In-process measurement can provide feedback for surface quality control and has the advantage of high efficiency. For in-process measurement on precision machining, the optical measurement method is one of the best choice considering its high resolution and precision. However, the coolant in precision machining would form an opaque barrier that prevents the light beam from passing through, therefore preventing the in-process optical measurement. To solve this problem, a multiple air beam approach is proposed. This approach can help light beam access to workpiece surface by displacing coolant away from the measurement point.

A test system has been developed for capability and measurement error studies on the multiple air beam approach. The test system includes a prototype of port...[ Read more ]

In-process measurement can provide feedback for surface quality control and has the advantage of high efficiency. For in-process measurement on precision machining, the optical measurement method is one of the best choice considering its high resolution and precision. However, the coolant in precision machining would form an opaque barrier that prevents the light beam from passing through, therefore preventing the in-process optical measurement. To solve this problem, a multiple air beam approach is proposed. This approach can help light beam access to workpiece surface by displacing coolant away from the measurement point.

A test system has been developed for capability and measurement error studies on the multiple air beam approach. The test system includes a prototype of portable in-process optical measurement profiler and a coolant system. A data collection program and data processing GUI were also developed for the profiler. Measurement error of the profiler was studied as a reference for studying on error induced by the multiple air beam approach.

The experimental results show that the multiple air beam approach can resist coolant from multiple directions. It can also resist coolant with thickness up to 15mm. Tests were conducted on different workpieces. The error induced by this approach can be as small as 0.13 μm with coolant thickness up to 3 mm and air flow rate up to 10 L/min when it is applied to a workpiece with convex feature.

To study the characteristics of the multiple air beam approach, a series of experiments were conducted. The results show that increasing the coolant thickness and air flow rate would induce larger measurement error. Besides, the bubble generation would induce vibration of the applicator, therefore vibrating the laser sensor and inducing measurement error. To minimize the error, it is necessary to minimize the air flow rate for different conditions of coolant thickness. The error can be as small as 0.041 μm with coolant thickness up to 3 mm and air flow rate up to 3 L/min. To resist 15 mm thick coolant, the air flow rate should be at least 6 L/min and the error is 0.092 μm.

Keywords: in-process optical measurement; coolant; opaque barrier; applicator; multiple air beams