The poka yoke method respects the intelligence of the worker.

1. What is Poka Yoke method?
The poka yoke method respects the intelligence of the worker, so according to this
method the repetitive jobs or the jobs which require the memory rather than the skill of
the worker is done by providing necessary arrangement and as a result of which the
worker can concentrate more on the creative and value added activities.
In a work place there is a chance that the mistake is committed every day due to
any process that will be working and many components that will be there for
manufacturing purpose. In poka yoke method an idea is believed that for competing with
the world the company should produce absolutely zero defective products and the same
should reach the customers. Poka yoke methods are simple concepts that can be adapted
in the production field so that goal of zero defects is obtained.
DESIGN, CALCULATION AND VALIDATION
According to the poka yoke method we need to select the operation that needed to
be redesigned. The component is back cover which is an assembly part of a complex
machine. The component or the work piece that is used for the development of the fixture
undergoes machining in in 3 stages. These stages are
Step 1: Boring of 70mm and then maintaining 75mm thickness.
Step 2: The spigot portion.
Step 3: port hole surface milling up to height of 70±0.3, 12mm port hole drilling
at a distance of 51±0.3 and M10x1.5 4holes drilling.
The current project is the designing and manufacturing of the milling fixture for
the step 3 of the production. According to the poka yoke method different ways in which
the process can be approached for an efficient design is understood. The designing is
done on the trial and error basis by developing more than one design and brain storming
for any advantages and disadvantages.
Design 1
Design 1 involves the machining of the component using the conventional
machine vice to hold the component, marking using instruments such as height gaugescriber,
machining in milling machine, drilling machine, manual tapping and grinding
process. The component sent for inspection so that the error can be identified
First the surface milling is done by vertical axis milling machining to form the
port hole surface, centres of the holes to be drilled are marked using the height gauge, the
holes are drilled under a radial drilling machining held in a machine vice then manual tap
is used to machine the internal thread and then it is grinded to remove marking lines. The
total cycle time taken for whole operation is around 20min to 25min.
Advantages
The cost of production is less.

2. The operation is simple and the required tools are inexpensive.
Dis advantages
The accuracy of the hole obtained is less and usually have high deviation from
actual dimension.
The flatness obtained at the port surface may have variations and bad surface
fininsh.
The cycle time required for the total process is more.
There is an unnecessary use for the grinding process.
The process is more prone to human errors.
The dis advantages in the above mention design forces us to rethink the mode in
which the problem has to be approached and using the jig or a fixture in one of them.
Design 2
The design 2 involves the designing of a drill jig for the radial drilling machine.
Here the concept of angular drill jig and box drill jig is used along with 2 way clamping.
It helps to hold the port hole surface milled component which is milled using a vertical
axis milling machine. It is kept under the radial drilling machine with the aid of the jig
and ensures perfect positioning of the holes.
This involves surface milling of the component using
vertical axis milling machine to machine a port hole surface, then the component is
placed inside the drill jig and placed under the radial drilling machine for drilling. After
drilling a manual tapping is done and then if needed a grinding is to be done. By
considering the data from similar kinds of operation on different component, the total
cycle time taken was be approximated to 15min to 17min by the process of brain
storming some of the advantages and dis advantages were found.
Advantages
The position of the drilled holes is accurate and within the specified limit.
Since there is no marking on the port surface grinding process may be eliminated
depending on the surface finish.
The time taken is reduced when compared to that of the first design.
The human error is reduced.
Dis advantages
The depth of the holes obtained is usually more than that of the specified in the
drawing.
The straightness of the drilled hole depends on the flatness and perpendicularity of
the milled surface.
The construction of the jig and assembly is time taking and expensive.
IMPROVEMENT OF POSITION ACCURACY USING MILLING FIXTURE
BY THE INFLUENCE OF POKA YOKE METHOD
Department Of Tool Engineering, GTTC Page 45
Tapping of M10x1.5 thread has to be done separately.
Even though the second design look promising the number of process involved for
machining the component is more and since there is a human involved as a major part of
the process for every operation, the manufacturing can be assumed to be influenced with
human prone errors. Hence another design is developed which reduces the number of
total number of process and also reduce human involvement.

3. Design 3
The design 3 aims at reducing the human involvement hence a change of machine
from vertical milling machine and radial drilling machine to BMV35 Series CNC Vertical
Machining Centre is needed and design of a milling fixture for the above said machine.
Here the CNC programming is done in order to perform milling, drilling and tapping
operations simultaneously. Since CNC technology is used the coordinates of the positions
that are to be machined are registered in the computer and hence the variation in the
position accurecy is reduced.
Here it uses the concept of angular fixture.
Here the milling fixture is bolted to the VMC bed using the allen screws. The component
is camped to the fixture using C clamp and a support is given to align the spigot
perpendicular to bed surface and keep it in that position during machining. Due to usage
of the VMC machine the milling and drilling operations are done in a single cycle. The
cycle time taken is 7 min to 8 min.
2 types of the poka yoke techniques are used in this design. The control type of
the regulatory method is used. Before starting of the machining for the port hole the
component is inspected in the previous machining stage and it is inspected after the port
hole in machined. This ensures that the process in monitored or controlled during
manufacturing and any defects are rectified for consequent parts. This represents the
control part of the poka yoke method.
Similarly the contact type setting method is also used. The locator acts as a one of
the contact part that allows the parts that have been bored to be selected for port hole
machining and also the support pin not only helps in orientation of the work piece but
also ensures that the spigot portion is completed. As a result the operator is forced to do
the port hole for the final operation. The inspection device, locator and the support pin
used as contact type of detection system. Depending on the above arguments some of the
advantages and disadvantages are listed below
Advantage
The cycle time is least when compared to other designs.
Since miling and drilling are done in a single cycle the perpendicularity between
hole axis and the milled surface is maintained.
The depth of drilling and tapping can be maintained with in the required
dimension.
The construction of fixture is easy and inexpensive.
The construction of setting block is avoided since the position of the zero point for
the component can be registered in the CPU of the machine using the sample
component given by the customer.
Since there is a usage of the CNC machining the human error is less.
Dis advantages
The cost of production is high when compared to the other machines.
The carbide tips have to be inspected for every 10 pieces to check for wear an
edge.

4. Since the design 3 fulfils almost all of the criterion, it is developed and tested in the VMC
machine