CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
The introduction of hard turning has provided an alternative to the usual processing technology used to manufacture parts made from hardened steels. Shorter product
development time along with being more environmentally friendly are among the benefits offered by hard turning, which potentially results in lower manufacturing cost
per part. However, common tool materials for hard turning applications are expensive. Due to the continuous developments in cutting tool materials and coating technology,
inexpensive coated carbide cutting tools are being investigated to determine the potential of using them for use in extreme conditions as in hard turning. Coated carbide tool was
selected to finish machine hardened steel. Performing hard turning dry at various cutting conditions, that is, cutting speed and feed rate, revealed that suitable tool life and surface
finish values that meet the strict range of finish machining were obtained when finish machining hardened steel of 58 HRC hardness Noordin, 2007.
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2.2 Hard Turning
One of the reasons hard turning is coming to the forefront of manufacturing is because people are trying to reduce the lead times it takes to get a part from raw material to the
customer. It’s a lean manufacturing initiative. The thing that can do with hard turning, that is difficult to do with grinding, is hard turning can start with a solid blank material
and produce a finished component complete on one machine. In hard turning, it can start with a pre hardened material and machine it and can skip several steps and actually cut
days out of the process. Choosing hard turning is really application driven, because it’s dependent on the part.
Grinding is better suited if it have really thin walled parts or parts that are delicate from a crushing perspective. If it have a surface finish that requires a different type of texture,
for example, when turning, it will creating a thread and when grinding it will get a checking. If look at it under a microscope, it would be a pitted surface finish. When
honing, it will get cross checking surface finish. If this part has oil lubrication near it or running across the surface, the turned part would actually screw the oil through from one
side to another. With grinding, the oil would be held there because it’s pitted or cross checked.
Places where hard turning is very well suited is when it have complex figures, such as contour radii, angles and diameters all on one part. Hard turning can do that in one
setting. Besides the actual process and efficiency of hard turning, this type of machining is gaining popularity because the overall function is less expensive today. It’s becoming
more popular because hard turning is usually less expensive to do because it is faster, the machines cost less and operator learning curve is less. The operator has to learn the one
machine and the one machine does it all. Hard turning also offers smaller benefits that can be time saving and environmentally friendly. When grinding, it will get a lot of fine
particles and have to clean it out and have a special filtration unit on which to have to
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clean regularly. With turning, it will producing steel chips, which are much easier to dispose of or recycle Ferguson, 2004.
2.2.1 Parameters in Hard Turning
Four typical characteristics of hard turning as opposed to grinding have been stated below:
a. The significantly higher cutting force. b. The omission of coolant.
c. The single point form generation. d. The minimum value of the depth of cut.
The cutting force occurring in hard turning is higher than conventional turning or grinding. The passive force occurring in hard turning is the component perpendicular to
the cutting speed and is a multiple of the main cutting force, while in traditional turning it is only a fraction of this value. The extraordinarily high passive force, which
contributes to the material removal, significantly loads the elements of the machining system. The disadvantageous effect of the high passive force must be compensated for
by an increase in machine tool rigidity. Hard turning can be done in dry conditions at relatively high speed. The relative high
friction coefficient and the passive force cause a significant friction force which transforms into heat. The other source of the generated heat is the high cutting speed.
The high temperature generated during material removal causes thermal expansion of the work piece.
The surface generating element of hard turning is the single point tool tip, which shapes the surface of the work piece and is accompanied by significant force and heat effects.
Under such conditions is the single point tool tip reacts sensitively to any irregularities. The last parameter discussed for hard turning is the depth of cut. In hard turning this
cannot be reduced significantly, although this is possible in grinding. Because of the necessity of a minimum depth of cut, hard turning is followed by higher forces than in
grinding, even in the finest smoothing operations. Kundrak, 2006.
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2.3 Hard Turning Using TiAIN Coated Carbide Tool
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