Additive manufacturing (AM) techniques such as fused deposition Modeling® (FDM®) and fused filament fabrication (FFF) are rapidly gaining popularity in a variety of manufacturing industries due to AM's ability to create unique geometries and process unique material compositions. In particular, AM can operate on a variety of length scales with a large number of thermoplastic feedstock materials.
An additive manufacturing process includes building parts from selectively dispensing material through a nozzle or orifice. Multiple layers are built on top of each other to create a part or solid object. Material such as polymer is delivered to an extruder as a filament coiled in a spool, and is then melted during extrusion. That is, the polymer, typically held in the machine as spooled filament, is fed by the extruder into the liquefier where it is heated and melted, by receiving heat by conduction with heated walls in the liquefier. The extruder therefore feeds the filament through the liquefier, such that molten polymer is dispensed through the nozzle at the end of the liquefier chamber, which reduces the diameter of the molten polymer at its output. The extruder and liquefier assembly are directed in the X-Y plane using a gantry to build a cross-section of the part. Parts are built on a movable build platform within a chamber designed to control the printing environment. When printing in thermoplastic, the platform and/or its chamber are typically heated to reduce residual stresses, within the part, that arise during cooling after the deposition from the nozzle.
Two important components during the additive manufacturing process are the filament extrusion mechanism and the filament liquefier. Typically, a pinch-wheel mechanism that includes a drive wheel and a pinch or knurled wheel form a filament extrusion mechanism that drives the filament linearly by applying force along the side of the filament. Traction between the drive wheel and filament is provided by the clamping force applied by the pinch wheel. Driving the filament in this way generally causes the filament to be compressed between itself and the drive wheel, particularly when the drive wheel employs knurls, which dig into the filament. A filament fails by shear when an amount of force applied to the filament by the drive wheel exceeds the average shear stress over the area of engagement with the filament. Generally, the filament liquefier heats the polymer by conducting heat energy to the polymer from the liquefier wall and melts the polymer within the cavity before reaching the extrusion nozzle where its cross-section is reduced.
The production of parts using additive manufacturing is limited, for instance, by the design of current extruders, liquefiers, and gantries. For example, traditional extruders inhibit extrusion rates by providing a filament engagement area that limits the force that can be applied or transmitted by the extruder on the filament; traditional liquefiers do not provide an adequate heat rate necessary for expedient extrusion; and traditional gantries are speed and acceleration limited and cannot move with the agility needed to match high-throughput extrusion rates.
That is, in general, extrusion force in current extruders is limited by the filament shear area. Extrusion failure occurs when the extruder stress is greater than the shear stress of the filament shear area but less than the pressure drop caused by the liquefier.
Moreover, current liquefiers are limited by the maximum heat rate into the filament during extrusion, because they generally rely on conduction heat transfer from the heated liquefier walls. Due to the poor thermal conductivity of the filament and the conduction heat transfer rate, filament feed rate must be kept slow to allow full heating of the filament to the required melt temperature. Thus, with increasing extrusion rates, the filament receives less heat from the conduction liquefier. If the filament is not heated to the required temperature, the filament does not melt in the liquefier and instead jams in the nozzle, thereby preventing extrusion.
Current gantries for positioning a nozzle and build platform are effective at low dynamic performance, but traditional stepping motors used with gantries are speed limited due to fundamental operating principles of the actuators and their open-loop control scheme. On the other hand, simply using larger actuators causes an increase in mass and inertia of the gantry, thereby slowing the gantry response time despite having a higher torque capacity.
As a result of the above limitations of current additive manufacturing techniques, including insufficiently heating the filament, a high pressure needs to be exerted on the liquefier in order to properly extrude the filament. However, the high pressure or force on the filament may cause filament shear failure.
Accordingly, there is a need for systems, devices, and methods for high-throughput additive manufacturing that, among other things, are designed to increase the maximum force capable by the extruder, the heat rate into the volume of the filament, and the rate of deposition of the material of the filament. Moreover, there is a need for such systems, devices, and methods to be applicable to polymer resins and high-performance thermoplastic, and adaptable to large scale extrusion AM systems, in a variety of sectors such as medicine, product design, cinematography, education, aerospace, and advanced materials, among other sectors.