Additive Manufacturing

How Fused Deposition Modeling (FDM) works

What Is Fused Deposition Modeling?

FDM is a simple, affordable way to fabricate customized and short-run consumer goods. A thermoplastic filament is heated to its melting point and extruded through a nozzle, which precisely deposits the material as directed by a computer. The extrusion process is repeated, layer by layer, until the desired 3D object is completed.

The hard durable plastics used in the FDM process make it highly relevant in the production of functional prototypes, automotive production tools and end-use aeronautical components.

How FDM Works

To create objects using FDM, a computer-aided-design (CAD) file must be converted to an STL file, which yields ultra-thin cross-sections of the digital object. A computer directs the FDM printer to create the desired object by referencing x, y and z-axis coordinates during the build process.

A thermoplastic modeling material in filament form is unwound from a spool and heated to a semi-liquid state. The build material is drawn through an extrusion nozzle and deposited on the print bed or the preceding layer. The material hardens and bonds to the preceding layer as it cools. The print bed is lowered incrementally to allow for the printing of each successive layer.

Similarly, a support material is drawn through another extrusion nozzle. The support material serves as a sort of scaffolding that prevents overhangs and intricate features from collapsing during cooling.

Once the object is fully built, the support material is dissolved away in a water and detergent solution, or it is blasted or broken away. Polyphenylsulfone (PPSF) is a popular support material useful in successfully printing overhangs and intricate internal structures.

FDM Materials and Applications

Since FDM-printed parts are created from the same polymers commonly used in traditional injection molding, they exhibit similar mechanical properties and durability. FDM is particularly adept at creating functional prototypes directly fabricated from planned production materials. Such prototypes allow for timely form and fit testing.

Acrylonitrile Butadiene Styrene (ABS) is a thermoplastic polymer widely used in FDM printing. Its high melting point yields heat-resistant objects. The hard, durable substance is used in a wide variety of consumer goods, including musical instruments, whitewater kayaks, golf clubs and motorcycle helmets. Its resistance to chemicals also makes it an ideal choice in petrochemical and other industrial applications.

Automotive Applications

Hard ABS parts produced by fused deposition modeling systems are widely used in the automotive industry. BMW is one of an increasing number of auto manufacturers benefiting from the savings FDM offers vis-a-vis design, engineering documentation, warehousing and manufacturing. Designers enjoy the freedom to design balanced, lightweight parts readily produced in small numbers -- qualities particularly advantageous when the goal is to produce relatively limited numbers of lightweight, luxurious sports performance vehicles.

Automaker Lamborghini uses FDM for rapid prototyping and printing of heat-resistant thermoplastic end-use parts. The Italian manufacturer’s designers enjoy the unparalleled freedom to create components well-suited to changing markets. Rapid production of functional prototypes makes Lamborghini more responsive and innovative in a competitive environment.

Biocompatible forms of ABS are appropriate for food and drug packaging as well as medical and dental models, implants and prototypes.

Polycarbonate (PC) is another popular build material because it is both impact and temperature-resistant PC and ABS are sometimes combined to create a versatile thermoplastic known as polycarbonate ABS. These PC-ABS blends offer the flexibility of ABS and the strength of PC, making them popular in the fabrication of automotive parts.

Polyetherimide (PEI) is also known by its brand name, Ultem. It is a lightweight, flame-retardant thermoplastic that is UL 94-V0 rated. It is used in aerospace and automotive applications as well as in the fabrication of production tools. PEI is a strong material possessing significant dielectric strength, high heat and solvent resistance and thermal conductivity. Thanks to its various aerospace certifications, Ultem 9085 is used to produce civil aircraft parts.

Medical Applications

3D printing in general, and fused deposition modeling in particular, will drive increased development of personalized medicine. For example, a 3D-printed tracheal splint is credited with saving the life of an infant with abnormal development of tracheal cartilage that makes the trachea prone to collapse. In 2012, a surgical team affiliated with the University of Michigan’s Department of Otolaryngology-Head and Neck Surgery implanted the splint printed with polycaprolactone (PCL). The long resorption time and ductility of the material made it an ideal choice. Since then, several other infants have received similar tracheal implants.

Synthetic organs printed from biocompatible polymers could eventually ease the unprecedented demand for donor organs. At the Wake Forest Baptist Medical Center, researchers have printed a variety of ear, muscle and bone components and implanted them in rats. These synthetic parts functioned for months without rejection by immune systems. They also produced their own blood vessels to achieve the necessary vascularity. Dr. Atala of the Wake Forest Institute for Regenerative Medicine believes that it will be possible to print fully functioning human organs in the future. Others suggest that a fully operative 3D-printed heart may arrive within two decades.

Functional prototypes printed from durable thermoplastics stand up to rigorous testing often required during product development.

FDM Advantages

While the FDM process is not as fast as 3D printing methods like stereolithography (SLA) and selective laser sintering (SLS), it does offer a number of advantages when production-grade thermoplastics are used to build detailed objects. For example, FDM is a less expensive solution when smaller quantities of high-quality durable tools are required.

The production of components with stable mechanical properties and constant electrical properties is attractive in many industries. Thermoplastics like ABS and PC are heat and chemical-resistant, and they respond well to mechanical stress.

Parts produced by fused deposition modeling are readily improved in post-processing. When engineering-grade polymers are used, it is possible to saw, drill and mill the parts. When FDM-produced parts have rough surfaces, they are easily sandblasted, burnished, smoothed and sealed. It is also possible to prime, paint and plate objects as needed. FDM parts can also be joined and bonded.