low-deposition rate, High-resolution process, Between and LCVD gas might be Medium Poor by point metals and semiconductors within layers involved High resolution, wide range of Solvent involved, shield gas materials, ability of writing in may blow off powders when Between and Aerosol Jet Printing 3D space, ideal for deposition High Good Line by line integrated with powder bed within layers of biological inks, noncontact, systems Hybrid & DW easy material handling Require machining process Between and SDM during fabrication, feature size Low Fair Line by line within layers Wide range of materials is limited by cutting tool Limited to good flowability Wide range of materials, DPP+binder printing or powders, overflow problem, Between and possible complex materials High Good Point by point laser sintering low compaction density of within layers and geometry control discharged powders Several research centres and institutes have been developing MMAM technologies to allow more materials to be used in a single process. Most of the MMAM systems discussed in this paper are still being investigated as research projects. There is still much effort to be made to incorporate multiple materials into AM commercially. In this section, some of the challenges that need to be faced so that MMAM becomes more widespread will be discussed. The general improvements and technological barriers that need to be considered in MMAM processes are as follows: Contamination in the material feeding system when changing to a Contamination: different material is an important in most MMAM systems. This makes the processes imperfect and the reuse of materials difficult. Bonding of dissimilar materials has often been a challenging issue even in Bonding: conventional manufacturing techniques. In the same way, achieving a good bond between dissimilar layers in MMAM is a matter that needs to be taken into consideration. Most AM systems currently take STL files as standard input which Data processing: is a surface approximation only and there is no information of the material content. A demand for a powerful CAD system for multiple material pre-processing has appeared so that the operator can be able to identify the type of materials from region to region in a part.
Hybrid & DW LCVD High-resolution process, metals and semiconductors low-deposition rate, gas might be involved Between and within layers Medium Poor by point Aerosol Jet Printing High resolution, wide range of materials, ability of writing in 3D space, ideal for deposition of biological inks, noncontact, easy material handling Solvent involved, shield gas may blow off powders when integrated with powder bed systems Between and within layers High Good Line by line SDM Wide range of materials Require machining process during fabrication, feature size is limited by cutting tool Between and within layers Low Fair Line by line DPP+binder printing or laser sintering Wide range of materials, possible complex materials and geometry control Limited to good flowability powders, overflow problem, low compaction density of discharged powders Between and within layers High Good Point by point Several research centres and institutes have been developing MMAM technologies to allow more materials to be used in a single process. Most of the MMAM systems discussed in this paper are still being investigated as research projects. There is still much effort to be made to incorporate multiple materials into AM commercially. In this section, some of the challenges that need to be faced so that MMAM becomes more widespread will be discussed. The general improvements and technological barriers that need to be considered in MMAM processes are as follows: Contamination: Contamination in the material feeding system when changing to a different material is an important in most MMAM systems. This makes the processes imperfect and the reuse of materials difficult. Bonding: Bonding of dissimilar materials has often been a challenging issue even in conventional manufacturing techniques. In the same way, achieving a good bond between dissimilar layers in MMAM is a matter that needs to be taken into consideration. Data processing: Most AM systems currently take STL files as standard input which is a surface approximation only and there is no information of the material content. A demand for a powerful CAD system for multiple material pre-processing has appeared so that the operator can be able to identify the type of materials from region to region in a part.
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