WHAT IS SAND CASTING

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Sand casting is a common forming method that mainly uses sand as a raw material to prepare a casting mold and pours a metal melt into the cavity of the casting mold (common sand casting production process, as shown in Figure 1-5). This technology can realize the preparation and forming of large and complex parts. It has the characteristics of good fluidity, fast and rapid forming, low cost, and low sensitivity to size and weight. Therefore, in the production of large auto parts, sand casting is often used. forming method.

However, sand casting technology also has disadvantages such as complicated mold making and mold modification, many structural design restrictions, large modulus of complex castings, and harsh production environment.

There are many types of sands that can be used for sand casting process, including green sand, resin sand, pre-coated resin sand, water glass dry sand etc. Accordingly, the sand casting processes include floor molding, automatic molding and shell molding process.In the total metal casting output in the whole world, 60% to 70% of metal castings are sand castings. Their unit weight could from dozens of gram to dozens of tons, and their dimensions could be from dozens of millimeters to several meters. Moreover, according to the castings produced by other casting processes, sand castings are the cheapest and have very high production rate.However, nowadays, the other casting processes are also use the sand to make the mold. They have their own names, such as shell mold casting, furan resin coated sand casting (no bake type), lost foam casting and vacuum casting.Need mold making and sand casting supplies for large quantities of production parts? Looking for a more cost effective and time efficient way of manufacturing parts? Don’t miss our sand casting services! At BE-CU foundry, we provide high quality and affordable sand casting service for prototypes and production parts with quick turnaround times.

Resin additive content

Before sand casting, it is necessary to use resin additives to solidify the sand in the mold to achieve a certain shape and strength. The content of resin additives in the sand mold has a great influence on the forming effect of the casting. Because sand molds are mostly used for high-temperature melt casting, resin additives with lower boiling points will rapidly vaporize during the melt casting process, thereby bringing airflow into the cavity; in addition, the melt may also be involved in the filling process. gas, and produce shrinkage porosity or porosity defects after solidification. When the mold is prepared, adding too little resin will also lead to low strength of the mold, which cannot be formed and used, or is impacted and collapsed by the high-temperature melt during pouring, resulting in a casting accident. Therefore, the appropriate resin additive content can ensure the use strength of the casting mold, and can also reduce the amount of gas generated during the casting process, which is beneficial to the high-quality forming of the casting.

Mold preheating temperature

The preheating of the mold before pouring mainly affects the heat exchange effect between the mold and the melt during the pouring process, and delays the cooling time of the melt so that it has sufficient power for mold filling. When the mold is not preheated or the preheating temperature is too low, the melt will transfer a large amount of heat energy to the mold, and the cooling speed will become faster, which is easy to cause insufficient filling power. In other words, it is easy to form solidification defects such as insufficient pouring and cold isolation; in addition, the mold with lower preheating temperature may also have dangerous effects such as thermal expansion and cracks under the action of high temperature melt. When the preheating temperature of the mold is too high, the melt has good fluidity, but it will cause unfavorable conditions such as longer solidification and forming time, excessive dendrite growth and precipitation of the second phase; the mold will also be deformed due to excessive heating , decrease in strength, etc. Whether the mold needs to be preheated and the size range of the preheating temperature need to be reasonably formulated according to the material characteristics and test conclusions.

Pouring initial temperature

The initial pouring temperature refers to the initial temperature of the melt just entering the sprue from the gate, and the initial pouring temperature significantly affects the casting quality of the casting [27]. Reasonable initial pouring temperature: the alloying degree of the metal melt is better, and at the same time, it can give the melt enough filling power, which is beneficial to the forming effect of the casting in the later stage of solidification. When the initial pouring temperature is too high, the internal elements of the melt may be damaged during smelting, resulting in inhalation, oxidation, etc., and the forming quality cannot be guaranteed, and the volume shrinkage rate during filling and solidification is large, which is prone to shrinkage cavities and shrinkage. , coarse dendrites and other undesirable phenomena; too high initial pouring temperature will also have a certain impact on the mold, such as: damage to the inner wall of the cavity, and overheating causes the mold to burst. Similarly, when the initial pouring temperature is too low, it will cause poor filling ability of the melt, premature solidification, and incomplete casting. For aluminum alloy materials, the initial pouring temperature should be in a certain range above the liquidus (20~100 ℃), the primary α-Al at this temperature can be solidified into spherical or granular, fine grain, uniform distribution, casting mechanics Better performance.

Filling speed

The filling speed in gravity casting refers to the flow rate of the melt entering the cavity through the gate in unit time. The filling speed of common aluminum alloy melts is 0.4~0.6 m/s. When the melt is filling, there is an oxide film at the front end. A reasonable filling speed can ensure the smoothness of the melt flow and the integrity of the oxide film, that is, no oxide slag will be formed due to turbulent flow [28]. When the filling speed of the melt is too high, the melt will break through the oxide film on the surface, causing the oxide film to crack and roll back, forming oxide slag inclusions, which has a great impact on the final mechanical properties of the casting, especially the fatigue performance of important castings. When the filling speed of the melt is too small, the heat loss of the melt itself is large, the solidification proceeds early, and the cavity cannot be filled completely.

Gating system design

Reasonable gating system design is a key link to ensure the quality of castings, which can effectively guide the filling and solidification of the melt and eliminate unfavorable factors [29]. Common gating systems include: open, semi-closed and closed. In the open gating system, the filling speed of the melt entering the cavity is small, the filling is stable, and the impact of scouring is low; but the melt filling type The speed of the cavity is slow. During the filling process of the runner, the melt is prone to turbulent flow, and the surface oxide film is easily broken, thus entering the cavity and affecting the quality of the casting. The closed gating system can ensure a faster filling speed, is conducive to the floating and removal of inclusions, has better slag resistance, and can also better prevent gas from being involved in the melt filling process; but its inner gate The filling pressure at the place is high, and the melt mostly fills the cavity at a high speed in a spray state, which is easy to cause splashing, thereby forming more secondary oxidation slag inclusions and other defects. Therefore, when designing the gating system, it is necessary to focus on the shape, structure and material properties of the casting, and select a reasonable gating system in combination with the principles of the casting forming process. Aluminum alloy materials generally use an open gating system design in the gravity casting process.

3D Printing Sand Casting

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At present, traditional manufacture technology is difficult to produce complex parts, while 3D printing sand casting, as a new casting method, is not sensitive to the complexity of parts. Therefore, combining the advantages of 3D printing with the advantages of traditional casting, it can realize the “integrated, short cycle, high precision and high value-added” manufacturing of casting products, and the advantages of fast production response, high efficiency, and low research cost. This technology can also meet the increasing needs of lightweight, green and intelligent equipments, and has broad application prospects in the fields of automotive, ship, aerospace and other industries.

With the emergence of the concept of intelligent factory and intelligent production, traditional manufacturing industry has begun to seek new technological growth points in the environment of “manufacturing power”, and “3D printing technology”, known as the new generation of industrial revolution, has begun to promote this a process.

Based on the concepts of rapid prototyping and topology design, the technology is gradually applied to traditional industrial manufacturing fields, such as the production of complex components for automobiles, ships, rail transit and aerospace. In the process of moving from a manufacturing country to a manufacturing power, my country’s basic manufacturing industry has been continuously upgraded and transformed, and high-precision manufacturing has been further developed. The demand for some high-value-added parts and components is also growing rapidly, especially aerospace and automotive castings manufacturing. and other mechanical components with critical feature requirements. The material and design of these parts have changed a lot compared to the traditional concept, and the manufacturing process and method need to be changed [4,5]. It is common that multiple traditional functional parts are gradually integrated and integrated, thereby reducing the occurrence of fatigue fractures or potential accidents at the joints during use.

The industrial scale of the 3D printing (additive manufacturing) market will also be huge under this trend. In recent years, major manufacturing enterprises in my country have begun to introduce 3D printing equipment or production lines one after another, and try to use this technology for industrial upgrading. Because the current traditional manufacturing parts production technology is generally more sensitive to complex parts, the production of a complex part often requires multiple sets of molds, and then splicing, testing and other processes. Those complex parts with high timeliness requirements are extremely disadvantageous in actual production. 3D printing technology has the advantage of being less sensitive to the complexity of parts, thereby reducing the production cost of complex structural parts and improving the production efficiency. However, the current 3D printing metal parts technology cannot meet the application standards of parts in terms of forming size and efficiency, and there is still a certain distance from the actual production application.

The Advantage Of 3D Printing Sand Casting

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With the globalization of the economic market, the accelerated iterative upgrade of the product system, and the continuous increase in the demand for design and development, it has begun to profoundly affect the traditional foundry industry. It is required that the traditional industrial model must be transformed and upgraded as soon as possible, and new technological growth points must be found to meet the market demand. As one of the representative technologies of the new industrial revolution, 3D printing technology is gradually being applied to the traditional casting field.

This technology is not sensitive to the complexity of the product, and combined with the advantages of the traditional casting industry, it will burst out huge technological advantages.

• The application fields of 3D printing are mainly divided into two aspects: direct forming and indirect forming of parts. The direct forming method of parts mainly includes: powder bed melting technology, material jetting technology, directional energy deposition technology, etc.; the method of indirectly forming parts by printing a mold is mainly adhesive jetting technology. Because the cost value of metal powder is high and the utilization rate is low, casting 3D printing mainly adopts the method of indirect forming parts, that is, after using 3D printing equipment to print the mold, and then using the molten metal casting technology, Figure 1-5 Production process for 3D printing sand casting process.
• 3D printing sand casting abandons the traditional manufacturing processes such as wooden molds and metal molds, and directly realizes the integrated manufacturing and shaping of the required sand molds. This technology does not require manual intervention, greatly improves the production efficiency of sand molds for complex parts, improves the production environment, reduces the overall production cost and manufacturing risk, and realizes the controllable production of sand mold preparation parameters.
• When 3D printing technology and traditional manufacturing technology are combined into 3D printing sand mold rapid casting technology, it has many advantages. For example: use binder and sand to print, bond and cure layer by layer, without the need for complex and expensive molds, to achieve economical production of parts; ideal prototype manufacturing and parts optimization, molding multiple parts at one time, no external frame restrictions , with fast efficiency, etc.; the product takes only a few weeks from design delivery to solid molding, without complicated procedures such as mold opening and mold trial, which greatly optimizes the production efficiency and level of the product.
• Compared with traditional modeling techniques, 3D printing has fewer restrictions, and product personnel can obtain the most detailed geometric contours without thinking about structural difficulties such as demolding and chamfering. And unlike metal 3D printing, binder jet printing does not require extra brackets, the unused sand can be recycled after printing, and the printed sand can also be used for other purposes through technical processing, so as to truly achieve green sand castings, zero waste discharge