ABRASIVE FLOW FINISHING PROCESS - A CASE STUDY

Transcription

1 ABRASIVE FLOW FINISHING PROCESS - A CASE STUDY T. S. Kavithaa 1, N. Balashanmugam 2, P. V. Shashi Kumar 3 Central Manufacturing Technology Institute, Bangalore kavithaats@cmti-india.net balashanmugam@cmti-india.net pvs@cmti-india.net Abstract The emergence of Abrasive Flow Finishing/Machining (AFFM) as an advanced fine finishing process is attributed towards the need for relaxation of tool limitations, relative motion of work piece with respect to tool and precise finishing of complex geometries and internal passages in components. Herein, the abrasive laden polymer media conforms to the work piece geometry overcoming shape limitation inherent in conventional finishing processes. The paper outlines the various functionalities of the AFFM system developed and the experimentation carried out for finishing and deburring of modular head of a hip joint, extrusion die and shuttle valve used in bio-medical, aerospace and pharmaceutical industries respectively are discussed. Surface characterization of the finished components using optimized process parameters are discussed in detail. The reported results signify the versatility and deterministic aspect of the developed AFFM machine for surface finishing of ferrous and non-ferrous components. Keywords: Abrasive Flow Machining, Roughness, Radiusing, Deburring 1 Introduction Abrasive Flow Finishing Machining (AFFM) is a non-conventional finishing process wherein number of cutting edges at randomized orientations results in material removal with smaller chip sizes compared to traditional methods. Rhoades (1988) Finishing is aided by the hydraulically forced flow of shear thickening polymer loaded with definite quantity of abrasives or abrasive mixtures between two cylinders. The work piece is held in position by a fixture designed, engineered and tailor made to suit the specific finishing requirements. Hence, AFFM results in better surface finish, tolerances, finishing of complex intricate features in hard/difficult to machine materials. Jain et al (2003) Rhoades(1987) The technical information and design specifications on the AFFM system developed by us are reported in detail elsewhere (4). The present study reiterates the deterministic aspects of the AFFM process by practical demonstration of the processing capabilities of the developed system. 2 Experimental Details The industrial test specimens taken up for finishing, radiusing and deburring in the present study include i. Shuttle valve incorporated in aircraft emergency systems ii. Die mould designed for pharmaceutical applications and iii. Aluminium workpiece. Ra, Rz and Rt are the standard parameters for 2D surface analysis. Average roughness R a denotes the arithmetic average of the absolute departure of the profile from the reference line throughout the sampling length. R z expresses the sum of the maximum value of profile peak height and the maximum value of profile valley depth in a sampling length. R t expresses the sum of maximum value of profile peak height and maximum value of profile valley depth on the profile curve in the entire evaluation length. R a could be used as a reasonable measure for achieving process control in finishing. The roughness measurements were made using MarSurf-GD25 and the scan length was uniformly maintained as 5.6 mm. Silicon carbide of various grit sizes was mixed with the polymeric carrier material in all the experiments reported and its weight percentage was maintained as 35%. The zero shear viscosity of the polymer used as the carrier for abrasives was approximately Pa.s. Experimental reports on nano finishing of modular head of a hip joint have been discussed earlier by the authors. A ten-fold decrease in Ra values (~38 nm) of Co-Cr bio-implants were 618-1

2 ABRASIVE FLOW FINISHING PROCESS - A CASE STUDY recorded after AFFM at two different extrusion pressures. Lower working pressures were recommended for achieving better surface finish which was attributed to the better conformity of the polymer abrasive mixture with the component. Balashanmugam et al (2013). The material composition of the shuttle valve used in the present study was a Fe - 15 Cr - 5 Ni precipitation hardened stainless steel designated as AMS 5659 (15-5PH) / ASTM A564. It is one among the primary components in brakes, landing gear extension, flap extension and canopy release mechanisms during emergency in an aircraft. Prefinishing operations of the shuttle valve (figure 1a) demanded the removal of hard-to-reach burrs at internal cross-hole intersections (figure 1b). measurement was done using a Veeco NT9100 Optical profiler which works on the principle of light interferometry for analysis of surface topography and roughness of the finished component. The internal features of a transmission component can be blended and surface smoothened by AFFM to allow easier sliding of the two components in a die assembly. In the present work a die mould (od - Ø 30.3mm; id - Ø 15.4mm; height mm) made of die steel of hardness 50HRC was taken up for finishing. The ability of the abrasive laden polymer media to conform to the complex shape of the component aided in finishing of processing dies. The initial Ra values recorded at three different positions are as shown in figure 2a. AFFM was operated in the two- way flow configuration at a hydraulic pressure of 100 bar using consecutively two media of different grit sizes of abrasives mixed with the dilatants polymer. The total cycle time taken for finishing of the die mould to the required R a value of 0.1µm from an initial value of 2µm was approximately 150 minutes. The die assembly components after AFM are shown in figures 2 b and c which are indicative of the quality of surface finish attained. a b The burr at the intersection of the cross hole was imaged using illumination from a red goose neck LED. A visual inspection system with a resolution of 1636*1236 pixel was used for subsequent imaging and data acquisition software was employed for associated image processing. A locally designed fixture was fabricated to hold the shuttle valve between the two vertically opposite cylinders (figure1c). The AFFM system was operated in one-way flow configuration at100 bar hydraulic pressure for ten strokes of the piston with total cycle time of 100 minutes. Radius Figure 1 a) Received die mould b) Die moulds after AFM c) Another die mould after AFM AFFM of the aluminum component (figure 3a) was taken up using two grades of media with silicon carbide abrasives of variable grit sizes. Initial Ra values were recorded at three different locations of the disc of thickness 20 mm and an c 618-2

3 outer diameter of 220 mm with drillings of 40 mm diameter as shown in figure 3b. Initially experiments were conducted on an aluminium component at an operating pressure of 55bar and the stroke length of the piston was maintained at 200mm. Further, the AFFM system was operated at the same pressure with decreased piston length (120mm) to verify the effect of piston stroke length on the surface finish. 3.2 Surface finishing of a die assembly It is to be noted that the surface roughness values recorded indicate that the reduction ratios at the three locations are not uniform. It could be inferred that the initial Ra values recorded before machining do not play a significant role in determining the quality of surface finish after AFF. The surface roughness measurements carried out before and after Abrasive Flow Finishing (AFF) of the die assembly are tabulated below. Surface roughness of 0.08µm on an average was achieved against the requirement of 0.1µm. It is notable that more than twenty-fold decrease in surface roughness values was recorded after 150 minutes of AFF. Table 1 Initial and final surface roughness values of the die assembly 3 Results and Discussion Ra (µm) 3.1 Deburring of Shuttle Valve Since the surface to be characterized included a curvature, vertical scanning interferometry with Z-axis range of 10 mm was used for analysis. The 2-D image of the finished surface and the corresponding cross sectional profile are shown in figure 4a and 4b respectively. Figure 4c shows the visual inspection image of the cross-hole intersection of the shuttle valve after deburring at the intersection of the outlet and inlet ports with diameters 3 mm and 8 mm. Component Before AFM Intermediate finishing After AFM

4 ABRASIVE FLOW FINISHING PROCESS - A CASE STUDY 3.3 Surface finishing of aluminium work piece The graphical representations (figure 5) reveal the surface roughness values recorded at three locations of the aluminium work piece before and after AFF. The decrease in stroke length results in an increase in the number of cycles. The initial Ra values recorded at three locations were ~ 0.65 µm and those recorded after AFM were ~0.06 µm as depicted in figure 6. Jain et al (2003) Thus decrease in stroke length effects increase in the quality of surface finish. Abbas et al (2014) Davies et al (1995) Further, it could be observed that the material removal rates are prominent during the initial cycles and subsequently fine finishing of the surface occurred. William et al (1989). The above mentioned results re-emphasize the versatility of the AFF technique. Further, the influence of work piece hardness on surface finish is clearly evident in the case of die assembly made of die steel and aluminium work piece. Jain et al (2000) 4 Conclusions The paper highlights the functional capabilities of the developed AFFM system designed for effective nano metric finishing, radiusing and deburring of complex components from biomedical, pharmaceutical and aerospace industries. The reported results indicate the consistency and deterministic aspect of the indigenized version of Figure 2 Graphical representation of the Surface roughness parameters recorded before and after intermediate and final AFF the AFFM system. Rhoades (1985,1988,1991) The versatility and capability of the system toward finishing of a broad range of materials as well as complex/difficult to machine components has been accomplished and established. Acknowledgement Figure 3 Variation in Roughness average (Ra) with number of cycles The authors thank Director, CMTI for the support, constant encouragement and infrastructural facilities extended throughout. The authors express their sincere thanks to Prof. V. K. Jain, IIT - Kanpur for his valuable guidance. Special thanks are due to M/s Imperial Pharmachines Pvt. Ltd. - Mumbai, M/s Satva Aero Accessories and Systems Pvt. Ltd. - Bangalore and M/s Sushrut Adler Pvt. Ltd. - Pune for providing us the industrial components for the present study. A fifteen fold decrease in surface roughness values were recorded after AFF at all the three locations (figure 6)

5 References 1. Abbas F. Ibrahim, SaadK Shather and Wissam K. Hamdan, Studying Abrasive Flow Machining Conditions by Using Taguchi Method, Eng. & Tech. Journal, Vol.32,Part (A), No.4 (2014), pp N. Balashanmugam, T. S. Kavithaa, R. Varun and P. V. Shashi Kumar, Abrasive flow finishing of modular head of a hip joint, Proceedings of the National Conference on Manufacturing: Vision for Future, Guwahati, (2013) 3. P. J. Davies and A. J. Fletcher, The assessment of the rheological characteristics of various Polyborosiloxane/grit mixtures as utilized in the Abrasive Flow Machining process, Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, Vol. 209, No.6 (1995), pp R. K. Jain & V. K. Jain, Effects of operating parameters on the performance of Abrasive Flow Machining Process, Proceedings of 20 th AIMTDR (2003), pp V. K. Jain and S. G. Adsul, Experimental Investigations into abrasive flow machining, International Journal of Machine Tools and Manufacture, 40 (2000), pp L. J., Rhoades, Abrasive Flow Machining, Manufacturing Engineering, 1988, pp L. J. Rhoades, Abrasive Flow Machining with not so silly putty, Metal Finishing, July 1987, L. J. Rhoades, Abrasive flow machining and its uses, Non-traditional Machining, Conference Proceedings, Ohio, December 1985, pp L. J. Rhoades, Abrasive flow machining: a case study, Journal of Materials Processing Technology, 28, (1991), pp R. E. William and K. P. Rajurkar, Metal removal and surface finish characteristics in abrasive flow machining, ASME, PED, 38 (1989), pp