Graphite mold introduction

Molds are widely used basic process equipment in industrial production, and the mold industry is the basic industry of the national economy. In modern industrial production, product parts are widely used in stamping, forging, die casting, extrusion, plastic injection or other forming methods, which are matched with forming molds to make the blanks formed into parts that meet the product requirements. Various tools and products used in our daily production and life, from the base and body shell of machine tools to the embryo head screws, buttons and the shells of various household appliances, are closely related to molds. The shape of the mold determines the appearance of these products, and the processing quality and precision of the mold also determine the quality of these products. In recent years, the mold industry has developed rapidly, and graphite materials, new processes and increasing mold factories have continuously impacted the mold market. Graphite has gradually become the preferred material for mold production with its good physical and chemical properties.

Excellent performance

1.Excellent thermal and electrical conductivity
2.linear expansion coefficient and good thermal stability and resistance to heating shock
3.Chemical resistant and not reactive with most metals
4.At high temperatures (most copper-based matrix sintering temperatures are above 800°C), the strength increases with increasing temperature.
5.Good lubrication and anti-wear properties
6. Easy to process, good machining performance, can be made into molds with complex shapes and high precision

Application

At present, graphite molds are widely used in the following aspects:
Graphite molds for continuous and semi-continuous casting of non-ferrous metals
In recent years, advanced production methods such as the direct continuous (or semi-continuous) manufacturing of rods or tubes from the molten metal state are being promoted at home and abroad. This method has begun to be adopted in copper, copper alloys, aluminum, aluminum alloys, etc. Artificial graphite is considered to be the most suitable material for continuous casting or semi-continuous casting of non-ferrous metals. Production practice has proved that the use of graphite molds, due to their good thermal conductivity (thermal conductivity determines the solidification rate of metals or alloys) and good self-lubricating properties of the mold, not only improves the casting speed, but also because the ingot has precise size, smooth surface, and uniform crystal structure, it can be directly processed in the next process. This not only greatly improves the yield rate and reduces scrap loss, but also greatly improves product quality. There are two continuous casting methods: vertical continuous casting and horizontal continuous casting.

Pressure casting molds

Artificial graphite materials have been successfully used in pressure casting of non-ferrous metals. For example, zinc alloy and copper alloy castings produced by pressure casting molds made of artificial graphite materials have been used in automotive parts and other aspects.

Graphite molds for centrifugal casting

Graphite molds have been successfully used in centrifugal casting. The United States has used artificial graphite molds with a wall thickness of more than 25 mm to centrifugally cast bronze sleeves. In order to prevent the burning of artificial graphite molds, certain anti-oxidation measures can be taken. After casting a certain number of castings, if the inner surface of the mold is found to be burned, the size of the inner hole of the mold can be enlarged to cast large-size sleeves.

Hot Press Die Mould

Artificial graphite hot pressing dies used in pressure sintering of cemented carbide have the following characteristics: First, if the pressing temperature is increased to 1350-1450 degrees, the required unit pressure can be reduced to 67-100 kgf/cm2 (that is, 1/10 of the cold pressing pressure); second, pressurization and heating are carried out in the same process, and a dense sintered body can be obtained after a short sintering time.

Glass molding molds

Because graphite is chemically stable , not easily infiltrated by molten glass, will not change the composition of glass, has good heat shock resistance , and has small size changes with temperature, it has become an indispensable mold material in glass manufacturing in recent years. It can be used to make molds for glass tubes, bent tubes, funnels and other special-shaped glass bottles.

Sintering molds and other diamond sintering molds

Taking advantage of the extremely small thermal deformation of artificial graphite materials, sintering molds and brackets for transistors can be manufactured. They are now widely used and have become an indispensable material for the development of the semiconductor industry.
 In addition, graphite molds are also used in castings for cast iron, durable castings for various non-ferrous metals, castings for cast steel, castings for heat-resistant metals (titanium, zirconium, molybdenum, etc.), and castings for aluminum thermite welding for welding rails. 
Graphite molds for hot-pressed sintered diamond tools play the dual role of heating elements and mold support in the manufacturing process of diamond tools. The quality of graphite molds directly affects the dimensional accuracy, appearance and shape of diamond tools.
 The hot-pressed sintering process requires: the temperature reaches (1 000±2)℃, the molding pressure is 16～50 MPa, the heat preservation and pressure holding time is 15～30 min, and the environment is non-vacuum state. 
Under this working condition, the graphite molds for molding and heating elements are required to have conductivity, high resistivity, sufficient mechanical strength, and good oxidation resistance and long service life to ensure the dimensional accuracy and excellent performance of diamond tools. 
At present, the graphite mold materials used in diamond tool manufacturing in developed Western countries are mainly ultra-fine particle structures, high-purity and high-graphitization graphite materials, requiring their average particle size to be less than 15μm, or even less than 10μm, and the medium pore size to be less than 2μm. The graphite mold made of this carbon raw material has a small porosity, a dense structure, a high surface finish, and strong oxidation resistance, with an average service life of 30 to 40 times. 
Diamond molds require high material hardness, good oxidation resistance, and high processing precision. The use of high-quality graphite raw materials greatly extends the service life of the mold and improves its oxidation resistance.

EDM

Molds are increasingly becoming the main process equipment for industrial mass production in the fields of home appliances, automobiles, electromechanics, aerospace, etc., and undertake the processing and production of 60%-90% of the product parts in these industries. 
In recent years, high-speed milling has broken through the limitation of traditional milling that it is difficult to process high-hardness, high-strength, and high-toughness mold materials. However, EDM has high processing accuracy and surface quality, and a wide processing range, especially in the processing of mold cavities of complex, precise, thin-walled, narrow gaps, and high-hardness materials. The advantages are incomparable to high-speed milling, so EDM will still be the main means of mold cavity processing. 
Because graphite electrodes (compared with copper) have the advantages of less electrode consumption, fast EDM speed, good mechanical processing performance, light weight, and small thermal expansion coefficient , they gradually replace copper electrodes and become the mainstream of EDM electrodes. 
Compared with copper, graphite electrodes have the advantages of less consumption, fast discharge speed, light weight, and small thermal expansion coefficient, so they gradually replace copper electrodes and become the mainstream of EDM electrodes. In contrast, graphite electrode materials have the following advantages:

Fast speed: Graphite discharges 2-3 times faster than copper. The material is not easy to deform and has obvious advantages in the processing of thin rib electrodes. The softening point of copper is around 1000 degrees and it is easy to deform due to heat. The sublimation temperature of graphite is around 3650 degrees. In comparison, the thermal expansion coefficient of graphite material is only 1/30 of that of copper.

Light weight: The density of graphite is only 1/5 of that of copper. When large electrodes are used for EDM, it can effectively reduce the burden on machine tools (EDM) and is more suitable for large mold applications.

Small loss: Since spark oil contains C atoms, during EDM, the high temperature causes the C atoms in the spark oil to be decomposed and form a protective film on the surface of the graphite electrode, compensating for the loss of the graphite electrode;

No burrs: After copper electrodes are processed, they still need to be manually deburred, while graphite electrodes are free of burrs after processing, which not only saves a lot of cost and manpower, but also makes it easier to realize automated production;

Easy to polish: Since the cutting resistance of graphite is only 1/5 of that of copper, it is easier to grind and polish manually;

Low cost: Due to the continuous rise in copper prices in recent years, the price of graphite with the same properties is now lower than that of copper; the price of graphite products of the same volume is 30 to 60 percent lower than that of copper, the price is relatively stable, and short-term price fluctuations are relatively small.

Processing Technology

First, the mold designer designs the mold structure according to the use requirements of the product (parts), draws the blueprint, and then technical workers use various mechanical processing (such as lathes, planers, milling machines, grinders, electric sparks, wire cutting and other equipment) to make each part on the mold according to the requirements of the blueprint, and then assemble and debug until qualified products can be produced.