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Metal injection molding MIM raw material


Applicable materials:


The MIM process is applicable to a wide range of materials, including low alloy steel, stainless steel, tool steel, nickel-based alloys, tungsten alloys, cemented carbide, titanium alloys, magnetic materials, Kovar alloys, etc.

An introduction to metal injection molding

Metal Injection Molding (MIM) is a kind of


Small, three-dimensional complex shapes


And the near-net shaping process of products with special performance requirements. The technology is the modern


Plastic injection molding technology


Introduce


Powder metallurgy


A new type of powder metallurgy


Net shape


technology.


its


Basic process


Yes: Various fine metal powders (generally less than 20μm) are combined with a preset binder in a certain ratio to make rheological properties


Feeding


, Injected into the mold cavity by the injection machine to form


Parts blank


, After removing the binder and sintering at high temperature, the blank parts can get various


Metal parts


. The flow chart is as follows:


2. What is the ideal MIM metal powder?


Powder size, tap density and particle shape


It is a key performance index that determines whether the powder can be successfully used in the MIM process. The MIM process requires the raw material powder to be very fine (~10μm)


,


To ensure uniform dispersion, good rheological properties and greater sintering rate.



Metal powder microstructure (*2500 times)



The ideal powder for MIM is:


Powder particle size 2~8μm


; Loose density 40


%~50


%


; Tap density 50


% Above; the powder particles are nearly spherical,


Larger than the surface.


At present, the raw materials of MIM metal powder include iron, nickel, titanium, stainless steel, precious metals, super alloys and other materials. At the same time


diversification


Development, such as structural materials, functional materials, magnetic materials, etc.



The main methods of producing MIM powder are:


Carbonyl method, ultra-high pressure water atomization method, high pressure gas atomization method, plasma atomization method and laminar flow atomization method. Different powder preparation techniques


Particle size, particle shape, microstructure, chemical properties, manufacturing cost


Etc. have different effects.



Atomized pulverizing



How does MIM choose a binder?



Figure: Small-sized workpieces have higher and higher requirements for the stability of the binder


The binder is


The core of MIM technology


, An important difference between MIM and conventional powder metallurgy methods is the high binder content. The main function of the binder is to act as


Bonded metal powder


Particle flow carrier and after forming


Keep the shape of the workpiece


.



The adhesive for MIM should meet the following requirements:


Small contact angle with powder, strong adhesion and no reaction with powder;


The viscosity does not change much within the injection temperature range, but the viscosity changes quickly during cooling


Not easy to stick mold;


Less dosage and less binder can make the mixture produce better rheology;



The choice of adhesive is very critical. If the choice of adhesive is not appropriate, the following defects may occur:



How are binders classified?



A practical binder is generally composed of several components, each component has its own unique function, according to the function can be divided into the main binder, secondary binder and additives. According to the main binder components and their properties in the binder system, the binder system can be divided into


Thermoplastic adhesives, thermosetting adhesives, gel systems, water-soluble adhesives and special systems


Wait.


among them,


Thermoplastic binder


The most widely used, divided into


Paraffin-based binder, oil-based binder, polymer-based binder


Wait. The following table lists the advantages and disadvantages of several main MIM binder systems:



Thermoplastic binder


Generally by


High molecular polymer, low molecular substance


And necessary


additive


Composition (paraffin-based adhesives, oil-based adhesives, etc. are classified according to low-molecular substances). The functions of each component are as follows:



High polymer:


High viscosity, high strength, maintain the shape of the compact after injection and during degreasing



Low molecular weight substances:


Low viscosity, good fluidity, can be removed first at a lower temperature during degreasing process, leaving interconnected voids in the briquettes, which is conducive to the rapid hot melt grease in the later stage



additive:


Improve stress, reduce viscosity, increase wettability or lubricity, etc.



Table: Main component characteristics of commercial thermoplastic adhesives


Tm-melting point, Tv-glass transition temperature, *-calculated value