Dimensional accuracy of die castings
The dimensional accuracy of die-castings is a key quality indicator. It refers to the degree of conformity between the actual dimensions of a die-casting and its designed dimensions, directly impacting the assembly performance and operational reliability of the component. In modern industrial production, especially in high-precision fields such as automotive, aerospace, and electronics, the dimensional accuracy requirements for die-castings are becoming increasingly stringent, typically requiring control at the micron level. Die-castings with poor dimensional accuracy can lead to assembly difficulties, excessive or insufficient clearances, functional failures, and even safety incidents. Therefore, in-depth research into the factors affecting the dimensional accuracy of die-castings and the implementation of effective control measures are crucial for improving die-casting quality and production efficiency.
Numerous factors influence the dimensional accuracy of die-cast parts, with the shrinkage characteristics of the alloy being the primary factor. Different die-casting alloys exhibit varying shrinkage rates. Even for the same alloy, shrinkage can be affected by factors such as composition, temperature, and casting structure. For example, the shrinkage rate of aluminum alloys generally ranges from 0.8% to 1.2%, that of zinc alloys from 0.5% to 0.7%, and that of magnesium alloys from 0.7% to 1.0%. When designing a mold, the mold cavity dimensions must be accurately calculated based on the alloy’s shrinkage rate to ensure that the casting will meet the required design dimensions after cooling. Inaccurate shrinkage estimates and improper mold design will inevitably lead to dimensional deviations in the die-casting. Furthermore, the alloy’s shrinkage process can be affected by factors such as uneven casting wall thickness and inconsistent cooling rates, resulting in uneven shrinkage and casting deformation, further compromising dimensional accuracy.
The manufacturing precision and stability of the mold have a direct impact on the dimensional accuracy of die-cast parts. The mold is a key tool in die-casting molding, and its cavity size, shape, surface roughness, and other factors are directly reflected in the die-cast part. If the mold machining precision is not high, such as deviations in cavity dimensions, uneven parting surfaces, and excessive clearances in the guide mechanism, the dimensional accuracy of the die-cast part will decrease. For example, if the dimensional error of the mold cavity is 0.02mm, the dimensional error of the die-cast part will be at least this value, or even greater. Furthermore, the mold’s accuracy will decrease over time due to wear, thermal deformation, and other factors. Therefore, regular mold maintenance and repair are necessary to ensure its accuracy and stability. Furthermore, mold temperature control can also affect dimensional accuracy. Uneven mold temperature can lead to different cooling rates and inconsistent shrinkage in different parts of the casting, resulting in dimensional deviation and deformation.
Controlling die-casting process parameters is crucial for ensuring the dimensional accuracy of die-cast parts. Process parameters such as injection speed, injection pressure, holding pressure, holding time, and pouring temperature all influence the molding process and shrinkage characteristics of the casting, which in turn affects dimensional accuracy. Excessively fast injection speeds can cause turbulence and impact in the molten metal cavity, resulting in internal stress and deformation in the casting. Too slow an injection speed can lead to insufficient filling, compromising the dimensional integrity of the casting. Insufficient injection and holding pressures can result in insufficient compaction of the casting, increasing shrinkage and undersize. Excessively high pressures can cause mold deformation, compromising the dimensional accuracy of the casting. Excessively high pouring temperatures increase the alloy’s shrinkage, leading to greater dimensional deviations in the casting. Excessively low temperatures reduce the fluidity of the molten metal, compromising filling efficiency. Therefore, it is necessary to optimize die-casting process parameters based on the part structure and alloy type, and to maintain these parameters consistently throughout production to ensure dimensional accuracy.
Inspection technology and quality control systems play a vital role in ensuring the dimensional accuracy of die-castings. High-precision inspection equipment can accurately measure dimensional errors in die-castings, providing a basis for process adjustments and quality improvements. Currently, commonly used inspection equipment includes coordinate measuring machines (CMMs), projectors, and dial indicators. CMMs, among others, enable high-precision measurements in three dimensions, with an accuracy of up to 0.001mm, making them suitable for dimensional inspection of complex die-castings. Furthermore, establishing a comprehensive quality control system encompassing first-article inspection, patrol inspections, and final inspections can promptly identify castings with dimensional deviations and prevent defective products from entering the next process. During production, methods such as statistical process control (SPC) are used to analyze die-casting dimensional data, identify patterns and causes of dimensional fluctuations, and implement targeted adjustments, such as correcting mold dimensions and optimizing process parameters, to achieve continuous improvement in dimensional accuracy.
As industry’s requirements for the dimensional accuracy of die-casting parts continue to increase, related technologies and processes are also evolving. The application of new mold materials and manufacturing technologies, such as high-speed machining and electrospark forming, has improved mold manufacturing accuracy and lifespan. The use of intelligent die-casting equipment enables real-time monitoring and automatic adjustment of process parameters, reducing the impact of human factors on dimensional accuracy. The application of numerical simulation technology can predict the shrinkage and deformation of castings before mold manufacturing and production, providing guidance for mold design and process optimization, thereby improving the dimensional accuracy of die-casting parts. In the future, with the development of intelligent manufacturing technology, the dimensional accuracy control of die-casting parts will be more accurate and efficient, better meeting the demand for high-precision parts in various industries.
