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Precision casting is the general term for the process of obtaining castings of precise size. Compared with traditional casting process, precision casting results in more accurate casting size and better surface finish. Its products are sophisticated, complex and close to the final shape of the part. Can be used without processing or processing. It is an advanced technology of near – net forming. It includes investment casting, ceramic casting, metal casting, pressure casting, lost casting.

casting tech

What is precision casting?

In the production of precision casting parts is the most commonly used precision investment casting, also known as lost wax casting. Widely used in the production of ferrous and non-ferrous metal castings. The embedding mold is made of paraffin wax and other suitable embedding materials. Repeat the refractory coating and refractory sand process on the investment mold. The shell hardens and dries. The internal melting die is then melted to obtain the cavity. Get the crust baked to get enough strength. Burn off the remaining embedding material and pour the required metal material. Solidification, cooling, peeling, sand clearing. To get a high precision finished product. Perform heat treatment, cold processing and surface treatment according to product requirements.
In addition, precision castings have a lot of freedom in the design of castings and the choice of materials. It allows investment in a variety of steels or alloyed steels. So in the casting market, precision casting is the highest quality casting.

The main process of precision casting

Because precision casting uses expendable models and ceramic casings, it is well suited to complex and detailed part designs. The process creates complex parts that are difficult, if not impossible, to machine, forge or cast. Examples include internal channels and ports in the valve body, curved blades in the impeller, and internal cooling channels in the turbine blades. The key barriers to prototype development and short-term production are the time and cost of injection molding. Each precision casting requires a wax mold, which is injection molded. As design complexity increases, tools often become too expensive and time consuming to make prototyping and small batch production feasible.It includes the following steps: waxing (wax mold) – repair – wax inspection – group tree (wax mold tree) – hulling – dewaxing (steam dewaxing) – baking mold – chemical analysis – casting (pouring molten steel in mold shell) – Vibration hulling – casting and casting rod cutting and pouring – grinding gate – initial inspection (wool inspection) – shot blasting – Machining – polishing – finishing inspection – packaging.

Precision Casting

Investment casting tools

The tool in investment casting is considered to be the wax injection mold used to create the wax mold. Each part starts with a wax mold, and the properties of wax — smooth surface, low melting temperature, and excellent flow characteristics — make highly complex investment castings possible. In terms of how investment casting molds are designed, usually, the customer is the person responsible for the casting design. A good foundry will work with customers to ensure that their designs are optimized for manufacturability and go through the quality process. Foundries can recommend design changes to improve product quality and functionality while improving manufacturing efficiency and reducing costs. Once the design is determined and agreed upon by the customer and supplier, the foundry will work directly with the tool manufacturer to design the tool. Foundries work directly with tool manufacturers to ensure that materials, dimensions, and critical surfaces are optimized.

precision-casting

What factors affect the cost of investment casting tools?

1.Casting complexity, an overly complex part may require the use of more moving parts in the tool, which increases the time and number of processes required to build it.
2.Size, larger parts means larger tools, which requires more materials to build the tool, and more time to process the mold cavities in the tool
3.In certain cases, a soluble core may be required. While soluble cores are an important asset for producing complex cavities, they require their own tools, which increases upfront tooling costs

Why choose precision casting?

 

Precision casting and sand casting

Sand casting is a casting process that uses sand to create a cavity for casting. The sand shell produces a rough shape. Therefore, for sand-cast products, rough surfaces may require more machining operation than investment castings.
Precision casting creates the desired shape through ceramic enclosures and can produce products with a better surface finish. We can meet strict tolerances as precisely as possible, thereby reducing the net shape product and possibly avoiding further processing.

Precision casting and machining

For some simple products with simple shapes, we can choose precision casting or machining. Machining is the process of machining parts directly from rods to their final dimensions. This will cause a large amount of waste of raw materials, will increase production costs virtually. In addition, if the quantity is large, a single production will extend the production time, thus delaying the delivery time.
Precision casting makes the product costly in further processing. Our foundry has both casting and machining workshops. We can offer machined precision castings at the best price, but allow our customers to receive good performance products that can be put straight into application.

Precision casting and precision forging

Precision forging is a metal forming process in which hot or cold metal bars are directly pressed into shape. In order to withstand high pressure, the material of forging die has high requirement. The commonly used material for forging die is die, which has higher cost. High die cost makes precision forging less competitive than precision casting. Precision forging also has regional control over the shape of the product.
In contrast, precision casting requires a lower mold cost and has no restrictions on product size. This enables our company to be used in all metal products.

Precision casting and metal manufacturing

Metalmaking is the process of cutting and bending sheets of metal into different shapes and thicknesses and welding them together to form a product. This will cost more labor costs and production time.
Precision Casting can greatly reduce production time by connecting multiple wax models to sprue or systems.

Factors affecting accuracy coefficient

Generally speaking, the dimensional accuracy of precision castings is affected by many factors, such as the structure of castings, molding, peeling, roasting and casting. Any link of the setting and operation is unreasonable will change the shrinkage rate of casting. The dimensional accuracy of the casting has deviated from the requirement. The following are the factors causing precision defects of precision castings:
(1) Influence of casting structure.
a. The casting wall is thick and the shrinkage hole is large. The casting wall is thin and the shrinkage hole is small.
b. Large free shrinkage hinders shrinkage.
(2) The influence of casting materials.
a. The higher the carbon content of the material, the smaller the linear shrinkage. The lower the carbon content, the greater the line shrinkage.
b. Casting shrinkage of common materials is as follows: casting shrinkage K= (lm-lj) /LJ×100%, LM is the cavity size, LJ is the casting size. K is affected by the following factors: wax type K1, casting structure K2, alloy type K3, casting temperature K4.
(3) Influence of mold making on shrinkage hole of casting line.
a. Wax temperature, wax pressure and residence time have the most obvious influence on melt size. The second is pressing wax. Pressure holding time has little influence on the final investment scale after injection molding.
b. The linear shrinkage of wax (molding) materials is about 0.9-1.1%.
c. Further shrinkage occurs when the investment mold is stored, and the shrinkage value is about 10% of the total shrinkage amount. However, after 12 hours of storage, the investment scale is basically stable.
d. The radial shrinkage rate of wax mold is only 30-40% of the longitudinal shrinkage rate, and the influence of wax temperature on the free shrinkage rate is much greater than that on the resistance shrinkage rate (the optimal wax temperature is 57-59 ℃, the higher the temperature, the greater the shrinkage).
(4) The influence of shell material.
Zirconium sand and zirconium powder are selected, and the expansion coefficient is small, only 4.6×10-6/℃, which can be ignored.
(5) shell baking effect.
Due to the small expansion coefficient of the shell, when the shell temperature is 1150℃, it is only 0.053%, which can be ignored.
(6) Influence of casting temperature.
The higher the casting temperature, the greater the shrinkage. Casting temperature is low and shrinkage rate is small. Therefore, the pouring temperature should be appropriate.
In general, precision casting or dewaxing casting is a manufacturing solution to industrial challenges. The design flexibility of this casting technology allows products to be manufactured in a variety of sizes and shapes. In addition, this technology is even more important today because a large number of products require complex shapes with high dimensional tolerances and repeatability. Most importantly, the smooth surface of the as-cast product is an added value of precision casting or lost wax casting.
The machining stage is one of the most tedious, if not the most, processing stages in manufacturing. Fortunately, the shape of investment casting or lost wax casting products is close to a network. As a result, the application of this manufacturing technique minimizes the machining stage and the cost of machining, material loss and labor work.

Investment casting tools

The tool in investment casting is considered to be the wax injection mold used to create the wax mold. Each part starts with a wax mold, and the properties of wax — smooth surface, low melting temperature, and excellent flow characteristics — make highly complex investment castings possible. In terms of how investment casting molds are designed, usually, the customer is the person responsible for the casting design. A good foundry will work with customers to ensure that their designs are optimized for manufacturability and go through the quality process. Foundries can recommend design changes to improve product quality and functionality while improving manufacturing efficiency and reducing costs. Once the design is determined and agreed upon by the customer and supplier, the foundry will work directly with the tool manufacturer to design the tool. Foundries work directly with tool manufacturers to ensure that materials, dimensions, and critical surfaces are optimized.
What factors affect the cost of investment casting tools?
Casting complexity, an overly complex part may require the use of more moving parts in the tool, which increases the time and number of processes required to build it.
Size, larger parts means larger tools, which requires more materials to build the tool, and more time to process the mold cavities in the tool
In certain cases, a soluble core may be required. While soluble cores are an important asset for producing complex cavities, they require their own tools, which increases upfront tooling costs.

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