Investigation of free shrinkage of the main types of powder- polymer mixtures used for manufacturing parts from analogues of 38khma (42crmo4) steel by the mim-method | Mekhanika | kompozitsionnykh | materialov i konstruktsii
> Volume 25 > №1 / 2019 / Pages: 76-86

Investigation of free shrinkage of the main types of powder- polymer mixtures used for manufacturing parts from analogues of 38khma (42crmo4) steel by the mim-method

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Abstract:

The paper discusses one of the advanced technologies of powder metallurgy, effective for serial and mass production of both metal and ceramic small-sized precision parts with a complex geometric configuration – the technology «Powder Injection Moulding» (PIM), based on the use of powder-polymer mixture (feedstock) for injection molding under high pressure. When using PIM technology, the quality of the final sintered metal or ceramic part in successive technological stages depends on the quality of the initial molded semi-finished product – the casting from the particulate filled polymer composite material. The dimensional accuracy of a molded composite semi-finished product is largely determined by its uncompensated shrinkage upon cooling and extraction from the mold, in turn, the value of this shrinkage is determined by the value of the coefficient of thermal expansion, which for feedstock primarily depends on the composition and properties of the polymer binder used. In this paper, we briefly consider theoretical methods for calculating the thermal expansion of powder-polymer mixtures (feedstocks). It was noted that for materials with a complex structure and weakly deterministic properties of components, such as, for example, feedstocks with a binder in the form of a polymer blends, definitive tests remain one of the most reliable means of studying effective thermomechanical characteristics. For feedstocks used for manufacturing parts made from analogues of 38KHMA (42CrMo4) steel with the two most common types of polymeric binder the temperature dependences of the average coefficient of linear thermal expansion were determined by linear dilatometry in the temperature range from minus 20 to plus 125C. The obtained experimental data, supplemented by an accurate pycnometric measurement of the density of the materials under study, made it possible to carry out for each of them an estimate calculation of the temperature dependence of the specific volume. As a result, based on the calculated dependencies, a comparative assessment of the values of free non-compensated shrinkage of feedstocks of compared types was made.

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