In-depth analysis of how Fraunhofer IFAM’s MoldJet 3D printing technology maximizes productivity

exist3D printingA lot of heat will not be generated in the process.This makes high-speed printing possible and avoids metal3D printingResidual stress in the process. Binder Jetting3D printingTechnology transfers the thermal processing process to the sintering step, which makes it easier to manage thermal stress because the sintering temperature is lower than other types of metals3D printingThe complete melting temperature required in the process, and the heat can be applied more uniformly. However, this does not completely eliminate the challenges of temperature gradients and residual stress.

It can be said that indirect metal represented by Binder Jetting3D printingThe technology was born for the printing application market of mass economical metal parts.However, indirect metal3D printingThe technology itself also contains different types of printing technology.In this issue, 3D Science Valley combines FraunhoferFraunhofer IFAM’s MoldJet 3D printingTechnology to appreciate how the combination of mold printing and metal filling printing can maximize productivity.

© Fraunhofer IFAM

Mold printing and paste filling

Printing process

The two basic process steps of Fraunhofer IFAM’s MoldJet® process are printing a mold to make it a frame for the desired part geometry, and filling the mold with a metal paste. These two process steps alternate with each other.

© Fraunhofer IFAM

First, it is a mold made of waxy polymer through an inkjet printing process. In this process, the polymer is heated in a container, and the material is applied drop by drop to the substrate through the print head. These droplets overlap and form a uniformly molded layer. In the next step, a roller can be used to smooth the mold layer and ensure that the layer height is uniform across the print area.

Then the metal sauce is filled into the mold, and these metal pastes are composed of the metal powder of the desired alloy and the organic binder system. The slurry is fed evenly from the cartridge to the slot die to ensure even transfer to the mold. Then, the slot die head moves evenly on the substrate and continuously fills the cavity of the mold with the slurry.

These slurries are pressed into the cavity to overcome capillary forces and avoid areas without material. At the same time, it can ensure that the excess material is removed and collected behind the mold area.

After filling each layer of the mold, it is the step of drying and hardening. These three process steps-mold printing, mold filling and drying-are repeated layer by layer until the required part is produced. The layout of each individual mold layer can be adjusted flexibly and independently. In this way, it is possible to produce internal structures and channels as well as parts with a 90° overhang. However, according to the understanding of 3D Science Valley, the manufacturing process is not completely free and unlimited. For example, it is necessary to avoid completely closed internal passages, otherwise the mold material cannot be removed in the future.

3D printingA major challenge in the process is quality control. According to the in-depth understanding of 3D Science Valley, Fraunhofer IFAM has specially equipped the MoldJet® process with detection and control (DAC) process steps. Thus, each printing layer can be scanned by a high-resolution camera, and the image data of each layer can be stored. In addition, the machine operator can decide the mechanical post-processing steps after each printing layer. In the case of a printing error, you can clear the last printed layer and print again.

Finally, a blank product consisting of a mold material and a closed printed green body can be obtained. Subsequently, a demolding process must be carried out. Here, the waxy mold material only needs to be melted, and the green body after demolding will remain. Then, these high-strength green bodies are also heat treated outside the machine in a heat treatment furnace and sintered into dense metal parts.

© Fraunhofer IFAM

Fraunhofer IFAM machine configuration

According to the understanding of 3D Science Valley, the concept machine developed by Fraunhofer allows the use of six independent workstations and six independent workbenches, so-called pallets. The workstations and trays are arranged in a circle. The workstation is fixed, and the tray is arranged on a rotating rotator to move from one workstation to the next.

© Fraunhofer IFAM

In Fraunhofer IFAM’s MoldJet® device, the first workstation can use four inkjet print heads at the same time. The resolution of each mold is 2400 x 1800 DPI, the resolution in the X direction is 11 µm, the resolution in the Y direction is 14 µm, and the resolution in the Z direction is 100 µm. Currently, the height of the manufacturable layer is 100 μm. In the near future, this will be flexible and adjustable to produce more parts or achieve higher productivity.

In the mold filling station, a slot die with a width of 235 mm and an effective filling width of 180 mm is used to fill the mold layer with slurry. In the current configuration, the MoldJet® equipment has two drying and one hardening stations. Compared with the first two stations, depending on the slurry, drying sometimes takes the longest time. The workstation with the longest working time determines the entire manufacturing cycle and thus the output of the entire machine. This is why the machine has multiple drying stations.

This means, for example, during the drying time of one tray, the drying process can be carried out separately, and drying can be continued during other printing processes.

The inspection and storage of each layer of data provides the possibility of processing these data in the future. According to the in-depth understanding of 3D Science Valley, in the future, through intelligent algorithms and machine learning processes, the machine, not the operator, must decide whether to rework.

The schematic diagram of the tray layout in MoldJet equipment, the size of the tray is 400 x 240 x 120 mm (length x width x height). © Fraunhofer IFAM

Using six independent trays, the MoldJet® process can achieve a productivity of up to 1600 cm³/h.

The shrinkage of parts in the furnace process is similar to other sinter-based additive manufacturing processes, about 11-15%. A relative component density of >99% can be achieved. A notable feature of MoldJet® process is high green strength. This allows the components to be transported without any damage until the heat treatment (thermal debinding, sintering). According to 3D Science Valley, there are almost no restrictions on the powders that can be used in the MoldJet® process. Those cost-effective MIM powders can be used directly in the MoldJet® process.

in conclusion

The MoldJet® process is a manufacturing process created for industrial applications in the field of sinter-based additive manufacturing.

According to the understanding of 3D Science Valley, the process currently has the following characteristics:

-Productivity up to 1,600cm³/h

-Can produce large quantities of parts

-Easy to expand the number of parts (from one piece to mass production)

-Almost no design restrictions (internal passage, even 90° overhang, etc.)

-Support structure without parts material

-High green strength

-The supporting structure can be dismantled or dismantled without spending a lot of operating time

-Low-cost standard powder (such as MIM powder) can be used

-Safe craftsmanship

-Multi-material system (all sinterable materials)

Generally speaking, the advantage of Fraunhofer IFAM’s MoldJet® process is that Fraunhofer IFAM can provide the entire process chain consisting of metal paste development, print testing, geometry optimization and heat treatment (thermal debinding, sintering) to achieve compact functional parts at low cost manufacture.

(Editor in charge: admin)