How powder quality influences printing results

3D printing has developed into a powerful production technology in recent years. Alongside the 3D printing processes based on modelling and photopolymer baths, the powder process has become a commonly used method. Be it metal, plastic, glass, ceramic or composite powder, all powders have one thing in common: their degree of dryness is a key factor for the quality of the printed product.

Powder process for a wide range of applications

With additive manufacturing, prototypes, components, and products can be economically manufactured now – in low numbers of pieces and even batches of 1. In the powder process, which is sometimes called the powder bed process, the printing or assembly space is a type of vat. Inside it, powder is applied layer by layer and solidified with a binding agent or by raising the temperature. There are basically two main processes: selective laser sintering (SLS) and electron beam melting or electron beam additive manufacturing (EBM or EBAM).

In laser sintering, the printing material is melted with a high-performance laser in a protective atmosphere. In electron beam melting, an electron beam ensures that the powder is melted in the vacuum. Printing in a vacuum offers the advantage of preventing oxygen inclusions in the printed product. The process is ideal for printing metals with an extremely high melting point: titanium at 1,668 °C and platinum at 1,768 °C, for example. The powder process is preferred for the creation of complex products such as those with complicated structures, protrusions, and hollow spaces. The non-solidified residual powder that can be removed and recycled downstream acts as an effective supporting structure during the printing process. Typical applications for products printed with the powder process range from toolmaking and mechanical engineering to plant engineering, and the aviation, aerospace and automotive industries to medical and dental technology.

Problem: Printing powder that is too moist

Printing powders always struggle with the fact that they are hydrophilic; in other words, they absorb moisture easily. In addition, the tanks in which dried printing powder is stored are often made of plastic and are typically not impermeable. That means that over time, the printing powder’s moisture content inevitably rises. Different powder qualities could be present in two containers from the same manufacturer, despite the fact that the original material was identical. Moist printing powder can lead to brittleness, cracks, zebra stripes, poor component surfaces, and inhomogeneity of the printed products. Such results are particularly a nuisance when printing products that require maximum strength and consistently high quality. These include special-purpose tools, mechanical engineering components or dental products that are frequently made with expensive powder materials such as titanium and platinum alloys. Aside from the type of powder material, the powder’s degree of dryness is a key factor in the quality of the results yielded by additive manufacturing processes. The drier the powder, the better its flowability and laser sintering ability, which in turn have a positive effect on the printed result.

Vacuum driers ensure that powder is evenly dried

Vacuum driers are a product innovation. For drying high-quality materials such as metal powders, a vacuum drying process and low temperatures are ideal. The vacuum drying process involves drying the powder at low temperatures and pressures to evaporate (sublimate) the water bonded to it. High-performance vacuum driers dry the powder to a residual moisture level of only 1 ppm.

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