Patent Application
20170157826
This invention relates to additive manufacturing systems, more particularly the extrusion head mechanism, or extruder, of a fused filament fabrication system.
Fused Filament Fabrication is one of several known methods of 3D printing, where physical components can be manufactured directly from a 3D CAD (Computer Aided Design) model using an additive approach where material is deposited on a horizontal building surface layer by layer. Such layers are typically between 0.05 to 1.0 mm thick depending on the technology used and interpreted by translating ‘slices’ of the 3D CAD model into movement of an extrusion head for depositing material. In fused filament fabrication, the deposition technology is extrusion of polymer via an extruder, whereby a polymer filament is fed by a feeding unit into a heated nozzle and extruded in melted form into a string through a vertically oriented nozzle onto the horizontal building surface. The space between the printing nozzle and the building surface determines the layer thickness. By moving the printing nozzle relative to the building surface in the horizontal X and Y directions, whilst feeding building material at a controlled rate, a build layer can be completed, after which movement of the nozzle relative to the building surface one layer thickness in the positive Z direction allows printing of the next X-Y layer on top of the previously printed layer, and so on. Each new extruded bead of plastic fuses and bonds to the previously deposited material in X, Y and Z directions, making it possible to gradually build up physical objects based on the 3D CAD model. Several examples of the above type of 3D printers exists in the Art. Expired US patent no U.S. Pat. No. 5,121,329 Crump by Stratasys describes the basic form of manufacturing 3D models using extrusion of fluid materials through a printing nozzle, whereby the extruded fluid material solidifies onto to a building surface upon a drop of temperature. The above patent also teaches the use of a flexible filament building material housed on a supply spool, whereby the filament is drawn off the spool by two feed rollers and into a heated nozzle, causing the filament to melt and pass through the nozzle by the pressure created by the feed rollers. U.S. Pat. No. 5,764,521 Batchelder et. al. describes an alternative method of feeding building material using a feeding screw.
U.S. Pat. No. 5,968,561 Batchelder et. al. discloses improvements in the relative movement of the extrusion nozzle and the build platform. A common aim for 3D printers is to achieve the finest possible build resolution in the shortest possible time. In the case of a 3D printer based on the fused filament fabrication, the resolution of the build is proportional to the nozzle diameter and layer thickness. The speed of the build is proportional to the speed of extrusion of molten material from the nozzle which is determined by nozzle area and maximum volume of extruded molten material per second. Extrusion speed is determined by volume of extruded molten material divided by area of extruded molten string of material. In fact as the resolution of the build is doubled by smaller size of the nozzle, the speed of the build slows down by a factor 4. This resolution vs. build speed dilemma makes speed of extrusion a critical factor in improvement. A key subsystem in a fused filament fabrication 3D printer is the extruder. One type of extruder is the screw type, described in U.S. Pat. No. 5,764,521, where polymer material is fed into a heated feeder with a rotating feeding screw, which is able to extrude molten polymer at high pressure through to a nozzle. Although this type is typically capable of achieving high extrusion pressure, an important drawback is its weight which limits acceleration in the x-y plane and therefore overall printing speed. Another drawback is the large size of the screw mechanism, which makes it difficult to install into the 3D printer. A different type of extruder more commonly and preferably used consists of a ‘cold’ end having a filament feeder unit and a ‘hot’ end having a heated extrusion nozzle. The feeder pulls filament material off a supply roll and feeds it by pressure into the heated nozzle which consists of essentially a heated tube. The feeder unit design is critical, and several variants are known: The most commonly used method is to feed the filament in a straight line between a driven pinch wheel and a sprung pressure plate or idler wheel. The pinch wheel can be knurled, toothed, hobbed or otherwise treated to increase the friction and therefore traction force applicable on the filament. For example, a toothed pinch wheel where the tooth profile is concave to provide a line contact with the filament instead of a point contact would be preferable. Extrusion of thinner melted material at higher feed-rates is desired for high resolution and faster build speed. Both increased resolution and increased extrusion speed result in higher nozzle pressure relative to the grippable surface area of the filament and therefore the available friction between the filament and the feeding device. The gap between theoretical and actual extrusion speed increases due to slippage in the feeding device. Current technology of 3D printers is limited to extrusion of around 10 mm3/s which is equivalent to 80 mm/sec extrusion speed with a 0.4 mm diameter nozzle, using ABS material. Over this limit slippage becomes unacceptable, which can lead to poor quality and build interruptions. It would be beneficial if the technology could allow thinner nozzle diameter and higher extrusion speed by means of higher feed rate of the filament material without slippage in the feeding mechanism. It would also be beneficial is the construction was compact and lightweight, thereby enabling fast acceleration and a higher printing speed as a result.
Disclosed is an improved extruder head for a fused filament fabrication 3D printer, which has a lightweight construction and enables extrusion of thinner extruded material at a higher extrusion speed without any slippage in filament feeding mechanism, thereby allowing higher overall building speed of the 3D printer. Higher feed-rate of the filament material is achieved by increased usable friction between pinch wheel and filament by increasing the grippable area of the filament. This is done by feeding the filament into the feeding mechanism at an angle different to the outlet angle and routing it around the pinch wheel, back-supported by a plurality of support rollers, so that the filament is in frictional contact with the pinch wheel along a greater part of its circumference, thereby increasing the surface contact area between the pinch wheel and the filament. Owing to non-slippage of the filament feeder, nominal volume of extruded material is exactly the same as desired volume with high filament feeding rate.
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In another embodiment of the extruder head 3, it should be obvious for anybody skilled in the art that the number of support rollers generally indicated at 9 may vary depending on the size of them or the filament contact angle 30 desired. Therefore the distance between support rollers 9 may be shorter or longer depending on need. For example, instead of using three support rollers 9a, 9b and 9c, it is imaginable that four or five support rollers could be used to fill the desired filament contact angle v 30, if the individual rollers size was smaller and adequate to fill the space available under filament contact angle v 30. Equally, it is imaginable that only two support rollers may be used as long as the filament contact angle v 30 is longer than if using only one support roller. In case a greater filament contact angle 30 is required, for example 180 degrees, as many as six support rollers 9 may be needed, as indicated in
In yet another embodiment of the extruder head 3, it is imaginable that the support rollers generally indicated at 9 may be substituted by a general support means of low friction. For example, an arc-shaped guide designed to support the filament 23 over a filament contact angle v 30 but relying in low friction against the filament 23 whilst still providing sufficient pressure against pinch wheel 10. Such low friction could for example be achieved by a PTFE coat or highly polished surface on a steel guide.
In still another embodiment of the extruder head 3, it should be well known by someone skilled in the art that friction between pinch wheel 10 and filament 23 could be maximized in a number of ways, for example the surface of the pinch wheel 10 could be knurled, toothed, hobbed or otherwise surface treated to increase friction.
In a final embodiment of the extruder head 3, the support rollers 9 or support means may be spring loaded to provide a controlled pressure against pinch wheel 10.
This application is a continuation of, and claims the benefit of PCT application PCT/IB2014/062163 filed Jun. 12, 2014, the contents of which are incorporated herein in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/IB2014/062163 | Jun 2014 | US |
| Child | 15372379 | US |
