The Complete Guide to Graphite Mold Casting Process

Casting process is widely used in modern manufacturing industry. Graphite mold casting process has unique advantages, with special material characteristics and excellent performance. It provides solutions for the manufacture of high-precision complex parts, which is of great significance to improve the overall level of manufacturing.

Graphite mold characteristics

Material characteristics

Graphite is a crystal structure material composed of carbon atoms and has good high temperature resistance. Its melting point is as high as 3652°C, which allows the graphite mold to maintain a stable physical form in a high temperature casting environment, without melting or deformation due to high temperature. At the same time, it has excellent chemical stability. In the casting process, it is not easy to react with most metals and fluxes. Ensuring the service life of the mold and the purity of the casting. In addition, its coefficient of thermal expansion is small, and its size change is relatively small in the case of rapid temperature changes. This is conducive to maintaining the accuracy of the mold.

Performance Advantages

High precision molding:

Graphite mold has good processing performance, you can process it into a variety of complex shapes. It can meet the high precision design requirements of different products. During the casting process, its smooth surface can significantly improve the surface quality of the casting and reduce subsequent processing procedures.

High thermal conductivity:

It makes the heat transfer quickly and evenly during the casting process. This helps the rapid solidification of liquid metal, shorting the production cycle and improving the production efficiency. At the same time, uniform heat dissipation is also conducive to reducing the stress concentration inside the casting and reducing the probability of defects such as cracks in the casting.

Good demoulding performance:

The adhesion between graphite and most metals is small, making the casting more smooth during demoulding. And reduce the casting damage caused by the difficulty of demoulding, improve the yield.

Detailed explanation of graphite mold casting process

Prepare graphite mold casting materials

Material selection

High-quality graphite material is the basis for ensuring the quality of the mold. Graphite materials with high purity and uniform density are usually selected. According to different casting needs, you should select fine-grained graphite or medium-grained graphite. Fine graphite can provide better surface finish, suitable for casting with high surface quality requirements. Medium particle graphite has better strength and toughness, and is suitable for molds that bear greater pressure and impact force.

Material processing

First of all, cut the selected graphite material. According to the mold design size, the graphite is cut into a rough shape using cutting equipment. Then mechanical processing, through the CNC machining center and other equipment for graphite milling, drilling and other operations, precisely machined mold cavity, core and other structures. To ensure that the dimensional accuracy of the mold meets the design requirements.

Create patterns

Design ideas

The design of the model needs to be comprehensively considered according to the shape, size, accuracy requirements and production batch of the final casting. In the design process, you should fully consider the shrinkage rate of the casting and reserve the appropriate processing allowance. For complex shapes of castings, it is also necessary to design a reasonable parting surface and pouring system. To ensure that the liquid metal can evenly and smoothly fill the mold cavity.

Processing method

This mainly includes mechanical processing and 3D printing. Machining is suitable for making models with regular shapes and large batches. And the dimensional accuracy and surface quality of models can be guaranteed by CNC machining equipment. For some models with complex shapes and unique structures, 3D printing technology has obvious advantages. It can quickly and accurately produce models with complex shapes, greatly shortening the model production cycle.

Heating Graphite Crucible

Equipment selection

Commonly used heating crucible equipment are resistance furnace, induction furnace, etc. The resistance furnace heats the crucible by heating the resistance wire. Its temperature control is more accurate, simple operation, suitable for small casting enterprises or high temperature stability requirements of the casting process. Induction furnace uses the principle of electromagnetic induction to generate heat, heating speed, high efficiency, suitable for large-scale production.

Temperature control

In the heating process, accurate temperature control is essential. Different metal materials have different melting points and pouring temperature ranges. And appropriate heating temperature curves need to be set according to the actual situation. Through the temperature control system, the heating power is monitored and adjusted in real time to ensure that the temperature in the crucible is stable within the required range. And to avoid the quality of liquid metal or casting defects caused by too high or too low temperature.

Metal pouring

Metal melting

Put the required metal into the heating graphite crucible to melt. When melting, add appropriate amount of flux according to the characteristics of the metal. Remove impurities and gas to improve the purity, and stir to make the liquid metal composition uniform.

Casting operation

After the metal liquid reaches the appropriate pouring temperature, it is quickly and smoothly poured into the mold cavity. Control the speed and quantity during pouring to prevent defects such as insufficient pouring and cold insulation. Large or complex castings may require different pouring methods such as bottom injection and side injection. To ensure that the metal liquid fills all corners of the mold.

Remove impurities

Refining agent method

Add an appropriate amount of refining agent to the metal liquid. It chemically reacts with impurities to generate slag or gas that floats to the surface for removal. Commonly used borax, sodium carbonate, etc., different metals need to choose the appropriate refining agent.

Filtration method

Ceramic filter is set in the pouring system. As the liquid metal flows through, impurities are filtered to improve the purity of the liquid metal entering the cavity. Select filter reasonably according to liquid metal flow and impurity size.

Demolding parts

Ejector time

Ejecting time is very critical, too early casting is not solidified easy to deformation and damage. Too late due to the increase of friction, increase the difficulty of stripping and even damage the mold. According to the casting material, thickness, mold structure, etc., determined by experience or simulation analysis.

Stripping operation

Ejecting castings with ejecting rod, ejecting block and other mechanical ejecting devices. During the process, the ejection force is even and the local deformation of the casting is avoided. You can also apply release agent to the surface of the mold to reduce friction and make the release smoother.

Conclusion

Graphite mold casting process, with its unique characteristics and advantages, plays an important role in modern manufacturing industry. Through reasonable selection of materials, fine molding, precise control, you can produce high-quality castings.

FAQS

How long does Graphite Mold Last?

Generally speaking, the service life of graphite molds is between 100-1000 times. Its life is affected by casting materials, process parameters, maintenance and other factors. Under normal use and maintenance, you can use it dozens to hundreds of times. Casting aluminum alloy such as the process of small mold loss, mold life is longer. High temperature, highly corrosive metal casting is shorter.

In the process of graphite molding, what are the key factors affecting the quality of the mold?

Graphite material quality:

Purity, density uniformity affect mold performance, low purity impurities are easy to cause high temperature defects.

Machining accuracy:

Dimensional accuracy and surface roughness are related to the quality of the mold. And insufficient accuracy will make the cavity size deviation and affect the casting molding.

Molding process parameters:

Pressing pressure, temperature, time is not appropriate. These will cause the internal structure of the mold uneven, affect the strength and life.

Is the graphite mold easily damaged?

During proper use and maintenance, it is not easily damaged. However, excessive temperature impact, mechanical stress, or improper external forces such as collisions during operation can lead to damage. After long-term use, surface wear and corrosion will also damage the mold, so correct operation and regular maintenance are very important.

Should you preheat graphite molds?

Preheating is usually recommended. Preheating can reduce the temperature difference between the mold and the metal liquid, avoid the crack caused by thermal impact. And it also makes the metal liquid flow more smoothly in the cavity, which is conducive to casting molding. The preheating temperature is generally determined according to the type of casting metal and the mold material, between 100°C and 300°C.