Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
1
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
ME6703 COMPUTER INTEGRATED MANUFACTURING SYSTEMS
UNIT III - CELLULAR MANUFACTURING Group Technology(GT), Part Families – Parts Classification and coding – Simple Problems in Opitz Part
Coding system – Production flow Analysis – Cellular Manufacturing – Composite part concept – Machine
cell design and layout – Quantitative analysis in Cellular Manufacturing – Rank Order Clustering Method -
Arranging Machines in a GT cell – Hollier Method – Simple Problems.
TEXT BOOK:
1. Mikell.P.Groover “Automation, Production Systems and Computer Integrated Manufacturing”, Prentice Hall of India, 2008. 2. Radhakrishnan P, Subramanyan S.and Raju V., “CAD/CAM/CIM”, 2nd Edition, New Age International (P) Ltd, New Delhi, 2000.
REFERENCES:
1. Kant Vajpayee S, “Principles of Computer Integrated Manufacturing”, Prentice Hall India, 2003.
2. Gideon Halevi and Roland Weill, “Principles of Process Planning – A Logical Approach” Chapman & Hall, London, 1995.
3. Rao. P, N Tewari &T.K. Kundra, “Computer Aided Manufacturing”, Tata McGraw Hill Publishing Company, 2000.
4.V.Jayakumar, “Computer Integrated Manufacturing”, Lakshmi Publications.
UNIT III CELLULAR MANUFACTURING
What is Group Technology (GT)?
GT is a theory of management based on the principle that similar things should be done similarly
GT is the realization that many problems are similar, and that by grouping similar problems, a single
solution can be found to a set of problems thus saving time and effort
GT is a manufacturing philosophy in which similar parts are identified and grouped together to take
advantage of their similarities in design and production
Where to implement GT?
Plants using traditional batch production and process type layout
2
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
If the parts can be grouped into part families
How to implement GT?
Identify part families
Rearrange production machines into machine cells
Types of Layout
In most of today’s factories it is possible to divide all the made components into families and all the machines
into groups, in such a way that all the parts in each family can be completely processed in one group only.
The three main types of layout are:
• Line (product) Layout
• Functional Layout
• Group Layout
Line (product) Layout
• It involves the arrangements of machines in one line, depending on the sequence of operations. In
product layout, if there is a more than one line of production, there are as many lines of machines.
• Line Layout is used at present in simple process industries, in continuous assembly, and for mass
production of components required in very large quantities.
Functional Layout
• In Functional Layout, all machines of the same type are laid out together in the same section under the
same foreman. Each foreman and his team of workers specialize in one process and work independently.
This type of layout is based on process specialization.
3
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Group Layout
• In Group Layout, each foreman and his team specialize in the production of one list of parts and co-
operate in the completion of common task. This type of layouts based on component specialization.
The Difference between group and functional layout:
4
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Process flow before the group technology
Process flow after the group technology
5
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Identifying Part Families
Large manufacturing system can be decomposed into smaller subsystems of part families based on similarities
in 1. Design attributes and
2. Manufacturing features
1. Design Attributes:
part configuration (round or prismatic)
dimensional envelope (length to diameter ratio)
surface integrity (surface roughness, dimensional tolerances)
material type
raw material state (casting, forging, bar stock, etc.)
2. Part Manufacturing Features:
Operations and operation sequences (turning, milling, etc.)
batch sizes
machine tools
cutting tools
work holding devices
6
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
processing times
Group technology emphasis on part families based on similarities in design attributes and manufacturing,
therefore GT contributes to the integration of CAD and CAM.
Part Families
A part family is a collection parts having similar design characteristics or manufacturing processes
Three methods for identifying parts families
• Visual inspection
• Classification and coding
• Production flow analysis
7
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Forming Part Families –
1. Visual Inspection Method
incorrect results
human error
different judgment by different people
inexpensive
least sophisticated
good for small companies having smaller number of parts
Forming Part Families – 2. Classification and Coding
8
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
9
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
10
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
11
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
12
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
13
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
( Eg. OPITZ coding system)
14
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Reasons for using a coding Scheme :
Selection of a coding system:
Coding systems:
15
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
i)OPITZ classification system
16
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Form Code (digits 1 – 5)
17
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Example: 1. Optiz part coding System
• Given the rotational part design below, determine the form code in the Optiz parts classification
and coding system.
18
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Solution
• Length-to-diameter ratio: L/D = 1.5 Digit 1 = 1
• External shape: both ends stepped with screw thread on one end Digit 2 = 5
• Internal shape: part contains a through hole Digit 3 = 1
• Plane surface machining: none Digit 4 = 0
• Auxiliary holes, gear teeth, etc.: none Digit 5 = 0
The form code in the Optiz system is : 15100
Example: 2. Optiz part coding System
Part class:
Rotational part, L/D = 9.9/4.8 ≈ 2.0 based on the pitch circle diameter of the gear, so the first digit = 1
External shape:
The part is stepped on one side with a functional groove, so the second digit is 3
Internal shape:
The third digit is 1 because of the through hole
Plain surface machining:
The fourth digit is 0 because there is no plain surface machining
Auxiliary holes and gear teeth:
The fifth digit is 6 because there are spur gear teeth on the part
The form code in the Optiz system is : 13106
3.
19
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
L / D = 4.2 / 35 = 0.12
4.
5.
20
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Selection of Classification and Coding Systems
Identified objectives, reasons and users
Robustness and Expandability
Automation and Efficiency
Simplicity and User Interface
Cost
ii) MICLASS
21
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
iii) DCLASS coding system:
3. Forming Part Families – Classification and Coding: Production Flow Analysis (PFA)
PFA is a method for identifying part families and associated machine groupings based on the required
manufacturing processes needed for each part.
22
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
23
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
24
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
25
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
26
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
BENEFITS OF GROUP TECHNOLOGY
It affects all areas of a company, including:
engineering
equipment specification
facilities layout
process planning
production control
quality control
tool design
purchasing
service
27
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Some of the well-known tangible and intangible benefits of implementing GT :
1. Engineering design
• Reduction in new parts design
• Reduction in the number of drawings through standardization
• Reduction of drafting effort in new shop drawings
• Reduction of number of similar parts, easy retrieval of similar functional parts, and identification of
substitute parts
2. Layout planning
• Reduction in production floor space required
• Reduced material-handling effort
3. Specification of equipment, tools, jigs, and fixtures
• Standardization of equipment
• Implementation of cellular manufacturing systems
• Significant reduction in up-front costs incurred in the release of new parts for manufacture
4. Manufacturing: process planning
• Reduction in setup time and production time
• Alternative routing leading to improved part routing
• Reduction in number of machining operations and numerical control (NC) programming time
5. Manufacturing: production control
• Reduced work-in-process inventory
• Easy identification of bottlenecks
• Improved material flow and reduced warehousing costs
• Faster response to schedule changes
• Improved usage of jigs, fixtures, pallets, tools, material handling, and manufacturing equipment
6. Manufacturing: quality control
28
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
• Reduction in number of defects leading to reduced inspection effort
• Reduced scrap generation
• Better output quality
• Increased accountability of operators and supervisors responsible for quality production, making it
easier to implement total quality control concepts.
7. Purchasing
• Coding of purchased part leading to standardized rules for purchasing
• Economies in purchasing possible because of accurate knowledge of raw material requirements
• Reduced number of part and raw materials
• Simplified vendor evaluation procedures leading to just-in-time purchasing
8. Customer service
• Accurate and faster cost estimates
• Efficient spare parts management, leading to better customer service
29
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Cellular Manufacturing
Cellular manufacturing: is an application of group technology in manufacturing in which all or a
portion of a firm’s manufacturing system has been converted into cells
A manufacturing cell: is a cluster of machines or processes located in close proximity and dedicated to the
manufacturing of a family of parts
Why cellular manufacturing?
Reduce setup times: „By using part family tooling and sequencing
Reduce flow times:„By reducing setup and move times and wait time for moves and using smaller batch
sizes
Reduce inventories
Reduce lead time
Design
Machine cell Design : Types :-
Type - 1
30
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Type 2
Type 3
31
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Type 4
Best Machine Arrangement
32
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
• Design of cellular manufacturing system is a complex exercise with broad implications for an
organization.
• The cell design process involves issues related to both system structure (Structural Issues)
and system operation (Procedures Issues)
Structural issues include:
• Selection of part families and grouping of parts into families
• Selection of machine and process populations and grouping of these into cells
• Selection of tools, fixtures, and pallets
• Selection of material-handling equipment
• Choice of equipment layout
Procedural Issues include:
• Detailed design of jobs
• Organization of supervisory and support personnel
• Formulation of maintenance and inspection policies
• Design of procedures for production planning, scheduling, control, and acquisition of related
software and hardware
33
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
• Modification of cost control and reward systems
Cell Formation Approaches
1. Machine - Component Group Analysis:
Machine - Component Group Analysis is based on production flow analysis
Production flow analysis involves four stages:
Stage 1: Machine classification.
Machines are classified on the basis of operations that can be performed on them. A machine type
number is assigned to machines capable of performing similar operations.
Stage 2: Checking parts list and production route information.
For each part, information on the operations to be undertaken and the machines required to perform each
of these operations is checked thoroughly. „
Stage 3: Factory flow analysis.
This involves a micro-level examination of flow of components through machines. This, in turn, allows
the problem to be decomposed into a number of machine-component groups.
Stage 4: Machine-component group analysis.
An intuitive manual method is suggested to manipulate the matrix to form cells. However, as the
problem size becomes large, the manual approach does not work. Therefore, there is a need to develop
analytical approaches to handle large problems systematically.
Example: Consider a problem of 4 machines and 6 parts. Try to group them.
34
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Rank Order Clustering Algorithm
Rank Order Clustering Algorithm is a simple algorithm used to form machine-part groups.
Step 1: Assign binary weight and calculate a decimal weight for each row and column using the
following formulas:
Step 2: Rank the rows in order of decreasing decimal weight values.
Step 3: Repeat steps 1 and 2 for each column.
Step 4: Continue preceding steps until there is no change in the position of each element in the row and
the column.
n
1=p
m
1=p
p-m
ip
2 = jcolumn for weight
2b = i rowfor weight
pn
pjbDecimal
Decimal
35
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
36
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Exceptional parts and Bottleneck machines:
• Not always to get neat cells
• Some parts are processed in more than one cell
o Exceptional parts
o Machine processing them are called bottleneck machines
Solutions for overcoming this problem ?
• Duplicate machines
• Alternate process plans
• Subcontract these operations
Problem1:-
37
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Problem 2:-.
38
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Problem 3:-.
39
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Problem 4:-. Solve the following part – machine incidence matrix by rank order clustering method.
**
Parts 1 2 3 4 5 6 7 8 9 10 11 12
A x x x x x
B x x x x
C x x x
D x x x x x
E x x x
F x x x
G x x x x
H x x x
Machines
40
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Parts 1 2 4 8 10 3 6 9 5 7 11 12
A x x x x x
D x x x x x
F x x x
C x x x
G x x x x
B x x x x
E x x x
H x x x
Machines
Machine cell Part family
1 2 4 8 10 A D F
3 6 9 C G
5 7 11 12 B E H
Hollier Method 1.
The first method uses the sums of flow "From" and "To" each machine in the cell. The method can be outlined
as follows:
1. Develop the From—To chart from part routing data. The data contained in the chart indicates number of
part moves between the machines for workstations)
2. Determine the "From” and "To" sums for each machine. This is accomplished by summing all of the
"From" trips and "To" trips for each machine (or operation ).The "From" sum for a machine is determined by
adding the entries in the corresponding row and the "To" sum is found by adding the entries in the
corresponding column.
3. Assign machines to the cell based on minimum "From" or To sums. The machine having the smallest
sum is selected. If the minimum value is a "To" sum, then the machine is placed at the beginning of the
sequence. If the minimum value is a “From” sum, then the machine is placed at the end of the sequence. Tie breaker rules:
(a) If a tie occurs between minimum. "To" sums or minimum "From" sums, then the machine with the
minimum “From/To” ratio is selected.
(b) If both "To" and "From" sums are equal for a selected machine, it is passed over and the machine with the
next lowest sum is selected.
41
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
(c) If a minimum "To" sum is equal to a minimum "From" sum, then both machines are selected and placed at
the beginning and the end of the sequence respectively.
Reformat the From-To chart : After each machine has been selected, restructure the From-To chart by eliminating the
row and column corresponding to the selected machine and recalculate the "From" and "To" sums. Repeat steps 3 and 4
until all machines have been assigned.
Example 1: Group Technology machine Sequence using Holier Method 1 Suppose that four machines 1, 2, 3,
and 4 have been identified as belonging in a GT machine cell. an analysis of 50 parts processed on these
machines has been summarized in the From-To chart of Table 2. Additional information is that 50 parts enter
the machine grouping at machine 3, 20 parts leave after processing at machine 1 and 30 parts leave after
machine 4. Determine a logical machine arrangement using Hollier Method 1.
Solution: Summing the From trips and To trips for each machine yields the "From" and "To" sums in Table
2(a). The minimum sum value is the "To" sum for machine 3. Machine 3 is therefore placed at the beginning of
the sequence. Eliminating the row and column corresponding to machine 3 yields the revised From To chart in
Table 3 (b).
Table: 1 From-to chart for example 2
Figure: 2.a From and to some example 2:first iteration
42
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Figure: 2.b From and to some example 2:second iteration with machine 3removed
Figure: 2.c From and to some example 2: third iteration with machine 2 removed
The minimum sum in this chart is the "To" sum corresponding to machine 2, which is placed at the front of the
sequence, immediately following machine 3. Eliminating machine 2 produces the revised From-To chart in
Table 2 (c). The minimum sum in this chart is the "To" sum for machine 1. Machine 1 is placed after machine 2
and finally machine 4 is placed at the end of the sequence.
Thus, the resulting machine sequence is 3 —> 2 —> 1 --> 4
Hollier Method 2. This approach is based on the use of From/To ratios formed by summing the total flow from
and to each machine in the cell. The method can be reduced to three steps:
1. Develop the From—To chart. This is the same step as in Hollier Method 1.
2. Determine the From/To ratio for each machine. This is accomplished by summing up all of the "From"
trips and "To" trips for each machine (or operation). The "From" sum for a machine is determined by adding the
entries in the corresponding row and the "To" sum is determined by adding the entries in the corresponding
column. For each machine, the From/To ratio is calculated by taking the "From" sum for each machine and
dividing by the respective "To" sum.
3. Arrange machines in order of decreasing From/To ratio. Machines with a high From/To ratio distribute
work to many machines in the cell but receive work from few machines. Conversely machines with a low
From/To ratio receive more work than they distribute. Therefore, machines are arranged in order of descending
From/Ip ratio. That is, machines with high ratios are placed at the beginning of the work flow and machines
43
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
with low ratios are placed at the end of the work flow. In case of a tie, the machine with the higher "From"
value is placed ahead of the machine with a lower value.
Example 1: Group Technology Machine Sequence using Holler Method 2
Solve Example using Hollier Method 2.
Solution: Table 2 (a), containing the "From" and "To" sums, is repeated in Table (2) along with the From/To
ratios given in the last column on the right. Arranging the machines in order of descending From/To ratio, the
machines in the cell should be sequenced as follows:
3 —> 2 —> 1 --> 4
Table: 2 From To Sums And From/To Ratios For Examples
Figure: Flow Diagram For Machine Cell on example
It is helpful to use one of the available graphical techniques, such as the flow diagram to conceptualize the work
flow in the cell. The work flow is mostly in line; however, there is some back flow of parts that must be
considered in the design of any material handling system that might be used in the cell. A powered conveyor
would be appropriate for the forward flow between machines, with manual handling for the back flow.
For example for data in figure , Hollier Methods 1 and 2 are provide the same solution. This is not always the
case. The relative performance of the two methods depends on the given problem. In some problems Method 1
will outperform Method 2 and in other problems the opposite will happen. In many problems the two methods
yield identical solutions, as in Examples 1 and 2.
Two performance measures can be defined to compare solutions to the machine sequencing problem:
44
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
• Percentage of in-sequence moves and
• Percentage of backtracking moves.
The percentage of in sequence moves is computed by adding all the values representing in sequence
moves and dividing by the total number of moves.
The percentage of back tracking moves is determined by summing all of the values representing back
tracking moves and dividing by the total number of moves.
45
[Type text] [Type text] PEC/ME/IV YR/ 7TH SEM/CIM/KRP
Cellular layout advantages
• Reduced material handling and transit time
• Reduced setup time
• Reduced work-in-process inventory
• Better use of human resources
• Better scheduling, easier to control and automate
• Less floor space required
• Reduced direct labor
• Heightened sense of employee participation
• Increased use of equipment & machinery
• Reduced investment on machinery & equipment
Cellular layout disadvantages
• Sometimes cells may not be formed because of inadequate part families
• Some cells may have a high volume of production and others very low. This results in poorly balanced cells
• When volume of production changes, number of workers are adjusted and workers are reassigned to various cells.
To cope with this type of reassignments, workers must be multi-skilled and cross-trained
• Sometimes, machines are duplicated in different cells. This increases capital investment