Weld penetration is defined as the distance the fusion line goes below the surface of the metal being welded. Something else to keep in mind is that the welding current has a major influence on the welding penetration. Increasing or decreasing the current will influence or decrease the penetration of the weld as well.
*Another definition for weld pentration (or depth of fusion) is the distance the fusion extends into the base or previous pass from the surface melted during welding.
Another thing that is directly related to penetration is the tip to work distance. This specific detail has the opposite effect that welding current has on penetration. The higher that the tip to work ratio is the lower that both current and penetration are and vis versa. Some find it helpful to use this ratio to control the penetration of the material being welded.
What variables affect welding penetration?
There are a few variables that affect welding penetration. Of these variables, the most important (and their corresponding effects) are:
What effect does voltage have on welding penetration?
The higher the voltage the less penetration. And vice versa for low voltage. When the voltage is higher (and usually hotter) that typically means the arc is more widely spread out and deposits a wider bead.
*On that same note, if the voltage is too low the arc will begin to behave erratically and will lose penetration.
Wire feed speed
The speed with which the electrode travels down the welding joint also has a direct affect on the length of time an arc’s energy has to transfer into the base plate at any point in the plate. As the speed of travel increases the length of time an arc is over a joint shrinks as well as the penetration. And vice versa for travel decreases.
Polarity
The type of polarity affects penetration level. With the majority of arc welding processes the following polarity types have the following effects:
Direct Current Electrode Positive: With DC + polarity more weld penetration is produced since more arc energy is focused into the base plate.
Direct Current Electrode Negative: With DC – polarity less weld penetration is produced because more of the arc energy is focused on the electrode and not the base plate.
The welding processes this is the case with are:
- FCAW
- SAW
- SMAW
- GMAW
The effect of DC+ and DC- is the opposite for GTAW (TIG)
Welding Process
Each welding process has different penetration characteristics.
SAW, FCAW, GMAW (using a globular, pulse spray, and spray mode): These welding processes are known for delivering higher than normal levels of weld penetration.
GMAW (in short-circuit metal transfer mode) and GTAW (metal core): These welding processes (in their respective metal transfer modes) are known for delivering lower levels of weld penetration. This is alo depends greatly on the type of electrode used.
Type of Electrode
Electrodes all have different penetration characteristics. The effect an electrode has on a weld also depends greatly on the welding process. SMAW for instance, has a penetration level that is completely different when it’s performed with different electrodes. When you use an E6010 electrode you typically get deeper penetration while using an E7024 electrode produces shallow weld penetration.
This also goes for Flux core arc welding as an E70T-1 electrode typically produces deeper weld penetration while a E71T-1 electrode produces less penetration.
CTWD Variations
When you’re using welding processes such as SAW, FCAW, and GMAW (on constant voltage, I might add) along with a set wire feed speed and voltage, with an increasing contact tip to work distance, more resistance to the flow of electricity through the electrode happens since the metal electrical conductor is longer. An increase in resistance (at a constant voltage level) causes current to decrease which will result in penetration decreasing. As welding current increases so does welding penetration.
Travel Angle
The degree of travel (whether it’s a drag or push travel angle) will affect the amount of arc force directed into the base plate. The degree of travel angle has a converse effect on weld penetration. As the degree of travel angle becomes more severe the level of weld penetration decreases.
Type of shielding gas
The type of shielding gas used also has a direct effect on welding penetration. Some types of shielding gasses have a higher rate of conductivity and therefore a broader, deeper penetration profile. Examples of such shielding gasses are:
- 100% Helium
- 100% CO2
Some shielding gasses have a lower rate of thermal conductivity an therefore a shallow, tapered penetration. Examples of such shielding gasses are:
- Argon and Carbon Dioxide blends
- Argon and Oxygen blends
- 100% Argon
How do you improve welding penetration?
To improve welding penetration, we have to first look at the common causes of poor welding penetration. The most common causes of poor weld penetration (and their fixes):
Slow wire speed
To fix slow wire speed all you have to do is adjust it to a faster setting.
Low voltage
If you’re welding with a gun set on low voltage all you must do is change the output to a higher setting and see if the penetration gets better.
Excessive wire stick out
To fix excessive wire stick out you’ll have to move the contact tip on the end of your welding gun closer to your workpiece to shorten the exposed length of wire.
Welding too thick of a material
To fix the issue of welding too thick of a material you must make sure your material doesn’t exceed the thickness noted in your welders manual.
Fast gun travel
If you are experiencing fast gun travel all you must do is slow down the travel speed of your gun while pull / drag molten metal puddle.
Poorly prepping your base metal
You want to make sure the materials you’re welding are thoroughly prepped before you begin welding. If the materials are heavy-gauge materials, you should increase the weld gap between them and bevel the edges on either side of the material.
Video credits to Weld.com. It explains how to clean and prep base metal.
