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Image Credit: Shutterstock.com/PanchenkoVladimir
Additive manufacturing (AM), or 3D printing, is a process of creating a three-dimensional (3D) solid object from a digital file by laying down successive two dimensional (2D) layers of the material until the object is created1.
The digital file, or computer aided design (CAD), is created by a 3D modelling application, or by use of a 3D scanner, which operates by using various technologies such as time-of flight, structured/ modulated light, volumetric scanning, etc1.
By a process known as slicing, the 3D model is then divided into hundreds or thousands of horizontal layers through the use of a slicing software, or a 3D modelling software, which are then printed to form the final object1.
As a result of the ability to customize the products, localized production methods and reduced operational logistics, the current $4 billion AM industry is estimated to quadruple by the year 2020. In fact, this industry is speculated to emerge as the next industrial revolution2.
Although it began as a small batch production technique, improvements in the manufacturing time, quality and the cost of production have allowed the AM technology to attract the attention of many businesses and consumers2.
In fact, along with metallic and ceramic 3D printing technologies, it is now possible for the polymer 3D printers to 3D print fiber-reinforced and nanocomposite materials. Selective laser sintering (SLS) and selective laser melting (SLM) technologies are used to print metallic parts by utilizing a high intensity laser to progressively fuse the metal powder2.
The 3D objects printed utilizing the high temperature SLS method are predicted to have a greater strength due to significant grain refinement and possible in situ reinforcement. Therefore, 3D printing technologies capable of printing structural and medical implants that are based on steel, aluminum and titanium alloys are being extensively investigated for human use, while some 3D printed medical implants are already being used for veterinary purposes2.
The globally distributed AM manufacturing process involving multiple parties of the manufacturing and supply chain, including trusted, partially trusted, and untrusted parties, is raising concerns about the reliability of the quality of the manufactured product3.
This CAD file can be subjected to cybersecurity attacks, for instance, hacking the software to change the orientation of printing or introducing fine defects, can have devastating effects on the product quality, as well as economic impacts in the form of product recalls and lawsuits3.
Researchers from the New York University’s Department of Mechanical and Aerospace Engineering examined the cyber security implications of printing orientation and the insertion of fine defects on the final 3D printed material2.
A soft elastomer-like polymer, Tango black plus, which has a lesser stiffness as compared to the main material, Vero clear, is embedded at the center of the specimen to mimic a scenario where a void in the specimen, or insertions of a nearly unattached foreign material, is introduced by compromising solid models or a modified G-code2.
A polymer material jetting- 3D printer is used to print these specimens with cube defects of an edge length of 150 mm, 250 mm and 500 mm, along with a control specimen comprised of just the Vero clear which has no defects2.
All of the specimens that are printed with the same geometry, slicing mode and software, were subjected to tensile testing with an initial strain rate of 10-3/s until the specimen fractures, or until the specimen withstands 20 % strain2. Finite elemental analysis (FEA) was also conducted to determine how the changes in the CAD files will result in changes in the FEA results.
Non-destructive ultrasonic testing was also performed using Ultrasonic C-scan to determine if the embedded defects can be detected during the quality control or validation inspections by carrying out mechanical, destructive and non-destructive (NDT) physical testing2.
The stress-strain curves revealed that the specimens showed ductile behavior, which minimized the effect of the stress concentration by allowing the material around the defect to deform rather than initiating a crack2.
The results of the ultrasonic C-scans revealed that the defects cannot be identified by the noise in the ultrasonic scans, even in the case of the largest 500 mm defect. The defects in the material were effectively masked by the inevitable artifacts that are created by the surface texture during the manufacturing process2. Inferior specimens created by changing the orientation have also gone undetected.
However, the viscoelastic polymer can be detected at a lower test frequency due to the higher attenuation of this polymer2. According to the FEA analysis, the intact control specimen showed a maximum stress at the shoulder of the curvature, while the defective specimens showed a maximum stress at the edges of the defect inside the model.
Furthermore, the results revealed that changing the printing direction significantly lowered the strength and modulus, therefore allowing for the creation of an inferior product2.
Overall, this research verifies that submillimeter defects created by malfunctioning of the printer, or by deliberate changes in the software, often goes undetected by common industrial monitoring techniques2. The presence of these undetected defects could make the products weak, and cause them to under-perform when exposed to conditions of fatigue, heat, light and humidity2.
The requirement for new design and process rules is warranted for the 3D printing technology in order to address challenges, such as cyber security risks, which can potentially compromise the quality of the product.
References:
- Strikwerda, Pieter, and Robert Dehue. "What Is 3D Printing? How Does 3D Printing Work? Learn How to 3D Print." 3D Printing. Web. https://3dprinting.com/what-is-3d-printing. .
- Steven Eric Zeltmann et al. Manufacturing and Security Challenges in 3D Printing, JOM (2016).
- "Researchers Report Cybersecurity Risks in 3D Printing." Phys.org. 13 July 2016. Web. https://phys.org/news/2016-07-cybersecurity-3d.html.
- Image Credit: Shutterstock.com/PanchenkoVladimir
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