interesting.

How do you know if you need metal-cored?

Ask yourself:

• Did I read a lot of meters a day?
• Is working time expensive?
• Do I want high welding rates?
• Do I want to minimize snail removal?
• Do I use robots or mechanization?
• Do I read mostly in favorable positions?

Then metal-cored can become very interesting financially.

When will solid wire remain the best choice?

Massive wire remains particularly strong:

• Dun sheet metal work
• Low current
• Small workshops
• Repair
• Changing Applications
• Low wire costs
• Simple equipment
• General steel work

Buying advice for hobby use

For normal hobby work we would not automatically recommend flux-cored just because no gas bottle is needed.

If you mainly load thin sheet material in a workshop, a small solid wire with shielding gas is common:

• Calm down.
• Cleaner las
• Less smoke
• Less slag
• Better adjustable on low current

Self-protective flux-core becomes particularly attractive when you want to weld outside or cannot use a gas bottle.

Buying advice for a small 230 V MIG/MAG machine

Check very carefully which wire diameter and which water catchment area the machine can handle.

A relatively thick flux-cored wire on a light machine can cause you to sit constantly at the bottom of the practical work area of the wire.

This allows the combination to fit on paper, while the welding characteristics is disappointing in practice.

Buying advice for structural fabrication

For medium to heavy structural fabrication gas protected flux-cored wire is very interesting when:

• Many thick how classes are laid
• Position welding is important
• High deposition rate required
• Slug removal is not a problem

Buying advice for outdoor work

For outdoor mounting, you can specifically look at self-protective flux-cored wire.

This removes the need for external shielding gas.

Please check:

• Correct polarity
• Wire classification
• Sheet thickness
• Weld position
• Minimum current
• Mechanical approvals

Buying advice for production

With large numbers metal-cored can be very interesting.

The higher wire price should then be compared to:

• Shorter welding time
• Less post-processing
• Higher welding speed
• Less snail work
• Higher robot output

Buying advice for robotic welding

Metal-cored is often particularly interesting with robotic welding.

A robot can take maximum advantage of:

• High wire speed
• High welding speed
• Long continuous seams
• Little slag
• Low manual post-processing

Buying advice for thin sheet metal work

For very thin sheet metal work we would usually first look at:

• Massive 0,6 mm wire
• Solid 0,8 mm wire
• Good mixture gas
• Suitable short-circuit arc programme

Flux-cored can work, but is usually not the most sophisticated solution there.

Buying advice for heavy production welding

Both cored wire types come out strongly here.

Choose:

• Flux-cored for position, penetration and heavy construction
• Metal-cored for maximum speed and minimal post-processing

What is cheaper: solid, flux-core or metal-core?

Per kilogram, solid wire is usually cheaper.

But the cheapest wire per kilo is not automatically the cheapest process.

Calculate in professional work as well:

• welding speed
• deposition rate
• Labour costs
• Remove slag
• Sharpening
• Stand still
• Robotic cycle time

From Cjays practice

Flux-cored wire is often presented on the internet as a kind of miracle wire for small MIG machines:

Oh, no gas needed, so easier.

For outdoors, that can be absolutely an advantage.

But with thin sheet metal work and low current we see an important disadvantage: the wire often needs more arc energy to really get into its process window.

If the machine is set too low to avoid burning, the weld can then become cold.

You may get an apparently large caterpillar, but that does not say anything about the fusion on the sides and the root.

That is why we would not just ask for a small machine:

Can he weld flux-core?

But most importantly:

Which wire type, diameter, plate thickness and current should it use?

For heavy structural fabrication the story turns around. There flux-cored can be much more productive and pleasant than solid wire.

Metal-cored we mainly see as a productivity thread. When a company suffers many identical meters, time savings can become much more important than the difference in kilos price.

Which wire to choose?

Steps to buy the right filled welding wire

• Determine the base material.
• Determine the plate thickness.
• Check the desired mechanical properties.
• Determine the welding position.
• Check whether you are burdened inside or outside.
• Determine whether external shielding gas is available.
• Check the power of welding machine.
• Check the appropriate wire diameter.
• Check the minimum and maximum parameters of the wire.
• Check the required polarity.
• Check the right drive rollers.
• Then choose between solid, flux-cored and metal-cored.

The main conclusion

Gas-filled flux-cored wire and metal powder-filled metal-cored wire are both filled welding wires, but they are developed for different purposes.

• Flux-cored: strong in heavy construction, positional welding, deep penetration and possibly outdoor work.
• Metal-cored: strong in high productivity, high welding speed and low slag.
• Massive wire: often remains the best all-round choice for lower current, thin sheet metal work and general work.

Flux-cored is especially not the ideal solution for low current levels. The process can work on low current, but many wires become noticeably more pleasant and technically reliable when sufficient power and arc energy are available.

For a small machine it is therefore not only necessary to consider whether flux-core is supported, but whether the chosen wire can actually be used within a usable power and voltage range.

Further reading

• How do you determine which MIG/MAG welding torch you need?
• What is the difference between SG1, SG2 and SG3 welding wire?
• What is Pulse MIG/MAG welding and when should you use it?

Frequently asked questions about filled welding wire

Is flux-core the same as gasless welding wire?

Self-protective flux-core is often called gasless wire. However, there are also many flux-cored wires that are used with external shielding gas.

Is there gas in flux-cored welding wire?

No. The wire contains flux and other powders. In case of self-protective wire, response to the filling during welding ensures protection.

Is flux-core suitable for thin sheet metal work?

It is possible, but solid wire with shielding gas is often easier and finer to regulate with very thin material.

Why does flux-core work less well on low current levels?

Because sufficient arc energy is needed for stable melting, good fusion and correct flux operation and slag. If the parameters are too low, the weld can become cold and irregular.

Can I weld flux-core to 50 A?

That depends entirely on wire type and diameter. The fact that an wire can create an arc at that current does not automatically mean that it is within the optimal range. Check the datasheet.

Is flux-core better than SG2?

Not universal. Flux-core is stronger in certain heavy and productive applications. SG2 is simpler, cheaper and often better for thinner and lower workload.

What is metal-cored wire?

Metal-cored wire has a metal outer shell with a metal powder core. The process is mainly focused on high deposition rate, good arc stability and little slag.

Is metal-core the same as flux-core?

No. They are both cored wires, but the core composition and scope are different.

Which cored wire is best for robotic welding?

Metal-cored is often particularly attractive for robotic welding due to high welding speed, high deposition rate and low slag.

Which wire do you use outside?

Self-protective flux-cored wire is often interesting because no external shielding gas is needed.

Should flux-core be on plus or minus?

This varies per wire. Many gas protected wires use DCEP and many self-protective wires DCEN, but the datasheet of the wire is always leading.

Which wire gives the most smoke?

Flux-cored wire generally produces more welding smoke than solid wire. Good suction is therefore important.

Which wire gives the least post-processing?

Metal-cored and solid wire usually give less snail work than traditional flux-cored wire.

Is metal-cored more expensive?

Per kilogram usually, but in production the higher welding speed and lower post-processing can still make the total process cheaper.

Which filled welding wire suits your welding machine and application?

In flux-cored and metal-cored wire, wire diameter, water catchment area, polarity, shielding gas and machine power are more important than just the word "recored wire" on the packaging.

Cjays Lastechniek can help to determine whether solid wire, flux-cored or metal-cored is the best choice for your application and which wire diameter, torch and machine settings fit.