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Method for generating metal structures optimized for machining used in powder bed-based additive manufacturing

Abstract

LPBF process for the generation of porous structures for the gentle machining of complex components with thin-walled and filigree structures

Background

For functional surfaces it is necessary to rework additively manufactured (AM) metal parts. This post-machining is currently based on decades of experience in the machining of conventional components. AM now offers new design options which help to influence the cutting process conditions locally and thus to improve the cutting conditions in a targeted manner. Powder bed-based (PBF) processes in particular offer a wide range of control options for this purpose.

These control options are required for reworking high-performance components used in aerospace and other demanding industries.

Problem

Additive processes, especially powder bed-based 3D printing processes (such as Laser Powder Bed Fusion (LPBF) processes), are comparatively cost-intensive. The components to be manufactured with LPBF technology are therefore usually highly optimized and often feature thin-walled and bionic structures. Due to the surface qualities that cannot be sufficiently achieved with the LPBF process in some cases, e.g. in the production of functional surfaces such as sealing seats or guide surfaces, machining finishing steps are often necessary. In addition, support structures are often used in the LPBF process, which also have to be machined or removed in a stressing manner. Post-processing, and also the clamping of the component, sometimes generate considerable process forces. Particularly in the case of complex, delicate or thin-walled components, exerting such high forces can have a negative effect on the quality of the component, but also on the tools used.

Solution

Scientists at the University of Stuttgart have developed a method to solve the problems described above and simplify the machining of AM components. During the LPBF process, the typical aim is to produce completely dense material. According to the invention, the areas of the component to be machined are designed in the form of a porous structure. These porous areas have a reduced density compared to the areas that are not to be removed. The porous structure can thus be removed more easily with minimum machining forces. During the production of the component, PBF processes involve melting powdered materials by means of an energy beam (e.g. laser (LPBF) or electron beam (PBF-EB)). By lowering the induced energy during the process, the density and strength of different areas of the component can be adjusted in a targeted manner. This is done by selecting the appropriate parameters required to produce solid or porous areas. In the subsequent processing step, the porous structure is then removed to create the finished component.

Initial analyses have shown that the weakened structure helps considerably reduce the machining forces during drilling and milling. As a result, the process forces that occur during milling have been reduced by up to 45%. During drilling, the improved chip shape led to high-quality surface finishes (Rz = 9.7 µm) and better cylindricity (< 0.09 mm). This helps with components that cannot withstand high machining forces and gives more freedom for the design and post-machining of optimized components. It is particularly advantageous for the demanding machining of advanced AM components.

 

Schematic diagram of the process according to the invention. Through the targeted use of porous structures, specific areas can be easily removed by means of machining. This helps reduce cutting process forces and protect tools and components.  Image: IfW, University of Stuttgart
Schematic diagram of the process according to the invention. Through the targeted use of porous structures, specific areas can be easily removed by means of machining. This helps reduce cutting process forces and protect tools and components. Image: IfW, University of Stuttgart

Advantages

  • The new method makes it easier to rework surfaces in order to achieve high-quality surface finishes
  • facilitates the removal of support structures
  • makes it easier to produce delicate, fragile components that are often destroyed/damaged when applying conventional post-processing methods
  • protects cutting tools during reworking by reducing the process forces by up to 45%

Fields of application

Thin-walled and filigree components, such as topology-optimized components, which require post-machining. Possible areas of application are components from aerospace, automotive, tool making, machine tool making, but also medical technology. Examples are heat exchangers, bicycle forks, implants and others. 

Publication and links

C. Maucher et al., Journal of Production Engineering 2021, Improving machinability of additively manufactured components with selectively weakened material

Exposé
Contact
Dr. Dirk Windisch
TLB GmbH
Ettlinger Straße 25
76137 Karlsruhe | Germany
Phone +49 721-79004-0
windisch(at)tlb.de | www.tlb.de
Development Status
TRL4
Patent Situation
DE 102020119258A1 pending
EP 3943218A1 pending
Reference ID
20/032TLB
Service
Technologie-Lizenz-Büro GmbH has been entrusted with the exploitation of this technology and assists companies in obtaining licenses.