HSS Material Network – Proof of Concept HDPE

The HSS Material Network is an interdisciplinary network of selected experts dedicated to making the development and qualification of new polymer materials for the additive manufacturing process High Speed Sintering (HSS) more flexible and faster.

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

Proof of Concept I – High Density Polyethylen (HDPE)

Customer/Material Manufacturer: Diamond Plastics GmbH
Development & qualification: Fraunhofer IPA / Universität Bayreuth

1. What exactly is HDPE and in which industries and products is it processed?

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 is characterized by a hard yet flexible appearance and, in addition to its very good mechanical properties, has low friction and increased wear resistance.

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

2. What are the advantages of processing HDPE via HSS compared to, for example, laser-based process technologies?

The process window of HDPE is very small when using laser sintering, i.e. a high laser power is required to melt the powder particles, however the mechanical properties of the HDPE are negatively affected by the high thermal load caused by the laser. This results in brittleness of the material.

HSS, on the other hand, uses an infrared lamp and an energy absorbing ink to melt the material. Wide-area energy exposure of the powder bed ensures that the duration of energy input is significantly longer compared to laser-based production systems. This allows significantly lower maximum temperatures, which reduces thermal stress on the material and preserves the good mechanical properties of HDPE.

3. What distinguishes HDPE from other common polymers such as polyamide 12 (PA12), polyamid 11 (PA11) or polypropylene (PP)?

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 regard to PP but also to PA12, HDPE offers a significant price advantage, since 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 ensures supply chains and delivery times.

4. The proof of concept for HDPE was successfully carried out. The material can be processed well using HSS. What further steps are planned?

The proof of concept was made from DiaPow HDPE HX, an HDPE powder developed by Diamon Plastics GmbH for laser sintering, which is characterized by a very uniform particle size distribution and excellent flowability. The process analysis and initial parameterization carried out by the Process Innovation Project Group of Fraunhofer IPA and the Chair of Environmentally Sound Production Technology at 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 layer time and thus higher print throughput. Finally, the adapted HDPE powder is made commercially available to the market.

Particularly noteworthy: When processing using HSS, it was possible to achieve a particularly high degree of flexibility. This type of flexibility is difficult to achieve in laser sintering, for example. The reason for this is the punctual thermal loading of the material. This has a negative effect on the mechanical properties of the material. In the case of 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. This preserves the flexibility of the HDPE.