1 1. INTRODUCTION 1.1 COMPANY PROFILE Wheels India is promoted by the TVS Group and was started in the early 60's to manufacture automobile wheels. Today, Wheels India has grown as a leading manufacturer of steel wheels for passenger cars, utility vs, trucks, buses, agricultural tractors and construction equipment in India. The company supplies 2/3 rd of the domestic market requirement and exports 18% of the turnover to North America, Europe, Asia Pacific and South Africa. The company also has a technical-financial collaboration with Titan Europe. Wheels India designs and manufactures wheels for the specific requirements of the customer. Our activities are driven by the following objectives: Maintain leadership in the domestic market and presence in export markets. Ensure customer satisfaction through timely delivery of quality products and services, at competitive prices. Continuously improve & innovative product design, process technology and work environment to offer better products. Bring about involvement of all employees in achieving the above objectives. Wheels India has the ability to design the complete range of steel-wheels to suit customer requirements, incorporating necessary styling and performance characteristics. 1.2 PRODUCTS The various types of products manufactured by Wheels India Limited are mentioned in the table 1.1 given below.
Transcript
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1. INTRODUCTION
1.1 COMPANY PROFILE
Wheels India is promoted by the TVS Group and was started in the early
60's to manufacture automobile wheels. Today, Wheels India has grown as a
leading manufacturer of steel wheels for passenger cars, utility vs, trucks, buses,
agricultural tractors and construction equipment in India. The company supplies
2/3rd of the domestic market requirement and exports 18% of the turnover to
North America, Europe, Asia Pacific and South Africa. The company also has a technical-financial collaboration with Titan
Europe. Wheels India designs and manufactures wheels for the specific
requirements of the customer. Our activities are driven by the following
objectives:
Maintain leadership in the domestic market and presence in export
markets.
Ensure customer satisfaction through timely delivery of quality products
and services, at competitive prices.
Continuously improve & innovative product design, process technology
and work environment to offer better products.
Bring about involvement of all employees in achieving the above
objectives.
Wheels India has the ability to design the complete range of steel-wheels
to suit customer requirements, incorporating necessary styling and
performance characteristics.
1.2 PRODUCTS The various types of products manufactured by Wheels India Limited are
mentioned in the table 1.1 given below.
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Table 1.1 PRODUCT TYPES
Product Type Click
Wheels for Heavy Vehicles (Trucks, Buses, Light Commercial Vs, Trailers, Tippers etc.)
Wheels for Light Vehicles
(Passenger Cars, Mini Vans, SUV's & MUV's)
Wheels for Agricultural Applications (Tractors, Combines, Farm Equipments etc.)
1.4 PRODUCT EXPLANATION 1.4.1TRACTOR DISC The dimensions and properties of the work piece used in tractor disc is
Figure 1.1 TRACTOR DISC
Weight : 40 kg (Approx)
Dimension : 700 X 700 mm (Approx)
Thickness : 10 mm (Approx)
1.4.2 COMMERCIAL VEHICLE DISC The dimensions and properties of the work piece used in commercial
vehicle disc are
Figure 1.2 COMMERCIAL VEHICLE DISC
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Weight : 25 kg (Approx) Dimension : 545 mm (diameter) (Approx) Thickness : 11 to 16 mm (Approx)
1.5 OBJECTIVE OF THE PROJECT The main objective of this project is to provide a feasible solution to
reduce the cycle time in forming operation and reduce the setup time during job
change thus increasing productivity.
The efforts in the project aim to reduce the cycle time by introducing
efficient problem solving techniques like QC story.
Using QC story the problem identification and solving becomes easier.
The effective solution for the problem achieved with this technique.
1.6 PROPOSED SOLUTION The proposed corrective action based on the QC story will reduce the
cycle time in forming operation and will reduce setup time during job change. It
will increase the productivity.
The other quality control tools like pareto diagram, fishbone diagram, why-
why analysis, brain storming and 4w1h table are also used.
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2. EXPERIMENTAL WORK 2.1 QUALITY CONTROL TOOLS The following quality control tools were used for the completion of the
project work.
2.1.1 PARETO CHART A Pareto Chart is a series of bars whose heights reflect the frequency
or impact of problems. The bars are arranged in descending order of height from
left to right. This means the categories represented by the tall bars on the left are
relatively more significant then those on the right. This bar chart is used to
separate the “vital few” from the “trivial many”. These charts are based on the
Pareto Principle which states that 80 percent of the problems come from 20
percent of the causes. Pareto charts are extremely useful because they can be
used to identify those factors that have the greatest cumulative effect on the
system, and thus screen out the less significant factors in an analysis. Ideally,
this allows the user to focus attention on a few important factors in a process.
Need of Pareto charts: You can think of the benefits of using a Pareto Charts in economic terms.
A Pareto Chart breaks a big problem down into smaller pieces, identifies the most
significant factors, shows where to focus efforts, and allows better use of limited
resources. You can separate the few major problems from the many possible
problems so you can focus your improvement efforts, arrange data according to
priority or importance, and determine which problems are most important using
data, not perception.
A Pareto Chart can answer the following questions:
What are the largest issues facing our team or business?
What 20% of sources are causing 80% of the problems?
A Pareto Chart is a good tool to use when the process you are
investigating produces data that are broken down into categories and you can
count the number of times each category occurs. A Pareto diagram puts data in a
hierarchical order, which allows the most significant problems to be corrected
first. The Pareto analysis technique is used primarily to identify and evaluate
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nonconformities, although it can summarize all types of data. It is the perhaps the
diagram most often used in management presentations.
2.1.2 BRAINSTORMING Brainstorming is a group or individual creativity technique by which efforts
are made to find a conclusion for a specific problem by gathering a list of ideas
spontaneously contributed by its member(s). Brainstorming was more effective
than individuals working alone in generating ideas, although more recent
research has questioned this conclusion. Today, the term is used as a catch all
for all group ideation sessions.
2.1.3 FISH BONE DIAGRAM Fish Bone Diagram generally called as “ISHIKAWA DIAGRAM” is
basically the Cause and Effect Diagram that identifies potential factors causing
overall effect. Each cause or reason for imperfection is a source of variation.
Causes are usually grouped into major categories to identify these sources of
variation. The categories typically include
People/ Men: Anyone involved within process.
Methods: How the process is performed and the specific requirements
for doing it, such as policies, procedures, rules, regulations and laws.
Machines: Any equipment, computers, tools, etc. Required to
accomplish the job.
Materials: Raw materials, parts, pens, paper, etc. Used to produce the
final product.
Measurements: Data generated from the process that are used to
evaluate its quality.
2.1.4 WHY-WHY ANALYSIS The Why-Why Analysis or 5 Why Analysis is a question-asking technique
used to explore the cause and effect relationships underlying a particular
problem. The primary goal of technique is to determine the root cause of a defect
or problem.
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2.1.5 4W1H TABLE The 4W1H is a process (What, Where, When, Who and How), this tool is
used to plan the troubleshooting for a raised issue. It defines, what problem has
risen, Who is responsible for it, when does it occur, How it is going to be solved
and where the corrective action is to be taken. For Any issue, if we apply this
method, it will be easy to find the solution and accomplish the given task at the
right time. The issues will be raised in the review meeting, where the member
who finds the problem in his task will raise in the meeting and an optimum
solution will be deduced from the discussion.
2.2 DISC MANUFACTURING LINE The process flow for the manufacturing of commercial vehicle disc and
tractor wheel disc are shown in the figure 2.1 and figure 2.2 respectively.
Figure 2.1 CV DISC PROCESS FLOW
Figure 2.2 TRACTOR DISC PROCESS FLOW
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BLANKING A shearing operation creates a hole in sheet metal by separating an
interior section. The removed piece of metal is the desired section.
FORMING A forming operation is a plastic deformation of a metal in order to produce
a useful shape. Sheet metal can be formed through operations that shear,
stretch, bend, or compress the metal.
PIERCING Piercing operations are defined as “forming a hole in the sheet metal “. In
piercing the punched out piece is called as scrap.
COINING A metal working operation is used to create raised surfaces and imprints in
metal. Coining is a relatively severe operation that creates variations in metal
thickness.
NOTCHING A shearing operation removes a section from the outer edge of the metal
strip or part.
DEBURRING The removal of burrs on a part by processes such as grinding or filing is
done during this operation.
PLANISHING The planishing operation is finishing the surface by finely shaping and
smoothing sheet metal.
2.3 PROBLEM SELECTION Various problems were reported by the workers to the management and
which was recorded as a problem bank by the management. The problems in the
problem bank are divided into three classes namely A, B, and C.
Type A - Minimum involvement of other department in solving them or can
be solved by the QCC Member itself.
Type B - Involvement of other department is necessary.
Type C - Problems can be solved with Management assistance.
Based on the above conditions the problems in the problem bank are
divided for better understanding which is shown in the table 2.1 given below.
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Table 2.1 CLASSIFICATION OF PROBLEM
SL.NO
PROBLEM DESCRIPTION A B C
1 Raw material delay
2 Raw material loading delay
3 Loading conveyor forward not
working
4 Loading conveyor chain cut
5 Handling unit forward and reverse
not working
6 Handling unit not pick the plate
properly
7 Blank end cut
8 Blank stopper not fixed
9 Blank taper
10 Unloading conveyor chain cut
11 Blanking tool shut height to be
standard
12 Machine loaded with tool
13 Setting time high
14 Auto oil apply unit not available
15 Blank stuck with conveyor
16 Forklift delay in blank scarp
removing
17 1000 Ton to 1500 Ton conveyor
length excess
18 Auto oil apply unit not available for
forming
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19 Loading power conveyor length
less
20 Loading power less conveyor bend
21 Tractor blank loading difficult
22 Tractor blank loading Handling unit
not available
23 Tractor blank square variation
24 Tractor blank stopper not properly
fixed
25 Tractor blank stopper height less
26 Cushion pin height
27 CV blank not seated properly in
pressure plate
28 Disc nave correction
29 Blank wrong location
30 Disc form correction
31 High cycle time
32 Disc height variation
33 Disc forming scoring mark
34 Knock out pin height variation
35 Extractor bar broken
36 Nave planishing operation
elimination
37 CV Disc unloading fatigue high
38 Tractor disc tilling fatigue high
39 Forklift delay in screw press tool
setting
40 Planishing tool search time high
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41 Screw press load adjustment
difficult
42 Bore locator searching time high
43 Disc loading fatigue high
44 Tractor disc loading fatigue high
As mentioned earlier the problems listed under the type a can be solved
using QC members itself. Therefore the problem no. 13 and problem no. 31 are
selected because they affect the productivity in large manner. The following
issues are due to the above mentioned problem
Unable to meet internal customers demand
Unit turnover affected
Manpower shortage issue
2.4 PROBABLE CAUSES Some of the probable causes for increased cycle time in forming
operations were found out by brain storming. The causes are
Change into once mode
Cycle time high
1000T forklift delay
Tool forming correction
Unloader break down
Machine break down
Untrained operator
Operator fatigue due to heavy weight disc
Dent mark in material
Want of material
2.5 CAUSE VALIDATION The cause validation QC tool is used to select the most significant issue
that causes this problem
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Table 2.2 CAUSE VALIDATION
PROBLEM RELATED TO
MEN/MACHINE/ MATERIAL/MET
HOD
DESCRIPTION OF THE CAUSE
CONSIDERED/NOT
CONSIDERED FOR FURTHER
ANALYSIS
REASON FOR ELIMINATING THE
CAUSE
MEN UNTRAINED OPERATOR
NOT CONSIDERED
TRAINED OPERATOR
ISONLY WORKING ON ALL M/C
MEN FORK LIFT DELAY
CONSIDERED TO BE CHECKED
MATERIAL WANT OF MATERIAL
CONSIDERED TO BE CHECKED
MATERIAL DENT MARK NOT CONSIDERED
VISUALLY CHECKED
MACHINE UNLOADER BREAKDOWN
NOT CONSIDERED
SPARE UNLOADER ARRANGED
MACHINE MACHINE BREAKDOWN
NOT CONSIDERED
WE NOTED THE BREAKDOWN LOSS
IT WAS BELOW AVERAGE
METHOD CYCLE TIME HIGH
CONSIDERED TO BE CHECKED
METHOD CHANGE INTO ONCE MODE
NOT CONSIDERED
CANNOT RUN IN CONTINUOUS DUE
TO SAFETY REASON
2.6 ROOT CAUSE ANALYSIS From the cause validation tool table shown above the significant causes
for reduced productivity are
Fork lift delay
Want of material
High cycle time.
By drawing a fish bone diagram we can find the root cause for the reduced
productivity. The effects of the first two causes are below the base line of
productivity. The figure 2.3 represents the fish bone diagram.
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Figure 2.3 FISH BONE DIAGRAM
WHY-WHY ANALYSIS Using the why-why analysis, the root causes for the actual causes found
above can be determined. The why-why made to find out the root causes are
given below.
Why CV and TR disc cycle time is high
Forming operation takes more time
Manual intervention is more
Unloading is done manually
No automatic unloading system for TR and CV disc
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Therefore from the why-why analysis it is clear that high cycle time is the
main reason for the reduced productivity. The graphical representation of cycle
time for CV disc and tractor disc is shown in the figure 2.4 and figure 2.5.
Figure 2.4 CYCLE TIME FOR CV DISC
Figure 2.5 CYCLE TIME FOR TRACTOR DISC
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As shown in the above figure 2.4 loading the blank takes 2 sec, pressing
the push button takes 2 sec, the operation takes place for 5 sec, and unloading
the disc takes place for 2 sec. therefore the time spent in the machine is 5
seconds and time spent by the labour during one cycle is 6 seconds.
Similarly from the figure 2.5 loading the blank takes 5 sec, pressing the
push button takes 2 sec, the operation takes place for 5 sec, and unloading the
disc takes place for 3 sec. therefore the time spent in the machine is 5 seconds
and time spent by the labour during one cycle is 10 seconds.
2.7 POSSIBLE SOLUTION
In order to reduce the unloading time, the unloading mechanism must be
automated and the use of separate operators can be avoided. Based on the work
place criteria a suitable automation system must be used.
A combination of electric motors with vacuum cups or magnetic cups
Pick and Place robots
Hydraulic Cylinder and
Pneumatic Cylinder.
In the following sections we will see in detail about the above mentioned
possible sections along with their pros and cons with respect to our problem.
2.7.1 ELECTRIC MOTORS
Motors convert electrical energy into mechanical energy by the interaction
between the magnetic fields setup in the stator and rotor windings. Industrial
electric motors can be broadly classified as induction motors, direct current
motors or synchronous motors. All motor types have the same four operating
components: stator (stationary windings), rotor (rotating windings), bearings, and
frame (enclosure).
MOTOR TYPES
The Electric motor may be broadly classified into:
1) Induction Motor
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2) Direct Current Motor
3) Synchronous Motor
4) Stepper Motor
5) Servo Motor
INDUCTION MOTORS
Induction motors are the most commonly used prime mover for various
equipments in industrial applications. In induction motors, the induced magnetic
field of the stator winding induces a current in the rotor. This induced rotor current
produces a second magnetic field, which tries to oppose the stator magnetic field,
and this causes the rotor to rotate.
The 3-phase squirrel cage motor is the workhorse of industry; it is rugged
and reliable, and is by far the most common motor type used in industry. These
motors drive pumps, blowers and fans, compressors, conveyers and production
lines. The 3-phase induction motor has three windings each connected to a
separate phase of the power supply.
DIRECT CURRENT MOTORS
Direct-Current motors, as the name implies, use direct-unidirectional,
current. Direct current motors are used in special applications- where high torque
starting or where smooth acceleration over a broad speed range is required.
SYNCHRONOUS MOTORS
AC power is fed to the stator of the synchronous motor. The rotor is fed by
DC from a separate source. The rotor magnetic field locks onto the stator rotating
magnetic field and rotates at the same speed. The speed of the rotor is a function
of the supply frequency and the number of magnetic poles in the stator. While
induction motors rotate with a slip, i.e., rpm is less than the synchronous speed,
the synchronous motor rotate with no slip, i.e., the RPM is same as the
synchronous speed governed by supply frequency and number of poles. The slip
energy is provided by the D.C. excitation power.
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STEPPER MOTOR
A stepper motor is a brushless DC electric motor that divides a full rotation
into a number of equal steps. The motor position can then be commanded to
move and hold at one of the steps without any feedback sensor as long as the
motor carefully sized to the application.
Figure 2.6 STEPPER MOTOR
SERVO MOTOR
A servo motor is a mechanical motorized device that can be instructed to
move the output shaft attached to a servo wheel or arm to a specified position.
Inside the servo box is a DC motor mechanically linked to a position feedback
potentiometer, gearbox, electronic feedback control loop circuitry and motor drive
electronic circuit.
There are other types of motor which are of less significant and rarely
used which are,
Reluctance Motor
Hysteresis Motor
Brushless DC Motor
Universal Motor.
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RELUCTANCE MOTOR
A reluctance motor is a synchronous‐induction motor. The rotor has salient
poles and a cage so that it starts like an induction motor, and runs like a
synchronous motor.
HYSTERESIS MOTOR
Hysteresis effect produces the torque which can be very tiny and used as
the driver for electric clocks.
BRUSHLESS DC MOTOR
Brushless DC motor is a close cousin of a permanent magnet stepper
motor with electronic controllers.
Figure 2.7 BRUSHLESS DC MOTOR
UNIVERSAL MOTORS
If a series of dc motors has a laminated stator frame, it can run effectively
from an ac supply as well as dc. This kind of motors is known as universal motor.
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2.7.2 MOTOR SELECTION FACTORS
The primary technical consideration defining the motor choice for any
particular application is the torque required by the load, especially the relationship
between the maximum torque generated by the motor (break-down torque) and
the torque requirements for start-up (locked rotor torque) and during the
acceleration periods.
The duty / load cycle determines the thermal loading on the motor. One
consideration with totally enclosed fan cooled (TEFC) motors is that the cooling
may be insufficient when the motor is operated at speeds below its rated value.
Ambient operating conditions affect motor choice; special motor designs
are available for corrosive or dusty atmospheres, high temperatures, restricted
physical space, etc.
An estimate of the switching frequency (usually dictated by the process),
whether automatic or manually controlled, can help in selecting the appropriate
motor for the duty cycle.
The demand a motor will place on the balance of the plant electrical
system is another consideration - if the load variations are large, for example as a
result of frequent starts and stops of large components like compressors, the
resulting large voltage drops could be detrimental to other equipment.
RELIABLITY
Reliability is of prime importance - in many cases, however, designers and
process engineers seeking reliability will grossly oversize equipment, leading to
sub-optimal energy performance. Good knowledge of process parameters and a
better understanding of the plant power system can aid in reducing over sizing
with no loss of reliability.
INVENTORY
Inventory is another consideration - Many large industries use standard
equipment, which can be easily serviced or replaced, thereby reducing the stock
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of the spare parts that must be maintained and minimizing shut-down time. This
practice affects the choice of motors that might provide better energy
performance in specific applications. Shorter lead times for securing individual
motors from suppliers would help reduce the need for this practice.
COST
Price is another issue - Many users are first-cost sensitive, leading to the
purchase of less expensive motors that may be more costly on a lifecycle basis
because of lower efficiency. For example, energy efficient motors or other
specially designed motors typically save within a few years an amount of money
equal to several times the incremental cost for an energy efficient motor, over a
standard-efficiency motor. The cost benefits can be worked out on the basis of
premium required for high efficiency vs. worth of annual savings.
MAINTAINANCE
Inadequate maintenance of motors can significantly increase losses and
lead to unreliable operation. For example, improper lubrication can cause
increased friction in both the motor and associated drive transmission equipment.
Resistance losses in the motor, which rise with temperature, would increase.
Providing adequate ventilation and keeping motor cooling ducts clean can help
dissipate heat to reduce excessive losses. The life of the insulation in the motor
would also be longer: for every 100C increase in motor operating temperature
over the recommended peak, the time before rewinding would be needed is
estimated to be halved.
DISADVANTAGES OF MOTORS
BRUSH WEAR: Since they need brushes to connect the rotor
winding. Brush wear occurs, and it increases dramatically in low
pressure environment. The brushes life time is too little that is an
average of one hour
Sparks from the brushes may cause explosion if the environment
contains explosive materials.
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RF noise from the brushes may interfere with nearby electronic
devices and control panel.
Few of these motors may be used only for low torque applications.
2.7.3 VACUUM CUPS
Vacuum cup is a hallow suction cup used as a port for the vacuum hose.
The various types of vacuum cups suitable are:
Flat cups
Single bellow cups
Multi bellow cups
Oval cups
Universal cups
Deep cups
Ultra miniature cups
Rigid cups and speciality cups
Vacuum cup fittings
FLAT CUPS
Flat cups are used for our problem because they are precision moulded
double lip flat cup for slightly curved surfaces. Double lip for additional security. If
outside lip bends and loses its seal, the inner lip remains sealed. Outer ribs
prevent the cup lip from being cut.
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Figure 2.8 FLAT VACUUM CUP
Though the flat vacuum cups may be used for the automation of the
unloading mechanism, the electric motor which supports the vacuum cups is not
suitable for this application.
2.7.4 PICK AND PLACE ROBOTS
The pick and place robots are used to feed and disengage parts or tools to
or from a machine, or to transfer parts from one machine to another.
It offers new opportunities for flexibility and repeatability in consumer goods
and other industries. This robot is a production developer, analyst and system
integrator in the food, pharmaceutical, logistics and material handling industries.
The robot saves time space and money and rugged industrial design ensures it
can meet the needs of the most demanding production operations.
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Figure 2.9 PICK AND PLACE ROBOTS
LIMITATIONS
Expensive when compared to other options
Magnetic cup holder has to be changed each time for different disc which
increases the setup time
Moreover programmes must be changed before the beginning of various
operation, taking more time for setting up the job
2.7.5 CYLINDERS
Cylinders are linear actuators which convert fluid power into mechanical
power. They are also known as JACKS or RAMS. Hydraulic cylinders are used at
high pressures and produce large forces and precise movement. For this reason
they are constructed of strong materials such as steel and designed to withstand
large forces. Because gas is an expensive substance, it is dangerous to use
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pneumatic cylinders at high pressures so they are limited to about 10 bar
pressure. Consequently they are constructed from lighter materials such as
aluminium and brass. Because gas is a compressible substance, the motion of a
pneumatic cylinder is hard to control precisely. The basic theory for hydraulic
and pneumatic cylinders is otherwise the same.
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3. RESULTS AND DISCUSSION
3.1 PROPOSED SOLUTION
From the possible solutions mentioned above the best possible solution is the use of cylinders. Two types of cylinders may be used which are
Hydraulic cylinders and Pneumatic cylinders.
3.1.1 PNEUMATIC VS HYDRAULIC CYLINDER
Pneumatic cylinder offers a very clean system, suitable for food
manufacturing processes and other processes which require no risk of
contamination. Hydraulic cylinder is generally not used in these environments
due to the risk of hydraulic oil leaks from faulty valves, seals or burst hoses.
Pneumatics offer rapid movement of cylinders and have the great
advantage of availability in very small sizes. This is mainly due to air compressor
flow rates, air is very agile and can flow through pipes very quickly and easily with
little resistance, while hydraulic oil is a viscous substance and requires more
energy to move. Also in pneumatics, cylinders and valves can dump their
compressed air straight to the atmosphere when they need to change direction or
alter their state quickly, compared with hydraulics where the oil must be routed
back to the reservoir.
Pneumatics does not have the potential force that hydraulics has to offer.
The lifting or moving of heavy loads is not best suited to pneumatics. Hydraulics
can smoothly lift and move loads because the hydraulic oil is not compressible,
compared to air which can become jerky and spongy as the air pressure
fluctuates with cylinder movement or load changes. In general a much larger
pneumatic cylinder is needed to obtain the same force that a hydraulic ram can
produce.
In terms of energy costs pneumatics is more costly than hydraulic cylinder;
this is mainly due to the amount of energy lost through heat production while
compressing air.
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From the above facts we may conclude that pneumatic cylinder is
preferred to our automation system.
3.2 PNEUMATIC CYLINDERS
Pneumatic cylinders (sometimes known as air cylinders) are mechanical
devices which use the power of compressed gas to produce a force in a
reciprocating linear motion. Like hydraulic cylinders, something forces a piston to
move in the desired direction. The piston is a disc or cylinder, and the piston rod
transfers the force it develops to the object to be moved. Engineers prefer to use
pneumatics sometime because they are quieter, cleaner, and do not require large
amounts of space for fluid storage.
Because the operating fluid is a gas, leakage from a pneumatic cylinder
will not drip out and contaminate the surroundings, making pneumatics more
desirable where cleanliness is a requirement.
GENERAL
Once actuated, compressed air enters into the tube at one end of the
piston and, hence, imparts force on the piston. Consequently, the piston
becomes displaced (moved) by the compressed air expanding in an attempt to
reach atmospheric pressure.
COMPRESSIBLITY OF GASES
One major issue engineers come across working with pneumatic cylinders
has to do with the compressibility of a gas. Many studies have been completed
on how the precision of a pneumatic cylinder can be affected as the load acting
on the cylinder tries to further compress the gas used. Under a vertical load, a
case where the cylinder takes on the full load, the precision of the cylinder is
affected the most.
FAIL SAFE MECHANISM
Pneumatic systems are often found in settings where even rare and
brief system failure is unacceptable. In such situations locks can sometimes
serve as a safety mechanism in case of loss of air supply (or its pressure falling)
and, thus, remedy [remedy] or abate any damage arising in such a situation. Due
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to the leakage of air from input or output reduces the pressure and so the desired
output.
TYPES
Although pneumatic cylinders will vary in appearance, size and function,
they generally fall into one of the specific categories shown below. However there
are also numerous other types of pneumatic cylinder available, many of which
are designed to fulfil specific and specialized functions.
Single-acting cylinder Single-acting cylinders (SAC) use the pressure
imparted by compressed air to create a driving force in one direction (usually
out), and a spring to return to the "home" position. More often than not, this type
of cylinder has limited extension due to the space the compressed spring takes
up. Another downside to SACs is that part of the force produced by the cylinder is
lost as it tries to push against the spring. Because of those factors, single acting
cylinders are recommended for applications that require no more than 100mm of
stroke length.
3.2.1 SINGLE ACTING CYLINDERS
A simple single acting cylinder is shown below. The cylinder is only
powered in one direction and needs another force to return it such as an external
load (e.g. in a car hoist or jack) or a spring. No hydraulic fluid is present on the
low pressure side.
Figure 3.1 SINGLE ACTING CYLINDER
3.2.2 DOUBLE-ACTING CYLINDERS
Double-acting cylinders (DAC) use the force of air to move in both extends
and retract strokes. They have two ports to allow air in, one for outstroke and one
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for in stroke. Stroke length for this design is not limited however, the piston rod is
more vulnerable to buckling and bending. Addition calculations should be
performed as well.
Figure 3.2 DOUBLE ACTING CYLINDER
3.2.3 MULTI-STAGE, TELESCOPING CYLINDERS
Telescoping cylinders, also known as telescopic cylinders can be either
single or double-acting. The telescoping cylinder incorporates a piston rod nested
within a series of hollow stages of increasing diameter. Upon actuation, the piston
rod and each succeeding stage "telescopes" out as a segmented piston. The
main benefit of this design is the allowance for a notably longer stroke than would
be achieved with a single-stage cylinder of the same collapsed (retracted) length.
One cited drawback to telescoping cylinders is the increased potential for piston
flexion due to the segmented piston design. Consequently, telescoping cylinders
are primarily utilized in applications where the piston bears minimal side loading.
3.2.4 RODLESS CYLINDERS
Some rod less types have a slot in the wall of the cylinder that is closed off
for much of its length by two flexible metal sealing bands. The inner one prevents
air from escaping, while the outer one protects the slot and inner band. The
piston is actually a pair of them, part of a comparatively long assembly. They seal
to the bore and inner band at both ends of the assembly. Between the individual
pistons, however, are clamming surfaces that "peel off" the bands as the whole
sliding assembly moves toward the sealed volume, and "replace" them as the
assembly moves away from the other end. Between the clamming surfaces is
part of the moving assembly that protrudes through the slot to move the load. Of
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course, this means that the region where the sealing bands are not in contact is
at atmospheric pressure.
Another type has cables (or a single cable) extending from both (or one)
end[s] of the cylinder. The cables are jacketed in plastic (nylon, in those referred
to), which provides a smooth surface that permits sealing the cables where they
pass through the ends of the cylinder. Of course, a single cable has to be kept in
tension.
Still others have magnets inside the cylinder, part of the piston assembly,
that pull along magnets outside the cylinder wall. The latter are carried by the
actuator that moves the load. The cylinder wall is thin, to ensure that the inner
and outer magnets are near each other. Multiple modern high-flux magnet groups
transmit force without disengaging or excessive resilience.
3.2.5 OTHER TYPES
Although SACs and DACs are the most common types of pneumatic
cylinder, the following types are not particularly rare.
Through rod air cylinders: piston rod extends through both sides of the
cylinder, allowing for equal forces and speeds on either side.
Cushion end air cylinders: cylinders with regulated air exhaust to avoid
impacts between the piston rod and the cylinder end cover.
Rotary air cylinders: actuators that use air to impart a rotary motion.
Rod less air cylinders: These have no piston rod. They are actuators that
use a mechanical or magnetic coupling to impart force, typically to a table
or other body that moves along the length of the cylinder body, but does
not extend beyond it.
Tandem air cylinder: two cylinders are assembled in series in order to
double the force output.
Impact air cylinder: high velocity cylinders with specially designed end
covers that withstand the impact of extending or retracting piston rods.
From the various type of cylinder, the double acting cylinder is most
suitable for our problem since it requires only two motions forward stroke and
reverse stroke.
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3.3 PARAMETERS
3.3.1 FORCE
The fluid pushes against the face of the piston and produces a force. The
force produced is given by the formula:
F = p x A
p is the pressure in N/m2 and A is the area the pressure acts on in m2.
This assumes that the pressure on the other side of the piston is
negligible. The diagram shows a double acting cylinder. In this case the pressure
on the other side is usually atmospheric so if p is a gauge pressure we need not
worry about the atmospheric pressure.
Figure 3.3 WORKING PRINCIPLE OF CYLINDER
Let A be the full area of the piston and’ a’ be the cross sectional area of
the rod. If the pressure is acting on the rod side, then the area on which the
pressure acts is (A - a).
F = p x A on the full area of piston.
F = p x (A-a) on the rod side.
This force acting on the load is often less because of friction between the
seals and both the piston and piston rod.
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3.3.2 SPEED
The speed of the piston and rod depends upon the flow rate of fluid. The
volume per second entering the cylinder must be the change in volume per
second inside. It follows then that:
Q m3/s = Area x distance moved per second
Q m3/s = A x velocity (full side)
Q m3/s = (A-a) x velocity (rod side)
Note in calculus form velocity is given by v = A dx/dt and this is useful in
control applications. In the case of air cylinders, it must be remembered that Q is
the volume of compressed air and this changes with pressure so any variation in
pressure will cause a variation in the velocity.
3.3.3 POWER
Mechanical power is defined as Force x velocity. This makes it easy to
calculate the power of a cylinder. The fluid power supplied is more than the
mechanical power output because of friction between the sliding parts.
P = F x v Watts 3.4 DESIGN CONSIDERATIONS
3.4.1 BODY
Depending on the job specification, there are multiple forms of body
constructions available
Tie rod cylinders: The most common cylinder constructions that can be
used in many types of loads. Has been proven to be the safest form.
Flanged-type cylinders: Fixed flanges are added to the ends of cylinder;
however, this form of construction is more common in hydraulic cylinder
construction.
One-piece welded cylinders: Ends are welded or crimped to the tube; this
form is inexpensive but makes the cylinder non-serviceable.
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Threaded end cylinders: Ends are screwed onto the tube body. The
reduction of material can weaken the tube and may introduce thread
concentricity problems to the system.
Tie rod cylinder is selected for our application since it is the most suitable
to the given problem.
3.4.2 MATERIAL
Upon job specification, the material may be chosen. Material ranges from
nickel-plated brass to aluminium, and even steel and stainless steel. Depending
on the level of loads, humidity, temperature, and stroke lengths specified, the
appropriate material may be selected
3.4.3 ENG FIXINGS
Depending on the location of the application and machinability, there exist
different kinds of mounts for attaching pneumatic cylinders. The different types
are
Direct Rear
Direct Foot
Front Flange
Rear Pivot
Trunion
Screwed Front
The direct foot is selected for our problem since it is the only suitable way
of supporting the cylinders by placing it on a table at a suitable height based on
the operation carried out.
3.4.4 CYLINDER SPEED CONTROL
The basic method of controlling the speed is by controlling the flow in or
out of the cylinder. The simplest way is to place a restrictor port but this reduces
the thrust and wastes energy through friction. This problem can be overcome and
the speed can be controlled using a quick exhaustive valve.
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3.4.5 SIZE
Air cylinders are available in a variety of sizes and can typically range from
a small 2.5 mm air cylinder, which might be used for picking up a small transistor
or other electronic component, to 400 mm diameter air cylinders which would
impart enough force to lift a car. Some pneumatic cylinders reach 1000 mm in
diameter, and are used in place of hydraulic cylinders for special circumstances
where leaking hydraulic oil could impose an extreme hazard.
Considering the forming operation of c v disc, a cylinder of diameter 40
mm with a stroke length of 500 mm may be used. Similarly the forming operation
of tractor disc, a cylinder of diameter 50 mm with a stroke length of 800 mm may
be used.
Two quick exhaustive valves are used; one for each cylinder and a shock
absorber is used for the cylinder with diameter of 50 mm. Four linear motion
bearing, in which two bearings are of diameter 40 mm and remaining two bearing
of diameter 50 mm are connected to the 40 mm and 50 mm cylinder respectively.
The guide shafts are connected to the respective cylinder through the bearings.
3.5 CALCULATIONS
3.5.1 TRACTOR DISC OPERATION
Weight of the work piece = 50 Kgs
Force = 50 x 9.8 x 1.5 (FoS) = 735.75 N
Pressure = 4 bars = 4 x 100000 = 400000 N/m2
Area of the cylinder = 735.75/40000 = 0.001839375 m2
Diameter of the cylinder = 48.39 mm = 50 mm
3.5.2 CV DISC OPERATION
Weight of the work piece = 40 Kgs
Force = 40 x 9.8 x 1.5 (FoS) = 441.45 N
Pressure = 4 bars = 4 x 100000 = 400000 N/m2
Area of the cylinder = 441.45/40000 = 0.001103625 m2
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Diameter of the cylinder = 37.49 mm = 40 mm
The schematic diagram of the automated unloader is shown in the figure 3.4
Figure 3.4 AUTOMATED UNLOADER
3.6 BILL OF MATERIAL
Table 3.1 BILL OF MATERIALS
SL.NO SPARES QUANITY
1 CYLINDER FESTODNC-40-500-PPV-A 163348 1
2 CYLINDER PNEUM FESTO DNC 50*800 PPV-A 1
3 LM BRG FOR PICK PLACE LMF 30UU (B31) 2
4 LM BRG LMF40 2
5 QUICK EXHAUST VALVE FESTO SEU-1/4 6753 4
6 SHOCK ABSORBER YSR-20-25-C FESTO 34574 2
7 GUIDE SHAFT 2
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3.7 COMPARISON The changes achieved before and after implementing the automation system is mentioned in the figure 3.5. Moreover by changing the conveyor system connecting the two presses in which forming and piercing operation is carried out has to be changed. By changing the position of the conveyor belt the setup time for CV and tractor disc operation can reduced significantly
Figure 3.5 PERFORMANCE COMPARISON
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Figure 3.6 LAYOUT OF CONVEYOR SYSTEM BEFORE CHANGES
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Figure 3.7 LAYOUT OF CONVEYOR SYSTEM AFTER CHANGES
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1. Loading conveyor 2. Unloading conveyor for tractor wheel 3. 1500T loading conveyor 4. Unloading conveyor for CV 5. Common unloading conveyor
The tractor wheel disc has to be unloaded manually by two operators. The
two operators who places the blank inside the forming machine has to push the
disc after the operation has been completed so that the work piece falls on the
conveyer system which carries it to the next operation. The systematic
representation of this process is mentioned below.
Figure 3.8 FORMING OPERATION OF TRACTOR DISC (EXISTING)
The c v disc has to be unloaded manually by the operator. The operator has to pull the work piece and let it place on the conveyer system which carries it to the next operation. The systematic representation of this process is mentioned below
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Figure 3.9 FORMING OPERATION OF CV DISC (EXISTING) Now by adding the newly designed automation system the operators need not push the disc each time after the forming operation is completed. The schematic representation of CV reverse forming operation is shown below.
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Figure 3.10 FORMING OPERATION OF TRACTOR AND CV DISC(AFTER AUTOMATION)
3.8 RESULT After the corrective actions are made in the manufacturing line, the line is run for one week and the results are given in the figure 3.11
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Figure 3.11 COMPARISON OF CYCLE TIME
The schematic representation of the automated system for CV disc and tractor disc are represented in figure 3.12 And figure 3.13 respectively
Figure 3.12 UNLOADER FOR CV DISC FORMING OPERATION
