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This experiment is concerning to
the study of a kinematic motion with the aid of the Whitworth’s quick return
mechanism. In this experiment, the
relative motion of the kinematic pairs is sliding which related to the movement
of the slider. This principle of
action is the same that applied to the reciprocating engine. As the objective is to investigate the performance of the
Whitworh’s quick return motion, several reading were taken with the increments
of ten degrees in order to study the rotation angle of the cutting and return
stroke from the plotted graph and hence determine the efficiency.
In addition, the motion of the slider is verified too for a quick return
stroke and a slow cutting stroke. The
result of the experiment, that is the determination of the slider position with
various rotation angle is related to the type of the apparatus whether it is a
quick return mechanism or not.
Theoretically, the rotation angle of the cutting and return stroke is
different, where the return stroke rotation angle must be smaller than the
rotation angle of the cutting stroke due to its quick return motion.
The smaller the return stroke rotation angle shows that the mechanism is
very efficient because cutting procedure can be done in many instances.
From the experiment, the recorded results of the slider position together with the crank angle will contribute to a graph as attached. Noted that initially, the slider position is at 3mm for crank angle of zero. Actually, the slider position must be at zero mm due to no movement of the mechanism. From the attached graphs, the value of the rotation angle for cutting and return stroke is 260 degrees and 100 degrees respectively. It can clearly be seen that the value of the return stroke rotation angle is smaller compared to the cutting stroke rotation angle due to the stated reason before (quick return motion). The determined efficiency in this experiment is 44.444 percent, which is much more higher than the efficiency determined by ‘crank and slotted lever quick return mechanism’ of 11.12 percent only.
Finally, it can be concluded that the application of the Whitworth’s quick return motion may increase the performance and efficiency of a machine tool mechanism. The initial position of the slider that should be at zero mm does not affect the intention to achieve the objective of the experiment (In this experiment, the initial slider position is at 3mm). It is evident that the experiment met the objective to study the kinematic motion of the mechanism.
The objective of the experiment is to investigate the performance of a Whitworth’s quick return motion and to verify that the motion does have a quick return stroke and a slow cutting or forward stroke. Additionally, the increase in efficiency of the system mechanism is also determined.
Data,
Observation and Result
From the above figure, the crank PC rotates about C in order to drive the
link POA about O. The rotation is
made at constant velocity. In this
experiment, the investigation is deeply related to the movement and motion of
the slider back and forth that can be define as the cutting and return stroke.
The following is the tabulated data of the experimental result together
with the attachment of the plotted graph.
From the experiment, it is evident that the rotation angle for the return
stroke is smaller than the cutting stroke due to the mechanism of the quick
return motion. The result of the
experiment does meet the objective to investigate the performance of the
Whitworth’s quick return mechanism. Therefore,
it shows that the equipment is in well condition in order to carry the
experiment task although the initial position of the slider is not be set at
zero mm. The fluctuation of the
experimental results may caused by personal error during taking the readings and
during setting the pointer at the specific angle, where the pointer is not
accurately set to the intended angle.
1.
From the tabulated data and the plotted graph, the crank angle is ranged
from zero to 360 degrees. Initially,
the slider starts for cutting operation at the maximum slider position of 40mm
with the crank angle of 150 degrees. Therefore,
this is the limit that the slider can reach for the cutting process.
For the return process, the slider is in operation from 50 to 150 degrees
with initial slider position at zero until the limit that the slider can
achieve.
2.
The percentage of the crank revolution for each stroke is as stated
below:
For
cutting stroke ……
(260 / 360) x 100 = 72.222 %
For return stroke …….
(100 / 360) x 100 = 27.778 %
The angle for the cutting and return stroke is 260 and 100 degrees respectively that can be determined from the plotted graph.
3.
The calculation of the efficiency of this mechanism is as shown below:
Find
percentage of crank revolution for both:
For cutting stroke ……
(260 / 360) x 100 = 72.222 %
For return stroke …….
(100 / 360) x 100 = 27.778 %
Therefore, the efficiency is given by:
Efficiency, h
= 72.222 % - 27.778 %= 44.444 %
4.
The graph that has been plotted based on the tabulated data shows that
the range of the return stroke is smaller than the range of the cutting stroke.
This is due to the condition of the slope for both cutting and return
stroke where the slope of the return stroke is more steep that the slope of the
cutting stroke. It is evident for
the investigation of the Whitworth’s quick return motion performance.
As a conclusion, it is confirm that the quick return motion may increase the efficiency of the machine tool because it can reduce the rotation angle for the return stroke. This is because; the time taken for the slider to return to its initial position is less than the time taken for the slider to accomplish the cutting operation with the same distance. Therefore, the occurrence of the cutting stroke can be done in many instances. From this experiment, the value of the efficiency of 44.444% is sufficient to prove the increased in performance of the Whitworth’s quick return mechanism. It is evident that the experiment met the objective in order to study the kinematic motion (sliding motion) of the slider in its path. Finally, the aid of the ‘Whitworth’s quick return mechanism’ has demonstrated to the students the difference of rotation angle for cutting and returning stroke that may increase the efficiency of machine tool such as power hack saw.