If you are familar with stainless steel investment casting, you may know the traditional stainless steel investment casting process contains these steps: process design, molding manufacturing, wax patterns manufacturing, wax patterns assembly, shell making, dewaxing and roasting, pouring, shell removing and post-processing. While, by using 3D printing, it can replace the procedures of molding and wax patterns manufacturing, which can improve production efficiency and save the molding cost for customers.
Stainless Steel Casting Process by 3D Printing
Designing the manufacturing process and pouring riser system are mainly decided ccording to the structure of cast stainless steel parts and pouring method. Generally, there are two types of pouring riser system: Top injection type is suitable for stainless steel castings in low height, while the side injection type is suitable for stainless steel castings with the pouring of multiple wax patterns at a time. Among them, side injection is the most widely used in stainless steel investment casting process.
Wax Pattern Manufacturing
The 3D model of the component to be manufactured needs to be pre-designed on the computer before 3D printing is conducted. The available software are Solidworks, OpenSCAD, Auto CAD, MAYA, 3-MATlC etc. The designed 3D model can be converted into STL format and export it to a computer associated with a 3D printer for printing. The printed resin model needs to be polished in order to improve the surface precision of stainless steel castings.
To glue the riser at the pre-designed riser position after checking the surface of patterns without defects. To check that there are no adhesives or gaps left in the pattern, riser, and joints after the gluing is completed.
There are two ways to manufacture the shell for patterns : pouring gypsum and applying refractory coating. Taking the application of refractory coating as an example, the polished pattern is placed in a pre-configured slurry refractory coating, and coated uniformly (the remaining coating on the investment mold flows uniformly and no longer drops continuously), then sanding is performed. To repeat the two steps of coating and sanding, each step should be fully dried and hardened. Silica sol is a commonly used casting shell coating. Bauxite is used as the main refractory material, it has superior high temperature strength and strong stability. The main evaporator of bauxite during drying and roasting is water, which is green and environmentally friendly and it has been widely used in many fields. It is necessary to wet the mold material before applying the coating since the wettability of the investment mold is poor.
Dewaxing & Roasting
After the shell is completely dried and hardened, the shell containing the pattern material is placed in a high-temperature furnace (700 ~ 900 ℃) and roasted until the pattern material is completely burned out. In addition to removing the resin mold, the purpose of roasting also includes removing moisture and salt from the shell, reducing the gas evolution of mold shell during pouring, improving breathability, reducing the temperature difference between the mold and the metal liquid, and effectively improving the mold-filling capacity of metal liquid .
The pouring temperature and pouring speed of the molten stainless steel will have many effects on the quality of stainless steel casting part, so they should be strictly controlled. The pouring method has something in common with other casting methods, the corresponding design should be made according to the structure and property of stainless steel castings.
Shell Removing & Post-Processing
After the molten stainless steel is completely solidified and cooled, the shell can be removed and stainlesss steel casting part can be cleaned. Checking the castings after cleaning, then removing some burr defects or conducting heat treatment, surface treatment (such as electropolishing, mirror polishing or color stainless steel castings) according to the requirement from our customers.
Above is the detailed stainless steel casting process of 3D printing technology combined with the traditional investment casting process, which is to replace the traditional wax pattern based on the resin matrix by the pattern which is made by 3D printing. Producing the patterns by 3D printing rapid prototyping directly can replace two steps in the traditional investment casting, which are producing the pressure type and suppressing the wax, and can erase the pattern founded by printing in dewax and baking as in the wax pattern. This new stainless steel casting method has the advantages of low cost, simple process, high efficiency and high precision of stainless steel castings in low volume. In addition, 3D printing is recommended especially when the design of cast stainless steel part is not confirmed.