Researchers from the Saarland University have developed a novel non-contact method of transforming 3D printed metal parts into high-precision technical components for specialist applications. The research team consisting of manufacturing technologists combine metal 3D Printing and Electrochemical Machining (ECM).
This method allows processing of strong and lightweight metal parts to produce precision-finished components with complex geometries and dimensional tolerances of a few thousandths of a millimetre.
NEED FOR THE NOVEL METHOD
The aim of the research, led by Professor Dirk Bähre, was to develop a highly efficient method to build complex technical systems like the engines that power cars, planes or rockets are made from a large number of highly specialized metal components. For these complex systems to perform efficiently, all the parts need to fit together perfectly and should be able to withstand extreme mechanical stresses.
Speaking about the significance of the new method, Professor Dirk Bähre from Saarland University explained, “While metal 3D printing is now an established means of fabricating components with complex geometries, these additive processes, which build up the part layer by layer, are not sufficiently precise for components that have to meet extremely strict dimensional requirements. And in some cases, the geometry of the part may be too complex to be produced by conventional metal 3D printing.”
According to Professor Bähre, ‘Our technology for post-processing additively manufactured metal parts offers a cost-effective means of producing high-precision functional surfaces for applications where extremely tight tolerances are crucial. It enables large numbers of parts to be post-processed efficiently and economically.”
Professor Bähre and his research team are specialists in the field of precision machining and finishing and they have set themselves the goal of refining the 3D printed metal part so that their dimensions are correct down to a few thousandths of a millimetre. By removing material electrochemically, even the most complex geometries can be created in the hardest of metals.
Professor Bähre added, ‘Our non-destructive, non-contact manufacturing technology enables us to efficiently machine parts with intricate geometries even when made from high-strength materials.”
ELECTROCHEMICALLY SHAPING THE 3D PRINTED PARTS
The workpieces, which are bathed in a flowing electrolyte solution, can be electrochemically machined to the required geometry working to tolerances of a few thousandths of a millimetre – without any mechanical contact and without imparting any mechanical stresses to the 3D printed metal part. All the engineers need is a source of electrical power.
A high electric current is made to flow between a tool (the cathode) and the conductive 3D printed metal part (the anode). The 3D printed metal part is immersed in a conducting fluid (the electrolyte), which is simply an aqueous salt solution. The electrochemical machining process causes minute particles of metals to be removed from the surface of the metal part. The metal atoms on the surface of the 3D printed metal part enter the solution as positively charged metal ions enabling the metal part to very precisely attain the required geometric form.
Professor Bähre explains, “By adjusting the duration of the current pulses and the vibration of the tool, we can remove surface material very uniformly leaving particularly smooth surfaces and achieving high dimensional precision.”
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The researchers rigorously examined not only the metals used, such as aluminium, titanium or steel alloys, but also the individual process steps involved.
Speaking about the rigorous research, Professor Bähre explained, “Optimizing post-processing requires a thorough understanding of both the material and the process. We need to know, for example, exactly what happened to the metal during the preceding 3D printing stage. That’s why we carefully study the microstructure of the metal produced in the 3D printing process. By meticulously examining both process technology and material behaviour, we can improve and optimize the electrochemical methods in order to obtain even smoother surfaces or more complex geometries at even higher levels of precision.”
The team carried out a large number of experiments in which they first 3D printed the metal part and then determined how the subsequent electrochemical machining stage can be optimized to yield the required results.
Professor Bähre elaborated, ‘We examined in detail how the different material and process parameters interact and then determined how the overall production process should be configured.”
In some cases, for instance, the order in which the process steps are performed proves to be critical. The researchers conducted a systematic analysis of all the influencing parameters, performing highly-precise measurements and detailed analyses. As a result, the engineers now have numerous means of fine-tuning the manufacturing process and tailoring the process parameters to meet application requirements.
The research projects, some of which are funded the European Regional Development Fund, are often collaborative in nature, with Dirk Bähre and his research group working closely with partners from business and industry.
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