PRODUCTIVITY IMPROVEMENT OF PRE-TREATMENTS & POWDER COATING PROCESS.
Report on Solution for reduction of cycle time in the manufacturing of Al Wheels
1. REPORT ON
REDUCING THE CYCLE TIME OF THE FORGING PROCESS IN
THE MANUFACTURING OF ALUMINIUM WHEELS
BY
LAVA KUMAR 2012A4PS297G
SHREYAS RAJAGOPAL 2012B4A4726G
AT
WHEELS INDIA LTD., CHENNAI
BIRLA INSTITUTE OF TECHNOLOGY & SCIENCE, PILANI
(July, 2014)
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ACKNOWLEDGEMENTS
We would like to thank Mr. Venkateshwarlu, the Deputy General Manager of
the Special Wheels Division (SWD) for suggesting us the project topic and
giving us various inputs regarding our project. We also express our gratitude to
Mr. Dillibabu (Assistant Manager-Methods) for guiding us through the project
and for the tremendous support we received from him. We would also like to
express our sincere thanks to Mr. B.S. Pallad and the various other employees
in the FAW department and to the operators of the forging machine who
answered our queries patiently and gave us all the information we needed.
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Station: Wheels India Limited Centre: Padi, Chennai
Duration: 2 months Date of Start: 23rd
May, 2014
Date of Submission: 15th
July, 2014
Title of the Project: Reducing the cycle time of the Forging Process
ID No./Names/ : 2012A4PS297G Lava Kumar B.E Mechanical
Disciplines if the students 2012B4A4726G Shreyas Rajagopal MSc. Maths +
B.E Mechanical
Names and : Mr. Venkateshwarlu, Deputy General Manager (SWD)
Designations of the Mr Dillibabu, Assistant Manager – Methods
Experts
Name of the PS faculty: Mr. Sundaresan Raman
Key Words: Reduction, Cycle time, Forging, Spray, Double doors.
Project Areas: Manufacturing
Abstract: The report gives an idea of the various processes in Forged
Aluminium Wheels division of Wheels India Limited. Focussing on the process
called forging, the problem of it consuming a lot of time is being dealt with in
this report and the approach to acquiring the required data has been clearly
explained. The solutions to the identified problems have been illustrated and
attention has been paid to the problems that could arise in the in the
implementation of these solutions. The implementation of these solutions can
successfully save about 50 seconds per wheel manufactured.
Signatures of the Students Signature of PS faculty
Date Date
4. 4
Table of Contents
Introduction 6
Working on the Project 9
The Solution 11
Conclusions and Recommendations 14
Appendix 15
References 16
Glossary 17
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Introduction
The project pertains to a process in the FAW division. Hence a basic idea of the processes in
FAW is necessary for which the following rough outline of the processes in FAW has been
highlighted.
This is a rough outline of the process. At times, some wheels may be packed just after
machining or sometimes the polished wheels may be painted before packing. It all depends
on the requirements of the customers.
The main focus will be on forging process as the project deals with reducing the cycle time
for the process. This requires looking into the forging process in a little more detail. Forging
is defined as “a manufacturing process involving the shaping of metal using localized
Billet Cutting
•Al 6061 alloy is cut into
billets.
Billet Heating
•The cut billets are heated.
Forging
•The heated billets are
forged into a dis shape.
Bore Piercing
•A hole is made in the centre
of the disc.
Spinning
•The disc now goven the
shape of the wheel.
Heat Treatment
•All wheels should undergo
this process to attain the
required hardness for
machining.
Manchining
•The wheel is brought to the
proper dimensions and
holes are drilled as per the
design.
Polishing
•The machined wheels are
washed and polished to give
them a mirror like finish.
Packing
•The polished wheels, after
inspection are packed to be
shipped to the customers.
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compressive forces.” Earlier this process was as simple as hammering a piece of hot metal
but nowadays this is achieved by using hydraulic presses.
Figure 1: Hydraulic Forging
Forging can again be classified into three categories depending on the temperature of the
billet used - hot, warm and cold forging. If the temperature is above the material's
recrystallization temperature it is deemed hot forging; if the temperature is below the
material's recrystallization temperature but above 30% of the recrystallization temperature
(on an absolute scale) it is deemed warm forging; if below 30% of the recrystallization
temperature (usually room temperature) then it is deemed cold forging. The main
advantage of hot forging is that as the metal is deformed work hardening effects are
negated by the recrystallization process. Cold forging typically results in work hardening of
the piece. The process used in Wheels India Limited is hot forging.
As mentioned earlier the project deals with reducing the cycle time for the forging process.
The reason behind selecting the forging process for reduction of the cycle time is that it is
the mother process that currently takes the maximum time. A mother process is one which
has only one station for processing i.e. there is only one forging press where all the wheels
are forged. The other mother process are billet cutting, billet heating, spinning and heat
treatment. The following chart shows the time taken by the mother processes:
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Data regarding the heat treatment process were not shared since they had to be kept
confidential. But it was said that the heat treatment furnace has the capacity to handle
more demand. It is clear from the chart that forging takes a lot of time. Hence reducing the
cycle time of the forging process was chosen as the project topic. Such a project had been
undertaken by Mr.Dillibabu once earlier and a significant reduction of the processing time
was achieved. The earlier project successfully reduced the time from 325 sec/wheel to
about 202 sec/wheel (when run efficiently). This project aims at further reducing the time
by about 50 seconds per wheel.
0
50
100
150
200
250
300
Billet Cutting Billet Heating Forging Piercing Spinning
Cycle times of the "mother" processes
Cycle time (seconds)
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Working on the Project
To reduce the cycle time, data pertaining to the current cycle time were required. For this
purpose a digital camera was provided using which a video of the forging process had to be
made. An eight minute long video was made which captured the forging of two wheels. The
video that was stored in the camera’s memory was made available to work on by the MIS
(Management Information System) department. Once the video could be accessed on the
computer, using the VLC media player the time duration for the various activities in the
forging process was calculated. The following is the tabulated form of the data collected:
S.No ACTIVITIES IN FORGING PROCESS TIME(sec) Percent time
1 Door closing 5 2.08%
2 Auto spraying 40 16.67
3 Door opening 5 2.08%
4 Manual spraying 65 27.08
5 Door closing 5 2.08%
6 Forging 60 25%
7 Door opening 5 2.08%
8 Ejection 25 10.42%
9 Unloading 30 12.5%
Table 1: Activity times of the forging process.
The activities that add value to the product are highlighted in red. The activities that have
been identified as “time consuming” have been highlighted as bold.
Forging is the only activity that adds value to the product during the process and the time
taken by it cannot be reduced any further. The above data indicates that manual spraying is
a huge time consumer. It is also an essential step in the process because though there is an
automatic spraying system in place, it is not able to spray the lubricant on the tool at a
specific point where it is important that the lubricant is applied. Hence the manual spraying
process is required to overcome this problem. Since it is done manually the inefficiencies of
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the operator add to the time of the manual spraying. Hence manual spraying is one
identified area of problem.
Another area that consumes a good deal of time is the opening/closing of the door. During
the processing of a single wheel, the door is opened/closed 4 times in totality: before and
after the automatic spraying and before and after the forging activity. Each time the door
takes 5 seconds to open/close. If the time of the opening/closing of the door is reduced, due
to the high frequency of opening and closing activities, a reduction in time can be achieved.
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The Solution
Identifying the problem was one aspect of the project. An equally important part of the
project was to come up with solutions to the problems that solve the problems efficiently
and at the same time are feasible to be implemented. With the required data at hand, an
analysis was conducted as to which activities were to be targeted on to accomplish the goal.
The following are the ways in which time reduction in any process is generally achieved:
1) Simplify – eliminate unwanted steps (steps that do not add value to the product).
2) Combine – merge two or more simple or repetitive steps into one.
3) Modify – replace the existing system with a more efficient system
4) Rearrange – rearrange the order of the activities to eliminate processing of
extra/unwanted material and hence reduce the time taken
Keeping in mind the above methods, it was decided to modify the manual spraying system
since none of the other methods would reduce the time. The modification that was planned
was introduction of another automatic spraying system in the machine that would eliminate
the need of manual spraying by spraying exactly only at the point on the tool where the
operator has to manually apply the lubricant. A diagram of the proposed system has been
depicted in the figure below:
Figure 2: CAD model of the new spraying system.
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Figure 3: Rack and pinion Figure 4: Pneumatic cylinder
The following is a rough sketch of the forging machine showing the cavity where the above
shown spraying system will be installed.
Figure 5: CAD model of the forging machine
The rack would be propelled by a pneumatic cylinder. The stroke length of the pneumatic
cylinder would be 50 mm but the required stroke length is only 41 mm (approx.)
(calculations in appendix 1). Hence a stopper will be introduced to restrict the stroke of the
cylinder to the required length. This rack will be in contact with a pinion of diameter 50 mm
which, for the calculated stoke length (see Appendix), will rotate by 90 degrees. This pinion
will house the nozzle that will spray the lubricant on the tool. When the automatic spraying
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cycle starts, the existing spray system will spray the lubricant on the tool. Simultaneously
the nozzle, initially in the cavity, will be rotated by 90 degrees by the rack-and-pinion
mechanism and it will spray the lubricant on the inner side of the tool. Once that is done,
the nozzle will be rotated back into the cavity.
Another issue to be taken care of is the splashing of the lubricant on the system. The
graphite in the lubricant my get deposited in the rack-and-pinion mechanism and jam the
motion of the system or the deposition on the pneumatic system could again restrict the
movement of the parts. For this it was decided to cover the cavity with a metal sheet and
leave a gap only for the nozzle to project out of the cavity through the metal sheet.
The biggest advantage of introducing this that the cycle time gets reduced drastically since
the manual spraying has been eliminated. Apart from the time gain, the system is not only
easy to fabricate but also easy to maintain and the investment required is not heavy either.
The other area of time wastage that had been identified was the opening-closing of the
door. The solution is again a modification which involves replacing the single door by two
doors that operate simultaneously.
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Conclusion and Recommendations
The solutions to the problem of time wastage in the forging process have been discussed
thoroughly in the previous section. The advantage of introducing the new spraying system is
that manual spraying will not be required. The direct effect of this on the cycle time would
be that it will reduce by 40 seconds roughly. But care needs to be taken to protect the spray
mechanism from the lubricant since exposure to the lubricant could lead to deposition of
the graphite particles in the lubricant on the rack and pinion mechanism and hinder the
functioning of the system.
The other solution of replacing the single doors by double doors would cut the activity time
by half meaning 10 seconds of the cycle time would be saved. The only point to be kept in
mind is that pneumatic operated doors function faster than motor operated doors. Hence
using motors to operate the two door mechanism would not show a time reduction as
significant as in the case of using pneumatic cylinders to operate the doors.
The life and efficiency of any system depends upon its usage and its maintenance. Usage
depends on the demand and hence cannot be controlled but to ensure that the above
suggested solutions give the best results, it is recommended that they be maintained
properly. This includes oiling the rack and pinion mechanism and cleaning it regularly to
prevent deposition of dust on the mechanism, cleaning the nozzle regularly to prevent
blockage and other such activities.
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Appendix
Calculation of the stoke length of the pneumatic cylinder.
Diameter of the pinion (d): 50 mm
Circumference of the pinion (c): π x d = π x 50 = 157.08 mm
Distance covered on the circumference on rotation by 90 degrees: (c x 90)/ 360
= c x 0.25
= 157.08 x 0.25
= 39.27 mm
Hence the stoke length of the pneumatic cylinder must be 39.27 mm.
Calculation of the bore diameter of the pneumatic cylinder.
We know,
Pressure = Force/Area (Pressure is Force per unit Area)
Hence, area of the piston of the pneumatic cylinder will be given by:
Area = Force/Pressure (1)
Force applied in this case depends on the load that needs to be moved (rotated) which is
nothing but the mass of the pinion gear along with the spray assembly mounted on the
pinion. Let this mass be M kg. Hence the force applied would be Mg N where g is the
Gravitational constant.
Pressure data required for the calculation is the air pressure in the working area which is
given to be 4.5 bar or 4.5 x 10⁵ N/m².
Area of the piston can be written as πd²/4 where d is the diameter of the piston. Hence
formula (1) can be re-written as,
Πd²/4 = Mg/4.5 x 10⁵.
d =√ (4Mg/π x 4.5 x 10⁵)
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Once the value of the mass of the spraying mechanism and the pinion is available, M can be
calculated and hence the diameter of the required piston can be calculated using the above
formula. The bore diameter, d₁ is given by
d₁ = 1.5d
And thus the bore diameter of the pneumatic cylinder can be obtained.
