A method for evaluating a casting and a casting for a low-pressure casting process

Abstract

The application provides a kind of casting for the evaluation of process rationality of low pressure casting, including sprue, two-stage sprue and cross gate, the sprue is the circular column of pouring inlet, and the two-stage sprue and cross gate are the column with rectangular cross section; the sprue is directly connected with the two-stage sprue, the cross gate is arranged at the connection of the sprue and the two-stage sprue, and the arrangement direction of the cross gate is perpendicular to the sprue; the cross gate is connected with the shrinkage block and multiple parallel arranged flow channels, and the arrangement direction of the shrinkage block and the flow channels is consistent with the arrangement direction of the two-stage sprue; the two-stage sprue is symmetrically provided with test bar and hot crack ring, and the arrangement direction of the test bar and the hot crack ring is consistent with the extension direction of the cross gate. The application can complete the flowability, shrinkage rate, hot crack tendency and mechanical property test of alloy through low pressure pouring test, and the test result data is used as the basis standard to evaluate the process of product, and the casting process is adjusted accordingly.

Description

Technical Field

[0001] This invention relates to a method for evaluating castings, and more particularly to a method for evaluating the process rationality of low-pressure castings, belonging to the field of casting technology. Background Technology

[0002] Low-pressure casting is a process in which molten alloy completes the filling and solidification process under reduced pressure to obtain castings. Due to its advantages such as stable filling, good formability, and dense microstructure, low-pressure casting is widely used in the field of light alloy casting, particularly for producing high-precision aluminum and magnesium alloy castings. During low-pressure casting, the fluidity of the molten metal, the shrinkage rate of the alloy, and its tendency to hot cracking play a crucial role in designing the low-pressure casting process and ensuring product quality. While there are standard testing methods for the casting process performance of alloys using gravity casting, the casting process of low-pressure casting, where the molten metal fills and solidifies under pressure, significantly improves its casting processability.

[0003] With the development of modern industry, parts are becoming lighter and more integrated, and products increasingly use lightweight alloys such as aluminum and magnesium. Furthermore, product structures are becoming more complex, posing significant challenges to the casting process. Although casting CAE technology has developed rapidly, it is still impossible to predict key parameters such as fluidity, cracking, and material properties during the casting process. To prevent product defects or over-quality issues caused by unreasonable casting processes, process experiments are conducted before designing the low-pressure casting process for new products to obtain the low-pressure casting process performance parameters of the materials. Combined with the product's structural characteristics, the product's casting process performance is determined, and appropriate adjustments are made to the corresponding structure. This allows for the development of reasonable casting specifications and the acquisition of high-quality castings.

[0004] A search revealed Chinese patent application number 201510332391.1, which discloses a casting and method for evaluating the hot cracking tendency of high-temperature alloy investment casting. By designing the evaluation casting and method, it guides the improvement of the casting process and provides reasonable suggestions for casting structural design, aiming to reduce the tendency of hot cracking in high-temperature alloy investment castings from the source. However, this scheme can only be used to evaluate the mechanical property parameters of hot cracking tendency, and does not involve the performance parameters of other casting processes. Its evaluation capability is limited and cannot comprehensively consider the rationality of low-pressure casting processes. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes an evaluation method for castings used in low-pressure casting processes. By conducting low-pressure casting tests on the evaluation castings, the fluidity, shrinkage rate, hot cracking tendency, and mechanical properties of the alloy can be tested in one go. Based on the test results, the processability of the product can be evaluated, and the casting process can be adjusted accordingly.

[0006] The technical solution of this invention to solve the above technical problems is: to provide a judging casting for low-pressure casting process, including a sprue, a secondary sprue, and a runner; the sprue is a cylindrical body with a circular pouring inlet, and the secondary sprue and runner are cylindrical bodies with rectangular cross-sections; the sprue and the secondary sprue are directly connected, and the runner is located at the connection between the sprue and the secondary sprue, and the direction of the runner is perpendicular to the sprue;

[0007] The horizontal runner is connected to shrinkage blocks and multiple parallel flow channels, and the arrangement direction of the shrinkage blocks and flow channels is consistent with the arrangement direction of the secondary sprue; test bars and hot crack rings are symmetrically arranged on the secondary sprue, and the arrangement direction of the test bars and hot crack rings is consistent with the extension direction of the horizontal runner.

[0008] In a further defined technical solution of the present invention, the aforementioned evaluation casting for low-pressure casting process has the horizontal sprue symmetrically arranged on both sides of the vertical sprue.

[0009] In the aforementioned evaluation casting for low-pressure casting, the runner is a flat strip of equal width and length, with its thickness gradually increasing from 4-14 mm. The runners are evenly distributed on the symmetrically arranged horizontal runners on both sides. During the casting process, the thinner the runner wall, the worse the filling capacity; the pouring length of runners of different thicknesses represents the alloy fluidity at that wall thickness. The runners on each side of the horizontal runner are connected to the runners through a first ingate, and the first ingates on both sides remain at the same horizontal plane.

[0010] The aforementioned evaluation casting for low-pressure casting processes comprises multiple annular bodies symmetrically arranged on both sides of the secondary sprue. Each annular body has the same outer diameter and thickness, while its width varies progressively. A conformal hot-crack ring chill is placed within each annular body. Under the rapid cooling effect of the chill, the annular portion solidifies preferentially, generating shrinkage stress at the relatively thick ingate, thereby achieving the purpose of testing the alloy's tendency to hot crack. Thinner rings cool faster and are more prone to hot cracking. The hot-crack rings are symmetrically distributed on both sides of the secondary sprue and connected to it via ingates.

[0011] In the aforementioned evaluation casting for low-pressure casting process, the shrinkage blocks are cylindrical structures of the same size distributed on the runner. Each cylindrical shrinkage block is connected to the runner through a shrinkage block ingate of different sizes. The shrinkage block ingate includes a flat ingate and a cylindrical ingate. A shrinkage block chill is provided on the top of the shrinkage block connected to the cylindrical ingate. The shrinkage block chill forms a solidification temperature field from top to bottom, ensuring that the internal structure of the shrinkage block is dense and free of casting defects.

[0012] The aforementioned evaluation castings for low-pressure casting process include test bars that are long bars with a semi-elliptical cross-section, symmetrically arranged on both sides of the end of the secondary sprue. After casting, they can be processed into tensile test bars to evaluate the mechanical properties of low-pressure casting.

[0013] A method for evaluating the rationality of a low-pressure casting process includes the following steps:

[0014] The first step, based on the above content, is to make low-pressure casting evaluation castings, and to make upper and lower sand molds using sand boxes and chills of corresponding sizes.

[0015] The second step is to apply casting coating to the inner cavity of the sand mold. After the coating dries, the sand mold is closed and secured with the help of the locating pins.

[0016] The third step is to melt the alloy according to the casting process requirements, test the liquid metal indicators, and if they are qualified, proceed to the casting process.

[0017] The fourth step involves using low-pressure casting to pour molten metal into the sand mold box from step two, following a pre-set pouring process.

[0018] Fifth step: After the sand mold has completely cooled, open the sand mold and remove the casting;

[0019] The sixth step involves measuring the length of the flow channel in the casting to obtain the flow properties of the alloy under different wall thicknesses during low-pressure casting; detecting the presence of cracks in the hot crack ring using penetrant testing to obtain the cracking tendency of the alloy under low-pressure casting conditions; removing the two shrinkage blocks and the ingate, and comparing their weight percentages to obtain the shrinkage rate of the alloy during low-pressure casting; and machining semi-elliptical test bars to produce standard mechanical property specimens to obtain material mechanical property data.

[0020] The seventh step is to use the above test results parameters as standard data to evaluate the product casting process.

[0021] Compare the pouring direction length dimension with the product drawing. If it is less than the corresponding wall thickness flowability data, the casting process is suitable and can ensure complete filling. Conversely, it indicates insufficient filling, requiring improvement of the casting process. Based on crack tendency data, if the material has a high crack tendency, the product structure, especially at the thick-thin joints, needs process modification to prevent hot cracking. If the material has a low crack tendency, no product process adjustment is needed. Calculate the shrinkage cavity size under free shrinkage conditions for different wall thicknesses based on material shrinkage rate data. Compare with the product technical requirements and apply strong cooling to hot spots exceeding the wall thickness standard. For areas below the wall thickness standard, self-feeding casting is sufficient. Compare with the material mechanical property data. If it meets the product technical specifications, the casting method is acceptable. Otherwise, the material forming process needs adjustment and optimization to meet the technical requirements.

[0022] The beneficial effects of this invention are as follows: Before designing the low-pressure casting process for a new product, this invention tests the relevant casting properties of the low-pressure casting alloy, including fluidity, shrinkage rate, hot cracking tendency, and mechanical property parameters, to determine the process performance of the product in low-pressure casting. This optimizes the product casting process and solves the problem of wasted time and money due to improper casting processes. This invention measures the relevant parameters of the casting in a single low-pressure casting process, thus obtaining the relevant performance parameters of the alloy in low-pressure casting in one go. This invention adopts a "flat casting and vertical pouring" casting process, which is simple to operate, has good process stability, meets the low-pressure casting production conditions for aluminum-magnesium alloys, and can qualitatively and quantitatively determine the low-pressure casting parameters of the alloy, effectively shortening the process development cycle and reducing R&D costs. Attached Figure Description

[0023] The present invention will be further described in detail below with reference to the embodiments given in the accompanying drawings.

[0024] Figure 1 This is a structural schematic diagram of Example 1;

[0025] Figure 2 yes Figure 1 AA section view;

[0026] Figure 3 yes Figure 1 BB cross-sectional view;

[0027] Figure 4 yes Figure 1 CC section view;

[0028] Figure 5 yes Figure 1 DD sectional view;

[0029] Figure 6 yes Figure 1 EE sectional view;

[0030] Figure 7 This is a schematic diagram of the aluminum alloy end cap product in Example 2;

[0031] Figure 8 This is a diagram showing the hot crack ring state of ZL205A low-pressure casting in Example 2.

[0032] In the figure: 1. Runner; 2. Test bar; 3. Hot crack ring; 4. Shrinkage block; 5. Sprue; 6. Stream runner; 7. Secondary sprue; 8. Hot crack ring chill; 9. Shrinkage block chill. Detailed Implementation

[0033] Example 1:

[0034] This embodiment provides a judgment casting for low-pressure casting process, with the structure as follows: Figures 1 to 6As shown, the system includes a sprue 5, a secondary sprue 7, and a runner 6. The sprue 5 is a cylindrical column with a circular inlet, a bottom opening of φ100mm, a height of 120mm, and a draft angle of 5°. The secondary sprue 7 and the runner 6 are cylindrical columns with a square cross-section of 75×75mm. The sprue 5 and the secondary sprue 7 are directly connected. The runner 6 is located at the connection between the sprue 5 and the secondary sprue 7, and its direction is perpendicular to that of the sprue 5. The runner 6 is connected to a shrinkage block 4 and six parallel runners 1, and their arrangement direction is the same as that of the secondary sprue 7. The secondary sprue 7 is symmetrically equipped with test bars 2 and hot crack rings 3, and their arrangement direction is the same as that of the runner 6.

[0035] In this embodiment, the runner consists of six long strips. These runners are used to evaluate the filling capacity of products with different wall thicknesses during low-pressure casting. Each runner has a width of 30mm and a different thickness, increasing from 4mm to 14mm. During the casting process, the thinner the wall, the worse the filling capacity. The pouring length of runners of different thicknesses represents the alloy fluidity of that wall thickness. The six runners are arranged symmetrically at both ends of the runner. Every three runners share a first ingate connected to the runner, and the two first ingates are kept at the same horizontal plane.

[0036] Four rings of hot-cracked alloy are used to evaluate the tendency of the alloy to crack during solidification in low-pressure casting. Each ring is 5 mm thick, with an outer diameter of φ108 mm, and widths of 12.5 mm, 10 mm, 7.5 mm, and 5 mm, respectively, representing the magnitude of the hot-crack tendency. A conformal hot-cracked alloy chill is placed inside each ring. Under the rapid cooling effect of the chill, the annular portion solidifies preferentially, generating shrinkage stress at the relatively thick ingate, thus achieving the purpose of testing the alloy's hot-crack tendency. The thinner the ring, the faster the cooling rate, and the more likely it is to develop hot cracks. The four hot-cracked alloys are symmetrically distributed on both sides of the secondary sprue, connected to the secondary sprue via the ingate.

[0037] The shrinkage blocks consist of two φ80×100mm cylinders used to evaluate the shrinkage rate in low-pressure casting. One shrinkage block has a flat ingate measuring 6×60×40mm. After the molten alloy fills the shrinkage block, the ingate cools and solidifies prematurely, preventing the shrinkage block from receiving compensation from the molten metal and resulting in free shrinkage. The other shrinkage block has a cylindrical ingate of φ45×40mm. It solidifies later than the shrinkage block after filling, thus providing a shrinkage block that receives compensation from the molten metal. Furthermore, a chill is placed on top of this shrinkage block to create a top-down solidification temperature field, ensuring a dense internal structure and eliminating casting defects.

[0038] The test bars consist of two long bars with a semi-elliptical cross-section, measuring 15×15×110mm. They can be machined into tensile test bars for evaluating the mechanical properties of low-pressure casting and are symmetrically arranged on both sides of the end of the secondary sprue.

[0039] Example 2:

[0040] This embodiment provides a method for evaluating the rationality of a low-pressure casting process, using the sand casting process performance of an aluminum alloy end cap made of ZL205A as an example. The product, for instance... Figure 7 As shown, the product wall thickness is 14mm.

[0041] The process performance evaluation method in this embodiment includes the following steps:

[0042] 1. In this embodiment, the same casting method as the product must be used when evaluating the low-pressure casting parameters. The aluminum alloy end cap is formed using sand casting. Based on the casting process diagram for evaluating the performance of the low-pressure casting process, sand molds and corresponding sand boxes and chills are manufactured.

[0043] 2. Using the evaluation casting of Example 1, a sand mold for casting process test is made and coated with casting coating. After the coating dries, the sand mold is closed and secured with positioning pins for later use.

[0044] 3. Melt ZL205A alloy according to the material composition requirements. After degassing and refining to meet the requirements, adjust the temperature of the molten aluminum to 700±10℃ and proceed to the casting process.

[0045] 4. Using low-pressure casting, molten metal is poured into the sand mold according to a pre-set pouring process. The process parameters are as follows: pouring temperature: 690-710℃; liquid rise time: 10-15s; liquid rise pressure: 180-200mbar; mold filling time: 15-30s; mold filling stage pressure: 430-500mbar; holding time: 500s; holding pressure: 600-750mbar.

[0046] 5. After pouring, keep the sand mold at a temperature of more than 8 hours. Once the sand mold has completely cooled, open the sand mold and remove the casting.

[0047] 6. The length of the runner in the casting was measured, and the results are as follows: the lengths of the runners for thicknesses of 4mm, 6mm, 8mm, 10mm, 12mm, and 14mm are 216mm, 227mm, 342mm, 410mm, 483mm, and 513mm, respectively, representing the flowability parameters of the corresponding wall thicknesses under low-pressure conditions in ZL205A alloy sand molds. The main wall thickness of the aluminum alloy end cap product is 14mm. If the Z-axis direction is used as the pouring direction, according to the standard of 513mm for a 14mm wall thickness, the total length of the product in the Z-axis direction is 645mm, which is greater than the standard flowability length of 513mm. Therefore, it is determined that there is a risk of incomplete pouring when pouring the casting in the Z-axis direction. The length in the Y-axis direction is 508mm, which is less than 513mm. According to the flowability standard, the Y-axis can be used as the pouring direction for the casting.

[0048] 7. Penetrant testing of the hot-cracked rings revealed a crack in the thinnest ring (5mm thick), while the other three rings showed no cracks. Figure 8 As shown, during the low-pressure sand casting of ZL205A alloy, hot cracking is prone to occur at the junction of the rapidly chilled iron section and the overheated area. Based on this standard, an inspection of the aluminum alloy end cap product's structural distribution revealed that oil baffles, 4mm thick, are connected to both sides of the bearing hole (50mm thick). During casting, the thin-walled oil baffles cool rapidly, while the thick bearing hole cools relatively slowly. Based on the hot cracking test results, it was determined that the end cap product has a risk of cracking at the junction of thin and thick sections. The casting structure should be optimized by adopting a smooth transition, or by implementing rapid cooling measures for the bearing hole to maintain synchronous cooling with the oil baffles, thus avoiding hot cracking during the casting process.

[0049] 8. After removing the two shrinkage blocks and grinding to remove the gates, their weights were 1.26 kg and 1.33 kg respectively. The percentage difference between the two weights was calculated, yielding a low-pressure shrinkage rate of 94.7% for the ZL205A alloy sand mold. Based on the shrinkage rate, it was determined that a shrinkage cavity of approximately 1 mm would occur at the 18.9 mm wall thickness location during free shrinkage. According to the product's technical requirements, unacceptable pore defects have a maximum diameter exceeding 1 mm. Based on the above test results, when designing the low-pressure casting process for end caps, chilling measures should be adopted for structures with a wall thickness exceeding 18.9 mm to prevent shrinkage defects.

[0050] 9. The two cast test bars were treated with T7 and then processed for tensile testing. The mechanical properties of ZL205A under sand casting conditions were obtained: Rm was 491MPa and 470MPa, Rp0.2 was 399MPa and 401MPa, A was 8.0% and 7.0%, and HB was 144 and 140. The technical requirements for the aluminum ingot end cap product are that the material properties of ZL205A are Rm≥460MPa, A%≥2%, and HB≥110. Through comparison of the results, the material properties of low-pressure cast ZL205A meet the product mechanical property standard requirements.

[0051] 10. Through the above steps 6-9, the fluidity, hot cracking, shrinkage rate and mechanical properties of ZL205A material were tested in low-pressure casting. Based on the data results, the low-pressure casting process of aluminum alloy end cap products was optimized.

[0052] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A judging casting for low-pressure casting process, comprising a sprue (5), a secondary sprue (7), and a runner (6), characterized in that... : The sprue (5) is a cylindrical column with a circular inlet, and the secondary sprue (7) and the horizontal sprue (6) are cylindrical columns with a rectangular cross-section; the sprue (5) is directly connected to the secondary sprue (7), and the horizontal sprue (6) is located at the connection between the sprue (5) and the secondary sprue (7), and the horizontal sprue (6) is arranged perpendicular to the sprue (5); The horizontal runner (6) is connected to a shrinkage block (4) and multiple parallel runners (1). The shrinkage block is a cylindrical structure of the same size distributed on the horizontal runner. The cylindrical structure of each shrinkage block is connected to the horizontal runner through a shrinkage block ingate of different sizes. The shrinkage block ingate includes a flat ingate and a cylindrical ingate. A shrinkage block chill is provided on the top of the shrinkage block connected to the cylindrical ingate. The arrangement direction of the shrinkage block (4) and the runner (1) is consistent with the arrangement direction of the secondary sprue (7). Test bars (2) and hot crack rings (3) are symmetrically arranged on the secondary straight sprue (7), and the arrangement direction of the test bars (2) and hot crack rings (3) is consistent with the extension direction of the horizontal sprue (6).

2. The evaluation casting for low-pressure casting process as described in claim 1, characterized in that... The horizontal gating (6) is symmetrically arranged on both sides of the vertical gating (5).

3. The evaluation casting for low-pressure casting process as described in claim 2, characterized in that... The flow channel (1) is a flat strip with equal width and length, and its thickness gradually increases from 4 to 14 mm; the flow channels (1) are evenly distributed on the horizontal runners (6) arranged symmetrically on both sides.

4. The evaluation casting for low-pressure casting process as described in claim 3, characterized in that... The runner (1) on each side of the horizontal runner (6) is connected to the runner (1) through the first ingate, and the first ingates on both sides are at the same horizontal plane.

5. The evaluation casting for low-pressure casting process as described in claim 1, characterized in that... The hot cracking ring (3) consists of multiple annular bodies symmetrically arranged on both sides of the secondary sprue (7). Each annular body has the same outer diameter and thickness, and the width of the annular body varies step by step. A conformal hot cracking ring chill (8) is placed inside the annular body.

6. The evaluation casting for low-pressure casting process as described in claim 1, characterized in that... The shrinkage blocks (4) are cylindrical structures of the same size distributed on the horizontal runner (6). The cylindrical structures of each shrinkage block (4) are connected to the horizontal runner (6) through shrinkage block inlets of different sizes.

7. The evaluation casting for low-pressure casting process as described in claim 6, characterized in that... The shrinkage block ingate includes a flat ingate and a cylindrical ingate, and a shrinkage block chill (9) is provided on the top of the shrinkage block (4) connected to the cylindrical ingate.

8. The evaluation casting for low-pressure casting process as described in claim 1, characterized in that... The test bar (2) is a long bar with a semi-elliptical cross section, symmetrically arranged on both sides of the end of the secondary straight sprue (7).

9. A method for evaluating the rationality of a low-pressure casting process, characterized in that... Includes the following steps: The first step is to manufacture a low-pressure casting evaluation casting according to the content of the evaluation casting for low-pressure casting process as described in claim 1, and to make upper and lower sand molds by selecting sand boxes and chills of corresponding sizes. The second step is to apply casting coating to the inner cavity of the sand mold. After the coating dries, the sand mold is closed and secured with the help of the locating pins. The third step is to melt the alloy according to the casting process requirements, test the liquid metal indicators, and if they are qualified, proceed to the casting process. The fourth step involves using low-pressure casting to pour molten metal into the sand mold box from step two, following a pre-set pouring process. Fifth step: After the sand mold has completely cooled, open the sand mold and remove the casting; The sixth step involves measuring the length of the flow channel in the casting to obtain the flow properties of the alloy under different wall thicknesses during low-pressure casting; detecting the presence of cracks in the hot crack ring using penetrant testing to obtain the cracking tendency of the alloy under low-pressure casting conditions; removing the two shrinkage blocks and the ingate, and comparing their weight percentages to obtain the shrinkage rate of the alloy during low-pressure casting; and machining semi-elliptical test bars to produce standard mechanical property specimens to obtain material mechanical property data. The seventh step is to use the above test results parameters as standard data to evaluate the product casting process.

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