METHOD FOR PRODUCE COMPONENTS FROM SOLID WOOD, ENDLESS STONE OF SOLID WOOD FOR THIS METHOD AND SOLID WOOD COMPONENT PRODUCED THEM

Description

[0001] The invention relates to a method for the additive production of spatial components made of wood and to a wooden component made of glued together continuous strands of solid wood, which is produced according to the aforementioned method.

[0002] DE 10 2008 027 706 A1 discloses an industrial robot for laying veneers and / or foils into layer packages or into an endless strand during the production of veneer laminated panels or plywood panels.

[0003] Additive manufacturing methods enable the production of three-dimensional products by applying materials layer by layer. Initial experiments in this field were conducted in the 1980s. Additive manufacturing is also known as "3D printing."

[0004] The most advanced processes currently are powder-based, extrusion, and photopolymerization processes. In powder-based processes, powder is applied layer by layer and melted into a defined contour using a laser (Laser Powder Bed Fusion L-PBF). In extrusion, thermoplastics are made malleable using a heated nozzle and also applied layer by layer (Fused Deposition Modeling FDM). In photopolymerization, liquid photosensitive resins are applied and solidified using UV radiation or heat.

[0005] According to CN 103 665 905 A, wood can be applied as a finely ground powder combined with polymers using the FDM process. Commercial products are available for this purpose. While this allows for a bio-based printing material, the destruction of the natural solid wood structure required for pulverization results in the loss of important properties, namely the excellent strength-to-weight ratio and the anisotropy resulting from the unidirectional, continuous fibers of the wood, which account for a large part of its structural stability.

[0006] In the field of three-dimensional application of fiber-based materials (Continuous Fiber Manufacturing CFM (cf. WO 2017 085 649 A1) such as carbon, there are various developments: US 4 707 212 describes the so-called Automated Tape Laying (ATL) process, US 7 063 118 B2 describes the Automated Fiber Placement (AFP) process, which use computer-controlled robotics to place one or more layers of carbon fiber tape onto a mold to create a component or structure. Typical applications include the manufacture of aircraft wings and aircraft or boat hulls.

[0007] Further prior art on this topic is provided by US 4 351 688 A, US 2007 004 4922 A and US 7 407 556 B2.

[0008] In the area of ​​wood products consisting of multiple layers of glued wood strips, solid surface elements made of cross-laminated timber are also worth mentioning. In this case, several layers of flat wooden slats are glued together crosswise. The individual layers can be placed on top of each other using a robot. The elements are then impregnated with wood glue and pressed together in a vacuum bag. A similar process is also used to process veneers into veneer plywood panels, e.g., in WO 2018 011 270 A1 and US 2011 0291 441 A1.

[0009] To enable robot-assisted additive manufacturing of a material, i.e., 3D printing, special tools and equipment are required to complement the robot, tailored to the specific material and process parameters. Such tools and equipment are not known for solid wood, which is why it has not yet been possible to combine the advantages of solid wood with those of 3D printing.

[0010] US 2016 / 0332369 A1 discloses a method for producing three-dimensional components. Several strips, for example made of wood, are provided, which have an inherently rigid structure. The wooden strips of various widths are then applied to respective rolls. To produce a three-dimensional component, the various widths are provided on the respective rolls in cassettes, and then the different widths are placed on top of one another. Thus, the envelope contour of a component is defined by the width of the respective strip. The strips are cut lengthwise before being placed on top of one another, so that the contour of the component in the longitudinal direction of the strips already essentially corresponds to the final contour.As a final cut, the three-dimensional body is machined using a machining process to smooth the dry structure created by the various strips, for example, made of wood. This document thus proposes a manufacturing method for three-dimensional components that is particularly advantageous for large series production. Solid components, especially those made of wood, no longer require large machining volumes. Instead, the contour of the component can be predefined by dimensioning the strips, especially those made of wood, so that ultimately only the final contour needs to be machined. However, the wooden strips are rigid and, in particular, not flexible in both directions transverse to their longitudinal extent.This means they cannot be laid out to form radii, which severely limits flexibility, especially when it comes to freely designing the three-dimensional shape to be created. This process is particularly unsuitable for the free design and production of components in batches of one, as the strips wound onto the spools must be very long in order to produce as many components as possible in the same size.

[0011] The object of the invention is to enable the processing of solid wood in an additive three-dimensional manufacturing process in order to produce building elements with minimal material usage and with the greatest possible efficiency.

[0012] This task is solved by a process for the additive manufacturing of spatial components made of wood, which comprises at least the following steps: a) serially connecting solid wood strips previously cut from branches or trunks to form a continuous strand of solid wood, wherein the solid wood strips (2) preferably have a square or rectangular cross-section so that they have flexibility in two spatial directions transverse to their longitudinal extent, b) layer-by-layer additive application of the continuous strand on a mold or on previously applied layers of solid wood while gluing it to an adjacent continuous strand and c) cutting off the continuous strand at a component boundary.

[0013] The process therefore starts in step a) with a solid wood strip, i.e. a strand of natural wood. The solid wood strip offers the typical wood properties, i.e. anisotropy in the longitudinal direction of the strip and thus high longitudinal strength paired with high flexibility. The solid wood strip is joined to other solid wood strips to form a continuous strand of solid wood in which the properties of the individual solid wood strip are retained. The solid wood strip preferably has a square or rectangular cross-section and its cross-sectional dimensions give it flexibility in two spatial directions perpendicular to its longitudinal extent while maintaining high longitudinal strength, which benefits its processability and imparts high strength to the final wooden component.

[0014] Subsequently, in step b), the continuous strand or its section currently being processed is applied to a mold or support structure if it forms a component boundary, or to a previously applied layer of solid wood, which in turn was formed by applying the continuous strand. Simultaneously with the application or positioning of the continuous strand, it is bonded to an adjacent continuous strand or to one or more sections of the continuous strand(s). Such adjacent sections can be located vertically below and / or horizontally adjacent to it with respect to a processing direction during application.

[0015] Finally, in step c), the continuous strand is cut as required, usually at a component boundary or an end point of the laying path. This does not necessarily have to be a visible boundary of the finished component, but can also be defined by a hidden edge or similar.

[0016] The printing material used, "solid wood," is bio-based and easy and economical to produce. By using solid wood, the process succeeds in leveraging the advantages of wood fibers without the complex processes of extracting fibers, processing them, and spinning them into a new thread, for example. The invention completely avoids destroying the anisotropic wood structure, for example, pulverizing wood and mixing it with polymers, as is done with conventional products and processes, such as FDM wood filaments. Instead, it pursues the principle of preserving the wood fibers of the starting material intact and in their anisotropic alignment of the solid wood structure, thereby transferring the positive properties of solid wood into the manufactured component.

[0017] The additive manufacturing or 3D printing process also enables planar, curved, flat, or hollow-profile components, as well as three-dimensional lattice structures. Their structural properties can be precisely defined by the targeted strand-by-strand application of the continuous strand. Compared to laminated wood products such as cross-laminated timber or laminated veneer lumber, the properties of 3D-printed solid wood components can be adjusted and controlled with much higher resolution and accuracy. This allows component properties to be designed on a scale of just a few millimeters, and components can be manufactured with minimal material usage and maximum efficiency. Furthermore, in contrast to cross-laminated timber products, the process offers significantly greater geometric freedom for three-dimensional shaping, even for complex geometries, without the need for molds such as press dies or the like.

[0018] The production of the virtually endless solid wood strand from strips previously cut from branches or trunks as the base material can be directly linked to the additive, preferably robotic, processing process in a process- and application-specific manner. This allows for a particularly high degree of independence from the geometric specifications of the wood starting material, a high degree of freedom in the geometry of the product to be manufactured, and high manufacturing precision. Alternatively, the production of the continuous strand and its processing can also be spatially and temporally decoupled.

[0019] In step a), several solid wood strips are joined to form a continuous strand of solid wood. According to an advantageous embodiment of the process, the serial joining can be achieved using joiner's or carpenter's wood joints such as single or double shank joints, by bonding specific joining geometries such as tongue-and-groove or groove-and-rabbet joints, or by bonding joints with undercuts, which may also include additional mechanical anchoring of the parts, and by bonding overlapping joints.

[0020] It is also possible to bond several wooden strips in layers, staggering the layers lengthwise, so that the continuous strip is not achieved solely by joining the ends, but by staggering the layers of several strips. This allows the continuous strip ready for processing to be thicker than its source material.

[0021] As an alternative to gluing, joining can be achieved by wood friction welding, in which the "binding agent" already present in the wood is broken down and activated by a friction process under pressure. While gluing usually involves applying adhesive to the surfaces to be joined, i.e., "inside," joining can also be achieved by coating the joint with an adhesive material, e.g., an adhesive film, tape, fleece, or the like, thereby creating an "outside" bond. If necessary, the joining processes may require chemical or mechanical pretreatment of the surface to be joined, e.g., with plasma, laser, or smooth planing.

[0022] A combination of the above-mentioned options for serially connecting the individual solid wood strips is also conceivable.

[0023] According to a further advantageous embodiment of the method, the cross-sectional dimensions of the solid wood strip or the continuous strand can be machined before or after step b). Suitable machining processes such as sawing, milling, planing, grinding, laser cutting, knife cutting, sandblasting, drilling, turning, etc. can be used to vary the width and / or thickness of the solid wood strip or the continuous strand. This allows different cross-sections of the solid wood strip to be produced and processed - if necessary in the same component - e.g., to absorb loads more specifically and reduce material usage. The sequence of processing, i.e., joining the solid wood strips and cross-sectional machining, is arbitrary and can be adapted, for example, to process or processing requirements.

[0024] After bonding wood, for example with glue, it is regularly pressed to create the thinnest possible adhesive joint, absorb the water contained in the adhesive, and allow the actual adhesive to begin to dry. Furthermore, during pressing, the adhesive is forced into the pores of the wood surface, effectively interlocking with the material. According to a further advantageous embodiment of the invention, bonding can therefore take place in step b) while simultaneously pressing the continuous strand with the adjacent solid wood strand(s). This eliminates the need to press the finished or, if necessary, only semi-finished component.

[0025] Compared to conventional materials, the continuous strand offers a far wider range of processing possibilities. According to a further advantageous embodiment of the invention, the continuous strand can be additively processed in layers of continuous strands arranged parallel to one another or at an angle to one another, whereby the extension direction of the continuous strands can also be at an angle to one another in different layers.

[0026] The continuous strand can be applied in multiple planes or curved layers, one on top of the other. It can be processed in a single layer in parallel rows or additively. The strand directions of adjacent continuous strands can be at an angle to each other from layer to layer, for example, for stability reasons. Alternatively, the directions of the continuous strands can also be at an angle to each other within the same layer.

[0027] Its slender and therefore flexible strand shape allows the continuous strand to be processed not only in a single plane, but also in three-dimensional curves, making it possible to create bodies with surfaces that are strongly curved, multiple times, and in different spatial directions. For example, a hollow wooden body with delicate structures or spherical surfaces can be produced that exhibits high mechanical strength.

[0028] The unlimited longitudinal dimension of the continuous strand allows for the production of undisturbed solid wood surfaces. According to a further advantageous embodiment of the invention, the continuous strand can be applied extending from one component boundary to an opposite component boundary of the same component. Continuous butt joints or other disruptive joints in the solid wood, which could result in visual disadvantages or limited load-bearing capacity, can be avoided with the inventive method.

[0029] The process allows not only the production of solid plate-shaped components, but also of solid bodies, especially those with curved surfaces, of hollow components made of solid wood that are light in relation to their load-bearing capacity and therefore material-efficient, and even the production of three-dimensional lattice structures made of solid wood.

[0030] According to a further advantageous embodiment of the invention, the adhesive for bonding the continuous strands to one another can be applied immediately before the currently processed continuous strand is deposited in its final position or by impregnating the continuous strand with adhesive before step b). The continuous strand can therefore already be provided with adhesive, e.g., impregnated, to simplify the processing step of applying the continuous strand. Suitable adhesives for pre-coating include contact adhesives such as "3M Scotch-Weld 10," "Universal Contact Adhesive - Sprayable," "Duro Spray Premium Contact Adhesive BlueGrip DS 775," or "UHU Contact Adhesive - Liquid," or thermosensitive adhesives such as "PU-Dispersion Thermal Activated Glue - Jowapur 150.00."With thermosensitive adhesives, the already coated endless strand is fed to the three-dimensionally movable working head and heated up, whereby the adhesive is activated shortly before the endless strand is applied to the already finished part of the wooden component or at the beginning on a worktop.

[0031] Alternatively, the adhesive can be added at the processing point of the continuous strand, for example, if only small quantities of adhesive are to be used. Suitable adhesives for this purpose include fast-setting two-component adhesive systems or hot melt adhesives and UV adhesives, such as "DELO Photo Bond 4436 (UV Activated Glue)".

[0032] According to a further advantageous embodiment of the invention, the method can be carried out mechanically and automatically, in particular using a robotic machine tool, for example, a multi-axis robot equipped with a CNC control system. This allows for high volumes of manufactured components to be produced consistently at the same high quality.

[0033] The starting material for the continuous strand is prefabricated strips of solid wood from locally renewable wood species, such as willow, spruce, pine, beech, or linden. Components made from these wood therefore have a low ecological impact. In order to utilize the advantages of fibers, the use of solid wood eliminates the process of extracting fibers, processing them, and spinning them into a new thread, for example, compared to fibers otherwise used in fiber-based additive manufacturing techniques such as carbon or glass fibers, since solid wood already consists of anisotropically aligned fibers. The continuous strand, for example, has a width of approximately 1 to 10 mm and a thickness of approximately 0.3 to 1 mm, so that the continuous strand can still be laid flexibly in two spatial directions. The dimensions of the continuous strand are therefore roughly in the thickness range of microveneer, although considerably narrower.The length of the solid wood strip starting material is, for example, approximately 0.5 to 2 m. The starting material essentially includes all lignocellulose materials, i.e. woody plants of any kind, such as bamboo or rattan, in particular those which can be given a rectangular or trapezoidal cross-section by chip removal.

[0034] The continuous strand of solid wood is created from serial connections of elongated solid wood sections by bonding with butt and / or angled joints, particularly tongue-and-groove or groove-and-rabbet joints, shanks, overlapping joints, wood friction welding, or by layering several wood strips under a staggered layer of several wood strips, as described in detail above. The different manufacturing options can be observed, at least microscopically, in the continuous strand and can also be detected in the finished component.

[0035] The result of the invention is a wooden component, in particular as a volume component, hollow component or three-dimensional lattice structure, made of layers of continuous strands of solid wood arranged parallel to one another or at an angle to one another and glued together, as described above, and / or produced in the process described in detail above.

[0036] The invention is explained in more detail below with reference to the figures, which show: Figure 1: a first basic structure for a manufacturing and processing device, Figure 2: examples of components manufactured using the method; Figure 3: a schematic view of a working head for implementing the method, and Figure 4: another basic structure for a processing device. Figure 1 shows a first basic structure of a robot-assisted system 1 as a continuous production and processing device for a continuous strand 13 of solid wood thread. This essentially consists of two devices: the cross-sectional processing device 4 and the joining device 7 for producing the continuous strand 13, as well as a multi-axis robot 15 for processing the continuous strand 13.

[0037] The starting material for the continuous strand 13 is prefabricated solid wood strips 2, for example, with a width of approximately 2 to 8 mm, a thickness of approximately 0.5 to 0.8 mm, and a length of approximately 0.5 to 2 m. They can be obtained from domestic solid wood, such as willow. Due to their small dimensions in width, thickness, and length, they can also be obtained from processing residues, for example, from the furniture industry, eliminating the need to harvest wood specifically for this purpose.

[0038] In a first production step, the solid wood strip 2 is inserted in the insertion direction 3 into a device 4 for cross-sectional processing. This device serves to cut the strips 2 to a uniform cross-section or, if necessary, to a specific cross-section required for processing. Different cross-sections can also be created for processing in the same component if necessary for geometric, static, or dynamic reasons of the component to be manufactured.

[0039] Machining processes such as sawing, milling, planing, grinding, laser cutting, knife cutting, sandblasting, drilling, or turning are suitable for cross-sectional machining. Successive strips 2 are thus homogenized in height and width in the device 4 in order to subsequently obtain a continuous, endless strand 13 without cross-sectional deviations, in particular without cross-sectional discontinuities at the joints between individual strips 2.

[0040] The processed, still individual strips 2 then enter a joining device 7 one after the other. There, they are joined to one another in series in their direction of extension, creating a virtually endless solid wood thread 13. Suitable joining methods can be methods known per se, namely from joinery or carpentry, e.g., double-shanked joints, bonding with butt and angled joints, overlapping, bonding of specific joining geometries such as tongue-and-groove or groove-and-rabbet geometries, wood friction welding, layered bonding, or combinations of the aforementioned options. The joining methods may also require chemical or mechanical pretreatment of the surface to be joined, e.g., with plasma, laser, or smooth planing.

[0041] The sequence of processing in devices 4 and 7 is arbitrary, so it can be selected, for example, according to the requirements of the subsequent processing method.

[0042] The endless strand 13 is then fed to a coating device 8 in which it is impregnated with adhesive.

[0043] After leaving the coating device 8, transport rollers 11 arranged opposite one another in pairs feed the impregnated continuous strand 13 to a reel 12 on the robot 15. From there, the continuous strand 13 is fed into a working head or end effector 14 of the robot 15, which processes the continuous strand 13 on a work plate 17 into a plate-shaped component 16. For this purpose, the continuous strand 13 is additively processed in parallel layers, with the strand directions of adjacent continuous strands 13 being at an angle to one another from layer to layer for stability reasons.

[0044] Figure 2 shows examples of possible components under each working head 14, namely in addition to the plate-shaped component 16 made of Figure 1 a three-dimensional solid volume component 18 with a multiply curved surface, a three-dimensional lattice structure 19, and a hollow component 20. The volume component 18 is created from several superimposed flat or curved layers of continuous strands 13. The slender strand shape of the continuous strand 13 enables its processing not only in a single plane, but also in three-dimensional curves, thus enabling the formation of bodies 18 with strong, multiply curved surfaces in different spatial directions. The hollow component 20 is mounted on a rotatably mounted cylinder 31, which can be rotated synchronously with the processing progress of the work head 14. The hollow component 20 made of solid wood, in particular, can contribute to high material efficiency in timber construction.

[0045] Figure 3shows a schematic view of the working head 14 during a movement in a working direction 30. It comprises an extruder 21, namely two spools which are pretensioned against each other, for example via a spring, and which extrude the endless strand 13 from the spool 12 ( Fig. 1 ) are transported precisely and at a programmed speed using stepper motors (not shown). The feed speed of the endless strand 13 corresponds to the movement speed of the working head 14 when applying the endless strand 13.

[0046] Downstream of the extruder 21 is a pneumatically or electrically driven cutting device 22, at which the continuous strand 13 can be cut off if necessary, for example before reaching a component edge.

[0047] As an alternative to the coating device 8, an adhesive dispenser 23 can be arranged in the working head 14 to bond the continuous strand 13 with a suitable adhesive shortly before its processing. The adhesive dispenser 23 includes an adhesive activator 27 acting on the processing point under a pressure roller 25, which enables the activation and bonding of the adhesive via heat or UV light.

[0048] A suitable guide 24 then guides the continuous strand 13 to the pressure roller 25, where it is applied to a mold or to previously applied layers of continuous strands 13 under the force of the pressure roller 25. For lattice structures, a pneumatic clamping tool 28, for example, is optionally arranged on the working head 14 to press the individual layers together.

[0049] Figure 4shows another basic structure for a processing device for the endless strand 13, which is designed as a three-axis CNC system 29. It has a working head 14 that is largely identical to the robot-assisted system 1 according to Figure 1 and 3 . The production of the continuous strand 13 prior to processing in the CNC system 29 can also be carried out as in Figure 1 shown can be accepted.

[0050] In contrast, the working head 14 is moved up and down in a z-axis direction on a vertical guide 32. The vertical guide 32 can be moved horizontally in an x-axis direction orthogonal to the y-axis direction on a transverse guide 33. Finally, a longitudinal guide 34 allows horizontal displacement in the y-direction orthogonal to the x- and y-axis directions in a third axis. This allows the working head 14 to move to any position within a defined space above a work surface 35 in order to produce not only plate-shaped components 16, but also solid bodies 18, lightweight and efficient hollow components 20 (cf. Fig. 2 ) and to produce three-dimensional lattice structures 19.

[0051] The invention is not limited in its implementation to the preferred embodiment described above. Rather, a number of variants are conceivable, which utilize the presented solution even in fundamentally different embodiments. All features and / or advantages apparent from the claims, the description, or the drawings, including structural details or spatial arrangements, may be essential to the invention both individually and in a wide variety of combinations. List of reference symbols

[0052] 1 Robot-assisted system 2 Solid wood strips 3 Feed direction 4 Device for cross-section processing 5 Height processing 6 Width processing 7 Joining device 8 Coating device 9 Adhesive coating 10 Rapid adhesive drying 11 Transport rollers 12 Reel 13 Continuous strand 14 Working head 15 Multi-axis robot 16 Product, wooden component 17 Worktop 18 Solid component 19 Lattice structure 20 Hollow component 21 Extruder 22 Cutting device 23 Adhesive dispenser 24 Guide 25 Pressure roller 26 Force direction 27 Activator 28 Clamping tool 29 CNC system 30 Working direction 31 Cylinder 32 Vertical guide 33 Transverse guide 34 Longitudinal guide 35 Work surface

Claims

1. A method for the additive production of spatial components (16, 18, 19, 20) made of wood, said method comprising the following steps: a) serially connecting solid wood strips (2) cut beforehand from branches or logs to form a continuous strand (13) of solid wood, wherein the solid wood strips (2) preferably have a square or rectangular cross-section so that they have flexibility in two spatial extents transversely to their longitudinal extents; b) additively applying the continuous strand (13) layer-wise to a mold or to previously applied layers of solid wood while adhesively bonding to an adjacent continuous strand (13); c) cutting off the continuous strand (13) at a component boundary.

2. A method in accordance with claim 1, characterized in that the serial connection in step a) takes place by adhesive bonding to blunt and / or slanted joints, in particular of tongue and groove joints or tongue and fold joints, shafts, overlap joints, or wood friction welding, or by a layering adhesive bonding of a plurality of wood strips (2) in offset layers of the wood strips (2).

3. A method in accordance with claim 1 or claim 2, characterized in that a shape cutting takes place, in particular by sawing, milling, planing, and grinding, to manufacture suitable cross-sectional dimensions of the continuous strand (13) before or after step b).

4. A method in accordance with one of the preceding claims, characterized in that the adhesive bonding in step b) takes place while simultaneously pressing the continuous strand (13).

5. A method in accordance with one of the preceding claims, characterized by an additive processing of the continuous strand (13) in layers of continuous strands (13) that are disposed in parallel next to one another or at angles with one another and whose directions of extent are also at angles with one another in different layers.

6. A method in accordance with one of the preceding claims, characterized in that the continuous strand is applied reaching from one component boundary up to an oppositely disposed component boundary of the same component.

7. A method in accordance with one of the preceding claims, characterized in that continuous strands (13) are in particular processed by means of step b) to form volume components, hollow components, and three-dimensional lattice structures.

8. A method in accordance with one of the preceding claims, characterized by an adhesive application directly before the placing down of the continuous strand (13) in its end position or by impregnating the continuous strand (13) with adhesive prior to step b).

9. A method in accordance with one of the preceding claims, characterized in that it is carried out mechanically, in particular with the aid of a robot machine tool or by means of a multi-axial robot (15).

10. A wooden component (16, 18, 19, 20), formed as a volume component (18), as a hollow component (20), or as a three-dimensional lattice structure (19) , composed of layers of continuous strands of solid wood arranged in parallel next to one another or at angles with one another and adhesively bonded to one another, manufactured in a method in accordance with one of the claims 1 to 9.