Research On Hot Embossing System For Plastic Chip

With characteristic of low cost,a rapid reaction rate and high efficiency,microfluidic chip achieve the functions in aspects of DNA analysis,drug screening,cell manipulation and immunology determination,which integrated highly into micro units including micro-channel,micro-valve and micro-pump,ect.Compared with traditional silicon and glass chips,polymer chips have become focus of microfluidic chip research because of their high machinability,electrical insulation,optical transparency and surface modifiability.In this paper,hot embossing system for plastic chips is established to meet the processing requirements of plastic microfluidic chips.According to requirements of manufacturing plastic chip,the processing technology,temperature actuator and pressure control actuator were analyzed.Based on the corresponding theoretical formula,the process curve of the hot pressing chip was determined.Specially,the hot pressing temperature was 120?,the pressing pressure was about 800N,and the pressing time was about 600s.Secondly,The heating mode of thermoelectric refrigeration was determined by comparing different heating modes,and theoretical heating power and the number of thermoelectric refrigeration reactor employed were calculated.The pressure actuator with servo motor and screw elevator was determined,torque and moment of inertia of servo motor and deceleration ratio of screw elevator were identified.Hot embossing machine composed of frame structure and pressing head structure was developed,and related performance of key parts were verified based on the finite element method.According to the selected pressure actuator,a closed frame structure composed of column,upper crossbeam,moving crossbeam and lower crossbeam was designed.In view of the column parts which plays a guiding and bearing role in the frame structure,the mechanical properties of the column parts was analyze.The numerical simulation results shown that:the column with shaft size of 30mm and material of Q235 possessed appropriate rigidity.Separate pressing heads of“?”,“?”and“?”types were established which achieve the separation of the pressing load and TRR's preload.And its deformation distribution in the feed direction was analyzed,the numerical results demonstrated that the pressing head of“?”had good deformation uniformity.Temperature-strain distribution of the pressing head plate directly involved in the machining was analyzed.The numerical analysis results shown that the deformation uniformity of the pressing head plate with the thickness of 16mm was the best under the mechanical-thermal coupling field,and its thermal stress was the smallest.In addition,K-type thermocouple,load cell in bridge type and grating ruler were selected to acquire temperature,pressure and displacement data respectively,and installations of above sensors were completed.Lower computer system was established to satisfy the requirements of control accuracy of temperature and pressure.Firstly,control strategies of temperature and pressure were developed.Secondly,the input signal adjusting unit and analog-to-digital conversion unit of temperature and pressure were determined,and the conversion of temperature and pressure signals were completed.the corresponding MCU was selected,and H-bridge of MOS tube circuit unit,switch control unit and relay control unit were respectively designed to realize power adjustment,heating/cooling function conversion of TRR;forward rotation,reverse rotation,speed and torque adjustment of servo motor and start of cooling circulating water machine.Additionally,serial communication circuit was integrated to complete displacement acquisition and upper computer communication.In this paper,performance tests of temperature and pressure were carried out.Firstly,K-type thermocouple and load cell in bridge type are calibrated to get accurate input-output relationship.the experiment of temperature rise and constant temperature control were carried out,the heating rate and the accuracy of constant temperature control were respectively about 0.5?/s and±2?.the experiment of pressure rise and constant pressure control were carried out,the pressure rise rate and the accuracy of constant pressure control were respectively about ION/s and ±10N.