The lost foam casting process is suitable for a large number of castings that have intricate structural features and are difficult to produce by other methods. From the actual situation of developed countries, such as the United States and several European countries that have lost foam process operations, this view is true. Lost foam process has been successfully used to produce aluminum alloy engine blocks and has been mass-produced in the United States for automobiles and ships. This casting method has given a demonstration to the world’s foundry industry, proving the advantages of the lost foam process.

In China, the development of lost foam technology shows the advantages of this process from different aspects. And has been mostly applied to cast iron and cast steel products. It has been used to investing in the production of various parts, from relatively simple to parts with relatively complex features. In addition, it is also suitable for different production operations including mass production, loose parts, and even prototypes.

In order to ensure that the lost foam raw sand has sufficient fluidity to fill the complex deep cavity parts of the foam pattern, plus a thick coating layer has a certain mechanical strength to prevent box collapse, therefore the lost foam casting requires roundness Be good enough. In addition, during the casting of lost foam casting, a large amount of gas or liquid pyrolysis products will be generated along with the cracking and burning of the foam pattern. Therefore, the sand must have sufficient air permeability to prevent the residue from overflowing.

Since the ceramic casting sand is close to a spherical shape, it has good fluidity and high air permeability. It can fill slender holes, angled parts of castings and complex inner cavity parts, and it is easier to compact. Material, which guarantees its wide application in cast iron and cast steel (including high manganese steel, etc.).

The use of ceramic casting sand has the advantages of high fire resistance, good fluidity and high air permeability, and is used for lost foam casting, which can increase the yield of castings, reduce costs, and improve the working environment.

Physical and chemical properties of ceramic foundry sand

Grain shape spherical Coefficient of expansion (20~1000℃)6×10-6/℃
Colour Black-brown Al2O3 65-85%
Refractory temperature ≥ 1800 ℃ Fe2O3 ≤5%
Bulk Specific Gravity 1.95 -2.05g /cm3 SiO2 8~22%
True density 3.4g /cm3 TiO2 3~4.5%
Thermal conductivity (1200 ℃)5.27W/M·K PH value 7~8
Granularity 6 ~ 320 mesh (φ0.053 ~ 3.36mm) /

Lost foam casting is a method of casting a refractory bonded paint, drying it and then performing dry sand molding, vibrating tightly, and then pouring the molten metal to heat the gasification to disappear, thereby obtaining a metal part having the same shape as the pattern. Lost foam casting is a new technology with no margin and precise forming. It does not need to take the mold and use the binderless dry sand to reduce the pollution. It is considered as the green casting technology.

Lost foam casting classification

The castings processed by lost foam casting have high dimensional accuracy, uniformity, clean environment and no pollution; low labor intensity, less labor, less technicians; less equipment investment. The processing for small and medium-sized enterprises reduces costs, improves the economics of the company, and understanding its process classification can help companies better choose the casting process.

1. Pressure lost foam casting technology

The pressure lost foam casting technology is a new casting technology combining the lost foam casting technology and the pressure solidification crystallization technology. It is in the pressure irrigation with a sand box. After pouring the molten metal to vaporize the foam, the pressure irrigation is quickly sealed. A casting method in which a certain pressure of gas is introduced to solidify and crystallize the molten metal under pressure. This casting technology is characterized by significantly reducing casting defects such as shrinkage, shrinkage, and porosity in the casting, increasing the density of the casting and improving the mechanical properties of the casting.

2. Vacuum low pressure lost foam casting technology

Vacuum low pressure lost foam casting technology is a new casting technology developed by combining negative pressure lost foam casting method and low pressure anti-gravity casting method. The characteristics of vacuum low pressure lost foam casting technology are: combining the technical advantages of low pressure casting and vacuum lost foam casting, the filling process is completed under controlled pressure, which greatly improves the casting filling ability of the alloy; compared with die casting, the equipment The investment is small, the casting cost is low, and the casting can be heat-treated and strengthened. Compared with the sand casting, the casting has high precision, small surface roughness, high productivity and good performance; under the action of anti-gravity, the sprue becomes the supplementary shortening channel and the pouring temperature. The loss is small, the liquid alloy is filled and solidified under the controllable pressure, the casting system of the alloy casting is simple and effective, the yield is high, and the structure is compact; the vacuum low pressure lost foam casting has a low pouring temperature and is suitable for various colored alloys.

3. Vibration lost foam casting technology

The vibration lost foam casting technology applies vibration of a certain frequency and amplitude during the lost foam casting process, so that the casting solidifies under the action of the vibration field. Since the solidification process of the lost foam casting is applied to the metal solution for a certain period of time, the vibration force makes the liquid The relative motion between the phase and the solid phase causes the dendrites to break, and the crystal core in the liquid phase is increased, so that the final solidification structure of the casting is refined, the feeding is improved, and the mechanical properties are improved. The technology utilizes the ready-made compact vibrating table in lost foam casting, and the mechanical vibration generated by the vibrating motor causes the molten metal to nucleate under dynamic excitation to achieve the purpose of refining the structure, and is an easy operation, low cost and no environment. The method of pollution.

4. Semi-solid lost foam casting technology

Semi-solid lost foam casting technology is a new casting technology that combines lost foam casting technology with semi-solid technology. Because the process is characterized by controlling the relative proportion of liquid-solid phase, it is also called transformation control semi-solid forming. This technology can increase the density of castings, reduce segregation, improve dimensional accuracy and casting performance.

5. Lost shell casting technology

The lost shell casting technology is a new casting method combining investment casting technology and lost foam casting. The method is to apply a plurality of layers of refractory material to the surface of the foam molding which is made of a foaming mold and has the same shape as the part, and after hardening and drying, the foamed plastic pattern is burned and disappeared to form a shell, and is fired. And then casting, to obtain a new precision casting method for higher dimensional precision castings. It has the characteristics of large size and high precision in the lost foam casting, and has the advantages of crust precision and strength in investment casting. Compared with ordinary investment casting, it is characterized by low cost of foam plastic molding, convenient combination of pattern bonding, easy disappearance of gasification, overcoming the problem of melt deformation caused by easy softening of investment casting mold, and can be produced. Large size of various alloy complex castings.

6. Lost foam suspension casting technology

The lost foam suspension casting technology is a new practical casting technology that combines the lost foam casting process with suspension casting. The technical process is that after the molten metal is poured into the mold, the foam plastic pattern is vaporized, and the suspending agent is mixed in the riser model (or the suspending agent is placed at a specific position of the pattern, or the suspending agent is foamed together with the EPS. Physicochemical reaction with molten metal to improve the overall (or partial) structural properties of the casting.

Due to the low cost, high precision, flexible design, clean and environmental protection, and suitable for complex castings, the lost foam casting technology meets the general trend of casting technology development in the new century and has broad development prospects.

Lost foam casting has strong vitality because of its quick and good green environmental protection characteristics. Especially in recent years, the development momentum has the potential to break the bamboo. The lost foam casting process has precise casting shape and almost no allowance, which is in line with the lightweight and precise casting. The development trend of complexity and complexity. However, the lost foam casting process covers many disciplines such as mechanics, chemical engineering, metallurgy, casting, and computer. It is a complex process technology that combines knowledge and application technology. Due to the use of dry sand molding, the change of objective conditions such as the actual gasification wall negative pressure greatly simplifies the production process, shortens the process flow, greatly facilitates production, improves productivity, improves the labor environment, and reduces labor. Strength, its advantages are obvious.

The lost foam casting is very special, the dry shape does not have any adhesive, and the real and casting system does not need to be taken out, which greatly improves the design freedom of the casting and improves the surface finish and dimensional accuracy of the casting.

1. Process analysis of lost foam casting aluminum

In the filling process, in the filling process, under the strong heat radiation of the high temperature molten metal, an irregular gap layer is formed between the liquid metal front and the foam pattern. Taking the bottom note as an example, the front edge of the molten metal is pushed forward in a “concave” shape, and the corresponding foam pattern end is zigzag or finger-type retracted. The solid slag and the liquid phase foam which are not completely cleared at the forefront of the alloy flow in the direction of escape of the gas. The gas exists in a small molecule state and is easily excluded by the negative pressure, and the solid impurities are blocked on the inner wall of the coating. That is, the surface of the casting forms a surface slag pit, which is the main reason why the lost foam casting has a smaller internal slag hole and the outer slag hole protrudes: the liquid phase foam is also discharged at the metal-coating interface, and is partially coated. Adsorption, partial secondary vaporization, and secondary vaporization of the gas mostly overflow, and a small amount of intrusive metal forms surface pores. The riser of the casting is generally designed at the top, and it is a dark riser. It cannot obtain high-temperature metal by means of refilling. The aggregated metal is all metal after being cooled by vaporization and heat absorption, the shrinking effect is not good, and the shrinkage ratio is increased. . The pores, slag holes, shrinkage holes, and carbon defects have similarities in the process control of many lost modes, and they are not contradictory. Therefore, the vanishing die pores are the main line here, and the prevention measures are explained together.

(1) Definition of pores: During the solidification process, the bubbles trapped in the metal form pores in the casting, which are called pores.

(2) The pores are divided into intrusive pores, wrapped pores, precipitated pores, endogenous reaction pores, and exogenous reaction pores.

2. Analysis of the causes of the porosity defects in the lost aluminum mold

The reasons for the occurrence of air holes in lost foam casting are as follows:

(1) Foam model gasification decomposition to generate a large amount of gas and residue can not eliminate the mold in time;

(2) Dehydration of aluminum water is poor, and the pouring process is unreasonable to cause slag holes;

(3) The pouring system is unreasonable;

(4) The pouring temperature is unreasonable;

(5) The location of the sprue is unreasonable;

(6) The permeability of the coating is poor or the negative pressure is unreasonable, and the permeability of the filling sand is poor;

(7) The pouring speed is too slow, fail to fill the pouring cup, expose the sprue, entrap the air, inhale the slag, and form the carrying hole and the slag hole;

(8) The capacity of the gate cup is too small, and the molten metal forms a vortex, which invades the air to generate pores;

(9) The joint between the sprue cup and the sprue and the gating system is not well sealed;

(10) The particle size of the sand is too fine, the dust content is too high, and the gas permeability is poor. The vapor can not remove the coating in time to form pores or wrinkles.

3. Process measures to control porosity defects

(1) selecting suitable model materials;

(2) the use of the gating system and the insulated riser;

(3) Improve the gas permeability of the coating, and the quality of the lost foam coating is critical. In the case of mass production, the gas permeability of the paint is regularly checked, and the particle size of the aggregate is adjusted in time. Since the binder and suspending agent of the coating contain organic matter, the summer and autumn seasons should pay special attention to the fermentation mildew of the coating. The qualified castings cannot be separated from the best coating, and the quality of the coating is not light;

(4) The pouring temperature should be suitable;

(5) Control of dehydrogenation and slag removal time of aluminum water;

(6) Reasonable pouring position;

(7) Reasonable casting process and negative pressure.

4. Production principle and process flow

The method is made into a foam molding model according to the EPS process, and the special coating is applied. After drying, it is placed in a special sand box, filled with dry sand, three-dimensional vibration is tight, pouring under vacuum, the model gasification disappears, and the metal replacement model The casting is the same as the foam molding mold, and after condensing, the vacuum is released, and the casting is taken out from the loose sand for the next cycle.

Casting is a process in which a metal is smelted into a liquid that meets certain requirements and poured into a mold, and cooled, solidified, and cleaned to obtain a casting having a predetermined shape, size, and performance. Casting blanks are near-formed to achieve machining-free or small-scale processing, reducing costs and reducing time to some extent. Casting is one of the fundamental processes in the modern manufacturing industry.

There are many kinds of castings. According to the modeling method, it is customarily divided into: ordinary sand casting, including wet sand type, dry sand type and chemical hardening sand type; according to modeling materials, it can be divided into special castings with natural mineral sand as the main modeling material (such as Investment casting, clay casting, shell casting, negative pressure casting, solid casting, ceramic casting, etc.) and special casting with metal as the main casting material (such as metal casting, pressure casting, continuous casting, Low pressure casting, centrifugal casting, etc.)

According to the forming process, it can be divided into gravity casting: sand casting, permanent mold casting, pouring molten metal into the cavity by gravity; pressure casting: low pressure casting, high pressure casting. The molten metal is instantaneously pressed into the casting cavity by an additional pressure.

The casting process usually includes:

(1) Preparation of molds, molds can be divided into sand type, metal type, ceramic type, mud type, graphite type, etc. according to the materials used, which can be divided into disposable type, semi-permanent type and permanent type according to the number of times of use. Advantages and disadvantages are the main factors affecting the quality of castings;

(2) Melting and casting of cast metal, the cast metal mainly consists of cast iron, cast steel and cast non-ferrous alloy;

(3) Casting treatment and inspection. The casting treatment includes removing foreign objects on the surface of the core and casting, cutting out the riser, burrs and burrs, and heat treatment, shaping, anti-rust treatment and roughing.

The casting process can be divided into three basic parts, namely casting metal preparation, mold preparation and casting processing. Cast metal refers to the metal material used for casting castings in casting production. It is an alloy composed mainly of a metal element and added with other metal or non-metal elements. It is customarily called cast alloy, mainly cast iron. Cast steel and cast non-ferrous alloys.

Metal smelting is not only a simple melting process, but also a refining process that allows the metal to be poured into the mold to meet the expected requirements in terms of temperature, chemical composition and purity. For this reason, various inspection tests for the purpose of controlling quality are carried out during the smelting process, and the liquid metal can be allowed to be poured after reaching various specified indexes. Sometimes, in order to achieve higher requirements, the molten metal is treated outside the furnace after being discharged, such as desulfurization, vacuum degassing, refining outside the furnace, gestation or deterioration treatment. Commonly used equipment for smelting metals are cupola, electric arc furnace, induction furnace, electric resistance furnace, reverberatory furnace and the like.

Process flow introduction

With the advancement of technology and the booming of the foundry industry, different casting methods have different mold preparation contents. Taking the most widely used sand casting as an example, the mold preparation includes two major tasks: modeling material preparation and modeling core making. Sand casting, various raw materials used for molding core, such as foundry sand, sand binder and other auxiliary materials, as well as molding sand, core sand, paint, etc., which are formulated by them, are collectively referred to as modeling materials. The task of preparing materials is to follow castings. The requirements, the nature of the metal, the selection of the appropriate raw sand, binder and auxiliary materials, and then they are mixed into a certain type of molding sand and core sand in a certain proportion. Commonly used sand mixing equipment are a roller-type sand mixer, a counter-flow sand mixer and a blade grooved sand mixer. The latter is designed for mixed chemical self-hardening sand, continuous mixing and fast speed.

The shape core is based on the requirements of the casting process, based on the determination of the modeling method and the preparation of the molding material.

The accuracy of the casting and the economics of the entire production process depend mainly on this process. In many modern foundry workshops, the styling core is mechanized or automated. Commonly used sand-type styling equipments include high, medium and low pressure molding machines, sand blasting machines, boxless injection molding machines, core shooting machines, cold and hot core boxes.

After the castings are removed from the cast-cooled mold, there are gates, risers, metal burrs, drapes and mold lines. The sand-cast castings are also adhered to the sand and must be cleaned. Equipment for performing such work includes a sander, a shot blasting machine, a pouring riser, and the like. The sand falling of sand castings is a process with poor working conditions. Therefore, when selecting the modeling method, it should be considered to create convenient conditions for the falling sand cleaning. Some castings are subject to special post-processing requirements such as heat treatment, shaping, anti-rust treatment, roughing, etc.

Industry characteristics

Casting is a relatively economical method of forming blanks, which is more economical for parts with complex shapes. Such as the cylinder block and cylinder head of a car engine, ship propellers and fine art. Some hard-to-cut parts, such as nickel-base alloy parts of gas turbines, cannot be formed without casting.

In addition, the size and weight of the cast parts are wide, and the metal types are almost unlimited. The parts have general mechanical properties, and also have comprehensive properties such as wear resistance, corrosion resistance and shock absorption. Other metal forming methods such as forging , rolling, welding, punching, etc. can not be done. Therefore, the number of blank parts produced by the casting method in the machine manufacturing industry is still the largest in terms of quantity and tonnage.

Materials commonly used in foundry production are various metals, coke, wood, plastics, gas and liquid fuels, modeling materials, and the like. The equipment required is a variety of furnaces for metallurgy, various sand mixers for sand mixing, various molding machines for core making, core machines, sand falling machines for cleaning castings, and shot blasting. Machine and so on. There are also machines and equipment for special casting and many transportation and material handling equipment.

Casting production has different characteristics from other processes, mainly due to its wide adaptability, the need for materials and equipment, and pollution of the environment. Casting produces dust, harmful gases and noise that pollute the environment. It is more serious than other mechanical manufacturing processes and requires measures to control it.

For casting and mechanical structural design engineers, heat treatment is a very meaningful and highly valuable method for improving the quality of materials. Heat treatment can change or affect the structure and properties of cast iron while achieving higher strength. , hardness, and improve its resistance to abrasion and so on.

Due to different purposes, there are many types of heat treatment, which can be mainly divided into two categories. The first type is the tissue structure, which does not change or should not change through heat treatment. The second is the change of basic organizational structure. By. The first heat treatment procedure is mainly used to eliminate internal stresses which are caused by different cooling conditions and conditions during the casting process. The structure, strength and other mechanical properties are not significantly changed by heat treatment. For the second type of heat treatment, al-Qaeda has undergone significant changes and can be broadly divided into five categories:

(1) Softening annealing: The purpose is mainly to decompose the carbide, lower the hardness thereof, and improve the processing property. For the spherical stone-milled cast iron, the purpose is to obtain a ferrite structure having a high fertility.

(2) Normalization treatment: It is mainly used to improve or to obtain a uniform distribution of mechanical properties of a cast iron-completed cast product.

(3) Quenching: Mainly to obtain higher hardness or wear strength, and at the same time to a very high surface wear resistance.

(4) Surface hardening treatment: mainly to obtain a surface hardened layer, and at the same time obtain a very high surface wear resistance.

(5) Precipitation hardening treatment: mainly in order to obtain high strength, the elongation does not change drastically.

Industry Trends

The trend in the development of foundry products is to require castings with better overall performance, higher precision, less margin and a smoother surface. In addition, the requirements for energy conservation and the voice of society to restore the natural environment are also increasing. To meet these requirements, new casting alloys will be developed, and new smelting processes and new equipment will emerge.

As the degree of mechanization automation in foundry production continues to increase, more will be developed towards flexible production to expand the adaptability to different batches and varieties. New technologies for energy conservation and raw materials will be given priority. New processes and new equipment with little or no pollution will be the first priority. Quality control technology will have new aspects in the detection, non-destructive testing and stress measurement of various processes. development of.

A mold is a variety of molds and tools for obtaining a desired product by injection molding, blow molding, extrusion, die casting or forging, smelting, stamping, and the like. Simply put, it is a tool for making shaped articles. It can make a variety of different items and some parts, and the mold has the title of “mother of industry”. Although it is very powerful, the mold will still appear during the production process. Some problems, especially in the heat treatment stage, are prone to defects, so what are the defects in mold heat treatment, and how to solve it?

1. Soft spots appear on the surface of the mold

After the heat treatment of the mold, there are soft spots on the surface. This situation will affect the wear resistance of the mold and reduce the service life of the mold. The main reason for this is that the mold has scale, rust and local decarburization on the surface before heat treatment. After quenching and heating, the cooling and quenching medium is improperly selected, and the impurities in the quenching medium are excessive or aged.

For this case, we can solve the problem by removing the scale and rust before the heat treatment of the mold, and properly protecting the surface of the mold during quenching and heating. It should be heated in a vacuum electric furnace, a salt bath furnace and a protective atmosphere furnace. When quenching and heating, select a suitable cooling medium. For long-term use, the cooling medium should be filtered frequently, or replaced regularly. Shading can prevent the occurrence of soft spots.

2. The mold is poorly organized before heat treatment

The final spheroidized structure of the mold is coarse and uneven, and the spheroidization is imperfect. The structure has mesh, band and chain carbides, which will cause the mold to be cracked after quenching, resulting in scrapping of the mold. This situation is generally due to the presence of severe carbide segregation in the original structure of the mold steel material. Poor forging process, such as forging heating temperature is too high, deformation is small, stop forging temperature is high, and the cooling speed after forging is slow, so that the forged structure is coarse and there are mesh, band and chain carbides, so that spheroidizing annealing It is difficult to eliminate. The spheroidizing annealing process is not good, such as the annealing temperature is too high or too low, the isothermal annealing time is short, etc., which may result in uneven spheroidizing annealing or poor spheroidization.

In this case, according to the working conditions of the mold, the production batch and the toughening performance of the material itself, try to select a good quality mold steel material. Improve the forging process or use normalizing heat treatment to eliminate the non-uniformity of the network and chain carbides and carbides in the raw materials.

High-carbon die steel with severe segregation of carbides that cannot be forged can be subjected to solution heat treatment. The correct spheroidizing annealing process specification for the forged blank can be tempered heat treatment and rapid uniform spheroidizing annealing. The furnace is properly installed to ensure the uniformity of the temperature of the mold blank in the furnace.

3. The mold produces quench crack

The cracking of the mold after quenching is a defect in the heat treatment process of the mold, which will cause the processed mold to be scrapped, causing great loss in production and economy. The reason for this is due to the presence of severe network carbide segregation in the mold material. There are mechanical or cold plastic deformation stresses in the mold. Improper heat treatment (heating or cooling too fast, improper selection of quenching cooling medium, low cooling temperature, too long cooling time, etc.).

The mold has a complicated shape, uneven thickness, sharp corners and threaded holes, which cause excessive thermal stress and tissue stress. The quenching heating temperature is too high to cause overheating or overheating. After quenching, the tempering is not timely or the tempering time is insufficient. When the quenching is heated, the quenching is performed again without intermediate annealing. Heat treatment, improper grinding process. When subjected to electrical discharge machining after heat treatment, high tensile stress and microcracks are present in the hardened layer.

At this time, the intrinsic quality of the mold raw materials should be strictly controlled, the forging and spheroidizing annealing processes should be improved, the mesh, ribbon and chain carbides should be eliminated, and the uniformity of the spheroidized structure can be improved. The mold after mechanical processing or after cold plastic deformation shall be subjected to stress relief annealing (>600 ° C) and then subjected to heat quenching. For molds with complex shapes, asbestos should be used to block threaded holes, and the dangerous section and thin wall should be wrapped, and graded quenching or austempering should be used.

Annealing or high temperature tempering is required when reworking or refurbishing the mold. Preheating should be adopted during quenching heating, pre-cooling measures should be taken during cooling, and suitable quenching medium should be selected. The quenching heating temperature and time should be strictly controlled to prevent overheating and over-burning of the mold.

After the mold is quenched, it should be tempered in time, the holding time should be sufficient, and the high alloy complex mold should be tempered 2-3 times. Choose the right grinding process and the right grinding wheel. Improve the mold EDM process and perform stress relief and tempering.

4. The microstructure of the mold after quenching

After the mold is quenched, the coarse structure will seriously affect the mechanical properties of the mold. When used, the mold will be broken, which will seriously affect the service life of the mold. The reason for this is that the mold steel is confused, and the actual steel quenching temperature is much lower than the quenching temperature of the required mold material. The steel was not properly spheroidized before quenching, and the spheroidized structure was poor. The quenching heating temperature is too high or the holding time is too long. Improper placement in the furnace and overheating in the vicinity of the electrode or heating element area. For molds with large cross-section changes, the quenching heating process parameters are not properly selected, and overheating occurs at thin sections and sharp corners.

The solution is to strictly inspect the steel before it is put into storage, so as to prevent the steel from being confused. Proper forging and spheroidizing annealing should be performed before the mold is quenched to ensure good spheroidization. Correctly formulate the mold quenching heating process specification and strictly control the quenching heating temperature and holding time. Regularly test and calibrate the temperature measuring instrument to ensure the normal operation of the instrument. Keep the proper distance from the electrode or heating element when heating in the furnace.

The above is the whole content of the mold heat treatment defects and solutions. In general, the above defects can be caused because there is no treatment before the production, and there is serious carbide segregation in the original structure of the mold steel material. The forging process is not good, and there is a possibility that the mold steel is confused. The actual steel quenching temperature is much lower than the quenching temperature of the required mold material.

Metal casting mold is one of the molds often used in cast aluminum plants. It is characterized by small casting tolerances, high efficiency, and beautiful surface of metal castings. Generally, after the acceptance, in order to maintain the performance state and the service life of the mold, the normal production and the quality of the product are ensured, and the production cost is reduced as much as possible, and regular inspection and maintenance are required.

First, preparation and inspection before casting

1. Wear protective equipment such as work clothes and safety shoes before you go to work.

2. Confirm the name of the casting and the metal casting mold number of the maintenance metal casting mold.

3. Find the casting sample and the two-mode aluminum casting of the metal casting mold, and inspect the faulty part of the metal casting mold aluminum casting.

4. According to the drawings and materials in the metal mold casting mold file, carry out the next step to confirm the required maintenance items, and develop a detailed maintenance plan.

5. Prepare the tools and accessories to be used, and do each step carefully and responsibly according to the maintenance plan.

Second, maintenance, grinding, assembly and cleaning of metal casting molds

1. After a period of production and use, a large amount of aluminum scraps and dirt accumulated on each movable part should be removed, and the parting surface, cavity, core, exhaust block and overflow trough should be more serious. During maintenance, the mold should be hung on the cleaning table with a cleaning tool such as a copper brush, a shovel, a rag, a brush, etc. to remove the aluminum slag products (aluminum, aluminum chips), oil stains, mold release residue or any other foreign matter on the mold. The dirt is removed. Be careful not to damage the cavity, core, etc. when cleaning.

2. When disassembling the mold, it should be noted that the combination of each component must have a relative number, which can be combined with the same number, and can not be misplaced. If the assembly is wrong, the phenomenon of flying aluminum will occur in the production, resulting in production failure.

3. Repair metal casting molds according to aluminum castings. Remove the residue in the cavity and save light in the cavity, the sticky aluminum on the core, and the collapse deformation. Repair the welds or changes in the meat to make it form and demould to prevent undercuts. Then check the slider, the guide rail and the position of the movable parts, and carry out effective mold repair and rectification.

4. Repair the mold parts that need to be replaced (such as cavity, ejector, cast pin, bolt, inclined guide post, slider and guide rail). If necessary, hand in the quality department inspection, and then replace the damaged parts after the inspection is correct, and assemble according to the installation identification code, beware of the wrong position and direction.

5. Cavity or core damage, can be modified as much as possible. If damage is required, replacement, repair or welding should be carried out as carefully as possible, and repair, replacement, excavation, and repair should be carried out under permitted conditions.

6. When assembling the disassembled mold parts, clean them before cleaning. Then apply rust prevention to the part of the mold (mold frame, cavity, insert, slider core, slider seat, splitter cone, barrel, cast pin, bead, wear block and exhaust block) The oil, as well as the guide pillar guide sleeve series and the moving parts such as the ejector rod and the reset rod, are rust-proof lubricating oil.

Third, the maintenance operation after the metal casting mold production operation

1. Regular cleaning and maintenance. In production and use, due to the uneven stress in the casting mold material under high temperature production, stress relief and tempering should be carried out to eliminate the internal stress generated during the production process. Prevent the casting mold from prolonging the production of high temperature conditions, and the material may be affected by deformation and fracture.

2. Tempering to do stress relief treatment. Maintenance is generally based on the size of the aluminum casting and the production batch size. When the mold is used in the production of 8 thousand molds to 10,000 molds, it is necessary to carry out secondary stress relief and tempering maintenance, and then carry out maintenance stress tempering treatment every 15,000 molds to 20,000 molds. Its service life.

3. When the mold is cracked or cracked, first check if there is any problem with the size. If there is no problem, first clean the surface residual aluminum residue product or any other foreign matter, and then use the abrasive cloth and oil stone thickness 150 particles to 400 particles for light treatment, and perform effective nitriding, ABP surface treatment or stress relief treatment, Improve product molding and surface quality. When there is a problem, the processing plan should be considered first, and the processing should be carried out after the processing is qualified.

4. Due to the wide variety of aluminum castings, the design structure of metal casting molds is complex and the conditions in production are different. Therefore, three points of stress relief processing, nitriding and ABP surface treatment are set as the maintenance basis.

5. The molds that have not been used for more than two months are cleaned and maintained by the staff. Open the mold and check the internal anti-rust effect. If there is any abnormality, it must be re-rustproofed. If you do not use it for a long time, you should apply butter to prevent rust and affect post-production. It must be cleaned and inspected before going to the machine.

Sand casting refers to a casting method for producing castings in a sand mold. Because the molding materials used in sand casting are cheap and easy to obtain, the castings are easy to manufacture, and can be adapted to the single-piece production, batch production and mass production of castings. For a long time, it has been the basic process in casting production.
Sand-type raw materials are foundry sand and sand binder.

The foundry sand has enamel sand, zircon sand, chromite ore, corundum sand and the like.

The binder is used to make the sand mold and the core made of the shaped sand have a certain strength, and the loose sand particles are joined together. There are clays, drying oils, semi-drying oils, water-soluble silicates or phosphates and various synthetic resins.

1. Clay wet sand type: The main binder of clay is made of clay and appropriate amount of water. After being made into sand type, it is directly combined and poured in a wet state. The strength of the wet sand depends on the clay slurry in which the clay and water are mixed in a certain ratio. The amount of clay and moisture are important process factors for the wet type of clay.


(1) Clay is rich in resources and cheap.

(2) Most of the used clay wet sand can be recycled after proper sand treatment.

(3) The cycle for manufacturing the mold is short and the work efficiency is high.

(4) The mixed molding sand can be used for a long time.

(5) After sand compaction, it can still withstand a small amount of deformation without damage, which is very advantageous for both drafting and lower core.


(1) Applying a thick clay slurry to the surface of the sand during sand mixing requires high-power sand mixing equipment with a smashing effect, otherwise it is impossible to obtain a good quality sand.

(2) Since the sand is well mixed, it has a relatively high strength. The molding sand is not easy to flow during the molding, and it is difficult to compact. The manual molding is both laborious and requires a certain skill. When the machine is used, the equipment is complicated and huge.

(3) The rigidity of the mold is not high, and the dimensional accuracy of the casting is poor.

(4) Castings are prone to defects such as sand washing, sand inclusion, and porosity.

2. The mold used for sand casting is generally composed of an outer sand type and a core. In order to improve the surface quality of the casting, a layer of paint is often applied to the sand and core surfaces. The main components of the coating are powdery materials and binders with high refractoriness, high chemical stability, and a carrier (water or other solvent) and various additives for ease of application.

3. Clay dry sand type: The wet moisture of the molding sand used to make this sand type is slightly higher than that of the wet type. After the sand mold is prepared, the surface of the cavity should be coated with a refractory paint, and then dried in an oven. After it is cooled, it can be combined and cast.

Disadvantages: It takes a long time to dry the clay sand type, which consumes a lot of fuel, and the sand type is easily deformed during the drying process, which affects the accuracy of the casting. Clay dry sand types are commonly used in the manufacture of steel castings and larger cast iron parts.

4. Chemically hardened sand type: The sand used for this type of sand is called chemically hardened sand. The binder is generally a substance which can undergo molecular polymerization under the action of a hardener to form a three-dimensional structure, and various synthetic resins and water glass are commonly used.

There are basically three ways of chemical hardening.

(1) Self-hard

Both the binder and the hardener are added during the sand mixing. After being made into a sand mold or a core, the binder reacts under the action of the hardener to cause the sand mold or the core to harden by itself. The self-hardening method is mainly used for styling, but it is also used to manufacture larger cores or to produce cores with a small batch size.

(2) Aerosol hardening

Add binder and other auxiliary additives during sand mixing without first adding hardener. After molding or core-making, a gaseous hardener is blown or blown into the gaseous carrier to atomize the liquid hardener, which is dispersed in the sand or core, resulting in sand hardening. Aerosol hardening is mainly used for core making and sometimes for small sand types.

(3) Heat hardening

A binder and a latent hardener which does not function at normal temperature are added during sand mixing. After the sand or core is made, it is heated, at which time the latent hardener reacts with certain components of the binder to form an effective hardener that hardens the binder, thereby hardening the sand or core. The heat hardening method is mainly used for core making except for the production of a small thin shell sand type.

Sand casting is one of the casting processes, and the mold used for sand casting is generally composed of an outer sand type and a core. Because the molding materials used in sand casting are cheap and easy to obtain, the castings are easy to manufacture, and can be adapted to the single-piece production, batch production and mass production of castings. For a long time, it has been the basic process in casting production. At present, internationally, in all casting production, 60 to 70% of castings are produced in sand, and about 70% of them are produced using clay sand.

The sand casting process is a casting method in which sand is used as a main molding material to prepare a mold. Sand casting is the most traditional casting method. Due to the characteristics of sand casting (not limited by the shape, size and alloy type, short production cycle and low cost), sand casting is still the most widely used casting method in casting production, especially single or small. Batch casting.

Advantages and disadvantages of sand casting process


1. Clay is rich in resources and cheap. Most of the used clay wet sand can be recycled after proper sand treatment;

2. The cycle for manufacturing the mold is short and the work efficiency is high;

3. Mixed sand can be used for a long time;

4. Adaptability is very wide. Small pieces, large pieces, simple pieces, complicated parts, single pieces, large quantities can be used;


1. Because each sand mold can only be cast-times, the mold is damaged after obtaining the casting, and must be reshaped, so the production efficiency of sand casting is low;

2. The rigidity of the molding machine mold is not high, and the dimensional accuracy of the casting is poor;

3. Castings are prone to defects such as sand washing, sand inclusion, and porosity.

Sand casting process

The basic process of the traditional sand casting process has the following steps: sand mixing, molding, core making, molding, pouring, falling sand, grinding processing, inspection and other steps.

1. In the sand mixing stage, the sand and core sand are prepared for the modeling. Generally, the sand mixer is used to put the old figure and the appropriate amount of clay to stir.

2. Mold stage, according to the parts drawings to make molds and core boxes, generally single pieces can be used to produce plastic molds or metal molds (commonly known as iron molds or steel molds) using wood molds, mass production, large-scale castings can be used to make models. Nowadays, the molds are basically made of engraving machines, so the production cycle is greatly shortened, and the molding generally takes 2 to 10 days.

3. The shape (core) stage: including the shape (formed cavity with casting sand to form the casting), core making (forming the internal shape of the casting), the mold to put the core into the cavity, the upper and lower sand box is good) . Modeling is a key link in casting.

4. The melting stage: according to the required metal components with chemical components, choose the appropriate melting furnace to melt the alloy material, forming a grid of liquid metal liquid (including qualified components, temperature qualified). Smelting generally uses a cupola or an electric furnace (due to environmental protection requirements, the cupola is now basically banned, and the electric furnace is basically used).

5. Pouring stage: the molten iron melted in the electric furnace is injected into the finished type with a ladle. The pouring of molten iron requires attention to the speed of pouring, so that molten iron fills the entire cavity. In addition, pouring molten iron is dangerous and needs to be safe!

6. Cleaning stage: After the pouring, after the molten metal solidifies, take the hammer to remove the gate and shake off the sand of the casting, and then use the sand blasting machine to spray sand, so that the surface of the casting will appear very clean! The casting blank is not strict. After inspection, it can be shipped out.

7. Casting processing: For some castings with special requirements or some castings that cannot meet the requirements, simple processing may be required. Generally, the grinding wheel or the sander is used for processing and polishing, and the burrs are removed to make the castings smoother.

8. Casting inspection: Generally, in the process of cleaning or processing, unqualified ones have been found out. However, some castings have individual requirements and need to be checked again. For example, some castings require a central hole to be inserted into a 5 cm shaft, so you need to wear a 5 cm shaft for a try.

After the above eight steps, the castings are basically formed, but for the castings that require precision, machining is still required.

Molds are various molds and tools used in industrial production for injection molding, blow molding, extrusion, die casting or forging, smelting, stamping, etc. to obtain the desired products. In short, a mold is a tool for making a shaped article, and the tool is composed of various parts, and different molds are composed of different parts. Next, let’s take a look at the mold design and production process!

First, manufacturing preparation

Prepare the molds to be made, whether it is materials or technicians, you need to be well prepared.

Second, feasibility analysis

Feasibility analysis of the products of the designed molds, taking the automobile parts as an example, firstly, the assembly drawings of each component are analyzed by the design software, that is, the set of drawings mentioned in our work, to ensure that the drawings of the products are correct before the mold design. On the other hand, you can familiarize yourself with the importance of each component in the entire car to determine the key size, which is very beneficial in the mold design. The specific set of drawings still needs to be designed by yourself.

Third, the structure

After the product analysis, the product to be analyzed, what kind of mold structure is used for the product, and the product is sorted, the content of each process is determined, and the product is developed by using the design software. To expand forward, for example, a product requires five processes, and the stamping is completed from the product drawing to the fourth, third, second, and first projects, and a graphic is copied and then the previous project is executed. The work of starting the work of the five projects is completed, and then the detailed work is carried out. Note that this step is very important and needs to be very careful. If this step is completed well, it will save a lot of time in drawing the mold diagram. After the stamping content of each project is determined, including in the forming mold, the inner and outer lines of the thickness of the product material are retained to determine the size of the convex and concave molds. The method for product unfolding is not described here, and will be in the product unfolding method. Specific introduction.

Fourth, preparation materials

According to the product development drawing, the template size is determined in the drawings, including the fixed plate, the unloading plate, the convex and concave mold, the insert, etc., pay attention to directly preparing the material in the product development drawing, which is of great benefit to the drawing mold drawing. I have seen that many mold designers directly calculate the product development drawings by hand. This method is too inefficient, draw the template size directly on the drawing, and express it in the form of a group diagram. The preparation of the material is completed, and on the other hand, a lot of work is saved in the work of the various parts of the mold, because in the work of drawing each component, it is only necessary to add the positioning, the pin, the guide post and the screw hole in the preparation drawing.

Fifth, draw drawings

After the preparation is completed, the mold drawing can be fully entered, and a copy can be made in the preparation drawing to draw the components, such as adding screw holes, guide post holes, positioning holes, etc., and in the punching die. The hole for each hole needs to be cut by the wire. In the forming die, the forming gap of the upper and lower molds must not be forgotten, so the mold drawing of one product after the completion of these work is almost completed 80%, and the process of drawing the mold drawing is also completed. Need to pay attention to: each process, refers to the production, such as the fitter scribing, wire cutting, etc. to the different processing steps have a complete production of the layer, which has great benefits for wire cutting and drawing management, such as color distinction, etc., size The labeling is also a very important job, but also a troublesome job, because it is too time consuming.

Sixth, proofreading

After the above drawings are completed, the drawings cannot be issued. It is also necessary to proofread the mold drawings, assemble all the accessories, make different layers for each different mold plate, and use the same reference as the guide post holes to perform the mold. Analyze the analysis and insert the product development drawings into the group diagrams to ensure that the hole positions of the template are consistent and the gap between the upper and lower molds of the bending position is correct.

Seven, production

During the production process, pay attention to check the glue position and check whether the glue position is uniform. If it is uneven, it will cause shrinkage and affect the appearance.

Eight, open the mold direction

Determine the parting surface and the draft angle

1. The parting surface selects the value projected in the mold opening direction and is as simple as possible.

2. Touching the position: Try to touch the back mold as much as possible. If you want to touch the front mold, it is easy to walk the front, affect the appearance, and use the plane contact.

3. Pillow: Pillow 5-8 mm, and then flat with the large part, the plastic part is pulled 3 degrees, the back is pulled 3 degrees or avoiding the air.

4. Insert the position: use the side work, pull 3 degrees, generally do inserts.

The above is the entire content of the mold design and manufacturing process. In general, the mold design and production process is mainly preparation preparation, production feasibility analysis and production design structure, preparation of production materials, drawing production drawings, and then in detail Proofreading, to ensure that the production is started after the error is correct, it is also necessary to pay attention to the direction of demoulding when demolding.

With the rise of lost foam casting, how to reduce the cost of castings, increase the yield and improve the quality is a problem. To solve such problems, the key is in the choice of sand type. Usually, in order to reduce the cost of sand, people will choose cheap quartz sand. However, due to the disadvantages of low refractoriness, poor gas permeability and poor fluidity, such sand has many casting defects during the casting process, such as: sand, pores. These defects are obvious in alloy steel casting. In addition, this kind of sand will generate a lot of dust in the subsequent treatment, which makes the environment of the production workshop very bad, the amount of waste sand increases, the sand is reduced, the sand recycling rate is low, and it is not durable. Therefore, from a comprehensive perspective, the cost of sand increases.

Nowadays, a new type of sand for lost foam casting has been widely concerned by the foundry industry and is known as the new sand “ceramic foundry sand” for green products. The major factors affecting the quality of castings and the excellent properties of ceramic foundry sand are summarized below.

1. Liquidity

Since the ceramic foundry sand is a spherical particle, its fluidity is very good, it is easy to compact when it is molded, and it can maintain good gas permeability, while quartz sand and forsterite sand are both polygonal sand, and the fluidity is poor. Originally, forsterite sand was used as the filling sand. Due to the poor fluidity of the polygonal sand, defects such as rat tail and scarring occurred many times. This phenomenon has been significantly improved after the use of ceramic foundry sand, improving the yield by 5%. Practice has proved that the fluidity of ceramic foundry sand is better than the existing various types of sand.

2. Refractoriness

The ceramic foundry sand is made of high-quality aluminum bauxite from Shanxi and is made by melting in a high-temperature electric furnace. Ceramic foundry sand is a spherical particle, the main component is aluminum oxide (Al2O3), its refractoriness can reach 1900 °C. The main component of quartz sand is silica (SiO2), which has a refractoriness of less than 1700 ° C. Quartz sand will have various crystals at different temperatures, which will reduce the refractoriness of the sand again during the casting process.

Practice has proved that the use of ceramic casting sand can significantly reduce mechanical and chemical sand, greatly reduce the labor intensity of sand cleaning, and is not easy to produce sand, sand, porosity and other defects. For example, the high-manganese steel castings produced by Jilin Innovation Lost Foam Equipment Co., Ltd., before the use of ceramic foundry sand, the sand-sanding and sand-sanding phenomenon is very serious, and each time it takes a lot of manpower and material resources to clean and polish the surface of the casting. It not only increases the production cost of the casting, but also causes the surface quality of the casting to be unattractive. This type of casting defect has been eliminated after the use of ceramic foundry sand. To this end, the cost savings are 6%. The ceramic refining sand is comparable to chromite ore and is now widely used in the casting of raw chromite ore.

3. Breathability

The permeability of the sand depends mainly on the size of the sand, the particle size distribution, the type of the grain and the type of binder. In the pouring process, if the permeability of the molding sand is poor, a large amount of gas generated by the internal heat due to high temperature cannot be immediately discharged, so that a bonfire phenomenon occurs, and defects such as pores, cold separation, and insufficient pouring are generated in the casting, and even scrapped.

Both quartz sand and magnesium olive sand are polygonal sands, which have poor gas permeability, while ceramic foundry sands are spherical particles with uniform particle size distribution and good gas permeability, which can avoid such casting defects. In the production of high-manganese wear-resistant steel castings, quartz sand and forsterite sand have been used successively, but the fruit is not ideal. Due to the poor gas permeability of the two sands, the molten bubble gas is not discharged, and a large number of knots are formed on the surface of the casting. Oh, and a large amount of gas generated by high-temperature heating during pouring cannot be discharged, resulting in defects such as porosity, crusting, and insufficient pouring, or the use of ceramic casting sand to solve this problem, and the yield is improved by 7%.

4. Thermal expansion coefficient

During the high-temperature casting process of castings, the thermal expansion of the molding sand will cause a slight change in the size of the molding sand, which in turn affects the accuracy of the casting size. The thermal expansion coefficient of the molding sand is too large, which may cause casting defects such as sand inclusion, crusting, and rat tail. The ceramic casting sand has a small coefficient of thermal expansion, and there is almost no expansion phenomenon during the casting process, which greatly improves the precision of the casting, and its performance is comparable to that of zircon sand. Henan Xinxiang has many manufacturers producing vibration equipment. There are many small holes in the wall panel. Due to its precision and refractoriness, zircon sand is used as casting sand. Ceramic casting sand is now used, and the cost of molding sand is reduced by 70%.

5. Reuse performance

Because quartz sand is polygonal sand, the strength is low, and the sand is easily broken during the modeling and sand treatment process. Not only will it generate a lot of dust, pollute the production environment, but also generate a lot of waste sand, which will make the sand not durable. According to statistics, The amount of waste sand cleared per pouring is about 5%. The ceramic foundry sand is spherical sand, which has high strength and is not easy to be broken. It can greatly reduce the amount of dust in the production workshop, reduce the labor intensity and production cost of the sand treatment workers, reduce the amount of waste sand, and increase the quantity of recycled sand. Thereby greatly reducing the amount of sand loss. According to statistics, the annual loss of ceramic foundry sand is below 5%. Therefore, the high cost caused by the high price of the ceramic foundry sand is directly offset, and the production cost is greatly reduced. According to the calculation of the manufacturer using the sand, the cost of the secondary increase can be recovered within 8-10 months.