| As a high-end CNC machine tool,precision horizontal machining centers are widely used in key manufacturing industries such as aerospace,automobile,and shipbuilding.The accuracy of a precision horizontal machining center is the core indicator to measure its quality,which directly affects the machining accuracy of parts.Research shows that when multiple axes of a machine tool are working simultaneously,the thermal error caused by thermal expansion deformation and thermal bending deformation can account for 40 to 70% of the total error of the machine tool.Among them,the large amount of heat generated during spindle operation can easily lead to significant thermal bending deformation of the machine tool key system,which has a serious effect on the thermal error.Therefore,researching on the thermal bending deformation of the machine tool key system caused by spindle operation and its effect on thermal error,and modeling and compensation for thermal error,which can better reveal the causes of thermal error,and improve the accuracy of the machine tool key system and machined part.Through theoretical analysis,thermal error experiments,mathematical modeling,and other research methods,this paper focuses on the spindle-column key system of a THM precision horizontal machining center,and conducts analysis and modeling of thermal bending deformation caused by spindle operation,research on the effect of thermal bending deformation on thermal error,thermal error modeling under the influence of thermal bending deformation,and design and verification of thermal error compensation system.The main research work and achievements are as follows:(1)The thermal bending deformation behavior of the spindle-column system of a precision horizontal machining center was analyzed,and experimental research was conducted.Firstly,the key component for thermal bending deformation of the spindlecolumn system was selected based on the component structure and temperature field distribution characteristics,which improved the analysis efficiency.From the perspective of heat generation and dissipation,the main internal and external influencing factors of thermal bending deformation of the spindle-column system were analyzed.Based on the axial thermal displacement vector characteristics of the top and bottom of the column,various possible thermal bending deformation postures of the system were analyzed.The column thermal displacement measurement experiment,environmental temperature monitoring experiment,and thermal bending deformation experiments of the spindle-column system under different working conditions were carried out,respectively revealing the significance of thermal bending deformation of the column,the fluctuation of external ambient temperature amplitude of the spindlecolumn system,and the thermal bending deformation law,laying a foundation for subsequent modeling of thermal bending deformation angles.(2)An analytical model for thermal bending deformation angle of spindle-column system based on column temperature and ambient temperature was established.Firstly,in order to improve modeling efficiency,the thermal bending deformation of the spindle-column system was equivalent to the thermal bending deformation of the column,and a thermal displacement functions based on the temperature of the top and bottom of the column were established.Then,through two experiments with the same operating parameters,the influence function of the ambient temperature amplitude fluctuation difference on the thermal displacement of the column was identified,and it was superimposed into the thermal displacement function based on the column temperatures.Finally,an analytical model of the thermal bending deformation angle of the spindle-column system based on the column temperature and ambient temperature was established.The model established took into account the impact of internal and external heat sources on the thermal bending deformation of the spindlecolumn system,which had clear physical significance and exhibited good prediction ability under different working conditions,providing support for studying the impact of thermal bending deformation of the spindle-column system on thermal error.(3)Aiming at the influence of thermal bending deformation on thermal error of spindle-column system,analytical models for axial and radial thermal bending deformation errors were established.Firstly,the thermal errors of the spindle-column system was decomposed into thermal bending deformation error and thermal expansion deformation error.Based on the geometric relationship between the axial displacement of the spindle end caused by thermal bending deformation and the axial thermal displacement of the top and bottom of the column,an analytical model for axial thermal bending deformation error was established.Based on the geometric relationship between the radial displacement of the spindle end caused by thermal bending deformation and the thermal bending deformation angle,an analytical model for radial thermal bending deformation error was established.The established thermal bending deformation error model could well reveal the effect of thermal bending deformation of the spindle-column system on axial and radial thermal errors,effectively explain the "self compensation" of axial thermal errors and the "reverse rapid growth" of radial thermal errors,and indicated the importance of considering thermal bending deformation when studying thermal errors in machine tool key systems.(4)Aiming at the problem of thermal error modeling under the influence of thermal bending deformation,a modeling method based on the combination of thermal error formation mechanism analysis and data driven was proposed.Firstly,the key temperature points of the column that reflected the cause of thermal bending deformation of the spindle-column system were selected.Then,thermal memory was revealed,and a dynamic temperature feature extraction method based on long shortterm memory neural networks(LSTM)and one-dimensional convolutional neural networks was proposed.The hyperparameters of the model were optimized using Bayesian optimization(BO).Finally,a BO-LSTM-TPA thermal error model was proposed,which took into account the effects of thermal bending deformation and thermal memory on thermal error.This model had a mechanism of temporal pattern attention,demonstrating better comprehensive prediction ability under different working conditions compared to multiple thermal error models.(5)A thermal error compensation system based on industrial gateway was built,an active repair method for system fault temperature signals was proposed,and thermal error compensation verification experiments were conducted.A thermal error compensation system was built to achieve interconnection between the machine tool end and the thermal error model unit end through the industrial gateway.Aiming at the problem of possible failure temperature signals in the system,an active repair method for failure temperature signals based on dynamic thermal change rate and Elastic Net algorithm was proposed.Thermal error compensation verification experiments were carried out under idling cutting and finishing conditions.The experimental results showed that the accuracy of the spindle-column system and the machining accuracy of the part were both significantly improved,verifying the effectiveness of the proposed BO-LSTM-TPA thermal error model and designed compensation system. |
