INTRODUCTION
With increasing demands for higher productivity and quality, there has been increased interest in monitoring all aspects of the machining process. Among various process conditions, surface finish is a very important factor determining the quality of a piece. As surface topography is of great importance in specifying the function of a surface. So, the present industrial practice is to inspect the surface roughness of one out of every fifty to a hundred parts due to the time and cost associated with surface roughness measurement. The part is removed from the manufacturing line and measured with a stylus based profilometer in a "clean" environment. This procedure is time consuming and can often result in damage to the part. So direct surface roughness measurement is, therefore, needed for machining control as there is no absolute, robust way to predict 'the roughness analytically or experimentally. To encounter this difficulty, the roughness measurement technique used in the present work uses an ultrasonic nondestructive testing.
Ultrasonic nondestructive testing is a versatile technique that can be applied to a wide variety of material analysis applications. While ultrasonic NDT is perhaps better known in its more common applications for thickness gauging, flaw detection, and acoustic imaging, whereas high frequency sound waves can also be used to discriminate and quantify some basic mechanical, structural, or compositional properties of solids and liquids. From this point of view, it can be seen that the use of ultrasound is well established as a NDT tool, and too many information can be obtained about the specimen being tested by using ultrasonic inspection.
On the other hand in every stage of life we are facing with some imperfections. This could be anything depending on the subject. But the fact is that, these imperfections are the nature themselves. Roughness is the nature of surfaces. In some applications you can make use of it (i.e. braking principle etc.) but whereas it may be a major problem standing against us in another application like in ultrasonic testing.
On the other hand, if, how the acoustical structure behaves is known when it faces with a rough surface and built a correlation between roughness and acoustical properties, than it may be possible to predict how test results of the ultrasonic inspection will be affected without altering the surface quality.
This study is based on this consideration. Several tests were made during this study to determine a correlation between roughness and ultrasonic inspection data. The specimens were prepared from commonly used industrial structure material AISI 1040 Steel. The results obtained from this study may be used for better estimation of the discontinuities at test pieces having rough front surface structure. The proposed ultrasonic technique can be implemented for online monitoring of surface roughness in end milling process. This completely eliminates the separate inspection station for surface roughness measurement.