ISO/ASTM definition: “sheet lamination, —an additive manufacturing process in which sheets of material are bonded to form a part.”
Sheet Lamination can also be known as (in alphabetical order):
➢ Computer-Aided Manufacturing of Laminated Engineering Materials or CAM-LEM
➢ Laminated Object Manufacturing or LOM
➢ Plastic Sheet Lamination or PSL (Solidimension Ltd.)
➢ Selective Deposition Lamination or SDL (Mcor Technologies Ltd.)
➢ Ultrasonic Additive Manufacturing or UAM
➢ Ultrasonic Consolidation or UC
The LOM process was developed by a company named Helisys and in 1991 they started selling a machine that made 3D parts using rolls of paper and a CO2 laser. The company eventually went bankrupt and later formed Cubic Technologies; however, in 1999, a company from Israel called Solidimension developed a system very similar to LOM using sheets of PVC plastic rather than paper. Also in 1999, a USA company called Solidica (now Fabrisonic) patented a new hybrid method which looked similar to LOM but used metal tapes and films which were joined using ultrasonic vibrations, and then a CNC machine used traditional subtractive manufacturing methods to remove material. In 2005, Japanese company Kira started production of a paper-based machine similar to LOM called the PLT-20 KATANA but using a steel cutter rather than a laser. By 2008 Mcor Technologies launched their first SDL machine called the Matrix which deposited individual sheets of A4 paper rather than rolls of paper like LOM or Kira and selectively glued down sheets which were then cut using a steel cutter. This process allowed Mcor to later develop full-colour parts by printing on the paper before being glued down.
Figure 1: Sheet lamination example setup
This process starts with a single layer of solid material put across the build surface, be it paper (LOM and SDL) or PVC plastic (PSL) or metal (UAM/UC) or ceramic (CAM-LEM). This layer may or may not be bonded to the previous layers first as it depends on the process. Some processes bond the entire layer to the previous and then cut the 2D slice into the layer as with SDL or UAM, while other processes cut the 2D slice into the layer first, and then bond it onto the previous layers afterwards like CAM-LEM. The bonding between each layer occurs by a number of different methods depending on the process. For SDL and PSL, bonding is performed by applying a type of glue to the build surface. Layers are bonded together in LOM through melting a polymer that is embedded within the roll of paper. In the case of UC, the layers have an atomic migration between layers in a very small zone which fuses the layers together. The 2D slice data is either cut into the layer with a laser (LOM/CAM-LEM) or a blade (SDL/PSL) or machined away with a traditional CNC cutter (UAM/UC), and then the process starts over with a new solid layer being placed on top. In the CAM-LEM process, all the 2D layers are first pre-cut from a ceramic tape and then assembled and stacked on top of each other. Then a binder is added to give it strength before it is placed in an oven and fired to sinter the material together. With CAM-LEM, there is potential to cut the layers tangentially to the surface so that the traditional steps that are seen in AM are reduced and nearly eliminated, although it does not appear to have made it past the demonstration phase.
Advantages of this process tie directly to the individual processes. SDL can do full-colour prints, is relatively inexpensive since the raw material is normal office paper, can be infused with materials to increase strength or colour saturation, and excess material can be recycled. UC can do metal, and has the ability to do multi-metal layers within the overall part but not in the same layer, but can also embed other things into the part like wires, sensors, or fibres. CAM-LEM can process ceramic parts. No support material is needed since each layer is already solid and can support itself, although there are limitations to this as certain geometries like internal voids and cavities may not be possible.
A common disadvantage of all processes is that the layer height can’t be changed without changing the thickness of the sheets of material being used. Thus the layer steps and surface roughness is directly tied to sheet thickness. Regardless of the size of part being made, an entire sheet is consumed per layer, so material waste can be high if parts don’t make full use of the build volume. When layers are bonded before the 2D layer is cut out, the removal of excess material can be quite labour intensive. Excess material removal may not even be possible for some internal geometry. Even though UC creates solid metal parts, the bonds between layers are weaker than in the other directions, which could result in delamination. LOM cutting is performed with lasers and there is smoke and a chance of fire, which is why that technology was not very popular and why it moved to steel cutters instead.
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