3D printing process for the production of three-dimensional plastic molded parts

Description

[0001] 3D is the abbreviation for three-dimensional.

[0002] In the past, printers were only suitable for two-dimensional works.

[0003] For some time now, 3D printers have also been able to be used to create three-dimensional objects. The material is applied either dot-by-dot and / or as threads / strips / bands. The threads / strips / bands can be short or long. In either case, the dots and / or threads are arranged in such a way that the desired shaped part is created.

[0004] 3D printers can also produce three-dimensional molded parts from thermoplastics. For this purpose, it is advantageous to molten the plastic before application. The molten plastic is then applied to the application site through a nozzle. The nozzle forms the print head.The insertion point is a point at which the production of the molded part should begin or continue. In a coordinate system with three axes (X-axis, Y-axis, and Z-axis), the point is determined by values ​​on all axes. The following options are available, among others: The nozzle is moved in a vertical position above a stationary support in a horizontal plane (determined by the X-axis and Y-axis). The extruder can be moved along with the nozzle.

[0005] For smaller extruders, this solution is the better option. The extruder, including the nozzle, is then preferably housed in a movable / sliding housing section, which in turn is housed in a movable / sliding housing section. The directions of movement of both housing sections are perpendicular to each other, allowing any position in the plane to be reached. The device's control system can be used to adjust the device to a specific construction product or to switch to a different construction product.

[0006] For larger structural components, such as building sections or entire buildings, it is advantageous if the extruder is moved along the building walls. In this case, a guide is provided for the extruder's movement along the building walls, allowing large movements to be achieved by moving the extruder along the walls. Furthermore, the extruder can also be mounted so that it can pivot, allowing melt strips to be laid side by side. As an alternative to the pivoting movement of the extruder, the nozzle can also be adjusted. Sliders, which can be used to direct the melt emerging from the extruder to the side of the wall, are particularly suitable for this purpose. The base is moved beneath a stationary, vertical nozzle in a horizontal plane (determined by the X-axis and Y-axis). The nozzle can be moved in a vertical position above a base in a horizontal plane (determined by the X-axis and Y-axis). At the same time, the base beneath the nozzle can be moved in a horizontal plane (determined by the X-axis and Y-axis). The nozzle is moved vertically in a vertical position to adjust to the respective height of the point (on the Z-axis). The base is moved vertically in a vertical position of the nozzle to adjust to the respective height of the point (on the Z-axis). Both the nozzle and the base can be moved vertically to adjust to the respective height of the point (on the Z-axis).

[0007] The movements are preferably carried out with computer support.

[0008] It is advantageous to use the data from a computer-aided drawing program with which the molded part is designed / imaged at the same time for the movement of the nozzle and / or the base. The most famous sign / The design program is the CAD program. This program, like other drawing programs, can serve as the basis for software development.

[0009] Independently of this, there are control programs that can be used directly or with minor modifications to control the 3D printing according to the invention. Such control programs for the movement of the print head / Nozzles can also be control programs from other machines, such as milling machines. Such controls are capable of executing the finest steps in all directions with a tool, both in a straight line and along a curved path. Only the data needed to determine the position of the melting points needs to be entered. / threads / Volumes / stripes are described.

[0010] Such controllers can also operate at a wide range of speeds. Such controllers are also capable of bridging a movement to another location in high-speed mode at speeds many times higher than the operating speed.

[0011] With uniform molded parts, a uniform melt discharge from the nozzle is possible. Such uniform molded parts are, for example, tubular molded parts. Tubular molded parts similar uniform molded parts However, they are extremely rarely produced using a 3D printer because all conventional manufacturing processes are economically far superior to 3D printing.

[0012] This is different with uneven molded parts.

[0013] This means that the more irregular a molded part is, the more economical its production using a 3D printer can be.

[0014] For the purposes of the invention, any molded part that requires a change in melt flow is considered non-uniform. This applies to thickness changes as well as to cracks / breakthroughs in walls, but also to corners. While thickness changes can be accommodated by changing the nozzle movement / support movement and / or by changing the amount of melt flowing out of the nozzle per unit of time, cracks / breakthroughs may require an interruption or change in the melt flow.

[0015] Even the production of products with different dimensions can make the 3D printing according to the invention economical.

[0016] Irrespective of this, it may be advantageous to print desired molded parts only on request using the 3D printer according to the invention in order to avoid stockpiling.

[0017] It is known to produce the melt using a melting device, which is essentially familiar from adhesive technology. In adhesive technology, a wire or rod of adhesive material is pushed into a heating device (glue gun) and liquefied at the tip. The liquefied material is pushed out of the heating device with the wire or rod. The pressure / feed of the wire or rod determines the adhesive output.

[0018] When using this technique for melting a thermoplastic, a wire or rod made of thermoplastic is used instead of the wire or rod made of adhesive material.

[0019] The disadvantage of this technology is that large quantities of plastic per unit of time are not yet available in this way. However, this is a prerequisite for the application of 3D printing for the industrial production of molded parts.

[0020] Although proposals for the use of extruders for melting thermoplastics for 3D printing have been made, for example, in the publications US 2005 / 015175 A1, CN 205 800 202 U, JP 2016 215581 A, EP 3 081 364 A1, DE 295 22 255 U1,

[0021] DE102016213439A1 and EP3020550B1 known.

[0022] However, the EP3020550B1 is a single-screw extruder, whose task is to convey the plastic to a print head, where the plastic is melted by heating. Three single-screw extruders are arranged side by side, each of which is designed for a different material, for example, a different color. Even using two extruders for material changes can be problematic, as one extruder always remains unused. Using three extruders seems impossible.

[0023] DE102016213439A1 does not specify how the plastic is melted. It only requires that the plastic be melted before exiting the nozzle.

[0024] Melting the material in the print head has the disadvantage that if the printing process is interrupted, molten material remains in the print head. A so-called dead space forms there, which poses the risk of very detrimental changes to the plastic.

[0025] The invention is based on the object of improving the handling of the melt during 3D printing with an extruder.

[0026] This is achieved by the features of the main claim. The subclaims describe preferred embodiments of the invention.

[0027] Important are a Closure that allows a safe and advantageous adjustment of the melt quantity to the respective requirements an extruder with a melt volume sufficient for the respective requirements

[0028] According to the invention, a closable nozzle and / or an extruder are optionally provided, the screw / spindle of which is axially adjustable and forms the adjusting element for a nozzle closure / plug from which the melt is discharged during printing. By moving the screw / plug, the nozzle can be fully or partially opened or fully or partially closed.

[0029] Optionally, the screw / spindle forms a tip that protrudes into the die opening, at least in the closed position. This can prove advantageous if the molded part is small and lightweight. In this case, the associated restriction of horizontal movement when the screw / spindle is positioned vertically is not significant when the support is horizontally movable.

[0030] However, there are also larger molded parts whose dimensions and weight make movement of the molded part and the supporting base / workbench somewhat difficult. When applying the inventive printing process to structures / buildings, movement of the molded part and the structure / building is virtually impossible. In this case, the entire system is moved with the extruder.

[0031] In the case of a screw / spindle that extends into the nozzle, the nozzle opening or the tip of the screw / spindle has a shape that tapers in the direction of melt flow.

[0032] The screw tip / spindle tip can have a wedge shape. In this case, the nozzle / nozzle opening is adapted accordingly.

[0033] Preferably, the nozzle opening and the screw tip / spindle tip have a conical shape.

[0034] The screw tip / spindle tip can also have a spherical shape or another, particularly spherical, round shape. Such a tip can be combined with a tapered nozzle or a nozzle with a cylindrical opening.

[0035] The nozzle opening, which tapers in the direction of melt flow, can correspond a screw tip / spindle tip that tapers in the same way as the nozzle opening and moves into the nozzle with an axial movement of the screw / spindle, partially or completely closing the nozzle, or moves out of the nozzle with an axial movement of the screw / spindle, completely or partially opening the nozzle.

[0036] Depending on the diameter of the screw tip / spindle tip, the screw tip / spindle tip can be in the closed position --extend beyond the nozzle tip. In this case, the screw tip / spindle tip is smaller in diameter than the nozzle opening at the end facing in the direction of melt flow. --or terminate at the nozzle tip. In this case, the screw tip / spindle tip is equal in diameter to the nozzle opening at the end facing in the direction of melt flow. --end before the nozzle tip. In this case, the screw tip / spindle tip is larger in diameter than the nozzle opening at the end facing in the direction of melt flow.

[0037] In every closed position, the outer surfaces of the screw tip / spindle tip run parallel to the outer surface of the nozzle opening. A screw tip / spindle tip that tapers differently than the nozzle opening. In wedge-shaped or conical shapes, the screw tip / spindle tip can have a smaller or larger inclination to the screw axis / spindle axis than the nozzle opening. If the screw tip / spindle tip is less inclined, depending on the diameter of the screw tip / spindle tip, an edge of the screw tip / spindle tip will touch the outer surface of the nozzle opening, or an edge of the nozzle opening will touch the outer surface of the screw tip / spindle tip.In the case of a spherical or otherwise round shape of the screw tip / spindle tip and a conical shape of the nozzle opening, depending on the diameter of the screw tip / spindle tip --there will be contact between the screw tip / spindle tip and the outer surface of the nozzle opening or --there will be contact between the edge of the nozzle opening and the outer surface of the screw tip / spindle tip.

[0038] The inventive movement of the screw / spindle is optionally realized by arranging the screw / spindle in the associated extruder housing so that it can be displaced axially. Various drives, both hydraulic and mechanical, are possible for the axial displacement. The hydraulic drives have a hydraulic cylinder / power piston with a position control / step control that acts axially on the screw / spindle. With electronic position measurement, even small positions / adjustments can be measured and controlled.

[0039] Electric lifting devices can also be used to drive the axial movement of the screw / spindle. Electric lifting devices / Power pistons are particularly suitable for fast and frequent closing and opening movements. That is, for short threads / Ribbons / Strips and correspondingly short melt flow intervals are electrical lifting devices / Power pistons are particularly suitable. This is even more true for extremes such as melting points.

[0040] Even with the axially movable arrangement, the screw / spindle can be set in rotation at the end facing away from the nozzle via a motor and gear. For this purpose, a drive gear with a splined connection can be mounted on the screw / spindle. The splined connection allows for the screw / spindle to be moved while the drive gear is held axially with the necessary play for rotation.

[0041] A cost-effective drive connection between the screw / spindle and the drive provides a belt drive with one or more V-belts. The V-belt allows a fixed arrangement of the drive wheel on the screw / spindle while simultaneously allowing displacement according to the invention. This is especially true for small displacements. The displacements can be kept small by adjusting the support, even with considerable height of the molded parts to be produced.

[0042] Instead of or in addition to the axial adjustment of the screw / spindle, axial adjustment of the nozzle is optionally provided to partially or completely open or close the nozzle. The nozzle is moved either toward the screw / spindle tip or away from the screw / spindle tip. The same drives and controls are suitable for the axial movement of the nozzle as for the axial movement of the screw / spindle.

[0043] Alternatively, a slider can also be used as a closure.

[0044] The nozzles described above are particularly advantageous for a system with a vertically / vertically moving nozzle or a vertically / vertically moving screw / spindle and both vertically and horizontally moving base / work table. The vertical / The vertical arrangement allows the melt to be deposited downwards. This works particularly well. Furthermore, the melt has no significant tendency to flow out of the deposit position.

[0045] In addition, the nozzles described above can also be used if the nozzles, together with the extruder feeding the nozzles with melt, are movable horizontally.

[0046] When 3D printing a structure / building as well as other molded parts with large weight and dimensions, the movement of the system can have great advantages.

[0047] According to the invention, the term building structure includes large building structures which constitute an essential part of the building, as well as small building structures the size of a slab or even the size of a brick or other stone as used in house construction.

[0048] When constructing structures / buildings, it is possible to build without joints or to limit the number of joints to a certain number of necessary expansion joints. Advantageously, the expansion joints can also be designed in such a way that joint tapes can be easily installed later. For adhesive joint tapes, a simple recess / groove with an adhesive surface at the base of the recess / groove is sufficient. In conventional structures, corresponding recesses / grooves for joint tapes are formed into the structure, unless the joint tapes are already encased in concrete. The recesses / grooves can also be incorporated into the structures / buildings according to the invention. This is preferably not done subsequently, but rather during production using 3D printing.

[0049] Particular advantages arise when the joint tapes can be welded to the structure / building manufactured according to the invention. For this purpose, the joint tapes and the structure / building must be made of weldable material, at least at the welding surface. The structure can be made entirely or partially of a material that can be welded to the joint tape, or a profile that can be welded to the joint tape can be molded into the structure during its manufacture or laminated onto the structure.

[0050] For welding, the joint tape and the structure / building do not have to be made entirely of the same plastic. It is sufficient if the joint tape and / or the structure / building consist of a plastic mixture with a plastic content that enables weldability. Depending on the material, a proportion of less than 40% by weight, preferably less than 30% by weight, even more preferably less than 20% by weight, and most preferably less than 10% by weight of weldable material in the joint tape may be sufficient for weldability. The % by weight refers to the total plastic mixture for the structure / building and the joint tape.

[0051] Weldability can significantly reduce costs. This can include significant savings during assembly. Furthermore, it offers a significant advantage where sealing is critical. Welding provides a significantly better seal than other joining techniques. The sealing effect is improved. Where sealing is critical, weld seams can be placed at a distance from one another, allowing compressed air to be applied to the space between the weld seams for testing.

[0052] The welded joint according to the invention can also be applied to construction products other than joint tapes, even independently of the 3D printing according to the invention.

[0053] One such application area is represented by plastic windows. Plastic windows usually have a plastic frame, while the pane is made of glass. The plastic frames are often made of PVC (polyvinyl chloride) or blends with PVC. The plastic frames consist of complex profiles that must fulfill various functions. The connection to the building is just one of these functions. Using the welding technology according to the invention, the windows can be welded directly to the structure / building if the above requirements are met. If the structure / building does not meet this requirement, simple plastic profiles can be attached to the structure / building or molded into it, which can then be welded to the plastic windows. For welding, a simple leg on the outer edge of the plastic windows may be sufficient.

[0054] The single leg of a plastic window can, for example, be welded flat on the outside or inside of the structure / building, if the leg of the plastic window lies flat on the outside or inside of the structure / building wall during installation. This is the case, for example, if the leg runs parallel to the front surface of the window. For mounting the window inside the window opening, a frame-like intermediate piece made of a Z-shaped profile can be helpful. The profile is then welded to one leg on the outside or inside of the structure, and the other leg is welded to the window frame.

[0055] Welding can be done thermally by melting the welding surfaces and then pressing them against each other.

[0056] Welding can also be performed cold, using solvent welding. The welding surfaces are coated with a solvent and, once they have swelled, pressed together. Solvent welding is also suitable for rigid PVC, which is primarily used for window construction. Tetrahydrofuran is a known suitable solvent.

[0057] Where welding is not desired, the window frame can be bonded to the structure / building using a suitable adhesive. Suitable adhesives include two-component adhesives. These adhesives offer high adhesion and a long service life.

[0058] At penetrations of the building structures / buildings for pipes (water / wastewater; electricity; gas; ventilation, etc.), fittings such as flanges may be found, which can be welded / glued in the same way as the windows

[0059] When moving the system, it is helpful if the nozzle not only has an on / off function and can deposit the melt not only in a line, but also simultaneously distributes the melt over an area wider than, for example, a melt thread / strip / band or a melt point. This is the case, for example, if a 3D printer is to build a wall in a single operation. In this case, the 3D printer should deposit the melt across the entire width of the wall. This can be done in dots or with threads or bands / threads / strips.

[0060] Walls can be constructed by forming closed layers or hollow spaces. Hollow spaces are particularly advantageous when the closed outer layers of the walls are connected by webs, and when the webs run at different angles between the layers. For example, some webs can run at a 45-degree incline along one length of the wall, while others can run at a 45-degree incline in the opposite length. Optionally, the webs can intersect. This creates a rigid connection and allows for ventilation of the walls if necessary. If necessary, the hollow spaces can also be used to carry pipes for individual or all of the media found in a building.

[0061] Optionally, the cavities are formed by forming uniformly thick layers. The cavities can be sealed. This is also possible with the formation of watertight cavities. This is advantageous in the ground-level areas of building walls. The cavities can be designed in any desired manner. Cavities with exceptional static strength and particularly favorable deformation behavior under load are advantageous. Suitable cavities are, for example, designed to resemble closed honeycombs. These closed cavities also provide advantageous thermal insulation.

[0062] Optionally, the cavities can also be at least partially connected to each other. This can be advantageously used to create a vertical connection between the cavities, allowing moisture that penetrates through diffusion to evaporate upwards.

[0063] The above designs can be implemented by applying melt ribbons and / or melt threads and / or melt strands and / or melt dots. Melt ribbons / threads / strands facilitate printing by allowing a longer melt flow in the form of melt threads / strands / ribbons. Melt threads involve a thin melt deposit. Melt ribbons / strands are many times the width of melt threads. They can have the same thickness as melt threads, but can also be many times the thickness of melt threads. The greater thickness is advantageous where higher deposition rates are required. Even with melt ribbons / threads / strands, interruptions in the ribbons / threads / threads must be considered. In contrast, the melt flow is extremely frequently interrupted with point-by-point melt deposit. Electrically operated lifting devices are particularly suitable for point-by-point melt laying.

[0064] While in two-dimensional printing works only a single layer / ply is created with the printing material, in three-dimensional printing works several layers / ply are placed on top of each other.

[0065] Typically, each layer / layer is processed line by line. This line-by-line approach has the disadvantage of significant idle movements of the printer and / or significant idle movements of the molded part. According to the invention, printing performance is significantly increased when line-by-line printing is limited to the bottom surfaces of the molded parts, i.e., the printing is reversed when an edge of the bottom surface is reached.

[0066] Advantageously, there's no need to interrupt the installation when switching to the adjacent row. The print then takes a meandering course.

[0067] If, after a floor area has been completed, the wall areas are treated like floor areas, the number of redirection processes increases. For wall areas, it is preferable to switch to a direction of movement along the wall areas. The new direction of movement can be programmed accordingly. Alternatively, for molded parts, the workbench on which the molded parts are built can be rotated until the direction of movement of the printer is towards a wall. Instead of rotating the workbench, or in addition to this, rotating the extruder with the nozzle and other accessories can make it easier to align the printer movement with the path of the wall to be printed. Even the ability of individual parts such as the nozzle to rotate can be helpful for aligning the direction of movement of the nozzle with a wall.

[0068] When manufacturing structures / buildings, it is advantageous if the extruder, including the nozzle and other printing accessories, can be moved in any direction above the structure / building.

[0069] Any structure / building can be equipped with travel paths for the system according to the invention. The travel paths and / or the extruder with the nozzle can also be height-adjustable. The control software should be configured to deposit all melt ribbons / threads / strands of the desired length at the desired location upon input of the dimensions of the travel paths, their relative positions, and their height.

[0070] Laser control of the system is also an option. Preferably, multiple lasers are used to guide the extruder and nozzle to any desired location.

[0071] For large structures, it is advisable to construct the structures / buildings in sections.

[0072] Below are some of the different possible processes with short and long melt ribbons: The printer can place a long melt ribbon / thread / strand along the length of the wall. The next long melt ribbon is also placed along the length of the wall, but slightly offset, next to the previously placed melt ribbon / thread / strand. The longer melt ribbons / threads / strands can be placed side by side, facing each other. The longer melt ribbons / threads / strands can be laid overlapping each other. The longer melt ribbons / threads / strands can be laid while maintaining a horizontal gap. At intervals, the two spaced-apart longer melt ribbons / threads / strands are connected by short melt ribbons / threads / strands.

[0073] By alternating the arrangement of long and short molten strands / threads / ribbons and / or offsetting the molten strands / threads / ribbons, a bond is created in each layer of molten strands / threads / ribbons. By offsetting the molten strands / threads / ribbons in each new layer relative to the molten strands / threads / ribbons in the previously laid layer, the bond is further improved.

[0074] A further improvement can be achieved by alternating (from layer to layer) entirely or partially narrower or wider melt ribbons / threads / strands. The wider melt ribbons / threads / strands can, for example, be twice as wide as the narrower melt ribbons / threads / strands. Optionally, the ratio of the narrower widths to the wider widths can be between 1 to 1.1 or up to 1 to 4. At intersection points / joints of melt strips / threads / strands, it is avoided that melt strips / threads / strands are placed on top of each other in one layer / position.

[0075] When two layers / layers are placed on top of each other, it is understood that melt bands / threads / strands are placed on top of each other.

[0076] Preferably, a consistent thickness is maintained in each layer / ply. According to the invention, this is achieved by having longer melt bands / threads / strands (e.g., melt band 1) end before another melt band / thread / strand (e.g., melt band 2) and restart after the other melt band 2. Melt band 1 is thus interrupted by melt band 2.

[0077] Proceeding in exactly the same way at every intersection / junction is a less effective solution than other approaches.

[0078] It is better to create a bond at all intersections / joints. Bonding means that the abutting components are connected to one another, with melt bands / threads / strands of one component intertwined with melt bands / threads / strands of the other component. A bond according to the invention is created with intersecting melt bands / threads / strands if, in the next melt layer / layer, melt band 2 ends before melt band 1 and is reattached after melt band 1. This allows melt band 1 to continue through this intersection, while melt band 2 is interrupted. Preferably, joints are designed accordingly. Joints are the points where two walls meet in a T-shape or L-shape, or where a wall meets --a bottom surface of the molded part --an intermediate base --a cover --a projection of the component --or the like.

[0079] A bond / composite is also advantageous at the T-shaped joints.

[0080] T-shaped butt joints differ from intersections in that the wall abutting a continuous wall does not continue on the opposite side of the continuous wall. Preferably, the principle explained above for melt belt 1 and melt belt 2 is retained. In one layer, melt belt 1 is laid continuously, and melt belt 2 abuts the continuously laid melt belt 1. In an overlying layer, melt belt 1 is interrupted across the width of melt belt 2, and melt belt 2 extends into this gap.

[0081] According to the invention, butt joints can also arise when they form a corner. In this case, the walls butt together in an L-shape. This butt joint differs from the T-shaped butt joint in that no wall is continuous (extends beyond the corner). Then, the melt strip 1 ends in a layer in front of the corner at a distance equal to the width of the melt strip 2, so that the melt strip 2 can be guided / placed into the gap. In the layer above, the melt strip 2 ends at a distance from the corner equal to the width of the melt strip 1, so that the melt strip 1 can be guided / placed into the gap.

[0082] As an alternative to the above-mentioned cornering, the melt ribbon / thread / strand can also be angled at the corner. The melt ribbon / thread / strand is angled at the corner and continued without interruption. In principle, this can be done with any melt ribbon / thread / strand. The best results are achieved with melt ribbons / threads / strands from a nozzle with a circular cross-section.

[0083] The connection of a wall to a floor surface or similar is preferably achieved in the same way as the T-shaped joint, because the floor surface is also assembled from various melt strips / threads / strands. This means that melt strips / threads / strands are laid on the wall-facing edge of the floor to be constructed in exactly the same way as for the creation of a continuous wall that abuts another wall.

[0084] In one layer / layer, a melt strip / thread / strand of the floor to be laid is interrupted over a length equal to the width of the melt strip / thread / strand of an adjacent wall, so that this melt strip can be guided into this gap.

[0085] In the layer / layer provided above, the respective melt strip / thread / strand of the floor is laid without interruption and butts the corresponding melt strip / thread / strand of the adjacent wall against the melt strip / thread / strand belonging to the floor. as far as a building wall is layered / is built up layer by layer, several melt bands / thread / Strands in one plane next to each other and / or one behind the other. Preferably, an offset between the melt bands / thread / Strands of a layer / Level and the melt bands / thread / Strands of an overlying layer / Level or a layer below / The offset is at least 1 mm, preferably at least 2 mm, even more preferably at least 3 mm, and most preferably at least 4 mm. This advantageously leads to interlocking of the different layers.

[0086] When laying melt threads, many more melt threads must be laid than when laying melt tapes to create the same volume of walls and surfaces.

[0087] The extruder can be a twin-screw extruder.

[0088] A single-screw extruder is preferably used as the extruder, with a planetary roller extruder even more preferred. All of the above-mentioned extruder types have a filling section into which the plastic to be printed is poured. The filling section is followed by an extruder section in which the plastic is melted, homogenized, and heated to and maintained at the temperature required for printing. If necessary, degassing can also take place, as well as mixing with additives, aggregates, and fillers. Alternatively, a compound can be used, which contains a premix of the plastic with individual, several, or all of the additives, aggregates, and fillers.

[0089] Particularly large quantities of fillers can be used in the manufacture of construction products. Fillers in construction are generally of mineral origin. However, fillers of organic origin are also increasingly being used. One example is fine wood particles that are mixed into plastic.

[0090] The more fillers are mixed in, the more the plastic becomes a binding agent. The goal here is to improve the strength of the plastic framework. This is particularly achieved with natural fibers.

[0091] The mixture of plastic and wood particles has its own product name: WPC. The wood content is usually higher than 50% by weight, based on the mixture. WPC can also contain wood content of 60% or 70% by weight.

[0092] In addition, building products must contain flame retardants if they may be exposed to fire. Common fire retardants are well known. One of the common fire retardants is aluminum hydroxide. The higher the proportion of flammable / combustible components in the building product, the higher the proportion of flame retardants. For a high proportion of wood particles and plastic (more than 70 to 90 wt%), the proportion of flame retardant can be 10 to 30 wt%. One of the flame retardants under consideration is aluminum hydroxide.

[0093] The components of the input material usually also include dyes.

[0094] The wt% refers to the entire building product.

[0095] The plastic is melted by appropriate heating. This heating can be achieved by heating the extruder. This heating is possible because conventional extruders are equipped with a temperature control system. For this purpose, the extruder barrels are provided with channels for a temperature control agent. The temperature control agent is water or oil. For heating, heated temperature control agent is fed into the barrel. There, the temperature control agent transfers some of its heat to the plastic. At the same time, the filled plastic heats up due to its constant deformation in the extruder. In this process, the drive energy of the extruder is converted into heat. After the melting temperature is reached, the further deformation of the plastic and the associated energy input lead to further heating unless this is counteracted by cooling. The temperature control agent then serves for cooling.To absorb the heat, cold temperature control fluid is fed into the housing's channels. Separate temperature control circuits are preferably used for heating and cooling.

[0096] In modular extruders (the screw / spindle extends from the drive through all modules to the nozzle), this is achieved by using separate extruder modules for heating and cooling. Optionally, a separate extruder module can also be used for the desired devolatilization. This module is referred to below as the devolatilization module. The devolatilization module has a jacket opening through which gas can escape. An idle side-arm extruder is preferably provided at this jacket opening. Even more preferably, the side-arm extruder is a twin-screw extruder that rotates without feed material as if it were feeding feed material into the devolatilization module. In this way, the side-arm extruder prevents the melt in the devolatilization module from escaping through the jacket opening. A particularly short side-arm extruder is preferably used.

[0097] A simultaneous suction draft on the side-arm extruder draws gas out due to deliberate leakage in the side-arm extruder. The necessary clearance between the screws of the side-arm extruder and the surrounding barrel can be sufficient to create a leak. If necessary, additional clearance is created between the screws of the side-arm extruder and the surrounding barrel. This can be achieved by machining the outer circumference of the screws.

[0098] The side arm extruder can be arranged to the side or above the degassing module or below the degassing module.

[0099] The plastic can be granules. In smaller extruders, the granules preferably contain a mixture with all the necessary components, which is fed into the extruder in a prepared compound. This eliminates the need for large equipment costs for metering the components. Smaller systems are extruders with a diameter of less than 70 mm, preferably less than or equal to 50 mm.

[0100] Especially in larger plants, the mixtures are produced entirely or partially in the extruder. The various mixture components are then metered into the extruder individually, in premixes, or together. After the mixture components have been added, the smaller amounts of the mixture are dispersed in the plastic or plastic melt.

[0101] Single-screw extruders and twin-screw extruders have either one or two screws with reduced conveying efficiency. Single-screw extruders and twin-screw extruders typically have high conveying power, resulting in significant pressures that make it difficult to adapt to a reduced demand for molten plastic.

[0102] Reducing the pumping effect results in reduced pressures, which make it easier to adapt to reduced demand.

[0103] The conveying effect is preferably reduced by incorporating one or more counter-rotating screw flights into the screw. This is optionally achieved by milling. Milling interrupts the existing screw flights at intervals.

[0104] Optionally, the screws of single-screw and twin-screw extruders can be provided with a reduced diameter, creating a larger gap between the screws and the surrounding barrel. Cylindrical screws can also be provided with flattened or recessed sections around the circumference.

[0105] Gaps are created through which the material can escape and even flow back. This creates a deliberate leakage flow.

[0106] The larger the gaps, the better the plasticized plastic can flow back through the extruder. This continues until the melt is again captured by the screw and pushed toward the extruder outlet. If no melt is removed at the nozzle, the melt can escape again via the leakage flow.

[0107] With single-screw extruders and twin-screw extruders, setting the correct leakage flow is much more complicated than with a planetary roller extruder.

[0108] The leakage flow can be viewed as a "circling" of the melt. In combination with a control of the melt outlet at the nozzle, this creates an extremely advantageous device because the melt is kept liquid in the extruder and circulated until the need for melt outlet arises. In this case, the nozzle opens and the desired melt outlet occurs. According to the invention, the extruder is controlled at the nozzle. At the same time, the amount of melt exiting the extruder is replaced by feeding additional feed material into the extruder. Fill level control can be used here, especially when the extruder is positioned upright rather than horizontally.

[0109] The larger the amount of melt moved in this way, the easier it is to maintain and regulate the melt required for 3D printing.

[0110] The leakage flow and the cavity volume of the extruder are decisive for the melt quantity.

[0111] After opening the nozzle, melt flows out for 3D printing.

[0112] The cavity volume of the extruder is the interior space of the extruder minus the volume of the screw and other internals that protrude into the extruder.

[0113] The extruder's fill level can be measured in various ways. This can be done by positioning a sensor in the shell of the filler. The sensor can incorporate any type of measurement that responds to melt flow. These include, for example, pressure, temperature, ultrasound, and other sound.

[0114] Preferably, the degree of filling is determined by weight measurement or by optical volume determination.

[0115] If the filling level falls below a predetermined level, additional feed material is added to produce the melt.

[0116] When determining the weight, it is best to measure the weight of the molded part being formed on the base / workbench. The melt consumption can be calculated from this weight.

[0117] Weight measurement is preferably carried out electronically using a microchip.

[0118] The electronic measurement can advantageously be performed when the base / workbench is in a stationary position, so that the measurement results cannot be distorted by acceleration and braking forces. Furthermore, the effects of acceleration and braking forces can also be subtracted from or added to the weight measurement results.

[0119] Optical volume measurement involves measuring the molded part in process on the support. There are several ways to do this. It is advantageous to measure the smallest distance between the nozzle and the molded part. A laser measuring device is suitable for this.

[0120] Distance measurement is advantageous anyway for ensuring consistent melt application conditions. The values ​​from the distance measurement can then be used not only to control the necessary melt feed into the extruder, but also to control the movement of the support / work table in the axial direction of the nozzle.

[0121] A reduced conveying effect according to the invention can also be achieved with a bypass that begins upstream of the nozzle in the conveying direction of the extruder and recirculates the melt completely or partially into a suitable section of the extruder. Only a portion of the melt is recirculated when the nozzle is partially closed or only partially open. The melt is recirculated entirely when the nozzle is completely closed. A suitable section for recirculating the melt that has escaped into the bypass can be the melt production area or a location spaced apart from it in the conveying direction of the extruder.

[0122] The bypass is a preferably thermally insulated (and possibly heated) pipeline. One end of this pipeline is flanged to an opening in the extruder's shell, upstream of the die in the extruder's conveying direction. The other end of this pipeline is flanged to another opening in the extruder's shell, located in the melt generation area or downstream of it in the conveying direction.

[0123] Planetary roller extruders are better suited for 3D printing than single-screw and twin-screw extruders. The leakage flow described in the invention can be generated much more easily with a planetary roller extruder than with a single-screw extruder.

[0124] In addition, the planetary roller extruder has other extremely important advantages over the single-screw extruder. These include, in particular, -a much better mixing effect -a much better tempering

[0125] The planetary roller extruder has a rotating central spindle located centrally within a housing. The central spindle has external gearing. Planetary spindles, also externally geared, rotate around the central spindle and mesh with the central spindle as they rotate. The planetary spindles simultaneously rotate within the extruder housing. For this purpose, the extruder housing, or the bushing in the case of a bushing located inside the extruder, is provided with internal gearing, with which the planetary spindles mesh simultaneously.

[0126] The planetary spindles slide with their rear end, in the extruder's feed direction, along a sliding ring mounted in the extruder housing. Otherwise, the planetary spindles are held solely by the gearing of the central spindle and the internal gearing of the housing.

[0127] The planetary roller extruder also begins with a drive and ends with the nozzle. Between these two parts, the planetary roller extruder can be equipped with a one-piece housing extending the entire length.

[0128] The planetary roller extruder can also be composed of several modules / sections between the drive and the nozzle.

[0129] Then a common central spindle is provided, extending between the drive and the nozzle through all modules.

[0130] The individual modules / sections can perform one or more different tasks. Ideally, all modules / sections of the planetary roller extruder are designed as planetary roller extruders. Modules / sections of planetary roller extruders can also be combined with modules / sections of other designs. This is especially true for the filling section. Previously, the modules / sections for the filling sections were mostly designed as single-screw extruders. In this case, the central spindle continued as a single-screw in the module / section for the filling section.

[0131] Planetary roller extruders used for printing 3D molded parts may also have a reduced conveying efficiency.

[0132] With planetary roller extruders, this can be achieved in a variety of ways. Preferably, this is done on the planetary spindles: The number of planetary spindles (number of rotating planetary spindles) can be reduced / changed. Depending on the size of the planetary roller extruder / planetary roller extruder module / section, the number of planetary spindles can be up to 24 or more. For smaller sizes, the number of planetary spindles can also be 5 or 6. Reducing the number of planetary spindles by 1 already represents a significant reduction for smaller sizes. For larger sizes, a comparable reduction only occurs when several planetary spindles are removed. The fewer the number of planetary spindles, the greater the circumferential spacing of the planetary spindles becomes, and the easier it becomes for the melt to flow back between the planetary spindles.

[0133] The reduction in the number of planetary spindles reaches a limit of 3 planetary spindles.

[0134] In addition, backflow / leakage can be influenced very advantageously by changing the number of planetary spindles. Similar options are not available with a single-screw extruder.

[0135] After each reduction or change in the number of planetary spindles, the planetary spindles are redistributed around the circumference of the central spindle to ensure even distribution. With even distribution, the central spindle is better supported in the housing and the risk of planetary spindles skipping is reduced. This skipping usually leads to an immediate blockage of the extruder and tooth breakage. At the very least, the even distribution of planetary spindles reduces wear.

[0136] The planetary spindle reduction / change in the distribution of the planetary spindles is performed while the extruder is shut down after disassembling the nozzle. Furthermore, the planetary spindle reduction / change in distribution is performed module-by-module / section-by-section. This involves removing not only the nozzle but also all modules / sections that follow the module / section whose planetary spindles are to be reduced and redistributed in the direction of melt flow. However, the central spindle remains.

[0137] For redistribution, inexperienced operators are recommended to use a template that slides onto the central spindle. The template has holes at the points where the planetary spindles are pushed between the central spindle and the surrounding housing. These holes have a diameter equal to the planetary spindle diameter, plus a generous amount of play. This allows the planetary spindles to be easily pushed between the central spindle and the associated housing at the holes, maintaining a distance from each other that is at least approximately equal.

[0138] Experienced operators can do without the use of a template. Backflow / leakage can also be influenced by reducing the number of teeth. Modern planetary roller extruders have involute gearing that is also designed as a helical gear. Advantageously, their teeth can be significantly modified. The unmodified gearing of planetary spindles is referred to as standard gearing. Various modification options are described below. Advantageously, the planetary spindles with modified gearing described below are all easily interchangeable with each other and with planetary spindles with standard gearing. By interchanging, essential effects of the planetary spindles can be increased or decreased as desired. The interchangeability of the planetary spindles on planetary roller extruders is an extreme advantage, one that cannot be found in a comparable form on single-screw extruders.

[0139] Various planetary spindle designs are available for the advantageous replacement or modification of backflow / leakage flow by replacing the planetary spindles: The number of teeth is reduced. The number of teeth can be reduced to three or even to one. This can be achieved subsequently by machining teeth out of the planetary spindles. The teeth are preferably removed by milling and then finished by grinding. The planetary spindles can also be manufactured directly with the teeth, like the planetary spindles from which teeth have been subsequently removed. The remaining teeth are preferably evenly distributed around the circumference of the planetary spindles.

[0140] Even with only one tooth, the planetary spindles still receive sufficient guidance and support from the external gearing of the central spindle and the internal gearing of the housing. This is achieved by each tooth winding helically around the planetary spindles several times along the length of the spindles.

[0141] All planetary spindle teeth can also be reduced in height if sections remain on the planetary spindles that provide sufficient guidance for the planetary spindles. Such guide sections can have standard gearing (unchanged gearing), which is preferably located at the ends of the planetary spindles. It is also advantageous to combine such planetary spindles with fully standard-toothed planetary spindles in an extruder, so that the standard teeth push all the feed material out of the tooth gaps of the central spindle and the tooth gaps of the housing's internal gearing during rotation around the central spindle, and prevent feed material from accumulating and caking in the tooth gaps. This can be referred to as cleaning the tooth gaps.

[0142] Preferably, not all of the planetary spindle teeth are reduced in height. At least one tooth retains its original height. This can provide the planetary spindles with the necessary guidance / support in the external gearing of the central spindle and the internal gearing of the housing, eliminating the need for guide sections.

[0143] In addition, the teeth on the planetary spindles, which are left at their original height, also clean the tooth gaps on the central spindle and the tooth gaps on the internal gearing of the housing.

[0144] The reduction in the height of the teeth can be achieved in the same way as with the complete removal of teeth, for example by milling and subsequent fine machining by grinding.

[0145] Preferably, the web height is reduced by at least 20%, even more preferably by at least 40% and most preferably by at least 60%.

[0146] It is also advantageous if the reduced-height / flattened teeth on the resulting new head are rounded. This improves the flow behavior of the insert material when displacing it into the corresponding tooth gaps of the central spindle and the corresponding tooth gaps of the internal gearing of the housing. The webs of the planetary spindle teeth can be interrupted completely or partially at regular or irregular intervals. A regular interruption occurs, for example, when the planetary spindles are toothed again in opposite directions after the normal toothing has been created. This results in a dimpled structure on the planetary spindle surface. Therefore, such planetary spindles are also called dimpled spindles.

[0147] The counter-rotating toothing goes to the bottom of the tooth gaps

[0148] If the counter-rotating gearing is cut less deeply into the planetary spindles, a different planetary spindle surface with a greater conveying effect is achieved.

[0149] A uniform interruption is also achieved by machining circular grooves into the planetary spindles at regular intervals. These planetary spindles are called hedgehog spindles.

[0150] The grooves are usually machined down to the tooth base.

[0151] However, the grooves can be machined less deeply to achieve different properties.

[0152] Likewise, the gearing can be varied by changing the number of threads of the opposing gearing. This means that planetary spindles with a different number of teeth can be used. You can choose between planetary spindles with more or fewer teeth removed.

[0153] Standard gearing has a specific number of teeth, depending on the tooth module / tooth dimensions and the pitch circle diameter of the gearing, circumferentially arranged along the pitch circle diameter. These teeth wind parallel to each other around the planetary spindles and incorporate the multiple threads of the planetary spindles.

[0154] With the same opposing toothing, the nubs described above are created. However, teeth can be cut into the standard toothing at greater spacing than in the standard toothing. This creates ridges instead of nubs, because the teeth of the standard toothing are interrupted at greater spacing.

[0155] Reducing the number of planetary spindles and reducing the tooth count on the planetary spindles can occur together or individually. The same applies to a bypass. The bypass can occur alone or in conjunction with reducing the number of planetary spindles and / or reducing the tooth count.

[0156] What the measures described above have in common is that openings are created in the planetary roller extruder through which melt not currently required for 3D printing can flow back. This involves intentional leakage. The backflow / leakage continues until the melt is again captured by the planetary spindles and conveyed toward the nozzle. If at this point no melt is removed for 3D printing, or only a small amount is removed for 3D printing, the melt cycle restarts.

[0157] When melt is expelled from the nozzle for 3D printing, new material is fed into the extruder. This can occur continuously, at intervals, or as needed, depending on the measurements above.

[0158] A particularly advantageous form of an extruder for 3D printing results from a vertical arrangement of the planetary roller extruder, as shown and described in DE19534813 C2.

[0159] The housing of the vertically arranged extruder can have a generous cavity at the top, in which even difficult feedstock can easily collect. The planetary spindles preferably extend at least partially into the cavity, allowing them to grasp the feedstock and pull it into a planetary roller extruder module / planetary roller extruder section arranged vertically below. The planetary spindles mesh with the external gearing of a central spindle and the internal gearing of the extruder module housing / extruder section housing.

[0160] In the cavity provided above there is a level sensor which immediately gives a signal to add more feed material when the level falls below a selected level.

[0161] The feed material is heated and melted in the planetary roller extruder module / section and then conveyed downward to a nozzle. Heating the module housing in the feed area is helpful for heating.

[0162] After the initial heating, the deformation of the feed material on its way down leads to further heating and melting.

[0163] The nozzle is optionally conical and has a tapered discharge end. This shape is aerodynamic. The axial length of the nozzle is preferably designed according to the nozzle diameter. A short length is recommended for small diameters, and a long length for large diameters. The nozzle outlet opening depends on the width of the melt strand / thread / ribbon to be discharged. The nozzle inlet opening depends on the size of the extruder used to melt the material for printing. The slimmer the cone, the more aerodynamic the nozzle.

[0164] However, a nozzle without a conical shape can also be used. No conical shape is present if the nozzle is formed by a cylindrical bore in the cylindrical end wall of the extruder on the outlet side.

[0165] In the illustrated example, the nozzle is movable in the axial direction of the extruder. This movement allows the nozzle to be fully or partially opened or fully or partially closed.

[0166] Optionally, the nozzle is mounted in a straight guide. This can be done by a rail or profile that runs parallel to the nozzle axis. Alternatively, several rails or profiles can be provided, spaced apart and running parallel to the nozzle axis.

[0167] When using multiple profiles, simple round profiles can be used as guides.

[0168] When using a single rail or profile, it is preferable to select a cross-section for the rail or profile that prevents the nozzle or its holder from rotating around the longitudinal axis of the rail or profile, but allows movement in the longitudinal direction of the rail or profile. The nozzle or its holder can encompass the rail or profile or engage within the rail or profile.

[0169] Optionally, the guide can also be in the form of a slider.

[0170] The slide valve can be a linearly moving slide valve or a rotary slide valve. The rotary slide valve can be mounted on a bolt, axle, pin, or other rotatable mounting. Such a mounting can also be a ring, collar, or cylinder that encloses a disc-shaped slide valve on the outside.

[0171] The guide can also be formed by a swivel arm. In this case, the nozzle is held by the swivel arm.

[0172] In this case, it is advantageous if the nozzle center axis is aligned with the center axis of the central spindle tip in the closed position. The closed position is the position in which the nozzle rests on the central spindle tip.

[0173] To open the nozzle, the swivel arm lifts it from the center spindle tip. The influence of a change in the center axis position of the nozzle relative to the center axis of the center spindle tip is negligible.

[0174] The linear nozzle movement can also be achieved with the help of a robot. Conventional robots have an arm with multiple joints, allowing movements in any direction. Of course, a robot can perform much more than just linear movements. Its design and control system are correspondingly complex. Due to the high volumes of commercially available robots and the associated series production, such a robot is still cheaper than other nozzle guides that are manufactured individually.

[0175] An electrically controlled drive is provided for the movement of the swivel arm, which responds to short control impulses.

[0176] When the nozzle is open, the melt flows as a thread, ribbon, or strand onto a work table that can be moved transversely to the center axis of the central spindle tip and simultaneously in the direction of the center axis of the central spindle tip. The movements of the work table and the nozzle are controlled in such a way that the emerging

[0177] A 3D molded part is created from a melt thread / ribbon / strand.

[0178] For the application of the inventive printing process on structures / buildings, a nozzle with multiple, interchangeable outlet openings is advantageous. Large outlet openings allow large melt volumes to be dispensed and high construction performance to be achieved. At the same time, the nozzle can be equipped with smaller outlet openings, for example, for thinner melt threads.

[0179] The interchangeability of the various outlet openings is advantageous. Preferably, the outlet openings can be changed during a manufacturing process. This allows a building to produce a floor with high melting power, while adjacent thin walls are better manufactured with a smaller outlet opening and correspondingly lower power.

[0180] Likewise, when producing the hollow walls explained above, it may be expedient to produce the outer layers of the wall with a larger nozzle outlet opening and the struts / chambers connecting the layers with a smaller nozzle outlet opening.

[0181] Such a nozzle can be formed by a slider equipped with an adjustment drive and controlled by a computer. The slider can be cylindrical and housed in a housing with a bore suitable for the slider. The slider has various (small and large) through-holes spaced from each other and running transversely to the longitudinal axis of the slider. The slider can also have nozzle openings inclined relative to the extruder's central axis. Nozzle openings with different inclinations can also be provided.

[0182] With the nozzle openings inclined in this way, the melt threads and melt ribbons / melt strands can also be deposited at a different location than with a nozzle opening whose axis is aligned with the central axis of the extruder.

[0183] The slider is mounted on or within the nozzle and can be moved and rotated perpendicular to the nozzle axis. By moving the slider, for example, longitudinally, the appropriate hole can be positioned. The nozzle can be opened or closed by turning it.

[0184] The nozzle can also be combined with a ball valve as a control valve for opening and closing. The nozzle can also be designed as a ball valve. In this case, the ball valve or nozzle contains a ball with an opening. By turning the ball, the opening is made smaller, closed, or opened. The ball can also fulfil other functions. For example, several different openings can be introduced into the ball. These openings are made at different points on the ball and guided through the center of the ball. It is advantageous if all of the holes are located on a circle around the circumference of the sphere, so that different openings can be brought into the melt flow by turning the ball. This can be used to regulate the melt flow and to shape the melt strand. Instead of the ball, a conical closure body can also be used in the valve or nozzle.be arranged in the nozzle, which is provided with one or more passage openings in the same way as the ball, but is lighter to manufacture than the ball and can be more easily brought into sealing contact with the surrounding jacket.

[0185] Alternatively, a robot arm can also be used as a nozzle by providing the robot arm with a passage opening for the melt and mounting it at the outlet opening of the extruder so that the melt flows through the robot arm and can be directed by the robot arm to any desired location.

[0186] Optionally, the nozzle can also be formed by a rotatable, pivotable, and / or movable cover equipped with a plurality of nozzle openings that can be positioned as desired in front of the extruder outlet by rotating, pivoting, or moving the cover. Smaller and larger nozzle openings, as well as nozzle openings with different cross-sectional shapes, are provided. This allows the exiting melt strand / ribbon / thread to be given a different cross-section, so that, for example, melt threads are created in one case and melt ribbons in another. The nozzle openings can be aligned with the central axis of the extruder or inclined to it, as is the case with the slide.

[0187] The rotating and / or pivoting lid can be guided and held centrally and / or at the outer edge. In the center, the guide and holder can be formed by a bolt / pin / mandrel / axle. At the edge, the guide and holder can be formed by a ring / collar / cylinder.

[0188] The extruder outlet is opened and closed by pivoting or turning a closed cover part in front of the extruder outlet.

[0189] According to the invention, the nozzles are heated or unheated.

[0190] Non-heated nozzles depend on the melt remaining meltable in the nozzle or the nozzle being heated after each melt burst. / The melt flow is cleaned. The melt remains liquid in unheated nozzles if an interruption in the melt flow does not result in cooling below the melting temperature. The cooling until the melt solidifies is time-dependent and dependent on the initial melt temperature. With short interruptions, the flowability of the melt is ensured. The usual melt temperature during extrusion is at least 5 degrees Celsius, preferably at least 10 degrees Celsius, even more preferably at least 15 degrees Celsius above the melting temperature, and most preferably at least 20 degrees Celsius above the melting temperature at which the plastic liquefies.

[0191] It is advantageous to adjust the melt temperature during extrusion operation so that an interruption duration of at least 2 seconds, preferably at least 4 seconds, even more preferably at least 6 seconds, and most preferably at least 8 seconds is possible. This significantly simplifies the handling of the device.

[0192] Alternatively or additionally, heating of the nozzle is provided. Heating the nozzle can slow the cooling of the melt in the nozzle in the event of an interruption, allowing a longer interruption. In extreme cases, the heating can be configured so that no cooling of the melt in the nozzle occurs. However, interruptions are preferably kept short to avoid negative effects of the temperature on the molecular structure.

[0193] Stepper motors are advantageous for the nozzle movements. Modern motors have a stepping speed of up to 400 steps per second with high precision.

[0194] If the entire extrusion line needs to be moved during the manufacture of buildings, servo motors can be suitable, as they can also move these loads with short response times and high precision.

[0195] Optionally, a nozzle can be installed in front of the extruder outlet, which can be pivoted in all directions in certain areas. The nozzle consists of a connection piece to the extruder outlet, a joint, and a nozzle outlet piece. The melt flows through the connection piece, through an opening in the joint, and through the nozzle outlet piece.

[0196] Optionally, the joint can also form the connection to the nozzle outlet and / or the nozzle outlet part.

[0197] The joint can also be designed as a ball joint.

[0198] A section of a hollow sphere can also be used as a nozzle. Hollow spheres have a spherical exterior and a spherical cavity inside with a common center point relative to the outer shape, thus creating a spherical shell. According to the invention, a section of this hollow shell is used.

[0199] It is optionally provided that the section of the hollow shell slides on the end of a melt feed line, which has the same radius as the section of the hollow shell at the contact surface with the section.

[0200] The hollow shell section is provided with various nozzle openings. The nozzle openings are distributed across the shell surface of the section. By shifting the section at the end of the melt feed line, a different nozzle opening can be aligned with the opening of the melt feed line, or a closed section of the hollow shell section can be positioned in front of the opening to close the melt feed line.

[0201] The movement of the hollow shell section can be controlled using power pistons. For example, three power pistons can be evenly distributed around the circumference of the hollow shell section, allowing them to move the hollow shell section in any direction and clamp it to the head of the melt feed line in the desired position.

[0202] Optionally, the hollow shell section can be supported by a guide on the side facing away from the melt feed line. This guide facilitates the movement of the hollow shell section.

[0203] For the slide valves and hollow shell sections, which can be moved to bring other nozzle openings upstream of the melt feed line, the smallest possible adjustment ranges are advantageous. This is especially true for point-by-point melt routing. The adjustment range between two adjacent slide valve positions or hollow shell section positions is preferably less than 10 mm, even more preferably less than 8 mm, and most preferably less than 6 mm.

[0204] The emerging melt usually encounters melt that has already completely or partially cooled. To ensure that the conditions for bonding the new melt with the previously applied melt are met, the previously applied melt is heated at the contact surface before the new melt impinges. This can be achieved using an electrically operated heating wire, which can be optionally attached to the nozzle and extends just above the surface to be heated.

[0205] Another option for reheating the previously applied melt is to apply hot air to the contact surface. The hot air can also be advantageously discharged at some distance from the contact surface. This is harmless to other areas of the molded part and facilitates the supply of hot air.

[0206] The heating of the contact surface can also occur by contact with a heated object that slides or rolls on the already laid and cooled melt threads / melt ribbons / strands.

[0207] The drawing shows an embodiment of the invention.

[0208] A pivoting arm 7 is pivotably mounted on a column 1. The pivoting arm 7 carries the motor and gear for a planetary roller assembly 2. The planetary roller assembly 2 is equipped with a feed hopper 4, which has a lateral feed opening 6 in the shape of a mouth. 3 denotes the inlets and outlets for the heating and cooling media, respectively.

[0209] The planetary roller part 2 has a closable outlet, which will be explained below. In its typical design, the planetary roller part 2 has a housing, a central spindle, and planetary spindles that mesh with both the central spindle and an internally toothed bushing arranged in the housing thanks to suitable toothing. In the exemplary embodiment, the pitch circle diameter of the internal toothing is 30 mm. The pitch circle diameter of the internal toothing also indicates the size, in this case size 30. In other exemplary embodiments, the size can be larger, for example, 50, or smaller.

[0210] In the exemplary embodiment, the number of planetary spindles is 3. The planetary spindles are evenly distributed around the circumference of the central spindle. With a typical number of 5 planetary spindles, this entails a 40% reduction in the planetary spindle count. In other exemplary embodiments, the reduction may be greater or lesser.

[0211] There is enough space between the planetary spindles to allow the extruder to continue running with the nozzle closed or only partially open, and the excess melt conveyed toward the nozzle flows back between the planetary spindles as a leakage flow until the planetary spindles recapture the melt and convey it toward the nozzle again. If the nozzle is not yet open, the backflow / leakage flow repeats.

[0212] Backflow / leakage flow is advantageously used to achieve perfect melt mixing when starting up the extruder with the nozzle closed, before the nozzle is opened. This allows for operation without start-up losses. Start-up losses are easier to tolerate in other extrusion processes than when producing a 3D print on a support / workbench. In the event of start-up losses, insufficiently prepared melt would settle on the support / workbench. Alternatively, the workbench would have to be moved out of the working direction of the nozzle, and the melt loss resulting from start-up would have to be disposed of without causing contamination. "Contamination-free" means that the system should not be contaminated by melt that is unusable during start-up.

[0213] A further advantage of backflow / leakage flow arises when the leakage flow extends as far as possible to the feed hopper / hopper through which the feed material is fed into the extruder. There, the solid particles still experience high friction. This friction is drastically reduced by the backflowing melt. The backflow / leakage flow acts as a lubricant between the solid particles. Furthermore, the mixing is improved.

[0214] Advantageously, the printing process according to the invention can be carried out not only with a vertical extruder, but also with a horizontal extruder or an inclined extruder. Printing with a vertical extruder has the advantage that the nozzle can be positioned close to the surface on which the melt is to be deposited. This facilitates precise printing and simplifies the design of the device. The same applies to an inclined arrangement of the support / workbench. The horizontal arrangement and movement of the support / workbench also offers significant advantages.

[0215] The Fig. 2 to 4 show non-scale details of the extrusion line after Fig. 1 .

[0216] Fig. 2shows the feed hopper with a housing 10, which is attached to the swivel arm 7 by an upper flange. The swivel arm carries a drive 5. A drive shaft 12 leads from the drive to the central spindle of the planetary roller part 2. The contour of the opening 6 in Fig. 2 is marked 11.

[0217] The Fig. 3 shows the actual hopper 15 of material feed 4. The central spindle is designated 16, the planetary spindles 17 and 18. The planetary spindles 17 and 18 have different lengths, so they extend into the hopper 15 at different heights. This gives the planetary spindles advantageous feed behavior with respect to the feed material fed into the hopper.

[0218] During operation, the rotating planetary spindles slide along a thrust ring. The housing 22 of the planetary roller part 2 is releasably attached to the lower edge of the feed hopper 4 with swivel screws. The swivel screws facilitate loosening and fastening by being able to be swiveled in or out of engagement.

[0219] Fig. 4shows a flange 23 at the lower end of the housing 22, which receives the thrust ring 25 for the planetary spindles. The central spindle ends in a tip 26, which determines the outlet opening 28 of the extruder in a screwed-on cover 24. The cover 24, together with the discharge opening and a closure 29, forms a nozzle. Pivoting screws 28 serve as screw connections for the cover. On the cover there is a rotatable closure 29. The closure 29 can fully or partially open or fully or partially close the outlet opening 28 of the extruder. In the exemplary embodiment, the closure is moved into the desired position by hand using a lever 30. There the closure can be locked with another lever 31. The locking is achieved by a screw connection.

[0220] When using the system described above for 3D printing molded parts with plastic melt, the melt required for laying a melt thread on a support / workbench or for laying it on a molded part in production is estimated by the operators and the outlet opening is manually adjusted to the required amount. This can be quite accurate, because excess or insufficient melt quantities are immediately visible during printing in the construction progress of the molded part.

[0221] The base / workbench is horizontally movable in all directions. For horizontal movement, the base / workbench in the example is held by two linear guides, one of which is held in the machine frame and the other carries the linear guide.

[0222] In the exemplary embodiment, the extruder is also held in a height-adjustable manner on the column 1 by means of the swivel arm 7. For this purpose, the swivel arm 7 is guided on the column 1 and provided with a lifting drive (not shown).

[0223] For testing purposes, the base / workbench can be moved manually to determine the optimal melt belt placement for each molded part. Once this optimal melt belt placement has been determined, the movement can be programmed into a controller for the movement drive of the base / workbench and the lifting drive of the swivel arm. In another embodiment, the controller is designed to store the data of the manual movement and repeat it on demand / at the push of a button.

[0224] The drive for the horizontal movement can be decoupled from the base / workbench for manual movement or coupled to the base / workbench for automatic movement.

[0225] In the exemplary embodiment, the lifting drive remains coupled to the swivel arm during the manual tests.

[0226] In the example, the drive for the horizontal movement consists of two servomotors. Each linear guide is assigned a servomotor. The servomotors are commercially available stepper motors. The control system operates both motors, as well as the lifting motor.

[0227] For automation, another embodiment provides a slider instead of the closure 29, which is moved by a stepping mechanism. The stepping mechanism is actuated as needed, with the melt requirement being determined in previous test series.

[0228] In yet another embodiment, the melt requirement is calculated by measuring a sample piece and the stepping mechanism of the slide is controlled with the obtained data.

[0229] In yet another embodiment, the melt requirement is determined using a computer-aided 3D design and thus the stepping mechanism of the slide is controlled.

[0230] Fig. 5 shows another embodiment of the invention.

[0231] Instead of the cover firmly screwed to the extruder housing, a cover 38 is provided, which is slidably mounted within the extruder housing. The cover 38 is guided through a bore (not shown) in the housing and is also sealed against unwanted melt leakage. In the exemplary embodiment, the seal is formed by a spring steel membrane. The flexibility of the membrane is designed for the necessary adjustment travel of the cover 38 for opening and closing the nozzle.

[0232] The cover 38 has a computer-aided adjustment drive. The cover forms a nozzle with the opening 50. The adjustment of the cover 38 serves to control the opening gap between the conical opening 50 of the cover 38 and the conical tip 35 as required. As demand decreases, the gap is reduced. As demand increases, the gap is increased. The demand is determined using a computer-aided 3D design. The data from the demand calculation can be directly fed into the control of the movable cover 38.

[0233] Fig. 5also shows a schematic of a base / workbench 39 onto which the melt emerging from the opening as a thread is placed. The base / workbench 39 is movable horizontally in all directions and also vertically. The vertical movement is provided in order to maintain a constant distance between the melt outlet from the extruder and the surface on which the melt thread or melt ribbon is deposited as the molded part grows, despite the molded part growing. In the example embodiment, the surface is always located vertically below the melt outlet. When building up the molded part, this is achieved by moving the base / workbench 39 horizontally with the growing molded part until the surface in question is exactly below the melt outlet.

[0234] In this example, the melt ribbon has a width of 4 mm and a thickness of 1.5 mm. The corresponding nozzle is adapted to the cross-section. In other example embodiments, different nozzle cross-sections are used, for example round nozzle cross-sections. In a first layer, two melt ribbons with a width of 4 mm are laid next to each other, making a total width of 8 mm. In the next, second layer, a nozzle is used first, through which a melt ribbon with a width of only 2 mm and a thickness of 1.5 mm is laid. In parallel, a melt ribbon with the original width of 4 mm and the same thickness is laid, along with another melt ribbon with a width of only 2 mm, so that the three melt ribbons together have a width of 8 mm. The middle melt ribbon of the second layer overlaps the two melt ribbons of the first layer.In the third layer, two 4mm thick fused tapes are again laid side by side, overlapping the fused tapes of the second layer. The layered laying of two or three fused tapes is repeated in the subsequent layers. The overlap gives the resulting wall greater strength than without it.

[0235] After Fig. 5 The tip 35 of the central spindle and the outlet opening 50 have the same conicity. The end 36 of the tip is so small that the end 36 of the tip 35 protrudes beyond the cover 38 in the closed position.

[0236] However, if the end 37 of the tip 35 of the central spindle is much larger, the end 37 of the tip is positioned behind the cover 38 in the closed position.

[0237] Fig. 6shows a central spindle tip 45 with different conicities for the same cover 38 and outlet opening 50. With a conical jacket 47 shown in dashed lines, the smaller end 48 of the tip 45 can protrude through the outlet opening in the closed position, so that the lower edge touches the conical jacket 47.

[0238] However, if the tip 45 has a conical shell with the taper 46 shown in dashed lines, the upper edge of the cover 38 touches the conical shell 46.

[0239] In the examples according to Figs. 7 and 8 an identical cover 38 with the same outlet opening 50 is combined with other tips of the central spindle. Fig. 7 shows a tip 55 with a spherical end 56 which, in the closed position, rests against the inner surface of the outlet opening 50.

[0240] The spherical shape of tip 55 simplifies the closing movement, as the lid no longer requires a plane-parallel position to the housing. This also makes a pivoting movement suitable for closing the nozzle.

[0241] Fig. 8 shows a tip 57 with a spherical end 58, which rests on the upper edge of the cover 38 due to a large diameter.

Claims

1. 3D printing with molten plastics to produce a moulded part using an extruder and applying the liquid plastics through a closable nozzle, the plastics being mixed with additives, additions and fillers, the melting occurring by liquefaction of the plastics in the extruder, characterized by a) the use of a planetary roller extruder b) the planetary roller extruder having a reduced conveying effect c) so that the extruder has a backflow / leakage flow of the melt at least when the nozzle is closed, d) an emerging melt strip or a melt thread or a melt strand or a melting point being produced.

2. 3D printing according to claim 1,characterized by the use of an extruder comprising a central spindle (17)having a tip (26, 35, 45, 55, 57) at the extruder outlet, a closable nozzle being arranged downstream of the outlet opening in the flow direction of the melt, the nozzle being closed or opened by a displacement of the central spindle (17) and / or by a movement of the nozzle and / or by a slider or hollow casing portion, even more preferably a nozzle being used which is movable in the axial direction of the central spindle (17) against the tip (26, 35, 45, 55, 57) of the central spindle in order to completely or partially close the nozzle, and being movable away from the tip (26, 35, 45, 55, 57) of the central spindle (17) in order to completely or partially open the nozzle.

3. 3D printing according to claim 1 or 2,characterized by the production of moulded parts by laying the melt strands / threads / strips in layers, the laying of a melt strand / thread / strip within a layer being interrupted when the melt strand / thread / strip abuts against a melt strand / thread / strip that has already been laid, or being continued at a point where no melt strand has yet been laid, preferably within the layers laying taking place line by line, the process being reversed when a moulded part edge is reached, and / or the laying of the melt strand / thread / strip at the transition to an adjacent row of a layer being carried out without interruption, resulting in a meandering course of the melt strand / thread / strip and / or the melt strands / threads / strip being laid at abutment points with other melt strands / threads / strips in the bond and / or the melt strands / melt strips / threads having an offset from adjacent melt strands / melt strips / threads of at least 1 mm, preferably at least 2 mm, even more preferably of at least 3 mm and at most 4 mm.