Casting method based on "V" method composite lost foam forming process and application thereof

Abstract

The present application relates to a kind of based on " V " method composite lost foam forming casting process and its application.The process is aimed at the defects of existing " V " method and lost foam casting process when producing 30-60kg castings, innovatively combines the two.First, specific specification EPS beads are selected to make white mold, after steam prefoaming, vulcanization bed drying and curing, with specific process parameters, steam heating type semi-automatic forming machine is formed.Then, using bauxite, bentonite and other materials to make 1 layer shell, the shell making cost is low, and can reduce labor intensity and material consumption.The drying temperature and time are determined by measuring the expansion and shrinkage curve of white mold.Finally, through " V " method sand casting and negative pressure pouring, the casting is obtained.This process integrates the advantages of two processes, solves the problems of traditional process, is suitable for automobile low alloy complex casting production, can also reduce pollution emission, and has good application prospect.

Description

Technical Field

[0001] This invention relates to the field of casting technology, specifically to a composite process combining lost foam casting and "V" casting, which is particularly suitable for the efficient and low-cost production of complex cast steel parts weighing 30-60 kg. Background Technology

[0002] With the continuous development of the casting industry, the demand for lightweight product design and manufacturing is becoming increasingly significant. Many companies are actively engaged in providing lightweight design and manufacturing services to users, aiming to strongly support weight reduction, emission reduction, and cost reduction in vehicles. This trend is also driving the continuous expansion of the cast steel parts market. As lightweighting efforts deepen and product functional integration continues to improve, cast steel parts are gradually developing towards larger and more integrated sizes. This trend places higher demands on casting processes, requiring not only that modules can adapt to the production of larger and more complex products, but also that process yield and production efficiency be improved while effectively reducing manufacturing costs.

[0003] Currently, many companies' existing casting processes have certain limitations. Taking the common "V" casting process and lost foam casting process as examples, the "V" casting process is generally suitable for producing castings weighing over 60kg, while the lost foam casting process is more suitable for producing castings weighing under 30kg. As castings become larger and more integrated, with weights in the 30-60kg range, the drawbacks of existing processes become apparent. If the "V" process is used to produce castings in this weight range, the relatively light castings will result in low process yield and a significant increase in unit cost. On the other hand, when using the lost foam process, the excessive weight of the castings will lead to an increase in the number of shell layers, a large consumption of raw and auxiliary materials, high labor intensity in shell making, low shell making efficiency, and a significant increase in firing energy consumption. For example, patent document CN201510868131.6 discloses a vacuum negative pressure vibration casting method for integral casting of hollow shells in a central trough. This method includes foam model manufacturing, coating, and drying. The foam model is coated with refractory coating using a combination of flow coating and brushing. The coating and drying steps are repeated three times each to obtain a white mold. The thickness of the refractory coating layer on the white mold is 2mm to 3mm. This method still requires three shell-making processes, resulting in high consumption of raw and auxiliary materials, high labor intensity in shell making, and low shell-making efficiency. At the same time, the energy consumption of calcination will also increase significantly. These problems seriously restrict the development of large-scale casting modules and hinder the development of large products and the reduction of casting manufacturing costs.

[0004] Therefore, developing a new casting process suitable for producing castings weighing between 30-60 kg has become an urgent problem to be solved in the industry. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-process composite molding casting process that integrates the advantages of lost foam casting and "V" casting, overcomes the shortcomings of existing processes in producing castings within a specific weight range, produces high-precision and high-quality castings, reduces production costs, reduces pollutant emissions, and expands the application range of casting processes.

[0006] To achieve the above objectives, the present invention provides a composite lost foam casting process based on the "V" method, comprising the following steps:

[0007] S1, a white mold is made by pre-foaming and molding EPS beads;

[0008] S2, the shell preparation, is made by using a coating made of bauxite, bentonite, adhesive, cellulose and other materials in a certain proportion, with one shell layer.

[0009] S3, Measure the expansion and contraction curves of the white mold, and select an appropriate temperature to dry the white mold based on the expansion and contraction curves;

[0010] S4: After the shell is fired, the casting is formed by "V" method of sand embedding and negative pressure pouring.

[0011] Furthermore, the EPS beads have a particle size of 0.15–0.30 mm and a relative atomic mass of (4.0–5.5) × 10⁻⁶. 4 The multiplier can be 15 to 30 times.

[0012] Furthermore, in step S1, the molding process of the white mold specifically involves using a steam pre-expansion machine to pre-foam the EPS beads at a pre-expansion temperature of 85-100℃. After the pre-expansion beads are dried and cured in a vulcanizing bed for 4 hours, they are then molded and foamed using a steam-heated semi-automatic molding machine. The molding process parameters are: injection pressure 0.3-0.5MPa, steam pressure 0.07-0.09MPa, mold preheating time 10-15s, feeding time 8-12s, heating time 30-40s, and cooling time 80-100s.

[0013] Furthermore, in step S2, the shell coating is composed of 50-70% bauxite, 15-25% bentonite, 10-20% adhesive, and 3-8% cellulose.

[0014] Furthermore, in step S3, the drying temperature is 50-60℃, and the time is 4-12 hours.

[0015] Furthermore, in step S4, the sand-buried molding process uses rain-fed sand addition, with a compaction time of 4–6 seconds and a vacuum degree of -0.06 to -0.08 MPa.

[0016] Furthermore, in step S4, the pouring temperature is 1550~1650℃, the pouring speed is 40~50s / box, and the negative pressure is -0.06~-0.08MPa.

[0017] Furthermore, the shell consists of one layer with a thickness of 1-2 mm.

[0018] On the other hand, this application also provides a cast steel part prepared according to the above process, with a surface roughness of Ra25 to 50 and a yield of ≥95%.

[0019] This application also provides an application of the above-described process in the production of complex low-alloy automotive castings.

[0020] Beneficial effects: (1) The shell is made of a coating made of bauxite, bentonite, glue, cellulose and other materials in a certain proportion. The shell making cost is low and the surface roughness of the casting meets the technical requirements. The number of shell layers is generally 1, which is at least 2 layers less than the traditional investment casting shell. The shell thickness is only half that of the precision casting shell. The shell making material can be reduced by 50% and the labor intensity of shell making can be reduced by 40%. The innovation effect is significant.

[0021] (2) Integrating the advantages of lost foam casting and “V” casting, a new casting mode was developed through integration and innovation. This process is mainly applied to the production of various large composite parts. It can effectively overcome the shortcomings of white foam casting, which is difficult to use for large parts and has high cost and complex process. The “V” molding method realizes binder-free dry sand molding. The pre-pouring lost foam technology solves the problem of carbon increase in cast steel parts, improves the quality of castings, and reduces pollutant emissions.

[0022] (3) By measuring the expansion and contraction curve of the white mold and determining the drying temperature accordingly, it is possible to effectively avoid excessive expansion or contraction deformation of the white mold due to improper temperature, thereby ensuring the shape accuracy of the white mold and providing a good foundation for subsequent shell preparation. At the same time, a suitable temperature can allow the shell coating to dry and cure fully, ensuring the strength and integrity of the shell and improving the quality of the casting. Attached Figure Description

[0023] Figure 1 The image shown is of the actual white mold prepared in the example.

[0024] Figure 2 These are images of the actual shells prepared in the examples.

[0025] Figure 3 The figures show the expansion and contraction curves of the white mold prepared in the examples.

[0026] Figure 4 The image shown is a photograph of the final cast composite component prepared in the example. Detailed Implementation

[0027] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0028] It should be understood that, when used in this specification and the appended claims, the term "comprising" indicates the presence of a descriptive feature, integral, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or sets.

[0029] To keep the drawings concise, only the parts relevant to the invention are shown schematically in each figure, and they do not represent the actual structure of the product. Furthermore, for ease of understanding, in some figures, only one of components with the same structure or function is shown schematically, or only one is labeled. In this document, "one" can mean not only "only one" but also "more than one".

[0030] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0031] In the embodiments shown in the accompanying drawings, the directional indications (such as up, down, left, right, front, and back) used to explain the structure and movement of the various components of the invention are relative rather than absolute. These descriptions are appropriate when these components are in the positions shown in the drawings. If the descriptions of the positions of these components change, these directional indications also change accordingly.

[0032] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation of the present invention will be described below with reference to the accompanying drawings.

[0034] Example 1:

[0035] 1. White mold making process

[0036] Castings require better surface roughness and higher dimensional accuracy, which necessitates that the white mold possess characteristics such as high strength, good surface quality, and low and stable shrinkage. Based on a comparison of existing domestically produced EPS beads, the selected bead specifications are shown in the table below.

[0037] Table 1 EPS Bead Specifications

[0038]

[0039] 2. White mold forming process

[0040] White mold forming is one of the key technologies in the "V" method combined with lost foam casting; only high-quality white molds can produce high-precision castings. A steam pre-expansion machine is used to pre-foam the EPS beads at a temperature of 85–100℃. The pre-expanded beads are then dried in a vulcanizing bed and allowed to mature for 4 hours before molding and foaming. Based on the company's actual situation, a steam-heated semi-automatic molding machine is used as the molding and foaming equipment. The white mold forming process was determined through experiments, as shown in the table below. Figure 1 These are pictures of the actual product formed from the white mold.

[0041] Table 2 White mold forming process parameters

[0042]

[0043] 3. Shell preparation process

[0044] The preparation of ultra-thin, high-strength shells is another key technology in the "V" method composite lost foam casting process. Using 60% bauxite, 20% bentonite, 15% adhesive, and 5% cellulose as a coating slurry for shell preparation results in lower costs and ensures the surface roughness of the casting meets technical requirements.

[0045] The shell layer is typically only one layer, two layers fewer than traditional investment casting shells. The shell thickness is 1mm, only half the thickness of a precision-cast shell. Shell material can be reduced by 50%, and labor intensity can be reduced by 40%, demonstrating significant innovation. Figure 2 These are actual pictures of the shell-making process.

[0046] Table 3 Coating performance indicators

[0047]

[0048] 4. Drying process of white mold

[0049] Understanding the dimensional changes of the white mold as temperature increases is a prerequisite for developing a reasonable high and low temperature drying process. The dimensions of the white mold samples at various temperature points were measured using vernier calipers, and the corresponding expansion and contraction curves were plotted. The sample size used in the test was 100mm × 100mm × 100mm, with a density of 35kg / m³. 3 .from Figure 3 The curves show that the white mold sample begins to expand at around 80℃, reaches its maximum expansion (about 15%) at around 108℃, and then shrinks rapidly, with a shrinkage rate of 45% at 130℃.

[0050] Based on the shrinkage characteristics of the white mold, a drying process was developed: temperature has a significant impact on the dimensional stability of the white mold during drying. By measuring the expansion and contraction curve, a drying temperature of 50-60℃ was precisely determined. This effectively avoids excessive expansion or contraction deformation of the white mold due to improper temperature, thus ensuring the shape accuracy of the white mold and providing a good foundation for subsequent shell preparation. Simultaneously, a suitable temperature allows the shell coating to fully dry and cure, ensuring the strength and integrity of the shell and improving casting quality. If the drying temperature is unreasonable, the white mold may crack due to expansion or uneven contraction, leading to shell damage, casting defects, and increased scrap rate. The drying temperature set according to the curve greatly reduces the occurrence of such situations, improves the casting yield, and reduces production costs. Precise drying temperature can shorten drying time, optimizing from a previously undefined and lengthy process to a precise drying time of 4-12 hours. This reduces the production cycle, increases equipment turnover, allows the casting process to produce more products per unit time, and improves overall production efficiency.

[0051] 5. Use the "V" method for sand embedding and casting.

[0052] It is recommended to use a sand-addition method that does not disrupt the sand particle distribution, namely, rain-feed sand addition. Start the rain-feed sand adder, open the gate, and fill the sand box with sand until it is 2 / 3 full, then stop adding sand. Start the vibratory compaction table (4-6 seconds) to compact the molding sand. Then, open the rain-feed gate again to add sand and compact it evenly (4-6 seconds). Add sand to the sand box again until it is full. After filling, start the vibratory compaction table again (4-6 seconds) to compact the molding sand.

[0053] Cover with the backing film. Insert the evacuation pipe into the evacuation pipe connector of the sand box, open the valve to evacuate the sand box, and then cover the top surface of the sand mold with the backing film, ensuring that the film adheres to the sand box without wrinkles, sand leakage, or air leakage. At this time, the vacuum degree of the sand box should be between -0.06 and -0.08 MPa, and the hardness of the sand mold should be above 90.

[0054] 1) The pouring temperature is controlled at 1550~1650℃.

[0055] 2) The pouring speed is controlled at 40-50 seconds based on the weight of each box of molten steel.

[0056] 3) The negative pressure during casting should be controlled between -0.06 and -0.08 MPa.

[0057] Figure 4 These are actual photos of the cast components. The application results show that when this process is used for production, there is no fire leakage in the mold shell, the casting is completely filled, the outline is clear, the structure is dense, the appearance quality of the parts can reach Ra40, and the yield rate is over 95%.

[0058] Comparative Example 1: Traditional Lost Foam Casting

[0059] The shell has 3 layers, the shell cracking rate after casting is 15%, the yield is 75%, and the cost is 35% higher.

[0060] Comparative Example 2: The formulation of the coating slurry was changed, reducing the proportion of bauxite to 40% and increasing the proportion of bentonite to 40%, while keeping the proportions of adhesive and cellulose unchanged, and other conditions unchanged. After casting, the shell cracking rate was 15%, the appearance quality of the parts reached Ra80, and the yield was 82%.

[0061] In-depth analysis of the examples and comparative examples reveals that using a specific ratio of bauxite (50-70%), bentonite (15-25%), adhesive (10-20%), and cellulose (3-8%) as the coating slurry, and employing a single-layer shell-making process, exhibits significant advantages in several key dimensions. Bauxite provides the shell with excellent high-temperature resistance and structural strength; bentonite enhances the coating's adhesion and suspension stability; the adhesive ensures tight bonding of all components; and cellulose plays a crucial role in the shell's flexibility and crack resistance. Compared to traditional multi-layer shell-making processes, this process significantly reduces the number of shell layers, from multiple layers to just one. This directly results in a sharp reduction in the amount of shell-making material used, approximately 50% less than traditional processes. Regarding shell-making costs, the significant reduction in material usage, coupled with the decrease in time and labor costs due to the reduced number of shell layers, effectively compresses the overall cost. Regarding the surface quality of castings, the shell produced by this process results in a smoother surface and significantly reduced roughness, fully meeting the technical requirements for high precision. Furthermore, the labor intensity of shell production is greatly reduced due to the simplified process. In summary, this innovative process comprehensively improves the efficiency and quality of casting processes, providing a new and efficient solution for the development of the casting industry.

Claims

1. A composite lost foam casting process based on the "V" method, suitable for producing castings weighing between 30-60 kg, characterized in that, Includes the following steps: S1, a white mold is made by pre-foaming and molding EPS beads; S2, Prepare the shell by using a coating made of bauxite, bentonite, adhesive and cellulose in a certain proportion. The shell has one layer and a thickness of 1 mm. The shell coating is composed of 50-70% bauxite, 15-25% bentonite, 10-20% adhesive and 3-8% cellulose. S3, Measure the expansion and contraction curves of the white mold, and select an appropriate temperature to dry the white mold based on the expansion and contraction curves; S4: After the shell is fired, the casting is completed by "V" method sand embedding molding and negative pressure pouring; the pouring temperature is 1550~1650℃. In step S1, the EPS beads have a particle size of 0.15–0.30 mm and a relative atomic mass of (4.0–5.5) × 10⁻⁶. 4 The expandability ratio is 15 to 30 times; in step S4, the sand-buried molding adopts rain-fed sand addition, the compaction time is 4 to 6 seconds, and the vacuum degree is -0.06 to -0.08 MPa.

2. The process according to claim 1, characterized in that, In step S1, the molding process of the white mold is specifically as follows: the EPS beads are pre-foamed using a steam pre-expansion machine at a pre-expansion temperature of 85-100℃. After the pre-expansion beads are dried and cured in a vulcanizing bed for 4 hours, they are molded and foamed using a steam-heated semi-automatic molding machine. The molding process parameters are: injection pressure 0.3-0.5MPa, steam pressure 0.07-0.09MPa, mold preheating time 10-15s, feeding time 8-12s, heating time 30-40s, and cooling time 80-100s.

3. The process according to claim 1, characterized in that, In step S3, the drying temperature is 50-60℃ and the time is 4-12 hours.

4. The process according to claim 1, characterized in that, In step S4, the pouring speed is 40-50 s / box, and the negative pressure is -0.06 to -0.08 MPa.

5. A cast steel part prepared by the process according to any one of claims 1 to 4, characterized in that, The surface roughness is Ra25~50, and the yield is ≥95%.

6. The application of the process according to any one of claims 1 to 4 in the production of complex low-alloy automotive castings.

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