Patent Application
20150147427
Three dimensional printing is an additive manufacturing process that can form virtually any shape of three dimensional objects from a digital model. To accomplish this, the three dimensional printer applies successive layers of materials in different shapes. A three dimensional printer may use a plastic filament or other material that is pushed into an extrusion head. The extrusion head is heated to melt the material and then selectively deposits the material to form the desired object.
Extrusion heads can be complex and expensive. The extrusion head should reliably handle the material over a wide range of conditions and for long periods of time to produce the desired three dimensional objects. The extrusion head should be configured to reliably heat the material to a desired temperature throughout a range of feed rates and with various different materials. Further, the extrusion head should operate without clogging or leaking the melted material. If an extrusion head clogs while printing an object, the geometry of the object may not be accurate or the object may be entirely ruined. Leaking of melted material out of the nozzle can result in contamination and reliability issues. In addition to a design that mitigates these issues, an extrusion head would ideally be designed to be simple, compact, and easily repaired.
The accompanying drawings illustrate various examples of the principles described herein and are a part of the specification. The illustrated examples are merely examples and do not limit the scope of the claims.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.
As discussed above, the extrusion head is heated to melt the printing material and is then moved over the work piece to selectively deposit additional material. The extrusion head should reliably control a variety of printing materials through a range of feed rates without leaking or clogging. For example, an extrusion head may be used to print a variety of materials including a range of acrylonitrile butadiene styrene (ABS) plastics, polylactic acid (PLA) plastics, polyesters, polycarbonates, polyphenylsulfone (PPSF), and a variety of other thermoplastics. These materials each have different melting temperatures and heat capacity. The feed rates for these materials may range during printing from no feed rate to hundreds of millimeters per second. The extrusion head should reliably heat the printing material to the specific temperature at the given feed rate.
In an effort to improve the performance of the extrusion head, a number of manufacturers have created large, complex and expensive extrusion heads. These extrusion heads have a number of disadvantages. A large extrusion head can reduce the total build area in a three dimensional printer and increase the mass that must be controlled during printing. The complexity of the extrusion head can result in difficulty in repair and/or replacement of components of the extrusion head.
The principles described below enable the design and construction of a compact extrusion head with a reduced part count. The extrusion head has increased reliability and allows for easy replacement of the nozzle, which is the most common consumable component in the extrusion head.
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present systems and methods. It will be apparent, however, to one skilled in the art that the present apparatus, systems and methods may be practiced without these specific details. Reference in the specification to “an example” or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least that one example, but not necessarily in other examples. Features shown and/or described in connection with one figure may be combined with features shown and/or described in connection with other figures. Further, as used in the present specification and in the appended claims, the term “a number of” or similar language is meant to be understood broadly as any positive number comprising 1 to infinity; zero not being a number, but the absence of a number.
A nozzle (250) is screwed into the heater block (255). The nozzle (250) conducts heat from the heater block (255) into the filament (210,
The thermal isolation block (235) is sandwiched between the heater block (225) and the mounting block (230). The thermal isolation block (235) may be made out of a variety of materials such as polyether ether ketone (PEEK) or other thermally and mechanically stable materials.
One common task in a three dimensional printer is to replace the nozzle (250). The nozzle (250) may need to be replaced for a variety of reasons, including wear, contact damage, to clear a jam/clogging, or a desire to change out the nozzle for a nozzle with a different orifice size. To easily replace a nozzle (250), the heater block (255) or other structure supporting the nozzle (250) should be secured so that it does not rotate or move while the nozzle (255) is being unscrewed. This allows the nozzle (250) to be replaced simply by lifting the extruder (115,
However, in contemporary designs, the heater block (or equivalent structure) is not secured so that it does not spin when torque is applied to the nozzle. In these situations, the entire extrusion head must be removed to replace the nozzle. The heater block can then be held while the nozzle is removed. However, this is inconvenient and can result in damage to wires and to other components.
In the implementation shown in
For example, the thermal isolation block (235) and polymer sleeve (280) may be formed from materials that have the desired mechanical characteristics and also have a low thermal conduction. The thermal isolation block (235) may have the same or different cross sectional shape/dimensions as the heater block (255). As shown in the embodiment of
This configuration of the extrusion head (200) creates a number of thermal zones: an actively cooled zone (402), an insulated zone (404), a melt zone (408) and a flow zone (412). These zones control the temperature of the filament (210) for improved performance and reduction of clogging and leakage. The actively cooled zone (402) is in the mounting block (230), which is actively cooled by the heat sink and fan (205, 220;
The insulated zone (404) occurs where the filament (210) is passing through the polymer sleeve (280). The temperature of the filament (210) may increase, but the filament (210) does not melt. As the filament (210) exits the sleeve/insulating zone (404), it contacts the hot walls of the nozzle (250) and rapidly melts in the melt zone (412). The temperatures of the nozzle (250), heater block (255), and thermistor bolt (245) are approximately equal due to their high thermal conductivity and direct mechanical contact. This allows the control circuitry in the three dimensional printer (100,
The examples given above are only illustrative of principles described herein. The principles can be used to form a wide range of extruders and extrusion heads with different geometries and components. In general, an extrusion head includes a mounting block, a heater block, and a heat resistant polymer sleeve extending between the heater block and the mounting block. A fastener also connects the heater block to the mounting block such that the polymer sleeve and the fastener create a fully constrained connection between the heater block to the mounting block. A fully constrained connection refers to a connection wherein no translational or rotational degrees of freedom are present between the two connected parts without plastic deformation of one of the components. For example, a pin and an offset fastener that bring two objects together creates a fully constrained connection between the two planar objects when the pin and offset fastener join a planar surface on a first object with a mating planar surface on the second object. An intervening planar component (such as the thermal isolating block) does not disrupt the fully constrained connection if the fasteners pass through the intervening planar component. The connection does not exhibit X, Y, Z translation or rotations about the X, Y, or Z axes between the joined components. For example, the fastener and the polymer sleeve may be parallel and offset to form a pin and fastener connection that prevents rotation of the heater block with respect to the mounting block such that the nozzle can be unthreaded from the heater block without the heater block rotating with respect to the mounting block.
As discussed above, the exterior surface of the polymer sleeve may be entirely enclosed by the surrounding structure (the blocks and the nozzle). In this context the exterior surfaces of the sleeve include the ends of the sleeve and outer cylindrical surface. The inside cylindrical surface that the filament passes through is an interior rather than an exterior surface. One end of the sleeve interfaces with the mounting block and another end of the sleeve directly interfaces with a nozzle connected to the heater block. The sleeve has an inside diameter that has the same size or larger than an entry inside diameter of the nozzle so that there is a smooth transition for the filament into the nozzle. The abutment of the sleeve with the nozzle can be useful for a number of reasons including preventing leakage of the melted material out of the throat.
The system may also include a heater that is thermally connected to the heater block. A wide variety of heater types and geometries could be used. The cartridge heater illustrated is only one example. A thermal insulation block can be interposed between the mounting block and heater block to reduce heat flow between the heater block and the mounting block. The sleeve and fastener pass through the thermal insulation and into the mounting block. A filament of print material passes through an actively cooled zone in the mounting block, an insulated zone as the filament passes through the polymer sleeve, and a melt zone in the nozzle threaded into the heater block. The extrusion head may also include a thermistor bolt threaded into the heater block. The thermistor bolt includes a bolt body with a cavity, a thermistor placed in the cavity, and potting material surrounding the thermistor and filling the cavity. The mounting block can be sandwiched between a heat sink and a mounting surface of a drive motor. The heat sink and fan actively cool the mounting block. In one implementation, the head includes only one metallic thermally conductive path between the heater and the mounting block. The metallic thermally conducting path in one example may be the fastener that is offset from the filament path through the extrusion head.
In one example, a three dimensional printing system includes an extruder with an extrusion head made up of three connected blocks with each block having a different temperature during operation of the extrusion head. The system also includes a nozzle and an insulating sleeve passing through at least three connected blocks such that each exterior surface of the sleeve is in contact with surfaces of the three connected blocks or a nozzle. A feed mechanism accepts the filament of printing material and an actuator actuates the feed mechanism to pass the filament through the three connected blocks and insulating sleeve to the nozzle. An active cooling device is connected to one of the three connected blocks. The system includes a build platform and at least three controlled axes for moving the extruder relative to the build platform. Melted material is dispensed out of the nozzle to form the desired three dimensional object.
The three connected blocks may be pinned together by the insulating sleeve and joined by a fastener passing through two of the three connected blocks and threading into the third connected block. The fastener and the polymer sleeve may be parallel and offset to form a pin and fastener connection that prevents rotation of the heater block with respect to the mounting block such that the nozzle can be unthreaded from the heater block without the heater block spinning. In some implementations, a first block of the three blocks is a heater block; a second block of the three blocks is a thermally insulating block, and the third block of the three blocks is an actively cooled mounting block, in which the second block is the same planar geometry as the heater block and a heater is connected to the heater block. There may be an actively cooled zone in the mounting block, an insulated zone in the polymer sleeve, and a melt zone in the nozzle. The filament passes the actively cooled zone, the insulated zone, and the melt zone in the nozzle, in which the nozzle is threaded into the heater block and abuts an end of the polymer sleeve. A temperature sensor may be a thermistor bolt threaded into the heater block. The thermistor bolt includes a bolt body with a cavity, a thermistor placed in the cavity, and potting material surrounding the thermistor and filling the cavity. The connection between the heater block and the mounting block may be a fully constrained by a pin (the sleeve), bolt (the fastener), and plane connection.
The polymer sleeve and the mounting screw are placed into a mounting block to secure the thermal isolation block, heater block, and nozzle to the mounting block (step 515). In one example, the connection between the heater block and the mounting block is fully constrained such that the nozzle can be removed from the heater block without motion of the heater block with respect to the mounting block.
Operation of the three dimensional printer includes threading a filament into a tapered conic cavity in a mounting block and into an insulated zone formed by a polymer sleeve connecting the mounting block to the heater block and abutting the nozzle. The filament passes out of the polymer sleeve into a melt zone in the nozzle. The melted material is selectively ejected out of the nozzle as the nozzle is moved over the platform. The melted material solidifies to form the work piece on the platform.
The preceding description has been presented only to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.
