The process performance of metal powder injection molding is overall performance, including powder flow, bulk density, tap density, compressibility, formability and sintering size change. Besides, powder with other chemical and physical properties shall be used for some special applications, such as catalytic performance, electro-chemical activity, corrosion resistance, electromagnetic performance and coefficient of internal friction. Comprehensive performance of metal powder injection molding reflects metal property and nature of single particle. Metal powder properties can be divided into chemical property, physical property and processing property. Chemical property means metal content and impurity content.
Metal powder injection molding is a group of metal particles whose size is less than 1mm, including single metal powder, alloy powder, and some refractory compound powder with metal nature. The powdered metal injection molding companies production of metal powder injection molding is: metal powder and adhesive, which satisfy injection molding requirements, are mixed evenly by proper method at certain temperature, after pelleting, and then injection molding.
Physical property includes powder's average grading and particle size distribution, powder's specific surface and true density, particle shape, surface morphology and internal microstructure. The basic performance can be determined by specific standard methods.
Along with accuracy improvement of injection powder molding, except for accurate material selection and modification, it is very important to select conditions accurately and analyze reasonably the relations between shrinkage and production. Especially shrinkage will affect greatly quality of products made by powder metallurgy. There are many affecting factors.
(1) Resin pressure
Resin pressure affects shrinkage of metal powder injection molding greatly. If resin pressure is big, shrinkage becomes smaller, then product size shall be big. Even within one die cavity, resin pressure will be different along with different product shapes. Therefore, difference in shrinkage appear. For family molds, resin pressure within each die cavity will easily become different, and shrinkage will be different too.
(2) Mold temperature
No matter amorphous resin or crystalline resin, if mold temperature is high, then shrinkage becomes bigger. Precision shaping shall keep mold temperature at certain degree. When designing molds, mim china pays attention to cooling circuit design.
(3) Gate section area
Generally speaking, if gate section area changes, shrinkage will change too. Shrinkage will become smaller when gate size becomes bigger. It relates to resin liquidity.
(4) Wall thickness
Products wall thickness also affects shrinkage. For amorphous resin, since resin has different impact tendency on shrinkage of wall thickness, when wall thickness is big, shrinkage is big too. Otherwise, shrinkage becomes smaller. Crystalline resin must avoid big change of wall thickness. For family molds, if die cavity has different wall thickness, then shrinkage will make a difference too.
(5) Content of reinforced materials
When using glass fiber reinforced resin, if glass filled fiber becomes more, shrinkage becomes smaller. Shrinkage of metal powder injection molding in flow direction is smaller than lateral shrinkage. According to big differential resin, to avoid warp and fly warp, please pay attention to gate shape, position of fly spare mouth and gate number.
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