Mold for manufacturing a molded fiber product

Abstract

This invention relates to a mold for manufacturing molded fiber products. The mold (11) includes a porous product surface (23) formed by additive manufacturing. The product surface (23) is arranged as a double-layer structure (40) comprising two layers (41, 42). A cavity (43) exists between the two layers (41, 42), wherein the first layer (41) has porosity from the cavity (43) to the product surface (23). The second layer (42) has perforations isolated from the cavity (43) and extends from the product surface (23) through the double-layer structure (40).

Description

Technical Field

[0001] The present invention relates to a mold for manufacturing molded fiber products, the mold comprising a porous product surface formed by additive manufacturing. Background Technology

[0002] European Patent No. EP3237680 discloses a mold produced in an additive manufacturing process (such as 3D printing). This additive manufacturing process may include the selective sintering of a powdered material having particles with an average size of 1-50 micrometers, preferably 5-30 micrometers. On the other hand, a powder particle size of 40-45 micrometers is common. During the sintering process, the powdered material is completely melted by the addition of energy from a laser beam. In the additive manufacturing process, the mold wall is equipped with a number of small through-holes to achieve dense perforation for penetration. Therefore, the tool wall portion has voids provided by a plurality of channels extending through the tool wall portion from the product surface to the back side.

[0003] Traditionally, manufacturing molds from a single solid raw material is laborious. Furthermore, machining complex structures is impossible. Additionally, the through-holes on the product surface may be too large, potentially causing blockages. Products with additional metal mesh may leave marks on their surface. These marks may persist even after hot pressing. Cleaning the mold is also laborious. The product surface roughens the final molded fiber product, making it suitable only for low-quality products due to the marks. Moreover, the aforementioned known molds are typically used only for fiber suspensions or slurries, where the mold is immersed in the fiber slurry, and the fiber product is subsequently drawn from the aqueous suspension onto the mold surface or injected with excess water through channels. Summary of the Invention

[0004] The object of this invention is to provide a new mold for manufacturing molded fiber products, which is more versatile and easier and faster to manufacture than previous molds. The features of the mold according to the invention are set forth below. The properties of the mold can be easily varied to achieve new porous structures and combinations thereof. In this application, porous means tiny gaps through which liquids, air, or vapors can pass via various undefined routes, as opposed to perforations or holes that serve as defined channels from one surface to another. Furthermore, the mold manufacturing time is shorter, thus saving costs. Additionally, the mold has good strength even if its shape may be complex. Moreover, the mold is easy to clean. Furthermore, product changes can be completed faster and easier than before, and manufacturing costs are also lower. Another object of this invention is to provide a new and efficient method for manufacturing molds for additive manufacturing of molded fiber products. Using the new mold, process time is short, and high pressure can be used. Simultaneously, downtime is minimal due to the quick and easy maintenance of the mold. Attached Figure Description

[0005] The present invention will now be described in detail with reference to the accompanying drawings, which illustrate some embodiments of the invention, wherein...

[0006] Figure 1 A top view of a mold for forming molded fiber products according to the present invention is shown;

[0007] Figure 2a A side view of a pair of molds according to the present invention is shown;

[0008] Figure 2b It shows Figure 2a A magnified view of a portion of the image;

[0009] Figure 3 A cross-sectional view of a portion of the mold according to the invention is shown;

[0010] Figure 4a A side view of the mold according to the invention is shown, wherein a portion is separated in the sectional view;

[0011] Figure 4b It shows Figure 4a The mold, in which parts are connected;

[0012] Figure 5a It shows Figure 4a The separated parts;

[0013] Figure 5b It shows Figure 4b The connecting part;

[0014] Figure 6 A pair of molds for hot pressing are shown. Detailed Implementation

[0015] Molded fiber products, also known as MFPs, are made from cellulose fibers. Examples of such products include disposable cups or plates. The cellulose fibers are first dispersed in water, then shaped, drained, and dried. One specific method of manufacturing molded fiber products is thermoforming. After shaping, the product is pressed under high temperature and pressure, which together drain and evaporate the water and moisture from the product. Advantageously, the raw material is foamed before shaping because, as will be described later, the mold according to the invention is perfectly suited for foaming, particularly in thermoforming. Therefore, oven drying is unnecessary, and high-quality, thin-walled products are readily available after manufacturing. Dimensional accuracy and rigidity are good, and the product surface is smooth.

[0016] Both forming and pressing require a die tool pair, consisting of a positive (male) die tool and a negative (female) die tool. In this die tool pair, at least one tool needs to have drainage properties in the product surface that comes into contact with the fiber product, achieved through perforation and / or some kind of permeable material. This allows water, steam, and air to pass through the perforated or other permeable surface during the forming and / or pressing process steps.

[0017] exist Figure 1 In this process, a mold 11 is assembled with a mold base 12. In principle, one mold is a negative mold, and the other is a corresponding positive mold. In this way, the product achieves a three-dimensional shape during molding. Water and air in the foam must be removed. This is primarily accomplished by closing the mold pair, and vacuum aids in water removal. During hot pressing, the blowing of steam and air also contributes to water removal. In other words, the distance between the opposing molds changes. When the mold pair is closed, pressure forces air and water out of the foam supplied between the molds. The permeable surfaces of the molds are arranged as outlets for water and air, while the remaining fibers form layers. After opening the mold pair, the product can be transferred to the next processing stage.

[0018] In the illustrated embodiment, foam is supplied between the molds via mold base 12, while the mold pair 13 is sealed from its sides. Figure 2aHere, the upper mold is supported to the mold frame 14. Therefore, even when the molds are separated (i.e., the mold pair is open), a closed cavity exists for the foam. In this way, the foam supply is rapid and the timing can be chosen more freely than before. The non-product surfaces of the molds can be used as foam inlets. Specifically, through-holes are located in selected edges of the molds, and particularly between the facing surfaces of adjacent molds. However, in the illustrated embodiment, the mold pair 13 is formed by an upper mold frame 14 and a lower mold base 12, and the upper mold frame 14 is movable while the lower mold base 12 is arranged to be stationary. In other words, the lower mold base 12 is stationary, and the foam is supplied through it. The upper mold frame is movable. In this way, the tubing and other conduits connected to the lower mold base can also remain in their position, and the movable upper mold frame can be lightweight. The lightweight upper mold frame can be moved quickly and precisely. This speeds up the process of the molded fiber production machine. Meanwhile, the tubing and other conduits remain stationary ( Figure 1 ).

[0019] As mentioned above, in principle, the foam is supplied through the mold. More precisely, the foam is supplied through the gaps between adjacent molds. The supply channel is formed to the outer edge of the mold, requiring two adjacent molds to form the entire supply channel, with portions of the channel walls of these two adjacent molds abutting each other. At the outer edge, the mold edge and the surrounding frame together form the channel. This saves more space for the actual product shape. Figure 1 The image shows a mold base 12 with inlets 15. More precisely, each inlet 15 is connected to a lateral channel 16 via the mold base 12, and a return conduit 17 is also present. Here, the inlets are connected to a supply manifold 18 for uniformly supplying foam to each inlet 15. Correspondingly, the return conduit 17 is connected to a return manifold 19. In this way, the foam flows constantly through the mold frame. Advantageously, the lateral channels 16 open between the molds 11 via a plurality of openings 20 on the mold surface, more precisely, to the neck region between the product areas of the mold. In this way, the foam will spread rapidly and uniformly between the molds. Here, the openings are located on the neck region between the products, and they are upward. Meanwhile, the opposing mold frame 14 has pins 21 at each point of the openings 20. Figure 2a and Figure 2bThese pins have two main functions. First, each pin guides the mold during closure. This keeps the mold pair in shape and the product precise. Second, each tapered pin closes its own opening and cleans that opening. Thus, closing the mold pair automatically shuts off the supply, preventing backflow into the inlet or side channels. Conversely, opening the mold pair opens the side channels and allows foam to fill the mold space. The foam supply channels (e.g., inlet 15 and opening 20 leading to the mold space) facilitate the connection of the mold sidewalls.

[0020] For sealing, the mold pair 13 has an outer sleeve 22, which is arranged to seal the mold pair 13 even when the mold base 12 and the mold frame 14 are a distance apart. In this way, a closed mold space is formed, and a large amount of foam can be supplied to the mold space, similar to a closed cavity. Advantageously, the outer sleeve 22 is adjustable relative to the mold pair 13. Therefore, when the product is removed and transferred to the hot press, the sleeve can slide and provide space for the product. A common sleeve may exist, or both molds may have their own sleeves.

[0021] As previously shown, lateral channels 16 are arranged between molds 11, and they include openings 20 leading to the mold surfaces. In this way, each mold is uniformly filled with foam. Therefore, the product is uniform, and the process is rapid. In practice, the foam circulates through the mold base. When the upper mold frame is lifted, a pin exits from the opening, and the foam flows into the mold space. Filling is rapid, and when the molds are closed, the pin closes the opening again. This valve feature can be used with existing valves preceding the manifold or independently.

[0022] As previously described, mold 11 includes a product surface 23 manufactured by additive manufacturing. According to the invention, the product surface 23 is arranged as a double-layer structure 40, comprising two layers 41 and 42, with a cavity 43 between them. Figure 3In fact, there are two cavities for a selected purpose. In addition to cavity 43, there is a second cavity 48. These cavities can operate independently using different fluids, whether for supplying or removing them. The layers can be very thin, and the separated layers together form a rigid structure. In the double-layer structure 40, the first layer 41 has porosity from cavity 43 to product surface 23. Meanwhile, the second layer 42 has perforations isolated from cavity 43 and extends from product surface 23 through the double-layer structure 40. Large-area, dense perforations exist through both the porous and solid layers. Through this unique structure, two different functions are achieved in the mold, or more precisely, on the product surface. First, during molding, water and air pass through the porous second layer. In other words, water and air pass through the product surface, while fibers accumulate on the product surface. Second, for example, after molding, fluid can be supplied to the cavities and thus through the first layer to the product surface. In this way, the product surface is cleaned and kept clean. For example, the fluid can be compressed air, water, steam, or a combination of two or more fluids. Air is advantageous because the cavity can be small and avoids the need for additional water. Furthermore, compressed air aids in the removal of the formed fibrous product from the mold. Moreover, both of the aforementioned cavities can have suction if more efficient water removal is required.

[0023] As mentioned earlier, the double-layer structure 40 can be thin, yet still rigid. Furthermore, the thin structure can be manufactured quickly, and the mold volume can be minimized as much as possible. In practice, the thickness of the double-layer structure is 4-10 mm. Meanwhile, the thickness of layers 41 and 42 is 0.2-2 mm. The thinner the layers, the larger the cavity. Moreover, the first layer can be thinner than the second layer, or vice versa. In particular, the thickness of the second layer can vary in different regions of the layer to, for example, optimize the rigidity of the layer.

[0024] Advantageously, the first layer 41 has a randomly generated porosity. This prevents fibers from penetrating the product surface. Furthermore, the fluid is uniformly distributed across the product surface. Moreover, the first layer can be very thin. The perforations in the second layer 42 consist of 3D-printed channels 44 extending from the product surface 23 through the double-layer structure 40. This provides sufficient filtration while minimizing permeability to retain fibers on the product surface. The channels also bind the layers together to form a robust structure with two layers and cavities between them. It is possible to have more open channels, further away from the product surface, instead of uniform channels. In practice, the orifice diameter of the channels 44 is 0.1-2 mm. These channels are very small but still possible to manufacture using 3D printing. Other channels can have irregular orifice shapes. Regardless of the type of channel or channel, the opening to the product surface is minimal, while the remaining channels may become larger. Depending on the diameter, there are 1-30 channels per square centimeter. It would be impossible to manufacture such a dense density of such small holes using conventional machining methods. Furthermore, it is easy to change the size and density of the pipes. Therefore, the characteristics of the second layer 42 can differ in different portions of the product surface 23. Moreover, when dense, tapered perforations extend to the surface, the surface area of ​​the second layer may be smaller than the product surface. In fact, the perforations can fill the entire surface.

[0025] exist Figure 3 In this embodiment, mold 11 is a uniform 3D printed body. In other words, the entire mold is printed in a single step, having two layers including channels and porous structures. This structure is compact, lightweight, and rigid. Moreover, because the product surface is kept clean by the fluid passing through the first layer, the long-life mold requires almost no maintenance. Here, the characteristics of the first layer 41 also differ in different parts of the product surface 23. For example, the porous nature of the first layer may be greater at the edges of the product to ensure filtration. During molding, perforations may be more suitable for filtration while porosity is more suitable for release.

[0026] In another embodiment, the double-layer structure 40 is arranged to be detachably fixed to the skin 24 of the base structure 25. Figure 4a and Figure 5a In this way, the skin can be easily removed for cleaning and maintenance. Furthermore, a base structure can have several skins of the same or different types. In other words, worn or dirty skins can be quickly replaced with new ones. Therefore, production can continue with the shortest possible interruption. Similarly, by using different types of skins, the product to be manufactured can be quickly changed. Besides rapid change, the base structure 25 using the skin can be made of a different material than the skin 24. Different materials can be cheaper or lighter, or can act as insulation or heat conductors.

[0027] At least one inlet is provided to facilitate the supply of fluid to the cavity. If space permits, the inlet may originate from the side of the mold. In the illustrated embodiment, inlet 45 is included inside the mold 11. In this way, the fluid can be supplied like… Figure 3 and Figure 4b The fluid is supplied from below. Several molds can then be arranged side-by-side. Advantageously, a fluid distribution chamber 46 is provided before inlet 45, which is arranged inside mold 11. Using this chamber, fluid is uniformly distributed to one or more inlets and further distributed into the cavity, and thus uniformly distributed across the entire product surface. Figure 4a and Figure 4b In this structure, the fluid distribution chamber 46 is circumferential and located on the outer edge of the base structure. Here, a supply port 47 is located at the bottom. Figure 3 In this design, the dispensing chamber 46 has a larger volume. As mentioned earlier, the dispensing chamber is optional. However, here, due to available space, the dispensing chamber is formed inside the mold. Simultaneously, manufacturing time is shortened and the mold becomes lighter. Figure 3 The location of the supply port 47 is indicated by a dashed line. In addition to the pressure connection, the fluid distribution chamber can also have a vacuum connection. In this way, the product can be controlled during lateral movement, especially when the mold is in the upper position. In other words, the product is held by suction. To release the product, the vacuum stops. If necessary, overpressure is used to assist in product release. This ensures fast and precise production.

[0028] During molding or hot pressing, water and moisture are forced through the double-layer structure via the second layer. Pressure and gravity assist in filtration. Here, a second cavity 48, defined on one side by the double-layer structure 40, also exists inside the mold 11. Filtration is further improved using a vacuum. With the large vacuum chamber, suction is evenly distributed throughout the entire area of ​​the double-layer structure. Meanwhile, even a single outlet 33 of the vacuum chamber 48 is sufficient. Figure 3 In this design, the vacuum chamber 48 is inclined toward the outlet 33. Therefore, water is rapidly and unobstructedly discharged from the mold. Both chambers can have both vacuum and pressure connections. Connections of the same type can be used simultaneously, or connections of different types can be used consecutively.

[0029] The aforementioned mold is dual-function. The second cavity is approximately a double-layered structure, with the first cavity inside. If necessary, water can be advantageously drained through pipes using a vacuum. After forming or pressing, compressed air can be supplied to the first cavity. At different stages of the process, as the formed product is lifted from the mold, pressurized fluid can introduce pressure peaks, along with a constant airflow, to continuously reduce adhesion and ensure the release of the formed product. The use of cavities in both the upper and lower molds can be varied to adjust production.

[0030] The second-layer conduit can be formed by orifices of any shape, such as square, circular, elliptical, or hexagonal. The conduit can also be curved or straight, and its dimensions may differ from one side to the other. For example, the conduit can be tapered. Furthermore, the diameter and / or profile shape of the conduit can be varied, and it may have rounded or chamfered inlets and / or outlets. Moreover, the length of the conduit may vary depending on the mold layout. The perforation density on the product surface may vary to accommodate different shapes and fluid drainage characteristics.

[0031] The first layer is porous. The thickness and / or porosity level of the product surface can be varied to suit the properties and functions of certain porous materials. This also applies if perforations are used instead of porous metal as air venting areas on the formed surface.

[0032] The double-layer structure and base structure can be optimized. In particular, the characteristics of the double-layer structure can be adapted to each production and product. Advantageously, the skin 24 can be detachably arranged to the base structure 25. In this way, the skin and base structure can be manufactured separately, even using different materials. At the same time, the skin is easy to remove for cleaning and replacement. Moreover, when the product changes, only the skin is changed. This facilitates modification.

[0033] Advantageously, the base structure 25 has a universal geometry for several skins 24 with different properties. In this way, the base structure can be retained in the production machine, and only the skins need to be changed when the product changes. Similarly, the skins can be quickly changed for cleaning and refurbishment. If the product to be manufactured remains unchanged, skins of the same type are attached to the base structure without immediate cleaning of the previous skin. Therefore, production downtime is minimized. Advantageously, several base structures are arranged within a mold base.

[0034] There are many ways to attach multiple parts together. Figure 5aThe diagram shows two at least partially tapering snap-fit ​​structures 26 arranged on one side of the skin 24. In fact, similar snap-fit ​​structures 26, each square in shape, exist on each side of the snap-fit ​​structure on the skin 24. In this way, the skin is rigidly attached to the base structure. Each snap-fit ​​structure 26 in the base structure 25 has a corresponding hole 27. The cone will be correctly aligned with the skin, and there will be no gaps at the attachment. Figure 5a In the design, the snap-fit ​​structure 26 has an annular protrusion 28, while the hole 27 has a corresponding groove 29. When the skin is assembled, the protrusion will snap into the groove. During the product's molding process, this shape-locking keeps the skin attached, but it can be easily removed by pulling. Alternatively or additionally, one or more bolts can be used to secure the attachment. Glue or other adhesives can also be used to attach and seal the skin. The skin can be attached to the base structure via a hinged frame, bayonet, shape-locking, or screws with or without seals using silicone or glue.

[0035] exist Figure 4a In this design, a double-layer structure forms the product surface 23, and a support structure 31 exists on the opposite side compared to the product surface 23. Depending on the manufacturing process, the layers have specific permeability. The support structure then has a more open construction. In practice, the support structure is placed on a base structure. In this way, loads from the product surface are transferred to the base structure via the support structure. Of course, the support structure provides rigidity to the double-layer structure. In this way, the skin can be easily manufactured, processed, and attached.

[0036] In one embodiment, the double-layer structure 40 and the support structure 31 form a uniform structure. In other words, they are printed simultaneously as a single unit. This allows for structural optimization. It reduces the size of the skin while maintaining a large open volume. Simultaneously, the skin printing time is shortened. Alternatively, the double-layer structure and the support structure 31 can be separate parts, which is disadvantageous due to strain tolerances. This allows for the use of different double-layer structures with a single support structure. However, the double-layer structure itself must have sufficient rigidity. Therefore, the thickness of the double-layer structure increases. This may increase the overall weight of the skin. On the other hand, only the double-layer structure of the skin can be changed while retaining the support structure. Similarly, different materials can be used.

[0037] exist Figure 4a and Figure 5a In this structure, the supporting structure 31 includes a three-dimensional lattice 32 manufactured by additive manufacturing. The lattice provides good stiffness and support for the double-layered structure, while still leaving ample open space for air, water, and steam. Alternatively or additionally, honeycomb, cavity, or other combined structures are also feasible.

[0038] A thin double-layer structure allows for more space in the product. Maximizing space within the mold can be important for more extreme product shapes. Manufacturing a slightly thinner double-layer structure (with lower porosity) helps increase space and thus allows for a slightly larger final product within a given tooling frame. The support structure portion can even be thicker than the double-layer structure. The double-layer structure is dense enough yet remains open and clean without clogging. Moreover, water can quickly pass through the thin double-layer structure, which is beneficial for product shaping and pressing. Furthermore, the first layer can be at least partially undefined, forming an undefined mesh where particles are melted together, leaving some open volumes in between. In practice, foam carries fibers for shaping. In foam molding technology, aqueous foam is used instead of water as the carrier medium in the manufacturing process of fiber-based products. The support structure can have complex cavities and protrusions between the base and the product surface. While the product surface is at least partially porous, there is a solid surface at least at the edges that prevents air leakage into the mold. Advantageously, only the very edge of the product surface is solid, which is particularly useful for preventing steam from escaping during hot pressing.

[0039] Depending on the product produced using the mold, a double-layer structure can consist of several parts with different properties. For example, the thickness of the double layer may be uneven across different parts of the product surface. For instance, recesses can be used on the surface away from the product surface to improve permeability in such locations. Furthermore, printing parameters can be varied to adjust the properties of the layers. In this way, the mold and its product surface can be easily optimized.

[0040] Water and air are collected by the base structure through a double-layered structure. Figure 4a and Figure 4b Similarly, an outlet 33 is located at the center of the base structure 25. The outlet is connected to a pipe or similar (not shown). Advantageously, a vacuum can also be used to assist in water removal. Because the outlet is in the center, the vacuum is evenly distributed, and the water flows smoothly towards the center. Advantageously, the base structure has a bucket-like geometry that slopes towards the center of the base structure 25. This aids in filtration. Moreover, the support structure 31 forms the outline of the shape of the base structure 25. In this way, the mold structure is rigid, and the load from the product surface is supported by the support structure and the base structure together. Therefore, the structure can be very lightweight when all parts are fitted. This also facilitates the printing process of the skin and the base structure.

[0041] Here, the mold size is 200 x 200 mm. Larger sizes are also possible if needed, for example, edge lengths can reach 300-500 mm. The thickness of the combined double-layer structure and base structure is less than 50 mm, but the thickness of the base structure can reach 100-300 mm. In the production machine, several molds are assembled side by side, with the support structure abutting against the mold base to obtain the mold base. In particular, the removable skin allows for better cleaning of each mold. The design of the mold with edge supply allows for some space in the edge for the attachment arrangement of the skin. The skin 24 may have a recess 34 at the location of the opening and pin. Here, a solid edge collar 35 is also present adjacent to the recess 34. This solid frame or collar surrounding the skin prevents air and pressure leakage. The solid edge is only 1-3 mm narrow. Therefore, the area of ​​the process surface is maximized while the size of the skin is minimized. In addition, the removable skin allows for quick or even tool-less skin changes. The open inner grid improves dehydration and drying using the double-layer structure. In particular, the dual-layer structure can be optimized, allowing for a lower profile. This reduces costs and shortens printing time.

[0042] Surprisingly, the first layer was manufactured at least semi-randomly through additive manufacturing, simultaneously printing the pipes. The semi-random structure has an uncontrolled geometry lacking through-holes. Therefore, the first layer resembles a mesh, exhibiting good porosity for air but still providing good constraint for the fibers. This ensures good forming and pressing properties at low energy levels. The characteristics of the first layer are determined by various parameters in the printing process, such as laser energy, laser speed, layer height, scan line distance, and overall scanning strategy. Furthermore, an electron beam can also be used.

[0043] Porosity and permeability levels can be easily adjusted via 3D printing. In other words, different porosity and permeability levels may exist in different parts of the product surface. Furthermore, the flow resistance of the first layer may increase linearly with increasing layer thickness. For example, when the thickness doubles, the flow resistance also doubles. Regardless, compared to traditional perforated mold surfaces, the porous first layer can be manufactured thinner while reducing porosity and increasing density. Even at high temperatures and during pressing loads, the support structure will maintain the shape of the double-layer structure. Any fluid will also flow in the lateral direction and in any direction within the grid. Therefore, the filtration aid will be effective and well-concentrated. The grid can be modified within the mold. In other words, the structure can be generated according to the load requirements within the mold.

[0044] The mold shown is suitable for both forming and hot pressing. One or more hot pressing units exist adjacent to the forming unit. Figure 6A pair of molds for the hot pressing units are shown. Advantageously, there are two consecutive hot pressing units, but more commonly there are one to three hot pressing units. Figure 6 In this configuration, the lower mold 11 has a double-layer structure according to the invention, while the upper hot press mold 36 has a smooth surface. The mold according to the invention is an excellent match for a heated mold with a smooth product surface. In another pair, the lower mold would be smooth while the upper mold is porous. Opposite porous molds in a continuous hot press unit are the optimal configuration for foam fiber molding machines. Therefore, both sides of the final product will be smooth and dense. Here, the upper hot press mold 36 has an electric heater 37 for heating the mold. Optional cooling or heating channels 38 are shown in dashed circles to improve tooling performance depending on the application. In additive manufacturing, channels can be easily applied inside any part of the mold, similar to the support structure or double-layer structure itself.

[0045] As previously described, in hot pressing, only one mold has a double-layer structure. The other mold is closed, smooth, and heated or cooled. Therefore, one side of the product is ground flat, while water and steam pass through the product via the opposing mold with the double-layer structure. The double-layer structure is highly advantageous for hot pressing because the large porous surface allows for the permeability of steam and water. This provides better support for the product surface compared to conventional solid molds. In the mold, the other mold has holes, leaving many solid-to-solid surface areas that are susceptible to temperature and pressure variations. Efficiency is also affected by the solid narrow edges, which prevent suction and steam from escaping from the sides. Furthermore, the product surface is ground extremely smooth. The new mold is quick and reliable in use. In particular, the disclosed mold is advantageous in hot pressing. Water and steam can quickly pass through the thin and porous layers to reach the open volume. Moreover, in practice, the product can be formed using any other known technique, but then hot-pressed using the mold according to the invention.

[0046] The mold according to the invention has a denser surface and remains sufficiently open across the entire product surface compared to prior art molds with locally manufactured holes, making it suitable for foam-molded fiber products. Additive manufacturing can also achieve porous metal structures in addition to constructing fine perforations. Porous metal structures can be used to replace defined perforations and mimic very fine, undefined meshes, specified by the process parameters of the 3D printer. In this way, the overall porosity of the metal structure can be controlled even if the microstructure is undefined. The porous bilayer structure is supported by a support structure that can be fused with the bilayer structure during the construction process; this is typically a suitable lattice structure. This is an advantage of porous metal structures compared to defined perforated structures; data preparation is less cumbersome because the placement of the support structure is less critical.

[0047] The porous layer allows fluid to drain while leaving fibers on top of the layer. In other words, the mold according to the invention is suitable for forming units in a foamed fiber molding machine. Additive manufacturing allows for optimization of the mold geometry. On the other hand, such a mold is advantageous for the hot pressing unit in a fiber molding machine, regardless of the preceding forming unit. However, compared to slurry, foam requires less water to drain.

[0048] The mold according to the invention is additively manufactured and preferably has a one-piece structure. Alternatively, the mold can have two parts attached to each other, similar to a removable skin. The skin, having a support structure such as a lattice and a base structure, forms a cavity that creates a large open space or void volume within the mold. In other words, said space is defined by the product surface and the base structure forming the bottom of the cavity, which has vertical or slightly inwardly sloping sidewalls towards the bottom of the mold. The cavity also ensures short routes for water, air, and steam to pass through all possible parts of the product surface, and the cavity shapes the contour of said surface, maximizing the space for the product surface within the mold area. Moreover, the thin structure allows for rapid 3D printing of the mold. In practice, the mold wall thickness is surprisingly thin, 2-6 mm, advantageously 2-4 mm, while the base structure thickness is 7-20 mm, advantageously 8-15 mm.

[0049] Advantageously, the bottom or base structure of the mold is slightly thicker than other parts, thus ensuring rigid support for the first layer forming the product surface. The surfaces or walls defining the cavity are as thin as possible, designed precisely to withstand the load during pressing. The bottom or base structure of the mold can have internal chambers with or without grids. These chambers can be used for fluids. At the very least, they reduce the weight of the mold and speed up printing.

Claims

1. A mold for manufacturing molded fiber products, said mold (11) comprising a porous product surface (23) formed by additive manufacturing, characterized in that, The product surface (23) is arranged as a double-layer structure (40) comprising a first layer (41) and a second layer (42) with a cavity (43) between the two layers, wherein the first layer (41) has a porous feature from the cavity (43) to the product surface (23), and the second layer (42) has perforations isolated from the cavity (43) and extends from the product surface (23) through the double-layer structure (40).

2. The mold according to claim 1, characterized in that, The double-layer structure (40) has a thickness of 4-10 mm.

3. The mold according to claim 1 or 2, characterized in that, The first layer (41) and the second layer (42) have a thickness of 0.2-2 mm.

4. The mold according to claim 1 or 2, characterized in that, The first layer (41) has a randomly generated porosity.

5. The mold according to claim 3, characterized in that, The first layer (41) has a randomly generated porosity.

6. The mold according to claim 1 or 2, characterized in that, The perforations of the second layer (42) are composed of 3D-printed pipes (44) that extend from the product surface (23) through the double-layer structure (40).

7. The mold according to claim 6, characterized in that, The diameter of the opening of the pipe (44) is 0.1-2 mm.

8. The mold according to claim 1 or 2, characterized in that, The mold (11) is a uniform 3D printed body.

9. The mold according to claim 1 or 2, characterized in that, The double-layer structure (40) is arranged to be detachably fixed to the skin (24) of the base structure (25).

10. The mold according to claim 9, characterized in that, The base structure (25) is made of a different material than the skin (24).

11. The mold according to claim 1 or 2, characterized in that, The cavity (43) has an inlet (45) that is included inside the mold (11).

12. The mold according to claim 11, characterized in that, The inlet (45) is preceded by a fluid distribution chamber (46) arranged inside the mold (11).

13. The mold according to claim 1 or 2, characterized in that, A second cavity (48) exists inside the mold (11), one side of which is defined by the double-layer structure (40).

14. The mold according to claim 13, characterized in that, An outlet (33) is located at the second cavity (48).

15. The mold according to claim 1 or 2, characterized in that, The properties of the first layer (41) are different in different parts of the product surface (23).

16. The mold according to claim 1 or 2, characterized in that, The properties of the second layer (42) are different in different parts of the product surface (23).

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