选区激光烧结覆膜砂后处理固化工艺及性能研究

Study on Post-treatment Curing Process and Properties of Selective Laser Sintered Coated Sand

选区激光烧结覆膜砂是增材制造的一个重要分支,应用于快速制造覆膜砂铸型(芯),极大缩短传统砂型铸造产品的开发周期。通过选区激光烧结制备覆膜砂试样并进行了后处理强化,通过拉伸、压缩及抗弯实验测试其力学性能,通过扫描电镜及红外分析揭示固化特性。研究表明:酚醛树脂低温时第一次固化乌洛托品与游离酚、残留水分反应,氮原子上的化学键与线性酚醛树脂反应,缩聚为体型结构产物,随着温度升高,一次固化的二羟基苄胺与三羟基苄胺进一步分解形成体型结构达到二次固化,强度得到提升。在后处理中添加玻璃微珠,190℃下覆膜砂强度最大,抗拉强度能达到4.22 MPa。覆膜砂试样后处理190℃下固化较完全,断裂方式为内聚断裂及附着断裂共存,160℃及220℃下存在碗状断口,断裂方式为附着断裂。

Selective laser sintering coated sand is an important branch of additive manufacturing,which is used to rapidly manufacture coated sand casting(core)and greatly shorten the development cycle of traditional sand casting products.The coated sand samples are prepared by selective laser sintering and strengthened by post-treatment.The mechanical properties are tested by tensile,compression and bending experiments.The curing characteristics are revealed by scanning electron microscopy and infrared analysis.Research has shown that phenolic resin for the first time when low temperature curing methenamine reaction and free phenol and water,the chemical bonds on the nitrogen atoms and linear phenolic resin reaction,condensation product for body structure,as the temperature increases,the decomposition of dihydroxybenzylamine and trihydroxybenzylamine gives methyramine,further formed shape structure to secondary curing,intensity is improved.When glass beads are added in the post-treatment,the strength of coated sand reaches the maximum at 190℃,and the tensile strength reaches 4.22 MPa.The coated sand samples are cured completely at 190℃,and the fracture mode is the coexistence of cohesive fracture and adhesion fracture.There are bowl-shaped fractures at 160℃and 220℃,and the fracture mode is adhesion fracture.