You can choose from a variety of different shielding gases and blends when you’re welding.

There are a few things you must understand before you’re able to make an informed decision on the type of shielding gas you need.

These are the questions you should ask yourself before you choose a shielding gas.

1. Do you care about the “look” of the weld?
2. Does spatter matter to you?
3. Does the weld require a deep penetration, or do you want to minimize weld penetration as much as possible?
4. Are you concerned about how many fumes your weld generates?

There are a few other questions you should ask yourself but, these are the base questions.

The following process can help you select the correct gas blend for your welds.

1. What kind of materials are you welding?
2. How thick is the material and what kind of condition is it in?
3. What kind of welding position do you want to use? Also understand that the process you use is also hindered by the equipment you have available as well as your skills and productivity levels you desire.
4. What are the requirements of the job? The chart below will give you a solid understanding of what you should be looking for.

What’s the function of shielding gas?

The main function of shielding gas is to reduce the weld’s exposure to outside contaminants such as oxygen, hydrogen, nitrogen, etc. When a weld is introduced to these elements it can cause imperfections to occur such as:

• Porosity
• Wormholes
• Etc.

Types of Shielding Gasses

Argon: Color-less, odor-less, and non-toxic noble gas that makes up about .93% of the earth’s atmosphere. Argon helps provide a clean and inert environment that’s rid of oxygen and nitrogen. For metal fabrication Argon is used to create an inert gas shield during welding. It’s also occasionally mixed with oxygen, helium, hydrogen, or carbon dioxide to facilitate metal transfer in MIG welding.

Argon has low conductivity and ionization potential, which are properties that result in a transfer of heat to the arc’s outer regions.

Helium: Color-less, odor-less, taste-less, chemically inert, and non-toxic, helium is non-flammabe while also having a high thermal conductivity. Helium usually helps increase travel speed and weld pool fluidity. Helium has a high ionization potential and conductivity, which yields opposite effects of Argon.

Carbon Dioxide: Co2 is an odor-less, taste-less, color-less, non-flammable. It’s typically used alongside Argon during welding or in its pure vapor state. Doing so prevents contaminants from the atmosphere to enter the weld. At the temperatures created in the arc Co2 tends to disassociate and turn into Co and O2. This results in oxidizing of the base metal as well as dealloying of the bead.

Oxygen: 21% of the earth’s atmosphere is made up of oxygen. It’s also a taste-less, odor-less, color-less gas and is used to support oxyfuel in curring operations. Oxygen creates a shallow penetration profile with high heat input at the surface of the work.

Propane: A color-less, liquified, and flammable gas that naturally smells like gas. The flame temperature of an oxy-propane flame is lower than that of propylene or acetylene.

Propylene: A liquified, flammable, color-less gas that smells slightly sweet. Propylene has the qualities of an acetylene flame and the secondary heating capacity of propane.

Nitrogen: Nitrogen that makes up about 78% of the earth’s atmosphere. It’s a non-toxic, taste-less, color-less, and is non-flammable at atmospheric temperatures / pressures.

Each of these gasses can be used separately or they can be mixed with one another to yield different effects. When gasses are blended with one another they’re mixtures are expressed in percentages.

Examples: Argon 95% – 5% Co2 (This means the blend is 95% Argon and the remaining 5% is Carbon Dioxide) or Argon 90% – 10% Co2 (This means the blend is 90% Argon and 10% Co2)

How to choose a shielding gas for MIG welding

When you MIG weld with a shielding gas (and the correct solid wire electrode) you produce a decent looking, clean weld and eliminate the need to constantly change your welding electrode. This means that using a shielding gas will make the welding process more efficient and much cleaner of a process.

The term “MIG” stands for Metal Inert Gas (it’s also called Gas Metal Arc Welding or Metal Active Gas) which means that welders typically use an inert gas to shield their welds with. Inert gasses typically used in MIG welding are Argon and Helium.

When you’re choosing a shielding gas it’s still a great idea to consult a professional at a welding store as they’ll be able to give you input designed to fit your needs. 

Typically, you’ll see mixed shielding gasses being used for MIG welding (with some of these gasses being active gasses).

Shielding gasses for MIG welding

A thing to keep in mind when you’re MIG welding is that there are a number of shielding gasses / mixes you can choose. Knowing that, there are a few considerations you’ll want to take before you choose your gas:

• How much does the shielding gas cost?
• How do you want the weld to look?
• The material you’re weld
• How the weld was prepped
• The post-weld clean up
• Weld transfer process
• How productive do you want to be?

A few of the commonly used mixes for MIG (MAG / GMAW) welding are: 

1. 2% Carbon Dioxide and 98% Argon: Is great for stainless steel.
2. 25% Carbon Dioxide and 75% Argon
3. 100% Carbon Dioxide: Is great for Carbon Steel and produces the deepest penetration, roughest weld, and smoke.
4. 100% Argon: Typically used for Aluminum, Copper, Copper Alloys, Magnesium, Nickel, Nickel Alloys, and Titanium.

Video credits to Lincolnelectrictv. It has a great explanation for choosing a shielding gas and goes over the costs of each kind.

How to choose a shielding gas for TIG Welding

The typical gas used for TIG welding is Argon while Helium can also be added to create a mixture that increases the fluidity and penetration of the weld pool.

A few of the commonly used mixes for TIG (GTAW) welding are: 

1. Ar + He^a    
2. Ar + (2-5)% H₂^a,b
3. Ar + (1-2)% N₂
4. Ar + 30% He + (1-2)% N₂

*a means that it improves flow when compared to Pure Argon

*b means that it’s preferable for Automatic welding, has a high welding speed, and runs the risk of porosity in multi-run welds.

Video credits to Weldingtipsandtricks. It explains the process of choosing a shielding gas for TIG welding.

What is optimal gas flow?

The flow rates for shielding gas are determined by the welding process, operating parameters, and welding position. With GTAW, the flow rate is typically between 10 and 20 CFH or cubic feet per hour. For GTAW when you use a torch alongside a gas lens you’ll ensure a laminar flow, something that contributes to high weld quality, as well as lower than 10 percent gas consumption rates.

With FCAW and GMAW, the flow rate that’s recommended will vary – between 30 and 45 CFH – varying with the welding position, shielding gas composition, and operating current. When it comes to flat position welding, the helium enhanced mixtures require a slightly higher flow rate than weld that’s argon based. The gas flow rates will likely be reduced if the work to nozzle distance is as close as possible. In a few instances, the production site surveys will determine that the shielding gas flow rates are typically set in excess of 50 CFH. This may contribute to a poor weld quality as the atmospheric gases will be drawn into the arc zone because of too much gas turbulence. An optimized flow will enhance the quality and will reduce shielding gas usage.

Cost effective joining and shielding gasses

The selection of a shielding gas is highly important to get cost-effective joining of aluminum, carbon steel, and stainless steel. One can select a gas, like argon when doing aluminum welding, to achieve a suitable bead shape, minimum spatter, and suitable arc stability.

2-part blends such as carbon dioxide/argon mixtures, could perform well in a number of stainless steel and carbon steel applications where one would use pulsed spray or conventional transfer.

A lower carbon dioxide content will lower the amount of welding fumes that are generated. When you need less post weld cleanup, enhanced bead appearance, and low spatter, 3 part gas blends will provide solid results and also improve upon the welding productivity.

The base metal thickness, operator skill level, production demands, and welding position will need to be carefully considered when one is optimizing and selecting a joining process. When you have an understanding of shielding gasses, you’ll be able to optimize the welding process so as to improve quality and lower cost.

As with any process, you are bound to encounter defects in the process. You can encounter things such as misshapes and off sizing of the metal. This can occur due to either a bad welding process or bad technique. Listed below are the most common defects that you’re likely to find.

There are 2 types of welding defects: External Welding Defects and Internal Welding Defects.

Internal welding defects include:

• Necklace Cracking
• Slag Inclusion
• Incomplete Penetration
• Incomplete Fusion

External welding defects include:

• Porosity
• Welding Cracks
  • Crater Cracks
  • Cold Cracks
  • Heat Cracks
• Spatter
• Overlap
• Undercut

What are External Welding Defects?

Overlap

What is Overlap in welding?

Overlap is the considered a protrusion of weld metal beyond the weld root. Overlap typically occurs in butt joints and fillet welds and results in notches occurring at the toe of the weld. These notches are undesirable due to the stress concentration that occurs under load. These discontinuities are caused by either insufficient current or incorrect welding technique.

How does overlap occur in welding? 

Overlap in welding occurs when the molten metal from the weld flows over the surface of the base material and then cools without fusing to the base material. A common cause of overlap in welding is having too much weld metal supplied because of the weld speed being too low. When there is overlap in fillet welds it’s typically caused by the effect of gravity on excessive molten metal.

How do you fix overlap in welding? 

To avoid overlap you must make sure to review your welding settings (welding speed and current).

Video credits to Weld.com. It goes over ways to prevent weld overlap.

Spatter

What is spatter in welding?

When you have particles that attach to the surrounding areas of the surface the result is spatter. Surprisingly it’s pretty common in welds done with gas metal arc welding. It’s also one of the defects that you can’t completely eliminate, no matter how hard you try. It is, however, possible to keep its occurrence as low as possible.

How does spatter occur in welding?

1. When your amperage is too high
2. When the setting of voltage is too low
3. When your welding surface is contaminated
4. When your arc is long
5. When you have an incorrect polarity

How do you fix spatter?

1. Make sure you welding surface is clean before you weld
2. Reduce your overall arc length
3. Fix your weld current
4. Fix the electrode angle

Cracks

What are cracks in welding?

A serious complication that many welders tend to encounter during the process are cracks in the weld. These cracks can manifest anywhere in the weld, such as in the metal, on the surface, or anywhere else that touches the heat of the welder.

The different types of cracks are:

• Heat cracks
• Cold cracks
• Crater cracks

What are heat cracks in welding? 

These typically occur in the crystallization portion of the welding process. Temperatures of the metal at this point typically rises to over 10000C

What are cold cracks in welding?

These types of cracks typically show up after the weld has been finished. They can sometimes take longer than average periods to show and will manifest as slight deformities in the metal.

What are crater cracks in welding?

These types of cracks tend to show at the end of the entire process and occur at the end of the weld. When there is not enough room at the end of the weld for shrinkage of the weld metal a crater crack forms.

Why do welding cracks occur?

1. When you use hydrogen while welding ferrous metals
2. When there’s residual stress from the solidification shrinkage
3. When the base metal is contaminated
4. When you are welding with a high welding speed but with a low current
5. When you don’t preheat before you weld
6. When there’s a bad joint design
7. When there’s a high sulfur content and alot of carbon in your metal

How do you fix welding cracks?

1. Preheat your metal when it’s required
2. Properly cool the welding area
3. Have a correct joint design
4. Take away any impurities
5. Use the right metal
6. Have a sufficient sectional area
7. Use the correct amperage and welding speed
8. Make sure your crater is properly filled

This is also one of the reasons why it’s important to hold these welding skills

Video credits to Garry Pace. It details the different types of welding cracks.

Porosity

What is porosity in welding?

When there is contamination in your weld porosity can result. When you have gases in your weld you have a weld that is weak and collapses over time.

Why does porosity occur in welding?

1. When there is not enough electrode deoxidant
2. When you use a longer arc
3. When there is moisture in the weld
4. When you don’t use a correct gas shield
5. When you use too much gas flow
6. When your surface is contaminated

How does porosity occur in welding?

1. Clean your welding material before you weld
2. Make sure your electrodes and materials are dry
3. Have the correct arc distance
4. Make sure that the gas flow to the machine is properly adjusted
5. Reduce your arc travel speed
6. Make sure you have the correct electrodes
7. Weld with the correct technique

Video credits to Miller Welders. It goes over how to fix porosity in your welds – The right way!

Undercut

What are undercuts in welding?

When you have a groove formation at the weld toe you come into contact with this imperfection. When you have an undercut you have a weakened weld.

Why does undercutting occur?

1. When you weld with too high a current
2. When you weld to quickly
3. When you use an incorrect angle when you weld
4. When the electrode you weld with is too large
5. When you use an incorrect amount of shielding gas
6. When you don’t have the right filler metal

How do you fix undercutting in welding?

1. Use the correct electrode angle
2. Make your arc length shorter
3. Weld with a lower electrode travel speed
4. Weld with the correct shielding gas
5. Use the right electrode angle

Video credits to Herbert Bartley. It talks about how to avoid undercut in welds.

What are Internal Welding Defects?

Unfinished Penetration

What is Unfinished Pentration in welding?

When the groove of the metal isn’t filled completely the result is an incomplete penetration. This also means that the weld metal won’t fully extend throughout the thickness of the joint.

How do unfinished penetrations occurs?

1. When there is to much space in the metal you’re welding
2. When you move the bead too quickly
3. When you’re using too low of an amperage setting
4. When there is too large of an electrode diameter
5. When there is an improper joint

How do you fix unfinished penetration in welding?

1. Make sure to have a proper joint geometry
2. Have a properly electrode size
3. Reduce your overall arc travel speed
4. Make sure to have the correct welding current
5. Have the correct alignment

Video credits to Kevin Caron, Artist. It goes over way to make sure you get good welding penetration.

Slag in the weld

What is slag in the weld?

When you have slag in your weld you can tell by simply looking at it. Slag is a byproduct of flux-cored welding, stick welding, and submerged arc welding. When the flux used in the welding melts you can encounter slag in your weld.

How does slag in the weld occur?

1. When you don’t clean the weld correctly
2. When the weld speed is too fast
3. When you neglect to clean the weld pass and move on to another one.
4. When you have an incorrect welding angle
5. When your weld pool cools too quickly
6. When the current you use to weld is too low

How do you fix slag in the weld?

1. Make your current denser
2. Fix the cooling rate of the weld
3. Fix the angle of the electrode
4. Remove the slag from the bead
5. Fix the speed of the weld

Video credits to xAZAZELx13. This video goes over how to repair slag in the weld.

Unfinished Fusion

What is unfinished fusion?

When there isn’t a proper fusion in the base of the weld and in the weld metal you have an improper fusion. You can also find this in the adjoining beads of the weld. When you have unfinished fusion, you have a weld with gaps that don’t have molten metal in them.

Why do unfinished fusions occur?

1. When you don’t have enough heat
2. When the surface of the weld is contaminated
3. When you have an incorrect electrode angle
4. When you weld with too fast a travel speed

How do you fix unfinished fusion?

1. Make sure to use the correct arc voltage for your weld
2. Clean the metal before you weld
3. Keep the molten metal from flooding the arc
4. Lower your disposition rate

Necklace Cracking

What is Necklace cracking in welding?

Necklace cracking occurs when the electron beam weld doesn’t fully penetrate fully and a blind weld occurs. In these instances molten metal neglects to flow into the penetration cavity and onto the side walls of the workpiece. This occurs in metals such as is carbon steel, nickel base alloys, stainless steel, titanium alloy.

What is the cause of necklace cracking in welding?

The common causes of necklace cracking in welding are:

• Improper welding tehnique

What are a few remedies for necklace cracking?

A few known remedies for necklace cracking are:

• Using proper welding technique
• Using proper materials for welding
• Making sure to use a constant speed while welding