Experimental study of the effects of key parameters for the air beam assisted form error in-process optical measurement method

In precision machining field, grinding machining method is widely used as the high precision machining process for hard material machining to pursue high form and surface quality. With the raise of form measurement applications, the grinding machine has been increasingly applied for high form quality surface machining. However, due to the opaque property of coolant in the machining process, the conventional in-process optical measurement methods, which can provide feedback for surface quality control and have the advantage of high efficiency and high precision, cannot achieve the form error measurement in the grinding machine. Therefore, an air beam assisted form error in-process optical measurement method was proposed. A transparent window will be generated by the air beam so that the coolant influence will be reduced. In the previous studies of transparent window, the parameters influence on window size and stability was investigated. The results provide guideline for the work of this thesis. To find out the potential parameters which may have influence on form error and to obtain the relationship between the parameters and form error, a series of work of error assessment, equipment design and manufacturing, experiments and data analysis were done. A new in-process optical profiler, which can imitate the measurement process of the grinding machine, was designed and established for the form error measurement research and a new profile comparison method between 2D and 3D data was proposed. To ensure the accuracy and precision of the new equipment and processing method, the random and systematic errors of the in-process optical profiler and the Wyko optical profiler were assessed. Based on the results of error assessments plus several preliminary tests of the equipment, a specification of the in-process optical profiler was summarized. The random errors will be effectively reduced after 10 times’ repeated measurements. The systematic errors of the in-process optical profiler and the Wyko optical profiler are 0.23 μm and 43 nm respectively. The repeatability error of the in-process optical profiler can reach 0.31%. In order to rank the input parameters, to find out the key input parameters and to investigate their basic effects on the form error measurement, a fractional factorial test was designed and conducted. In accordance with the results of the test, table velocity vt and coolant concentration cc were found as the most important input parameters. The basic relationships of other five parameters were also obtained. As the most important input parameters, table velocity vt was studies. Through the studies, the particular relationship between vt and form error was found. The lowest form error is 0.59 μm when the vt=0.5 mm/s and the largest form error is 1.54 μm when the vt=30 mm/s. Based on the comparison experiments, the residual coolant was fixed as the reason of error variation. From the analysis of results, the influence of sampling interval Δx on form error was obtained. The profile error will be unstable when Δx is larger than 100 μm due to the big surface variation of the workpiece. These results and findings will provide useful guidelines for the sensor improvement and the future in-process optical form error measurement in the grinding machine