GENERATION OF QUALITY SURFACE IN EXTRUDE HONING

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1 GENERATIN F QUALITY SURFACE IN EXTRUDE HNING K. Narayanasamy, H..Raju EIL, Department of Mechanical Engineering Indian Institute of Technology Madras, Chennai- 3 India kns@iitm.ac.in 1. INTRDUCTIN Surface is a boundary that separates an object from another object or substance; it is either in contact with some other surface or will be open to atmosphere. Hence the surface quality assumes greater importance for proper functioning of any product with due importance to aesthetic aspect also. This necessitates production of required surface texture to perform a specific function. Now a days surfaces are being engineered to suit end application (1-). rocesses like traditional honing, lapping, grinding can be used to regular shapes. But for lapping, a flexible process, others being rigid in nature, are of little/no use to finish machining of irregular intricate shapes or contours like turbine blades. This has led to the development of a flexible abrasive process called Extrude honing (EH) process. Extrude honing is relatively a new non traditional machining process used to finish, deburr, radius, polish, remove recast layer and to produce compressive residual surfacial stresses. This process removes material in small quantities by forcing abrasive laden viscoelastic polymeric material normally known as medium, which is the best candidate for finishing internal passages or holes which are inaccessible by any other processes (3-). Finishing of I.C.Engine manifolds, hydraulic components, and bio medical components are few areas of application. It is an alternative environmental friendly process for removal of protective aluminium nickel coating applied to certain turbine engine blades. Removal of sharp corners enhances the edge quality. It is a proven, reliable and accurate method that provides consistent results(5). Abrasive laden medium can be thought of as a flowing flexible grinding wheel. The irregular cutting edge geometry of abrasive grits and extremely small chips produced in this process makes it possible to concentrate the machining stress at very local points on the work. It is this ability which makes finishing of difficult to machine material possible. Large number of cutting edges with indefinite orientation and geometry makes the failure of any grits insignificant and does not affect the overall process performance(). Medium being a proprietary item, is not easily available. In view of this, present study on extrude honing is concerned with an alternative medium for abrasive carrier, its performance and consequent surface texture production in extrude honing.. EXERIMENTAL wing to their higher impact resistance and higher order fatigue life, SG Cast irons are very popular material in many applications. Considering the cost efficiency, SG Cast iron of grade is selected as

2 work material. Apart from rheological properties better grit retention, bond uniformity, and higher abrasive exposure are few properties a material required to posses for satisfactory performance as a carrier medium. A select grade of silicone polymeric medium is thoroughly mixed with a volume fraction of 5% SiC abrasives of 3 grit size using a polymer mixing device. An experimental set-up was designed and developed to implement extrude honing process. Details of work material, carrier medium, process parameter used in the trials are presented in Table1. Table1. Details of work material, carrier medium, process parameter Work material SG Cast Iron Carrier medium Silicone polymer rocess parameter Carbon ( % ) 3.1 Appearance Translucent Temperature Ambient Tensile Strength (N/mm ) 1 Density (kg/m 3 ) 1.13X1 3 Volume fraction.5.% roof Stress (N/mm ) 37 Viscosity(a.s) 5 Velocity (m/min)...,1.,1. 3. RESULTS AND DISCUSSIN 3.1 Surface roughness Typical observed parametric influence of surface characteristics of extrude honed SG Cast Iron bored specimen is illustrated in Fig.1. It is seen that there is a visible / drastic reduction in R t, R a values during early phase of honing, followed by progressive reduction with number of passes.removal of waviness/dominant asperities present over the bored surface during early phase of extrude honing results in appreciable reduction in R t, R a values. Roughness parameter Ra, µm 3 1 V=.m/min V=.m/min V=1.m/min V=1.m/min Roughness parameter Rt, µm V=.m/min V=.m/min V=1.m/min V=1.m/min Fig.1. Typical observed parametrical influence of surface roughness characteristics 3. Bearing area characteristics A surface texture can be better defined by referring to its bearing area fraction characteristics; a study on bearing area characteristics will bring about typical characteristics of a surface texture in terms of its core roughness, depth of profile allowing for crest flattening and valley fill up. It is observed from pass wise monitored individual profile (Fig.) that, with progressive honing crest flattening gets saturated, there after improvement in core roughness, followed by change in valley depth.

3 Fig.. Typical observed profiles of surface roughness and bearing area fraction 3.3 Acoustic emission signal n-line monitoring of acoustic emission signal using a broad band acoustic emission sensor presented mixed mode of emission during early phase indicating waviness correction/crest flattening. With subsequent passes a steady rise in rms value of the monitored acoustic emission signal as well as predominant peaks over lower frequency range 5-1 khz were observed (Fig.3) indicative of progressive honing. In subsequent passes, a reduction in rms value as well as low power high frequency peaks were observed, indicative of glazing associated with localised spalling of material N=1pass RMS=.1 1 N= passes RMS= N=1passes RMS= Fig.3 Typical power spectrum at different stages of stages of extrude honing 3. Residual stress induced Measurement of residual stress on honed surface indicates tensile residual stress during early phase of honing, followed by compressive mode, with progressive honing and subsequent glazing (Fig.). Impart of compressive residual stress on the surface results in enhanced fatigue life of the component.

4 Residual stress Ma Fig. Residual stress induced at the surface during extrude honing. 3.5 Scanning electron macrographs For better understanding of the nature of texture produced by extrude honing, surfaces as bored and as honed were observed (Fig.5) through scanning electron microscope. (a) as bored (b) after 5 passes (c) after 1 passes Fig.5 Scanning electron macrographs of surface at different stages of extrude honing After extrusion honing fairly uniform lay pattern with localised folding of asperity can be seen. Further, due to continuous honing, surface has experienced localised discrete glazed texture.. CNCLUSIN The major conclusions drawn based on the trials conducted are as follows. 1. A progressive improvement in surface roughness parameter and bearing area fraction is seen till eighth pass, beyond which the surface starts deteriorating.. Higher order residual compressive stresses induced on the surface with number of passes. 3. With the increased surface finish, characteristics of acoustic emission spectrum changes, this can be used for on line monitoring of the process. 5. REFERENCES 1. Chris J. Evans., James B. Bryan., Structured, Textured or Engineered Surfaces Annals of the CIR, Vol. // A.R.Jones., J.B.Hull., Ultrasonic flow polishing, Ultrasonics, 3 (199) L J.Rhoades., H. A.Clouser., Abrasive Flow Machining, ASM Metals Handbook,1 (199) R.E. Williams, K..Rajurkar, Stochastic Modeling and of Analysis of Abrasive Flow Machining, Trans.ASME. Journal of Engineering for Industry 1 (199) J. Matechen, John., Advantages of abrasive flow machining, Abrasives, (1995) -1. I.Inasaki, H.K.Tonshoff, T.D.Howes, Abrasive Machining in the Future, Annals of the CIR, Vol. //

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