3DP printing sand mold structure for aluminum alloy anti-gravity casting

Abstract

The utility model relates to the technical field of casting, in particular to a 3DP (three-dimensional printing) sand mold structure for aluminum alloy anti-gravity casting, which comprises an upper sand mold, a middle sand mold and a lower sand mold for 3DP printing, the three sand molds are sequentially overlapped and combined from top to bottom to form an integral sand mold, a hollow cavity is reserved on the inner side of the middle sand mold, and a mold core is sleeved in the hollow cavity in a non-contact manner. A casting cavity is formed in a gap between the mold core and the hollow cavity, the mold core and the lower sand mold are integrally and fixedly connected, a pouring gate correspondingly communicated with the casting cavity is formed in the bottom of the lower sand mold on the periphery of the mold core, an exhaust hole used for exhausting during pouring is formed in the upper sand mold, and a reserved groove used for installing a chilling block is further formed in the upper sand mold. The 3DP printing sand mold adopts a tenon-and-mortise structure combination design, a chilling block is cast in advance and placed in a sand mold reserved groove, the air exhausting and chilling effects are achieved, the casting forming quality is guaranteed, the casting production efficiency is improved, the single-piece and small-batch casting production period is guaranteed, and the casting requirements of large, complex and thin-wall aluminum alloy castings can be well met.

Description

Technical Field

[0001] This utility model belongs to the field of casting technology, specifically relating to a 3DP printed sand mold structure for anti-gravity casting of aluminum alloys. Background Technology

[0002] Aluminum alloys possess characteristics such as high specific strength, good corrosion resistance, and ease of forming, making them widely used as important structural materials in fields such as aerospace, automotive, and electronic communications. In recent years, the number of single-piece and small-batch prototype aluminum alloy parts has been increasing, creating opportunities for the development and application of new aluminum alloy casting processes.

[0003] One of the main factors currently limiting the production cycle of single pieces and small batches of aluminum alloy castings is the long time required for mold production. By adopting 3D printing sand mold technology, the dimensional accuracy of the castings is guaranteed because the installation accuracy of the sand spreader and scraper is ensured to be within 0.02mm. Furthermore, compared with traditional casting processes, this not only saves costs and time but also improves the yield rate of the castings.

[0004] Current research, focusing on complex aluminum alloy shell castings, demonstrates that sand mold 3D printing technology can alleviate the constraints of mold manufacturing on the design of complex aluminum alloy casting processes, providing a certain technical foundation for the future preparation of aluminum alloy products with higher dimensional precision.

[0005] However, the aforementioned sand mold design principles primarily aim to achieve overall integration without affecting the application of coatings, chills, and other composite mold assembly processes, thereby eliminating problems such as misalignment, gaps, and cumulative errors that occur during operator mold assembly. However, since 3D sand core printing is computer-controlled, issues arise such as poor overall mold permeability due to resin spraying based on the cross-sectional shape of the sand core, and excessive porosity in the casting due to poor venting of the sand mold during pouring. Utility Model Content

[0006] In view of the above situation, this utility model provides a 3DP printed sand mold structure for anti-gravity casting of aluminum alloy. It adopts a 3DP printed sand mold combination design and a chill pre-pouring method, which can effectively solve the air venting problem during the casting of integrated printed sand molds in the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A 3DP-printed sand mold structure for anti-gravity casting of aluminum alloy includes an upper sand mold, a middle sand mold, and a lower sand mold. All three molds are 3DP-printed sand molds, and are sequentially overlapped from top to bottom to form a single integral sand mold. The middle sand mold has a hollow cavity inside, and a core is non-contactly fitted inside the cavity. The gap between the core and the hollow cavity forms a casting cavity, serving as the forming cavity for the casting. The core is integrally fixed to the lower sand mold. A gate corresponding to and communicating with the casting cavity is opened at the bottom of the lower sand mold around the core. Because it is applied to anti-gravity casting of aluminum alloy castings, a bottom gate injection method is used. The upper sand mold has vent holes for venting during pouring and a reserved groove for installing chills. The upper sand mold has both quenching and venting functions.

[0009] Furthermore, the upper sand mold and the middle sand mold, as well as the middle sand mold and the lower sand mold, are detachably connected and interlocked with each other through mortise and tenon joints.

[0010] Furthermore, the upper and lower edges of the middle sand mold are respectively provided with annular tenons and annular mortises, the lower edge of the upper sand mold is provided with annular grooves that engage with the annular tenons, and the upper edge of the lower sand mold is provided with annular bosses that engage with the annular mortises.

[0011] Furthermore, the chill is pre-cast using molten aluminum alloy of the same material as the casting. When pre-casting the chill, a layer of barrier sand is required between the reserved groove and the casting cavity to prevent the molten aluminum alloy from flowing into the casting cavity. The chill after casting is embedded in the corresponding reserved groove.

[0012] Furthermore, during casting, the integral sand mold is placed on a low-pressure casting machine, the gating port at the bottom of the lower sand mold is aligned with the upper port of the riser pipe of the low-pressure casting machine, and is filled and sealed with asbestos material before anti-gravity casting is performed.

[0013] This utility model also includes other components that enable its normal use, all of which are conventional means in the field. In addition, devices or components not limited in this utility model, such as low-pressure casting machines and their riser pipes, all adopt existing technologies in the field.

[0014] The beneficial effects of this utility model are as follows:

[0015] This 3DP-printed sand mold structure for anti-gravity casting of aluminum alloys features embedded chills placed in the cooling and venting sections of the sand mold within pre-reserved slots. The sand mold assembly design utilizes 3DP integral printing for all parts, with mortise and tenon joints connecting the components. Furthermore, process design and optimization can be performed directly on the 3D part model, saving time on process testing and mold making, and ensuring production cycles for single-piece and small-batch castings. The resulting castings exhibit high quality and operational safety, meeting current production and environmental requirements, and are particularly suitable for producing large, complex, and thin-walled aluminum alloy castings.

[0016] The design and fabrication of chills are simple. By pre-pouring chills, the joint surfaces of the combined sand molds and the initial lifting of the chills during pouring serve to vent air. Additionally, by applying pressure to the surface of the molten aluminum, the molten aluminum alloy moves upward within the riser pipe, achieving anti-gravity pouring. This ensures that the molten aluminum alloy flows at a stable speed within the mold cavity, preventing cold shuts and defects such as porosity in the castings, thus facilitating the formation of thin-walled parts.

[0017] By adopting this 3DP printed sand mold combination design and the method of pre-casting chills, it is possible to quickly achieve single-piece and small-batch production of aluminum alloys. The castings are free of porosity and cold shut defects, meeting production delivery requirements. The 3DP printed sand mold has a simple structure, is easy to manufacture and promote, and has high production efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the three-dimensional disassembly structure of the 3DP printed sand mold in the embodiment.

[0019] Figure 2 This is a schematic diagram of the longitudinal section structure of the 3DP printing sand mold in the embodiment.

[0020] Figure 3 a and b are schematic diagrams showing the rise of the chills during the initial stage of casting and the fall of the chills during the later stage of solidification, respectively.

[0021] Figure 4 A schematic diagram illustrating the principle of placing a 3DP-printed sand mold onto a low-pressure casting machine for anti-gravity casting. Detailed Implementation

[0022] The technical solution of this utility model will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments.

[0023] Example

[0024] like Figure 1-2As shown, a 3DP-printed sand mold structure for anti-gravity casting of aluminum alloy includes an upper sand mold 1, a middle sand mold 2, and a lower sand mold 3. All three sand molds are 3DP-printed sand molds. The upper and lower edges of the middle sand mold are respectively provided with annular tenons 5 and annular mortises 6. The lower edge of the upper sand mold is provided with annular grooves 7 that engage with the annular tenons. The upper edge of the lower sand mold is provided with annular bosses 8 that engage with the annular mortises. The three sand molds are detachably overlapped and interlocked from top to bottom through a tenon and mortise structure to form a whole sand mold. This facilitates assembly and reduces excessive positional errors during assembly, and also facilitates venting during pouring.

[0025] Based on 3D printing technology, the casting process is designed and manufactured using aluminum alloy anti-gravity casting structure design. The casting process is simulated using simulation technology to verify the casting gating system. Based on the simulation results, a combined sand mold is designed, which can be used to vent air at the joint surface of the combined sand mold.

[0026] The inner side of the medium sand mold has a hollow cavity, and a core is non-contactly fitted inside the hollow cavity. The gap between the core and the hollow cavity forms a casting cavity, which serves as the forming cavity of the casting. The core and the lower sand mold are integrally printed.

[0027] The bottom of the lower sand mold on the outer periphery of the core has a gate 10 that communicates with the cavity of the casting. Because it is used for anti-gravity casting of aluminum alloy castings, a bottom gate injection method is adopted. During casting, the integral sand mold is placed on the low-pressure casting machine 12, the gate at the bottom of the lower sand mold is aligned with the upper port of the riser pipe 11 of the low-pressure casting machine, and the interface between the riser pipe and the gate is filled and sealed with asbestos material, and then anti-gravity casting can be carried out.

[0028] The low-pressure casting machine, also known as the anti-gravity casting machine, and its corresponding riser pipe and asbestos material, are all existing technologies in this field, and their specific configurations will not be described in detail here.

[0029] The upper sand mold is provided with vent holes 9 for venting during casting. Venting is prioritized through the vent holes during casting, and the combined sand mold joint surface can also assist in venting.

[0030] like Figure 3 As shown in a and b, the 3DP printed sand mold also provides a chill venting method, and the gap at the edge of the reserved groove for the chill to float during the initial stage of casting also has a certain auxiliary venting function.

[0031] The upper sand mold has a reserved slot for installing the chill 4. After the chill is installed in the reserved slot, it also has the function of venting in the early stage of pouring, and in the later stage, it mainly plays the role of chilling the aluminum alloy liquid to accelerate the cooling and produce sequential solidification. Therefore, the reserved slot of the upper sand mold has the dual functions of chilling and venting after the chill is installed.

[0032] Although the medium sand mold is mainly used to support the shape of the casting, according to the simulation results, it can also be used to reserve grooves in some thick parts for the assembly of chills. It also has a certain venting function in the early stage of pouring, and can be used to adjust the solidification temperature field of the casting during solidification.

[0033] The chill is pre-cast using molten aluminum alloy of the same material as the casting. When pre-casting the chill, a layer of barrier sand is required between the reserved groove and the casting cavity to prevent the molten aluminum alloy from flowing into the casting cavity. The chill after casting is embedded in the corresponding reserved groove.

[0034] In the initial stage of casting, since the density of the chill is similar to that of the molten aluminum, the buoyancy of the molten aluminum and the air trapped near the chill create an upward force, causing the chill to rise, widening the gaps, and making it easier for gas to escape. In the initial stage of solidification, due to the rapid cooling effect of the chill, the molten aluminum near the chill solidifies faster.

[0035] like Figure 4 As shown, the specific steps for anti-gravity casting using this 3DP-printed sand mold are as follows:

[0036] Step 1: Place the aluminum alloy into a melting furnace and melt it at 730℃~760℃ to remove slag, while heating the mold at 140℃~160℃.

[0037] Step 2: Place the sand mold on a flat plate, pour a spoonful of molten aluminum into the pre-reserved groove, and allow it to cool to form a chill. If the sand mold has a pre-reserved groove, a layer of sand should be placed between the groove and the cavity. Pour a spoonful of molten aluminum into the groove, and allow it to cool to form a chill.

[0038] Step 3: After the sand mold and chill have cooled, assemble them together, place them in the sand box, fill the surrounding area with furan resin self-hardening sand, and after solidification, place the mold directly on the anti-gravity casting sealing cover plate, align the gating gate with the upper end of the riser pipe, and seal the mold with asbestos.

[0039] Step 4: Apply pressure to the surface of the molten aluminum alloy using a pressurizing device, causing the molten aluminum alloy to enter the mold cavity from bottom to top along the riser pipe, achieving anti-gravity casting. The casting process parameters are: riser speed 45m / s, riser pressure 8KPa, filling speed 50m / s, filling pressure 40KPa, shell formation time 5s, shell formation pressurization pressure 8KPa, crystallization time 300s, crystallization pressurization pressure 5KPa, and resistance coefficient 1.5.

[0040] The technical solution of this utility model is not limited to the specific embodiments described above. Without departing from the scope and spirit of the described embodiments, many modifications and changes will be obvious to those skilled in the art. Any technical modifications made within the spirit and principles of this utility model shall fall within the protection scope of this utility model.

Claims

1. A 3DP-printed sand mold structure for anti-gravity casting of aluminum alloys, comprising an upper sand mold, a middle sand mold, and a lower sand mold, characterized in that: The upper, middle, and lower sand molds are all 3DP printed sand molds. They are stacked and combined sequentially from top to bottom to form an integral sand mold. The middle sand mold has a hollow cavity inside, and a core is non-contactly fitted inside the hollow cavity. The gap between the core and the hollow cavity forms the casting cavity. The core is integrally fixed to the lower sand mold. The bottom of the lower sand mold on the outer periphery of the core has a gate that communicates with the casting cavity. The upper sand mold has vent holes for venting during pouring and a reserved groove for installing chills.

2. The 3DP-printed sand mold structure for anti-gravity casting of aluminum alloy according to claim 1, characterized in that: The upper sand mold and the middle sand mold, as well as the middle sand mold and the lower sand mold, are detachably connected and interlocked with each other through mortise and tenon joints.

3. The 3DP-printed sand mold structure for anti-gravity casting of aluminum alloy according to claim 2, characterized in that: The upper and lower edges of the middle sand mold are respectively provided with annular tenons and annular mortises. The lower edge of the upper sand mold is provided with annular grooves that engage with the annular tenons. The upper edge of the lower sand mold is provided with annular bosses that engage with the annular mortises.

4. The 3DP-printed sand mold structure for anti-gravity casting of aluminum alloy according to claim 1, characterized in that: The chill is pre-cast from molten aluminum alloy, the same material as the casting, and is embedded in the corresponding pre-reserved slot.

5. The 3DP-printed sand mold structure for anti-gravity casting of aluminum alloy according to claim 1, characterized in that: During casting, the integral sand mold is placed on the low-pressure casting machine, and the gate at the bottom of the lower sand mold is aligned with the upper port of the riser pipe of the low-pressure casting machine.

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