2015. január 23., péntek, 18:10
Regardless of whether you’re using laser-, resistance-, WIG-, MAG- or MIG-welding technologies, specific areas of components invariably need to be cleaned both before and after the joining process. As far as the aspects of manufacturing and cost-effectiveness are concerned, processes that are efficient, selective, dry, and which can be easily integrated into automated production lines are especially suitable. The CO2 snow-jet technology fulfills these requirements.
In order to meet rising demands concerning the quality and long-term reliability of welded joins, surfaces have to be free of grease and particles. After welding, the joins need to be cleaned in preparation for the next processing step, for example painting or coating. Despite the fact that the contamination often only has to be removed from a localized area, wet-chemical cleaning methods are generally implemented. These have several disadvantages: firstly, components invariably have to be removed from the production line in order to be cleaned. Secondly, the workpieces and their transport containers or pallets need to be dried using an energy-intensive process and the cleaning agents required are costly to dispose of or recycle. Lastly, when returning components to the production line, there is a risk that they will become recontaminated due to environmental factors. Cleaning processes, such as the environmentally-neutral CO2 snow-jet technology from acp – advanced clean production GmbH, are ideal for dry-cleaning components selectively and reproducibly within short cycle times directly before and after the welding step – either manually or as an automated process integrated into the production line.
Here, the weld seam of transmission components is selectively cleaned in-line directly before the laser-welding step
Efficient, selective cleaning before and after welding
As opposed to blasting with dry ice, this CO2 cleaning system uses liquid carbon dioxide as a medium which is generated by chemical and other industrial processes. It is fed to the cleaning step from cylinders or tanks and has an indefinite shelf life.
The heart of the cleaning system is a patented cleaning head made of a supersonic two-component ring nozzle. Liquid carbon dioxide is guided through the nozzle and expands on exiting to form a mixture of snow and gas. Oil-free compressed air is fed to the core jet as a jacketed jet, accelerating the non-toxic, non-combustible CO2 snow crystals to supersonic speed. That's what makes the acp cleaning process so effective: when the easy-to-focus jet impacts on the surface to be cleaned, the snow crystals liquefy and then sublimate. The sublimation impulse causes any particulate contamination present on the surface, such as particles, chippings, dust or polishing paste, to be detached and carried away. In its liquid state, carbon dioxide also acts as a solvent that reliably removes organic contamination, for example oils, grease, wax, processing media, anti-corrosive coatings or graphite.
The cleaning module can be integrated into a welding line or an assembly line in a space-saving way
At the same time, the low degree of hardness of the snow crystals ensures gentle and reproducible cleaning results, even for sensitive surfaces and delicate structures. The technology can therefore be implemented not only to selectively clean rotationally-symmetrical transmission components or sheet metal parts before welding but also for the targeted removal of smoke residues from components such as from injection valves after laser-welding and laser-structuring. To avoid recontamination, the detached contaminants can be extracted continuously with the carbon dioxide.
As the carbon dioxide changes completely into a gaseous state during cleaning with the result that workpieces being cleaned dry immediately, there is no need for the typical, energy-intensive, drying step required in the case of wet-chemical processes. Furthermore, after cleaning the detached contamination is sorted and can thus generally be disposed of easily and cheaply.
The smoke residues forming on steel components from laser-welding (left) can be removed by the snow-jet cleaning system without leaving any residues (right)
Easy to automate and adapt to applications
The modular design of the CO2 snow-jet technology from acp means it can be easily adapted to customer requirements. For example, it can be integrated as a space-saving solution into an assembly or welding plant in the one-piece flow of a serial production. Alternatively, the CO2 snow-jet system can be installed as a separate process step for cleaning directly before or after welding, or before the next processing step. The system can be fitted with several nozzles functioning either in cycles or continuously. The cleaning heads can be switched in series or be freely arranged “in space” to enable a specific component area to be cleaned. To remove contamination in a targeted and efficient way, either the nozzle moves over the surface of the component or the component is moved past the stationary nozzle. In both cases, a robot or axial system, which is specifically motion-programmed for the component, ensures an optimum and reliable cleaning result.
In consequence, the cleaning system offers a high degree of flexibility and can be rapidly adapted to new cleaning requirements or different component geometries. What’s more, a range of programs can also be filed for different workpieces in the system controls.
Because of its special features, the CO2 snow-jet technology offers major potentials for cleaning applications before and after welding, reducing throughput times in production whilst making processes more efficient and gentler on resources at the same. And that with the controlled quality needed to produce even, pore-free, maximum-strength weld seams or to subsequently coat/paint the welded surface.
Author: Doris Schulz