Research On Precision Casting Process Of Cast Steel Gear Blank With Coated Sand Based On 3D Printing Technology

Rapid mold technology is the combination of 3D printing technology and mold technology,which is a new method and process for rapid manufacturing of molds.This study takes helical cylindrical gears as the research object and develops a precision casting technology for helical gears by combining 3D printing technology,silicone rubber rapid mold technology,epoxy resin rapid mold technology,water-glass sand and laminated sand casting technology,and uses the casting simulation software Any Casting to simulate the filling process and the solidification process simulation for flow analysis and temperature field analysis.The technology developed in this work enables the production of gear blanks with approximate tooth shapes,shortening the development cycle of precision gear casting and reducing development costs.Based on the analysis of the structural characteristics of the casting,the related process design was carried out,the pouring position was selected,the location of the parting surface was determined,the size calculation and model design of sand core and core box were carried out,the gating system and feeding system were designed,and the open bottom injection pouring system was designed,which provided the process basis for the subsequent numerical simulation process.Any Casting software was used to simulate the casting process and analyze the results.The feeding system was optimized.The results showed that when the pouring temperature was 1650 °C and the gate filling speed was 20cm/s,the casting filling process was stable,the solidification sequence was appropriate,and there was no obvious shrinkage defects.The simulation results met the requirements of casting production.After printing out the prototype mold with 3D printing technology,the refurbishment of the silicone rubber mold was carried out.The silicone rubber has a high surface replication rate and good elasticity,which can better replicate the surface shape of the prototype mold.In order to ensure that the thickness of the mold is suitable,the curing time is short,the viscosity is appropriate,and the brushing accuracy is high,an experimental study on the ratio of silicone rubber is carried out.When the mass ratio of silicone rubber to curing agent is 100:2,the viscosity of silicone rubber is appropriate,the curing time of the mold is the shortest,the thickness of each application is 5mm,and the silicone rubber mold is obtained by multiple applications.Because the silicone rubber mold is soft,plaster was chosen as the backing layer of the silicone rubber mold to make the mold have enough strength.In order to make the gypsum backing layer with high enough precision and suitable viscosity of gypsum slurry,the best ratio of gypsum and water was experimentally studied,and the mixing ratio of gypsum powder and water was 100:40,which resulted in the suitable viscosity of gypsum backing layer and the highest precision of the obtained gypsum backing layer.The prepared silicone rubber mold is used to remake the epoxy resin mold.The epoxy resin mold is used to make coated sand molds and needs to meet the requirements of high temperature resistance.In this experiment,high temperature resistant epoxy resin is used to make the mold,and the resulting mold has enough strength and hardness to ensure that the mold can maintain its original strength and not be deformed during the heating process.When exploring the process of preparing epoxy resin mold,adding aluminum powder can increase the thermal conductivity of the mold,adding alumina and silicon carbide powder can increase the hardness and wear resistance of the mold,and adding glass fiber wire in the backing material can improve the strength of the mold,resulting in a mass fraction of epoxy resin base material of 40%,curing agent of 10%,aluminum powder of 20%,silicon carbide of 14%,alumina of 7%,short glass fiber is 9%,the brush viscosity of epoxy resin is suitable,and the resulting epoxy resin mold has high hardness.The composite casting mold is used because the coated sand mold has a fast forming speed and higher precision,and is suitable for forming a gear tooth profile with a complex curved surface.The upper and lower cavities are composed of water glass sand,and the coated sand mold is used to form the tooth profile of the gear.This process method can not only ensure that the casting of the approximate tooth shape is obtained,but also can effectively reduce the production cost and obtain the product with higher precision.