The hardness model was developed for aluminium metal matrix composites having Al7075 matrix reinforced with particles of Al 2 O 3 and fabricated by stir-casting. Four factors, five levels, central composite, rotatable design matrix was used to optimize the number of experiments. Adequacy of the model was tested by employing analysis of variance (ANOVA). The experimental results showed that size of reinforcement was the major parameter influencing the hardness of the composites among the other control factors, followed by weight fraction of reinforcement. However, the holding temperature and time had lower effects. The model suggests that one must take into account the interaction of parameters for predicting hardness of composites so that the optimal combination of the testing parameters could be determined and predicted.
Aluminium matrix based metal matrix composites (MMCs) are being extensively used in various industrial applications that need high strength combined with low weight, high hardness, wear resistance, high temperature resistance, improved impact strength, etc. They are amenable to secondary manufacturing processes such as extrusion, rolling, forging, welding, etc. However, because of their complex nature, both in terms of composition and difficulty in manufacturing by the standard fabrication techniques, researchers are keen to study various combinations of constituent materials -matrix and reinforcement, their processing, property evaluation, and extending their applications in various fields. This article presents the details of the investigation comprising stir casting of Al7075 matrix material reinforced with Al 2 O 3 particulates. An attempt has been made to predict the impact strength of these MMCs, which is an important property that decides their suitability in shock loading environment, both in the as-cast and forged conditions. Multi-factor, rotatable, central composite design has been used to predict the impact strength in terms of charpy-V. The mathematical models developed are validated using Fisher's F-test.
Roller burnishing process was carried out on free cutting brass materials in the presence of fine silicon carbide abrasives in the form of paste on a pre-machined surface. The results of ‘without-paste’ burnishing (plain burnishing, PB) and ‘with-paste’ burnishing (abrasive assisted burnishing, AAB) processes are compared to examine the effect of abrasive particles in the burnishing process. A 24 full factorial design is adopted to develop the mathematical model for surface roughness regarding four process parameters like burnishing force, burnishing speed, burnishing feed and number of passes for both the cases, i.e. PB and AAB. Analysis of variance (ANOVA) was carried out to find the effect of process parameters and to check the adequacy of the models. The results show that the parameters have a significant effect on the response in PB to improve the surface roughness by 75 % than the turned components. Whereas in AAB, fine abrasive particles as a single entity controlling the response and making other parameter effects as non-significant. Surface roughness further improved by 15 % in AAB process.
The burnishing process is becoming an attractive way among post-machining, metal finishing techniques due to its excellent features. The burnishing process carried out with ball or roller, smooth out the protrusions due to the plastic deformation and increases the surface texture. This paper presents the results of three ball burnishing conditions carried out on cylindrical free machining brass components. Influence of abrasive particles (abrasive assisted burnishing, AAB) during burnishing is investigated and compared with the burnishing carried out without (plain burnishing, PB) and with-coolant (lubricated burnishing, LB) conditions. The response surface methodology (RSM) is used to optimize the microhardness in terms of four process parameters. Result obtained indicates that the microhardness of the pre-machined surfaces increases by 12-29 percent. The AAB results in 141.67 percent higher microhardness than the PB and 41 percent more than the LB condition.
Burnishing is becoming popular post-machining surface finishing technique due to its excellent features. The use of high finish and hard, ball or roller on pre-machined surface with pressure smooths out protrusions to fill the valleys and thus, resulting in lower surface roughness. In present work, ball burnishing has been carried out on free cutting brass in different burnishing conditions such as dry (Plain Burnishing, PB), lubricated (LB) and with abrasives (Abrasive Assisted Burnishing, AAB) to establish the relationship between surface roughness and the four process parameters like burnishing force, burnishing feed, burnishing speed and number of passes. The effect of using lubricants and abrasive particles is compared over PB. Design of Experiments based on Response Surface Methodology (RSM) is adopted to develop the mathematical models of second order for each above said conditions. Analysis of Variance (ANOVA) is carried out to study the effect of burnishing parameters on response and to check the adequacy of the models developed. The results showed significant reduction in the surface roughness with all cases. Surface roughness of level 0.1043 µm can be achieved from the burnishing of the turned surface having roughness level of 2.7838 µm.
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