In the recently published ‘Effect of unit cell shape and strut size on flexural properties of ordered Copper foam,’ Pulak M. Pandey and Gurminder Singh (Mechanical Engineering Department, Indian Institute of Technology Delhi, New Delhi, India) study the relationship between cells and copper, employing both 3D printing and ultrasonic vibration-assisted pressure-less sintering.
Copper foam—and metal foams overall—are becoming fabrication materials of greater interest to industrial users lately, classified as either open (allowing enormous impact on heat exchanger applications) or closed (porous, and used for impact absorption). Both types of foams show potential in applications like aerospace, auto, heat exchangers, the biomedical field, and more.
Because open-cell foams have a high surface area, they demonstrate superior mechanical properties over closed foam, as well as high thermal features and good electrical conductivity. Historically, however, 3D printing and additive manufacturing processes using metal foam have been challenging, posing fabrication issues like curling, swelling, and more. In using EBM 3D printing, replacing the laser, prints still demonstrated over 12 percent shrinkage. More recently, however, success has been reported in using 3D printing with UV-assisted sintering:
“It was observed that the process was able to fabricate uniform copper metal foams with different unit cell shape having maximum of 8.07 % shrinkage. Metal foam strut size and unit cell shape are the important parameters to acquire better strength with low weight,” stated the researchers.
Flow chart of the adopted rapid manufacturing process
Some researchers found increased mechanical properties while using open-cell iron foam, and others had success with aluminum, relying on unit cell shape effect. There has been little research performed with uniform copper metal foam, with the exception of some peripheral testing pointing toward potential. For this study, the researchers used copper powder with an average particle size of 8 µm. Two different sample shapes were created: simple cubic (SC) and body-centered cubic (BCC). Three different strut sizes were used in examining the shape of the unit cells.
(a) Fabricated flexural specimens by adopted rapid manufacturing of SC and BCC foams and (b) flexural experiment on Instron UTM
The researchers used an SLA 3D printer to create samples out of a polymer, with printed parts serving as the pattern for a mold. During testing, the researchers noted isolated micropores, demonstrating good diffusion of the copper particles; however, the foam exhibited brittle behavior, and unit cell shape samples possessed a ‘shorter plateau area’ in comparison to body-centered cubic (BCC) unit cells.
“Rough dimples were observed in SC samples as compared to BCC samples during the necks study after the fracture,” concluded the researchers.
“The thick struts size samples possessed high strength properties for both types of unit cell shapes. The SC unit shape flexural samples showed the high flexural modulus (310-843 MPa) and flexural strength (14-32 MPa) as compared to the BCC samples flexural modulus (230-515 MPa) and flexural strength (8-22 MPa).”
Copper is used increasingly more in 3D printing applications today, as seen in antimicrobial 3D printing, copper composites, fabricated coils and conductors, and more.
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SEM observations of(a) SC and (b) BCC flexural samples after bending test