INVESTIGATION OF CUTTING FORCES AND CHIP FORMATION CHARACTERISTICS IN ORTHOGONAL MACHINING OF ALUMINIUM

ABSTRACT

In the last century, a large amount of research has been done to study and understand the various machining processes with a view to improving the processes for further economic (cost and productivity) gains. However, many aspects of the cutting processes and cutting performance remain to be fully understood in order to increase the cutting capability and optimize the cutting processes. Cutting is a process of extensive stresses and plastic deformations. The high compressive and frictional contact stresses on the tool face result in a substantial  cutting force  F.  Cutting forces  are the background for the  evaluation  of the necessary power in machining (choice of the electric motor). They are also used for dimensioning of machine tool components and the tool body. They influence the deformation of the work piece machined, its dimensional accuracy, chip formation and machining system stability. The aim of this work is to study the influence of feed rate, and tool rake angle and depth  of cut  on  the main  cutting force  and  chip  morphology during  a  turning process, Aluminium alloy 6061 was used as workpiece material. In total,27 experiments were performed in order to measure the main cutting force (Fc). The experiments were performed with cutting depths of 0.5mm, 1.0mm and 1.5 and cutting speeds of 71, 90 and119 m/min, three different feed rates of 0.15, 0.20 and 0.25  mm/ rev. and three different rake angles 18o, 20o and 28o. During the experiment, the removed chips were collected and evaluated together with the main cutting forces. The experimental results showed that main cutting force has an increasing trend with the increasing of the feed rate between 0.05 to 0.7 mm rev. In contrast, the main cutting force has a decreasing trend as the rake angle increases from 0o to 200. There were indications that deformation occurred during the machining process, though the chip is generally continuous, chip length decreases as the cutting speed and feed rate increases. The experiment was done with the optimum of 12o rake angle for specimen.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background

Kadrigama et al (2005) stated that, cutting force is one of the most important factors for metal cutting process. Metal cutting process is common and important process for machining and fabrications.

For a long time, manufacturing engineers and researchers have been realizing that in order to optimize the economic performance of metal cutting operations, efficient quantitative and predictive models that establish the relationship between a big group of input independent parameters and output variables required for the wide spectrum of manufacturing processes, cutting tools and engineering materials currently used in the industry according to them. Armarego (1994) observed that the improvement in the output variables, such as tool life, cutting forces and surface roughness, through the optimization input parameters, such as feed rate, cutting speed and depth of cut, may result in a significant economic performance of machining operations.

One of these output variables that may have either direct or indirect effect on other variables such as tool wear rate, machined surface characteristics and machining cost, is cutting forces. Many researchers have conducted studies on predicting cutting forces produced in machining operations  using  theoretical  and  analytical  Approaches.  Strenskowski  et  al  (1987)  and affirmed by Shih et al (1993).

On the other hand, many other researchers have followed purely experimental approaches to study the relationship between cutting forces and independent cutting conditions. This has reflected on the increased total cost of the study as a large number of cutting experiments is required. Furthermore, with this purely experimental approach, researchers have investigated the effect of cutting parameters on cutting forces using machining experiments based on a one-factor-at-a-time design, without having any idea about the behavior of cutting forces when two or more cutting factors are varied at the same time. Kadrigama et al (2005)

The knowledge of cutting forces developing in the various machining processes under given cutting factors is of great importance, being a dominating criterion of material machinability, to both: the designer-manufacturer of machine tools, as well as to user. Furthermore, their prediction  helps  in  the  analysis  of  optimization  problems  in  machining  economics,  in adaptive control applications, in the formulation of simulation models used in cutting databases.  Petropoulos et al (2005).

In this regard, cutting forces being a substantial dependent variable of the machining system has been investigated by many researchers in various cutting processes through formulation of appropriate models for their estimation.

1.2   Significance of study

The relationship found between high speed machining and chip, morphology, and the cutting forces and workpiece surface finish has an important practical implication since it allows selecting the best cutting condition combination from the points of view, both for the security and  the  economy  for  the  established  requirements  in  each  case.  Results  are  of  great importance in selection of parameters that aid in tool design, considering machining as an economic activity that is a compromise between observed parameters, (Abu, 2009). Similarly the knowledge of cutting force facilitates the:-

      Estimation of cutting power consumption, which also enables selection of the power source(s) during design of the machine tools

    Structural design of the machine – fixture – tool system

    Evaluation of role of the various machining parameters on cutting forces

     Study the machinability characterization of the work materials

1.3  Justification of study

In machining industries and Research and Development   sections, the cutting forces are desired and required to be measured (by experiments):

      for  determining  the  cutting  forces  accurately,  precisely  and  reliably  (unlike analytical method),

      for determining the magnitude of the cutting forces directly when equations are not available or adequate,

      to explore and evaluate role or effects of variation of any parameters, involved in machining, on cutting forces, which cannot be done analytically.

1.4     Objectives of Research

    Understand the basic mechanics of chip formation,

    Investigate the Effect of Rake angle on the Cutting Forces

    Investigate the Effect of Depth of cut on the cutting forces

     Investigate the Effect of Feed rate on the cutting forces

     Investigate the Effect of cutting speed on the cutting forces

1.5 Scope

For the purpose of this work, Aluminum Alloy 6061was used as workpiece material turning operation was carried out on lathe machine. This due to the fact that is the least expensive and most versatile of the heat-treatable aluminum alloys, It has most of the good qualities of aluminum. It offers a range of good mechanical properties and good corrosion resistance. It can be fabricated by most of the commonly used techniques. In the annealed condition it has good workabilityand this grade is used for a wide variety of products and applications from truck bodies and frames to screw machine parts and structural components. 6061 is used where appearance and better corrosion resistance with good strength are required.

At variable Speeds and depth of cut three cutting tools with different rake angles will be selected with three selected feed rates (0.15, 0.20 and 0.25). Each experiment will be carried out with new sharp tools in order to keep the cutting conditions unchanged. The cutting-test were conducted without coolant and, as a result, totally 27 experiments will be performed. Dynamical forces (both vertical and horizontal) will be measured and results evaluated, while types of chips formed are being collected and measured.

1.6 Research Methodology

Tyan etal (1992).Manufacturing technology has been a driving force behind modern economics since industrial revolution (1770). Metal forming processes, in particular, have created machinery and structures that permeate almost every aspect of human life today. Although manufacturing techniques have become more sophisticated, many process and tool design  are  still  based  on  experience  and  intuition.  Advances  in  computer  and  material sciences have greatly enhanced our ability to develop predictive capability and to achieve the goal of optimization for a wide variety of application.

In achieving the main objective of this research work will be achieved through the following

    Defining the selected parameters

    Measure cutting Forces

    Analyze cutting force

    Discussing the results

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