The soft plasma welding process for thin-walled workpieces is used when thin sheets, small components, and delicate materials need to be joined with high precision. It combines the clean process control of TIG welding with a more concentrated heat source and highly controlled heat input. This makes soft plasma a strong alternative to conventional TIG welding for many applications.
What makes Soft Plasma so special for thin-walled parts?
Soft plasma is particularly well-suited for thin-walled components because it operates in a highly controlled manner; when welding such parts, precision, minimal distortion, and a stable molten pool are of paramount importance. This is precisely where the advantages of this welding process lie: the heat-affected zone remains small, the process runs more smoothly, and the weld quality is more consistent. This makes it possible to safely process even delicate geometries.
Soft plasma is typically used for material thicknesses ranging from about 0.5 to 4 mm. Small gaps—up to about 10 percent of the material thickness—can often be bridged more effectively than with conventional plasma welding. Compared to TIG welding, welding speeds up to 20 percent higher are also possible—provided the settings are correct.
Plasma Fundamentals and Gases
Plasma is a high-energy state of gas in which electrons are separated from atoms, causing the gas to become conductive. Plasma welding makes use of precisely this effect: an arc is sharply constricted by a fine, water-cooled nozzle. This creates a concentrated plasma jet with high power density, excellent arc stability, and controllable energy. This is the main reason why the process is more precise than many other welding methods.
Two gas streams: plasma gas and shielding gas
In plasma welding, a distinction is made between two gas flows:
- Plasma gas: Located at the center of the torch, it forms the actual heat source together with the arc.
- Shielding gas: Protects the workpiece, weld bead, and molten pool from air, oxidation, and contaminants.
Argon is typically used as the plasma gas, while argon or mixtures of argon with hydrogen or helium are used as shielding gases. Argon-hydrogen mixtures are often suitable for stainless steel. Argon and helium are frequently used for aluminum, titanium, or nickel alloys.
Soft Plasma Compared: TIG, MIG, and Plasma
Soft Plasma vs. TIG Welding
The basic principle of TIG and tungsten plasma welding is similar: Both use a non-consumable tungsten electrode, an arc, and a shielding gas. The main difference lies in the focusing of the arc. In TIG welding, the arc is more open, whereas in plasma welding, it is compressed by the plasma nozzle. This increases the energy density, makes heat input more precise, and keeps the plasma arc more stable.
| Characteristic | TIG Welding | Soft Plasma / Tungsten Plasma Welding |
| Arc | more open, softer | more focused, more stable |
| Energy density | medium | higher |
| Heat-affected zone | larger | smaller |
| Tolerance for small gaps | lower | higher |
| Delay | rather higher | lower |
| Welding speed | lower | often higher |
| Suitability for very thin parts | good | very good |
Soft Plasma vs. MIG Welding
MIG welding is a high-productivity process that uses a wire electrode and continuous wire feed. It is often too coarse for thin-walled workpieces and is therefore less suitable when the highest precision and minimal heat input are required. This is precisely where the difference lies: MIG excels in speed and efficiency, while soft plasma excels in controlled heat management, fine weld beads, and delicate workpieces. MIG is therefore ideal for rough production, but it is usually not the first choice for small, thin, and high-quality welds.
Advantages of Soft Plasma Welding at a Glance
- Highly precise control of current and heat
- Small heat-affected zone, resulting in minimal warpage
- A steady, stable pilot arc with high ignition reliability
- Good weld quality on very thin sheets of metal
- lower consumption of filler material
- Good tolerances and high process stability
- Suitable for stainless steel, aluminum, titanium, and other delicate materials
- Well-suited for automated systems and repeatable welding operations
Tungsten Plasma Welding: Variants and Operating Modes
There are two main operating modes in tungsten plasma welding:
- Transferred arc: The arc burns directly from the electrode to the workpiece. This is the standard method for actual welding.
- Non-transfer arc: The arc burns between the electrode and the nozzle inside the torch body. This operating mode is used primarily for special applications or for ignition.
In both cases, the tungsten electrode remains protected inside the plasma torch, which extends its service life and ensures stable process control.
Microplasma (Micro-PAW)
Microplasma is the most delicate form of the plasma welding process. It uses very small currents, sometimes for material thicknesses as low as 0.01 mm, and operates within very low current ranges. The process is suitable for ultra-thin films, membranes, delicate electronic components, and small precision parts where even a conventional TIG process would generate too much heat.
Push-through technique
The push-through technique is typically used for thin sheets up to about 3 mm. Unlike the pierce technique, the material is not pierced but is melted in a controlled manner. This results in a very clean molten pool with good surface tension and a smooth weld bead. This is the appropriate method for many thin-walled workpieces because the penetration depth can be precisely controlled.
Keyhole technique
The piercing technique operates at significantly higher energy levels and creates a through-hole in the molten material. This process becomes more practical for material thicknesses of 3 mm and above and can be used for thicknesses up to approximately 12 mm. It is therefore less typical for conventional soft plasma, but it clearly demonstrates how flexible plasma welding can be overall.
Process Parameters: A Few Millimeters and Amperes Make All the Difference
In plasma welding, even a few millimeters or a few amperes can often make all the difference in the weld. For thin sheets, therefore, welders usually deliberately select low welding current ranges to prevent the material from burning through.
The most important things are:
- Current
- Distance between the nozzle and the workpiece
- Nozzle size
- Gas volume
- Choice between DC and pulse operation
Pure argon is the standard plasma gas. The gas flow rate is usually between 15 and 35 l/min, and the shielding gas flow rate is typically between 3 and 12 l/min. Additionally, pulsed operation can help control heat input even more precisely.
Equipment: Torch, nozzle, and tungsten electrode
A plasma torch consists of a torch body, a plasma nozzle, a shielding gas nozzle, a gas guide, and an internal tungsten electrode. The nozzle is particularly important in soft plasma welding, as it determines the shape, focus, and stability of the arc. The nozzles should be water-cooled to prevent overheating, ensuring that the geometry remains stable even during longer welding operations.
Suitable tungsten alloys are usually used for the electrode, as they ignite easily and promote a uniform arc shape. In any case, one thing is certain: properly adjusted equipment and skilled operation are the number one prerequisite for consistent welding results.
Applications: Where Soft Plasma Shines
Soft Plasma is used wherever high-quality machining of delicate materials and thin walls is required.
Typical industries include:
- Automotive Industry: Thin-Walled Precision Components
- Medical Technology: Surgical Instruments, Very Small Stainless Steel Parts
- Aerospace: Heavy-Duty Components
- Equipment Manufacturing and Precision Engineering: Precision Joining Tasks
- Metalworking Industry: Toolmaking, Sensor Technology, Small Metal Assemblies
Advantages and Limitations: When Soft Plasma Is Appropriate and When It Isn't
The advantages for thin-walled components are significant and range from a small heat-affected zone to exceptionally high precision. However, despite all its strengths, the soft plasma process is not a one-size-fits-all solution: For very thick steel sheets or heavy-duty welded structures, for example, other welding processes are often more cost-effective. Furthermore, soft plasma requires proper joint preparation and experienced specialists. Without qualified personnel and process knowledge, the advantages of the process diminish rapidly.
Professional Soft Plasma Welding Process and More at Schnelldorfer Maschinenbau
Since 1986, Schnelldorfer Maschinenbau has been synonymous with technical expertise in welding technology. We develop and manufacture complete technical solutions, from design through to the documentation of manufacturing conditions. We manufacture not only standard systems but also custom-built special-purpose machines for laser, plasma, TIG, MIG/MAG, and microplasma processes. Our goal is clear: optimal welding conditions, ergonomic working environments, the highest level of workplace safety, and maximum productivity and profitability for our customers.
We know that if you want to use soft plasma welding for thin-walled workpieces in your production process, it’s worth taking a close look at the material, wall thickness, quantity, and quality objectives. Talk to our experts about your project—we’ll then develop a welding solution that effectively combines precision, reliability, and cost-effectiveness.
Submit a non-binding inquiry now and schedule a free consultation—we look forward to hearing from you!
Frequently asked questions (FAQ)
For which applications is plasma welding suitable?
Plasma welding is suitable for thin to medium material thicknesses, high weld quality, and applications with tight tolerances. It is particularly effective for stainless steel, aluminum, titanium, thin components, and quality-critical industries.
What's the best way to weld thin sheet metal?
For very thin sheet metal, TIG welding, soft plasma, or microplasma are usually the best options. Soft plasma is often the better choice, especially when precise positioning and minimal distortion are required.
Which three welding processes are most commonly used in practice?
TIG, MIG/MAG, and plasma welding are particularly common. Depending on the task, other technologies may also be used, but these three cover many industrial welding applications.
What should you keep in mind regarding wear, the nozzle, and the electrode?
The nozzle and tungsten electrode must be inspected regularly. The reason: Wear on the plasma nozzle, shielding gas nozzle, or electrode alters the arc and compromises weld quality, penetration, and arc stability.
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