Patent ID: 12186975

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

An known a 3D printing device for the additive manufacture of metallic components is described in DE 10 2014 018 081 A1.

The use of screw extruders for the additive manufacture may be limited by their weight and their overall size, which typically depends on the length of the screw conveyor (extruder screw), as the screw extruders are either of traversable design or the entire working field is moved. The latter variant, however, requires making the entire 3D printing device distinctly oversize. Furthermore, in previously known extrusion methods for additive manufacture, it typically is to be observed that when processing fiber-reinforced plastic material a desired or even required material strength of the component to be manufactured can be realized only with difficulty or not at all.

FIG.1shows a 3D printing device schematically and in a perspective view, in which an embodiment of a proposed extrusion apparatus in the form of a screw extruder2is provided as part of a printing head of the 3D printing device. By the screw extruder2, fiber-reinforced plastic material can be used for the additive manufacture of a component1by way of thermoplastic melt layering. Via a triaxial kinematic system, the screw extruder2is traversable above a platform or base11on which the component1to be manufactured is formed. Material threads of molten fiber-reinforced plastic material are applied on the base11via an extrusion nozzle10of the screw extruder2. The extrusion process is controlled via an electronic control device20of the screw extruder2.

As is illustrated for the screw extruder2, with reference to the enlarged cross-sectional views ofFIGS.2and3and with reference to the top view ofFIG.4, the screw extruder2includes a screw conveyor3for conveying fiber-reinforced plastic material8, which is supplied in the form of powder or granules, in the direction of the extrusion nozzle10. With a total length, this screw conveyor3extends along a (screw) longitudinal axis via an intake section31, an adjoining melting and compression zone32up to an ejection nozzle33. The screw conveyor3is accommodated in a housing4of the screw extruder2so as to be rotatable about its longitudinal axis and can be rotated via a non-illustrated motor drive.

In the cross-sectional view ofFIGS.2and3, the housing4at least partly accommodating the screw conveyor3is shown with different housing portions41g,42gand43g. The individual housing portions41g,42g,43gcan also form independent housing parts that are interconnected and collectively define the housing4. A first housing portion41gdefines a funnel-shaped inlet5for the supply of the powdery or granular fiber-reinforced plastic material8, which as a composite material includes, for example, a thermoplastic matrix material with fibers embedded therein. In a conveying direction to the extrusion nozzle10, the first housing portion41gwith the inlet8, which defines a feed zone41for the supply of the plastic material, is adjoined by a second housing portion42gfor forming a thermal barrier zone42. The barrier zone42separates the feed zone41from a heating zone43, which is formed by a succeeding third housing portion43gof the housing4. For the thermal separation of the feed zone41from the heating zone43, the second housing portion42gis made, for example, from a high-strength, but thermally very poorly conductive, for example ceramic, material and possibly includes an additional intake cooling. For example, the housing portion42gof the thermal barrier zone42is made of zirconium oxide or aluminum oxide.

For the configuration of the heating zone43, the third housing portion43gincludes a heating element9or a plurality of heating elements9distributed around the circumference. The fiber-reinforced plastic material8conveyed in the direction of the extrusion nozzle10is molten by the heating elements9so that said plastic material can be extruded from the extrusion nozzle10in a material thread whose thickness is determined by the geometry of the extrusion nozzle10here exchangeably fixed to the housing4.

The screw conveyor3, which in the properly mounted condition is arranged vertically, extends within the housing4in such a way that the intake section31of the screw conveyor3is completely enclosed by the first housing portion41gand the feed zone41formed thereby. Via the compression and melting zone32of the screw conveyor3, which adjoins the feed zone31, within the third housing portion43gand hence within the heating zone43, the plastic material8is compressed by the screw conveyor3. The screw conveyor3therefor is configured as a stuffing screw in which the diameter of a shaft6of the screw conveyor3in the vicinity of the melting and compression zone32conically increases with an angle of 7° to 10° and up to 1.5 to 2 times a smallest diameter of the screw conveyor3.

In an ejection zone33of the screw conveyor3adjoining the melting and compression zone32, which likewise is still located within the heating zone43, the (larger) diameter of the shaft6of the screw conveyor3remains constant. The ejection zone33and hence an axial end of the screw conveyor3is adjoined by a reservoir7in the conveying direction of the fiber-reinforced plastic material. This reservoir7is formed between the axial end of the screw conveyor3and the extrusion nozzle10and at least partly defined by a conical taper V of inner shell surfaces of the third housing portion43gfacing the screw conveyor3in the heating zone43. In this reservoir7, molten fiber-reinforced plastic material is maintained under excess pressure, the reservoir7here having a maximum length of 1/15 of a total length of the screw conveyor3. The internally provided conical taper V in the third housing portion43gin the direction of the extrusion nozzle10here has an opening angle φ of 58° or more, for example.

In the illustrated screw extruder2, the plastic material8initially is received in the funnel-shaped inlet5in the intake section31of the screw conveyor3and is transported downwards through the screw conveyor3along the conveying direction. Due to the thermal barrier zone42in the housing4, the plastic material8flows freely up to the second housing portion42gforming the barrier zone42. Furthermore, it is provided that until reaching the heating zone43within the housing4, there is no compression due to a change in pitch of the screw flights or a change in diameter of the shaft6of the screw conveyor3.

It is only in the heating zone43directly adjoining the barrier zone42in downward direction that the plastic material8is molten and compressed. For this purpose, the radially arranged heating elements9are provided on the housing side of the heating zone43, which heating elements extend along the entire length of the heating zone43and provide for a very local input of thermal energy. On the housing side, the heating zone43here maximally has a length that corresponds to half the length of the screw conveyor3. The third housing portion43gforming the heating zone43has a greater thermal conductivity than the second housing portion42gforming the barrier zone42and also has a greater thermal mass with respect to this second housing portion42g.

In the illustrated extrusion apparatus in the form of the screw extruder2, the volume in the interior of the housing4provided in the heating zone43for fiber-reinforced plastic material8is limited to less than 5.5 cm3, in the present case to about 3.30 cm3. In other words, a maximum volume of 3.30 cm3is available in the heating zone43for the plastic material8to be conveyed along the longitudinal axis of the screw conveyor3in the direction of the extrusion nozzle10. This volume is calculated from the difference of the cavity in the third housing portion43g, in which the screw conveyor3extends with its melting and compression zone32and its ejection zone33, and the volume occupied by the screw conveyor3itself

Via the electronic control device20, a maximum rotational speed of the screw conveyor3also is limited to 30 revolutions per minute about the (screw) longitudinal axis. Taking account of this speed limitation, a volumetric feed rate of the screw conveyor3here is set in such a way that the fiber-reinforced plastic material8to be conveyed in the direction of the extrusion nozzle10remains in the heating zone43for a maximum of 20 minutes, here e.g., for at least 1.5 seconds, but not more than 20 minutes. In the present case, a simultaneously comparatively high output of the screw conveyor3in the range of up to 7500 cm3per hour, such as 5500 cm3per hour, 2500 cm3per hour, 1000 cm3per hour or 250 cm3per hour is achieved. Combined with a length-diameter ratio of the screw conveyor3of below 10 it is achieved that the fiber-reinforced plastic material8remains in the heating zone43for a comparatively short period, whereby a degradation of the plastic material8is avoided. This is also promoted by the configuration of the heating zone43with a maximum length of 24 mm and a diameter of less than 18 mm. In addition, it was found that in an extrusion method implemented with the screw extruder2corresponding to the above-mentioned process parameters, fibers contained in the powdery or granular plastic material8are sheared off only for a comparatively small portion and about 70% of the fibers are deposited in the direction of movement of the extrusion nozzle10. This allows to influence the fiber orientation and hence the strength of the component1to be manufactured regardless of the component geometry. In a 3D printing process, merely the path of movement of the extrusion nozzle10has to be manipulated.

The throughput time in the heating zone43and along the melting and compression zone32of the screw conveyor3in principle is dependent on the fiber-reinforced plastic material8used. Corresponding to the proposed solution, the maximum rotational speed of the screw conveyor3is limited to a maximum of 30 revolutions per minute. In combination with the length-diameter ratio of the screw conveyor3of less than 10 this provides low shear forces, and the throughput time is chosen such that the residence time of the plastic material8in the heating zone is not more than 20 minutes. Due to the short residence time, which, for example, is also fixed by the feed rate, of the amount of plastic material8of less than 5.5 cm3, which is kept small by definition as a result of the specified volume, in the heating zone43of geometrically comparatively short design (in particular relative to the length of the screw conveyor3), the plastic material8remains in the hot state only briefly and the melt kept in stock in the melting and compression zone32has a sufficiently short throughput time.

The compact screw extruder2shown inFIGS.1to4is capable of processing fiber-reinforced plastic material8, which, for example, contains at least one of the following matrix materials: polycarbonate, polylactate, polyethylene, polyethylene terephthalate, polymethylmethacrylate, polybutylene terephthalate, acrylonitrile-butadiene-styrene copolymer, polyoxymethylene, polypropylene, polystyrene, polyvinyl chloride, polyamide. Furthermore, various reinforcing materials in the form of glass fibers, aramide fibers, steel fibers, carbon fibers, synthetic fibers, plastic-based fibers, natural fibers, and/or ceramic fibers can be embedded in the matrix material. As additional reinforcements, flour or fragments of glass or other materials can also be utilized. The plastic material can also be mineral-reinforced.

In an application scenario, the fiber-reinforced plastic material8has a fiber content of greater than or equal to 10%, without containing any endless fibers.

By the screw extruder2or the 3D printing device, in which the screw extruder2forms part of a printing head, a component1can effectively be manufactured additively. For example, corresponding to the schematic representation ofFIG.5, layers (material webs) containing 70% of fibers that are deposited in the direction of movement of the extrusion nozzle10can be applied for the component1by extruded material threads of fiber-reinforced plastic material8by using the extrusion process implemented with the screw extruder2. The remaining 30% of the fibers protrude from the applied (printed) layers in all directions in space, which results in a mechanical interlocking between the layers deposited on each other. In this way, a comparatively high material strength is achieved in the finished component1and a deformation behavior of the finished component1can be specified in a targeted way.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.

The following is a list of reference numbers shown in the Figures. However, it should be understood that the use of these terms is for illustrative purposes only with respect to one embodiment. And, use of reference numbers correlating a certain term that is both illustrated in the Figures and present in the claims is not intended to limit the claims to only cover the illustrated embodiment.

LIST OF REFERENCE NUMERALS

1component10extrusion nozzle11base2screw extruder (extrusion apparatus)20control device3screw conveyor/extruder screw31intake section32melting and compression zone33ejection zone34end region340chamfer4housing41feed zone42(thermal) barrier zone41g,42g,43ghousing portion43heating zone5inlet6shaft7reservoir8fiber-reinforced plastic material9heating elementV taperφ opening angle