HSS Material Network growing further with HDPE

The VX200 HSS from voxeljet is designed as an open source 3D printing system and provides full access to process parameters and temperature management to best match the additive manufacturing process and material. The HSS Material Network offers customers a flexible and low-risk outsourcing option for material development of additive manufacturing technologies. The addition of the competencies of the HSS Material Network partners enables companies of all sizes to receive unique support, from an initial suitability assessment, through specific development and parameterization, to certification or market-ready qualification of the material. Here we present our partners, projects and proof of concepts.

HDPE is a high-density polyethylene (0.94-0.97 g/cm³) and is particularly characterized by its very good resistance to chemicals and greases as well as its water-repellent effect. At room temperature, HDPE has a hard yet flexible appearance and, in addition to its very good mechanical properties, has good sliding behavior and increased wear resistance.

HDPE is therefore used, among other things, for the manufacture of products for the food and packaging industries, especially for the chemical industry. Thus, containers, bottles and pipes for chemicals, fuels, water, gas or oil are manufactured from HDPE as standard.

The process window of HDPE is very small for processing in laser sintering and, furthermore, a high laser power is required to melt the powder particles. The mechanical properties of the HDPE are negatively influenced by the high thermal load due to the punctual or line-by-line exposure by laser. This results in embrittlement of the material.

In the case of HSS, on the other hand, the energy is applied to the powder bed surface by means of an infrared lamp with the aid of an ink, which is selectively applied to the powder bed surface via a print head. The two-dimensional exposure ensures that the duration of the energy input is significantly longer compared to laser-based production systems. As a result, significantly lower maximum temperatures can be realized, which reduces thermal stresses on the material and preserves the proven mechanical properties of HDPE.

Unlike PA12, HDPE is a pure hydrocarbon. This makes HDPE non-polar, water-repellent and highly resistant to chemicals. At room temperature, HDPE is therefore not attacked by many solvents, alkalis and acids. Similar to PA12 or PP, up to 100% of the unprinted powder can be reused.

With respect to PP but also to PA12, HDPE offers a significant price advantage, as HDPE is a widely used mass plastic which is much cheaper to produce than PA12 or PA11. In addition, HDPE is manufactured in Europe, which secures supply chains and times.

The proof of concept was manufactured from the HDPE powder DiaPow HDPE HX developed by Diamond Plastics GmbH for laser sintering, which is characterized by a very uniform particle size distribution and very good flowability. The process capability analysis and initial parameterization carried out by the Fraunhofer Project Group Process Innovation of the Fraunhofer IPA and the Chair Manufacturing and Remanufacturing Technology of the University of Bayreuth demonstrate that the HDPE powder has very good processability in HSS. Therefore, the HDPE powder will be optimized and fully parameterized by the partners specifically for the HSS process. The focus will be on reproducibility, part quality and productivity in terms of reduced shift time. Finally, the adapted HDPE powder is made commercially available to the market.

Particularly noteworthy is the fact that a particularly high degree of flexibility was achieved during processing using HSS. This kind of flexibility is difficult to achieve in laser sintering, for example. The reason for this is the selective thermal loading of the material. This has a negative effect on the mechanical properties of the material. With HSS, on the other hand, the powder bed is exposed over a large area, which increases the duration of the energy input and reduces thermal stress. In this way, the flexibility of the HDPE is retained.