How to Make Graphite Mold?

Graphite mold plays an important role in modern industry. It has good high temperature resistance, excellent thermal conductivity, low coefficient of thermal expansion and excellent chemical stability. This makes the graphite mold widely used in many fields such as metal casting, glass manufacturing and so on. For example, in the pressing of glass products with graphite mold, the graphite mold can make the glass uniformly heated and formed. And it can produce high-precision glass products.

Characteristics and selection of graphite materials

Graphite materials have many unique properties. Its excellent high temperature resistance, can still maintain good mechanical properties in high temperature environments. It can withstand temperatures of up to thousands of degrees Celsius. This makes it able to adapt to a variety of high temperature processing processes. Graphite has good thermal conductivity and can transfer heat quickly and evenly. This is conducive to maintaining the temperature balance during the working process of the mold and reducing product defects caused by local overheating or undercooling. At the same time, the coefficient of thermal expansion of graphite is extremely low. And its dimensional stability is high when the temperature changes. This can ensure the accuracy of the mold. In addition, graphite also has good chemical stability. It is not easy to react in most chemical media such as acid and alkali. And it can resist the erosion of metal liquid and glass liquid.

Purity and particle size of graphite material

When choosing graphite materials, you should consider many factors need. The first is the purity of the material. High purity graphite has better performance. Low impurity content can reduce the adverse impact on the performance of the mold. For example, for some high-precision graphite molds used in the manufacture of electronic products, the purity of graphite is usually required to be above 99.9%. The second is the particle size of graphite. Different particle size of graphite affects the strength, density and processing properties of the mold.

Fine graphite has high strength and smooth surface, which is suitable for making molds with complex shapes and high precision requirements. The coarse graphite has good gas permeability and machinability. It is suitable for some mold parts that do not have particularly high strength requirements but need rapid processing. Furthermore, you need to select graphite materials with corresponding thermal shock resistance, electrical conductivity and other special properties. (A ccording to the specific use environment and process requirements of the mold.) For example, in the production of metal casting molds, it may be more focused on the stability and erosion resistance of graphite materials in high temperature metal environments. For some special molds such as how to make metal jewelry, there may be higher requirements for the fineness and surface finish of the mold. This affects the choice of graphite materials.

Processing technology of graphite mold

Cutting Processing

Cutting processing is the basic link of graphite mold production. The commonly used cutting methods are mechanical cutting and laser cutting. Mechanical cutting, such as sawing, is suitable for the preliminary cutting of large-size graphite materials. You can use tools such as diamond saw blades. During the sawing process, you should pay attention to controlling the cutting speed and feed rate to avoid the burning and edge collapse of graphite materials due to excessive heat.

For graphite mold parts with high precision and complex shape, laser cutting has obvious advantages. Laser cutting can achieve high-precision cutting. Its cutting width is narrow, the heat affected zone is small. It can cut out a variety of complex shapes, such as fine Outlines, narrow slots and so on. During laser cutting, you should set parameters such as laser power and cutting speed reasonably. According to the thickness and properties of graphite materials to ensure cutting quality. Graphite manufacturers can custom-cut any graphite molds you need based on the drawings.

Numerical control machining

The processing of graphite mold mainly adopts numerical control processing technology. Numerical control milling is a commonly used machining method. By writing accurate numerical control program, various complex mold structures such as surface and cavity can be machined. In the milling process, it is necessary to choose the appropriate tool. Such as diamond coated tool, which has high hardness and good wear resistance. And it can effectively improve processing efficiency and processing accuracy.

Due to the brittle texture of the graphite material, it is necessary to use a smaller cutting depth.  And it can feed amount during processing to avoid excessive impact force of the tool on the graphite material. This results in blade breakage and material damage. At the same time, a good cooling and lubrication system should be used to reduce tool wear and the generation of graphite dust. For example, the use of compressed air or special coolant for cooling and lubrication can not only ensure the smooth progress of the processing process, but also timely remove the graphite debris generated during the processing process. This can prevent its adverse impact on the processing accuracy and machine tool equipment.

Surface Treatment

The surface treatment of graphite mold is very important to improve the performance and service life of the mold. Common surface treatment methods are coating treatment and polishing treatment. The surface of the graphite mold can be coated with a layer of high-temperature, wear-resistant, corrosion-resistant materials. Such as silicon carbide coating, boron nitride coating, etc. The coating methods include chemical vapor deposition (CVD) and physical vapor deposition (PVD). CVD coating has the advantages of uniform coating thickness and strong binding force. This can effectively improve the oxidation resistance and wear resistance of graphite mold. PVD coating has the characteristics of low deposition temperature, little influence on the mold matrix, etc.. This is suitable for some graphite molds with high precision requirements and not suitable for high temperature treatment.

Polishing can smooth the surface of the graphite mold, reduce the surface roughness. And also reduce the adhesion of metal liquid or other processing materials on the mold surface. And it can improve the release performance and product surface quality. Polishing can be mechanical polishing, chemical polishing or electrolytic polishing and other methods. According to the surface accuracy requirements and shape characteristics of the mold to choose the appropriate polishing process. For example, for optical glass molds with extremely high surface roughness requirements, you can use a chemical-mechanical composite polishing method to remove the microscopic roughness of the surface through chemical corrosion. And then further improve the surface finish by mechanical polishing.

 Graphite mold casting

Graphite mold casting is the process of injecting liquid metal or other materials into the graphite mold cavity. And this obtains the formed product after cooling and solidification. Before casting, the graphite mold should be preheated. The general preheating temperature is between 200-500 ℃. The purpose is to reduce the temperature difference between the mold and the high-temperature liquid material. And to prevent the liquid material from having defects due to sharp cooling during injection. Such as cold isolation, insufficient pouring, etc.. But also to improve the service life of the mold.

During the casting process, the position and size of the gate and riser should be reasonably designed. The role of the gate is to guide the liquid material to flow smoothly into the mold cavity. Its position should be selected in the part conducive to the liquid material filling the cavity. And it can ensure that the size of the gate is appropriate. And to avoid the difficulty of filling the mold due to the small gate. Or the flow rate of the liquid material is too fast, resulting in turbulence, enrolling and other defects. The riser is mainly used to compensate for the volume contraction of liquid materials in the cooling and solidification process. This prevents the casting from appearing shrinkage holes, shrinkage and other defects. The size and height of the riser should be designed according to the shape, size and solidification characteristics of the casting.

Graphite mold manufacturing considerations

When selecting the casting material, you should consider its suitability with the graphite mold. For example, for the casting of low melting point metals such as aluminum and magnesium, graphite molds have good adaptability. For the casting of some high melting point metals such as iron, nickel-based alloys, etc., it is necessary to carry out special treatment of graphite molds or select higher performance graphite materials to withstand the erosion and erosion of high temperature metal liquids.

At the same time, in the casting process to strictly control the casting process parameters. Such as pouring temperature, pouring speed, mold temperature and so on. The high pouring temperature will increase the suction and oxidation of the liquid material. And it may also lead to excessive erosion of the graphite mold. If the pouring temperature is too low, the fluidity of the liquid material will become poor. And it is difficult to fill the cavity. Too fast pouring speed is easy to produce turbulence and enfranchisement. Too slow pouring speed may lead to insufficient pouring and other problems. The mold temperature should also be kept within a suitable range to ensure that the solidification process of liquid materials in the mold is normal, and castings with uniform organization and good performance are obtained.

Assembly and debugging of graphite mold

The assembly of graphite mold is the process of assembling each processed part according to the design requirements. Before assembly, you should clean each part and inspect to remove surface impurities and processing allowance. To ensure that the dimensional accuracy and surface quality of the parts meet the requirements. When assembling, you should use appropriate assembly tools and methods to ensure that the installation position of each component is accurate and firmly connected. For example, for some parts connected by bolts, it is necessary to control the tightening torque of the bolts. To avoid mold deformation or connection failure due to too tight or too loose.

After the assembly is complete, you need to debug. Debugging mainly includes the inspection of the mold opening and closing action to ensure that the mold can open and close smoothly. And the opening and closing stroke and speed meet the process requirements. At the same time, the cooling system and heating system (if any) of the mold should be tested to check whether it can operate normally. And whether the temperature control is accurate.

For example, in the injection mold, the good operation of the cooling system is essential to control the molding cycle and quality of the product. And it is necessary to ensure that the cooling water channel is unimpeded through debugging. And the flow and temperature of the cooling medium can meet the heat dissipation needs of the mold. For die casting molds, it is necessary to check whether the ejection mechanism is flexible and reliable. And it can successfully ejection the casting from the mold cavity after solidification. In the debugging process, if the problem is found, it should be adjusted and repaired in time until the performance indicators of the mold meet the design requirements.

 Quality control and testing

Quality control runs through the whole process of graphite mold production. In the raw material inspection link, the performance indicators of graphite materials should be tested. Such as purity, density, particle size, etc., to ensure that raw materials meet the production requirements. In the processing process, the product quality of each processing process should be inspected. Such as the dimensional accuracy after cutting, the shape accuracy after processing and the surface roughness, etc.. The measurement equipment such as measuring tools, profilometers and roughness meters should be used for accurate measurement. And the out-of-tolerance should be corrected in time.

After the graphite mold is made, you should carry a comprehensive performance test out. For the die casting mold, the die casting test can be carried out to observe the molding quality of the casting. And check whether there are defects such as pores, shrinkage holes, cracks, and so on. And measure whether the dimensional accuracy of the casting meets the requirements. For the injection mold, the injection molding test is carried out to investigate the appearance quality of plastic products, dimensional accuracy, and the opening and closing performance of the mold.

In addition, thermal performance tests can also be carried out on graphite molds. Such as thermal conductivity tests, thermal expansion coefficient tests, etc.. To evaluate the performance of the molds in the actual working temperature environment. Through strict quality control and testing, the quality and reliability of graphite mold can be guaranteed. And you can improve its use effect and service life in industrial production.

 Maintenance and maintenance of graphite mold

The graphite mold needs regular maintenance and maintenance during use. After each use, it is necessary to timely clean the residual metal scraps, glass slag and other impurities on the surface of the mold. This can be blown by compressed air and cleaned by brush. For some dirt that is difficult to remove, you can use a suitable chemical solvent for cleaning. But you should note it that the solvent can not cause corrosion to the graphite mold.

In the process of long-term use, the graphite mold may appear wear, surface coating off and other problems. When the mold surface is found to be slightly worn, you can repaire it by polishing and other methods to restore its surface finish and dimensional accuracy. For the parts where the coating falls off, it should be re-coated in time to ensure the performance of the mold. At the same time, it is necessary to regularly check the structural integrity of the mold. Such as checking whether the mold cavity and core have deformation, cracking and other phenomena. And repair or replace the parts in time when the problem is found.

In addition, the graphite mold should pay attention to environmental conditions when stored. And it should be stored in a dry and well-ventilated environment to avoid moisture and oxidation. When stored, you can apply a layer of anti-rust oil or protective agent on the surface of the mold to prevent the surface of the mold from rusting or being contaminated by other impurities. Through scientific and reasonable maintenance and maintenance measures, the service life of graphite molds can be extended. Production costs can be reduced, and production efficiency can be improved.

 Schlussfolgerung

The production of graphite mold is a complex process involving many links and technologies. From the characteristics of graphite materials research and selection, to the application of advanced processing technology, to precision casting, assembly and commissioning, strict quality control and testing and scientific maintenance. Each link has an important impact on the final performance and service life of graphite molds.