Workshop Measurement And Processing Compensation For Box Parts Based On Comparative Measurement

Conventional coordinate measurement of the workpiece needs to be carried out in a constant temperature room to ensure the comparability of the measurement results,which result in a delayed feedback to the production site.During continuous processing at production lines,the hysteresis of the measurement may cause economic losses due to the occurrence of unaccepted products.In this paper,a new kind of measurement equipment named as Equator is used as an instant tool to examine workpiece accuracy in workshop with unstable temperature,by means of comparison measurement philosophy.The investigation results can be summarized as follows:The measurement error analysis of the Equator and the optimization of the measurement parameters for thin-walled box parts.The Equator works on the parallel mechanism to achieve high acceleration measurement thanks to the small inertia of its moving parts.The relationship between three linear inputs and the end effector of the Equator was examined by means of the iterative method to reveal the motion errors of the probe fixed on the end effector along coordinate axes in Cartesian coordinate system.The probe positioning error can then be determined according to the resolution of the grating scale mounted on the linear input guideway.The selection of probe material against workpiece material is analyzed to avoid heavy adhesive wear and abrasive wear on probes.The approaching velocity in probe detecting is optimized at a rate of 0.3～0.35 by measuring standard gauge block.The vibration mechanism dominating the measuring errors is used to illustrate the large error in high approaching speed.The comparison measurement parameters in metrology of thin-walled box parts are optimized.On-site measurement method for thin-walled box parts in workshops based on coordinate comparison.The coordinate comparison was proposed to solve the problem of time delay in standard measurement room as well as temperature undulation in workshop.The relationship between measurement results with Equator in production sites and that with CMM in standard measurement room was established by means of the metrology comparison of Golden Parts.The coordinate comparison measurement was validated with gearbox rear shells,where flatness,plane offset,location and diameter of different holes were measured with both Equator in workshop at 25°C,and CMM in standard measurement room.The results show that the measurement errors with Equator in production sites are less than 8% as compared with metrology with CMM in standard measurement room.The compensation strategy on cutting depth based upon the comparison measurement for mounting surface array of the engine cam bearing covers.The errors in the measurement data are screened by means of root mean square error and correlation entropy estimation to eliminate gross errors and random errors.The compensation was followed to modify cutting depths with the same value for the same column according to the processing track.The compensation was validated with 18 cam bearing cover planes in the engine head.The overall flatness of the 18 array surfaces is improved by 57.5% by compensation in five sets corresponding to five columns,where the standard deviation of the array surface height is reduced by 63.3%,and the range of the array surface has been reduced by 67.6%,The experimental results show that after five sets of data compensation of the same column with the same value the overall flatness of the 18 array surfaces is improved by 57.5% and the standard deviation of the array surface height is reduced by 63.3%,the range of the array surface has been reduced by 67.6%,and the processing quality has been significantly improved.The processing consistency of the array surface is significantly improved after the compensation of the cutting depth.