International Conference on Mechanical, Automobile and Robotics Engineering (ICMAR'2012) December 14-15, 2012 Singapore Surface Topography Characterization of Surfaces Fabricated by Linear vs. Angular and Hand Scraping. Tejas Bhosale, Rahul Waikar. specimen to qualify with respect to the required surface finish. Abstract— A light weight and portable automatic linear scraping Automation of scraping process has been achieved by using tool powered by an oscillating motor was developed to substitute the robotic arms and computer controlled grinding wheels [7]. traditional hand scraping process. Its performance in terms of surface However such methods can scrape jobs of fixed size and finish and material removal rate was compared with the commercially available angular scraping and hand scraping shape. In order to facilitate scraping irrespective of the job technique. Mild steel blocks finished by face milling were subjected nature, a portable tool holder configuration is developed that to the three types of scraping. 2D surface profiles and the material mechanizes linear scraping, thereby reducing dependence on removal rates of resulting surfaces were measured. The results point operator skill and reducing operator effort. In this work the out to linear scraping as the best among the three scraping processes linear scraping configuration is compared with the widely as the resulting surface parameters (Ra, Rq, Rpk, Rk and Rvk) are available angular scraping configuration, highlighting its superior to the other two processes. Hence the resulting surface can give better tribological performance as it can be less susceptible to distinct advantages. The paper mainly focuses on the wear. The linear scraping tool was also found ergonomic better than comparison of surfaces generated by linear scraping with hand hand scraping and angular scraping by reducing operator effort and scraping and angular scraping in terms of the surface increasing the scraping efficiency. topography obtained by machining an individual high point, and material removal rate. In addition, the paper specifies the Keywords—metal scraping, surface roughness, abbott curves, ergonomic advantages of the linear scraping configuration ergonomics. over the angular scraping and the hand scraping. The paper finally explores the performance range of the scraping process I. INTRODUCTION and its limitations and advantages as a finishing process. AND Scraping is an art which is mastered by years of H practice with the objective of removing precise amount II. EXPERIMENTAL SETUP AND PROCEDURE of material so as to alter the geometry of the areas for matching surfaces [1]-[3]. It requires great skill so as to A. Linear scraping and Angular scraping tool maintain optimum pressure throughout the stroke. The effects of human skill variations become predominant in areas where surfaces need to mate with precision. In such cases the tribological properties of the surfaces are governed by the quality of the surface finish [4]. The blue matching procedure for scraping involves use of markers that transfer the geometrical profiles from the master to the specimen surface that needs to be scraped so as to reveal the number of high points or peak points per square inch (PPI) and the percentage of points (POP) [5], [6]. Firstly the areas highlighted through Fig. 1 Top view of scraping machines representing the AS and LS configurations (schematic). blue matching must be scraped only up to the required extent. Secondly the adequately scraped high point must help the The schematic top view of the Angular Scraping (AS) and Linear Scraping (LS) is shown in Fig. 1. The Angular Tejas Bhosale is with the Department of Industrial and Production Engineering, Vishwakarma Institute of Technology, Pune, MH 411037 Scraping is a widely used configuration in which the direction INDIA. of oscillations is perpendicular to the feed of the scraper. Rahul Waikar was with the University of Alabama, Tuscaloosa, AL 35404 Material is removed in the form of ridges with this type of USA. He is now with the Department of Industrial and Production Engineering, Vishwakarma Institute of Technology, Pune, MH 411037 INDIA configuration. On the other hand, as shown in Fig. 1 (b), the (phone:+91-2024202272; fax:+91-2024280926; e-mail: tool holder in LS configuration is designed to give the [email protected]). direction of the oscillations same as the direction of the feed and hence the name Linear Scraping. 165 International Conference on Mechanical, Automobile and Robotics Engineering (ICMAR'2012) December 14-15, 2012 Singapore The LS assembly uses the oscillatory output of a 2.5 A and was machined was noted. This set of processes was designated 120 V motor shaft to give 8000 oscillation per minute (OPM) as Scraping Round 1 (SR1). The blocks were scraped to obtain at no load condition. The mild steel tool holder weighs 80g a smooth and a uniform surface. The scraping process did not and on coupling to the motor oscillates at 7500 OPM (loaded completely remove the underlying milling feed marks. The condition). Since the arc swept by the cutting tool is only 2.8 weight of the blocks after SR1 was noted and designated as degrees its motion can be approximated to linear oscillatory W1; time for each sample was noted and designated as T1 and motion. the surface topography parameters created by the SR1 process was designated as SF1. The SF1 values are show in Table II. B. LS Tool Holder Design and Assumptions The blocks were then again subjected to scraping in the The scraping tool bit used in LS configuration is the same same order as stated above. This time scraping was done to tool used in hand scrapers. It is made from M2 tool steel and entirely remove the milling feed marks on the surface. This set is 25 mm by 28 mm in size with a thickness of 2.15 mm. of processes was designated as Scraping Round 2 (SR2). The Cutting force calculations are done assuming the tool to be a weight of the blocks after SR2 was noted and designated as single point cutting tool. This is because the cutting edge of W2. Time for each sample was noted and designated as T2. the tool bit is an arc with the middle portion protruding The surface finish created by the SR2 process was measured forward due to which the metal first comes in contact with the and designated as SF2. The SF1 values are show in Table III. tool at this point. The chances of the tool or tool holder failure The material removal rates for SR1 and SR2 are calculated are highest at this point and hence the assumption. Apart from and shown in Table IV and Table V respectively. this orthogonal cutting is assumed since the cutting edge is perpendicular to the direction of scraping. The cutting force is calculated using the Merchant Force circle diagram and the III. EXPERIMENT RESULTS strength calculations for the links of the tool holder are done TABLE I using the Flexural formula. The maximum stress developed in SURFACE FINISH0 Position Ra Rq Rt the tool holder was less than the yield strength of steel due to Job Name Rsk which mild steel was chosen as the fabrication material. Number (μm) (μm) (μm) Resilience & Stiffness are not considered since the cutting 1 1.545 1.951 10.892 -0.11 force and the bending moment values are on the lower side. A 2 1.825 2.235 12.57 0.048 3 1.731 2.151 12.176 -0.291 C. Experiment Procedure The aim of the experiment was to quantify the performance 1 1.544 1.944 11.86 -0.203 B 2 1.403 1.755 9.996 0.213 of the machine equipped with linear scraping (LS) 3 1.78 2.121 11.004 -0.033 configuration and compare it with those of the hand scraping (HS) and the angular scraping configuration (AS). The 1 1.796 2.184 12.774 -0.085 scraping involved in the experimental procedure was C 2 2.009 2.414 12.296 -0.191 performed by a skilled worker who was trained to use both the 3 1.673 2.063 11.182 -0.353 configurations and at hand scraping. The quality of the surface generated by the processes was measured by using a “Dektak TABLE II 150” surface profilometer (contact type) of “Veeco” make. SURFACE FINISH1 The traces were taken at three positions for each samples and Type of Job Position Ra Rq Rt Machinin Rsk the sampling length for each position was 5 mm. Name Number (μm) (μm) (μm) Three mild steel blocks of size 50 mm × 40 mm × 18 mm g were chosen as the material for scraping and were named as 1 0.205 0.233 1.007 0 × A LS 2 0.225 0.256 1.213 0.24 A, B and C. One surface (50 mm 40 mm) of each block was 3 0.296 0.344 1.225 -0.1 face milled at a cutting speed of 120 SFM and 0.25 mm as the depth of cut to obtain a semi finished surface on which the 1 3.795 4.632 27.872 -0.19 further experimentation of scraping was done. The weight of B AS 2 4.506 6.054 36.298 0.14 the blocks was noted and designated as W 0 and the quality of 3 3.695 4.412 21.708 -0.05 the surfaces created by the milling process was measured using a surface profilometer and designated as SF0. The 1 1.17 1.454 6.35 -1 parameters are abbreviated as follows throughout the paper: C HS 2 1.867 2.397 11.882 -0.79 Ra: Arithmetical Mean Deviation or Average Roughness, Rq: 3 1.339 1.627 7.394 -0.27 Root Mean Square Roughness, Rt: Maximum peak to valley height, Rsk: Skewness.