Research On Injection Molding Equipment And Technology Of Piezoelectric Ceramics Based On Grain Orientation Technology

Piezoelectric ceramics have been widely used in sensors,actuators,transducers and other fields.The traditional piezoelectric materials are mainly lead-based ceramics,which cause harm and pollution to human body and environment in preparation and use.At present,a lot of research has been carried out on lead-free piezoelectric ceramics at home and abroad,and many achievements have been made,but it has not completely replaced lead-based piezoelectric ceramics.The research direction is mainly based on different preparation processes and doping modification,and the problem of low piezoelectric properties has not been solved.Ceramic Injection Molding,?CIM?is a kind of net size forming process of a variety of complex components,which are widely used in aerospace,precision machinery,electronic communications and other fields.Compared with the traditional molding method,CIM technology has the advantages of high automation,short cycle,high production efficiency,and can be shaped into shaped parts with complex shape,uniform density and high size requirements.In this paper,the development status of injection molding equipment and the preparation methods of lead-free piezoelectric ceramics are summarized.Aiming at high precision,low cost and intelligence,this paper attempts to produce high performance lead-free piezoelectric ceramics by injection molding under the action of applied electric field.A piezoelectric ceramic injection molding platform was built.The injection molding process was simulated based on finite element method.The injection molding experiment of lead-free piezoelectric ceramics was carried out on the injection platform.Finally,the microstructure of lead-free piezoelectric ceramics under external electric field is simulated.The work in this paper has some reference value and significance for the research of injection molding of lead-free piezoelectric ceramics.The main research contents and results are as follows:?1?The injection molding platform of piezoelectric ceramics is built with the modular design idea.The platform is divided into four functional modules:injection device,temperature control system,applied electric field and hydraulic control system.The injection structure of cylinder,mould and nozzle was designed,and the static analysis and optimization of the fixed base of the injection device were carried out.The injection temperature is controlled by digital display temperature controller and thermocouple detecting resistance wire heating.Based on the circuit design of sawyer-tower,the applied electric field was applied.Considering the safety of injection experiment,the injection device and electrode were connected by epoxy resin board.The applied electric field is designed based on sawyer-tower circuit.Based on the analysis of the working condition of the platform,the hydraulic system scheme is a single-stage pressure regulating circuit composed of overflow valve and quantitative pump.Finally,the functional modules are integrated as a whole to build a piezoelectric ceramic injection molding platform.?2?The injection molding process of lead-free piezoelectric ceramics was analyzed by finite element method.Based on the non-Newtonian fluid theory,the Cross parameter viscosity model of piezoelectric ceramic slurry was established,and the influence of process parameters such as mold filling time,injection pressure and injection temperature on the ceramic blank was simulated by finite element analysis.The analysis found that the injection pressure was 1 MPa and the filling time was 50?.The maximum filling time was 6.623 s and the flow rate was 20-40cm³/s.As the temperature and pressure increase,the filling end pressure and filling time gradually decreases,the flow rate gradually increases.?3?NBT-BT lead-free piezoelectric ceramics were prepared using an injection platform.In the preparation process,there are defects such as filling,cracks,pores,deformation,etc.,and the dense ceramic is finally obtained through the adjustment process.The XRD pattern showed that the intensity of the?011?and?001?plane diffraction peaks of the sample under the applied electric field was significantly enhanced compared with the conventional method.The sample was oriented at the?011?plane and showed anisotropy in the structure.SEM pattern showed that compared with the traditionally formed ceramics,the ceramic grains after the applied electric field became significantly larger,the compactness was higher,and the grain boundaries were more obvious,mainly square,and the size was about 10?m.The piezoelectric constant of traditional piezoelectric ceramics d₃₃=109pC/N,the piezoelectric constant of ceramics d₃₃=132pC/N under the external electric field.The ferroelectric property test showed that the residual polarization intensity of the ceramic was increased and the coercivity was decreased under the applied electric field.?4?The microstructure of piezoelectric ceramics under electro-mechanical coupling is analyzed by finite element method.The piezoelectric ceramic microstructure model is established based on the piezoelectric constitutive equation.The microstructure of the piezoelectric ceramics under the action of the injection force and the applied electric field is analyzed by finite element analysis.It is found that the internal electrical balance of the ceramic is broken under the action of the applied load,and the domain wall moves along the polarization direction.The domain structure in the direction of the vertical electric field becomes wider and wider,and the domain structure is evenly distributed.The electric field strength is increased under the coupling of force and electric power,and the electric dipole reverses under the action of the external electric field.