Sintratec: Cold Metal Fusion

A lightweight gear wheel used in the automotive industry is produced to illustrate the cold metal fusion (CMF) process. The complex geometry of the part makes it an ideal example, as this can only be realized additively. For printing, we use the Sintratec All-Material Platform with the Sintratec S2 and the MCU-160 Build Module. As part of the CMF-Lab system, we currently have two materials available that have been specially developed by Headmade Materials for SLS technology: M2 tool steel and 17/4PH stainless steel. As this is a common material in the automotive industry, we will use 17/4PH for our gearbox.

First step: Print preparation

Similar to the standard selective laser sintering (SLS) process, the print job is first prepared in the Sintratec Central software. The 3D model is imported, duplicated and arranged in the available build volume. With regard to the CAD design, the shrinkage during the sintering phase must be taken into account, which can vary depending on the material - at 17/4PH it is 14 percent. After set-up, the print job is sliced - 3D objects are converted into 2D layers - exported and sent to the system via a USB stick or a local network. At the material handling station, the powder containers of the Build Module are filled with the 17/4PH material from Headmade; the powder quantity is calculated automatically.

Printing and depowdering

As soon as the build module is filled, it is passed to the Fusion Module - in this case the Sintratec S2. The print job is selected via the touchscreen and the printing process is started. The cold metal fusion process is "cold": the powder bed is only heated to around 50 degrees Celsius, which is a low temperature compared to conventional polymers. As a result, the printing process is stable and the entire unsintered material can be reused. Once the printing process is complete, the build module is removed in order to depowder the so-called green parts in the material handling station, similar to the polymer process.

Post-processing

After depowdering, the last powder residues are removed in a washing station with a 30 bar water jet. This step ensures a smooth surface finish and high part accuracy. As green parts are usually brittle in industry, such simple handling and post-processing is a novelty. The reason for this is the ingenious material, which consists of a plastic binder matrix with protruding metal tips. When the plastic component melts during the printing phase, all cavities are filled, resulting in high green part strength.

Debinding the green parts

After post-processing, the green parts are taken to the debinding station on a tray. Here, after closing and sealing the door, the chamber is flooded with an acetone solvent at a gradually increasing temperature. Viewed under a microscope, the solvent penetrates the wall of the parts and begins to dissolve out one of the plastic components. After overnight debinding, the converted brown parts are removed from the station for further processing.

Sintering the brown parts

The next processing step takes place in the sintering furnace. The chamber is heated to a good thousand degrees Celsius. As the temperature rises, the metal particles begin to grow together to form a dense solid metal component, while the last remnants of the plastic burn away. This sintering process takes around ten to 15 hours - but is always the same regardless of the size of the oven or the number of parts to be processed. As soon as the metal parts have been sintered, they can be removed and processed further if required.

Finished parts and conclusion: new standards in the metal AM sector

The components made of pure 17/4PH stainless steel are now finished. There is no longer any residue of the previously used plastic. Compared to conventional production, these parts have the same mechanical performance - with much greater design freedom and complexity. In fact, the CMF process can produce components with an excellent elongation at break of 13.2 percent after curing, which is higher than the MIM standards. Combined with the CMF Alliance hardware, this technology allows users to manage porosity, incorporate flow channels into their designs and achieve outstanding mechanical properties. With these unique capabilities, the CMF process sets new standards in the metal AM sector.

The Cold Metal Fusion process from Sintratec is nominated in the Additive Manufacturing category.