Error Analysis Of Cutting Heat Based On The “S” Shaped Test Specimen

The importance of five-axis CNC machine tools’ accuracy has been well recognized in the machining research domain. The cutting heat plays a great important role in the influence on the machining precision, because it could give rise to temperature transformation and thermal deformation, which are the sources of the error of cutting heat. The “S” shaped test specimen, designed by AVIC Chengdu Aircraft Industrial according to the actual cutting experience, could detect the precision of five-axis CNC machine tools when producing the aeronautical thin-wall components. Selecting the “S” shaped test specimen as the research object, the error of cutting heat has been analyzed in this paper. Cutting mechanism has been analyzed to establish the mathematical model of temperature field, and thermal-mechanical simulation has been done to predict the temperature field and thermal deformation, the results of experiment have proved the validity of simulation prediction. At last, the thermal deformation, caused by temperature variation, has been predicted by thermal-mechanical simulation to analyze the error of cutting heat. The main contents are:1. The calculating model of cutting heat source has been established on the basis of the analysis of cutting mechanism. The heat distribution ratios on the shear area and tool-workpiece friction area have been calculated to establish the mathematical model of temperature field, and the principle that the temperatures of two contact surfaces are instantaneous equality has been used to support the calculation. The whole process of cutting heat variation has been divided as two parts, intermittent heating and cooling process, this makes the temperature model more accurate than the former models established by other researchers. Then the model of cutting temperature field has been established on the basis of the principle of the linear heat source’s superposition2. Based on the LS-DYNA platform, the FEM analysis model of cutting heat has been established. The value and acting time of thermal load have been calculated on the basis of actual machining parameters and the means of loading heat in the simulation has been proposed. The calculating method of the forced convection coefficient has been presented, then the model of simulation boundary conditions has been established. This thermal-mechanical simulation model is more actual than the former models, because it not only simulates the actual motion trail of tool and the separation of chips, but also analyzes the influence of coolant liquid.3. The experiment has been designed to measure the temperature of “S” shaped test specimen when it was machining on the PARPAS PM20 five-axis CNC machine tools. The temperature curves that measured by thermocouples on the “S” shaped test specimen under 4 operating conditions has been recorded. The compare between experimental results and simulation results has showed that cutting heat simulation was reasonable and accurate.4. Simple Variable Method has been used to analyze the influence of the cutting speed, feed rate, cutting thickness on the cutting temperature of “S” shaped test specimen, and the thermal deformation of the cutting process of “S” shaped test specimen has been predicted through the thermal-mechanical simulation. Based on the thermal deformation, the error of cutting heat has been predicted and analyzed.