Image 1: An orbital micro-plasma arc-welding process during lamination of a cylindrical component surface. Image 2: Evaluation of the orbital micro-plasma powder welding torch prototype featuring a compact guidance system for weld-cladding metal pipe surfaces

Well Welded, Whatever the Position

Steinbeis experts develop orbital micro-plasma powder welding torch

Tubes and pipes, cylindrical components, and containers made of steel have become an indispensable part of plant facilities in many sectors of industry. They are needed for transporting, processing, and storing abrasive and aggressive media. Such equipment is typically subjected to a wide variety of corrosive stress and wear. To address this, the inner and outer surfaces of pipes and cylindrical components require special surface treatment, which not only needs to be economically viable but also has to provide protection against wear and corrosion. The experts at the Steinbeis Innovation Center for Intelligent Functional Materials, Welding and Joining Techniques, Implementation have been working with the mechatronic systems specialist Loesch T-P-L as part of an R&D project looking at the development of an orbital micro-plasma powder welding torch. The device is fitted with a compact guidance system for coating the insides and outsides of metal tubes and components similar to pipes using a whole variety of welding angles.

Adding coatings to improve the resistance of the inner and outer surfaces of materials, in this case rotationally symmetrical parts, helps protect them from material stress caused by abrasion and corrosion. More and more specialists are now turning to orbital micro-plasma powder welding to coat the inner surfaces of cylindrical parts, which not only have small diameters but also now tend to have thin walls. They are using this technique to add premium-quality protective layers in order to combat wear and corrosion on all kinds of material shapes and formats. The specific advantages of this method – such as the flexibility it offers in terms of varying welding consumables and layer thickness (0.5 to 5mm), excellent layer reproducibility, and the low levels of short-term energy required in combination with a low incidence of melting in base materials – make the process highly suitable for such applications. This is also because the process makes it possible to produce near-net-shape layers with predefined layer properties.

The project team used a new design for the welding torch. This has an efficient cooling circuit and offers a reliable process gas and powder supply system within the plasma jet to generate the required reproducible layer quality. The new method for producing the material makes it possible to determine, quantify, and ultimately optimize the complexity of influences on the micro-plasma welding process, such as gas flow mechanics and thermo-physical process effects. The experts working on the research project developed a process for matching the size of the burner head and its guidance system to specified inner tube diameters of at least 40 millimeters. This also made it possible to develop combustion function modules in terms of the required technical and design parameters. The following technical and financial factors played an important role in the development and design of the orbital microplasma powder welding torch:

  • Maximum torch head size of 25 x 25mm for inner layers added to tubes or similar parts (internal diameter at least 40mm)
  • Different coat thicknesses possible starting at 0.5mm
  • Improved welding thanks to mechanically controlled components or module units for adding layers of a suitable quality
  • Development and design of a special technical plasma and protective gas nozzle, for welding torch ranges of 100 – 200A
  • Electric torch output of 200A with an electrode diameter of 3.2mm

As a result of the new development, the project team was able to raise the level of automation for adding plasma coatings to metal tubes and similarly shaped components. At the same time, they made it possible to add predefined layers to specific areas in keeping with stress requirements and thus protect materials from wear and corrosion, even with complex component surfaces. The required welding times have now been reduced to a minimum, which helps improve productivity.

The covered surfaces of metal tubes: inner surface coating,

The covered surfaces of metal tubes: outer coating

The experts at the Steinbeis Innovation Center in Dresden have also been working with Loesch T-P-L to investigate the newly developed welding prototype by conducting comprehensive evaluation tests. To examine coatings on the inner and outer surfaces of cylindrical parts, they added surfaces using high torch power levels and fast welding speeds. The aim was to investigate and evaluate the impact of different process parameters and the internal diameter of plasma jets on electric arcs and arc intensity. They also wanted to examine the formation of layers and their properties. To do this, they used flux consisting of hard alloys based on cobalt and nickel, but also hard alloys consisting of hard particles (cast tungsten carbide). By varying the process parameters of the welding current, voltage, and speed, and by adjusting the volume of process gas (plasma/protective gas) and powder delivery, the experts succeeded in adding layers of the required quality. The welding tests showed that it was possible to achieve a stable plasma welding process, flawless torch ignition and function, and good powder distribution and dosing below the necking nozzle into the plasma column. The quality of the added coating depended on chosen process parameters. Once assessment of the newly developed welding prototype and the guidance system had been completed, it was possible to produce high-quality coatings on the outer and inner surfaces of metal tubes and achieve the required component properties. After examination, the layers were found to be reproducible and the surface coatings were of suitable quality, providing sufficient evidence of the functional reliability of the prototype orbital micro-plasma powder welding torch, which was also easy to handle and offered an automated guidance system.


Associate Professor Dr.-Ing. habil. Khaled Alaluss, Oleg Nuss, Prof. Dr.-Ing. Gunnar Bürkner, Dr. Lars Kulke
Steinbeis Innovation Center Intelligent Functional Materials, Welding and Joining Techniques, Implementation (Dresden)

Michael Loesch
Loesch T-P-L mechatronic systems GmbH (Darmstadt)