Casting method of semi-arc thin-wall complex structure casting

Abstract

The invention relates to a casting method of a semi-arc thin-wall complex structure casting, and belongs to the technical field of casting. During process scheme planning, an anti-deformation structure is designed; a disc-shaped cross gate and a multi-point flow gate matched with the shape of a casting are designed, so that the casting structure can be stabilized while the internal quality of the casting is guaranteed through feeding of the casting; anti-deformation ribs are designed, so that the structural stability of the casting is improved, and the casting is prevented from deforming in casting and heat treatment processes; a process boss is designed, so that the stability of the machining process is ensured, and the part deformation problem caused by the machining process is reduced; through fluorescence detection and X-ray detection, the surface quality and the internal metallurgical quality of the casting produced according to the method meet the standard requirements of II-type castings in 11-CL-113B; the percent of pass of parts after casting machining can reach 95% or above.

Description

Technical Field

[0001] The invention relates to a casting method for a semi-arc thin-walled complex structure casting, belonging to the technical field of casting. Background Art

[0002] ZL116 aluminum alloy offers excellent casting properties, including high fluidity, airtightness, and a low tendency to hot cracking and porosity. It also possesses good corrosion resistance and weldability. This alloy is suitable for complex, load-bearing parts and parts requiring high airtightness, operating at temperatures below 200°C for extended periods. Due to its excellent casting properties and lack of cracking or porosity, it is suitable for a variety of casting methods, including sand, metal, and investment casting. It can be used to manufacture parts with complex shapes, thick or thin walls, or those requiring airtightness. Complex curved parts integrally cast using ZL116 aluminum alloy exhibit multi-surface, irregular structures, large dimensions, and uneven wall thicknesses. These parts contain both thick areas prone to forming hot spots and thin areas prone to undercasting. Therefore, the gating system design must ensure both mold filling quality and control casting deformation. Its quality and precision directly impact the subsequent assembly of related components.

[0003] The presence of defects inside castings is the main reason for the low qualification rate of castings. The defects are mainly looseness in thick parts, inclusion defects in thin-walled parts, or defects exposed on the surface of castings after processing, which lead to the scrapping of castings, resulting in cost waste and extended production cycle. Summary of the Invention

[0004] The purpose of the present invention is to provide a casting method for semi-arc thin-walled complex structure castings, thereby improving the qualified rate of castings and reducing production costs and production cycles.

[0005] According to one aspect of the present application, a method for casting a semi-arc-shaped thin-walled complex structure casting is provided, wherein the semi-arc-shaped thin-walled complex structure casting has a symmetrical triangular arc shape, wherein the two sides of the triangular arc are variable thickness arc surfaces that are thick at both ends and thin in the middle, the outward side of the arc surface is a smooth surface, and the inward side of the arc surface is provided with horizontal and vertical cross-intersecting ribs, one longitudinal rib is located on the symmetry axis of the triangular arc structure, and the remaining longitudinal ribs are symmetrically distributed on both sides;

[0006] Specifically, the casting has a complex structure and a symmetrical triangular arc structure. The two sides of the triangle are curved surfaces with gradually changing wall thickness, and the middle belly plane is a large curved surface. The arc width on both sides is 121mm and the length is 949mm. There are three layers of structure on the arc surface, and each layer is 15mm thick. The middle of the two arc abdomens is connected by a curved surface with a wall thickness of 4mm. One side is a smooth curved surface, and the other side is divided and supported by 5 horizontal and vertical ribs. The middle longitudinal rib is located in the center of the symmetrical triangle, with a length of 712mm and a thickness of 8mm. The height follows the arc surface and the maximum height is 50mm. There is a rib on each side, 575mm long and 6mm thick, and the distance between each two ribs is 199mm. There are 2 ribs in the horizontal direction, with a length of 996mm and 775mm, a distance of 215mm and 135mm (the distance from the bottom airtight groove), and a thickness of 8mm. The intersection of the cross ribs forms a total of 6 hot spots. The nearly triangular opening at the bottom of the arc surface is connected by a U-shaped airtight groove with a thickness of 35mm, and the rest of the parts are naturally transitioned.

[0007] It is formed by precision sand mold differential pressure casting process;

[0008] The following steps are involved:

[0009] A bottom pouring system is used to fill the mold from bottom to top. The mold is provided with a disc-shaped runner according to the shape of the casting, and an inner gate is provided on the disc-shaped runner. After molding, the pouring gate is cut and cleaned, heat treated and shaped to obtain the semi-arc-shaped thin-walled complex structure casting.

[0010] The specific position of the ingates is determined by simulating the filling process and solidification process of the casting to find out the parts of the casting that are prone to undercasting and the parts that are prone to shrinkage and shrinkage cavities, and the ingates are set at these specific positions.

[0011] The inner gates of the thinner arc surface and the cross-intersection of the ribs are rounded to prevent undercasting defects in the thin-walled areas and facilitate shrinkage compensation at the cross-rib areas.

[0012] The inner gate of the thicker arc surface is square to reduce the occurrence of loose defects.

[0013] The disc-shaped runner can cover all the ingates.

[0014] The mold is provided with anti-deformation ribs at the arc surface and opening of the casting, and the anti-deformation ribs are cleaned after heat treatment.

[0015] The heat treatment comprises the following steps:

[0016] First, solution heating is performed, then quenching is performed, and finally aging heating is performed;

[0017] The temperature of the solution heating is 530-540°C and the holding time is 10-16 hours;

[0018] The quenching temperature is 20-100°C and the transfer time is less than 15s;

[0019] The aging heating temperature is 170-180° C., and the holding time is 6-8 hours.

[0020] The shape correction is carried out 2 to 4 hours after solution heating;

[0021] After the shaping is completed, quenching and aging heating are carried out.

[0022] Specifically, based on the structural characteristics and performance requirements of the casting, a precision sand mold differential pressure casting process is used. First, the casting is simulated without a gating system to determine the location of the casting's thermal nodes. The thickness of the casting varies greatly, and the solidification time and sequence will show a step difference during the solidification process depending on the wall thickness. The casting solidifies in several stages from the beginning to the final solidification. The order of solidification is large thin wall areas, cross rib junctions, thin-thick junctions, and the thickest wall areas. The gating system is designed based on the thermal nodes that appear in these four stages.

[0023] Its core technologies are as follows:

[0024] The gating system utilizes a bottom-pouring method, ensuring smooth, bottom-up filling of the molten aluminum, making it less susceptible to oxidation and slag inclusion defects. An ingate is designed at the bottom of the casting, along with a disc-shaped runner and multi-point dispersed gates that conform to the casting's shape. This ensures smooth feeding channels in the disc-shaped runner before the casting solidifies. The runner design follows the disc shape of the casting, with multi-point ingates positioned on the curved surface. The runner covers all ingates, ensuring both mold filling and feeding. Cylindrical ingates are also positioned on thin-walled surfaces and cross ribs to prevent undercast defects in thin-walled areas and facilitate feeding of the cross ribs. The cross-sectional area of the conformal runner is 80mm×60mm; the ingates are 8 square ingates with a cross-sectional area of 60mm×40mm and 3 square ingates with a cross-sectional area of 60mm×50mm; in order to prevent under-casting defects in thin-walled areas and facilitate shrinkage compensation of cross ribs on thin walls, 14 ingates with a diameter of Φ35mm and 7 ingates with a diameter of Φ30mm are set on the 4mm thin wall surface and cross ribs.

[0025] Specifically, casting includes the following steps:

[0026] Step 1: Modeling: Modeling is done according to the process plan, and key dimensions are measured during the modeling process.

[0027] Step 2: Melting: Heat the crucible to 200°C-300°C and add the ZL116 ingot charge. The charge is preheated to above 150°C and the surface is degreased and rusted. Once the alloy reaches 690°C-700°C, pure magnesium is added. After the alloy is uniformly melted, perform a pre-furnace chemical composition analysis and a sample is cast for rapid spectroscopic analysis. Refining is performed after the spectroscopic analysis passes. Refining is performed using an argon rotary injection process. After refining, the refining effect is measured using an online density test method. Samples with a density ≥2.62 kg / dm³ are considered qualified. Modification: The modifier is an aluminum-strontium alloy (Al-Sr) with a strontium content of 10%. Add 0.015%-0.03% of the total charge weight. After the Al-Sr alloy is completely melted for one hour, pour the alloy.

[0028] Step 3: Pouring: Adjust the furnace temperature and pouring parameters before pouring. The molten metal temperature is 710°C ± 5°C, the rising speed is 40 mm / s, the filling speed is 50 mm / s, the filling pressure is 40 kPa, and the holding time is 10 minutes.

[0029] Step 4: Cleaning: After the casting is cast, the pouring mouth is cut and cleaned, and the anti-deformation ribs are retained after cleaning.

[0030] Step 5: Heat Treatment and Reshaping: Follow the ZL116 alloy T5 heat treatment protocol. The heat treatment process requires solution heat treatment followed by artificial aging. Solution heat treatment temperature: 535±5°C, holding time: 10-16 hours, quenching water temperature: 20-100°C, transfer time: less than 15 seconds; aging heat treatment temperature: 175±5°C, holding time: 6-8 hours.

[0031] After shape adjustment, key dimensions are checked and aging treatment is carried out after the key dimensions meet the requirements of the drawing;

[0032] Step 6: After the casting completes the heat treatment process, the anti-deformation ribs are removed.

[0033] Step 7: Inspection: The casting is subjected to X-ray inspection and fluorescence inspection. After passing the inspection, the casting is subjected to dimensional inspection. The dimensional inspection uses non-contact laser scanning equipment to conduct a comprehensive inspection of the casting size.

[0034] Advantages of the present invention:

[0035] Anti-deformation structures and deformation correction methods are designed for complex arc-shaped structures and irregular curved surface structures, which are difficult to detect and correct deformation intuitively.

[0036] (1) Design anti-deformation structure when planning the process plan: Design a disc-shaped cross runner and multi-point gate that follows the shape of the casting to help stabilize the casting structure while ensuring the internal quality of the casting during shrinkage compensation; design anti-deformation ribs to increase the stability of the casting structure and prevent deformation of the casting during casting and heat treatment; design process bosses to ensure the stability of the processing process and reduce the deformation of parts caused by the processing process;

[0037] (2) Process planning to control dimensional deformation: The anti-deformation ribs of the casting are removed after the heat treatment process to prevent the opening of the casting from being deformed during the heat treatment process and causing dimensional disqualification.

[0038] The surface quality and internal metallurgical quality of castings produced according to this method meet the requirements of Class II casting standards in 11-CL-113B after fluorescence and X-ray testing; the qualified rate of parts after casting processing can reach more than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a front view of the casting of Example 1;

[0040] Figure 2 is a rear view of the casting of Example 1;

[0041] Figure 3 is a schematic diagram of the disc-shaped runner of Example 1;

[0042] Figure 4 Schematic diagram of the position of the ingate provided in the disc-shaped runner of Example 1;

[0043] Figure 5 is a side view of the disc-shaped runner and ingate of Example 1;

[0044] Figure 6 Schematic diagram of the position of the ingates on the casting in Example 1. DETAILED DESCRIPTION

[0045] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0046] Example 1

[0047] For example, a complex "back arc" structure weighs approximately 42 kg and has dimensions of 1200 mm x 880 mm x 500 mm. The casting is a symmetrical triangular arc structure, with curved surfaces of gradually varying wall thickness on either side of the triangle and a large curved surface in the center. The arc width on both sides is 121mm and the length is 949mm. There are three layers of structure on the arc surface, and each layer is 15mm thick. The middle of the two arc abdomens is connected by a curved surface with a wall thickness of 4mm. One side is a smooth curved surface, and the other side is divided and supported by 5 horizontal and vertical ribs. The middle longitudinal rib is located in the center of the symmetrical triangle, with a length of 712mm and a thickness of 8mm. The height follows the arc surface, and the maximum height is 50mm. There is a rib on each side, 575mm long and 6mm thick, and the distance between each two ribs is 199mm. There are 2 ribs in the horizontal direction, with a length of 996mm and 775mm, a spacing of 215mm and 135mm (the spacing from the bottom airtight groove), and a thickness of 8mm. The intersection of the cross ribs forms a total of 6 hot spots. The nearly triangular opening at the bottom of the arc surface is connected by a U-shaped airtight groove with a thickness of 35mm, and the rest of the parts are naturally transitioned. The schematic diagram of the casting structure is as follows Figure 1 、 2 .

[0048] Castings have areas with large differences in wall thickness. Due to the different cooling rates of each area, thermal stress is easily formed, causing cracks in the wall thickness joints. At the same time, metal accumulates in thick walls and condenses slowly, forming thermal nodes. If shrinkage is not compensated, defects such as shrinkage cavities and shrinkage porosity will occur. When the molten metal rises to the large arc surface during the pouring process, the sudden expansion of the cross-section causes the rising speed of the molten metal level to become very slow. This causes the high-temperature molten metal to heat the sand mold surface at the top for a long time and at a close distance, which is prone to rapid expansion, causing the sand mold surface to crack or even partially detach from the sand mold body, resulting in sand inclusion defects in the casting. On the other hand, the gas and slag in the molten metal in the large arc surface are difficult to remove and are easily retained in this area to form pores and slag inclusion defects. At the same time, it is not conducive to the filling of the molten metal and is prone to insufficient pouring defects.

[0049] The specific steps for implementation are as follows:

[0050] Step 1: Solidification simulation of the casting without the gating system.

[0051] First, a solidification simulation without a gating system was performed on the casting to determine the location of the casting's hot spots, thereby preventing the formation of metallurgical defects. The results showed that the casting solidified in four stages from initial to final solidification: the first stage was the thin-walled surface, the second stage was the cross ribs, the third stage was the curved areas, and the fourth stage was the extra-thick areas at both ends.

[0052] Step 2: Optimize the casting simulation in one go.

[0053] Then, the filling process and solidification process of the casting are simulated by computer to find out the parts of the casting that are prone to undercasting and the parts that are prone to shrinkage and shrinkage holes, and the casting system is designed based on the simulation results. The gating system adopts the bottom pouring type, with an ingate designed at the bottom of the casting for filling from bottom to top. At the same time, due to the large outer dimensions of the casting, the molten metal flows a long distance, and the thin-walled area cools quickly. To better ensure smooth filling of the casting, a disc-shaped cross runner is designed to follow the shape of the casting, which can cover all the ingates, so that the ingates play a role in filling and shrinkage compensation; the cross-sectional area of the conformal runner is 80mm×60mm; to avoid local overheating, multiple ingates are set on the curved surface, with 8 square ingates with a cross-sectional area of 60mm×40mm and 3 square ingates with a cross-sectional area of 60mm×50mm respectively; to prevent undercast defects in thin-walled areas and facilitate shrinkage compensation of cross ribs on thin walls, 14 cylindrical ingates with a diameter of Φ35mm and 7 Φ30mm ingates are set on the 4mm thin-wall plane and cross ribs.

[0054] Step 3: Secondary optimization of process plan.

[0055] According to the trial production results, there is a loose defect in the tail of the triangle, so the cross-sectional size of the two gates at the opening is adjusted from 50mm×40mm to 60mm×50mm; at the same time, to ensure more complete filling of the large flat surface, 7 Φ30mm inner gates are added.

[0056] Step 4: Carry out trial production and inspection of castings according to the optimized process plan.

[0057] The specific casting process is as follows:

[0058] Step 1: Modeling: Modeling is carried out according to the process plan. During the process, key dimensions are measured to ensure that the opening dimension meets the requirements of 1200±2.3mm and the height dimension meets the requirements of 490±1.8mm.

[0059] Step 2: Melting: Heat the crucible to 200°C-300°C and add the ZL116 ingot. Preheat the charge to above 150°C and remove any surface oil or rust. Once the alloy reaches 690°C-700°C, add pure magnesium. Once the alloy is uniformly melted, pour a sample for rapid spectral analysis. Refining is performed after the sample passes the spectral analysis. Refining is performed using argon rotary injection for 10-15 minutes at a temperature of 730°C-745°C. After refining, perform an online density test. A density ≥2.62 kg / dm³ is considered acceptable. Modification: Use an aluminum-strontium (Al-Sr) alloy modifier with a strontium content of 10%. Add 0.015%-0.03% of the total charge weight. Allow one hour for the Al-Sr alloy to fully melt before pouring.

[0060] Step 3: Pouring: Adjust the furnace temperature to 710°C and proceed with pouring. Stop pouring when the remaining alloy liquid at the bottom of the crucible reaches 100mm-150mm. The time from refining and slag removal to pouring should not exceed 1.5 hours.

[0061] Step 4: Cleaning: After casting, cut and clean the pouring riser, and retain the anti-deformation ribs after cleaning.

[0062] Step 5: Heat treatment and shape correction: Heat treatment is carried out according to the process requirements: solution heating temperature 535±5℃, holding time 16h, quenching water temperature 40℃, transfer time less than 15 seconds; aging heating temperature 175±5℃, holding time 8h. Shape correction should be carried out within 3 hours after solution heating.

[0063] Correction work should be carried out within 3 hours after the casting is solution treated;

[0064] After the shape is corrected, the opening size is checked to meet the requirements of 1200±2.3mm and the height size meets the requirements of 490±1.8mm before aging treatment is carried out;

[0065] Step 6: After the casting completes the heat treatment process, the anti-deformation ribs are removed.

[0066] Step 7: Inspection: The casting undergoes X-ray and fluorescence testing. After passing the X-ray and fluorescence tests, the casting undergoes dimensional inspection. Dimensional inspection uses non-contact laser scanning equipment to conduct a comprehensive inspection of the casting's external dimensions. The casting's wall thickness and external dimensions meet the tolerance requirements of CT9 level specified in HB6013.

[0067] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art may make various modifications or substitutions within the technical scope disclosed in the present invention, and all such modifications or substitutions shall be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A casting method for semi-arc thin-walled complex structure castings, characterized in that: The semi-arc thin-walled complex structure casting has a symmetrical triangular arc shape. The two sides of the triangular arc are arc surfaces with variable thickness, which are thick at both ends and thin in the middle. The outward side of the arc surface is a smooth surface. The inward side of the arc surface is provided with horizontal and vertical cross-intersecting ribs. One longitudinal rib is located on the symmetry axis of the triangular arc structure, and the remaining longitudinal ribs are symmetrically distributed on both sides. It is formed by precision sand mold differential pressure casting process; The following steps are involved: A bottom pouring system is used to fill the mold from bottom to top. The mold is provided with a disc-shaped runner according to the shape of the casting, and an inner gate is provided on the disc-shaped runner. After molding, the pouring gate is cut and cleaned, heat treated and shaped to obtain the semi-arc-shaped thin-walled complex structure casting.

2. The casting method according to claim 1, characterized in that The specific position of the ingates is determined by simulating the filling process and solidification process of the casting to find out the parts of the casting that are prone to undercasting and the parts that are prone to shrinkage and shrinkage cavities, and the ingates are set at these specific positions.

3. The casting method according to claim 1, characterized in that The inner gates at the thinner arc surface and the cross-intersection of the ribs are circular.

4. The casting method according to claim 1, wherein: The inner gate of the thicker curved surface is square.

5. The casting method according to claim 1, wherein: The disc-shaped runner can cover all the ingates.

6. The casting method according to claim 1, characterized in that The mold is provided with anti-deformation ribs at the arc surface and opening of the casting, and the anti-deformation ribs are cleaned after heat treatment.

7. The casting method according to claim 1, characterized in that The heat treatment comprises the following steps: First, solution heating is performed, then quenching is performed, and finally aging heating is performed; The solution heating temperature is 530-540°C and the holding time is 10-16 hours; The quenching temperature is 20-100°C and the transfer time is less than 15s; The aging heating temperature is 170-180° C., and the holding time is 6-8 hours.

8. The casting method according to claim 1, wherein: The shape correction is carried out 2 to 4 hours after solution heating; After the shaping is completed, quenching and aging heating are carried out.

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