Stratasys’s Fused Deposition Modelling [60]
Fused Deposition Modelling (FDM) uses a solid filament of material that is forced, using drive wheels, through a heated nozzle that melts the filament and distributes it onto the printing surface where it re-solidifies (Figure 2-16).
FIGURE 2-16-FUSED DEPOSI TION MODELLING PROCE SS [59]
This process could be utilised with only a few materials such as butter or chocolate, and the material would have to be combined with other additives to create a complete food printing mixture. The phase change that this process requires is undesirable due to the complex nature of food rheology. However, the idea of being able to store the material as a solid at room temperature is potentially desirable.
Solidscape’s Benchtop System [61]
The Benchtop system uses a similar principle to FDM, but rather than just being extruded out of the nozzle, the filament material is jetted out onto the printing surface. Along with the build material, a support material (soluble wax) is jetted out in a second nozzle. Once a layer has been printed, a precision milling head removes a thin portion off the top of the partially completed model (Figure 2-17).
FIGURE 2-17-BENCHTOP SYSTEM [59]
Again, this method would require additional material to be added to the melted material to create a complete food printing mixture. The materials used for food printing in our research are far too viscous to be jetted onto the printing surface, but the use of a second deposition head for a support material is a viable option. If an appropriate support material could be designed, this would allow more flexibility in the food batter mixture. An appropriate support material would melt, vaporise or create a non-joining boundary between itself and the food batter material. This would mean that the material would be easily removed during post- processing. The intra-layer milling would most likely be unnecessary for food printing, but something like a wiper could be used to improve surface finish. This may only be appropriate on the sides and top of a food model rather than in between every layer.
Solidimension’s Plastic Sheet Lamination [62]
Layers of material are cut using a cutting knife and these layers are then bound together using adhesive. The result is a stack of material with cross-sectional outlines cut into each layer. Post processing is required to remove the waste material. To employ a process similar to Plastic Sheet Lamination using food materials for food printing, a pre-cooked, solid mixture would be required to allow carving. An effective interlayer binding material (such as cake icing) would be required to bind dry layers. It would be difficult to create layers thin enough to give reasonable resolution and positioning, and alignment mechanisms would have to be employed to place the layers. However using dry layers would open up the very appealing possibility of ink jetting food dyes onto each layer, which would mean no mixing would be required. If liquid material was to be used, something as excessive as a vacuum could be used to remove liquid from unwanted areas. This would possibly mean solidification between layers would be more important to prevent unwanted material removal.
3D System’s Multi-Jet Modelling [63]
This process is almost identical to SolidScapes Benchtop System, as it jets a build material as well as a support material. But rather than using a filament of thermoplastic material that solidifies once it cools, Multi-Jet Modelling uses Ultraviolet (UV) sensitive non-toxic wax materials, which solidify when exposed to UV light (Figure 2-18).
FIGURE 2-18-MULTI JET MODELLING [59]
As mentioned before, photo-curable RP processes can practically be ignored, however, if the UV light source is substituted for a heat source, the food mixture could be cooked or solidified as the printing progressed. This method has a potential advantage and a potential disadvantage when considering its application to food printing. The disadvantage is that it is not a conventional way to cook food. The potential advantage is that it may give a more consistent and controllable cooking rate as thin layers are cooked in sequence with more even heat distribution possible.
Rapid CNC machining or Subtractive RP
Subtractive RP (SRP) take standard CNC machining to a level where is can be applied as a RP technique. This involves minimising user input by avoiding manual reorientation of parts and automating the process planning of the CNC machining [64]. By using a rotary axis and a number of layer-based (2½-D) tool paths, prototypes can be manufactured without continued user input. The standard technique to allow parts to be machined from multiple directions is to use an indexed rotary axis in order to rotate the part. This rotary axis generally consists of either one or two 3-jaw chucks to hold the stock material. Figure 2-19 shows a commercially available Roland Rapid CNC machine.
FIGURE 2-19-SUBTRACTIVE CNCRAPID PROT OTYPING [65]
Once the machining of the model shape is complete, final support materials are removed to release the model. All tool paths and operations are generated automatically in software, allowing unskilled machinists to operate SRP machines. This would most likely be an unachievable process with food materials due to the rigidity required.