Injection molding die made by additive manufacturing

Abstract

The mold is an injection molding mold made by additive manufacturing, comprising a mold body (10) having a plurality of boundary surfaces (10a-10f), the plurality of boundary surfaces having at least one molding surface (10b) configured to define a mold cavity, the mold body being formed with the plurality of boundary surfaces and molding surfaces, a functional area portion which is solid and consists of a continuous material structure covering a portion of the mold body (10), and an application area portion (14) which is complementary to the functional area portion (13) of the mold body (10) and consists of a three-dimensional material lattice structure having a regular repetition of unit cells including periodic minimal surfaces, and at least one geometric shape parameter of the periodic minimal surfaces is locally adjusted to form unit cells with different material densities.

Description

[Technical Field]

[0001] The present invention relates generally to injection molds. [Background technology]

[0002] The production of plastic parts by injection molding requires long cooling times, which on average represent two-thirds of the total production cycle, leading to high scrap rates due to part warpage (deformation) caused by thermal stress. Traditional mold manufacturing techniques have several practical problems.

[0003] First of all, the techniques used, such as the use of CNC machines, do not allow the production of cooling channels that match the geometry of the mold. Indeed, these machines use drilling tools with limited movement, so they are only able to drill straight channels in the metal. The channels that result from this process involve very long cooling periods, which lengthen the production cycle and therefore increase the costs for the mold user.

[0004] A further problem resulting from the inadequacy of cooling channels produced by CNC machines is the uneven cooling of the object produced by the mold: because the straight channels cannot match the geometry of the object, some parts cool faster than others, resulting in increased deformation and therefore more of the final product being discarded.

[0005] Finally, traditional production techniques require long planning periods, especially since the programming stage of CNC machines requires the intervention of people with different specific skills. As a result, there is a significant time lag between the customer's request for a mold and its actual production using traditional CNC machines.

[0006] Today, the above mentioned problems are solved using additive manufacturing techniques and matching cooling system designs. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent Application Publication No. 2019 / 0111590A1 Summary of the Invention [Problem to be solved by the invention]

[0008] This solution, however, causes an even bigger problem: the cost of the mold is much higher compared to molds manufactured by conventional techniques. Because the mold is designed in the same way as the conventional technique, it requires a long manufacturing time and a lot of material, which induces a relatively high manufacturing cost.

[0009] From the perspective of potential injection molder customers, high costs represent a deterrent factor, as they require a significant increase in the financial investment required to purchase the molds, with uncertain subsequent savings in return.

[0010] The object of the present invention is to provide an alternative solution for molds for plastic molding made by additive manufacturing.

[0011] It is a further object of the present invention to provide a method for manufacturing such a mold. [Means for solving the problem]

[0012] According to the present invention, there is provided a mold for resin molding, the mold having a mold body having at least one molding surface having a plurality of boundary surfaces, the plurality of boundary surfaces being configured to define a mold cavity, the mold body being made by additive manufacturing, and the mold body comprising: the plurality of boundary surfaces and the at least one molding surface are formed; solid a functional region portion, which is a continuous material structure covering a portion of the mold body; an application area portion, which is a complement of the functional area portion in the mold body, and which is composed of a three-dimensional material lattice structure having a regularly repeating unit cell including periodic minimal surfaces, and at least one geometrical parameter of the periodic minimal surfaces is locally adjusted to form unit cells with different material densities; It has the following characteristics.

[0013] Furthermore, according to the present invention there is provided a method for designing a mold according to any of the preceding claims, the method comprising the steps of: a) providing a three-dimensional geometric model of the mold to be designed; b) determining a functional area portion and an application area portion on the mold body of the mold; c) adjusting the at least one geometric parameter of the periodic minimal surfaces based on a physical model of the mold; d) creating an electronic file storing data representing a digital model for constructing a mold by additive manufacturing; Contains:

[0014] The present invention combines the benefits arising from the full implementation of additive manufacturing with the associated cost reductions, through an optimized design of the molds that allows for significant savings in machining time as well as significant savings in the material used during the manufacturing process.

[0015] The use of additive manufacturing techniques allows for the creation of designs and cooling channels that match the geometry of the mold, allowing for faster and more uniform cooling, resulting in both a reduction in production cycles and the occurrence of deformation and distortion that can cause the object to have to be scrapped.

[0016] Furthermore, the nature of additive manufacturing does not result in the production of material waste, thereby reducing the environmental impact of the activity. Finally, molds are designed and subsequently manufactured with optimal periodic minimal surface structures, such as Triple Periodic Minimal Surface Structures (TPMS structures), leading to a reduction in the amount of material required and machine usage time, two fundamental cost drivers in additive manufacturing.

[0017] The present invention uses additive manufacturing technology, more commonly known as 3D printing, to reduce cooling times by up to 75%, distortion by up to 40%, and manufacturing costs by up to 60% compared to molds manufactured with CNC technology.

[0018] The inventors have found that the TPMS structure outperforms the pillar-based lattice structure disclosed in U.S. Patent Application Publication No. 2019 / 0111590A1, particularly for the injection molding and die casting industries.

[0019] The present invention provides an efficient "green" solution that uses as little as 10% of the material volume required to manufacture a conventional mold.

[0020] In summary, providing a conformal cooling system leads to improved mold cooling cycles with shorter cooling times, reduced effects of warpage or distortion, and better microstructure of the objects being produced by the mold.

[0021] On the other hand, providing a TPMS lattice structure leads to a lighter mold with material only where needed and just enough strength to withstand the localized loads of the mold. [Brief explanation of the drawings]

[0022] Further features and advantages of the invention will be presented in the following detailed description, with reference to the accompanying drawings, given purely by way of non-limiting example, in which: [Figure 1] FIG. 1 is a cross-sectional view of a mold according to the present invention. [Figure 2] Figure 2 shows a comparison between the reticular phase lattice derived from the gyroid plane and the matrix phase lattice. [Figure 3] Figure 3a-c shows a comparison between TPMS structures with different wall thicknesses. [Figure 4] FIG. 4 is a block diagram illustrating a design method according to the present invention. [Figure 5]Figure 5 is a conceptual diagram of a mold showing different stages in the design method. [Figure 6] Figure 6 is a conceptual diagram of a mold showing different stages in the design method. [Figure 7] Figure 7 is a conceptual diagram of a mold showing different stages in the design method. [Figure 8] Figure 8 is a conceptual diagram of a mold showing different stages in the design method. [Figure 9] Figure 9 is a conceptual diagram of a mold showing different stages of the design method. [Figure 10] FIG. 10 is a block diagram further detailing the method of FIG. [Figure 11] FIG. 11 is a further diagram showing the different stages of the design method. [Figure 12] FIG. 12 is a further diagram showing the different stages of the design method. [Figure 13] FIG. 13 is a further diagram showing the different stages of the design method. [Figure 14] FIG. 14 is a further diagram showing the different stages of the design method. [Figure 15] FIG. 15 is a further diagram showing the different stages of the design method. [Figure 16] FIG. 16 is a further diagram showing the different stages of the design method. [Figure 17] FIG. 17 is a further diagram showing the different stages of the design method. [Figure 18] FIG. 18 is a further diagram showing the different stages of the design method. [Figure 19] FIG. 19 is a further diagram showing the different stages of the design method. DETAILED DESCRIPTION OF THE INVENTION

[0023] FIG. 1 illustrates an injection molding die according to the present invention. The die includes a die body 10, which may be fabricated, for example, by additive manufacturing of a metal material. The die body 10 includes multiple boundary surfaces, designated 10a-10f. In the illustrated example, reference 10a indicates the top surface of the die, which includes at least one molding surface 10b configured to define a die cavity MC. Reference 10c indicates the bottom surface of the die, reference 10d indicates the side surface of the die, reference 10e indicates the surface of an injection channel 11 formed in the die body 10, and reference 10f indicates the surface of a conformal cooling channel 12 formed in the die body 10. For simplicity, only one surface of the conformal cooling channel 12 of the die is designated by reference numeral 10f in FIG. 1.

[0024] The mold body 10 has a functional area 13 on the boundary surface where the boundary surfaces 10a-10f are formed. The functional area 13 is solid The functional area portion 11 is a continuous material structure that covers a portion of the mold body 10. In other words, the functional area portion 11 is a portion of the mold body 10 that is free of a grid.

[0025] The mold body 10 further has an application area 14 which is the complement of the functional area 13 in the mold body 10. In other words, the application area 14 is the remaining part of the mold body 10 once the functional area 13 is removed.

[0026] The application area 14 is composed of a three-dimensional material lattice structure with a regular repetition of unit cells containing triply periodic minimal surfaces, such as gyroid surfaces. At least one geometric parameter of the periodic minimal surfaces is locally adjusted to form unit cells with different material densities. In the example shown in Figure 1, this geometric parameter is the wall thickness of the periodic minimal surfaces, which is thicker in the area of ​​the application area 14 facing the injection channel and thinner in the area of ​​the application area 14 facing the mold side 10d.

[0027] The functional area 13 surrounds the ejection channel 11 and the application area 14 surrounds the functional area 13 around the ejection channel 11 .

[0028] The functional area portion 13 also surrounds the conformal cooling channels 12. According to an alternative embodiment (not shown), the application area portion also covers the area where the conformal cooling channels are located. TPMS or other periodic minimal surfaces incorporated inside the conformal cooling channels induce turbulence, thereby improving the cooling transfer efficiency. According to a further embodiment (not shown), the conformal cooling channels are omitted and the TPMS structure is used. structurally necessary The voids formed in the voids can be used to provide cooling channels.

[0029] A method for designing conformal channels 12 in a mold can be as follows.

[0030] An initial thermal simulation of the mold is performed to determine the thermal improvement potential of the mold, leading to improvements in the cooling cycle of the object being manufactured by the mold. This object can be metal in a die-casting process or plastic in an injection molding process. A conformal cooling system is then designed using commercially available CAD software.

[0031] The effect of introducing the conformal cooling system is measured by other thermal simulations to confirm the improvement of the newly designed conformal cooling over the initial thermal simulations.

[0032] After this is done, a structural analysis simulation is performed on the mold to check for any deformation in the mold.

[0033] The method for designing periodic minimal surfaces on the mold can be as follows, assuming the TPMS is a gyroid for simplicity.

[0034] A gyroid is a triply periodic minimal surface discovered by NASA scientist Alan Schoen in 1970. A gyroid divides space into two regions of equal area. The mathematical description of a gyroid surface can be approximated trigonometrically by a short formula (1).

[0035]

number

[0036] ki is the periodicity of the TPMS function, defined by equation (2); ni is the number of cell repetitions in x, y, and z; and Li is those is the absolute size of the structure in the dimension of . The lattice of the matrix phase borders two disconnected void regions. solid These differ from network phase structures, which are composed of a single solid and contains only one void area. This is illustrated in Figure 2.

[0037]

number

[0038] The TPMS formula accounts for 3D surfaces, which are voids and solid By finding the isosurface of U = 0 in equation (1), we can generate matrix-phase gyroid structures with any cell number and volume fraction.

[0039] Filling one of the two separate regions results in a porous solid with a volume fraction of 0.5. Another approach to obtaining a solid from a gyroid surface is to "offset" the original surface, i.e., to create two oppositely oriented surfaces where any point is a fixed distance from the original surface, and fill the space between them. The resulting solidThe third approach is a hybrid of the previous two methods, creating an "offset" of the original surface, separating the space into two non-equivolumetric regions (one with a volume fraction greater than 0.5 and the other less than 0.5), and filling one of these regions to form a solid.

[0040] In equation (1), t effectively controls the cell wall thickness and therefore the volume fraction ρ* of the resulting lattice structure. The relationship between t and ρ* is specific to each TPMS. Figures 3a-c show a comparison between three lattice structures with different wall thicknesses and, therefore, different material densities. In particular, Figure 3a shows a lattice structure with thinner walls, while Figure 3c shows a lattice structure with thicker walls.

[0041] Furthermore, the three basic concepts described above can be applied to other periodic minimal surfaces or surfaces such as gyroids to expand the scope of geometric shape design.

[0042] These periodic solids, called gyroid lattices, offer a promising alternative to classical truss-like lattice structures. One of the major drawbacks of using such structures is the stress concentrations resulting from abrupt changes in curvature at the outer surface. These stress concentrations dramatically reduce the structure's resistance to loads and its lifespan under cyclic loading. Gyroids, on the other hand, belong to the family of triply periodic minimal surfaces (TPMSs), a subset of a larger class of surfaces with constant mean curvature (CMC). In particular, TPMSs are classified by having zero or controlled changes in mean curvature at all points, addressing a major drawback of implementing standard strut-based lattice structures in solids.

[0043] Additionally, pillar-based lattice structures have overhang issues that require support structures for successful manufacturing, which is not required with TPMS, as each layer acts as a support for the successive layer.

[0044] Referring to Figure 4, the method of the present invention includes providing a three-dimensional geometric model of the mold to be designed (step 100). This model defines the geometric features of the mold, such as the interface, molding surfaces, injection channels, cooling channels, etc. Figures 5 and 6 show a perspective view and a cross-sectional view, respectively, of this 3D model.

[0045] The above-mentioned grid structure is then implemented in the 3D model (step 110). This step is performed by defining a so-called "application domain". The initial 3D model is a closed region bounded by surface boundaries. solid These surface boundaries are divided into two categories: functional surface boundaries that should remain unchanged, such as the mold cavity / core surface 10b and the cooling channel surface 10f, and non-functional surface boundaries, such as the mold base plane 10c. Once the two surface boundaries are defined, a lattice structure is incorporated into the model by the following method.

[0046] First, the offsets of the functional boundaries are obtained, i.e., a set of surfaces where any point is at a given distance from the original functional boundary set is obtained. The set of closed boundaries is then constructed by adding surfaces that fill the space between the offset set of surfaces and the original functional boundary surfaces, ultimately closing them. solid A so-called functional area 13' (shown in FIG. 7) is obtained.

[0047] Second, subtract the functional areas from the initial 3D model. This can be done with Boolean operations. The resulting solid is referred to as the "application area", indicated at 14' in Figure 8. Figure 9 shows a 3D model with both a functional area 13' and an application area 14'.

[0048] Third, the application area 14' is filled with a grid structure, and the resulting grid is finally summed into a functional area.

[0049] With reference to Figures 10-18, a method for applying the lattice structure to the application area 14' will now be described.

[0050] As shown in Fig. 11, a mesh is generated for the entire mold (functional area and application area), and physical models (forces, pressures, thermal loads, support constraints, etc.) are applied to the nodes of the generated mesh (steps 200 and 210 in Fig. 10). Fig. 12 shows an example of applying boundary conditions to the molding surface (forces on mesh nodes).

[0051] Topology optimization is then performed to provide an optimal solution by placing materials within the application domain to achieve the required loads imposed by the boundary conditions defined in step 210 .

[0052] The optimization problem can be divided into three main parts. 1- Model mesh definition: This involves the meshing of the application and functional domains. Model attributes, e.g., the materials used, are also defined at this stage. Figures 13 and 14 show the mechanical properties (elastic modulus) of one cell of the gyroid structure in greyscale. 2- Optimization Objective: The optimization function is determined at this stage. The objective function used here is to identify the optimal distribution of material density to minimize structural compliance. 3-Optimization constraints: Finally, optimization constraints are specified, for example, that the total amount of material removed should not exceed 30% of the total amount of material available.

[0053] After several optimization iterations, an optimal density is obtained for the entire structure (step 220). Figure 15 shows the optimal volume fraction for each FE element.

[0054] For optimization, the "application domain" is mapped so that each node of the FEM model is assigned to a given cell unit of the lattice structure. This map of nodes to lattice cells is called the "geometry map." As mentioned above, gyroid lattice properties can be locally adjusted by geometric parameters, such as wall thickness. These geometric features indicate the local density of a given lattice cell. These geometric features can be captured in the FEM calculation by appropriately fitting local polynomial functions that describe the lattice behavior. Thus, a "property map" of the lattice structure is created within the "application domain," and local polynomial functions for the elements of the FEM calculation are obtained as the average property of the nodes based on their respective positions in the "geometry map" and the property of the corresponding cell unit in the "property map."

[0055] Once FEM provides a solution field, the "property map" of the lattice can be modified to optimize the entire structure. All local properties are reset to aim for a more homogeneous solution and reduced stress or thermal load for a given criterion. This last method is repeated until the solution meets the engineering specifications. This ensures an improved lifespan and reduces the chance of early cycle failure of the parts.

[0056] The final lattice design is then obtained by setting the local geometry of each unit cell according to their density (step 120 in FIG. 4 and step 230 in FIG. 10) based on the optimized "characteristic map" at the end of the FEM homogenization process. Figure 16 shows the application area before the optimization process, while Figures 17 and 18 show the application area after the optimization process. Figure 18 is a 45-degree cross-sectional cut of the application area.

[0057] The digitized, e.g., CAD file, along with the manufacturing parameters is then stored in a cloud / server and accessed by the customer to initiate the additive manufacturing process (step 30 in Figure 4). Figure 19 shows a cross-section of the sliced ​​model incorporating the manufacturing parameters.

Claims

1. An injection mold having a mold body (10) having a plurality of boundary surfaces (10a-10f), the plurality of boundary surfaces having at least one molding surface (10b) configured to define a mold cavity, the mold body being produced by additive manufacturing, the mold body comprising: a functional area portion (13) in which the plurality of boundary surfaces and the at least one molding surface are formed, the functional area portion (13) being a solid, continuous material structure covering a portion of the mold body; an application area (14) of the mold body (10) that is complementary to the functional area (13), and that comprises a three-dimensional material lattice structure having a regular repetition of unit cells containing periodic minimal surfaces, at least one geometrical parameter of the periodic minimal surfaces being locally adjusted to form unit cells with different material densities; A mold comprising:

2. the periodic minimal surface is a triply periodic minimal surface; The mold according to claim 1 .

3. the periodic minimum surface is a gyroid; The mold according to claim 2.

4. The mold body has at least one injection channel (11), the functional area (13) surrounds the at least one emission channel (11); The application area (14) surrounds the functional area (13) around the at least one ejection channel (11). The mold according to any one of claims 1 to 3.

5. the mold body having at least one conformal cooling channel (12); the functional area (13) surrounding the at least one conformal cooling channel (12); The mold according to any one of claims 1 to 4.

6. the mold body having at least one conformal cooling channel; the application area portion surrounding the at least one conformal cooling channel; The mold according to any one of claims 1 to 4.

7. cooling channels are formed by voids inevitably generated by the periodic minimum surface structure; The mold according to any one of claims 1 to 4.

8. A method for designing a mold according to any one of claims 1 to 7, comprising: a) providing a three-dimensional geometric model of the mold to be designed; b) determining the functional area and the application area (13, 14; 13', 14') on the mold body (10) of the mold; c) adjusting at least one geometric parameter of the periodic minimum surfaces based on a physical model of the mold; d) creating an electronic file storing data representing a digital model for constructing said mold by additive manufacturing; A method having the following.

9. The step c) c1) generating a mesh for both the functional domain portion and the application domain portion, and applying the physical model to a plurality of nodes of the generated mesh; c2) determining material density values ​​at the nodes of the generated mesh based on the applied physical model; c3) determining the value of said at least one geometric parameter of said periodic minimal surfaces according to said determined value of material density; 9. The method of claim 8, comprising:

Images