Wear 266 (2009) 688–698 Contents lists available at ScienceDirect Wear journal homepage: www.elsevier.com/locate/wear Experimental investigation and mechanism of material removal in nano ﬁnishing of MMCs using abrasive ﬂow ﬁnishing (AFF) process Mamilla Ravi Sankar, J. Ramkumar, V.K. Jain ∗ Department of Mechanical Engineering, Indian Institute of Technology, Kanpur 208016, India article info Article history: Received 25 August 2007 Received in revised form 26 July 2008 Accepted 26 August 2008 Available online 22 October 2008 Keywords: Abrasive ﬂow ﬁnishing (AFF) Change in average surface ﬁnish (Ra) Al alloy Al alloy/SiC MMCs abstract Aluminum alloy and its composites appear to have a good future as a candidate material for engineering and structural components. Finishing of these materials is a big challenge as they are heterogeneous in nature having abrasive particles randomly distributed and oriented in the matrix material. Metal matrix composite (MMC-aluminum alloy and its reinforcement with SiC) workpieces were initially ground to a surface roughness value in the range of 0.6 ± 0.1 m, and later were ﬁnished to the R a value of 0.25 ± 0.05 m by using Abrasive Flow Finishing (AFF) process. The effects of different process param- eters, such as extrusion pressure, number of cycles and viscosity of the medium were studied on a change in average surface roughness (R a ) and material removal. The relationship between extrusion pressure and R a shows an optimum at about 6 MPa. In the same way, the relationship between weight percentage of processing oil (plasticizer) and R a also shows an optimum at 10wt%. Further, an increase in work- piece hardness requires more number of cycles to achieve the same level of improvement in R a . Material removal also increases with an increase in extrusion pressure and number of cycles while it decreases with an increase in processing oil content in the medium. It is also concluded that the mechanism of ﬁnishing and material removal in case of alloys is different from that in case of MMC. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Depending upon the reinforcing element type, MMCs are clas- siﬁed into two broad categories: continuous and discontinuous. With the development of non-continuous reinforcement materi- als like whiskers, ﬁbers and particles the reinforced composites not only have good properties, but they are economical also. SiC particles reinforced aluminum alloy matrix composites belong to the discontinuous MMCs. The properties of MMCs are controlled by the matrix material, the reinforcing material and their interface. Al alloy/SiC composite has better mechanical and physical proper- ties such as improved wear properties, higher modulus of elasticity and strength to weight ratio than Al alloy. This MMC ﬁnds its appli- cations in various sectors, for example, automobile, sports and aerospace. In order to meet stringent manufacturing demands, the composites though made to near net shape [1] have to be ﬁnished to higher tolerances [2,3]. Reinforcement agglomeration is a major problem in MMCs. It may be due to process constraint and micro size of reinforcement. The bonding strength among reinforcements in agglomerated area is very weak due to particle–particle interface compared to bonding between matrix and reinforcements. ∗ Corresponding author. Tel.: +91 512 597 916; fax: +91 512 590 260. E-mail address: vkjain@iitk.ac.in (V.K. Jain). Traditional ﬁne ﬁnishing processes such as grinding, lapping, honing and super-ﬁnishing have many applications but their use is limited to the production of workpieces having mainly basic forms such as ﬂat and cylindrical. Abrasive Flow Finishing (AFF) is an advanced ﬁnishing process that can be used to deburr, radius and polish difﬁcult to reach surfaces by ﬂowing semi-solid visco-elastic abrasive laden medium to and fro under pressure across the sur- face to be ﬁnished [4]. AFF is becoming popular due to its ability to give predictable, repeatable and consistent results. The advantage of the AFF process lies in the uniformity of the polished surface, especially when compared to the tedious manual ﬁnishing meth- ods. The process is capable of achieving 50 nm surface ﬁnish and deburring holes as small as 0.2 mm diameter. Rhodes [5–7] studied the basic principle of the AFF process and reported that the depth of indentation of abrasive grain primarily depends upon the size, relative hardness and sharpness of abrasive grain, and extrusion pressure. The types of machining processes used to prepare the specimens prior to AFF and hardness of the workpiece are found to have signiﬁcant effect on the improvement in surface ﬁnish [8,9]. The rheological properties of the abrasive laden medium, determine the pattern and aggressiveness of the abrasive action [10]. Perry [11] reported that abrasion is high where medium velocity is high. An increase in pressure and medium viscosity, increase material removal rate while surface roughness value (R a ) decreases. The abrasive particles penetrate the workpiece 0043-1648/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2008.08.017