Question: 

Discuss the differences in LOM and FDM process.

Answer: 

Process and Principle

• FDM is an additive process. It works by extruding a thermoplastic filament through a heated nozzle, which deposits layers of melted material to build up the object. The final part is composed of these solidified lines of plastic.

• LOM is a hybrid additive and subtractive process. It adds layers of material (paper, plastic, or metal sheets) but then uses a laser or blade to cut away the excess material from each layer, leaving only the desired cross-section.

Materials

• FDM uses thermoplastic filaments, such as PLA, ABS, PETG, and nylon. These are polymers that soften when heated and harden when cooled, allowing for the extrusion process.

• LOM typically uses sheets of material that are coated with adhesive. The most common material is paper, but it can also use plastic or metal foils. This makes LOM a low-cost option.

Part Properties and Accuracy

• FDM parts have a distinct anisotropic nature, meaning they are weaker in the direction perpendicular to the layers (the Z-axis) due to weaker layer-to-layer bonds. The surface finish often shows visible layer lines, and accuracy is affected by thermal warping.

• LOM parts have a wood-like feel and are often more isotropic in mechanical properties than FDM parts due to the strong lamination of the sheets. The primary accuracy challenge comes from the laser's kerf (cut width) and the manual "decubing" process.

Support Structures and Waste

• FDM often requires the creation of separate support structures for overhangs and complex geometries. These supports must be manually removed after printing, a process that can be difficult and time-consuming.

• LOM does not need separate supports. The surrounding, uncut material serves as a natural support for the part during the build process. However, removing this cross-hatched "waste" material is a post-processing step that can be labor-intensive, especially for parts with intricate internal features.

Applications

• FDM is a versatile technology used for functional prototypes, jigs, fixtures, and low-volume production of end-use parts. Its range of materials allows for varying levels of strength and durability.

• LOM is best suited for creating large, non-complex visual and architectural models where cost and speed are more important than fine detail or high mechanical strength.