Term Project
Modeling Analysis of Manufacturing Systems
Ernesto Gutierrez-Miravete
Bryan Baker
April 12, 2001
Table of Contents:
Body of report……………………………………………………………………………..3
Abstract…………………………………………………………………………..3
Table 1: Layout comparison……………………………………………………..4
Table 2: Operating times…………………………………………………………5
Table 3: Demand………………………………………………………………….6
Table 4: Theoretical Machine Lower Bound……………………………………..7
Table 5: Actual Machine Lower Bound…………………………………..8
Table 6: Part Assignment…………………………………………………9
Table 7: Results comparison……………………………………………………..10
Appendix:………………………………………………………………………………….12
Cell Unit A- Grinding Model 1 no buffer…………………………………………………13
Layout…………………………………………………………………………….14
Output from ProModel……………………………………………………………15
Cell Unit A- Grinding Model 2 modified layout with buffer………………………………17
Layout…………………………………………………………………………….18
Text Listing of Model…………………………………………………………….19
Output from ProModel……………………………………………………………24
Cell Unit C- Hole Drilling Model 3 no buffer………………………………………………27
Layout…………………………………………………………………………….28
Text Listing of Model…………………………………………………………….29
Output from ProModel……………………………………………………………32
Cell Unit C- Hole Drilling Model 4 modified layout with buffer …………………………37
Layout…………………………………………………………………………….38
Text Listing of Model…………………………………………………………….39
Output from ProModel……………………………………………………………43
Cell Unit C- Hole Drilling Model 4 modified layout with 1 laser buffer………………… 45
Text Listing of Model…………………………………………………………….46
Output from ProModel……………………………………………………………49
Cell Unit D- Finishing Model 5 no buffer…………………………………………………51
Layout…………………………………………………………………………….52
Text Listing of Model…………………………………………………………….53
Output from ProModel……………………………………………………………56
Cell Unit D- Finishing Model 6 modified layout with buffer………………………………58
Layout…………………………………………………………………………….59
Text Listing of Model…………………………………………………………….60
Output from ProModel……………………………………………………………64
2
Cell Layout and Performance
Term Project
Modeling Analysis of Manufacturing Systems
Bryan Baker
April 12, 2001
1 Abstract
This paper describes an analysis of the performance of a manufacturing cell in the Pratt &
Whitney Turbine Module Center. Since the cell is moving to East Hartford, the opportunity is
available to change the layout in order to maximize performance. Its previous layout was more
geared toward cellular manufacturing, however some performance was lacking due to some dated
equipment. The analysis will include verification of layout type best suited for the desired
throughput of product in order to meet customer demand. Some of the different types of layouts
that can be focused on include Product Layout, Process Layout, and cellular layout, or Group
Technology.
In Product Layout, the machines are placed according to the necessary product being produced.
They are usually dedicated to producing a fewer number of parts and have the necessary
equipment to complete that part from start to finish. Most often called Flow Lines, because the
product flows from one operation to the next, the equipment in Product layout can also be seen as
“dedicated” equipment and are set up more conveniently for mass production.
Another type of equipment layout is the Process layout, also known as a job shop. Process layout
is usually necessary when parts are not necessarily mass produced, and the equipment needs to be
able to perform a higher variety of operations on a variety of different parts. The equipment is
usually located in like departments or with the same processing needs. The equipment for
producing the above mentioned part will be laid into a footprint with like equipment being
grouped together. This will allow a more flexible work system but the parts may not all follow the
same route through the departments.
The third possible layout is Group technology or cellular manufacturing. Cellular layout of
equipment seems to take the best of both layout types of Process and Product. A cell is usually
laid out with just the equipment to produce a certain part. Difficulties can arise when attempting
to use cell layout, however. Cellular layout may depend more on technology needed to
accomplish certain operations or to achieve better flow of parts. Layout of equipment to facilitate
good floe of parts through the cell may sometimes prove to be difficult. A cell for the Turbine
Module center High Pressure Turbine manufacturing operations will be set up as effectively as
possible for the different needs for each of the three parts that will be analyzed.
2 Comparison of types:
Some advantages of Product Layouts are low throughput time, and low Work In Process
inventories. Product layouts also have advantages of being able to keep WIP at lowest levels to
avoid inventory costs, storage costs, movement, damage, etc. However, in flow lines such as
3
these, equipment is usually completely tailored to the production of one or few products, and
thus, are very difficult to adapt to other parts.
Advantages of using Process layout seem to lie mostly in transfer of technology readily and
easily. With equipment and processes being located together problems can be addressed more
quickly by Engineering personnel. Other advantages include higher flexibility of machinery and
flexibility for producing different parts more easily. Usually, more skilled operators are assigned
to each area and can also perform each task more effectively. Some fallbacks of Process layout
are part flow through the department is sometimes confusing, and also depends on exactly what
each part needs, and is usually different for each part.
Cell Layouts can be advantageous in the fact that they take advantage of some of the strengths of
both of the other layouts. However, sometimes more technologically advanced equipment is
needed to perform some of these operations and still keep part flow through the cell uniform.
Cell Layouts are usually dedicated to a family of parts and have some flexibility, but to some
extent. Cells are not geared toward mass production like the Product layout, but usually have the
capability of producing parts much faster than the Process Layout or the Job Shop.
These advantages and Disadvantages can be summarized in the table below as seen in Askin and
Standridge pp. 11:
Characteristic
Product
Process
Group
Throughput time
Low
High
Low
WIP
Low
High
Low
Skill Level
Choice
High
Med-High
Product Flexibility
Low
High
Med-High
Machine Utilization
High
Med-Low
Med-High
Worker Utilization
High
High
High
Unit Production Cost
Low
High
Low
Table 1: Layout comparisons
To simplify the problem and the model significantly, only three of the higher volume parts that
are manufactured by the cell will be looked at to determine optimal layout and cell efficiency.
There are many ways that cell efficiency could be improved, but some of the specific ways that
are applicable to this problem, are buffer location and shop scheduling, since only part of the
product line will be looked at. Some of the simplification to the problem is also assisted by new
machining equipment that will be integrated in to the cell to help improve a more “one piece
flow” manufacturing process from start to finish. Some batch operations still exist in the cell, but
this may be able to be improved in the future by reducing cycle time or other process
improvements.
Important issues in Design, Planning and Operation of a Multiple cell manufacturing system.
Major issues in design of cells comes about is the allocation of function and products to cells, this
4
in turn actually determines the overall structure of the cell. Which determines which cells will be
connected by flows of parts and products.
3 Theoretical Modeling
In this example, a bit simplified due to number of parts, the Parts chosen for the cell are all High
Thrust parts. The three parts that are looked at are from the same family of parts from the same
engine. They are also from the same turbine stage, with slight modifications to cooling and hole
requirements. Another difference between the parts is the coating that the parts receive. These
processes are still to be done in a different department since small cellular friendly equipment and
technology is not available for us at this point. The coating processes will not be analyzed, but
will be assumed to meet demand so as not to hinder the final section of the cell
Another important factor of the design stage of a cell is the allocation of machines. Allocation of
machinery is to decide on the number of machines that will be located and used in the cell and the
number of workers that will be available necessary to run the machines for the cell. Larger cells
tend to have a wide variety of parts produced in them, but in the case at hand, only 3 will be
analyzed.
Since the cell is actually a collaboration of machining, hole drilling, and finish equipment, and
not all three parts go through every operation, then the cell will be modeled using three separate
modeling systems and analyses for the three parts examined. The first part of the cell deals
mostly with the machining of the parts. The second part of the cell deals with the hole drilling of
the parts, and the end of the cell is where all the part finishing is performed. It will be easier to
see where inefficiencies lie by separating the cell into units. The designation for the cell units
will be referred to as Unit A - Grinding, Unit C – Hole Drilling, and Unit D – Finishing, which
can all be seen in the appendix on pages 11, 21, and 36 respectively. First we look at cycle times
for the parts vs. operations that need to be performed to find an average wait time for the parts.
The operation times for the three different parts can be seen in the table below.
Cell Unit A - Grinding
Dept
Operation (min)
Blade1
(52L472)
2754-A WIRE EDM"V" NOTCHES
15.000
2754-A CMM INSPECT EDM NOTCHES
2.000
2754-A FILL TURBINE BLADE WITH
3.000
POLYETHYLE
2754-A GRIND ROOT FACES
3.830
2754-A GRIND MATE FACES
3.890
2754-A GRIND CC & CV ROOT SERRATION
3.890
2754-A GRIND BOTTOM OF ROOT AND
3.800
AIRFOIL T
2754-A GRIND SEALS
3.500
2754-A Forced air to remove excess coolant
3.400
(DRY)
2754-A BUFF EDGES OF ROOT SERRATIONS 1.380
AND
2754-A IN-LINE INSPECTION OF MACHINED
1.800
FEA
2754-A BAKE TO REMOVE POLY FILL
2.000
2754-A BREAK EDGES, ROOT BOTTOM
1.380
Blade2
(53L822)
Blade3
(54L422)
Wt.
Average
15.000
2.000
3.000
15.000
2.000
3.000
15.000
2.000
3.000
3.800
3.890
3.890
3.890
3.800
3.890
3.890
3.800
3.810
3.890
3.890
3.830
3.500
3.500
3.500
3.500
3.500
3.467
1.380
1.380
1.380
1.600
1.800
1.733
2.000
1.380
2.000
1.380
2.000
1.380
5
2754-A INSPECT & MARK ,
2754-A INSPECTION CODE 5
1.200
1.500
1.200
1.350
1.200
1.400
Cycle time
1.200
1.417
51.497
3.000
3.000
3.000
3.000
7.651
7.320
0.000
9.437
2.000
2.000
2.000
2.000
0.780
0.780
0.000
0.520
0.870
0.000
0.000
0.290
Cycle time
15.247
Cell Unit C – Hole Drilling
2754-C FILL TURBINE BLADE WITH
POLYETHYLE
2754-C LASER DRILL (63) AIRFOIL HOLES
PER
2754-C BAKE TO REMOVE BACKING
MATERIAL F
2754-C AIRFLOW LASER DRILLED HOLES
PER PO
2754-C REMOVE RAISED EDGES FROM
LASER DRI
Cell Unit D - Finishing
2754-D PRECIPITATION HEAT TREAT PER
PWA 1
2754-D REMOVE OXIDE ON END OF ROOT
2754-D SHOT PEEN BLADE ROOT PER
NMOP-0016
2754-D X-RAY BLADE
2754-D WELD COVER TO BLADE PER SPEC.
PWA
2754-D WATERFLOW BLADE FOR
OBSTRUCTIONS
2754-D AIRFLOW ALL AIRFOIL HOLES
2754-D FINAL INSPECTION
9.910
9.910
9.910
9.910
0.410
0.684
0.410
0.684
0.410
0.684
0.410
0.684
0.880
1.300
0.880
1.300
0.880
1.300
0.880
1.300
0.590
0.590
0.590
0.590
0.780
0.800
0.780
0.700
0.780
0.800
Cycle time
0.780
0.767
15.321
Table 2: Operation Times
For each unit of the cell being analyzed, machine cycle time, operation assignment to
workstations, part sequence for production, and buffer sizes will need to be looked at in order to
provide a better understanding of the requirements for complete cell layout. ProModel can help
to assess this information, but first a more theoretical approach will be taken, then Promodel will
be used to verify the findings and recommendations.
To understand how to start assigning machines and product in order to produce an estimate for
layout, demand of the product must be known. From this, cycle time, and machine requirements
can then be determined. Demands for the particular three blades in review are as follows:
Part
Blade 1
Blade 2
Blade 3
Avg. Weekly demand
320
230
290
Table 3: Demand
Deviation +/- (10%)
32
23
29
If the production is targeted toward the higher end of the demand, then there will tend to be too
much idle time. However, on the other hand, if the production rate is targeted toward the lower
end of the demand, then there will not be enough available time on the machines to do all the
6
work. For this reason average demand per week will be used and when necessary, overtime can
be used if necessary to account for the higher demand periods.
Demands for the different parts are independent so variances can be found using the formula:
(b  a) 2
var( X ) 
12
For X, a random variable uniformly distributed between a and b. Since demand for the different
parts varies approximately ten percent from the average demand for the part, total weekly demand
variance, Y, is found to be:
var(Y ) 
(352  288) 2  (253  207) 2  (319  261) 2
 798
12
Since the standard deviation is approximately 30, the guideline that will be used for target
capacity will be average demand plus 2 standard deviations. This gives a good estimate for target
capacity of: 840 + 2(29) = 898
This information can be used to compute average cycle time, however weekly available time
must be determined. Working time will be estimated at 8 hours per shift,2 shifts per day, 5 days
per week, with only 2 fifteen-minute breaks per shift. This gives total available minutes per week
of approximately 4500. Calculating cycle time based on the demand yields:
c
4500
 5.011 min
898
Using the average processing time as seen in the first table, the lower bound on number of
workstations needed to perform each operation in order to meet the demand can be calculated.
The lower bound provided that all the operations could be done on the same machines would
simply be calculated as processing time divided by cycle time shown in the table below.
Cell Unit
Processing time
Cycle time
Lower Bound
(min)
A- Grinding
51.497
15.41
10.276
C – Hole Drilling 15.247
15.41
3.0427
D - Finishing
15.3211
15.41
3.057
Table 4: Theoretical Machine Lower Bound
Rounding the lower bound to the highest whole number would yield 11, 4, and 4 machines
respectively.
However, since not all of the operations can be done on similar machines, the lower bound of
equipment needed must be calculated for each different operation. The chart below shows the
lower bound of machines for the operations in each of the four cell units.
7
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
WIRE EDM"V" NOTCHES
CMM INSPECT EDM NOTCHES
FILL TURBINE BLADE WITH
POLYETHYLE
GRIND ROOT FACES
GRIND MATE FACES
GRIND CC & CV ROOT SERRATION
GRIND BOTTOM OF ROOT AND
AIRFOIL T
GRIND SEALS
Forced air to remove excess coolant
(DRY)
BUFF EDGES OF ROOT
SERRATIONS AND
IN-LINE INSPECTION OF
MACHINED FEA
BAKE TO REMOVE POLY FILL
BREAK EDGES, ROOT BOTTOM
INSPECT & MARK ,
INSPECTION CODE 5
FILL TURBINE BLADE WITH
POLYETHYLE
LASER DRILL (63) AIRFOIL HOLES
PER
BAKE TO REMOVE BACKING
MATERIAL F
AIRFLOW LASER DRILLED HOLES
PER PO
REMOVE RAISED EDGES FROM
LASER DRI
PRECIPITATION HEAT TREAT PER
PWA 1
REMOVE OXIDE ON END OF ROOT
SHOT PEEN BLADE ROOT PER
NMOP-0016
X-RAY BLADE
WELD COVER TO BLADE PER
SPEC. PWA
WATERFLOW BLADE FOR
OBSTRUCTIONS
AIRFLOW ALL AIRFOIL HOLES
FINAL INSPECTION
Machine lower bound
Average processing 3 Shifts 2 shifts 1 shift
time
15.00
2
3
6
2.00
1
1
1
3.00
1
1
2
3.81
3.89
3.89
3.83
1
1
1
1
1
1
1
1
2
2
2
2
3.50
3.47
1
1
1
1
2
2
1.38
1
1
1
1.73
1
1
1
2.00
1.38
1.20
1.42
48.15
3.00
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
9.44
2
2
4
2.00
1
1
1
0.52
1
1
1
0.29
1
1
1
15.25
9.91
2
2
4
0.41
0.68
1
1
1
1
1
1
0.88
1.30
1
1
1
1
1
1
0.59
1
1
1
0.78
0.77
1
1
1
1
1
1
Table 5: Actual Machine Lower Bound
8
The machines needed in case management decided to try to squeeze production down to only one
shift is shown for verification that 2 shifts are needed. The cost of all the extra machines needed
would not greatly outweigh the savings in workforce for manning a second shift.
Assigning operations to workstations then becomes a simple task, since most of the operations
can only be run on one piece of equipment. The only operations where multiple machines are
needed are operation 1, operation 17, and operation 21. The assignment of parts to these
machines becomes pretty simple also, since there are only three parts to go through operation 1, 2
parts to go through operation 17, and all three parts to go through operation 21. The assignment
will be as follows:
Operation 1
Operation 17
Operation 21
Part 1
Part2
EDM 1
EDM 2
Laser 1
Laser 2
PHT 1
PHT2
Table 6: Part Assignment
Part3
EDM 3
PHT3
Scheduling parts through the shop is also another large factor in maintaining the efficiency and
meeting customer demand, and since the current layout is to be compared to any improvements
that can be made, the layout is modeled in Promodel first as it currently is. Additions and layout
changes can then be analyzed to improve the efficiency of the cell to meet demand. For the
starting layout for each unit of the cell refer to Models 1, 3, and 5.
4 Simulation Modeling
For modeling purposes, ProModel will be used, and is a computer simulation of a discreet event
simulation. Discreet Event Simulation is basically a snapshot in time where a system, or entities,
changes due to events at a particular instant of time. In the case at hand our entities are the
machines, and the particular changes at a particular part of time is really part movement. The
addition and placement of buffers will allow the changes to be viewed and tracked over time to
see whether performance meets the demand.
All Models are numbered and can be seen in the Appendix.
Unit A - Grinding: Model 1 no buffers, and Model 2 with buffers
For the grinding Unit, or front end of the cell, the layout was modeled in general layout criteria
for a U shaped flow of work through the cell. The in coming and outgoing area was put on the
right to be closer to the incoming and outgoing areas of Unit C – Hole Drilling. From running the
model first with no buffers, poor performance is seen. The idle times for machinery can be seen
as all being greater than 50% and the throughput is poor, and definitely does not meet customer
requirement. The cell only produced 248, 177, and 117 of the three parts, where 320, 230, and
290 were required. In its current layout, the cell is not meeting customer demand.
Great blockages can also be seen, and to improve this, buffers are added to the three EDM
machines, and to the PolyFill machine. The throughput is greatly improved as well as blockage
and as well as machine usage, but maximum usage for the EDM equipment was still around 75%,
and the PolyFill machine still showed some blockage. Layout was changed slightly to help close
distance between equipment and provide a better routing for the parts, but the cell is still not
meeting customer demand, with only 220, 222, and 220 delivered. As mentioned before, there
9
may have to be some overtime used here to meet customer demand. Modeling the output over
three shifts per day gives ample time to meet customer demand.
Unit C – Hole Drilling: Model 3 no buffers, and Model 4 with buffers
The Hole drilling Unit shows similar blockages and low utilization with no buffers. The unit is
much smaller and less complex than the Grinding Unit, but still gets much improvement from the
use of buffers. The best location for the buffers is located between the PolyFill workstation and
the Laser Drilling machines. This improves efficiency significantly to well over the
requirements. The cell actually is capable of drilling 448 and 446 parts in this configuration.
Since the throughput and machine usage went up so drastically for this Unit, the cell is modeled
with only 1 laser to see if only one piece of equipment could be used to meet customer demand.
The one laser however only is capable of producing about 132 and 113 parts respectively, unless
more shifts were used to run the equipment. This would increase cost, and since the equipment is
already in house, the operating cost for more shifts is not justified when compared to machine
operating costs for the second machine. Utilization’s are still around 50 percent which leaves
room for more product to be drilled, along with future parts and demand.
Unit D – Finishing: Model 5 no buffers, and Model 6 with buffers
The finishing end of the cell Model 5, as looked at in the actual existing layout, seems a bit
cumbersome due to part travel locations. The cell is not laid out for uniform flow of each part.
The PHT operations are located on the end away from the rest of the cell due to the fact that the
temperature they operate at was deemed undesirable for inner cell safety. The End of the cell also
receives product from the coating units located toward the end of the cell from the various coating
departments. As shown in the machine lower bounds previously calculated, three furnaces are
theoretically needed to provide enough capacity to keep throughput high enough to meet
customer demand. However, in the non-buffered state the best efficiency is around 65 percent.
For a bottleneck operation such as this, it is critical that the furnaces receive work in a better
fashion to keep them loaded at a higher, more efficient rate.
The Layout was then changed to provide the cell with more uniform flow to accommodate the
three parts being analyzed, and to include buffers to more effectively use the bottleneck
operations. As shown in Model 6, the buffers are placed before the PHT furnaces and before the
next highest bottleneck operation, the PolyFill station. This then raises efficiency significantly to
445, 447, and 444 for the week for the three different parts!
The summary of the findings from the models can be shown in the table below:
Unit A
Unit C
Unit D
Throughput – Throughput –
Buffer
No buffer
With buffers
Locations
(part 1,2,3)
(part 1,2,3)
248,177,117
220,222,220
EDM, Polyfill
132,113
448,446
Laser, Polyfill
265,196,184
445,447,444
PHT, Polyfill
Table 7: Results comparison
Demand
320,230,290
320,230,290
320,230,290
Machine
usage before
50%
23%
65%
Machine
usage - after
75%
97%
98%
10
5 Conclusion and Discussion
The production cell to produce the demanded quantity of product is still best configured in a
cellular type layout. It actually ends up to be more of a combination between Product Layout
and Process Layout. The layout may also change a bit if other parts were looked at.
The best configuration for the Grinding Unit, however, is the only part of the cell that was still
struggling to meet demand. Since the demand was actually targeted lower than the maximum,
then it may be possible to use over time to take care of some of these issues. Possibly since there
were some issues with blockage of PolyFill, the parts could be done on the machine in the Hole
Drilling unit. The travel distance would go up but since travel time was modeled to be relatively
high, this may not matter.
The Hole Drilling Unit and the Finishing Unit succeeded immensely in improving efficiency
simply by strategically adding large buffers to the higher processing time or bottleneck
operations. With production levels capable of much more than the demand, it may be wise to
scale back in order to more effectively use the equipment. Unfortunately there were many
operations which could not be performed on other equipment.
There appears to be quite a bit of idle time on machines. Part of the reason for this could be that
there are only two part numbers being looked at in the model, but the machines should not be idle
with the production rate turned up to what normal production levels would look like with all the
parts combined.
Layout and Buffer size and location is to be modeled in ProModel to verify the best location to
maximize cell throughput. Modeling cells like this in ProModel significantly helps plan a cell
layout, and can start to maximize efficiency even before machines hit the floor.
11
Appendix:
12
Unit A – Grinding Model 1
13
Unit A – Grinding Model 2
14
Unit C – Hole Drilling Model 3
15
Unit C – Hole Drilling Model 4
16
Unit D – Finishing Model 5
17
Unit D – Finishing Model 6
18