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Galling Studies for IT-based Methods for Reduced Maintenance Costs

Mikael Schönning
Göteborg : Chalmers tekniska högskola, 2010. 69 s. Diploma work - Department of Materials and Manufacturing Technology, Chalmers University of Technology; 2010 24, 2010.
[Examensarbete på avancerad nivå]

The motivation for this work is the industrial interest for reliable measurement techniques for galling and wear in sheet metal forming tools. On the basis of these measurements, one should be able to conclude when tool maintenance is needed. In particular, in-line measurements of tool wear and galling are not common in the forming industry. It is therefore of interest to examine which type of sensors that can be built into the tool and give reliable information on tool wear and galling. The aim of this Master thesis was to investigate and suggest suitable sensors for in-line tool measurements and to test selected sensors and evaluate their performance in a small scale industrial test at Alfa-Laval Lund AB. In order to make a correct assessment of which sensors are most suitable for galling and wear detection, the galling phenomenon during stainless forming was studied in more detail. Apart from a literature survey, galling was studied during accelerated test conditions by means of a strip reduction test (SRT) performed at DTU, Lyngby, Denmark. The SRT allows comparing the resistance to galling of different tool steels and tool surfaces. The SRT tool surfaces were investigated using optical microscopy, interference microscopy, and SEM, in order to recognize the different stages of galling. A survey of possible sensor solutions, initiated by Swerea IVF, was extended by a literature study and interviews with experts in the field. The sensors selected for further practical testing were thermocouples (TC) and accelerometers, for temperature and vibration measurements, respectively. A cross-die tool was designed and equipped with these sensors, and the signals during forming of up to 8000 parts were monitored with a LabVIEW program developed for this application. Two different tool materials: tool steel and Alumec were used, and two sheet materials: stainless 1.4401 and Ti. The vibration measurements were meant to detect galling by detecting the so called stick-slip phenomenon. The vibration signals were analysed in the frequency domain using Fast Fourier Transform (FFT) algorithm. No evidence of stick-slip could be detected in the frequency spectra, presumably because the galling layer was not sufficiently thick to give rise to stick-slip, or because the stick-slip peak amplitude was too low to be distinguished from the background noise. The temperature measurements were meant to detect galling by monitoring the frictional heat that is generated during the sheet metal forming process. It was found that a temperature signal from a TC placed close to the tool surface could give qualitative information about tribological changes at that particular spot. Thus, both galling and wear can be detected using this type of sensor. However, further tests are recommended to verify this result.

Nyckelord: galling, tool wear, sheet metal forming

Publikationen registrerades 2010-11-15. Den ändrades senast 2013-04-04

CPL ID: 129101

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