1. Working Process
FDM is an additive manufacturing technology, works on the principle of sintering. The plastic polymer is feeded to a heated nozzle, which will lay down it in layers to produce a product. The number of layers on a product is the deciding factor of manufacturing time. The principle of SLS completely differs from FDM. It works on the principle of sintering. In FDM filament is heated in the nozzle, whereas in SLS, the powder is heated by controlled laser pulse. The laser heats the powder and it forms solids by fusion. SLS don’t require support material since the power itself can act as support.
2. Process Variations
Some FDM machine uses pellet form instead of filament. Some manufacturers introduced a support material that dissolves when placed in bath of chemicals. It requires long wait but no need to break any supports from the part. Gel type support structure also used and it rinses away with pressurized water. FDM works with plastic polymers, whereas SLS works with the material like ceramic composite parts. DMLS don’t require any binders and use very high power laser to sinter the powder at insert atmosphere. Typically this process requires post manufacturing process like support removal, shot peening etc., for polishing and finishing.
3. Processing materials
FDM technology works with production-grade thermoplastics to build tough and durable parts. Thermoplastics can endure heat, chemicals and mechanical stress which makes them an ideal material for FDM products. Most commonly ABS (Acrylonitrile Butadiene Styrene) material is used and some machines may also use Polycorbonate, Polyactic Acid and Nylon (Polyamide). FDM works with polymers whereas, SLS works with variety of materials like plastics, glass, ceramics (with binder). FDM use thin filament or pellet type material whereas SLS use powder form of material with binder to increase strength of parts. SLS also works with metals like stainless steel, tungsten and nickel super alloys etc.,
4. Design aspects
FDM offers complex geometrics and not suitable to print small features, details and thin walls. FDM also has limitations and constraints in the printing and same can be avoided with key design considerations. Optimal layer height, printing speed, nozzle temperature are the major key design factors of FDM. Generally low printing speed = accurate printing. SLS doesn’t require any supports; the un-sintered powder can be used as supports for hanging parts and undercuts; whereas in FDM, special care required for support design and removal of supports. SLS surface finish is not up to the industry standard; however it is much better than FDM.
5. Quality aspects
The FDM product has excellent strength to weight ratio with great stability. The surface quality of FDM products are not up to industry standard and it requires some sand blasting, painting and coating to get smooth surface finish. The time required for post manufacturing activities vary based on the surface quality. SLS provides good quality products when compared to FDM printing. SLS parts offer good design accuracy whereas the same is little difficult in FDM. SLS offers greater than 99% densities, where the same is not possible in FDM. Finished parts surfaces are rough and requires painting and coating.
6. Economical aspects
FDM is office environment friendly; and it does offer some real cost advantages in so many applications. However it takes longer time to manufacture a product. Longer production time will affect the industry economically and increase delivery time. There is no tooling cost / setup cost and consumables are cheaper in FDM. SLS medium build speed and lead time is approximately 1 week. The material utilization is high on both printing methods; however SLS offers low material cost in many applications. The equipment cost is very high when compared to FDM. The production rate depends on the size and compatibility of parts.