DE102019106873B4 - extruder - Google Patents

Abstract

Extruder (1) for the extrusion of filaments (2), in particular for a 3D printer, with a feed area (4) for drawing in the filaments (2), which has a screw (8) and a cylinder (9 ) has, with a melting region (5) for melting the filaments (2) adjoining the feed region (4) in the direction of movement of the filaments (2), with a discharge region (6) for discharging the melting of the filaments (2) resulting molten material (7) and with a drive device (12) for driving the screw (8), characterized in that the screw (8) has a conical outer diameter (8a) within the feed area (4), and that the cylinder (9 ) within the catchment area (4) has a conical inner diameter (9a).

Description

The invention relates to an extruder for the extrusion of filaments, in particular for a 3D printer, according to the type defined in more detail in the preamble of claim 1.

Additive manufacturing, also known as 3D printing, makes it possible to produce highly complex shapes and structures without complex and expensive tools. However, not all requirements for industrial series production can be met with this technology. The process is still too slow and the component size too limited.

Different embodiments of such printers and in particular extruders for such printers are known from the prior art. One of the most widespread methods is the strand laying method, which is also known as the FDM method.

A printer that works according to the strand-laying process consists of a movable print head with a filament feed and a melting chamber. In addition, a construction platform and usually a heated construction chamber are required. Thin plastic wires, so-called filaments, are used as the starting material. For ease of storage and processing, these filaments are unwound from a spool. Standard strand lay printers process 1.75mm or 2.85mm diameter filaments. The filament diameter required for the respective printer is determined by the size of the nozzle diameter.

In the strand laying process, the filament is continuously pushed into the heated nozzle (hot end) by a feed mechanism (cold end). There the filament is melted by an electrical heater and extruded from the nozzle by the pressure of the filament that is being fed. The profile and the size of the nozzle determine the shape and strand diameter of the melt. The strand of melt is then placed on the heated build platform, after which the object is built up layer by layer by lowering the build platform by one layer thickness before the next layer is applied. The applied layers solidify as they cool and bond with the layer below. In order to prevent overhanging layers from sinking, supports are often required for these areas, which are usually printed from a different plastic with a second print head and have to be separated from the component after the printing process has ended.

Compared to other additive manufacturing processes, the strand laying process is able to process a relatively large amount of material in a short time. Most plastics can be processed that will later be used in series production. In addition, only a small amount of waste is generated during the manufacture of components. However, the low melting capacity of the extruder nozzles limits the printing speed, since the filament is melted solely by heat conduction. In addition, no homogeneous temperature distribution is achieved in the melted filament. Ultimately, these disadvantages result in the low output capacity of FDM printers.

Due to the relatively large layer thicknesses of 0.1 mm to 0.25 mm, the surface of the components has a clear stepped effect. In addition, the fineness of the component geometry is limited to the diameter of the melt strand, so that structures with smaller dimensions than the melt strand cannot be printed. Another problem with the strand laying process is the frequent clogging of the nozzle, which is why a suitable cleaning mechanism is required. Due to the many individual layers, a printed component also has a large anisotropy with regard to the mechanical properties, i. H. the properties depend on the direction of the load, which makes it difficult to design the components.

Conventional extruders for processing plastic granules consist of a cylinder and a screw that is set in rotary motion by a drive unit. At the hopper, the granules are picked up by gravity, conveyed by the feed zone of the screw and compacted into a solid block. In the plasticizing zone of the extruder, the solid block is melted and then ejected as a strand of melt. Ordinary plasticizing zones consist of a smooth cylinder and a classic three-zone screw or a barrier screw if higher melting rates are required.

In extruders that process standard granules with a particle size of 3 - 5 mm in diameter, the screw diameter cannot be reduced arbitrarily, since the granules still have to be conveyed in the intake. So-called mini-extruders are used in which the thread depth of the screw has exactly the depth of the granulate diameter. However, the core diameter cannot be chosen as small as you like, otherwise the torque to be transmitted is too large for the remaining part of the worm and the worm would shear off in the feed area. Furthermore, such mini extruders have a comparatively high weight and low melting capacity.

Another type of extruder is the so-called welding extruder, in which no granules are processed, but a filament is drawn in, which is crushed into granules and fed to a conventional three-zone screw. Although the position of the compactly built device is independent of the position, the drill drives used are very imprecise, which leads to fluctuations in the output.

In order to make 3D printing faster according to the strand laying method and also to be able to print larger prototypes, there is no extruder system according to the prior art that offers sufficient mass throughput performance with maximum melting effectiveness.

From the DE 696 26 131 T2 discloses a device for producing a three-dimensional object by sequentially disposing multiple layers of a solidifiable material on a support member. A solid is conveyed via a belt drive and liquefied in a heated channel. The liquefied material is then discharged through a nozzle by means of a partially conical screw.

The DE 601 07 569 T2 describes a filament cassette with a rotatable spool on which a modeling filament is wound.

An extrusion screw with a decreasing diameter is from the U.S. 3,517,095 known.

It is the object of the present invention to create an extruder for the extrusion of filaments which has both a high mass throughput and a good melting efficiency.

According to the invention, this object is achieved by the features mentioned in claim 1.

The solution according to the invention, in which the screw has a conical outer diameter within the feed area used for drawing in the filaments and the cylinder has a conical inner diameter within the feed area, ensures a constant contact pressure between the screw, the filament and the cylinder, so that the filaments are conveyed very constantly, which means that a relatively high conveying speed of the same can be set.

For use in a 3D printer, this enables very precise printing. Furthermore, due to the high output of the material from the extruder, very fast printing is possible compared to known solutions, which results in considerable cost savings.

Further advantages of the solution according to the invention can be seen in the more effective melting of the filament for subsequent processing in a 3D printer, the precise dosing and the position-independent printing. In addition, the extruder according to the invention can be connected very easily to a robot or to a similar device.

In a very advantageous development of the invention, it can be provided that the outer diameter of the worm and the inner diameter of the cylinder have essentially the same cone angle. This enables a constant contact pressure between the screw, the filament and the cylinder and thus a very precise conveying of the filaments.

In order to increase the accuracy of the drawing-in of the filaments into the drawing-in area, it can also be provided that the screw has at least one groove running helically around the outer diameter of the same, the distance between a groove and the groove following in the axial direction being 2-20 times, in particular 5-10 times, greater than the width of the groove in the axial direction.

If the groove has essentially the same depth over its entire length, this also ensures exact conveying and a constant contact pressure.

A further very advantageous embodiment of the invention can consist in the fact that the filaments are wound up on a filament roller which can be driven synchronously with the rotation of the screw. In this way, the filaments unwound from the filament roll can be drawn into the feed area at a constant speed.

A constructively simple way to synchronize the movement of the filament roll and the snail can be that the filament roll is in direct driving connection with the snail.

An alternative embodiment can consist in the screw and the filament roller having separate drive devices which are synchronized with one another in terms of their rotational speed are. This offers greater design freedom with regard to the arrangement of the filament roll.

In another very advantageous embodiment of the invention, it can be provided that the inside diameter of the cylinder has at least one groove. Such a groove on the inner diameter of the cylinder can increase the friction of the filaments relative to the cylinder, so that a dependence on the coefficients of friction between a completely smooth inner surface of the cylinder and the filaments is avoided. Another advantage of this solution is that it increases the rigidity of the conveyance and improves the forced conveyance of the filaments, which allows the molten material to be ejected with even greater accuracy.

In order to further increase the friction between the screw, the filaments and the cylinder or to be able to set certain desired friction values, it can also be provided that the at least one groove runs helically around the inner diameter of the cylinder or that several grooves running in the axial direction are provided.

If the worm can be adjusted in the axial direction and locked in any desired axial position, the contact pressure between the worm and the cylinder can be adjusted very precisely to the desired values. As a result, different contact pressures can also be set.

An exemplary embodiment of the invention is shown in principle using the drawing.

• 1 eine schematische Schnittansicht des erfindungsgemäßen Extruders;
• 2 eine sehr schematische Darstellung einer alternativen Anordnung der Filamentrolle relativ zu dem Extruder;
• 3 eine weitere schematische Schnittansicht des Einzugsbereichs des erfindungsgemäßen Extruders; und
• 4 eine schematische Schnittansicht eines im Einzugsbereichs des erfindungsgemäßen Extruders verwendeten Zylinders.

It shows:

• 1 a schematic sectional view of the extruder according to the invention;
• 2 a very schematic representation of an alternative arrangement of the spool of filament relative to the extruder;
• 3 a further schematic sectional view of the feed area of the extruder according to the invention; and
• 4 a schematic sectional view of a cylinder used in the feed area of the extruder according to the invention.

1 shows in a very schematic representation an extruder 1, which is used for the extrusion of filaments 2, which are wound on a filament roll 3. The extruder 1 is intended in particular for a 3D printer, not shown in its entirety, which can be used for additive manufacturing according to the strand laying process, and has a feed area 4 for feeding in the filaments 2, a melting area 5 adjoining the feed area 4 for melting the filaments 2, and a discharge area 6 for discharging the molten material 7 resulting from the melting of the filaments 2. The filaments 2 can be made of plastic, for example, but can also be made of other materials. In principle, the extruder 1 described herein could also be used for other purposes.

The feed area 4 has a worm 8 and a cylinder 9 accommodating the worm 8 . The term "cylinder" is a common description in the field of extruders for the component that accommodates a screw of the extruder and there is no reference whatsoever to the geometric shape also referred to as "cylinder". The cylinder 9 could accordingly also be referred to as an extrusion cylinder. In the present case, the screw 8 not only extends through the intake area 4, but also runs through the melting area 5.

As can be seen from the 1 and 3 results, the screw 8 within the catchment area 4 has a conical outer diameter 8a. The cylinder 9 accordingly has a conical inner diameter 9a within the catchment area 4, which is reflected in the 1 , 3 and 4 is recognizable. In the present case, the outer diameter 8a of the worm 8 and the inner diameter 9a of the cylinder 9 have essentially the same cone angle. The statement "essentially" refers to unavoidable manufacturing tolerances.

To receive the filaments 2 and to convey them in the direction of the melting region 5, the screw 8 has at least one groove 10 running helically around the outer diameter 8a thereof. The basic principle of the promotion of the filament 2 within the catchment area 4 thus corresponds to the nut-screw principle. Accordingly, the filament 2 is not comminuted in the feed area 4 , but only conveyed in the direction of the melting area 5 . The groove 10 can have a pitch change from an infinite pitch in the area of the largest cone diameter to a pitch greater than 0.5 times the cone diameter in the area of the smallest cone diameter.

Solutions known per se and familiar to a person skilled in the art can be used in the melting region 5 . For example, barrier screws with a grooved plasticizing zone can be used here in order to achieve the highest possible melting capacity to achieve. In the present case, the melting area 5 has a plurality of heating strips 5a.

The groove 10 has such a pitch angle that it runs several times around the circumference of the screw 8 in the axial direction of the extruder 1 denoted by “x”. As a result, are in 3 several grooves of groove 10 can be seen. The area between these individual grooves of groove 10 can be referred to as web 11 . In other words, the worm 8 has the web 11 as a helically circumferential projection, the grooves of the groove 10 being provided between the webs 11 spaced apart from one another in the axial direction x. In the present case, the distance between a groove and the groove that follows in the axial direction x is 2-20 times, in particular 5-10 times, greater than the width of the groove 10 in the axial direction x. In contrast, the groove 10 has essentially the same depth over its entire length. The width and the depth of the groove 10 are preferably adapted to the size of the filament 2. In principle, the groove 10 could also have multiple threads.

To drive the worm 8 is used in the 1 and 2 very schematically illustrated drive device 12, which can be designed for example as an electric motor. If necessary, a gear can be provided between the drive device 12 and the worm 8 . In the present case, the drive device 12 is a servo-geared motor. Such an embodiment of the drive device 12 enables very precise control.

The filament roll 3 on which the filaments 2 are wound can be driven synchronously with the rotation of the screw 8 . in the in 2 In the embodiment shown, the filament roller 3 is in direct drive connection with the worm 8. In other words, in this case the worm 8 is driven by means of the drive device 12 and the worm 8 in turn drives the filament roller 3. As an alternative to this, the screw 8 and the filament roller 3 can also have separate drive devices which are synchronized with one another in terms of their rotational speed. Such an embodiment shows 1 , However, the drive device of the filament roller 3 is not shown there.

In both cases, the filament roller 3 should be positioned in such a way that the filament 2 is pulled in while the screw 8 is rotating without the filament 2 tearing off.

In principle, the filament roll 3 could also be stored in the idling state and only rotate from the same due to the unwinding of the filament 2 .

The worm 8 can be adjusted in the axial direction x and locked in any desired axial position. In order to set the axial position of the worm 8 in the cylinder 9, an adjustment mechanism (not shown) can be provided, for example in the area of the drive device 12. In this case, the worm 8 can be mounted through a hollow shaft 12a of the drive device 12 . This also enables a simple axial adjustment of the worm 8. The filament 2 unwound from the filament roll 3 can also be passed through this hollow shaft 12a.

This possibility of axial adjustment of the worm 8 within the cylinder 9 allows a different gap size to be set between the outer diameter 8a of the worm 8 and the inner diameter 9a of the cylinder 9 . With a smaller gap between the outer diameter 8a of the screw 8 and the inner diameter 9a of the cylinder 9, the filament 2 is pressed more strongly against the inner diameter 9a of the cylinder 9, as a result of which the conveying behavior of the filament 2 can be influenced, i. H. The contact pressure between the screw 8, the filament 2 and the cylinder 9 can be adjusted by an axial adjustment of the screw 8 within the cylinder 9 .

In principle, it is also possible to dispense with the axial adjustability of the worm 8 within the cylinder 9 if, for example, a specific axial alignment of these two parts to one another has been determined and they can be manufactured with sufficient accuracy relative to one another.

In 4 It can be seen that the inner diameter 9a of the cylinder 9, like the worm 8, has at least one groove 13. The at least one groove 13 of the cylinder 9 can run helically around the inner diameter 9a of the cylinder 9, but a plurality of grooves 13 running in the axial direction x can also be provided. The at least one groove 13 of the cylinder 9 achieves a supporting effect when the filaments 2 are being conveyed.

For example, the grooves 13 in the barrel 9 may be perpendicular to the grooves 10 in the worm 8. The grooves 13 are thus opposite to the grooves 10, d. H. for example, if the grooves 10 run in the manner of a right-hand thread, the grooves 13 run in the manner of a left-hand thread.

Both the screw 8 and the cylinder 9 can be composed of several individual components, so that optimizations can be carried out quickly and cost-effectively if adjustments are necessary.

Claims (10)

Extruder (1) for the extrusion of filaments (2), in particular for a 3D printer, with a feed area (4) for drawing in the filaments (2), which has a screw (8) and a cylinder (9) receiving the screw (8), with a melting area (5) for melting the filaments (2) adjoining the feed area (4) in the direction of movement of the filaments (2), with a discharge area (6) for discharging the material caused by the melting of the filaments (2) resulting molten material (7) and having driving means (12) for driving the screw (8),characterizedthat the screw (8) within the catchment area (4) has a conical outer diameter (8a), and that the cylinder (9) within the catchment area (4) has a conical inner diameter (9a). extruder after claim 1 , characterized in that the outer diameter (8a) of the screw (8) and the inner diameter (9a) of the cylinder (9) have substantially the same cone angle. extruder after claim 1 or 2 , characterized in that the worm (8) has at least one groove (10) running helically around the outer diameter (8a) of the same, the distance between a groove and the groove following in the axial direction (x) being 2-20 times, in particular 5-10 times, greater than the width of the groove (10) in the axial direction (x). extruder after claim 3 , characterized in that the groove (10) has substantially the same depth over its entire length. extruder after one of the Claims 1 until 4 , characterized in that the filaments (2) are wound on a filament roller (3) which can be driven synchronously with the rotation of the screw (8). extruder after claim 5 , characterized in that the filament roller (3) is in direct drive connection with the screw (8). extruder after claim 5 , characterized in that the screw (8) and the filament roller (3) have separate drive devices (12) which are synchronized with one another in terms of their speed. extruder after one of the Claims 1 until 7 , characterized in that the inner diameter (9a) of the cylinder (9) has at least one groove (13). extruder after claim 8 , characterized in that the at least one groove (13) runs helically around the inner diameter (9a) of the cylinder (9) or that a plurality of grooves (13) running in the axial direction (x) are provided. extruder after one of Claims 1 until 9 , characterized in that the worm (8) is adjustable in the axial direction (x) and can be locked in any desired axial position.

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