What is Sand Casting?

In the modern manufacturing system, sand casting is an extremely important process method that has been continuously providing key components for numerous fields for a long time.

Essentially, sand casting is a method that uses molding sand as the main molding material and manufactures molds through specific process steps to obtain castings. Its history is long. Thousands of years ago, when ancient civilizations were exploring means of forming metal products, they discovered that moistened and shaped sand could serve as a temporary “mold” for liquid metal. Later, with the continuous development of technology, it has gradually evolved into the precise and complex process system we have today.

The pattern is equivalent to the model of the casting and is usually made of wood, metal, or plastic. It accurately replicates the external shape and size of the required casting and enlarges the size appropriately according to the cooling and solidification shrinkage characteristics of the metal material to offset the shrinkage of the casting after forming. For example, when casting an automobile engine block, pattern engineers need to design a three-dimensional model using CAD technology based on the complex internal cavity structure, cylinder wall thickness, and detailed dimensions of the connecting parts of the block. Then, they use a CNC machining center to process the material into a physical pattern, strictly controlling the error to ensure the high precision of subsequent castings.

Immediately after the pattern is made, the molding process follows. Molders compact the prepared molding sand around the pattern. Common manual molding methods include ramming and jolting, etc. These traditional methods rely on the skilled operation skills of workers and can meet the production needs of small batches and complex-structured castings. Machine molding, on the other hand, is widely used in mass production due to its high efficiency and stability. For example, an automated high-pressure molding machine can compact the molding sand into a uniformly hard mold in a short time, making full preparations for subsequent pouring. During the molding process, it is also necessary to reasonably set up gates and risers. The gate is the the channel through which the liquid metal flows into the mold cavity and can guide the liquid metal to enter smoothly and quickly; the riser is used to supplement the liquid metal during the solidification and shrinkage stage of the casting to prevent shrinkage holes and porosity.

After completing the molding, the melting and pouring links follow. According to the material requirements of the casting, raw materials such as pig iron, steel scrap，and various alloys are put into electric furnaces, cupolas, etc. in precise proportions. Furnace operators rely on rich experience and advanced spectrometers to monitor in real time to ensure that the chemical composition and temperature of the liquid metal accurately meet the standards. When the liquid metal reaches the ideal state, it is injected into the mold cavity at a specific speed and angle using a crane or an automatic pouring system. The speed control in this process is crucial. If it is too fast, the molding sand will be washed away, resulting in sand holes; if it is too slow, the liquid metal will cool and solidify, causing the casting to fail to form completely.

After the casting has fully solidified and 冷却 in the mold and is demolded, the casting is initially formed, but a large amount of molding sand and oxide scale adheres to its surface. At this time, sand cleaners start to work. They hold tools such as pneumatic picks, grinding wheels, and sandblasters. According to the characteristics of different castings, they either knock and vibrate forcefully, grind finely, or spray at high pressure to carefully remove the attachments and make the surface of the casting smooth. Subsequently, after heat treatment, machining, and other processes, it finally becomes a high-quality product that meets industrial standards.

Sand casting has the advantages of low material cost and strong adaptability. It can produce both small precision parts, such as watch gears, and large industrial components, such as bridge supports. It can be used for common cast iron, steel scrap，as well as aluminum alloys, copper alloys, and other materials, providing strong support for the diversified development of the manufacturing industry. Although facing challenges from emerging processes such as die casting and investment casting, sand casting is still constantly improving and innovating, continuously playing an important role in the casting field and promoting the development of human industry.