Application of EDM Hole-Drilling Method to the Measurement of Residual Stress in Tool and Carbon Steels

Abstract

This study adopts the application of the electrodischarge machining (EDM) hole-drilling method to the measurement of residual stress in AISI D2 cold work tool steel, AISI H13 hot work tool steel, and AISI 1045 medium carbon steel. A calibration procedure based on the thermal conductivity of the material is conducted to compensate for the additional compressive stress induced in the workpiece by the EDM hole-drilling operation. Since the formation of this white layer influences the magnitude of the induced stress, the scanning electron microscopy, transmission electron microscopy, and nanoindentation techniques are used to examine the microstructure and hardness of the white layer resolidified on the EDMed surface. The experimental results reveal that combination of the hole-drilling strain-gage method (ASTM standard E837) with an EDM drilling process provides the effective means of determining the residual stress in materials with high hardness and good wear resistance.

Optimizing the EDM hole-drilling strain gage method for the measurement of residual stress

“…However, the application of this calibration scheme requires the use of a separate machining operation in order to determine the value of IS for the particular material of interest. Consequently, the objective of the study (Lee et al, 2006) was to enhance this correction scheme such that the calibration factor, IS , can be predicted directly from the material properties of the specimen without the need for any auxiliary machining trial. Furthermore, Lee and Liu (2008) found that provided the dielectric fluid retains a high level of purity, the value of IS is determined primarily by the thermal conductivity and carbon equivalent of the specimen.…”

An Enhanced Calibration Scheme for the EDM Hole-Drilling Strain Gage Method for the Measurement of Residual Stress in Ferrous Materials

“…(1) should thus be the principal stress, IS,min and IS,max , induced by the hole-drilling operation. [10][11][12] Further step required was to explore the correlation between the hole-drilling induced stress and the thermal conductivity coefficient of the sample. Derivation of a more robust calibration scheme was aimed at.…”

“…Accordingly, the objective of the current study is to enhance this correction scheme such that the calibration factor can be predicted directly by the properties of the specimen without the need for any auxiliary measurement. In a previous study by the current group, 12) it was shown that of the various properties of a specimen, its thermal conductivity has the greatest effect on the EDM hole-drilling induced stress. In order to establish the relationship of the induced stress and thermal conductivity, a series of measurement experiments was performed using the optimal parameter setting of 12A/6 ms/30 ms in six different ferrous materials, namely AISI 1045, 4140, L6, H13, M2 and 304, respectively.…”

“…Because the EDM condition of 12A/6 ms/30 ms ensured that the C sta coefficient is kept within 0.99-1 throughout the drilling operation, we suggest that this condition is optimal for EDM hole-drilling strain gage method. In previous studies [10][11][12] performed by the current group demonstrated that the hole-drilling induced stress ( IS ) was insensitive to the magnitude of the original residual stress within the specimens. Therefore, the IS value obtained from stress-free sample could be used to calibrate the value of the measured stress.…”

“…In previous studies by the current group, it was shown that the hole-drilling induced stress ( IS ) measured on stress-free specimens could be useful in compensating the measurement error. [10][11][12] However, it was also noted that the value of IS was highly sensitive to the working parameters such as pulse current and pulse-on duration. Thus it is required to specify the appropriate EDM working conditions in order to ensure the validity of the calibration.…”