Research On Porous Metal Mold And Its Efficient Heat Exchange

Mold is the core of manufacturing industry. Products produced in the process of molding encounter many issues, such as, exhaust is poor, temperature is hard to control, and demoulding problems. These problems can be solved by porous metal mold, which has permeability and enhanced heat transfer characteristics. Solving mold venting problem can improve the rate of finished products and quality of plastic molded parts. Improving heat exchange efficiency of mold can shorten the manufacturing cycle of molding products and enhance production efficiency. This has important theoretical value and the practical meaning of application. Key technologies on manufacture of porous mold and efficient heat exchange of mold are systematically studied in this paper.To improve the performance of porous mold made by sintered stainless steel material, short-cut stainless steel fibers are used as a strengthen phase. A novel cutting setup, which used to cut long metal fiber rope bundle into short fibers was developed. The setup takes a rotary cutter and a stationary cutter as cut die to cutting off long metal fiber rope bundle The cutting setup has high productivity, 1681680 fibers are obtained in one minute. The produced short-cut fibers have the advantages of uniform diameter, crackless surface, and high mechanical strength.Short stainless steel fibers and stainless steel powder particles are accumulated layer after layer using the method of Layered paving, which makes fibers and powder particles mixed well. A removable mold is designed and manufactured to produce green bodies of sintered stainless steel porous mold material, by which, green bogies are well shaped without defect of corners loss due to zero stripping force in the process stripping. Large pieces of sintered stainless steel porous mold material using vacuum sintering process are improved, which guarantees that the porous mold material is not cracked in sintering process. Heat treatment method of sintered stainless steel porous material with different material composition is studied. The door and cooling systems of vacuum sintering furnace are upgraded, and high temperature nitriding heat treatment is conducted to sintered stainless steel porous mold material in the upgraded vacuum sintering furnace. Therefore, sintered stainless steel porous mold material is strengthened by chemical heat treatment. Performance test and co MParison are conducted to sintered stainless steel porous mold material, which contains different mesh powder and different fiber content under vacuum sintering and high temperature nitriding heat treatment. The results showed that, compressive strength of sintered stainless steel porous mold material can be improved greatly by short stainless steel fibers. High temperature nitriding heat treatment can significantly improve the compressive yield strength of sintered stainless steel porous mold material. Mesh of powder particles has a great effect on the permeability of porous materials. Performance parameters provide theoretical guidance and data support for sintered stainless steel porous mold material used in the mold.A new method for the preparation of fiber molding dies by sintered stainless steel porous mold material is proposed. The fiber molded cold compacting and suction mold is manufactured by sintered stainless steel porous mold material with large porosity and large pore while the lower hot compacting and adjusting shape mold is manufactured by sintered stainless steel porous mold material with large porosity and small pore. The effect of machining methods on surface pore blocking of sintered stainless steel porous mold material is analyzed. The fiber molding die made of sintered stainless steel porous mold material was designed and the process flow of manufacturing is studied. Molding trials of fiber molded products are carried out using the porous fiber molding dies. Fiber molded products are well shaped, which proves that the new method can be used to replace the traditional manufacturing method of fiber molding mold by “drilling and network covered”.To use the permeability of porous materials, a porous plastic injection mold is designed and manufactured by sintered stainless steel porous mold materials as blank, and injection molding experiment is conducted by ABS plastic/Si C composites as raw materials. The results showed that the porous sintered stainless steel mold can smoothly exhaust gas from cavities, and composite plastic part is well filled. This proves mold cavity directly manufactured by sintered stainless steel porous mold material can produce good exhaust in injection molding of ABS plastic/Si C composites, and porous injection mold can replace traditional exhaust means, such as exhaust ducts and venting plug which traditional exhaust system needed.To enhance cooling of high temperature casting mold, an experimental system, which is used to simulate the cooling process of high temperature casting mold was constructed, where porous copper foam was inserted into the cooling channel. The effect of cooling performance of the porous copper foam was investigated at different flow rate of cooling water. The results show that, taking 0.4 m3/h flow rate of cooling water, in 80 s of cooling time, the temperature at the same position near cooling channel of mold with insert gets 29.4℃ lower than that of mold without porous copper foam inserted. If the flow rate increases, the temperature at the same position of the mold with insert decreases while the local temperature gradient and the heat flux increase. It is shown that the copper foam inserted in the cooling channel of casting mold facilitates rapid cooling and sequential solidification temperature controlling. In addition, the application of porous copper foam also brings great flow resistance.The single-flow resistance in sintered stainless steel particles porous media was studied experimentally. The SC model was selected as the geometrical model according to the size of the porosity and it was studied numerically by solving N-S equation and k-ε turbulence model in pore scale simultaneously. The relation between the pressure drop per unit in sintered stainless steel particles porous media and the equivalent Reynolds number was analyzed. Two constant coefficients in Tadrist equation indicating the relation between the pressure drop per unit and particles diameter, porosity, flow velocity was obtained by experimental data fitting. The complete Tadrist equation could be taken as a prediction model to predict the flow resistance in sintered stainless steel particles porous media in the macro scale.