The effects of oxygen in welding: How forming affects welding quality
Welding is about more than just the welding process itself. The welding environment, in particular the composition of the surrounding gases, has a decisive influence on the quality of the weld seam. The oxygen content plays a particularly important role here. This article looks at the effects of oxygen on the weld seam, the protective measures that can be taken with gas-shielded welding and forming and why forming in particular is a crucial step in many high-quality welding processes.
Overview of relevant welding processes
Various processes are used in welding, which differ in terms of their technology, the materials and gases used. In order to better understand the importance of oxygen and its reduction, we will first take a brief look at the most important processes that work with shielding gas:
MIG/MAG welding (metal inert gas / metal active gas welding)
MIG/MAG welding is one of the most frequently used welding processes. A continuous wire coil is used as an electrode and the weld pool is shielded by a shielding gas. While inert gases (such as argon or helium) are used for MIG welding, active gases (such as CO₂ or mixed gases) are used for MAG welding. Oxygen can be both desirable and undesirable here, depending on the material and welding process.
TIG welding (tungsten inert gas welding)
TIG welding uses a non-melting tungsten electrode and is known for precise weld seams. Argon is usually used as a shielding gas to create a clean welding environment. Even small amounts of oxygen can contaminate the weld pool and impair the quality of the weld seam.
Manual electric welding (manual electrode welding)
This is a process in which a coated electrode is used. Whilst this process does not require any additional shielding gas, a layer of gas is created during welding to protect the weld pool. Due to its simplicity and flexibility, it is often used on construction sites or in areas that are difficult to access.
The role of forming in welding
Focus on root protection
While shielding gas has the function of protecting the weld pool surface from atmospheric influences such as oxygen during welding, forming (also known as root protection) goes one step further. Here, the oxygen on the root side of the weld seam, i.e. the back, is reduced or removed by adding a forming gas (usually argon or a nitrogen mixture). This results in a clean and oxidation-free root seam.
Moulding is particularly important for materials such as stainless steel, titanium and other corrosion-sensitive metals, as the root seam and the surface of the weld pool must be protected from oxidation.
The effects of oxygen on welding quality
Oxidation and contamination
Oxygen is a reactive gas and can significantly impair the quality of the weld seam. If oxygen gets into the weld pool, it can lead to undesirable reactions that form oxides. These oxides are usually brittle and impair the mechanical properties of the weld seam.
Some of the most common problems caused by oxygen in the welding process are
- Oxidation of the molten bath surfaceThis can lead to visible discolouration and weaken the strength of the weld seam.
- PorosityBubble formation in the weld pool due to oxygen can lead to pores in the weld seam, which favours seam weakness and possible cracks.
- Contaminated root seamIf the root side of the weld seam is exposed to oxygen, this can lead to severe oxidation and make the welded joint brittle.
Effects on various materials
The sensitivity to oxygen varies depending on the material:
- Stainless steelThis material is extremely sensitive to oxygen, as a protective chromium oxide layer is required, which can be destroyed by contact with oxygen in the molten bath.
- AluminiumAs aluminium oxidises quickly, even a low oxygen content can lead to a superficial oxide layer that prevents good mixing of the molten bath.
- TitaniumTitanium and its alloys are extremely reactive with oxygen and therefore require an almost oxygen-free environment during welding.
Protective measures against the influence of oxygen during welding
Optimised shielding gas compositions
Choosing the right shielding gas is crucial to minimise the influence of oxygen. Inert gases such as argon are often used for sensitive materials such as stainless steel or titanium. When forming, special forming gases such as argon or nitrogen mixtures are used to displace the oxygen and ensure a clean welding environment.
Correct technology and tightness
When welding, it is important to work carefully in order to minimise the influence of oxygen. Particularly when welding pipes or containers, the areas to be welded must be sealed to ensure that the forming gas can be introduced effectively.
Gas flow control and venting
An optimal gas flow rate is crucial to completely displace the oxygen and avoid turbulence that could carry oxygen back into the welding zone.
Comparison: gas-shielded arc welding vs. forming in relation to oxygen
Similarities
Both processes are used to protect the welding process from oxygen and other gases from the atmosphere. While gas-shielded welding aims to shield the weld pool from oxygen, forming also protects the root seam from oxygen.
Differences and advantages of moulding
Forming offers the advantage that the entire weld seam - both the top and the root - is protected from oxygen, especially for high-quality welded joints. This is particularly important for materials that are sensitive to oxidation, such as stainless steel or titanium.
Conclusion: The importance of oxygen protection in the welding process
Oxygen can have a significant influence on welding quality. Both gas-shielded welding and forming are important processes for achieving a high-quality weld seam. While gas-shielded welding protects the weld pool, forming also ensures a clean and protective root seam, which is particularly important for demanding welding work. The right choice of gases and techniques is therefore crucial to achieving a high-quality, stable and durable welded joint.