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How to control the shrinkage rate in precision casting
Category：answer Publishing time：2025-12-06 01:30:54 Browse： Times
Precision casting is a high-precision, high-surface-quality metal forming process widely used in aerospace, automotive manufacturing, medical devices, and other fields. However, during the precision casting process, metals will undergo volume shrinkage during the solidification and cooling process, resulting in changes in casting size and even the formation of defects such as shrinkage holes and shrinkage cavities. Therefore, how to effectively control the shrinkage rate is one of the key factors to improve the quality of precision casting products.
1. Understanding the formation mechanism of shrinkage rate
Metals usually undergo three stages of shrinkage during the solidification process: liquid shrinkage, solidification shrinkage, and solid shrinkage. Among them, the shrinkage in the first two stages mainly leads to internal defects in castings, while the third stage mainly affects the final size accuracy. The shrinkage rates of different metal materials vary, for example, the shrinkage rate of cast steel is about 1.6% to 2.0%, while that of aluminum alloys is between 0.5% and 1.0%. Therefore, when designing castings and molds, it is necessary to make size compensation according to the material characteristics.
2. Material Selection and Proportion Control
The selection of materials directly affects the size of the shrinkage rate. By optimizing the alloy composition ratio, the shrinkage rate can be reduced to some extent or its solidification characteristics can be improved. For example, adding an appropriate amount of silicon to aluminum alloys can effectively reduce solidification shrinkage and improve fluidity, thereby reducing the formation of shrinkage holes and gas holes. In addition, the use of high-purity raw materials and the reduction of impurity content also help to improve the uniformity of metal solidification and reduce the risk of shrinkage defects.
3. Rational Design of Casting Structure and Gating System
Reasonable casting structure design is the foundation for controlling shrinkage rate. It should avoid uneven thickness, dead corners, and abrupt structures to reduce shrinkage differences caused by local overheating and uneven cooling. At the same time, the design of the gating system is crucial. By adopting the principle of sequential solidification, reasonable risers and feeding channels are set to guide the metal liquid to achieve effective compensation during the solidification process, reducing defects such as shrinkage holes and shrinkage cavities. In addition, the position and size of the sprue should also be carefully designed to control the flow direction and cooling speed of the metal liquid.
4. Optimization of Mold Design and Manufacturing Accuracy
The design accuracy of the mold directly affects the dimensional accuracy of the casting. To compensate for shrinkage, the mold cavity size needs to be enlarged according to the material shrinkage rate. Modern precision casting often adopts computer simulation technology (such as ProCAST, MAGMAsoft) for virtual casting, predicts shrinkage trends, and carries out pre-deformation design of the mold to optimize the structure in advance, thus achieving precise control.
In addition, the selection of mold material also affects cooling speed and thermal conductivity, thereby indirectly affecting shrinkage behavior. High thermal conductivity mold materials help to accelerate heat dissipation, reduce temperature gradients, and improve tissue uniformity.
5. Control of Casting Process Parameters
Accurate control of process parameters during the casting process is the key to controllable shrinkage. This includes pouring temperature, cooling speed, holding time, and so on. Although a higher pouring temperature can improve fluidity, it will exacerbate liquid shrinkage; while a too fast cooling speed may lead to surface hardening, hindering internal compensation. Therefore, the optimal process window should be selected according to the characteristics of the alloy to ensure that the metal liquid solidifies uniformly and smoothly in the mold.
6. Application of Advanced Simulation and Detection Technology
With the development of digital manufacturing, the use of casting simulation software for process optimization has become a trend. Through simulation analysis, the shrinkage of castings under different process parameters can be predicted, potential defects can be discovered in advance, and mold and process design can be optimized. At the same time, combined with non-destructive testing methods such as three-dimensional scanning and X-ray flaw detection, a comprehensive evaluation of the internal structure and dimensional accuracy of castings can be carried out to ensure that the product meets the design requirements.
---
Conclusion
The control of shrinkage in precision casting is a systematic project, involving multiple aspects such as materials, structure, molds, and processes. Only through scientific design, precise process control, and the assistance of advanced simulation technology can the stable production of high-precision and high-quality castings truly be realized. In the future, with the development of intelligent manufacturing and new material technologies, precision casting will move towards a higher level in shrinkage control.
Precision casting is a high-precision, high-surface-quality metal forming process widely used in aerospace, automotive manufacturing, medical devices, and other fields. However, during the precision casting process, metals will undergo volume shrinkage during the solidification and cooling process, resulting in changes in casting size and even the formation of defects such as shrinkage holes and shrinkage cavities. Therefore, how to effectively control the shrinkage rate is one of the key factors to improve the quality of precision casting products.
1. Understanding the formation mechanism of shrinkage rate
Metals usually undergo three stages of shrinkage during the solidification process: liquid shrinkage, solidification shrinkage, and solid shrinkage. Among them, the shrinkage in the first two stages mainly leads to internal defects in castings, while the third stage mainly affects the final size accuracy. The shrinkage rates of different metal materials vary, for example, the shrinkage rate of cast steel is about 1.6% to 2.0%, while that of aluminum alloys is between 0.5% and 1.0%. Therefore, when designing castings and molds, it is necessary to make size compensation according to the material characteristics.
2. Material Selection and Proportion Control
The selection of materials directly affects the size of the shrinkage rate. By optimizing the alloy composition ratio, the shrinkage rate can be reduced to some extent or its solidification characteristics can be improved. For example, adding an appropriate amount of silicon to aluminum alloys can effectively reduce solidification shrinkage and improve fluidity, thereby reducing the formation of shrinkage holes and gas holes. In addition, the use of high-purity raw materials and the reduction of impurity content also help to improve the uniformity of metal solidification and reduce the risk of shrinkage defects.
3. Rational Design of Casting Structure and Gating System
Reasonable casting structure design is the foundation for controlling shrinkage rate. It should avoid uneven thickness, dead corners, and abrupt structures to reduce shrinkage differences caused by local overheating and uneven cooling. At the same time, the design of the gating system is crucial. By adopting the principle of sequential solidification, reasonable risers and feeding channels are set to guide the metal liquid to achieve effective compensation during the solidification process, reducing defects such as shrinkage holes and shrinkage cavities. In addition, the position and size of the sprue should also be carefully designed to control the flow direction and cooling speed of the metal liquid.
4. Optimization of Mold Design and Manufacturing Accuracy
The design accuracy of the mold directly affects the dimensional accuracy of the casting. To compensate for shrinkage, the mold cavity size needs to be enlarged according to the material shrinkage rate. Modern precision casting often adopts computer simulation technology (such as ProCAST, MAGMAsoft) for virtual casting, predicts shrinkage trends, and carries out pre-deformation design of the mold to optimize the structure in advance, thus achieving precise control.
In addition, the selection of mold material also affects cooling speed and thermal conductivity, thereby indirectly affecting shrinkage behavior. High thermal conductivity mold materials help to accelerate heat dissipation, reduce temperature gradients, and improve tissue uniformity.
5. Control of Casting Process Parameters
Accurate control of process parameters during the casting process is the key to controllable shrinkage. This includes pouring temperature, cooling speed, holding time, and so on. Although a higher pouring temperature can improve fluidity, it will exacerbate liquid shrinkage; while a too fast cooling speed may lead to surface hardening, hindering internal compensation. Therefore, the optimal process window should be selected according to the characteristics of the alloy to ensure that the metal liquid solidifies uniformly and smoothly in the mold.
6. Application of Advanced Simulation and Detection Technology
With the development of digital manufacturing, the use of casting simulation software for process optimization has become a trend. Through simulation analysis, the shrinkage of castings under different process parameters can be predicted, potential defects can be discovered in advance, and mold and process design can be optimized. At the same time, combined with non-destructive testing methods such as three-dimensional scanning and X-ray flaw detection, a comprehensive evaluation of the internal structure and dimensional accuracy of castings can be carried out to ensure that the product meets the design requirements.
---
Conclusion
The control of shrinkage in precision casting is a systematic project, involving multiple aspects such as materials, structure, molds, and processes. Only through scientific design, precise process control, and the assistance of advanced simulation technology can the stable production of high-precision and high-quality castings truly be realized. In the future, with the development of intelligent manufacturing and new material technologies, precision casting will move towards a higher level in shrinkage control.
