3D Printing with Metals

Faster Powder Production for SLM

| Author/ Editor: Gregor Graf / Alexander Stark

Who is ready to wait months for their first test batch? Rosswag has found a way to shorten the qualification chain for metal powders - and improve component simulation at the same time.

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To ensure faster response to customer inquiries, Rosswag has purchased an atomizing system that is designed for frequent material changes and quantities of less than 50 kg.
To ensure faster response to customer inquiries, Rosswag has purchased an atomizing system that is designed for frequent material changes and quantities of less than 50 kg.
(Source: Rosswag)
  • Only a fraction of the metals is qualified as metal powder for additive production.
  • With an atomization system for small quantities, Rosswag significantly reduces the production times of the first powders for test specimens.
  • The data obtained from the qualification process can be used to improve simulation programs and thus better plan the construction job in advance.

Whereas there are thousands of different alloys for conventional processes, only a handful of standard alloys are available for selective laser melting (SLM). These are too few for the many users of this additive method. Daniel Beckers, project engineer at Rosswag Engineering, is also familiar with this problem: “Our customers frequently ask for complex material and process solutions that do not yet exist and are also rarely or incompletely available in the scientific environment.” This is because the production of a new material in powder form takes time.

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Who wants to wait months until the material has been atomized into metal powder? Subsequent parameter studies and material scientific evaluations can also take several weeks or months. Rosswag was looking for a faster way to go through the entire qualification chain within a few weeks. In some cases, throughput times of less than three weeks have already been achieved. This allows decisions as to whether the planned procedure is target-oriented to be made quickly and based on experimental results. As a result time-to-market for end customers can be sped up effectively.

The Fast Way to Test Specimens

A fast conversion of material requirements to first specimens requires an appropriate equipment. Since the end of 2017, Rosswag has been operating an AU3000 atomization system from Blue Power, which was developed specifically for frequent material changes and high purity for the production of quantities < 50 kg of special metal powder. As soon as the raw material is available or individually alloyed in the crucible, a small quantity of 10 kg of special metal powder can be produced within one working day and prepared for the SLM process by sieving and sifting. Particle size distribution, particle shape, flowability and other relevant parameters are checked before the metal powder is fed into an SLM system.

These 10 kg of metal powders are sufficient for initial parameter studies on SLM systems. At present, Rosswag still varies the process parameters on the basis of experience values in a suitable process window; in future, the company will also be using process simulations from Ansys. “With this simulation software, we want to reduce qualification times and further improve the quality of the results," says Beckers.

Rosswag then analyzes and tests the specimens produced in this way, mostly ground cubes and flat tensile specimens, in the materials laboratory, where a full chemical analysis, including CS/ONH, is also carried out using Bruker devices. In addition to testing the porosity and microstructure in etched microsections under the stereomicroscope, deviations in the chemical composition can also be detected across the entire process chain and compared to the raw material used. In further development iterations, these results can lead to alloy adjustments prior to metal powder production in order to obtain specifically influenced alloy compositions in the additively produced component at the end of the process chain. In combination with suitable heat treatment procedures, the desired material properties can be achieved.

Preliminary Planning of Component Production - As Detailed as Possible

At the end of the qualification process extensive data sets are available, consisting of metal powder properties, SLM process parameters and mechanical-technical, chemical or metallographic material properties of the materials to be examined. They serve, for example, as a basis for further optimization iterations. This approach in turn leads to an extended application of the simulation. An essential objective is not only to optimize the material properties and the qualification in the additive manufacturing process, but also to plan the component production as detailed as possible in advance. “In the manufacturing process, typical characteristics of the future component can be considered in conjunction with the manufacturing process," explains Beckers. This is especially interesting for critical component areas, such as large cross-sectional changes or filigree geometries, and the associated process influences with regard to heat conduction and residual stresses.

Especially in the case of demanding geometric features and highly functional components, it can happen that process parameters are suitable for a component of average quality, but do not perform optimally in demanding areas and thus lead to increased porosity or poor surface quality.

Such an interplay of powder metallurgy and process parameters and the resulting adjustments can, however, only be achieved with an end-to-end process chain that is tailored to these requirements. This creates a synergy between the component geometry, the additive manufacturing process and the metal alloy used.

This article was first published by MM MaschinenMarkt.

Original: Simone Käfer / Translation: Alexander Stark

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