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Prediction the effect of Pb on the roughness of the machined

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 باسم محيسن محمد الزبيدي
5/15/2011 5:46:52 AM
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Prediction the effect of Pb on the roughness of the machined  
heat-treated (Al-Zn-Mg-Cu) alloy  
        Dr.Haydar A.Hussain                   Saad Hameed Najem                  Basem M. Mohammed  
       
University of
Babylon                 
University of  
Babylon              

University of 
Babylon  
       
College of
Material s Eng            
College of
Material s Eng          

College of
Material s Eng  
        Dept. of Metallic Material s        Dept. of Metallic Material s        Dept. of Metallic Material s  
        Engineering.                                 Engineering.                                Engineering.      
 
Abstract:  
   The present investigation is aimed to predict the effect of Pb additions on surface roughness of a machined (Al-Zn-Mg-Cu) alloy. Three percentages of Pb (0.5, 1.0, 1.5wt%) were added to the alloy. The alloy had been prepared by casting. Samples from the prepared alloy were heat treated by a solution heat treatment (at 5100C for 2hrs) and an artificial aging (at 1200C for 24hrs), and then turned using high speed steel tools (HSS) under dry conditions and at a constant depth of cut with  different cutting speed and feed rate. Results showed that Pb has a noticeable effect on the roughness of the machined samples with a clear effect on the cutting force required. A mathematical prediction model for surface roughness had been developed in terms of cutting speed, feed rate, and the percentage of added lead. According to the developed mathematical model, the low percentages of Pb additions have a slight effect on the smoothness of the machined surfaces, while experiments showed that these low percentages lead to lower the force required for cutting by a percentage  close to 20%. The model may be utilized to enhance the machining efficiency of this type of Al- alloys by using an optimum cutting conditions related to the added lead percentage to machine for a suitable surface roughness with a  lower cutting force.
Introduction:  
The investigated alloy is belong to the 7xxx Al alloys. These alloys show a highest strength among all commercial Al-alloys and are widely used in airframe structures, mobile equipment, and other highly stressed parts. Many papers were published to enhance the performance of such alloys. Most of these papers were aimed to study the influence of the ceramic additives or the influence of the manufacturing processes or heat treatments on the mechanical and physical properties of the alloy [1], but relatively little works reported on the machineability of such alloys [2].        
The present paper is aimed to study the influence of different percentages of lead on the surface roughness and force required to machine (Al-Zn-Mg-Cu) alloy. This influence will be studied through a mathematical prediction model for surface roughness specially developed in this work basing on a statistical experimental information. The developed model differs from other models for surface roughness published in a lot of work in such a way that it includes the percentage of the added element to a base alloy. Samples of the alloy under study are  to be prepared by casting and suitably heat treated.  

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  • the effect of Pb , roughness of the machined