Deformation Characterisations for the WEDM Contour Cut Surfaces

Nida Naveed,University Of Sunderland, The Open University, Uk

doi:10.21535/ijrm.v4i1.958

Abstract

The contour method is a destructive technique to measure the residual stresses. The contour method involves cutting a specimen into two halves and provides a full cross-sectional map of the residual stress acting normal to the cut surface. The cutting process is the first and most important step of the method. Any error in this step can adversely affect all the subsequent steps of the method. Wire Electric Discharge Machining (WEDM) is the best choice cutting process for the contour method. Any deviation can cause inaccuracy and uncertainty in the contour stress results. Therefore, the most appropriate cutting conditions must be selected in order to minimise undesirable cutting effects and to obtain the best surface finish. This research covers the design of a test specimen to benchmark the quality of cutting for contour method measurement. The design allows sequential trial cuts on a nominally stress-free specimen. A high yield strength mild steel (EN3B) has been selected for this research on the basis that it is widely used in industrial applications. This research helps to identify the extent, nature and causes of undesirable effects of cutting process and aids to identify the important parameters that can be used to demonstrate the quality of the contour cut to help optimise the cutting process.

Highlights

THE contour method involves cutting a specimen into two halves and provides a full cross-sectional map of the residual stress normal to the cut surface [1], [2]
The root mean squared (RMS) values for stress and displacement variations across the area of the cut surface were calculated and are listed in the TABLE IV, that is a stress of 59 map for the cut surafce (MPa) (16 % of yield strength) and displacement of 3 μm respectively
These results show that the second cut MS-A-2 contains similar variations as the first cut MS-A-1

Summary

Introduction

THE contour method involves cutting a specimen into two halves and provides a full cross-sectional map of the residual stress normal to the cut surface [1], [2]. The cutting process is the first and most important step of the contour method. Any error in this step can adversely affect all the subsequent steps of the method. Wire Electric Discharge Machining (WEDM) has previously been identified as the best choice for the cutting step of the contour method [2]–[4]. WEDM cutting is based on a thermo-electric process, and it is performed by generating a series of electrical sparks between the EDM wire (electrode), and the component [5]–[7]. WEDM is a non-contact machining process; there is no direct contact between the electrode and the work piece during cutting. The absence of mechanical loads during cutting eliminates the vibration problem that often occurs with other mechanical machining methods

Methods

Results

Conclusion