Mr. Bernhard Mueller Profile

Bernhard Mueller

at RWTH Aachen

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Proceedings Article | 15 March 2002 Paper

Thermographic measurements of high-speed metal cutting

Bernhard Mueller, Ulrich Renz

Proceedings Volume 4710, (2002) https://doi.org/10.1117/12.459559

KEYWORDS: Cameras, Infrared cameras, Temperature metrology, Infrared imaging, Infrared radiation, Metals, Image processing, Titanium, Pyrometry, Image resolution

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Thermographic measurements of a high-speed cutting process have been performed with an infrared camera. To realize images without motion blur the integration times were reduced to a few microseconds. Since the high tool wear influences the measured temperatures a set-up has been realized which enables small cutting lengths. Only single images have been recorded because the process is too fast to acquire a sequence of images even with the frame rate of the very fast infrared camera which has been used. To expose the camera when the rotating tool is in the middle of the camera image an experimental set-up with a light barrier and a digital delay generator with a time resolution of 1 ns has been realized. This enables a very exact triggering of the camera at the desired position of the tool in the image. Since the cutting depth is between 0.1 and 0.2 mm a high spatial resolution was also necessary which was obtained by a special close-up lens allowing a resolution of app. 45 microns. The experimental set-up will be described and infrared images and evaluated temperatures of a titanium alloy and a carbon steel will be presented for cutting speeds up to 42 m/s.

Proceedings Article | 23 March 2001 Paper

Time resolution enhancement of a fiber optic two-color pryometer

Bernhard Mueller, Ulrich Renz

Proceedings Volume 4360, (2001) https://doi.org/10.1117/12.421023

KEYWORDS: Pyrometry, Temperature metrology, Sensors, Data acquisition, Amplifiers, Data acquisition boards, Signal detection, Optical amplifiers, Fiber optics, Resolution enhancement technologies

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A fiber optic two-color pyrometer has been developed at the Institute of Heat Transfer and Air Conditioning at RWTH Aachen to measure temperatures at surfaces with low emissivities with a high time and space resolution. A fused silica fiber is used to transmit the radiation to the pyrometer from measuring positions with limited optical access. The two-color principle allows accurate measurements of absolute temperatures of surfaces with unknown emissivities if the assumption of a gray body behavior at the measurement wavelengths is valid. The minimum temperature which can be measured with the pyrometer is limited due to the small radiation energy at low temperatures given by Planck's law, the emissivity of the body and the size of measurement area. At present temperatures of low emissivity metallic surfaces with sizes of 0.4 mm can be measured down to 250 degree(s)C. A new application to measure temperatures during high speed turning required a time resolution above the maximum of 2 microsecond(s) . To enhance the time resolution of the pyrometer the electronics was modified and a 30 MHz data acquisition board has been applied to the system. With this configuration a nanosecond time resolution is possible but the minimum measurable temperature increases. Different aspects for the limitation of the time resolution will be discussed. A new set-up with a nanosecond spark-flashlight will be described for the test of the transient response of the pyrometer and some test measurements will be presented.

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