Research Background Problem Statement

1

1.1 Research Background

Demand for the next generation, cost effective, high performance aircrafts has motivating the aerospace industry to use non-traditional materials and new aircraft structural design. New aircraft are design with one piece flow of monolithic component to replace large number of assembled component. This new monolithic structural components allows for higher quality and reduce the manufacturing times. Figure 1.1: Aerospace monolithic component. The monolithic component consists of several thin-wall rib and flange sections that need to be machine as shown in Figure 1.1. Because of the poor stiffness of thin-wall feature, deformation is more likely to occur in the machining of thin-wall part which resulting a dimensional surface errors. The surface dimensional error is induced mainly by the deflection of the tool and the workpiece during milling, which results INTRODUCTION CHAPTER 1 2 in a deviation of the depth of cut. If the cutter and workpiece have high rigidity, the deflection of the cutter and workpiece are small and can be neglected in the distribution of surface dimensional error. However, in the peripheral milling of a very flexible component, the deflection is significant. The process is further complicated by periodically varying milling forces, which statically and dynamically excite the tool and part structures, leading to significant and often unpredictable deflections.

1.2 Problem Statement

Machining errors can be broadly classified as geometric errors, thermal induced errors cutting force induced errors and other errors. The errors caused by cutting forces depend on the type of tool and workpiece and the specific cutting conditions and parameters. For machining low rigidity thin-walled parts, the force induced part deflection has a significant contribution to the total surface error. The tight dimensional tolerance of aerospace component poses a great challenge for the manufacturer especially for machining component that contains a thin wall feature. Tool geometry has a direct influence on the cutting performance such as the cutting forces, quality of machined surface, shapes accuracy, cutting edge wear and tool life. The geometric parameters of end mills include the number of flute, edge shape, rake angle, relief angle, helix angle and clearance angle. Each of the geometric features has their own function and need to be considered for a specific machining application. 3

1.3 Research Objectives