Precision casting is also called investment casting. This casting process minimizes or does not cut during the casting process. It is a casting method with a wide range of applications, high dimensional accuracy of the casting, and excellent surface quality. It is not in ultra-high temperature conditions, and is more suitable for casting components in high-precision industries such as aerospace and national defense. It was the first to use stainless steel precision casting method to cast the turbine blades in its leading aero-engine at that time. The finished product was praised by all aspects, and this method was widely promoted. Stainless steel precision casting is a technology in the foundry industry, but it is different from the traditional foundry industry because the added value of precision casting products is higher.
Silica Sol Shell Process
The silica sol shell making process is generally used in the more sophisticated internal combustion engine parts casting industry. The coating used in this method has better stability, does not require a chemical hardening process, is resistant to high temperatures, and has better resistance to deformation. However, this technology also has this certain shortcoming, that is, the warmth of the wax mold is relatively poor, which can be improved by adding surfactants, but it will increase the investment to a certain extent.
Water Glass Shell Process
This method was invented very early. Our country also introduced this technology from the Soviet Union in the 1950s and 1960s. This method has low cost, relatively simple operation, and low raw material requirements. The basic characteristics of the process use paraffin-stearic acid low-temperature mold material, and the binder in the shell making process uses water glass, which is widely used in stainless steel precision casting. However, the biggest problem of this method compared to the silica sol shell making process is that the surface quality of the obtained castings is average and the dimensional accuracy is low. Since the introduction of this technology, relatively large improvements have been made, mainly in the following aspects:
1. Improve the shell coating.
The main improvement is to add a certain amount of refractory clay to the back coating of the shell, which greatly improves the strength of the shell, and realizes the single shell roasting and firing.
2. Optimization of hardener.
The traditional hardener mostly uses ammonium chloride, but this material will release a large amount of ammonia and nitrogen oxide gas during the casting process, which will pollute the atmosphere. Therefore, aluminum chloride solution is used instead, and aluminum chloride crystal is further used. The effect of the agent is similar to that of ammonium chloride, but in recent years, the use of magnesium chloride hardener has a relatively large advantage in terms of hardening speed and residue, so now it is more inclined to use magnesium chloride as a hardener.
3. Composite shell.
Because the surface quality of the shell of the water glass coating has certain defects, many original parts are cast in the form of multi-layer mold composite casting, which saves costs on the one hand and improves the surface quality of the casting on the other hand.
4. Development of new technology.
At present, the more mature new processes should be self-priming casting process, foam plastic mold, molten mold shell casting and other processes. These processes have leading advantages in some aspects, but future improvements will still attract scientific and technological workers.
Multi-technology Cross Use with Rapid Prototyping Technology
The design and mold manufacturing in the process of making stainless steel precision casting wax molds are more complicated and time-consuming, but rapid prototyping technology can make up for this shortcoming. The rapid prototyping technology alone can not be implemented because of material limitations, so many in recent years The use of polymer technology to obtain the round shape of the casting, and then manufacture the wax mold, which is used in stainless steel precision casting. For example, light curing three-dimensional modeling technology (SLA) and selective laser sintering technology (SLS). These two technologies are currently relatively mature technologies used in combination with investment casting. SLA technology can provide higher dimensional accuracy, especially for parts. The accuracy of the outer surface, SLS, to a certain extent, the raw materials are slightly cheaper, but the accuracy also has a certain gap compared with the SLA technology, which is suitable for some casting work with cost requirements. However, it is still necessary to pay attention to control the key combination of rapid prototyping technology and stainless steel precision casting technology during use, such as comprehensive consideration of cost control and casting accuracy of parts, and selecting the appropriate balance point is rapid prototyping technology and investment casting technology. The key issue of organic integration.
Multi-technology Cross Use with Computer Technology
The plan design and optimization work in the stainless steel precision casting process is a relatively labor-consuming and time-consuming work. In recent years, with the continuous development of computer technology, many industries that require a large amount of calculation and precision calculation have introduced computer work, and correspondingly Various calculation softwares have been developed, such as ProCAST, AutoCAD, AFSolid, Anycasting and other software. These softwares can calculate or simulate the design and casting process of stainless steel precision casting. The current optimization scheme can be optimized by data calculation. The development of casting has played a good role in promoting. However, in the current process of use, we also found that we should pay attention to the modeling applicability of computer software and the thermophysical parameters of the material itself. A good solution to these problems can greatly shorten the development time of stainless steel precision casting.
Post time: Oct-21-2021