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CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Machining involves the shaping of apart through removal of material. A tool, constructed of the material harder than the part being cut, is force against the part,
causing material to be cut from it. Machining, also referred to as cutting, metal cutting or material removed, is the dominant manufacturing shaping process. It is
both a primary as well as a secondary shaping process. Machining is the term generally used rather than material removal or cutting. The device that does the
cutting or material removal is known as cutting tool. Drilling is one of the major machining operations which are currently carried out on
fiber-reinforced composite materials. There are typical problems encountered when drilling fiber-reinforced composites. These problems include the delaminating of the
composites, rapid tool wear, fiber pullout, presence of powdery chip, etc. [1-3], and the delaminating of the composites is generally the main concern. This is so because
the occurrence of delaminating will reduces the strength against fatigue, result in a poor assembly tolerant, and affect the composite’s structure integrity [4,5]. Thrust
force has been widely cited as the main cause of delaminating. Ho-Cheng used a fracture mechanics approach to analyze the delaminating of fiber-reinforced material
[6]. His analysis predicts the critical thrust force above which delaminating is initiated. Tagliaferri and his co-researchers studied the effects of machining
parameters and tool conditions on the damage, finish and mechanica1 properties of fiber-reinforced composite materials [7,8], and the cutting mechanism in drilling [9].
5 A close relationship between the thrust force and amount of damage was confirmed.
It was also found that the width of damage zone is correlated to the ratio between drilling speed and feed rate. The higher ratio is the better the cut quality rate. Another
possible benefit of increasing cutting speed is the reduction of cutting forces. It has already been found that the increase of cutting speed may decrease the cutting force
when cutting aluminum [10,l1] If the thrust forces can be reduced by increasing cutting speed, the delaminating may be overcome. However, increasing cutting speed
wil1 accelerate tool wear, and the thrust force may increase as dril1 wear increases. Therefore, it is of interest to study the effects of increasing drilling speed on thrust
forces as wel1 as other drilling characteristics. In this paper, the results of a series of experimental tests are presented. The effects of increasing drilling speeds on thrust
force and torque are studied first. The effects of tool wear on dril1 geometries are also examined. The effects of tool wear on cutting mechanism are then discussed.
Finally, conclusions are drawn based on these results.
2.2 Machining parameters
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