复杂陶瓷铸造型芯分层沉积挤出成型及其精确控制研究

The production of hollow single-crystal blade for aircraft engine is considered as the “crown jewel”, the key technology of which is fabricating the complicated ceramic mold with core that can work stably for a long time at a high temperature. However, their fabrication has so many difficulties, such as complicated process, low yield, high controlling demanding. Based on integral three dimensional printing of ceramic mold with core, this project combines high-strength ceramic mold with core material and layered deposition extrusion (LDE), in order to solve the problems of integral direct forming and precision control of complicated ceramic mold with core. The high-accuracy complicated ceramic mold with core will be obtained by studying new material system and its curing method of ceramic slurry for LDE, using the process of which includes integral precision forming, substep sintering and precise post-processing, and realizes patternless rapid precision forming of ceramic mold with core for complex castings. The main studies include the new ceramic material and binder system for LDE, controlling method of high-accuracy ceramic mold with core using integral precision forming method, controlling system of integral LDE forming equipment for ceramic mold with core, controlling method of precise post-processing and accuracy of complicated ceramic mold and core, et al. This study can provide the set of new technology for integral precision forming of the ceramic mold with core for complex precision castings, which has great theoretical and practical significance.

航空发动机空心单晶叶片的铸造成形被认为是制造业“皇冠上的明珠”，其首要的关键是制备耐高温不变形的精密复杂陶瓷型芯，制造过程复杂、成品率低、控制难度大。本项目基于三维整体打印陶瓷型芯思想，将高强度陶瓷型芯材料与分层沉积挤出成型（Layered Deposition Extrusion，简称 LDE）结合起来，研究复杂陶瓷铸造型芯整体直接成型及精确控制难题。拟通过研究LDE用陶瓷浆料新材料体系及其固化方法，实现整体精确成形、分步烧结陶瓷化、精准后处理等过程控制，获得高精度复杂整体陶瓷型芯，实现复杂铸件用陶瓷型芯的无模快速精确成形。主要研究基于LDE的陶瓷型芯材料及其粘结剂新体系、高精度陶瓷型芯整体精确成形控制方法、陶瓷型芯整体LDE成形装备控制系统、复杂陶瓷型芯精准后处理措施与精度控制策略等。本项目研究成功将为复杂精密铸件用陶瓷型芯整体精确成形提供成套新技术奠定基础，具有重要的理论与实际意义。

针对航空航天、汽车领域复杂铸件陶瓷型芯制造的过程复杂、成品率低、控制难度大等难题，本项目将高强度陶瓷芯材料与分层沉积挤出成型相结合，制备复杂铸造陶瓷型芯。研制构建了基于分层沉积挤出成型原理的陶瓷型芯高精度成形装置及控制系统，研究了陶瓷浆料挤出成型特征；研究了陶瓷浆料分层沉积挤出成型的精度影响因素，进行了铁基与铝基合金浇注；研究了基于分层沉积挤出成型陶瓷型芯的铸造特征及性能改善机理；研究了可用于制备复杂悬空陶瓷型芯试样所需的支撑材料体系；为提高陶瓷芯的溃散性降低铸后清理难度，研究了可溶性陶瓷芯、盐芯等材料及制备工艺方法。研究结果表明：1）单头与双头挤出成型装备，通过气压控制可实现较高精度的陶瓷坯体挤出成形，浆料经针管挤出时，针管直径越大、长度越小，浆料沿程能量损失就越小；2）当氧化铝固含量为50vol.%，挤出头内径为0.40mm，层高取值为挤出头内径的70%，打印速度为10mm/s时，陶瓷型芯坯体试样的尺寸精度与表面精度较好，优化材料配方后，采用0.26mm内径挤出头，陶瓷型芯试样表面粗糙度为12.5微米，浇注后的铸件表面粗糙度（Ra为6~9微米）良好，且不会发生界面反应，此外表面涂层可进一步提高型芯试样的表面精度；3）采用淀粉基与盐基支撑材料结合双头沉积成型装置可制备陶瓷悬空构件，其中淀粉可在陶瓷烧结过程中（约500℃）完全去除，盐基可在陶瓷烧结后在水或弱酸中去除；4）以氧化铝与高岭土质量比为4:1粉末为基体材料，当纳米MgO加入量为1wt.%时，氧化铝基陶瓷型芯试样综合性能最好；5）通过复合粘结剂改性，低温烧结（700~900℃）制备可溶氧化铝芯，低温烧结后不仅具有较高强度（10MPa以上）还具有良好的溃散性，尺寸收缩1%以下，通过加入氧化硅改善氧化钙基陶瓷芯的吸湿与溃散性，当氧化钙与氧化硅摩尔比为2.45时，1200℃烧结后氧化钙基陶瓷芯抗弯强度强度10MPa以上，100℃水温下，陶瓷芯试样在70s左右即可完全溃散。本项目研究为复杂精密铸件用陶瓷型芯整体精确成型提供了一套新技术方法，具有重要的理论与实际意义。