How to finish the casted product from lost wax casting?

Lost wax casting, also known as investment casting, is a time - honored and highly precise manufacturing process that has been used for centuries to create intricate and high - quality casted products. As a professional lost wax casting supplier, I am excited to share with you the detailed steps on how to finish a casted product from lost wax casting.

1. Pattern Creation

The first step in the lost wax casting process is pattern creation. Patterns are typically made from wax, as the name “lost wax casting” implies. Wax has several advantages, such as being easy to shape, having a low melting point, and being able to replicate fine details accurately.

There are different methods to create wax patterns. One common way is to use injection molding. In this method, molten wax is injected into a mold cavity that has the exact shape of the desired product. The mold is usually made of metal or silicone, which can withstand the pressure of the injected wax. After the wax cools and solidifies, the mold is opened, and the wax pattern is removed.

Another method is hand - carving. This is often used for creating unique or one - off patterns. Skilled artisans use specialized tools to carve the wax into the desired shape, adding fine details and textures by hand.

2. Assembly of Wax Patterns

Once the individual wax patterns are created, they are assembled onto a central wax sprue. The sprue acts as a channel through which the molten metal will flow into the mold during the casting process. Multiple wax patterns can be attached to the sprue to create a wax tree, which allows for the simultaneous casting of multiple parts.

The wax patterns are attached to the sprue using wax solder or by melting a small area of the wax and pressing the pattern onto the sprue. Care must be taken to ensure that the patterns are properly aligned and securely attached to prevent any movement or detachment during the subsequent steps.

3. Shell Building

After the wax tree is assembled, it is time to build the ceramic shell around the wax patterns. This is a multi - step process that involves dipping the wax tree into a ceramic slurry and then coating it with a layer of refractory sand.

The ceramic slurry is a mixture of fine ceramic powder and a binder. The wax tree is first dipped into the slurry, ensuring that all surfaces of the wax patterns are fully coated. Then, it is covered with a layer of fine sand, which adheres to the wet slurry. This process is repeated several times, with each layer of slurry and sand adding to the thickness and strength of the shell.

As the shell builds up, coarser sand may be used for the outer layers to provide additional strength. The shell building process typically takes several days to complete, as each layer needs to dry and harden before the next one can be applied.

4. Dewaxing

Once the ceramic shell is fully formed and hardened, the next step is dewaxing. This involves removing the wax from inside the shell, leaving behind a cavity in the shape of the desired casted product.

There are several methods of dewaxing. One common method is steam autoclaving. The ceramic shell is placed in an autoclave, and high - pressure steam is introduced. The heat from the steam melts the wax, which then drains out of the shell through the sprue.

Another method is firing in a furnace. The shell is heated in a furnace to a temperature high enough to melt and vaporize the wax. The wax vapors escape through the porous ceramic shell, leaving behind a clean cavity.

5. Melting and Pouring of Metal

After the wax has been removed, the ceramic shell is ready for the casting of metal. The type of metal used depends on the requirements of the final product. Common metals used in lost wax casting include stainless steel, bronze, aluminum, and titanium.

The metal is melted in a furnace at a specific temperature depending on its melting point. For example, stainless steel typically needs to be melted at a temperature of around 1500 - 1600°C. Once the metal is fully melted and has reached the appropriate temperature and fluidity, it is poured into the pre - heated ceramic shell.

The pouring process must be carefully controlled to ensure that the molten metal fills the cavity completely and evenly, without any air bubbles or voids. Gravity pouring is a common method, where the molten metal is simply poured into the shell under the force of gravity. In some cases, vacuum or pressure pouring may be used to improve the quality of the casting.

6. Cooling and Shell Removal

After the metal has been poured into the shell, it is allowed to cool and solidify. The cooling rate is an important factor that can affect the microstructure and properties of the casted product. Slow cooling may result in a coarser grain structure, while rapid cooling can produce a finer grain structure, which may improve the strength and hardness of the product.

Once the metal has fully solidified, the ceramic shell is removed. This can be done by mechanical means, such as using a hammer or sandblasting, to break the shell away from the casted metal. Care must be taken not to damage the casted product during the shell removal process.

7. Finishing Operations

After the shell is removed, the casted product undergoes a series of finishing operations to achieve the desired final appearance and dimensional accuracy.

One of the first finishing steps is cutting off the sprue and any other casting gates. This is usually done using a saw or a cutting torch. Then, the surface of the casted product is ground and polished to remove any rough edges, surface imperfections, and casting marks.

Machining operations may also be required to achieve the precise dimensions and tolerances specified by the customer. This can include turning, milling, drilling, and tapping, depending on the design of the product.

Heat treatment may be applied to improve the mechanical properties of the casted product. For example, annealing can be used to relieve internal stresses and improve ductility, while quenching and tempering can increase the hardness and strength of the metal.

8. Quality Inspection

Before the casted product is ready for delivery, it undergoes a thorough quality inspection. This includes visual inspection to check for any surface defects, such as cracks, porosity, or inclusions. Dimensional inspection is also carried out using precision measuring tools, such as calipers, micrometers, and coordinate measuring machines (CMMs), to ensure that the product meets the specified tolerances.

Non - destructive testing methods, such as ultrasonic testing, X - ray testing, and magnetic particle testing, may be used to detect internal defects that are not visible to the naked eye.

If you are interested in high - quality lost wax casting products, we offer a wide range of services. We specialize in OEM Stainless Steel Precision Casting Lost Wax Casting Investment Casting, Steel and Stainless Steel Precision Lost Wax Investment Casting, and Lost Wax Precision Investment Casting 316L Stainless Steel Valve Pump Parts for Ship Marine Building. Our experienced team and advanced manufacturing facilities ensure that we can meet your specific requirements. If you have any casting needs, please feel free to contact us for procurement and negotiation.

References

• “Investment Casting Handbook” by Peter F. McLean
• “The Science and Engineering of Materials” by Donald R. Askeland and Pradeep P. Phule
• “Foundry Technology” by A. K. Biswas