In recent years, with advancements in science and technology, significant progress has been made in casting equipment. Production technologies in areas such as molding and core-making, alloy melting, and solidification control have seen substantial development, moving toward green and intensive casting practices. Near-net-shape forming currently enables castings to be used with little to no additional machining. Computer-aided design and simulation analysis have been widely adopted in casting production, significantly reducing development cycles and costs while markedly improving quality. 3D Printing rapid prototyping technology has further propelled advancements in casting, enhancing the efficiency of new product development and the flexibility of structural design.
I. Molding and Core-Making Technology
Molding and core-making are key processes in casting formation, significantly impacting casting quality, manufacturing costs, production efficiency, labor intensity, and environmental pollution.
(1) Clay Sand Green Sand Molding Process
Air impulse molding offers advantages such as high mold compactness, uniformity, the ability to produce complex castings, low noise, and energy efficiency. Static pressure molding eliminates the noise pollution associated with jolt-squeeze molding machines, greatly improving the working environment. A final compaction using a pressure plate ensures effective compactness and uniform hardness across the mold, resulting in high dimensional accuracy of castings. Highly mechanized, automated, and high-density green sand molding processes like shot molding, air impulse molding, and static pressure molding offer benefits such as low cost, minimal pollution, high efficiency, and excellent quality, making them the primary methods for producing small and medium-sized castings.
(2) Vacuum Sealed Molding (V-Process)
The basic principle of the V-process involves filling a specially designed flask with dry, binder-free sand, sealing it with a plastic film, and creating a vacuum to compact the sand through the pressure difference inside and outside the mold. This method is suitable for producing castings with large surface areas, thin walls, smooth surfaces, and clear contours. In recent years, the V-process has been widely used in the production of railway vehicle castings, forklift counterweights, artistic castings, large-scale signs, piano string frames, and bathtubs.
(3) Resin Sand Molding and Core-Making Process
Resin sand offers high strength and dimensional accuracy for molds and cores, resulting in excellent surface quality for castings. However, it can cause environmental pollution. Developing low-pollution binders, catalysts, hardeners, and supporting environmental treatment equipment is key to promoting and advancing resin sand molding and core-making processes.
(4) Sodium Silicate Sand Molding and Core-Making Process
Sodium silicate sand exhibits good fluidity, ease of compaction, and lower energy consumption. Its high-temperature collapsibility makes it particularly suitable for steel castings prone to cracking. However, sodium silicate sand has poor shakeout properties, and used sand regeneration is challenging. Therefore, research into modifying sodium silicate and developing new regeneration and recycling processes and equipment for sodium silicate sand is a priority. The application of ester-hardened sodium silicate sand has improved the recycling rate of used sand and has been adopted for medium and large steel castings.
(5) Core Assembly Molding Process
Core assembly molding, known as "precision sand casting," is suitable for producing near-net-shape complex castings (such as engine blocks and cylinder heads) and requires high dimensional accuracy of cores. With the development and application of various chemical binders that cure at room temperature, it is now possible to produce highly precise sand cores. The cold box core assembly molding method has been successfully used for producing near-net-shape castings like automobile engine blocks.
(6) Casting Coatings
The quality of the working surface of sand molds (cores) in direct contact with molten metal significantly impacts casting quality. Applying coatings to these surfaces is an economical and effective method to improve quality. The development and application of high-performance organic and inorganic coatings are important technological approaches to enhancing casting dimensional accuracy and surface quality.
II. Special Casting and Near-Net-Shape Technology
As modern manufacturing equipment demands higher dimensional accuracy and surface quality for castings, special casting is evolving toward near-net-shape forming. In recent years, as a precision forming technology for achieving minimal or no machining allowances, the application and development of special casting are mainly reflected in the following two aspects:
1) Developing new processes and advancing composite casting technologies. Strengthen research and application of magnesium alloy die casting and squeeze casting technologies to meet the demands of automotive lightweighting. Enhance research on titanium alloy investment casting processes to address mold material challenges. Use rapid prototyping technology to replace traditional wax pattern forming methods, shortening production cycles. Investigate new differential pressure casting technologies and equipment to promote the transition from low-pressure casting to differential pressure casting.
2) Near-net-shape casting technology (Near Net Shape Process) has changed the traditional perception that casting can only provide rough blanks, enabling the production of castings without machining allowances. For example, squeeze casting technology is characterized by "stable filling, solidification under pressure, feeding, and plastic deformation," resulting in castings with high metallurgical quality, dimensional accuracy, high process yield, and reduced machining requirements. Near-net-shape technology represents the future of the casting industry, as it can reduce material consumption, energy use, labor costs, and improve casting quality, better meeting the needs of manufacturing equipment development.
