What Is Investment Casting?

Investment casting, also known as lost wax casting, includes pressing wax, repairing wax, grouping trees, dipping, melting wax, casting molten metal and post-processing. Lost wax casting is a wax mold made from wax to make parts, and then the wax mold is coated with mud. This is the mud mold. After the clay mold is dried, put it in hot water to melt the internal wax mold. Take out the molten clay mold and bake it into a ceramic mold. Once roasted. In general, a casting port is left when a mud mold is made, and a molten metal is poured from the pouring port. After cooling, the required parts are made.

Investment casting

Investment casting, also known as lost wax casting, includes pressing wax, repairing wax, grouping trees, dipping, melting wax, casting molten metal, and post-processing. Lost wax casting is a wax mold made from wax to make parts, and then the wax mold is coated with mud. This is the mud mold. After the clay mold is dried, put it in hot water to melt the internal wax mold. Take out the molten clay mold and bake it into a ceramic mold. Once roasted. In general, a casting port is left when a mud mold is made, and a molten metal is poured from the pouring port. After cooling, the required parts are made.

Chinese name

Investment casting

nickname

China's lost wax law originated at the latest in the Spring and Autumn Period. The bronze ban during the Spring and Autumn Period unearthed from Chu Tomb No. 2 in Chuanxia Temple, Henan is the earliest known method of losing wax.

The copperware cast by this method has neither fan marks nor traces of gaskets. It is better to cast hollowware with it. Chinese traditional investment casting technique

When using wax to make patterns, investment casting is also called "lost wax casting". Investment casting generally refers to making patterns in fusible materials, covering the surface of the pattern with several layers of refractory materials, and then melting the pattern out of the mold shell to obtain a mold without a parting surface. Can be sand-filled casting scheme. Because the pattern is widely made of waxy materials, investment casting is often referred to as "lost wax casting".

The types of alloys that can be produced by investment casting are carbon steel, alloy steel, heat-resistant alloy, stainless steel,

Investment castings have high dimensional accuracy, generally up to CT4-6 (CT10 ~ 13 for sand casting and CT5 ~ 7 for die casting). Of course, due to the complicated process of investment casting, there are many factors affecting the dimensional accuracy of castings, such as mold The shrinkage of the material, the deformation of the investment mold, the linear change of the mold shell during heating and cooling, the shrinkage of the alloy, and the deformation of the casting during solidification, etc., although the dimensional accuracy of ordinary investment castings is high, but Consistency still needs to be improved (size consistency of castings using medium and high temperature wax materials is much improved). ^[1]

The first step of investment casting production is to create an investment mold. The investment mold is used to form a cavity in a refractory shell. Therefore, to obtain castings with high dimensional accuracy and surface finish, the investment mold itself should have a high size Precision and surface finish. In addition, the performance of the investment mold itself should be as simple as possible in the subsequent steps of forming the shell. In order to obtain the investment mold with the above-mentioned high quality requirements, in addition to having a good profile (a mold for pressing the investment mold), it is also necessary to select a suitable molding material (referred to as a molding material) and a reasonable molding process.

The performance of the molding material should not only ensure that the investment mold with accurate dimensions, high surface smoothness, good strength, and light weight should be easily produced. It should also create conditions for the manufacture of the shell and obtain good castings. Molding materials are generally formulated with wax materials, natural resins and plastics (synthetic resins). Whereas the molding compound mainly made of wax is called wax-based molding, they have a lower melting point, which is 60 to 70 ° C. The molding compound mainly made of natural resin is called resin-based molding, which has a slightly higher melting point, about 70 ~ 120 ° C.

Investment casting molds can be divided into solid and multilayer shells

After the module is dip-coated with the refractory coating, sprinkle the material-like refractory material, and then dry and harden. Repeat this many times to make the refractory coating layer reach the required thickness, so that a multilayer shell is formed on the module. Usually, it is left for a period of time to allow it to fully harden, and then the module is melted to obtain a multilayer shell.

Some multi-layer shells need to be packed in sand; others are not needed. After firing, they can be directly poured.

When the melting mold is lost, the mold shell is subjected to the pressure of the molten mold material whose volume is increasing; during firing and pouring, each part of the mold shell will produce mutually contracted and uneven expansion and contraction, so the metal may also be High temperature chemical reaction with the shell material. Therefore, the shell has certain performance requirements, such as a small expansion and contraction rate; high mechanical strength, thermal shock resistance, fire resistance and chemical stability at high temperatures; the shell should also have a certain permeability, So that the gas in the shell can escape smoothly during pouring. These are related to the refractory materials, binders and processes used in the manufacture of the shell.

The materials used to make the shell can be divided into two types, one is to directly form the shell, such as refractory materials, adhesives, etc .; the other is to obtain high-quality shells, simplify operation and improve process. Materials such as flux, hardener, surfactant, etc.

The main procedures and processes in the shell making process are:

1) Module degreasing and degreasing

When using wax-based molding materials to make investment molds, in order to improve the ability of the coating to wet the surface of the module, the oil on the surface of the module needs to be removed.

2) Apply paint and sand on the module

Before coating the coating, the coating should be stirred evenly to minimize the precipitation of refractory materials in the coating bucket, and adjust the viscosity or specific gravity of the coating so that

Common casting methods in investment casting are:

1) There are several methods of thermal gravity casting.

This is the most widely used form of casting, that is, after the shell is removed from the roasting furnace, it is cast at high temperature. At this time, the metal cools slowly in the mold shell, and can fill the mold with high fluidity, so the casting can well replicate the shape of the cavity and improve the accuracy of the casting. However, the slow cooling of the casting in the hot mold will make the grains coarse, which reduces the mechanical properties of the casting. When casting carbon steel castings, the surfaces of the slowly cooled castings are also susceptible to oxidation and decarburization, which reduces the surface hardness, smoothness and dimensional accuracy of the castings.

2) Vacuum suction casting

Place the mold in the vacuum casting box, suck the gas in the cavity through the tiny pores in the mold, so that the liquid metal can better fill the cavity, replicate the shape of the cavity, improve the casting accuracy, prevent air holes, Inadequate defects. The law has been applied abroad.

3) Crystallization under pressure

The mold shell is placed in the pressure tank for pouring. After the end, the pressure tank is closed immediately, and high-pressure air or inert gas is passed into the tank to solidify the casting under pressure to increase the density of the casting. The maximum pressure abroad has reached 150atm.

4) Directional crystallization (

The content of investment casting cleaning is mainly

(1) Remove the shell from the casting;

(2) Remove the casting from the pouring system;

(3) Remove the shell refractory material adhered to the casting;

(4) Cleaning after casting heat treatment, such as descaling, trimming and cutting gate residue.

The task of investment casting process design is

(1) Analyze the processability of the casting structure;

(2) Select a reasonable process plan, determine the relevant casting process parameters, and draw a casting diagram based on the above;

(3) Design the pouring system and determine the module structure.

It should be noted here that when considering the above three issues, the main basis is still the basic principles of the general casting process, especially when determining the process plan and process parameters (such as casting fillets, machining allowances, process ribs, etc.) Except that the specific data is slightly different due to the technical characteristics of investment casting, the design principles are exactly the same as those of sand casting.

Tasks and importance of investment casting process design

Investment casting is a casting process with little or no cutting. In the past, it was also called lost wax casting. Because the casting produced by the investment casting process has more dimensional accuracy and surface quality than other casting methods. The castings must be high. In addition, the investment casting method can complete the production of some highly complex and difficult to process castings, so it is deeply loved by enterprises.

Regarding the investment casting process, the investment casting process design is one of the most important links in the entire investment casting process. The technical difficulty factor of this step is large and it plays a very important role in the entire investment casting process. This link is mostly due to some professional and technical people.

As with other casting process designs, the design tasks of investment casting process are: a. Analyze the technicality of the casting structure according to specific requirements; b. Plan a reasonable process plan, determine relevant casting process parameters, and draw a casting diagram based on this C. Design the pouring system and determine the module structure. Except that the specific data is slightly different due to the technical characteristics of investment casting, the design principles are exactly the same as those of sand casting.

Because the investment casting process design link is of great significance to the entire casting process, and this link has very high requirements for the designer's own quality, enterprises should pay considerable attention to this link. ^[3]

Foundry is one of the basic processes of the modern machinery manufacturing industry, so the development of the foundry industry marks the production strength of a country. China has become one of the world's largest foundry machinery and has made great achievements in the foundry machinery manufacturing industry.

During the Eighth Five-Year Plan period, the foundry machinery manufacturing industry was highly valued by the former Ministry of Mechanical and Electrical Engineering. It invested the largest loan for special technological reforms and research expenses since the founding of the People's Republic of China, and supported the development and development of products in the foundry machinery industry. "Manufacturing of large-scale shot blasting machine", "Vertical partless boxless injection molding machine", "Research and development of water glass sand used sand recycling equipment", "Metal mold casting equipment" and so on have been developed and applied successively.

During the "Ninth Five-Year Plan" period, the foundry machinery industry undertook and completed the task of "Complete technology and equipment for refined and efficient modeling and cleaning of passenger car casting blanks", and "the development and development of efficient continuous shot blasting and cleaning lines for cylinder bodies" also achieved complete success In 1999, it completed the success of the national high-level gas-impact molding line project.

During the "Tenth Five-Year Plan" period, the annual average growth of major economic indicators of the foundry machinery industry is more than 30%, which is higher than the average growth rate of the machine tool industry. In particular, the profit growth is faster, and the average annual profit growth is as high as 46%. Higher market sales. In addition, the resin sand casting complete set of equipment can basically meet the domestic market demand, which has changed the situation of relying mainly on imports in the past; it has been able to produce a high level of automatic casting production line, which can partially replace imports, and partially solve the car engine Casting blanks such as cylinder blocks and cylinder heads must also be imported; high-level automatic core making machines, automatic casting cleaning machines, automatic sand processing machines, large-scale automatic die-casting machines, and precision casting equipment such as casting machinery can basically be produced in China . It should be said that the product level of the foundry machinery industry has greatly improved during the Tenth Five-Year Plan period, laying a good foundation for the further development of China's foundry machinery industry in the future.

During the "Eleventh Five-Year Plan" period, the casting industry will continue to maintain a relatively high growth rate under the stimulation of huge market demand. As the technological level of foundry machinery products is still far from the market demand, there is huge development potential and expansion space for the development of the industry, which brings opportunities for the rapid growth of the foundry machinery industry. (source:

When considering the above three issues, the main basis is still the basic principles of the general casting process, especially when determining the process plan and process parameters (such as casting fillet, draft angle, machining allowance, process ribs, etc.), In addition to the specific data due to the slightly different process characteristics of investment casting, the design principles and

Information technology is very important for the development of various industries, especially for the development of die-casting mold industry. Develop and make good use of information resources, so that production and operation activities rely on the timely processing of information, smooth circulation and high-quality and efficient operations. In order to make the industry better and faster.

From the perspective of the country's macroeconomic policies, industry development, and international and domestic market capacity, the international and domestic markets for large-scale precision and complex investment casting molds and die-casting molds are large. The mold order for manufacturing intention is 300 million yuan. As long as the technical equipment strength of the partner company is available, the order can be obtained. At the same time, the investment casting molds in China are exquisite in materials, well-made, high in dimensional accuracy, in line with customer standards and service life And the quality of castings has reached the international advanced level, and has obvious price advantages.

The investment casting molds exported by China are concentrated in Europe, North America, Japan, South Korea and other places. The export mold volume of some enterprises has accounted for more than 30% of the total output value. Investing in large-scale precision mold projects has theoretical and practical basis, so as not to be blind and it is possible to obtain better returns. ^[4]

It is reported that the automobile oil chassis die-casting molds exported from China to Europe have been repeatedly recognized by foreign investors due to their strong price advantages, advanced design, and exquisite production. It can be seen that the overseas market of China's investment casting mold industry is developing very rapidly, and it will definitely rise in the future. ^[5]