Intermittent Dynamic Thermal Characteristics Research On Build-in Electric Spindle Used In Mini Lathe

With the development of driving technology, the electric spindle of machine tool hasgradually becomed an important combination part between modern machine tools andelectrical systems, and it is playing an important role in the development of CNC machinetools. The manual clamping time of traditional lathe processing occupys a large proportion inthe whole processing time. Designing and manufacturing a special machine with automaticclamping function, and it is used for processing small disc type parts. It has a broad prospectof application. Besides, it will shorten the time of clamping workpieces and improve thedegree of automation of machine tool. Electric spindle of machine tool has the advantages ofsimple structure and motor direct driving spindle etc. It has becomed the preferred spindlescheme of special machine with automatic clamping function. The working process ofautomatic special machine tool makes the heat transfer state of the spindle alternating betweenthe active heat transferring and the passive heat transferring. Special machine tool spindleswith the intermittent working system, as well as reducing the heat load and the shaft itself. Atthe same time it alleviates the problem of spindle temperature influencing on machiningprecision. The built-in motor is in the active heat transfer condition for spindle machiningparts. The copper loss and iron loss produced by the built-in motor emits through heattransferring between the various components. In the process of clamping workpiece whenspindle stops, built-in motor has no loss produced. Thermal energy that each componentstorages doing heat transferring continuelly, because of the existence of the temperaturedifference between inside and outside of the spindle. Therefore, an effective calculation ofelectric spindle in actual machining process temperature state is the key point of electricspindle design and machine tools thermal error compensation.Combined with automatic feeding function of inverted vertical lathe chuck R&D projectin the machine tool processing condition. The electric spindle cooling structure and heatingdissipation processing are considered in detail. The calculation model of lathe electric spindletemperature rises with the transient thermal network method is established. The simulasionusing the finite element method is carried out to validate the calculation results. Thetemperature rising checks to scheme in a variety simulation of the actual working conditions, and calculates the shaft axial thermal deformation. In order to improve the machiningprecision of Inverted vertical chuck lathe, a compensation method to improve the machiningprecision of inverted vertical lathe is provided on the basis of electric spindle transienttemperature rising under calculation intermittent load. Finally, A temperature experiment usinga spindle prototype is carried out to verify the correctness of the calculation model oftemperature rise, and the experimental conditions is similar with the actual working process.Through the above research, the following conclusions could be reached:(1) The dynamic cutting process and main processing parameters of vertical lathe areanalyzed in detail in this paper. The type and electrical parameters of buildin motor ware arealso determined. The stiffness and natural frequency of lathe electric spindle ware arecalculated by using finite element method in the design process, then the heat dissipationstructure of the design scheme is analysised. Finally, considering the overall using of machinetool, the heat dissipation scheme which determines natural cooling. The cooling process ofpermanent magnet synchronous spindle is analyzed in detail. The set series solution of therotor and staror unsteady heat transferring equation ware decides the separation of variablesmethod as well as providing a theoretical basis for determining the boundary conditions andsolving method.(2) The calculating model is built with heat transferring theory and transient thermalnetwork method. The temperature rising of the Electric spindle interior ware is calculatedunder various actual working conditions, such as high speed and light load, low speed andheavy load and so on. The same actual working condition ware is analysised with finiteelement method, and the calculation results of transient thermal network method are verifiedpreliminarily. The temperature rising is checked to scheme in a variety simulation of the actualworking conditions. The results show that the calculated results of finite element method isslightly higher than transient thermal network method.(3) The electric spindle finite element analysis model based on the thermal structurecoupling is built with thermal elastic mechanics and finite element theory. The axial thermaldeformation of electric spindle caused by the change of temperature field is calculated ininverted chuck vertical lathe which is actually machining process.(4) The thermal deformation of electric spindle is analyzed in detail in actually machining.The radial thermal deformation of spindle is in the allowable range. The the axial thermal deformation continuously increases from the beginning of processing until the spindlereaching the dynamic thermal equilibrium. The spindle has not yet occurred more hotdeformation as the processing time is short in the processing of single parts. The machiningprecision of the single parts is in the range of allowable error. The precision of parts processedby automatic machine later is beyond the range of allowable error in the whole batch of partsprocessing. In view of this situation, a method based on calculation of electric spindle lathetransient thermal characteristics of error compensation is put forward in order to reduce theaxial size error caused by the thermal deformation of inverted chuck vertical lathe spindle. Anew method for thermal error prediction and compensation under various different conditionsusing built-in electric lathe spindle is provided.(5) The transient temperature rising experiment simulating automation machining isdoing in different speed and load torque taking the lathe spindle prototype as the researchobject. Comparing experimental data with the corresponding calculated values of thermalnetwork model, it shows that the result of the built-in electric lathe spindle which is underintermittent load is in the range of allowable error. The transient temperature of lathe spindlecan be calculated effectively in the automatic machining which processes in the conditions ofchoosing the right premise parameters and boundary.In conclusion, the mechanism and law of the structure parameters of lathe spindledesigning and effects of intermittent load on the thermal state performance ware are revealedwith thermal network method and finite element method. The theoretical calculation results inthe range of allowable error are confirmed by lathe spindle temperature experiment, providinga theoretical basis for the thermal error compensation of electric spindle used in invertedchuck vertical lathe machining process.