Stainless Steel Investment Casting

What is Stainless Steel Investment Casting?

Some of the products are of strange shape and cannot be produced by techniques such as pipe bending when producing stainless steel products. In order to produce such products with irregular shape (hollow or solid inside), a stainless steel casting process of filling and forming with wax mould, sand mould and liquid material is adopted. Such process is called stainless steel investment casting.

Advantage: Can make a variety of products according to different wax models.
Disadvantage: The precision of the blank is low and the surface roughness is relatively high.

Stainless Steel Investment Casting Process

1. Mold according to different shapes of products. The mould is divided into upper and lower concave die and completed through turn-milling, plane milling, milling, etching, electric spark and other comprehensive processes. The shape and size of the pit are consistent with the half edge of the product. Because wax mould is mainly used for industrial wax pressing, the aluminum alloy material with low melting point, low hardness, low requirement, low price and light weight is selected to make the mould.

2. Use aluminum alloy mould to produce a large number of industrial wax real core models. Under normal circumstances, an industrial wax real core model can only correspond to one blank product.

3. Fine repair the residual around the wax mould. After deburring, a plurality of single wax molds is attached to the pre-prepared mould head (also known as group tree), which is also an industrial wax real core model produced by wax molds (The outline looks like a tree).

4. Spray the first layer of fine sand (A kind of fireproof sand with high temperature resistant feature, we usually use silica sand) uniformly after applying industrial glue to the wax molds that have been fixed on the die head.

5. The wax mould with the first layer of fine sand is naturally air-dried at the set temperature (or at constant temperature), but the shape of the wax mould inside cannot be affected. The natural drying time depends on the complexity of the product itself. Generally, the first air-drying time of precision casting is about 5-8 hours.

6. Continue to put industrial glue (silica soluble slurry) on the wax mold surface and spray the second layer of sand after the first sand spraying and natural air drying. The second layer of sand is larger and thicker than the previous one. After spraying the second layer of sand, the wax mold will dry naturally under the set temperature.

7. After the second sand spraying and natural air drying, conduct the third, the fourth and the fifth sand spraying and other processes. Requirements: Adjust sand spraying times according to the product surface requirements, volume size, self-weight and others. In general, sand spraying times are 3-7 times. The size of sand particles is different in each sandblasting process. Usually, the sand particles in the later process are thicker than those in the previous process, and the time of air drying is also different. The production period of sand on a complete wax mould is about 3~4 days generally.

8. Apply a layer of white industrial latex (silica slurry) evenly for bonding and solidifying the sand mold and sealing the wax mold to prepare for the later baking process. It can also improve the brittleness of the sand mold, so as to break the sand layer and take out the blank after the baking process.

9. Baking process: Heat the wax mould fixed on the die head and completed the sandblasting and air drying process in a special metal closed oven (usually a steam furnace for burning kerosene). For industrial wax melting point is not high, the temperature at about 150゜, wax mould is dissolved by heat to form wax water flowing along the gate, this process is called dewaxing. The dewaxed wax mould is just an empty sand shell. The key to precision casting is to use the empty sand shell (Generally, this kind of wax can be used repeatedly for many times, but these wax must be re-filtered, otherwise, the dirty wax will affect the surface quality of the blank, such as: surface sand holes, hemp spots, and will affect the shrinkage rate of the precision casting products at the same time).

10. Baking sand shell: Before pouring into the stainless steel water, you must bake sand shell, usually roasted at high temperature furnace (temperature is about 1000゜) to make the waxed sand shell more solid and stable.

11. Pour the molten stainless steel water into the dewaxed sand shell. Liquid stainless steel water fills the space in which the wax mold was formed until it was fully filled, including the middle die head.

12. The factory must check the percentage of the material because of the mixed material of different components in the dissolved stainless steel boiler. Then adjust to the required ratio, such as adding aspect elements to achieve the desired effect.

13. After the liquid stainless steel is cooled and solidified, the outermost sand shell is broken by means of mechanical tools or manpower to reveal the solid stainless steel product, which is the original wax model shape, that is, the final required blank. Then cut, separate and roughed into a single blank.

14. Inspecting blank: The surface of blank with sand holes and air holes must be repair welding by argon arc. Serious defect blank is cleaned as waste and returned to bake again.

Benefits of Stainless Steel Investment Casting

Compared with other casting methods or other metal forming processes, stainless steel precision castings general adopt lost wax investment casting. There are several benefits of stainless steel investment casting:

Can Improve the Utilization Rate of Materials
Investment casting can significantly reduce the machining amount of products and save the consumption of machining time and machining tools. Waste stainless steel materials can be recycled: almost all the casting risers and waste stainless steel castings in the casting workshop are reused, so the utilization rate of stainless steel materials can be greatly improved. Take CA6140 ordinary lathe as an example, when 64 kinds of 74 parts are used in investment casting, the material utilization rate can reach 81.72%, and some parts can reach 100%. When the interphase parts are produced by forging method, the material consumption is 2.8 times that of cast ones.

Precise Dimensions and Smooth Surface
The main characteristics of stainless steel investment castings are: high dimensional and geometric accuracy, and fine surface roughness. At present, the dimensional accuracy of stainless steel investment castings can exceed ±0.005cm/cm, and the surface roughness can be up to 0.63-1.25 micron (equivalent to 7-8 micron)

Can Cast Stainless Steel Parts with Complex Shape
Investment casting can cast very complex shape of stainless steel parts. For example, it can cast stainless steel castings with wall thickness 0.5mm, weight as small as 18kgs. Can also cast a complete stainless steel part instead of several parts made up of welding or assembly, and reduce the weight of parts. Therefore, investment casting can greatly improve the degree of similarity between blank and final parts, which brings great convenience for the structural design of parts.

No Limitation On Stainless Steel Grades
As stainless steel casting is a custom service for all types of stainless steel components, so it can customize a same part with different grades. Take horse stirrups for example, at beginning of sampling process, our customer is a bit puzzled at the working performance of CG8M stainless steel and 2205 duplex stainless steel for casting. Thus, CFS Foundry provides several samples with both grades for our client’s inspection, while all the dimensions are the same. So this casting method bring our customer great convenience when it is difficult to make a decision on the casting grade.

CFS’ Capabilities of Stainless Steel Investment Casting

CFS Stainless Steel Casting Company is a comprehensive company involved in both stainless steel casting and post machining. With casting experience more than 30 years, we are able to produce stainless steel components ranging from 0.02kg-50kg by stainless steel investment casting process. Currently, all our stainless steel investment castings are mainly exported to USA, UK, Canada, Australia, South Africa, etc. Thanks to our high quality and comprehensive service, we have achieved good reputation from our customers.

Our Capabilities Include:

  • Moulding: All the moulds developed in CFS are automatic, although the tooling cost is a bit higher, the production efficiency is higher. What’s more, we can control general casting tolerance within ISO 8062 CT5.
  • Casting: Can produce stainless steel investment castings with all types of stainless steel grades, for example, SS304(L), SS316(L), CG8M, PH17-4, 2205 duplex stainless steel, etc.
  • Machining: Our in-house machining can meet a variety of machining requirement, such as drilling, milling, boring, cnc machining, ect. Our machining capability can help our customers to receive finished components directly with less lead time. More important is that cost can be saved compared with some outsourced companies.
  • Surface Finish: To meet different demands of surface finish, CFS Company can provide different types of surface treatments, like shot blasting, sand blasting, vibratory polishing, mirror polishing, etc.

Typical Stainless Steel Investment Castings We Made:

Any interest on cooperating with our company for your stainless steel investment casting project? Pls contact us or email directly, we will go back to you within 12 hours!

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