Surface roughness evaluation in turning based on Abbott – Firestone curve The Romanian Review Precision Mechanics, Optics & Mechatronics, 2010 (20), No. 38 163 SURFACE ROUGHNESS EVALUATION IN TURNING BASED ON ABBOTT – FIRESTONE CURVE Adriana Carmen Cîrstoiu Materials, Equipments, Installations and Robots Department, VALAHIA University of Târgovişte, România, e-mail: adriana_cirstoiu@yahoo.com , Abstract – The paper presents experimental determination of the influence of the cutting tool nose radius on surfaces roughness in case of external turning. A roughness evaluation by its correlation with Abbott- Firestone curve and statistical distribution of the amplitudes of roughness profiles has been undertaken in the frames of this paperwork. Key words – Surface Roughness, roughness profile, nose radius, Abbott - Firestone curve 1. Introduction The measurement of surface state evaluates the defects of surface inevitably generated during the manufacture of parts. A good knowledge of these defects can take the necessary steps to keep within limits acceptable to the work piece assumes the function for which it was designed in the best economic conditions [1]. The factors that play a major influence on the quality of machined surfaces are: the machining parameters, the geometry of cutting tool, the properties of the material worked, the nature and mode of lubrication, the phenomenon of work hardening and the machining method [2]. In this paper are presented the data on the experimental influence of tool geometry on surface quality machined by turning. It was shown by theoretical and experimental research to the favorable effect of increasing nose radius r ε on quality machined surfaces by turning, expressed by the parameters Ra and Rt. Parameters are numerical values assigned to a surface, the most common being Ra, which averages the peak and valley displacement from a mean line but provides no information about the height of the peaks and valleys or the ability of the material to bear a load (bearing ratio). A study of bearing area ratio, T p and the Abbot-Firestone curve (bearing area curve) allows the display of statistical distribution of depths of points on the profile [3]. Bearing area ratio (Tp) is the length of the bearing surface expressed as a percentage of the assessment length L at a depth, or "slice level," below the highest peak [4]. It is useful because it simulates wear at various cutting depths of the surface. Ra is an important parameter of roughness, but two different surfaces may have similar Ra, but could function differently. It is therefore necessary to analyze other parameters such as Rq, Rsk or Rku [5]. 2. . Design of the experiment We measure the parameters of surface roughness machined by turning, thanks to a modified nose radius tool. Experimental investigations were conducted on cylindrical surfaces 20 mm in length and 41 mm in diameter, separated by gorges, as illustrated by Figure 1. Fig. 1. The configuration and dimension of the machined work piece The material in cylindrical bar XC18 is a non-alloy steel low carbon (0.16% - 0.22%) C. The steel also contains: Si (0, 15 - 0.35%), Mn (0.40 to 0.70 %), P ≤ 0.035% S ≤ 0.035%. Experimental investigations were performed on a CNC machine, an NC lathe Challenger 300. The experiments consisted of processing the four areas, with 20 mm length and initial diameter of 41 mm, with the same cutting parameters, but with different geometry of the cutting plates. Geometry of cutting plates are different because of different nose radius, r ε .