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现代熔模精密铸造的方法

Modern investment casting method

现代熔模精密铸造方法在工业生产中得到实际应用是在二十世纪四十年代。当时航空喷气发动机的发展，要求制造象叶片、叶轮、喷嘴等形状复杂，尺寸精确以及表面光洁的耐热合金零件。由于耐热合金材料难于机械加工，零件形状复杂，以致不能或难于用其它方法制造，因此，需要寻找一种新的精密的成型工艺，于是借鉴古代流传下来的失蜡精密铸造，经过对材料和工艺的改进，现代精密铸造方法在古代工艺的基础上获得重要的发展。所以，航空工业的发展推动了精密铸造的应用，而精密铸造的不断改进和完善，也为航空工业进一步提高性能创造了有利的条件。

The modern investment casting method was applied in industrial production in 1940s. The development of jet engines at that time required the manufacture of heat-resistant alloy parts with complex shapes, precise sizes and smooth surfaces, such as blades, impellers and nozzles. Because the heat-resistant alloy material is difficult to machine and the shape of the parts is complex, so it is impossible or difficult to manufacture by other methods. Therefore, it is necessary to find a new precise forming process. Therefore, it is necessary to learn from the ancient lost wax precision casting. After improving the material and technology, the modern precision casting method is used in the ancient technology. On the basis of important development. Therefore, the development of aviation industry has promoted the application of precision casting, and the continuous improvement and perfection of precision casting has created favorable conditions for further improving the performance of aviation industry.

我国是于上世纪五、六十年代开始将精密铸造应用于工业生产。其后这种先进的精密铸造工艺得到巨大的发展，相继在航空、汽车、机床、船舶、内燃机、气轮机、电讯仪器、武器、医疗器械以及刀具等制造工业中被广泛采用，同时也用于工艺美术品的制造。

China began to apply precision casting to industrial production in five and 60s of last century. Since then, this advanced precision casting technology has been greatly developed, and has been widely used in aviation, automotive, machine tools, ships, internal combustion engines, gas turbines, telecommunications instruments, weapons, medical devices and knives manufacturing industries, but also for the manufacture of Arts and crafts.

所谓精密铸造工艺，简单说就是用易熔材料（例如蜡料或塑料）制成可熔性模型（简称熔模或模型），在其上涂覆若干层特制的耐火涂料，经过干燥和硬化形成一个整体型壳后，再用蒸汽或热水从型壳中熔掉模型，然后把型壳置于砂箱中，在其四周填充干砂造型，最后将铸型放入焙烧炉中经过高温焙烧（如采用高强度型壳时，可不必造型而将脱模后的型壳直接焙烧），铸型或型壳经焙烧后，于其中浇注熔融金属而得到铸件。

The so-called precision casting process is simply to use fusible materials (such as wax or plastic) to make a fusible model (for short, investment mold or model), coated with a number of layers of special refractory coatings, after drying and hardening to form a whole shell, and then use steam or hot water from the shell to melt the model, and then the shell. Place the mold in the sand box and fill it with dry sand. Finally, put the mold into the calciner and bake it at high temperature (for example, when the high strength mold shell is used, the mold shell can be baked directly without molding). After baking, the mold or shell can be cast with molten metal.

熔模铸件尺寸精度较高，一般可达CT4-6（砂型精密铸造为CT10~13，压铸为CT5~7）,当然由于精密铸造的工艺过程复杂，影响铸件尺寸精度的因素较多，例如模料的收缩、熔模的变形、型壳在加热和冷却过程中的线量变化、合金的收缩率以及在凝固过程中铸件的变形等，所以普通熔模铸件的尺寸精度虽然较高，但其一致性仍需提高（采用中、高温蜡料的铸件尺寸一致性要提高很多）。

Investment casting has a high dimensional accuracy, generally up to CT4-6 (sand casting for CT10-13, die casting for CT5-7). Of course, due to the complex process of investment casting, there are many factors affecting the dimensional accuracy of the casting, such as the shrinkage of the mold, the deformation of the investment mold, the change of the linearity of the shell during heating and cooling, and the recovery of the alloy. Because of the shrinkage and deformation of the casting during solidification, the dimensional accuracy of the ordinary investment casting is higher, but its consistency still needs to be improved (the dimensional consistency of the castings with medium and high temperature wax should be improved a lot).

压制熔模时，采用型腔表面光洁度高的压型，因此，熔模的表面光洁度也比较高。此外，型壳由耐高温的特殊粘结剂和耐火材料配制成的耐火涂料涂挂在熔模上而制成，与熔融金属直接接触的型腔内表面光洁度高。所以，熔模铸件的表面光洁度比一般精密铸造件的高，一般可达Ra.1.6~3.2μm。

When pressing the investment mold, the high surface finish of the cavity is used, so the surface finish of the investment mold is also relatively high. In addition, the shell is made of high temperature resistant special binder and refractory, and the refractory coating is coated on the investment mold. The surface of the cavity directly contacted with the molten metal has high smoothness. Therefore, the surface finish of investment castings is higher than that of ordinary precision casting parts, generally up to Ra.1.6~3.2 m.

精密铸造最大的优点就是由于熔模铸件有着很高的尺寸精度和表面光洁度，所以可减少机械加工工作，只是在零件上要求较高的部位留少许加工余量即可，甚至某些铸件只留打磨、抛光余量，不必机械加工即可使用。由此可见，采用精密铸造方法可大量节省机床设备和加工工时，大幅度节约金属原材料。

The greatest advantage of investment casting is that investment casting has a high dimensional accuracy and surface finish, so it can reduce the mechanical processing work, but the parts require a little machining allowance, and even some castings only leave grinding, polishing allowance, without mechanical processing can be used. Thus it can be seen that the precision casting method can greatly save machine tool equipment and processing time, and greatly save metal raw materials.

精密铸造方法的另一优点是，它可以精密铸造各种合金的复杂的铸件，特别可以精密铸造高温合金铸件。如喷气式发动机的叶片，其流线型外廓与冷却用内腔，用机械加工工艺几乎无法形成。用精密铸造工艺生产不仅可以做到批量生产，保证了铸件的一致性，而且避免了机械加工后残留刀纹的应力集中。

Another advantage of the precision casting method is that it can be used to cast complex castings of various alloys, especially superalloy castings. For example, the blade of jet engine, its streamlined profile and cooling cavity, with mechanical processing technology can hardly be formed. The precision casting process can not only produce in batches and ensure the consistency of castings, but also avoid the stress concentration of the residual knife grain after machining.