Metal powder injection molding technology is a product of multi-disciplinary penetration and intersection, such as plastic molding technology, polymer chemistry, powder metallurgy technology and metal material science. the blank can be molded by mold and the structural parts with high density, high precision and three-dimensional complex shape can be quickly and accurately materialized into products with certain structural and functional characteristics.
And can directly mass produce parts, which is a new change in the manufacturing technology industry.
This technology not only has the advantages of few conventional powder metallurgy processes, no or less cutting, and high economic benefits, but also overcomes the shortcomings of traditional powder metallurgy products, such as uneven material, low mechanical properties, difficult to form thin wall and complex structure, and is especially suitable for mass production of small, complex and special metal parts.
Process binder "mixing" injection molding "degreasing" and "sintering" post-treatment.
Powder metal powder.
The particle size of metal powder used in MIM process is generally 0.5 ~ 20 μ m. Theoretically, the finer the particle is, the larger the specific surface area is, and it is easy to be formed and sintered.
However, the traditional powder metallurgy process uses thicker powder larger than 40 μ m.
Organic adhesive.
The function of organic adhesive is to bond metal powder particles, so that the mixture has rheology and lubricity when heated in the barrel of the injection machine, that is to say, the carrier that drives the flow of the powder.
Therefore, the choice of adhesive is the carrier of the whole powder.
Therefore, the selection of adhesive drawing is the key to the whole powder injection molding.
Requirements for organic adhesives:
1.
With less dosage and less binder, the mixture can have better rheological properties.
two。.
No reaction, no chemical reaction with metal powder in the process of removing adhesive.
3.
It is easy to remove and there is no residual carbon in the product.
Mixed material.
The metal powder is uniformly mixed with the organic adhesive to make all kinds of raw materials become the mixture for injection molding.
The uniformity of the mixture directly affects its fluidity, thus affecting the injection molding process parameters, as well as the density and other properties of the final material.
The injection molding process is consistent with the plastic injection molding process in principle, and its equipment conditions are basically the same.
In the process of injection molding, the mixture is heated into a plastic material with rheological properties in the barrel of the injection machine and injected into the mold under appropriate injection pressure to form the blank.
The injection molded blank should be uniform microscopically, so that the product can contract uniformly in the process of sintering.
Extraction.
The organic binder in the blank must be removed before sintering, which is called extraction.
The extraction process must ensure that the adhesive is gradually discharged from different parts of the blank along the micro-channel between the particles without reducing the strength of the blank.
The removal rate of binder generally follows the diffusion equation.
Sintering can make the porous defatted blank shrink to densify into products with certain microstructure and properties.
Although the properties of the products are related to many technological factors before sintering, in many cases, the sintering process has a great or even decisive influence on the microstructure and properties of the final products.
Post-processing.
For the parts with more precise dimensions, the necessary post-processing is needed.
This process is the same as the heat treatment process of conventional metal products.
Characteristics of MIM process.
Comparison between MIM process and other processing processes.
The particle size of raw powder used in MIM is 2-15 μ m, while that of traditional powder metallurgy is 50-100 μ m.
The high density of the finished product in the MIM process is due to the use of fine powder.
MIM process has the advantages of traditional powder metallurgy process, but the high degree of freedom in shape can not be achieved by traditional powder metallurgy.
Traditional powder metallurgy is limited to the strength and filling density of the mold, and the shape is mostly two-dimensional cylindrical.
The traditional dedrying process of precision casting is a very effective technology for making complex shape products. In recent years, ceramic core can be used to assist to complete the finished products of slits and deep holes, but due to the strength of ceramic core and the limitation of the fluidity of casting liquid, this process still has some technical difficulties.
Generally speaking, this process is more suitable for manufacturing large and medium-sized parts, while MIM process is more suitable for small and complex parts.
Compare the project manufacturing process MIM process traditional powder metallurgy process powder particle size (μ m) 2-1550-100relative density (%) 95-9880-85 product weight (g) less than or equal to 400g 10-hundreds product shape three-dimensional complex shape two-dimensional simple shape mechanical properties.
Comparison between MIM process and traditional powder metallurgy die casting process is used in materials such as aluminum and zinc alloys with low melting point and good liquid fluidity.
Due to the limitation of materials, the products of this process have limits in strength, wear resistance and corrosion resistance.
There are many raw materials that can be processed by MIM process.
Although the precision and complexity of precision casting process have been improved in recent years, it is still not as good as dewaxing process and MIM process. Powder forging is an important development, which is suitable for mass production of connecting rod.
But generally speaking, there are still some problems in the cost of heat treatment and the life of the die in forging engineering, which need to be further solved.
The traditional machining method, which has recently improved its machining ability by automation, has made great progress in effect and precision, but the basic procedure is still inseparable from the gradual machining (turning, planing, milling, grinding, drilling, polishing, etc.) to complete the shape of the parts.
The machining accuracy of the machining method is much better than that of other machining methods, but because the effective utilization rate of the material is low, and the completion of its shape is limited by equipment and cutting tools, some parts can not be machined.
On the contrary, MIM can make effective use of materials without restriction. For the manufacture of precision parts with small and difficult shapes, compared with mechanical processing, MIM process has low cost and high efficiency, and has strong competitiveness.
MIM technology does not compete with traditional processing methods, but makes up for the shortcomings of traditional processing methods in technology or can not be made.
MIM technology can give full play to its advantages in the field of parts made by traditional processing methods.
The technical advantages of MIM technology in parts manufacturing can form structural parts with highly complex structures.
The injection molding technology uses the injection machine to mold the product blank to ensure that the material is fully filled with the mold cavity, which ensures the realization of the high and complex structure of the parts.
In the past, in the traditional machining technology, individual components are first made into individual components and then combined into components, which can be considered to be integrated into a complete single part when using MIM technology, which greatly reduces the steps and simplifies the machining process.
The comparison products of MIM and other metal processing methods have high dimensional accuracy and do not need secondary processing or only a small amount of finishing.
The injection molding process can directly mold thin-walled and complex structural parts, the shape of the product is close to the requirements of the final product, and the dimensional tolerance of the parts is generally kept at about ±0.1-±0.3.
In particular, it is of great significance to reduce the processing cost of cemented carbide which is difficult to be machined and to reduce the processing loss of precious metals.
The product has uniform microstructure, high density and good performance.
In the pressing process, due to the friction between the die wall and the powder and between the powder and the powder, the pressing pressure distribution is very uneven, which leads to the non-uniform microstructure of the pressed blank, which will result in uneven shrinkage of the pressed P / M parts in the sintering process, so the sintering temperature has to be reduced to reduce this effect, resulting in large porosity, poor compactness and low density of the products.
Seriously affect the mechanical properties of the products.
On the other hand, the injection molding process is a kind of fluid molding process, and the existence of the adhesive ensures the uniform distribution of the powder, which can eliminate the uneven microstructure of the blank, and then make the density of the sintered product reach the theoretical density of the material.
In general, the density of pressed products can only reach 85% of the theoretical density.
The high compactness of the products can increase the strength, strengthen the toughness, improve the ductility, electrical conductivity and thermal conductivity, and improve the magnetic properties.
High efficiency, easy to achieve mass and large-scale production.
The life of the metal mold used in MIM technology is equivalent to that of engineering plastic injection molding tools.
Due to the use of metal moulds, MIM is suitable for mass production of parts.
Because the blank of the product is molded by injection machine, the production efficiency is greatly improved, the production cost is reduced, and the consistency and repeatability of injection molding products are good, which provides a guarantee for large-scale and large-scale industrial production.
It is suitable for a wide range of materials and a wide range of applications (iron-based, low alloy, high-speed steel, stainless steel, gram valve alloy, cemented carbide).
A wide range of materials can be used for injection molding. In principle, any powder material that can be poured at high temperature can be made into parts by the MIM process, including difficult-to-process materials and high melting point materials in the traditional manufacturing process.
In addition, MIM can also study the material formula according to the requirements of users, make any combination of alloy materials, and mold the composite materials into parts.
Injection molded products have been widely used in all fields of national economy and have broad market prospects.
Metal powder injection molding technology is a product of multi-disciplinary penetration and intersection, such as plastic molding technology, polymer chemistry, powder metallurgy technology and metal material science. the blank can be molded by mold and the structural parts with high density, high precision and three-dimensional complex shape can be quickly and accurately materialized into products with certain structural and functional characteristics.
And can directly mass produce parts, which is a new change in the manufacturing technology industry.
This technology not only has the advantages of few conventional powder metallurgy processes, no or less cutting, and high economic benefits, but also overcomes the shortcomings of traditional powder metallurgy products, such as uneven material, low mechanical properties, difficult to form thin wall and complex structure, and is especially suitable for mass production of small, complex and special metal parts.
Process binder "mixing" injection molding "degreasing" and "sintering" post-treatment.
Powder metal powder.
The particle size of metal powder used in MIM process is generally 0.5 ~ 20 μ m. Theoretically, the finer the particle is, the larger the specific surface area is, and it is easy to be formed and sintered.
However, the traditional powder metallurgy process uses thicker powder larger than 40 μ m.
Organic adhesive.
The function of organic adhesive is to bond metal powder particles, so that the mixture has rheology and lubricity when heated in the barrel of the injection machine, that is to say, the carrier that drives the flow of the powder.
Therefore, the choice of adhesive is the carrier of the whole powder.
Therefore, the selection of adhesive drawing is the key to the whole powder injection molding.
Requirements for organic adhesives:
1.
With less dosage and less binder, the mixture can have better rheological properties.
two。.
No reaction, no chemical reaction with metal powder in the process of removing adhesive.
3.
It is easy to remove and there is no residual carbon in the product.
Mixed material.
The metal powder is uniformly mixed with the organic adhesive to make all kinds of raw materials become the mixture for injection molding.
The uniformity of the mixture directly affects its fluidity, thus affecting the injection molding process parameters, as well as the density and other properties of the final material.
The injection molding process is consistent with the plastic injection molding process in principle, and its equipment conditions are basically the same.
In the process of injection molding, the mixture is heated into a plastic material with rheological properties in the barrel of the injection machine and injected into the mold under appropriate injection pressure to form the blank.
The injection molded blank should be uniform microscopically, so that the product can contract uniformly in the process of sintering.
Extraction.
The organic binder in the blank must be removed before sintering, which is called extraction.
The extraction process must ensure that the adhesive is gradually discharged from different parts of the blank along the micro-channel between the particles without reducing the strength of the blank.
The removal rate of binder generally follows the diffusion equation.
Sintering can make the porous defatted blank shrink to densify into products with certain microstructure and properties.
Although the properties of the products are related to many technological factors before sintering, in many cases, the sintering process has a great or even decisive influence on the microstructure and properties of the final products.
Post-processing.
For the parts with more precise dimensions, the necessary post-processing is needed.
This process is the same as the heat treatment process of conventional metal products.
Characteristics of MIM process.
Comparison between MIM process and other processing processes.
The particle size of raw powder used in MIM is 2-15 μ m, while that of traditional powder metallurgy is 50-100 μ m.
The high density of the finished product in the MIM process is due to the use of fine powder.
MIM process has the advantages of traditional powder metallurgy process, but the high degree of freedom in shape can not be achieved by traditional powder metallurgy.
Traditional powder metallurgy is limited to the strength and filling density of the mold, and the shape is mostly two-dimensional cylindrical.
The traditional dedrying process of precision casting is a very effective technology for making complex shape products. In recent years, ceramic core can be used to assist to complete the finished products of slits and deep holes, but due to the strength of ceramic core and the limitation of the fluidity of casting liquid, this process still has some technical difficulties.
Generally speaking, this process is more suitable for manufacturing large and medium-sized parts, while MIM process is more suitable for small and complex parts.
Compare the project manufacturing process MIM process traditional powder metallurgy process powder particle size (μ m) 2-1550-100relative density (%) 95-9880-85 product weight (g) less than or equal to 400g 10-hundreds product shape three-dimensional complex shape two-dimensional simple shape mechanical properties.
Comparison between MIM process and traditional powder metallurgy die casting process is used in materials such as aluminum and zinc alloys with low melting point and good liquid fluidity.
Due to the limitation of materials, the products of this process have limits in strength, wear resistance and corrosion resistance.
There are many raw materials that can be processed by MIM process.
Although the precision and complexity of precision casting process have been improved in recent years, it is still not as good as dewaxing process and MIM process. Powder forging is an important development, which is suitable for mass production of connecting rod.
But generally speaking, there are still some problems in the cost of heat treatment and the life of the die in forging engineering, which need to be further solved.
The traditional machining method, which has recently improved its machining ability by automation, has made great progress in effect and precision, but the basic procedure is still inseparable from the gradual machining (turning, planing, milling, grinding, drilling, polishing, etc.) to complete the shape of the parts.
The machining accuracy of the machining method is much better than that of other machining methods, but because the effective utilization rate of the material is low, and the completion of its shape is limited by equipment and cutting tools, some parts can not be machined.
On the contrary, MIM can make effective use of materials without restriction. For the manufacture of precision parts with small and difficult shapes, compared with mechanical processing, MIM process has low cost and high efficiency, and has strong competitiveness.
MIM technology does not compete with traditional processing methods, but makes up for the shortcomings of traditional processing methods in technology or can not be made.
MIM technology can give full play to its advantages in the field of parts made by traditional processing methods.
The technical advantages of MIM technology in parts manufacturing can form structural parts with highly complex structures.
The injection molding technology uses the injection machine to mold the product blank to ensure that the material is fully filled with the mold cavity, which ensures the realization of the high and complex structure of the parts.
In the past, in the traditional machining technology, individual components are first made into individual components and then combined into components, which can be considered to be integrated into a complete single part when using MIM technology, which greatly reduces the steps and simplifies the machining process.
The comparison products of MIM and other metal processing methods have high dimensional accuracy and do not need secondary processing or only a small amount of finishing.
The injection molding process can directly mold thin-walled and complex structural parts, the shape of the product is close to the requirements of the final product, and the dimensional tolerance of the parts is generally kept at about ±0.1-±0.3.
In particular, it is of great significance to reduce the processing cost of cemented carbide which is difficult to be machined and to reduce the processing loss of precious metals.
The product has uniform microstructure, high density and good performance.
In the pressing process, due to the friction between the die wall and the powder and between the powder and the powder, the pressing pressure distribution is very uneven, which leads to the non-uniform microstructure of the pressed blank, which will result in uneven shrinkage of the pressed P / M parts in the sintering process, so the sintering temperature has to be reduced to reduce this effect, resulting in large porosity, poor compactness and low density of the products.
Seriously affect the mechanical properties of the products.
On the other hand, the injection molding process is a kind of fluid molding process, and the existence of the adhesive ensures the uniform distribution of the powder, which can eliminate the uneven microstructure of the blank, and then make the density of the sintered product reach the theoretical density of the material.
In general, the density of pressed products can only reach 85% of the theoretical density.
The high compactness of the products can increase the strength, strengthen the toughness, improve the ductility, electrical conductivity and thermal conductivity, and improve the magnetic properties.
High efficiency, easy to achieve mass and large-scale production.
The life of the metal mold used in MIM technology is equivalent to that of engineering plastic injection molding tools.
Due to the use of metal moulds, MIM is suitable for mass production of parts.
Because the blank of the product is molded by injection machine, the production efficiency is greatly improved, the production cost is reduced, and the consistency and repeatability of injection molding products are good, which provides a guarantee for large-scale and large-scale industrial production.
It is suitable for a wide range of materials and a wide range of applications (iron-based, low alloy, high-speed steel, stainless steel, gram valve alloy, cemented carbide).
A wide range of materials can be used for injection molding. In principle, any powder material that can be poured at high temperature can be made into parts by the MIM process, including difficult-to-process materials and high melting point materials in the traditional manufacturing process.
In addition, MIM can also study the material formula according to the requirements of users, make any combination of alloy materials, and mold the composite materials into parts.
Injection molded products have been widely used in all fields of national economy and have broad market prospects.
