The Study of EDM Hole Drilling Method for Measuring the Residual Stress in SKD11 Tool Steel
| Autor: | Edward Hsu, 許多 |
|---|---|
| Rok vydání: | 2001 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 89 Due to its simplicity and precise in measurement, High-Speed Hole-Drilling Strain Gauge Method is widely used in industries for residual stress measurement. The standard procedure is specified in ASTM E837. However, this method is not applicable for stress measurement on materials with high hardness, high toughness or wear resistance where the severe wear of drilling tool lead to enormous deviations. EDM hole drilling instead, without concerning the limitation of material machinability, combined with strain gauge method for stress measurement is introduced here. SKD11 and S45C were used in this studies as working materials and EDMed. Characteristics of the EDM drilled hole with different working conditions were studied. The hole contour, surface morphology, white layer formation and their influence on stress evaluation were examined. Further, SKD11 specimens were uni-axial tensile pre-stressed with 0%, 15%, 30%, and 50% yield stress individually and EDM hole drilled with working condition of 4A/9μs and 12A/3μs respectively where the EDM energy were chosen to be equal and as small as possible. The stress measured by EDM Hole-Drilling Method were discussed. By working conditions selected in the range of discharge current by 4A~12A and pulse-on duration by 3μs~23μs, the morphology and surface of the most EDM drilled hole can meet the requirement of specification. The amount of hole-enlargement increased with increasing discharge current. The average thickness of white layer formed on SKD11 specimens shows no apparent difference by changing working conditions, but increases with increasing pulse-on duration on S45C specimens. Stress measured by EDM hole drilling method with 4A/9μs on various pre-stressed specimens reveals a nearly linear relationship with the pre-stress. Furthermore, EDM process causes a much severe extra stress on specimen of SKD11 than S45C. Working with 12A/3μs revealed the same trend. Besides, experimental results depicted that the amount of induced stress caused by EDM did not vary as the specimens are different pre-stressed. A constant value was obtained which can be used for stress calibration. The value is of 347Mpa by 4A/9μs and 210Mpa by 12A/3μs. The measured stress after calibration yield a reduced discrepancy within 43.2MPa and 29.7MPa. It thus proven the feasibility of EDM hole drilling strain gauge method in measuring the stress in metallic materials with high hardness, high toughness, or wear resistance. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|