Step thermoforming die, method for manufacturing the same, and use thereof

Abstract

This invention provides a stepped thermoforming mold with internal water channels. The mold's elemental composition includes carbon, silicon, and manganese, with the following mass fractions: carbon content 2.8%–3.2%, silicon content 1.5%–1.8%, and manganese content 0.8%–1.0%. This stepped thermoforming mold enables the application of stepped thermoforming processes and meets the quality requirements for stepped thermoforming molds, ensuring the smooth operation of the process.

Description

Technical Field

[0001] This invention belongs to the field of thermoforming mold cooling technology, specifically relating to a stepped thermoforming mold, its preparation method, and its application. Background Technology

[0002] Step-by-step thermoforming, as a novel thermoforming production technology, has broad application prospects. Referring to the invention patent with publication number CN 111515287 A, entitled "A Step-by-Step Hot Stamping Forming Method for Ultra-High Strength Steel Plates," the ultra-high strength steel plate is formed through a series of operations including blanking, cold stamping, heating and holding, hot stamping, quenching and pressure holding, and surface treatment. This method, through segmented temperature control of the ultra-high strength steel plate, can achieve integrated forming of complex-shaped parts while simultaneously meeting the performance requirements of different components.

[0003] Meanwhile, this process further improves water cooling efficiency and surface fit by setting water channels inside the hot mold, ensuring the uniformity of crystal structure in all areas of the product.

[0004] However, hot molds require high-pressure water flow without leakage during the quenching and holding process, which poses a significant quality challenge for current hot mold castings. In commonly used technologies, the quality defects of ordinary hot molds are fully exposed when applied to tiered thermoforming processes, leading to unexpected conditions such as water leakage and posing safety hazards to the operation of the tiered thermoforming process. Summary of the Invention

[0005] To address the technical problem of water leakage under high pressure caused by quality defects in the hot forming molds used in the aforementioned common technologies, this invention provides a stepped thermoforming mold with internal water channels. The stepped thermoforming mold is composed of carbon, silicon, and manganese, with the following mass fractions: carbon content of 2.8%–3.2%, silicon content of 1.5%–1.8%, and manganese content of 0.8%–1.0%.

[0006] Furthermore, the thickness of the auxiliary ribs of the stepped thermoforming mold is 25-35mm, the thickness of the main ribs and the panel direction ribs of the stepped thermoforming mold is 35-45mm, and the thickness of the ribs at the component connection points and processing hole positions of the stepped thermoforming mold is 80-85mm.

[0007] Furthermore, the auxiliary ribs of the stepped thermoforming mold have a thickness of 30mm, the main ribs and panel ribs of the stepped thermoforming mold have a thickness of 40mm, and the ribs at the component connections and machining hole positions of the stepped thermoforming mold have a thickness of 80mm.

[0008] Furthermore, the rib spacing of the stepped thermoforming mold is 200-300mm.

[0009] Furthermore, the ribs in the stepped thermoforming mold are arranged in an interlaced manner to avoid the formation of cross-shaped ribs.

[0010] This invention also provides a method for preparing a stepped thermoforming mold, comprising the following steps:

[0011] Molten iron is poured into a mold and cooled to obtain a stepped thermoforming mold as described above; wherein the elemental composition of the molten iron includes carbon, silicon, and manganese, and by mass fraction, the carbon content in the stepped thermoforming mold is 2.8% to 3.2%, the silicon content is 1.5% to 1.8%, and the manganese content is 0.8% to 1.0%; the contents of the mold include gravel and lost foam.

[0012] Furthermore, the material of the lost foam casting is an expandable copolymer resin material.

[0013] The present invention also provides the application of the tiered thermoforming mold as described in any one of the above claims or the tiered thermoforming mold prepared by the preparation method described in any one of the above claims in the tiered thermoforming process.

[0014] Further steps include:

[0015] The base material is cut to obtain ultra-high strength steel plates;

[0016] The ultra-high strength steel plate is cold-stamped at room temperature to obtain a pre-formed part;

[0017] The preformed part is heated and kept at a temperature greater than 870°C.

[0018] The preformed part is transferred to a stepped thermoforming mold, and the upper mold of the stepped thermoforming mold is heated to a set temperature as it descends until it comes into contact with the preformed part.

[0019] After the tiered thermoforming mold is closed, water is circulated into the water channel of the tiered thermoforming mold under pressure holding conditions to cool it until the temperature of the preformed part drops below 200°C, thus obtaining the formed part; wherein, the pressure holding time is 5 to 8 seconds, and the pressure holding pressure is 20 to 30 MPa.

[0020] The formed parts are cooled to room temperature by air cooling, and then the formed parts are subjected to surface treatments in sequence, including shot blasting, dust extraction and oil spraying.

[0021] Furthermore, the substrate is selected from 22MnB5, 27MnCrB5 or 37MnB4.

[0022] Compared with the prior art, the present invention has at least the following advantages:

[0023] This invention adjusts the chemical composition of the material of the tiered thermoforming mold, increasing the carbon and silicon content while reducing the manganese content, significantly improving the fluidity of molten iron, reducing the differences in structure and properties caused by cooling due to different wall thicknesses, improving the consistency of cast iron structure, and reducing the probability of shrinkage cavities.

[0024] In addition, this invention promotes metallographic graphitization and stabilizes pearlite during the hot die casting process through the synergistic adjustment of various components. The enhanced strength and hardness of the hot die make it highly adaptable to stepped thermoforming processes, avoiding common water leakage issues during application and preventing plastic deformation of the hot die during stamping, thereby improving the service life of the hot die. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the stepped thermoforming mold structure in Embodiment 1 of the present invention;

[0027] Figure 2 This is a schematic diagram of the wall thickness control of the stepped thermoforming mold in Embodiment 1 of the present invention;

[0028] Figure 3 This is a schematic diagram of the rib spacing adjustment of the stepped thermoforming mold in Embodiment 1 of the present invention;

[0029] Figure 4 This is a schematic diagram illustrating how the tiered thermoforming mold avoids the generation of cross-shaped ribs in Embodiment 1 of the present invention.

[0030] Figure 5 This is a schematic diagram illustrating the use of a stepped thermoforming mold to avoid deep hole machining in Embodiment 1 of the present invention;

[0031] Figure 6 This is a combustion experiment scene diagram of lost foam casting applied to the casting of tiered thermoforming molds in Embodiment 2 of the present invention;

[0032] Figure 7 The images shown are from Embodiment 4 of the present invention and are related to the state detection of the stepped thermoforming mold after water and penetrant are introduced (the left column shows the state detection of the stepped thermoforming mold after water is introduced, and the right column shows the state detection of the stepped thermoforming mold after penetrant is added).

[0033] Figure 8 This is a metallographic diagram of the casting before corrosion in Embodiment 3 of the present invention;

[0034] Figure 9 This is a metallographic structure diagram of the gradually corroded structure in Example 3 of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0037] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0038] Among commonly used technologies, the stepped thermoforming process, as a novel thermoforming production technology, requires water to be pumped into the water channels of the stepped thermoforming mold under high temperature and pressure conditions to achieve temperature drop of the pre-formed parts. Although this process can achieve uniform cooling of the formed parts in the water cooling system with high water cooling efficiency and surface fit rate, it places extremely high demands on the strength and water leakage prevention performance of the stepped thermoforming mold (the influencing indicators include the generation of quality defects such as cold shuts, incomplete filling, porosity, sand adhesion, sand inclusion, sand holes, bulging sand, and shrinkage cavities).

[0039] The above-mentioned stepped thermoforming process includes the following steps:

[0040] S1. The base material is cut to obtain an ultra-high strength steel plate.

[0041] In some embodiments, the substrate is selected from 22MnB5, 27MnCrB5 or 37MnB4.

[0042] S2. The ultra-high strength steel plate is cold-stamped at room temperature to obtain a pre-formed part.

[0043] S3. The preformed part is heated and kept at a temperature greater than 870°C.

[0044] In some embodiments, the heating time of the preformed part is 250s, the holding time is 50s, the temperature inside the heating furnace is 900℃, and the holding temperature of the preformed part is >870℃.

[0045] S4. The preformed part is transferred to the stepped thermoforming mold. The upper mold of the stepped thermoforming mold is heated to the set temperature during the descent until it contacts the preformed part.

[0046] In some embodiments, the set temperature can be 680°C.

[0047] In some specific embodiments, a robotic arm can be used to quickly remove the preformed part from the heating furnace and transfer it onto a stepped thermoforming mold.

[0048] S5. After the stepped thermoforming mold is closed, water is circulated into the water channel of the stepped thermoforming mold under pressure holding conditions to cool it until the temperature of the preformed part drops below 200°C, thus obtaining the formed part; wherein, the pressure holding time is 5 to 8 seconds, and the pressure holding pressure is 20 to 30 MPa.

[0049] S6. The formed parts are cooled to room temperature by air cooling, and then the formed parts are subjected to surface treatments of shot blasting, dust extraction and oil spraying in sequence.

[0050] Based on the foregoing, in order to meet the strength requirements and water-proof requirements of the tiered thermoforming mold in the tiered thermoforming process, the present invention provides a tiered thermoforming mold with water channels inside. The chemical composition of the tiered thermoforming mold includes: carbon 2.8% to 3.2%, silicon 1.5% to 1.8%, and manganese 0.8% to 1.0%.

[0051] By adjusting the chemical composition of the tiered thermoforming mold, the proportions of carbon, silicon, and manganese were adjusted, while copper was added to promote graphitization and stabilize pearlite, thus enabling the tiered thermoforming mold to balance strength and toughness.

[0052] For example, the chemical composition of the stepped thermoforming mold includes: 2.9% to 3.0% carbon, 1.6% to 1.7% silicon, and 0.9% to 1.0% manganese.

[0053] In some embodiments, the stepped thermoforming mold can be obtained by casting, including the steps of: pouring molten iron into a mold filled with lost foam and gravel, and cooling to obtain a casting, namely the stepped thermoforming mold.

[0054] Among these methods, by adjusting the chemical composition of the tiered hot forming mold: increasing the carbon and silicon content and reducing the manganese content, the fluidity of molten iron is improved, the differences in structure and properties caused by cooling due to different wall thicknesses are reduced, the consistency of cast iron structure is improved, and the probability of shrinkage cavities is reduced.

[0055] The present invention also enhances the strength and toughness of the tiered thermoforming mold by adding copper to promote graphitization and stabilize pearlite.

[0056] In other embodiments, the material of the lost foam casting can be an expandable copolymer. The copolymer (STMMA) has the characteristics of low carbon residue, large decomposition amount, and fast gas emission of small molecules. The application of expandable copolymer can improve the quality problems such as porosity, shrinkage cavities and shrinkage porosity inside the casting, thereby significantly improving the water-proof performance of the stepped thermoforming mold.

[0057] In comparison, common EPS materials used in conventional technologies are not only inferior to expandable copolymer materials in various parameters, but also often cause various quality problems during the casting process, failing to meet the requirements of tiered thermoforming processes.

[0058] In order to make the stepped thermoforming mold meet the requirements for water leakage prevention under high water pressure, the present invention uses the following means to optimize the casting structure and improve the internal quality of the casting, thereby avoiding defects such as cold shut, insufficient pouring, porosity, sand adhesion, sand inclusion, sand hole, and sand expansion.

[0059] Reference Figure 2 As shown, in some embodiments, the thickness of the auxiliary ribs of the tiered thermoforming mold can be controlled to be 25-35 mm;

[0060] The thickness of the main ribs and panel directional ribs of the tiered thermoforming mold can be controlled within 35-45mm;

[0061] The rib thickness at the component connection points and machining hole locations of the tiered thermoforming mold can be controlled to 80mm.

[0062] By controlling the rib thickness, defects such as air holes and cracks inside the stepped thermoforming mold can be reduced, thereby optimizing its water-proof function.

[0063] For example, the wall thickness of castings that do not play an important role in the tiered thermoforming mold can be hollowed out to make the wall thickness of each functional rib casting uniform.

[0064] Among them, the main reinforcement refers to the main reinforcing bars.

[0065] Auxiliary ribs refer to thin ribs.

[0066] Panel ribs refer to the ribs that run horizontally.

[0067] Reference Figure 3As shown, in some embodiments, the rib spacing can be controlled between 100mm and 300mm. This ensures the strength of the stepped hot forming mold while making it easier to fill and clean sand during the casting process, resulting in more uniform heat dissipation. It also helps to keep the flow of molten iron stable during the pouring process, avoiding casting defects such as sand adhesion, sand inclusion, sand holes, and sand expansion.

[0068] For example, the rib spacing of the stepped thermoforming mold can be 200-300mm.

[0069] Reference Figure 4 As shown, in some embodiments, the ribs in the tiered thermoforming mold can be staggered to avoid the formation of cross-shaped ribs. The principle is that staggering the ribs can avoid the formation of large hot spots and allow the gas generated by lost foaming to escape, thereby ensuring the compactness of the internal structure of the tiered thermoforming mold and reducing quality problems such as porosity, shrinkage cavities, and shrinkage porosity inside the casting.

[0070] Reference Figure 5 As shown, in some embodiments, the water passage position of the casting can be avoided during deep hole machining. The reason is that deep hole machining will expose areas with large internal hot nodes and significant casting defects in the casting, causing water leakage in the mold at these locations. Therefore, the deep hole machining location is adjusted to be outside the water passage position.

[0071] The present invention also provides an application of the stepped thermoforming mold as described above in the stepped thermoforming process.

[0072] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided:

[0073] Example 1

[0074] Optimization of the structure of tiered thermoforming molds

[0075] See Figure 1 The schematic diagram of the stepped thermoforming mold structure shows that the casting structure is optimized by reasonably controlling the wall thickness of the casting (i.e., the stepped thermoforming mold), adjusting the rib spacing of the stepped thermoforming mold, avoiding the generation of cross ribs, and avoiding deep hole machining at the water passage position of the casting.

[0076] See Figure 2To ensure the performance of the thermoforming mold is met, the thickness of auxiliary ribs in the casting should be controlled between 25mm and 35mm, with a value of 30mm. The thickness of main ribs and panel directional ribs should be controlled between 35mm and 45mm, with a value of 40mm. The rib thickness at locations where other components are installed should be controlled between 45mm and 55mm, with a value of 50mm. The rib thickness at locations with deep machined holes should be controlled at 80mm. Non-critical ribs should be hollowed out to ensure uniform wall thickness for all functional ribs. Properly controlling the rib thickness can improve defects such as cold shuts, incomplete pouring, and uneven cooling rates that cause internal porosity and cracks in the casting.

[0077] See Figure 3 The spacing of the ribs in the casting was adjusted to be controlled between 100mm and 300mm. This not only ensures the strength of the mold, but also facilitates the filling and cleaning of sand during casting, ensures uniform heat dissipation, and keeps the flow of molten iron stable during the pouring process, thus avoiding casting defects such as sand adhesion, sand inclusion, sand holes, and sand expansion.

[0078] See Figure 4 The cross ribs, while ensuring the normal performance of the mold, adjust the position of the ribs and stagger them to avoid large hot spots at the center of the cross ribs. This also facilitates the discharge of gas and carbon slag generated by lost foam casting, ensuring the density of the internal structure of the casting and reducing quality problems such as porosity, shrinkage cavities, shrinkage porosity, and cracks in the casting.

[0079] See Figure 5 By moving the deep holes requiring further machining outside the water passage, the surface quality of the casting is better during the casting process due to its good heat dissipation and rapid expulsion of gases and impurities. If deep holes are machined at the water passage location, the surface layer of the casting will be damaged, exposing poor-quality internal parts and causing leakage. Moving the deep holes away from the water passage location avoids this problem.

[0080] Example 2

[0081] Material change for lost foam model:

[0082] Table 1. Comparison of EPS and STMMA Material Parameters

[0083]

[0084]

[0085] The table above compares the parameters of ordinary EPS material and expandable copolymer (STMMA) material in lost foam casting models. Figure 6This is a comparison of the residues after combustion experiments of the two materials. The residues of EPS and STMMA copolymer boards after combustion are approximately one-eighth to one-tenth of those of EPS of the same volume. Furthermore, the copolymer (STMMA) material has characteristics such as less carbon residue, greater decomposition volume, and faster emission of small molecule gases. Replacing the foam model material with copolymer (STMMA) can improve quality problems such as porosity, shrinkage cavities, and shrinkage porosity inside the casting.

[0086] Example 3

[0087] Adjustment of chemical composition of casting material

[0088] Table 2. Experimental Reports on Adjusted Chemical Composition of Castings

[0089]

[0090]

[0091] The table above shows the experimental test report after adjusting the casting material composition. Regarding the adjustment of the casting material's chemical composition, the carbon and silicon content was increased, while the manganese content was decreased. This improved the fluidity of the molten iron, reduced differences in microstructure and properties caused by cooling variations due to different wall thicknesses, improved the consistency of the cast iron microstructure, and reduced the likelihood of shrinkage cavities. Because the increased carbon and silicon content and decreased manganese content reduced the casting's hardness and strength, copper was added to promote graphitization, stabilize pearlite, and increase the casting's hardness and strength.

[0092] Example 4

[0093] Pre- and post-implementation inspection of casting condition for leak-proofing process

[0094] See Figure 7 The casting showed no leakage after the anti-leakage process was implemented, and no defects such as cracks or pores were found in the casting under the penetrant test after the anti-leakage process was implemented.

[0095] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A stepped thermoforming mold, characterized in that, The stepped thermoforming mold has internal water channels. The elemental composition of the stepped thermoforming mold includes carbon, silicon, and manganese. By mass fraction, the carbon content in the stepped thermoforming mold is 2.8%~3.2%, the silicon content is 1.5%~1.8%, and the manganese content is 0.8%~1.0%. The auxiliary ribs of the stepped thermoforming mold have a thickness of 25~35mm, the main ribs and panel ribs of the stepped thermoforming mold have a thickness of 35~45mm, and the ribs at the component connections and processing hole positions of the stepped thermoforming mold have a thickness of 80~85mm. The rib spacing of the stepped thermoforming mold is 200~300mm; The ribs in the stepped thermoforming mold are arranged in an interlaced manner to avoid the formation of cross ribs.

2. The stepped thermoforming mold according to claim 1, characterized in that, The auxiliary ribs of the stepped thermoforming mold have a thickness of 30mm, the main ribs and panel ribs of the stepped thermoforming mold have a thickness of 40mm, and the ribs at the component connections and machining hole positions of the stepped thermoforming mold have a thickness of 80mm.

3. A method for preparing a stepped thermoforming mold, characterized in that, Including the following steps: Molten iron is poured into a mold and cooled to obtain a stepped thermoforming mold as described in any one of claims 1 to 2; wherein the elemental composition of the molten iron includes carbon, silicon, and manganese, and by mass fraction, the carbon content in the stepped thermoforming mold is 2.8% to 3.2%, the silicon content is 1.5% to 1.8%, and the manganese content is 0.8% to 1.0%; the contents of the mold include gravel and lost foam.

4. The preparation method according to claim 3, characterized in that, The material of the lost foam casting is an expandable copolymer resin.

5. The application of a tiered thermoforming mold as described in any one of claims 1 to 2, or a tiered thermoforming mold prepared by the preparation method as described in any one of claims 3 to 4, in a tiered thermoforming process.

6. The application according to claim 5, characterized in that, Including the following steps: The base material is cut to obtain ultra-high strength steel plates; The ultra-high strength steel plate is cold-stamped at room temperature to obtain a pre-formed part; The preformed part is heated and kept at a temperature greater than 870°C. The preformed part is transferred to a stepped thermoforming mold, and the upper mold of the stepped thermoforming mold is heated to a set temperature as it descends until it comes into contact with the preformed part. After the tiered thermoforming mold is closed, water is circulated into the water channel of the tiered thermoforming mold under pressure holding conditions to cool it until the temperature of the preformed part drops below 200°C, thus obtaining the formed part; wherein, the pressure holding time is 5~8s, and the pressure holding pressure is 20~30 MPa. The formed parts are cooled to room temperature by air cooling, and then the formed parts are subjected to surface treatments in sequence, including shot blasting, dust extraction and oil spraying.

7. The application according to claim 6, characterized in that, The substrate is selected from 22MnB5, 27MnCrB5 or 37MnB4.

Images