VOL. 21 July ISSUE YEAR 2020
MFN Trainer Column
in Vol. 21 - July Issue - Year 2020
New Levels of Flexibility Are Required
In addition to economic and ecological requirements for the final product, the modern production of industrially manufactured goods is also increasingly subject to the challenges of flexibility with increasing design requirements. In conventional production (turning, milling), the processes are designed in such a way that the increasing variety (e.g. in automotive engineering) with ever-shorter product life cycles faces a machine concept that has the greatest possible flexibility and productivity - even beyond one cycle.
In addition to the choice of processing machine, the different processing concepts also play an important role. Because even if there is always machining at the beginning of the process chain, which can be adapted to the requirements of the component through different cutting materials, coatings, geometries, etc., technologies should also be considered in this step for reasons of resource and energy savings that enable an additional improvement in component quality. These could be used hand-in-hand with machining in the same setting or at least in a chain with existing machines.
In addition to welding or hardening operations, roller burnishing or deep rolling processes are particularly suitable. Both processes are identical in themselves, but the pursued goal is different. While roller burnishing solely pursues the goal of achieving a certain surface topography, deep rolling should, for example, increase the life of a component.
Additive manufacturing is the next step in increasing the flexibility of the components and reducing the use of raw materials. The combination of these three process steps: production of the raw part, machining and finish processing would correspond to the previously requested requirements. If this can take place on one machine - or at least in a chain - there is nothing standing in the way of the individually adapted component.
A further approach to the integration of mechanical surface treatment processes can be seen in the targeted component conditioning. This means that the influence of machining is specific and dependent on the geometric conditions but also on the actual requirements with regard to load.
By building up the workpiece in layers from a powder, a supplied wire or liquids, in certain circumstances, 100 percent density of the workpiece may not be achieved. In some cases, methods are used after the complete additive construction of the workpiece in order to achieve subsequent compaction. However, the internal structures of a component cannot be achieved by this procedure.
In addition, continuous compression is not possible for thick-walled components, since the depth of penetration of the process is limited. In the case of thin-walled components, only very small forces can be used to prevent the component from being deformed, so that continuous compression is also ruled out here.
The stress state in the component is also problematic in additive manufacturing. It can be expected that due to the high number of melting and cooling phases, tensile residual stresses will occur at least at certain points. These residual tensile stresses in connection with the comparatively poor surface quality of the additive manufacturing processes can contribute significantly to the early failure of the component.
The various problems and challenges that arise in additive manufacturing with regard to surface quality, residual stress and component density can be solved by incremental compression. In this method, one or more previously applied component layers are post-compressed by a compression process. This can be achieved both by a rolling process and by a hammering process - but also by any other mechanical hardening method such as shot peening. By means of rolling or hammering, specific residual stress states can be set in components, which can be used to influence complex geometries.
Results, influences and findings that have been shown and established in the conventional manufacture of components should also be taken into account and integrated early on in additive manufacturing. This is the only way to bring these processes to higher levels of performance and flexibility. The combination of all the advantages of additive manufacturing with the process combinations in conventional manufacturing will enable structures that have not yet been able to be manufactured, which will give a new basis to economic and ecological requirements.
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Author: Sirko Fricke