Improving Quality of MIG Welds and Weld Starts 

EXCESS GAS FLOW RATE: 

At Each Weld Start a blast of shielding gas exits the torch nozzle at very high flow rates with typical gas delivery systems.   We have measured peak flow surge rates exceeding 200 CFH. (Click Graph for details of measurements made in this production application) This is well above the flow rate that creates turbulence in the shielding gas stream.  This turbulence pulls moisture laden air into the gas stream creating poor shielding.  The turbulence takes a short time  to stabilize even after the flow returns to the preset level.  This creates excess spatter and often internal weld porosity.  The ideal starting gas flow control is shown by the graph labeled GSS.  This limits excess gas surge while still providing extra gas needed to purge the torch nozzle and weld start area.

 Also Welders Often Set excess shielding gas flow rates believing "if some is good more must be better."  Just how much gas flow is excess?  A recent article published in Practical Welding Today by Kevin Lyttle, Manager Welding R&D for Praxair states;  “In many instances production site surveys  determine that shielding gas flow rates typically are set in excess of 50 CFH.  This can contribute to poor weld quality as atmospheric gases are drawn into the arc zone because of excess gas turbulence.  Optimized flow enhances quality and reduces shielding gas usage.”   Other technical articles confirm this 50 CFH maximum level for a 5/8 inch ID torch nozzle size which is typically used for industrial welding.

NITROGEN POROSITY:

With solid steel MIG wires, some Oxygen can be tolerated.  The silicon and manganese contained in the wire can combine with the Oxygen to form silicon  and manganese oxide and avoid the carbon in the weld puddle forming a CO bubble.  These oxides float to the weld surface.  However published information indicates Nitrogen at levels less than 2% in the shielding gas can cause porosity in single pass welds (Reference ESAB, former L-TEC/ Linde MIG Welding Handbook; ".. 2% Nitrogen produced porosity in single pass welds made in mild steel; additions of 0.5% produced porosity in multipass welds." )  Unlike Oxygen, chemically combining Nitrogen into harmless compounds is not viable with solid wire. Elements like titanium can be employed but only at low levels since significant amounts cause embitterment. 

Remember Air contains 78% Nitrogen;  5% contamination in the shielding gas stream due to turbulence gives 3.9% Nitrogen in the gas stream.  That is sufficient to produce at least internal porosity.  Be sure your getting what you pay for - SEE ARGON PURITY BELOW.

Excess gas flow rate at the weld start is bad but insufficient extra gas creates similar problems.  This was stated best by Stauffer's 1982 patent.    He clearly understood the problem and designed around it using a "surge storage tank"; he states in the patent teaching, "... air leaks back into the torch and lines when welding is stopped.  The air must be quickly purged and replaced with inert gas to produce high quality welds. Also, it is critical to displace the air at the weld zone of the work piece upon initiating the weld. " 

Some devices that attempt to reduce gas surge create a weld start problem.  These devices set gas flow at the wire feeder such as simple orifices, regulators, flowmeters or needle valves.  Welders often observe this lack of start gas needed to purge the air from the start area.  They try to counter by increasing the steady state gas flow rate to achieve more gas at the weld start!  But increasing the steady state flow still does not sufficiently purge the weld start area and just increases needed flow while welding, wasting gas!

CLICK for More Information About Needing Extra Gas at the Weld Start?

Case 1: Low Pressure Gas Control Device Mounted at Wire Feeder Caused Weld Quality Problems

A Welding Engineer at a major Midwest heavy construction equipment company was having porosity in the same weldment in one plant and not in another.  He performed a very careful, systematic  analysis of the problem.  A fishbone troubleshooting diagram was developed with over 30 items considered in attempt to solve the problem.  It appeared to be a nitrogen porosity problem so he looked at all the possible causes.  He checked for pipeline, solenoid, feeder plumbing leaks, putting on cylinder gas supply to validate the quality of shielding gas and many others items.  He even tried a different type and manufacturer of the solid wire they were using. 

After all this testing and elimination of differences he found one of the major causes was the plant with the porosity problem was using low pressure surge reducing devices on their wire feeders (photo right.)  These controlled flow at the feeder providing insufficient extra gas to purge the torch nozzle and weld start area of moisture laden air. These were removed and the problems went away!  

This particular regulator flow control device used low pressure to control flow.  This creates a double problem!  In our tests of this device we found only 9 psi was needed to flow 31 CFH.  With the range of flow restrictions found in production flows varied from 16 to 37 CFH while the flow calibrated pressure gauge read a steady 31 CFH (CLICK FOR TEST RESULTS.)  In addition to the lack of sufficient start gas; variability in flow was probably allowing nitrogen to enter the shielding gas stream even when welding.  If shielding gas flow rate is too high or too low this can occur. 

BE CAREFUL SOME OF THESE DEVICES SOLD TO REDUCE SURGE DO NOT MENTION THAT THEY USE LOW PRESSURE TO CONTROL FLOW !  ALSO ANY DEVICE THAT MOUNTS DIRECTLY AT THE FEEDER WILL NOT PROVIDE SUFFICIENT EXTRA START GAS.  EMAIL IF YOU HAVE A QUESTION ABOUT A SPECIFIC MODEL.

See more production examples of problems encountered with low pressure devices and orifices placed at the wire feeder to control flow.  There is also an explanation of why the developers of MIG and TIG understood the need for "Automatic Flow Compensation" which some have forgotten!

Case 2: Removing Orifice Mounted at Feeder Showed Benefits of Having a Limited Amount of Extra Gas at a Controlled Flow Rate at Weld Start:

If sufficient shielding gas is not provided at the start, welders may try to compensate by using higher overall gas flow.  A bar joist manufacturer was using flow control orifices mounted at the wire feeders.  Argon/CO₂ shielding gas is supplied in a pipeline through about 15 feet of gas delivery hose.  The flow control orifice established the flow at 45 CFH.  However the welders wanted higher flow rates with some even drilling out the orifice!  The welding engineer wanted to avoid wasting shielding gas. With this flow setting arrangement where control is mounted at the feeder there is insufficient extra gas provided at the weld start.  This lack of extra gas prevents  to purging the weld start  area of moisture laden air.  

A test was made to check weld performance and potential shielding gas savings using two cylinders of  gas on two adjacent welders instead of their pipeline gas supply.  One was set with their standard flow control orifice system and a regulator providing a pressure that matched their pipeline, 50 psi.  The other with a regulator/flowmeter (also of a 50 psi design) using a 15  foot GSS without their flow control orifice.  Both steady state flows were set at 45 CFH.  Since welders stand side by side, it was easy to observe the weld start quality!   Instantly the welder using the GSS noticed  improved  starting.  After about an hour with observably better results the  welding engineer suggested we lower the shielding gas flow on the  welder with the GSS to 35 CFH!  The same improved weld start quality was observed and the welder was "happy."  In fact even though we lowered the steady-state flow to 35 CFH there was still about the same controlled amount of extra gas available at the start (that stored in the GSS hose when welding stopped.) The higher start gas flow rate established by the surge flow orifice in the GSS maintained the higher flow at the start.   This higher start flow rate quickly flooded and purged the weld start area of moisture laden air.  It was this air that was casing excess spatter and lack of shielding on all their other welders! After about 4 hours of observation it was obvious the spatter at the weld start was less with the GSS.  We also measured a reduced use of shielding gas of 25%.   After several months of testing to check this one system during windy days etc, this shop now has GSS's installed on all 50 welders!   

Bottom Line - - "Some extra gas flow at the start is very beneficial."  In addition, after about a year of use their gas supplier called to see if their business had turned down since they were using about 30% less gas- it had not!

Also note that any flow control device installed right at the feeder, be it an orifice flow control or a flowmeter will have the same lack of sufficient initial shielding gas to purge the weld start area. 

One of the major welding companies has been utilizing an oscilloscope and has documented the "Improved Arc Characteristics" at the weld start when using one of our Patented Gas Saving Systems.

Note: Don't confuse our Patented Gas Saver System (GSS) with other devices you may have tried in the past.  The GSS provides a controlled amount of extra gas at the weld start at a flow rate that avoids excess turbulence to properly purge air.  It also does not alter system pressure so "Automatic Flow Compensation" is maintained. Welders Love The Results!  SEE DETAILS

Hydrogen Also A Problem:

Eliminating Oxygen and Nitrogen at the weld start to reduce the possibility to weld porosity and excess weld spatter requires good shielding.  In addition to Oxygen and Nitrogen the surrounding air contains Moisture or Water Vapor.  The Water Vapor can also be drawn into the arc where it will disassociate into Oxygen and Hydrogen.  Hydrogen can cause more than porosity problems.  Some amount can dissolve in the molten steel and will only come out when the weld cools.  Since they are very small, Hydrogen atoms it can migrate through the steel accumulating near defects, dislocations, etc. forming Hydrogen gas.  This can cause cracking.  These cracks may be in the weld itself or in the adjacent parent metal called the heat affected zone. 

Argon Purity

Argon is 0.9% of air.  It is generally produced by liquefying air and separating  the Argon in a elaborate, expensive distillation column.   However Argon can be produced at lower cost and  quality levels and is referred to as "Crude Argon."  Crude Argon may contain about 2% Oxygen.  For most steel welding applications that may not present problems.  However "Crude Argon" contains Nitrogen perhaps about 0.5% !  That is a problem.  Even if the Nitrogen percentage is lower, when combined with moderately turbulent shielding Nitrogen porosity can result. 

The American Welding Society produces a "Specification For Welding Shielding Gases; AWS A5.32."  It defines the Minimum Purity of Gases to be labeled as meeting the AWS standard.  It can be obtained at www.awspubs.com   That specification defines the Minimum Purity for Argon as 99.997%.  That would allow no more than 0.003% Nitrogen if no Oxygen or other gases were present.  It also defines the Maximum Moisture at 10.5 ppm (= 0.00105%.)  There is no reason to get less- that's what you paying for!  Ask for a Certified analysis.

WARNING The AWS Document also warns that Argon and Carbon Dioxide are heavier than air and may concentrate in low areas such as the bottom of pressure vessels, tanks, pits and ships.  This can result in asphyxiation and death.  See our page on "Weld Safely"

Having Variations in Chary Impact Test Results? 

We did also.  We found out why the same weldment achieved 45 ft-lbs and 7 ft-lbs in the same deposit!  Want to know why?

Saving Shielding Gas and Improving Weld Start Quality is Easy...

"Just Replace Existing Gas Delivery Hose with Our

Gas Saver System"

Want to Limit the Maximum Flow Rates That Can be Set? 

Hear a Message from the President of WA Technology   (Who was also the 2007 President of the 53,000 Member American Welding Society)

Click to Hear

Want a way to control the maximum shielding gas flow that can be used?

SEE "Lean Welding Manufacturing" Learning Program

Optimizing Shielding Gas Use and Eliminating Waste