10-05-2013, 01:57 PM
Experimental Investigation of Hot Machining Process of High Manganese Steel using Design of experiments by Taguchi Method
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Abstract
The experiment is conducted in an auto feed lathe. The temperature is controlled by a thermocouple and automated flame heating system. The statistical analysis is done by Taguchi method. Taguchi designs provide a powerful and efficient method for designing products that operate consistently and optimally over a variety of conditions. The primary goal is to find factor settings that minimize response variation, while adjusting (or keeping) the process on target. A process designed with this goal will produce more consistent output. A product designed with this goal will deliver more consistent performance regardless of the environment in which it is used. Taguchi method advocates the use of orthogonal array designs to assign the factors chosen for the experiment. The most commonly used orthogonal array designs are L8, L16, L9 (i.e. eight experimental trials), L16 and L18. The power of the Taguchi method is that it integrates statistical methods into the engineering process. The significance of the control factors are found in the following order. Cutting speed – 19.55 m/min, Depth of Cut - 0.5 mm, Temperature - 600 degree, Feed - 0.05 mm/rev. From statistical design of experiments by Taguchi method (MINITAB software) and Hot Machining we find that the power required is decreased and the tool life is increased by 14.8 %.
INTRODUCTION:
With advancement in science and technology, there is a need of materials with very high
hardness and shear strength in the market. So many materials which satisfy the properties are
manufactured. Machining of such materials with conventional method of machining was
proved to be very costly as these materials greatly affect the tool life. So to increase tool life,
to decrease the power consumption and for improving the machinability an innovative
process Hot Machining came into existence. Here the temperature of the work piece is raised
to several hundred or even thousand degree Celsius above ambient, so as to reduce the shear
strength of the material. Various heating method has been attempted, for example, bulk
heating using furnace, area heating using torch flame, plasma arc heating, induction heating
and electric current resistance heating at tool-work interface.
From the past experiments it was found the power consumed during turning
operations is primarily due to shearing of the material and plastic deformation of the metal
removed. Since both the shear strength and hardness values of engineering materials decrease
with temperature, it was thus postulated that an increase in work piece temperature would
reduce the amount of power consumed for machining and eventually increase tool life. In
figure 1.1 and figure 1.2 the variation of Spindle power with Depth of cut is shown [1] for
different materials. In figure 1.3 the variation of decrease in hardness of material with
increase in temperature is given [1].
BASIC REQUIREMENTS OF WORKPIECE HEATING TECHNIQUE:
There are certain basic requirements for hot machining process [1]. These are as follows:
1. The application of external heat should be localized at the shear zone, i.e. just ahead of the
cutting edge, where the deformation of the work piece material is maximum amount.
2. Heating should be confined to a small area as possible limiting work piece expansion, so
that the dimensional accuracy can be tolerated.
3. The method of heat supply should be incorporated with fine temperature control device as
the tool life is temperature sensitive.
4. The method of heat supply should be such that the limitations imposed by the work piece
shape and size, conditions and machining process are minimal.
5. Machined surfaces must not be contaminated or over heated, resulting in possible
metallurgical change or distortion to the uncut material.
6. The heat source must be able to supply a large specific heat input to create a rapid response
in temperature ahead of the tool.
7. The heating equipment used should be low in the initial investments well as in operation
and maintenance.
8. It is absolutely essential that the method employed is not dangerous to the operator.