Sand core structure for die casting, die casting mold, and die casting molding process

Abstract

The application relates to the technical field of die casting, and particularly discloses a sand core structure for die casting, a die casting die and a die casting forming process. The sand core structure for die casting comprises a positioning filling rod and a sand core main body wrapping the positioning filling rod. The compressive strength of the positioning filling rod is greater than that of the sand core main body. The positioning filling rod is made of a breathable material. The positioning filling rod is embedded in the sand core main body, the compressive strength of the sand core is improved, the wall thickness of the die casting part can be well controlled, the air holes formed in the die casting part can be reduced, the internal cracking and deformation of the sand core can be reduced, the problems of poor filling of the die casting part, cold lines, internal air holes, slag holes and non-standard wall thickness can be improved, and the surface smoothness of the inner cavity of the die casting part and the yield of the finished product can be improved.

Description

Technical Field

[0001] This application relates to the field of die casting technology, and more specifically, to a sand core structure, a die casting mold, and a die casting process for die casting. Background Technology

[0002] As machinery and equipment develop towards lightweight and high-performance designs, the structures of aluminum alloy castings, as components of these devices, are becoming increasingly complex, leading to significantly higher requirements for the quality and safety performance of castings across the industry chain. For castings with complex internal structures or undercuts, companies typically employ investment casting, using salt cores or sand cores to assist in the casting process. However, investment castings often suffer from drawbacks such as low surface finish, low dimensional accuracy, low surface hardness, and unsuitability for forming thin-walled parts.

[0003] Die casting effectively overcomes the aforementioned shortcomings of traditional casting. However, die casting involves filling the mold in a very short time, which can easily lead to gas entrapment and affect the quality of the die casting. Furthermore, the sand cores used in die casting require very high strength. During the filling process, the sand core must withstand the impact of the molten metal at high speed and pressure. For workpieces with at least some areas having a wall thickness of less than 3mm or uneven thickness, pressure-boosting die casting is necessary. Pressure-boosting die casting generally presents the following problems: Figure 1 The cracking of the sand core results in a low yield of die castings, mainly manifested in poor filling, internal porosity of die castings, and substandard wall thickness of die castings. Summary of the Invention

[0004] In order to improve the yield of die-cast parts, this application proposes a sand core structure, a die-casting mold, and a die-casting process from the perspective of improving sand cores and die-casting molding process, and adopts the following technical solutions.

[0005] In the first aspect, this application proposes a sand core structure for die casting and adopts the following technical solution.

[0006] A sand core structure for die casting includes a positioning filler rod and a sand core body enclosing the positioning filler rod; the compressive strength of the positioning filler rod is greater than the compressive strength of the sand core body; the positioning filler rod is made of a permeable material.

[0007] By adopting the above technical solution, a permeable and high-strength positioning filler rod is embedded in the sand core body, which improves the compressive strength of the sand core, reduces internal cracking and deformation problems, helps to solve problems such as poor filling, cold lines, internal porosity, slag porosity and substandard wall thickness in die castings, and improves the yield of die castings.

[0008] In some embodiments, the positioning filler rod is made of solid breathable steel, hollow extruded sintered copper, or hollow breathable steel.

[0009] By adopting the above technical solutions, these materials have high strength and high permeability, which can meet the requirements of pressure die casting, help solve the problem of internal cracking of sand cores and the problem of substandard wall thickness of die castings, and improve the yield of die castings.

[0010] In some embodiments, the end wall thickness of the sand core body is 10-20 mm.

[0011] By adopting the above technical solution, the sand core body of this thickness balances permeability and strength, meeting the requirements of die casting. If the wall thickness is too large, the risk of internal cracking increases and the compressive strength will decrease; if the wall thickness is too small, the protection of the positioning filler rod is weakened, which is not conducive to the recycling of the positioning filler rod after multiple uses.

[0012] In some embodiments, the end wall thickness of the sand core body is 14–16 mm.

[0013] By adopting the above technical solution, using a sand core body with a wall thickness of 14-16mm helps to avoid phenomena such as poor filling of die castings, internal porosity of die castings, substandard wall thickness of die castings, and cold lines, and the effect of improving the yield is more significant.

[0014] In some embodiments, the positioning filler rod is made of hollow, breathable steel.

[0015] In some embodiments, the positioning filler rod has a protruding end that extends beyond the core body, the protruding end serving as a gas inlet for heptafluoropropane gas.

[0016] By adopting the above technical solution, heptafluoropropane gas can be introduced through the air inlet, reducing the probability of oxidation of the die casting. The positioning filler rod made of breathable material is conducive to venting during die casting, reducing the probability of defects such as porosity in the die casting.

[0017] In some embodiments, the positioning filler rod includes a first rod and a second rod; the sand core body includes a first core and a second core; the second core has an integrally formed main stem and branches; the first rod penetrates the first core and the main stem, so that the first core is in close contact with the second core; the second rod is embedded in the branches.

[0018] By adopting the above technical solution, and by setting multiple positioning filler rods and multiple sand core bodies, the wall thickness of the irregular or branched sand core bodies is within an appropriate range, so that the sand core structure has good air permeability and high strength. This split structure design is beneficial to the preparation of die castings with branched structures.

[0019] Secondly, this application proposes a die-casting mold and adopts the following technical solution.

[0020] A die-casting mold includes a sand core structure for die casting as described above, and further includes a mold frame and an injection punch. The mold frame has a feed port, an injection chamber for containing molten metal, a runner, a forming cavity, and a slag and vent outlet connected in sequence; one end of the runner and the forming cavity is an ingate; the sand core structure is installed in the forming cavity; and the injection punch is movably embedded in the injection chamber.

[0021] By adopting the above technical solution, the yield of die-cast parts prepared using this die-casting mold is significantly improved compared to solid sand cores or hollow sand cores without positioning filler rods.

[0022] Thirdly, this application also proposes a die-casting molding process and adopts the following technical solution.

[0023] A die-casting process is disclosed, which uses a die-casting mold as described above for die casting. The die-casting process includes an initial stage, an injection chamber stage, an inner gate stage, a filling stage, and a compaction stage.

[0024] In the initial stage, the injection punch pushes the molten metal through the feed port at a first velocity of 0.06-0.10 m / s.

[0025] During the injection chamber stage, the injection punch pushes the molten metal to fill the injection chamber at a second velocity of 0.12-0.18 m / s.

[0026] During the ingate stage, the injection punch pushes the molten metal to fill the ingate at a third velocity, which is 0.16-0.28 m / s.

[0027] During the filling stage, the injection punch pushes the molten metal to fill the forming cavity at a fourth velocity, which is 0.26-0.30 m / s.

[0028] During the compaction stage, when the molten metal is just poured into the slag discharge and exhaust port, the injection punch is activated to pressurize the molten metal in the forming cavity, and the molten metal fills the mold and cools to form the shape.

[0029] By adopting the above technical solution and setting four injection speeds, it helps to eliminate air bubbles in the cavity during die casting, making it less prone to gas entrapment, improving die casting defects such as porosity and cold lines, and increasing the yield. This die casting process is a pressure-boosting die casting process, which can produce workpieces with at least some parts having a wall thickness of less than 3mm and uneven thickness. Due to the use of a sand core filled with positioning filler rods, the sand core has strong resistance to high-speed and high-pressure impact of molten metal, significantly reducing die casting defects and improving the yield. When the molten metal is just poured into the slag and vent, it cools at the slag and vent. At this time, the pressure boosting is started, and the molten metal in the forming cavity still has good fluidity, making it easy to fill various small spaces, such as narrow thickness spaces, resulting in good forming. If the pressure boosting is delayed, the molten metal cools and its fluidity decreases, which may cause insufficient filling of small spaces. If the pressure boosting is started too early, the molten metal is prone to spraying out of the slag and vent, reducing the sealing of the forming cavity, which may also cause insufficient filling of small areas. Filling the mold means filling the small areas of the forming cavity.

[0030] In some embodiments, prior to the initial stage, heptafluoropropane gas is introduced into the positioning filler rod, the heptafluoropropane gas passing sequentially through the positioning filler rod and the sand core body, and filling the molding cavity.

[0031] By adopting the above technical solutions, the probability of oxidation of castings is reduced and the surface finish of the inner cavity of castings is improved.

[0032] In some embodiments, the second velocity is 0.14 m / s, the third velocity is 0.18 m / s, and the fourth velocity is 0.28 m / s.

[0033] By adopting the above technical solution, the yield of die-cast parts is higher compared to other speed solutions within the range.

[0034] In summary, the sand core structure, die casting mold, and die casting process proposed in this application have at least one of the following beneficial effects: This sand core structure incorporates a permeable and high-strength positioning filler rod within the sand core body, enhancing the sand core's compressive strength. When applied to die-casting molds, it can reduce internal cracking and deformation issues within the sand core, helping to improve defects such as poor filling, cold lines, internal porosity, slag inclusions, and substandard wall thickness in die-castings. This also improves the wall thickness accuracy of die-castings, enhances the surface finish of the die-casting cavity, and increases the yield of die-castings.

[0035] This die-casting process features four injection speeds, which helps eliminate air bubbles in the cavity during die casting, reduces the risk of gas entrapment, and improves die-casting defects such as porosity and cold marks, thereby increasing the yield. This pressure-boosting die-casting process can produce workpieces with at least some areas having a wall thickness of less than 3mm and with uneven thickness. Due to the use of a sand core filled with positioning filler rods, the sand core has strong resistance to high-speed, high-pressure impacts from molten metal, significantly reducing die-casting defects and improving the yield. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating the cracking phenomenon in sand cores as described in the background art.

[0037] Figure 2 This is a cross-sectional view of a sand core structure for die casting and a die casting part proposed in Example 1.

[0038] Figure 3 This is a cross-sectional view of another sand core structure for die casting and a die casting as proposed in Example 2.

[0039] Figure 4 for Figure 3 A cross-sectional view of the main body of the sand core in the sand core structure.

[0040] Figure 5 This is a schematic diagram of a die-casting mold proposed in Example 3.

[0041] Figure 6 This is the main effect diagram of the signal-to-noise ratio of each factor proposed in Example 4.

[0042] Figure 7 This is the main effect diagram of the mean values ​​of each factor proposed in Example 4.

[0043] Figure 8 The image shows a comparison of the smoothness of the inner cavity of the die casting obtained by die casting with a solid sand core and without heptafluoropropane gas as proposed in Example 4, and the die casting obtained by die casting with a sand core wrapped with a positioning filler rod and filled with heptafluoropropane gas.

[0044] Reference numerals: 1. Positioning filler rod; 2. Sand core body; 201. End; 3. Die casting; 3. Air inlet; 101. First core; 21. Second core; 22. Main body; 221. Branch; 222. First rod; 11. Second rod; 12. Mold frame; 4. Injection punch; 5. Molten metal; 6. Feed port; 41. Injection chamber; 42. Flow channel; 43. Molding cavity; 44. Slag discharge and venting port; 45. Ingate; 46. Detailed Implementation

[0045] The following description, in conjunction with the accompanying drawings, details the sand core structure, die-casting mold, and die-casting process of this application.

[0046] Example 1 like Figure 2 A sand core structure for die casting includes a positioning filler rod 1 and a sand core body 2 that wraps around the positioning filler rod 1. The preparation process of the sand core structure can be as follows: wrapping the sand core on the surface of the positioning filler rod 1, extruding and molding, and drying to obtain the sand core structure, so that the sand core body 2 is tightly attached to the outer surface of the positioning filler rod 1.

[0047] Embedding the positioning filler rod 1 into the sand core body 2 reduces the wall thickness of the sand core, improves its compressive strength, reduces internal cracking and deformation, and shortens the drying time, thus achieving energy conservation and emission reduction. Using this sand core structure for die casting helps solve problems such as poor filling, cold lines, internal porosity, slag inclusions, and insufficient wall thickness in the die casting 3, improving the yield of the die casting 3. If the sand core is made hollow without filling it with the positioning filler rod 1, although the permeability of the sand core is improved, its resistance to molten metal impact is significantly reduced, failing to meet the requirements of die casting, especially pressure die casting, and making it impossible to produce thin-walled parts.

[0048] The positioning filler rod 1 can be made of solid permeable steel, solid sintered copper, solid gypsum, hollow extruded forged aluminum, hollow extruded sintered copper, or hollow permeable steel, etc. These materials have high strength, can meet the requirements of pressure die casting, and help improve phenomena such as insufficient wall thickness of die casting 3, thereby increasing the yield. Among them, solid permeable steel, hollow extruded sintered copper, or hollow permeable steel have better permeability, which has a better effect on improving the yield of die castings.

[0049] Solid sintered copper is made by sintering copper powder, causing the surface of the copper powder to melt and adhere, such as a solid round bar, and has good air permeability. Hollow extruded forged aluminum is made by melting, casting, and extruding aluminum, such as a hollow aluminum bar, and has high strength but poor air permeability. Hollow extruded sintered copper is made by first extruding copper powder into a hollow structure, such as a hollow round bar, and then sintering it, causing the copper powder to adhere, and has good air permeability.

[0050] The positioning filler rod 1 can be designed as a round rod or an irregular shape, and can be recycled after the sand core body 2 is removed.

[0051] The size of the positioning filler rod 1 can be designed in various specifications to control the thickness of the sand core body 2. The wall thickness of the end 201 of the sand core body 2 can be 10-20mm, such as 10mm, 15mm, 20mm, etc. This thickness range of the sand core body 2 balances permeability and strength, meeting the requirements of die casting. If the wall thickness is too large, the risk of internal cracking increases and the compressive strength will decrease. If the wall thickness is too small, the protection of the positioning filler rod 1 is weakened, which is not conducive to the recycling of the positioning filler rod 1 after multiple uses. Setting the positioning filler rod 1 in the sand core body 2 saves the amount of sand used in the sand core, and the positioning filler rod 1 can be recycled, thus reducing the cost of the sand core.

[0052] To improve the porosity and slag inclusions that occur during die casting of the die casting part 3, using a permeable material to prepare the positioning filler rod 1 is an effective method. The permeable positioning filler rod 1 facilitates venting during die casting, preventing slag inclusions and porosity inside the die casting part 3, and also preventing issues such as insufficient wall thickness, thus improving production yield. Furthermore, the positioning filler rod 1 can also have a protruding end extending from the sand core body 2. This protruding end can serve as a gas inlet 101, through which heptafluoropropane gas can be introduced to expel air and reduce the probability of oxidation of the die casting part 3. Heptafluoropropane also has flame-retardant and fire-extinguishing properties, significantly reducing the possibility of the sand core (such as a resin sand core) burning due to contact with high-temperature molten metal.

[0053] If the material used to prepare the positioning filler rod 1 is solid aluminum or solid iron, although the cost is reduced and the strength meets the requirements of pressure die casting, it is not breathable and is not conducive to venting during die casting. This will lead to a large number of defects such as slag holes, air holes, and thickened walls inside the die casting 3, resulting in a low production yield.

[0054] In some embodiments, the end 201 of the sand core body 2 has a wall thickness of 15mm, and the positioning filler rod 1 is made of hollow, breathable steel. Through testing, the 15mm wall thickness of the sand core body 2 and the hollow, breathable steel positioning filler rod 1, compared to sand core bodies 2 with adjacent wall thicknesses and positioning filler rods 1 made of other materials, significantly improve defects such as cold lines and increase the yield.

[0055] Example 2 like Figure 3 As shown, this embodiment provides a sand core structure for die casting, including a positioning filler rod 1 and a sand core body 2 that wraps the positioning filler rod 1. It adopts the same technical solution as Embodiment 1. The only difference from Embodiment 1 is that the sand core body 2 includes a first core 21, a second core 22, a first rod 11 and a second rod 12.

[0056] like Figure 4 The second core 22 has an integrally formed main stem 221 and branch 222, which can be two forked structures of the second core 22. A first rod 11 penetrates the first core 21 and the main stem 221, ensuring the first core 21 is tightly attached to the second core 22. A second rod 12 is embedded in the branch 222. By using multiple positioning filler rods 1 and multiple sand core bodies 2, the wall thickness of the sand core bodies 2 is kept within an appropriate range, giving the sand core both high strength and good permeability, and also facilitating demolding. This design solves the problem of preparing die-cast parts 3 with branched structures.

[0057] Example 3 like Figure 5A die-casting mold includes the sand core structure for die casting as described in Example 2, and also includes a mold base 4 and an injection punch 5. A positioning filler rod 1 can be positioned within the mold base. The mold base has a feed port 41, an injection chamber 42 for containing molten metal 6, a runner 43, a forming cavity 44, and a slag and vent 45 connected in sequence. The end connecting the runner and the forming cavity is an ingate 46. The thickness of the ingate 46 is 0.5-2 mm; the sand core structure is installed within the forming cavity 44. The injection punch 5 is movably embedded within the injection chamber 42.

[0058] When using this die-casting mold for die casting, the air in the forming cavity 44 can be evacuated first, and then heptafluoropropane gas can be introduced. The heptafluoropropane gas passes through the positioning filler rod 1 and the sand core body 2, thus filling the entire forming cavity 44 to replace the air and other gases in the cavity. Then, the molten metal 6, such as aluminum liquid, is injected. This die-casting mold can reduce the back pressure in the forming cavity 44 during die casting (the pressure inside the forming cavity 44 that is pressurized and then directed in the opposite direction towards the feed port 41), effectively controlling the wall thickness of the die casting 3. It also reduces the porosity formed inside the die casting 3 due to the large amount of gas generated by the sand core (such as resin sand core) coming into contact with the high-temperature molten metal 6 (such as molten aluminum liquid) caused by the sand core (such as resin sand core). This improves the surface finish and mechanical properties of the casting's inner cavity. Compared with solid sand cores or hollow sand cores without the positioning filler rod 1, the yield of die castings 3 prepared using this die-casting mold is significantly improved.

[0059] Example 4 This embodiment provides a die-casting process. A curved pipe-type die-cast part 3 for robots is used as the manufacturing object, with wall thicknesses ranging from 2.0 to 4.5 mm in various parts. Through improvements in the sand core structure and die-casting process, the requirements of pressure-intensified die-casting can be met, thereby improving the quality of the die-cast part 3, including improving the surface finish, dimensional accuracy, and porosity of the inner cavity of the die-cast part 3.

[0060] In this embodiment, the die-casting mold of Embodiment 3 is used for die casting, with Toyo 350T as the die-casting machine, the molten metal 6 being molten aluminum at 660-670℃, and the mold temperature being 280-290℃.

[0061] The die casting process includes the gas filling stage, the initial stage, the injection chamber stage 42, the ingate stage 46, the mold filling stage, and the compaction stage, as detailed below.

[0062] During the inflation stage, the die-casting mold is first evacuated, and then heptafluoropropane gas is injected through the inflation port 101 of the positioning filler rod 1. The inflation time is 3 seconds. The heptafluoropropane gas passes through the positioning filler rod 1 and the sand core body 2 in sequence and fills the molding cavity 44. After inflation, the gas pressure in the molding cavity 44 is 0.3 MPa.

[0063] In the initial stage, the injection punch 5 pushes the molten metal 6 through the feed port 41 at a first velocity. The first velocity is set to 0.08 m / s.

[0064] In stage 42 of the injection chamber, the injection punch 5 propels the molten metal 6 to fill the injection chamber 42 at a second velocity of 0.12-0.18 m / s.

[0065] In the ingate 46 stage, the injection punch 5 pushes the molten metal 6 to fill the ingate 46 at a third velocity. The third velocity is 0.16-0.28 m / s.

[0066] During the filling stage, the injection punch 5 pushes the molten metal 6 to fill the forming cavity 44 at a fourth velocity. The fourth velocity is 0.26-0.30 m / s.

[0067] During the compaction stage, when the molten metal 6 is just poured into the slag discharge and exhaust port 45, the injection punch 5 is activated to pressurize the molten metal 6 in the forming cavity 44, and the molten metal 6 fills the mold and cools to form the shape.

[0068] This pressure-boosting die-casting process features four injection speeds, which helps eliminate air bubbles in the cavity during die casting, reduces the risk of gas entrapment, and minimizes die-casting defects such as porosity and cold spots, thereby improving the yield. This pressure-boosting die-casting process can produce workpieces with at least some areas having a wall thickness of less than 3mm and with uneven thickness. Due to the use of a sand core filled with positioning filler rods 1, this sand core has strong resistance to high-speed, high-pressure impacts from molten metal, significantly reducing die-casting defects and improving the yield.

[0069] The first speed has a relatively small impact on the yield. The following will verify the impact of the second speed, third speed, fourth speed, the timing of pressurization during the compaction stage, the thickness of the end 201 of the sand core body 2, and the material of the positioning filler rod 1 on the yield.

[0070] For the fourth, third, and second velocities, which are the injection velocities at each stage, the values ​​were verified to be 0.26, 0.16, 0.12; 0.28, 0.18, 0.14; and 0.30, 0.28, 0.18, respectively, with the unit being m / s.

[0071] Regarding the timing of pressurization during the compaction stage, this process involves activating the injection punch 5 to pressurize the molten metal 6 in the forming cavity 44 as soon as the molten metal 6 is poured into the slag discharge and venting port 45. The molten metal 6 then fills the mold and cools to form the final shape. In this machine and mold, when the molten metal 6 is just poured into the slag discharge and venting port 45, the corresponding "pressurization switching position" in the machine parameters is 315mm, which is the stroke position of the injection punch 5. The following verifies the cases where the "pressurization switching position" is 315mm, 323mm, and 331mm.

[0072] The thickness of the end 201 of the sand core body 2 was verified to be 10mm, 15mm, and 20mm respectively.

[0073] For the material of the positioning filler rod 1, the following scenarios were verified: solid permeable steel, solid sintered copper, solid gypsum, hollow extruded forged aluminum, hollow extruded sintered copper, and hollow permeable steel.

[0074] The above four verification factors (positioning filler material, end 201 thickness of the sand core body, pressurization switching position, and injection speed) are summarized in Table 1 below.

[0075] Table 1. Validation factors and factor levels For the four important factors affecting the yield, Taguchi orthogonal verification was performed respectively, as shown in Table 2 below. The optimal embodiment was calculated based on the data obtained from the die casting verification.

[0076] Table 2. Four factors affecting yield (orthogonal experiment) The average wall thickness of the castings in Table 2 is 4.07–4.25 mm, and the wall thickness in some parts of the castings is 2–3 mm.

[0077] After the experiment, the signal-to-noise ratio response tables for each factor were obtained as shown in Table 3 below. Figure 6 The mean response tables for each factor are shown in Table 4 below. Figure 7 We will conduct data and effect diagram analysis.

[0078] Table 3. Signal-to-noise ratio response of each factor Signal-to-noise ratio response table Wang Da Regarding Table 3 and Figure 6 The Taguchi signal-to-noise ratio analysis is as follows.

[0079] The order of significant factors is: material > pressurization location > core thickness > injection velocity. The order of significant factors is based on the signal-to-noise ratio variation of each factor in Table 3, or... Figure 6 The range of change of each curve is used to determine this.

[0080] The optimal combination of factors is as follows: the material is hollow, breathable steel; the pressure switching position is 315mm; the thickness of the sand core body 2 is 15mm; and the injection velocities are 0.28m / s (fourth velocity), 0.18m / s (third velocity), and 0.14m / s (second velocity). The optimal factor is the level value with the highest signal-to-noise ratio for each factor, which is obtained from the parameters in Table 1.

[0081] Table 4. Response Table of Mean Values ​​for Each Factor Mean Response Table Regarding Table 4 and Figure 7 The Taguchi signal-to-noise ratio analysis is as follows.

[0082] The order of significant factors is: material > pressurization location > core thickness > injection speed.

[0083] Optimal combination of factors: material is hollow permeable steel, pressure switching position is 315mm, thickness of sand core body 2 is 15mm, and injection speeds are fourth speed 0.28m / s, third speed 0.18m / s, and second speed 0.14m / s.

[0084] The predicted optimal combination of factors was introduced for verification and designated as Experiment 19. The die-casting production verification was carried out under the same machine and conditions, and the final yield was 85%, which was higher than Experiment 1-18 in Table 2.

[0085] In addition, test example 20 was added, with the thickness of the sand core body 2 being 20 mm. All other test conditions were the same as in test example 19. The final yield of the die casting was 82%, which was lower than the yield of the die casting in test example 19.

[0086] In Experiments 16, 17 and 18, the surface finish of the inner cavity of the die-cast part 3 obtained from the experiment was Ra25-Ra12.5.

[0087] For test examples 16, 17 and 18, if the test is changed to a non-gas-filling stage, that is, the mold cavity is not evacuated and heptafluoropropane gas is not filled, while other test conditions are the same, test examples 21, 22 and 23 are obtained by changing the test conditions in sequence. After die casting, the surface finish of the inner cavity of the die casting 3 is Ra50.

[0088] like Figure 8 As shown: A is the die casting obtained in Experiment 22 without the introduction of heptafluoropropane gas, and its inner cavity surface is relatively rough; B is the die casting obtained in Experiment 17 by first removing the air from the molding cavity 44 before die casting, and then introducing heptafluoropropane gas, so that the heptafluoropropane gas passes through the positioning filling rod 1 and the sand core body 2, and then fills the entire molding cavity 44 to replace the air and other gases in the cavity, and then injecting the molten metal 6. The inner cavity surface of the die casting is relatively smooth.

[0089] Experiments show that filling the casting with heptafluoropropane gas before die casting reduces the probability of oxidation and improves the surface finish of the casting's inner cavity.

[0090] In summary, the permeability of the positioning filler rod 1 material, the pressure switching position, the thickness of the sand core body 2, and the injection speed all affect the wall thickness accuracy and yield of the die casting 3. The sand core structure and die casting process designed in this embodiment can reduce slag porosity and air porosity inside the die casting 3, improve the wall thickness accuracy and inner cavity surface finish of the die casting 3, and significantly improve the yield.

[0091] The above are merely preferred embodiments of this application. The scope of protection of this application is not limited to the above embodiments. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of this application should also be considered to fall within the scope of protection of this application.

Claims

1. A die-casting molding process, characterized in that, Die casting is performed using die casting molds; The die casting mold includes a sand core structure for die casting, and also includes a mold frame (4) and an injection punch (5); the mold frame (4) has a feed port (41), an injection chamber (42) that can hold molten metal (6), a runner (43), a forming cavity (44), and a slag discharge and venting port (45) connected in sequence; one end of the runner (43) and the forming cavity (44) is an ingate (46); the sand core structure is installed in the forming cavity (44); the injection punch (5) is movably embedded in the injection chamber (42); The sand core structure includes a positioning filler rod (1) and a sand core body (2) that wraps the positioning filler rod (1); the compressive strength of the positioning filler rod (1) is greater than the compressive strength of the sand core body (2); the positioning filler rod (1) is made of a breathable material. The end (201) wall thickness of the sand core body (2) is 10-20mm; The positioning filling rod (1) includes a first rod (11) and a second rod (12); the sand core body (2) includes a first core (21) and a second core (22); the second core (22) has an integrally formed main stem (221) and branch (222); the first rod (11) penetrates the first core (21) and the main stem (221), so that the first core (21) is in close contact with the second core (22); the second rod (12) is embedded in the branch (222); The positioning filling rod (1) has a protruding end that protrudes from the sand core body (2), and the protruding end is used as a gas filling port (101) for heptafluoropropane gas. The core body (2) is a resin core; The die casting process includes an inflation stage, an initial stage, an injection chamber (42) stage, an inner gate (46) stage, a mold filling stage, and a compaction stage; During the inflation stage, the die-casting mold is first evacuated, and then heptafluoropropane gas is injected through the inflation port (101) of the positioning filling rod (1). The inflation time is 3 seconds. The heptafluoropropane gas passes through the positioning filling rod (1) and the sand core body (2) in sequence and fills the molding cavity (44). After inflation, the gas pressure in the molding cavity (44) is 0.3 MPa. In the initial stage, the injection punch (5) pushes the molten metal (6) through the feed port (41) at a first speed of 0.06-0.10 m / s; in the injection chamber (42) stage, the injection punch (5) pushes the molten metal (6) to fill the injection chamber (42) at a second speed of 0.12-0.18 m / s; in the ingate (46) stage, the injection punch (5) pushes the molten metal (6) to fill the ingate (46) at a third speed of 0.16-0.28 m / s; During the filling stage, the injection punch (5) pushes the molten metal (6) to fill the forming cavity (44) at a fourth speed; the fourth speed is 0.26-0.30 m / s; during the compaction stage, when the molten metal (6) is just poured into the slag discharge and exhaust port (45), the injection punch (5) is activated to pressurize the molten metal (6) in the forming cavity (44), and the molten metal (6) fills and cools to form.

2. The die-casting molding process according to claim 1, characterized in that, The second speed is 0.14 m / s, the third speed is 0.18 m / s, and the fourth speed is 0.28 m / s.

3. The die-casting molding process according to claim 1, characterized in that, The end (201) wall thickness of the sand core body (2) is 14~16mm.

4. The die-casting molding process according to claim 1, characterized in that, The positioning filler rod (1) is made of solid breathable steel, hollow extruded sintered copper or hollow breathable steel.

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