الفهرس 
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Abstract
Machining processes are developing very fast nowadays, this development has
opened the door for searching for new techniques that can overcome the limitations of
traditional techniques, one of the newly developed techniques is wire electrical discharge
turning, this technique is a non-traditional metal cutting technique that creates
axisymmetric workpieces on difficult to cut metals.
The process involves an electrical discharge taking place between a traveling wire
“electrode” and a rotating electrically conductive workpiece, when the electrical
discharge takes place a transient spark passes through the dielectric fluid with a high
amount of thermal energy, removing a small amount of material from the workpiece
surface.
The main challenge when developing new techniques is determining the main
influencing factors on the process of parameters to obtain an acceptable surface finish
with a maximized mate rial removal rate.
In this research, two sets of experiments are performed, one to study the influence
of changing machining parameters (Rotational speed, pulse-on time, and current) on
material removal rate. The other is to study the surface roughness of the machined parts
concerning changing some of the machining variables (wire feed, workpiece rotational
speed, and pulse-on time).
The study is performed on AISI M42 HSS steel, using a CNC WEDM machine,
with the assistance of a well-designed spindle to enable the manufacturing of cylindrical
geometry. An L9 (3 x 3) Taguchi standard orthogonal array is chosen for designing the
experiments, the analysis for the results is done using ANOVA to get the most significant
factor on material removal rate and surface roughness Ra, and regression analysis is used
to define the relationship between involved process variables and material removal rate
and surface roughness Ra.
The results of the experiments that study material removal rate indicated that
increasing current value increases material removal rate. In contrast, material removal
rate increases with increasing of workpiece rotational speed to a certain speed (30 rpm)
and then decreases again at workpiece rotational speed (42 rpm). This decrease in
material removal rate is referred to as the high speed of the workpiece. The higher speed
does not allow enough time for the spark to erode the material. In addition, the increase
of pulse on time increases the material removal rate until reaching 200 μs, then the
material removal rate decreases by the increasing of pulse on time at 250 μs. This is
according to the duty ratio which is the period of time it takes for a signal to complete an
on-and-off cycle. When the duty ratio is so high it causes lesser material removal rate
because pulse on time is higher than pulse off time. So, the reaction products that are
formed during machining cannot be completely flushed out during pulse off time which
affects the linear dissolution.
ANOVA analysis indicated that affects the material removal rate is the current
with (p= 1.5% < significant level α = 10 %), the second and third variables that affect the
material removal rate are pulse on time, and the workpiece rotational speed, respectively.
Surface roughness Ra is found to have significant dependency on workpiece
rotational speed, wire feed and pulse on time respectively. The results showed that the
optimum surface roughness Ra obtained is 4.32 µm, by setting factors at wire feed at 18
m/s, workpiece rotational speed at 42 rpm, and pulse on time at 150 µs. The level of
significance of each variable is determined using ANOVA. It is found that the main
parameter that affects surface roughness Ra is the workpiece rotational speed with (Pvalue = 0 < α = 5) the second and third variables that affect surface roughness Ra are wire
feed with (P-value = 0.001 < α = 5%), and pulse on time with (P-value = 0.012 < α =
5%). The relationship between the affecting parameters and Ra is concluded by the mean
of means analysis.