One of the key components to ensuring that your welds are as strong as humanly possible is to have the correct consumable. The heat generated from the welding process is enough to melt the consumable down to a point capable of filling the space between the two pieces of material that are being welded together.
What is matching?
There are a number of different filler metals
One of the most important things to know in order to succeed as a welder is the difference between the different types of consumables. This is what we’ll go over in this article today.
As many of already know, there are a variety of different filler materials used for different welding processes. Listed below are a few examples of this.
- In SMAW you will typically use a coated electrode or flux. The coating shields the weld from oxygen when it’s burned off. Sometimes filler metal gets added to the coating to enhance the process.
- GTAW typically uses a tungsten rod to heat both the metal and filler material up. The rod is just used to heat the metal up but isn’t added to the filler metal.
- Wire consumables are used for GMAW
How to match the strength of the consumable to a metal
It’s critical to make sure that the consumable has an equivalent melting point and is as strong as the base material it’s being used to weld together. It’s not a simple process to match these characteristics together. It’s important to match both the yield and tensile strengths of the materials being welded and this requires a certain expertise.
In fact, the process of matching materials requires a bit more than just looking at charts- it’s highly difficult to match exactly. The process actually just requires that one look at all of the possible material strengths and choosing one that is just as strong or stronger than that being welded together. Also keep in mind that undermatching materials can also sometimes offer one a good result.
Despite all the things said above about the difficulties associated with welding there are a few factors any welder should consider when they’re choosing a filler metal. Below are these factors:
- What’s your base metal?
- What’s your welding position?
- What’re the regulatory specifications and codes?
- What’re the design requirements?
- Is your shielding gas compatible?
- What post-weld heat treatment will you use?
- What welding eqipment will you use / have at your disposal?
1. Base Metals
Much like a relationship the joining of metals is chemistry-based. It’s a matter of figuring out which metal works best with which base material. A good rule of thumb is that you want the filler material you’re using to match the lower strength of the base metals.
*when you’re welding the dilution from the higher strength base metal is what strengthens the deposit of the weld metal.
2. Welding Position
It’ a good idea to rotate parts so they can be welded in flat positions. The reason for this is that welding in a flat position is considered the most inexpensive position as compared to vertical, horizontal, and overhead positioning.
3. Regulatory Specification and Codes
Either the requirements of your job or having an understanding of the requirements (service requirements) of the weld will give the welder an understanding of the type of wire they should use.
Examples:
Mild steel for example tends to rust when exposed to harsh elements – meaning that it’s important to use a filler metal that will be able to withstand the environment / conditions the weld will be exposed to.
4. Shielding Gas
You’ll also want to make sure the shielding gas you use is compatible with the filler metal you use. Shielding gases each effect welds in different ways.
Example:
When you add argon to CO2 (carbon dioxide) you can add more of the chemistry of the filler metal into the weld deposit. This helps improve the consistency of the weld quality, reduces spatter levels, and allows for weld pool control.
Not only that, but adding CO2 will burn some of the elements of the filler metal.
5. Design Requirements
You’ll want to make sure the filler metal you choose meets/exceeds the needs of the joint’s design. When you’re welding on a thin material, you’ll want to make sure the characteristics of the arc are appropriate. If the wire is designed for deep penetration it can result in the you burning through. If you’re welding a thick part with a “V” joint, you’ll want a filler metal with better penetration characteristics.
6. Heat Treatment
Preheating to certain temperatures is important for certain material thickness and steels before you actually begin to weld. When you preheat you’re essentially allowing the part to cool which helps avoid cracking and weld shrinking issues.
Some welds, however, may require a post-weld heat treatment. Post weld heat treatment helps reduce stresses as well as lower the residual heat introduced while welding which allows the weld joint to return to it’s desired properties.
Video credits to John Park.
7. Welding Equipment Used / At your disposal
The type of equipment you use will play a very important role in what filler metal you use. For example, the power source you have will need to have enough amps for the wire you’re using (more specifically the diameter of the wire). If there is not enough amperage you’ll want to get a wire with a different diameter – this will possibly cause the weld to be produced more slowly (keep that in consideration).
You’ll want to have a power source that offers a welding current that fits the filler material you choose. When you weld using an incorrect current your weld can end up being of poor quality or you can end up producing more splatter than you’d like to.
Desired Weld Characteristics
Understanding the desired weld characteristics plays a very important role as well.
Reverse Polarity: Greater weld penetration
Straight Polarity: Produce shallower joint penetration
