Study On The Support Material And Accuracy Of The Suspended Component Via Layered Extrusion Forming

Compared with the preparation methods of ordinary ceramics,additive manufacturing has the advantages of flexible forming,short cycle,suitable for complex shape,etc.,and is widely used in functional ceramics,bioceramics and other fields.In the foundry industry,ceramic mold(core)plays an important role in the manufacturing of high-end complex castings because of its high strength,high fire resistance and other advantages.Layered extrusion forming ceramic mold(core)is a new method which combines the advantages of additive manufacturing with the casting ceramic mold(core).The ceramic slurry is used to extrude the green body without mold,and then the ceramic mold(core)is prepared by drying,trimming and ceramics.Compared with selective laser sintering,3D printing and other ceramic components preparation,the layered extrusion method has the advantages of low equipment cost and friendly material system,which is suitable for rapid prototyping of small and medium-sized complex ceramic components.At present,there is a lack of effective and easy to remove support materials when layered extrusion has complex cavity like ceramic body.Therefore,this paper studies the base support material and its application in layered extrusion,and discusses the precision control of ceramic body,which lays a theoretical foundation for the integrated die-free forming of complex ceramic mold(core).The main contents of this paper include:(1)In order to extrude the main material and supporting material of the component separately,the double head layered extrusion ceramic(slurry)forming equipment was developed and constructed.The equipment is mainly composed of mechanical control part,slurry extrusion part and control unit.After design and verification,the mechanical control part selects the synchronous belt system and the ball screw system frame part to form the base plate moving with the Z axis.This mechanism has the characteristics of simple structure and high stability.The motion range of the final design is 220mm×220mm×150 mm.The slurry is evenly and stably extruded through the pneumatic piston mechanism.The control logic of interrupt control is adopted,which has the characteristics of high control accuracy and easy to modify.(2)Using PVP as binder,ethanol as dispersion medium and magnesium sulfate as skeleton material,a kind of supporting material slurry suitable for layered extrusion process was developed.The influences of the content of magnesium sulfate and Si O₂ in the slurry on the flowability,bending strength and size deviation of the formed sample were studied.The results show that with the increase of solid content,the viscosity and yield stress of the slurry will increase;when Si O₂ is added,the viscosity and yield stress of the sample will decrease greatly;while with the increase of solid content,the strength of the wet green sample increases first and then decreases,and the size deviation will decrease.After adding Si O₂,the bending strength of the green sample increased,but after sintering,the strength of the sample decreased,and with the addition of Si O₂,the strength decreased.When the amount of Si O₂ is 5wt.%,the bending strength reaches 21.61mpa at 900?.According to thermogravimetric analysis and water solubility test,magnesium sulfate sample can be completely dissolved in 90?hot water within 60 minutes.(3)The influence of the main process parameters of double extrusion on the accuracy of components was analyzed.The main process parameters that affect the accuracy of the components include:extrusion needle diameter,layer height,needle speed,slurry flow speed,slurry solid content,critical support angle and support distance of double extrusion,etc.According to the simulation results,the conical needle can make the slurry flow better.The reasonable layer height should be determined by the needle speed,extrusion speed and other parameters.For the base slurry,when the solid content is 60wt.%,the sample has better forming quality,lower lamination depth and higher forming accuracy.The critical support filling angle of alumina slurry is 50°,and a reasonable support distance is helpful to improve the surface quality of the main material.The hemispherical and suspended square members were formed by the optimized process parameters,and the support materials could be dissolved automatically by glacial acetic acid.It is verified that the base slurry can be used as a good support material.