Multi-material 3D printing based on modified LPBF

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Chao Wei and Lin Li discuss how different material properties could be integrated into single parts using additive manufacturing

Additive manufacturing is a group of technologies that bind raw materials layer by layer, based on data of sliced 3D models to form solid components. Metal-based AM has been widely used in high-end industries such as aerospace, nuclear and biomedical. 

Conventional metal-based AM methods can only fabricate components made of a single material. To achieve the functional integration and performance optimisation of AM-processed components, customers hope to integrate the advantages of different materials into one part through AM.

This will enable specified zones of one component to have special properties, such as better corrosion resistance, higher temperature resistance, zero thermal expansion, better thermal conduction, electrical insulation and better nuclear radiation resistance. Therefore, multi-material AM technologies have become a new research field in the international academic community and industries.

Laser-based powder bed fusion (LPBF) and laser-based directed energy deposition (LDED) are commonly used for AM of metallic components. Compared with LDED, LPBF allows higher processing resolution (20-100μm) and better surface quality (Ra 5-18μm).

At the same time, LPBF not only enables the printing of common metallic materials (such as stainless steel, titanium alloy, nickel alloy, aluminium alloy, and copper alloy) but also allows the printing of ceramics and polymers under the premise of suitable laser wavelengths and process configurations.

Therefore, LPBF is a promising candidate to be developed for multi-material AM.

The challenge

The technical challenge in using LPBF for multi-material AM is how to deposit different powder materials to different regions on the same powder layer of the powder bed. Restricted by the ‘powder-blade’ material spreading mechanism widely used on commercial LPBF systems, previous LPBF studies could only fabricate parts with changes in the material composition in the vertical direction. In 2008, researchers from The University of Manchester1 proposed using ultrasonic wave vibration to accurately dispense powder particles in powder bed AM, and successfully demonstrated the laser printing of 2D multiple metallic material components. Ultrasound is a type of mechanical wave with a frequency higher than 20kHz, which can travel long distances in powder, solid and liquid mediums, and can precisely control the flow of fine powder particles. Ten years later, they successfully integrated this technology with homemade LPBF equipment for the printing of 3D multi-material components2. The processing procedure and system setup are illustrated in figures 1a and 1b respectively. A process animation video was also made3

A group of LPBF processed 316L-Cu10Sn bimetallic parts were demonstrated (see figures 1c1-c3). However, directly joining two dissimilar materials often leads to defects, such as cracks and pores at the material interface, which may lead to the fracture of components in service. To address this, they added a functionally graded material (FGM) transition layer at the interface of the two materials, to make the material composition transition from A to B smoothly. Demonstration samples are presented in figures 1d1-d3. In addition to metal-based multi-material combinations, they also further used this technology to process metal-glass, metal-ceramic and metal-polymer combinations, as shown in figures 1e and 1f.

Figure 1: a) Process procedure of the multi-materials L-BPF technology2, b) Relevant schematic diagram of the experimental setup, c1)-c3) L-PBF-processed 316L-Cu10Sn samples2, d1) 316L-Cu10Sn FGM turbine disk sample, d2) Eiffel tower sample4, e) Cu10Sn-glass pendant sample5, f) Cu10Sn-PA11 sample6.

Researchers from The University of Manchester7 demonstrated how this technology can be used for embedding anti-counterfeiting features inside AM-processed 316L components. A QR code of high-density copper alloy, as shown in Figure 2a, can be used. The density of copper alloy is higher than stainless steel, so the QR code can be easily identified by x-ray inspection and thermal imaging, as in figure 2b and c respectively. In addition, they also demonstrated easy-to-remove support structures made of a metal-ceramic mixture composed of silicon carbide (SiC) and stainless-steel powder in the LPBF processed 316L component8. The high melting point SiC cannot be easily melted by a laser, which increases the porosity of the support structure and deteriorates its strength, so it is easier to remove.

Figure 2: a) A copper QR code embedded in AM processed stainless steel components, b) X-ray image, c) IR image of the sample with an embedded QR code7.

Application areas and further challenges

This technology has many potential applications including the production of aerospace components (bimetallic temperature sensors, zero thermal expansion parts), nuclear components (plasma-facing components, heat exchangers), electronic products (multi-material circuit boards, embedded sensors, micro-electromechanical systems), and biomedical components (biocompatible implants).

Although it is feasible to integrate multiple materials into the same part through LPBF, this method still faces challenges from the viewpoint of materials science. Significant differences in the physical properties of dissimilar materials can easily lead to defects in the microstructure of AM-processed materials, such as pores, cracks, brittle intermetallic compounds, and lack of fusion. The University of Manchester is co-operating with industrial partners, including those from the nuclear industry, to carry out in-depth materials research, and it is hoped that the real application of this technology in the industry can be seen in the near future.

Dr Chao Wei is a postdoctoral research associate and Professor Lin Li is the director of the Laser Processing Research Centre, at The University of Manchester

References

  1. OM Al-Jamal, S Hinduja, L Li, Characteristics of the bond in Cu-H13 tool steel parts fabricated using SLM, CIRP Ann. - Manuf. Technol. 57 (2008) 239–242. doi:10.1016/j.cirp.2008.03.010.
  2. C Wei, L Li, X Zhang, YH Chueh, 3D printing ofmultiple metallic materials via modified selective laser melting, CIRP Ann. 67 (2018) 245–248. doi:10.1016/j.cirp.2018.04.096. 
  3. www.youtube.com/watch?v=TtY5nPqMvqU
  4. C Wei, Z Sun, Q Chen, Z Liu, L Li, Additive manufacturing of horizontal and 3D functionally graded 316L/Cu10Sn components via multiple material selective laser melting, J. Manuf. Sci. Eng. 141 (2019) 1–14. http://dx.doi.org/10.1115/1.4043983.
  5. X Zhang, C Wei, YH Chueh, L Li, An integrated dual ultrasonic selective powder dispensing platform for three-dimensional printing of multiple material metal/glass objects in selective laser melting, J. Manuf. Sci. Eng. Trans. ASME. 141 (2019) 1–12. doi:10.1115/1.4041427.
  6. Y Chueh, X Zhang, JC-R Ke, Q Li, C Wei, L Li, Additive manufacturing of hybrid metal/polymer objects via multiple-material laser powder bed fusion, Addit. Manuf. 101465 (2020).
  7. C Wei, Z Sun, Y Huang, L Li, Embedding Anti-counterfeiting Features in Metallic Components via Multiple Material Additive Manufacturing, Addit. Manuf. 24 (2018) 1–12. doi:10.1016/j.addma.2018.09.003.
  8. C Wei, Y-H Chueh, X Zhang, Y Huang, Q. Chen, L Li, Easy-To-Remove composite support material and procedure in additive manufacturing of metallic components using multiple material laser-based powder bed fusion, J. Manuf. Sci. Eng. 141 (2019) 1–18. http://dx.doi.org/10.1115/1.4043536.

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