Careful! It’s Hot and Cuts Like a Knife

Steinbeis experts develop a plasma cutting torch for the thermal cutting of multi-material components

Materials development is advancing in leaps and bounds in a number of areas of industry, especially in the automotive sector, rail vehicle construction, and plant engineering. All of these areas use a variety of materials such as steel, aluminum, plastics, composites, and components made from a mixture of materials. An increasing number of metallic parts offering particularly high material strength are also finding their way into car body construction. But at the same time, rescue workers attending road accidents must be able to use thermal means to take strong car body parts apart quickly and precisely in order to free injured passengers. Having recognized this issue, a team of researchers at Intelligent Functional Materials, Welding and Joining Techniques, Implementation – the Chemnitz-based Steinbeis Innovation Center – joined forces with SGE, an equipment development specialist, to develop an innovative plasma torch that uses thermal energy to cut through electrically conductive and non-conductive components, independent of material type.

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The project team was quick to realize that the technical and technological complexity of the project could only be addressed by leveraging the principles of non-transferred plasma arc welding. This involves using an internal burning arc to thermally ionize the outflowing process medium within the torch head in the form of plasma gas or pure air. The process would make it no longer necessary to apply current to components, such that the flame cutter can also be used on thermoelectrically non-conductive materials. A prerequisite for developing such a cutting torch is a flame cutting system with the required strength and efficient cooling.

Requirements for the prototype

Before the engineers could get down to business, they first had to define and determine technical process data. This information formed the basis of the overall process engineering concept for the plasma arc cutting process, including which materials to use, the functional parts of the torch, process engineering performance, and the newly designed torch cooling system. The team working on the project defined the following technical parameters and criteria for the torch prototype:

A functionally reliable flame cutter system based on non-transferred plasma arc technology with a maximum torch capacity of 200A
Error-free arc ignition, delivering strong arc performance and high process stability
The possibility to use untreated air and inert gases as the process medium
Double cooling in the torch head to provide a powerfully cooled electrode/cathode (round electrode) and plasma nozzle/anode
Adjustable spacing controls between the cathode and anode
The possibility to determine process parameters for the thermal cutting of metallic and non-metallic materials, based on defined cutting depths, cutting speeds, and burner intensity

Referring to these criteria, the Steinbeis experts worked with SGE to build a prototype burner. Non-transferred plasma arc technology proved to be suitable for the plasma cutting torch to achieve the required electrical torch rating of 200A. As required, the head of the plasma cutting torch was fitted with the powerfully cooled round electrode/cathode, offering regulated cathode spacing and a cooled anode. As a result, the plasma cutting arc formed between the cathode and anode is capable of burning independently of current being applied to components.

Putting the prototype through its paces

The new prototype burner was subjected to rigorous testing. Numerous cutting tests were conducted on steel components and non-metallic materials, and the prototype proved effective not only in terms of the process, but also when it comes to function and performance: electric potential, ignition, gas-tightness, watertightness, process performance, burner cooling – flawless on all counts. For the ignition process, use was made of a high-frequency ignition unit from a power inverter or plasma current source. The project team conducted detailed testing of the process on the prototype, looking at thermal cutting performance on multi-material components and composites. The result: a torch prototype offering zero defects and a reliable plasma arc, effective torch cooling, and powerful cutting, especially when using air as the process medium.

To conclude the project, validation work was carried out on the new prototype of the plasma cutting torch. Cutting tests were conducted on steel materials, concrete, and plastics, looking at component thicknesses and cutting depths ranging from 1 to 30mm, cutting speeds of 500 to 2,200mm/min, currents ranging from 45 to 150A, and air pressure flow rates of between 5.0 and 5.8 bar. As expected, the team detected no signs of wear or thermal damage on the electrode/cathode and plasma nozzle. The temperatures measured at the cooled plasma nozzle/anode ranged from 60 to 120°C, at currents of between 45 and 150A as well as different cutting depths and speeds. The tests clearly showed that the double cooling method applied to the torch head to cool down the active electrode/plasma nozzle areas works well with the defined torch output of 200A. For the project team at the Steinbeis Innovation Center for Intelligent Functional Materials, Welding and Joining Techniques, Implementation and the experts at SBU, it was thus clear that they had achieved what they set out to and successfully completed the project!