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Study Shows Tamping Better for BAAM
Posted on February 1st, 2017 by Ken Klapproth in New Materials & Applications
When it’s time to go big or go home in additive manufacturing, how have researchers successfully addressed long deposition times for thermoplastics leading to reduced material strength between layers?
You can’t overcome physics, but a recently published study based on a collaboration between the University of Tennessee, the University of California, and Oak Ridge National Laboratory shows you can use it to your advantage. The report entitled Structure and mechanical behavior of Big Area Additive Manufacturing (BAAM) materials identifies issues that are unique to large-scale polymer deposition and how they impact properties and strength of printed materials.
Big Area Additive Manufacturing (BAAM) – like any deposition process – is limited to the working range of the filler material being used. Proper bonding between layers requires thermal fusion and polymer inter-diffusion. If the temperature of the semi-molten polymer drops below a prescribed value or the contact area between the layers is insufficient the bond properties are negatively impacted.
Maintaining a sufficient feed-rate for deposition is also an issue when “going big”. ORNL’s BAAM process uses a screw extruder feeding polymer pellets rather than the traditional filament of smaller machines. The report claims that this not only decreases material costs but also increases feed rates making the process up to 200 times faster than traditional methods. However, the shape of the pellets can lead to voids in the part due to insufficient bonding between the pellets.
Back to physics – either temperature or pressure can help improve bonding between layers. While other research has focused on infrared preheating to improve bonding and reduce voids, ORNL researchers have developed a “z-tamping” attachment that effectively vibrates subsequent layers while the material is still in its semi-molten state. You can see the attachment at work in the video below between 50 sec and 1 minute 8 seconds:
Innovating a new product or process is not about the limitations you encounter, it’s about how they are overcome. Pushing the physical boundaries of any material provides ample opportunity for unconventional knowledge and creative thinking. When it comes to additive manufacturing, the team at ORNL is all too familiar with the concept of going big, securing a Guinness World Record for the title of largest solid 3D printed item as we previously reported here.
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All opinions shared in this post are the author’s own.
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