SURFACE ROUGHNESS ASSESSMENT IN CNC TURNING OF POLYMER NYLON-6 S. B. Bhosale, A. A. Chavan, R. S. Pawade, P. K. Brahmankar Department of Mechanical Engineering, Dr. Babasaheb Ambedkar Technological University, Lonere - 402 103, Raigad, MS INDIA Email:
[email protected],
[email protected] Telephone: 91-2140–275101, Fax: 91-2140–275142 ABSTRACT Nylon-6 is a polymeric material extensively used in manufacturing of car lights, traffic lights, mobile telephone displays, contact spectacle lens, laser lens, micro structured arrays and projection lenses. It has good mechanical properties and fabricability. The paper presents the results on surface roughness assessment of nylon-6 after CNC turning operation. The optimization of machining parameters and tool geometry using 2k type full factorial experimental design was carried out. The response (output) variables were considered as the arithmetic average surface roughness, Ra, maximum peak to valley height, Rt, and amplitude distribution parameter Rsk. The input turning parameters selected were cutting velocity, feedrate, depth of cut and nose radius. Sixteen experiments were performed as per the factorial design array. Total thirty-two experiments were conducted with one replicate. The experiments were performed on CNC Lathe (Make- Jobber XL) using PVD coated carbide inserts. Surface roughness was measured using surface roughness tester (Make - Mitutoyo, Japan). The surface roughness parameters Ra, Rt and Rsk were measured at three locations 120 apart on the periphery of the turned surface of the workpiece. Subsequently, the average values of the readings were determined and considered for the output response variable.
The observed data were analyzed using statistical software. The analysis in terms of main effects plots that represents analysis of means, ANOVA, a mathematical representation of analysis of variance and the pareto analysis as a graphical representation. The analysis of results indicates that the feedrate has the most significant parameter influencing the surface roughness Ra, and amplitude distribution parameter Rsk at 95% confidence interval. Also, depth of cut and nose radius too show statistical influence at 95%
confidence interval but limited to Rsk alone. It is observed that the better surface quality is achieved when the federate was 0.1 mm/rev. However, the surface quality degrades with an increase in the feedrate to 0.5 mm/rev. This trend is well justified with the fundamental correlation of surface roughness with the feedrate. The nose radius also shows the trend as per the fundamental correlation similar to the feedrate. The following parameter combination produced the lower surface roughness, Ra: 0.4 mm nose radius, 0.02 mm depth of cut, feedrate of 0.1 mm/rev with cutting velocity of 250 m/min. On the other hand, the machining parameters giving lower value of the amplitude distribution parameter Rsk is: 1.2 mm nose radius, 0.02 mm depth of cut, feedrate of 0.1 mm/rev with cutting velocity of 150 m/min.
Keywords: Polymer nylon 6, Machining, Surface roughness, Design of experiments, ANOVA.
Main Effects Plot for Rsk
Main Effects Plot for Ra
Data Means
Data Means
nose radius
DoC
Feed
Velocity
0.5
nose radius
DoC
Feed
Velocity
6
0.4 5
Mean
Mean
0.3 4
0.2
3
0.1 2
0.0 1 0.4
1.2
0.02
0.08
0.1
0.5
150
250
0.4
1.2
0.02
0.08
0.1
0.5
150
250
