Precision castings have high dimensional accuracy and small surface roughness. Suitable for castings with complex structure and shape.

    The geometric accuracy of precision castings is determined by the machining allowance, the deviation of the casting size and weight from the rated value. Under the same conditions, the geometric accuracy reflects the machining of precision castings in terms of machining workload and metal consumption. The advanced level of the process.

    The allowable deviation of size and weight and the machining allowance of castings are determined according to the GB6414-86GB/T11351-89GB/T11350-89 standard and the technical conditions of the order, and the actual deviation is determined according to the data of the technical inspection department. The so-called casting size control is to control the dispersion degree of the measured value under the premise that the measured average value is consistent with the nominal size of the casting. This discrete reason is usually caused by random changes or systematic errors such as production technical conditions and raw material characteristics. Precision castings should make judgments and corresponding countermeasures according to the nature of the error, and improve the dimensional accuracy to meet the requirements of the standard.

    Sometimes, there are only one or two dimensions on the entire casting that require stricter rough size tolerances. At this time, it is not necessary to specify tolerances for all dimensions at the same level. In order to improve the precision level of castings, metal molds can generally be used. When significant improvement is required, the molding method must be changed, such as shell casting or other precision casting processes. However, it will inevitably lead to higher mold costs, prolonged production preparation periods, and lower casting costs. Increase exponentially.

    When evaluating the accuracy of the casting geometry, in addition to the machining surface allowance and the weight deviation of the casting, the tolerance range or deviation range of the most representative wall thickness and rib thickness should also be given. The wall thickness necessary for the structure is determined by the casting designer, and the minimum allowable wall thickness is determined by the casting technologist. In most cases, the decision of the designer of the precision casting results in the wall thickness marked on the drawing. The allowable deviation between the design wall thickness and the actual wall thickness is an important indicator of the accuracy of the casting geometry.