Topic 4 Chapter 12.pdf

Integrated Manufacturing Systems Topic 4. PP & Control - 12. Process Planning
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Sistemas Integrados de Fabricación. UJAEN Máster en Ingeniería Industrial
1
CHAPTER 12. Analysis of Manufacturing Systems
Manufacturing Systems
Definition, components and classification
Cellular manufacturing
Group technology
Analysis of flexible manufacturing systems

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Manufacturing System
Definition: “a collection of integrated equipment and human resources that performs processing
or assembly operations”
Components
Machines,
tools,
fixtures etc
Workers
Material
Handling
system
Computer
control

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Manufacturing Systems Classification
Classification parameters
Number of workstations:
Single station n=1 (I) or Multi-station systems n>1 (II)
Station a place where an operation is performed
System layout: Fixed or Variable routing
Types of operations performed: Process or Assembly
Automation level: Manual (M), semi-automated (H), fully automated systems (A)
Manning level: proportion of time that a worker is at a station. High value  Manual
operation
Average System Manning level: M=(wu+∑ 𝑤𝑖
𝑛
𝑖 )/n, wu  utility workers manning level, wi 
workers manning level at station i, n  Number of stations
Product-Part variety:
Single (identical products-parts), Batch (different products), Mixed model (Different models)

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Fixed (a) and variable (b) routes
Automation levels

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Variety: Single (a), batch (b), mixed (c)

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Operations n Route M Variety
Single Station (I) 1
Manned workstation Process-Assembly Fixed >1 Single-Batch-Mixed
Automated workstation Process-Assembly Variable <1 Single-Batch-Mixed
Production Lines (II) >1 Fixed
Manual Assembly Lines Assembly >1 Single-Batch-Mixed
Automated Assembly Lines Assembly & process <1 Single-Mixed
Transfer lines Process <1 Single
Multi-station Cells (II) >1 Variable
Group technology machine
cell
Process >1 Mixed
Flexible Manufacturing Sys. Process <1 Mixed

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Cellular Manufacturing: Layout definition by GT
Traditional process Layout
Cellular layout

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Cellular Manufacturing: Manufacturing systems for mixed production where machines are
grouped in cells that produce a family of parts
Group Technology GT: “A manufacturing philosophy in which similar parts are identified and
grouped together to take advantage of their similarities in design and production”
 GT minimize batch production disadvantages:
o Downtime for changeovers
o High inventory costs
 GT exploits the part similarities by utilizing similar processes and tooling to produce them.
 Machines are grouped into cells, each cell specializing in the production of a part family
called cellular manufacturing.
 Cellular manufacturing can be implemented by manual or automated methods. When
automated, the term flexible manufacturing system is often applied.
GT main steps:
1. Identifying part families
2. Rearranging machines into cells.

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Part family: “A collection of parts that possess similarities in geometric shape and size, or in the
processing steps used in their manufacture”
Method to identify part families
Visual inspection
Part classification and coding: “Identification of similarities among parts and relating the
similarities by means of a numerical coding system”. Group parts with similar code
Classification based on: design attributes, manufacturing attributes, both attributes; design and
manufacturing
Example of coding system: Optiz classification system
 Digits 1 through 5 = form code – primary shape, design attributes, manufacturing features
 Digits 6 through 9 = supplementary code – attributes that are useful in manufacturing
 Digits 10 through 13 = secondary code – production operation type and sequence

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Production flow analysis: “Method for identifying part families and associated machine
groupings based on production route sheets rather than part design data”. Group parts with
similar route sheet
Advantages of using route sheet data
 Parts with different geometries may nevertheless require the same or similar processing
 Parts with nearly the same geometries may nevertheless require different processing
Main steps:
 Data collection – operation sequence and machine routing for each part (number)
 Sortation of process routings – parts with same sequences and routings are arranged into
“packs” by means of:
o PFA (Production Flow Analysis) chart – each pack is displayed on a PFA chart. Part-
machine incidence matrix
o Cluster analysis – purpose is to collect packs with similar routings into groups

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Grouping machines in cells that produce similar parts or similar part families
Manual handling system
Semi-integrated handling

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Types of part movements in a production system

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Method for grouping parts and machines: Rank Order Clustering
Idea: reduce the part-machine incidence matrix to a set of diagonalized blocks that represent
families or cells.
Steps 1. In each row of the matrix read the series of 1’s and 0's from left to right as a binary
number. Rank the rows in order of decreasing value. In case of a tie, rank the rows in the same
order as they appear in the current matrix
Step 2. Numbering from top to bottom, is the current order of rows the same as the rank order
determined in the previous step? If yes, go to step 7, If no, go to the following step.
Step 3. Reorder the rows in the part-machine incidence matrix by listing them in decreasing
rank order, starting from the top
Step 4. In each column of the matrix read the series of 1's and 0's from top to bottom as a
binary number. Rank the columns in order of decreasing value, In case of a tie rank the columns
in the same order as they appear in the current matrix.
Step 5. Numbering from left to right, is the current order of columns the same as the rank order
determined in the previous step? If yes go to step 7 If “no” go to the following step.
Step 6. Reorder the columns in the part-machine incidence matrix by listing them in decreasing
rank order, starting with the left column. Go to step 1.
Step 7. Stop

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It is not uncommon that one part needs to be processed in several groups. A way to overcome
this  placing the same machine in different cells.
Grouping efficiency Eg
𝐸𝑔 =
𝑛1 − 𝑛𝑒
𝑛1 + 𝑛0
n1  number of ones
ne  number of exceptions
n0  number of voids
Example 1. Apply the rank order clustering technique to the part-machine incidence matrix in
the following Table.
Parts
Machines A B C D E F G H I
1 1 1 1
2 1 1
3 1 1 1
4 1 1
5 1 1
6 1 1
7 1 1 1

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Method for Arranging Machines in a Logical Sequence: Hollier Method
Idea: maximize the proportion of in-sequence moves within the cell.
Step 1. Develop a From-To chart
Step 2. Determine From-To ratio
Step 3. Arrange machines in order of decreasing From-To ratio
Example 2. Determine the most logical machine sequence for the cell with a From-To chart
described in the following Table.
To
From 1 2 3 4
1 0 5 0 25
2 30 0 0 15
3 10 40 0 0
4 10 0 0 0

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Flexible Manufacturing Systems FMS
Definition: “A highly automated GT machine cell, consisting of a group of processing stations
(usually CNC machine tools), interconnected by an automated material handling and storage
system, and controlled by an integrated computer system”
FMS classification according to the number of machines
Number of Machines > 3
Machine Cell Flexible Manufacturing Cell
Flexible Manufacturing
System

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FMS Quantitative Analysis Techniques
It is a complex task
Parameters to estimate: production rate, capacity, utilization
1. Deterministic models: Bottleneck method is described in Groover (2014)
2. Queuing models
3. Discrete event simulation
4. Other approaches, including heuristics
Bottleneck method. The production system has an upper limit (determined by the bottleneck
station).
This method can be applied to every system with a bottleneck.
Notation: iStation (s stations), jpart-product (n parts), koperation (mi operations in
station i), pjpart mix (proportion of j parts), si  number of servers in station i, tijk 
processing time at ijk, fijk  frequency of operation k at ij

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Work load of station I
𝑊𝐿𝑖 = ∑ ∑ 𝑡𝑖𝑗𝑘𝑓𝑖𝑗𝑘𝑝𝑗
𝑚𝑖
𝑘
𝑛
𝑗
Work load of transport system n+1
𝑊𝐿𝑛+1 = ((∑ ∑ ∑ 𝑓𝑖𝑗𝑘𝑝𝑗
𝑚𝑖
𝑘
𝑛
𝑗
𝑠
𝑖
) − 1) 𝑡𝑛+1
tn+1 mean transport time between workstations
Performance measures:
Bottleneck station  Max {WLi/si}
Production Rate
Maximum production rate (production rate of the bottleneck station)  𝑅𝑝
∗
=s*/WL*
Production rate of part j  Rpj=pj𝑅𝑝
∗
.
Utilization
Utilization of station i  Ui=𝑅𝑝
∗
(WLi/si) Overall FMS utilization: 𝑈
̅ =
∑ 𝑠𝑖𝑈𝑖
𝑛
𝑖=1 ∑ 𝑠𝑖
𝑛
𝑖=1
⁄
Number of busy servers in station i  BSi=WLi𝑅𝑝
∗

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Example 3. An FMS consists of four stations. The stations are connected by a part handling
system that has two work carriers and whose mean transport time = 3.5 min. The FMS produces
four parts A, B, C, and D. The part mix fractions and process routings for the four parts are
presented in the table below. Station servers: s1=1, s2=3, s3=2, s4=1. Determine: (a) maximum
production rate of the FMS, (b) corresponding production rate of each part, (e) utilization of each
station in the system, and (d) the overall FMS utilization.
Part j pj k Description i tijk fijk Part j pj k Description i tijk fijk
A 0,1
1 Load 1 4 1
C 0,3
1 Load 1 4 1
2 Mill 2 20 1 2 Drill 3 23 1
3 Drill 3 15 1 3 Inspect 4 8 0,5
4 Inspect 4 12 0,5 4 Unload 1 2 1
5 Unload 1 2 1
D 0,4
1 Load 1 4 1
B 0,2
1 Load 1 4 1 2 Mill 2 30 1
2 Drill 3 16 1 3 Inspect 4 12 0,333
3 Mill 2 25 1 4 Unload 1 2 1
4 Drill 3 14 1
5 Inspect 4 15 0,2
6 Unload 1 2 1

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Problems
Problem 1. Use GT to arrange the machines of the following table in 2 cells of 3 elements with
at least Eg > 30%.
Parts
Machines A B C D E F
1 1 1
2 1
3 1 1 1
4 1 1 1 1
5 1 1 1
6 1 1 1

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Part j pj k Description i tijk
A 0,2
1 Load 1 3
2 Mill 2 20
3 Drill 3 12
4 Unload 1 2
B 0,3
1 Load 1 3
2 Mill 2 15
3 Drill 3 30
4 Unload 1 2
C 0,5
1 Load 1 3
2 Drill 3 14
3 Mill 2 22
4 Unload 1 2
Problem 2. A flexible manufacturing cell consists of 2
machining workstations plus a load/unload station. The
load/unload station is Station 1. Station 2 performs milling
operations and consists of one CNC milling machine. Station3
has one server that performs drilling (one CNC drill press). The
three stations are connected by a part handling system that
has one work carrier. The mean transport time is 2.5 min. The
FMC produces three parts: A, B, and C. The part-mix fractions
and process routings for the three parts arc presented in the
table. The operation frequency ,fijk = 1.0 for all operations.
Determine: (a) maximum production rate of the FMC, (b)
corresponding production rates of each product, (c) utilization
of each machine in the system, & (d) number of busy servers
at each station.

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Problem 3. Apply the Rank Order Clustering technique to identify logical families and cells from
the following table.
Parts
Machines A B C D E F
1 1 1
2 1 1
3 1 1
4 1 1
5 1 1
6 1 1 1

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Problem 4. Four machines used to produce a family of parts are to be arranged into a GT cell.
The From-To data for the parts processed by the machines are shown in the table below. (a)
Determine the most logical sequence of machines for this data using Hollier Method.
To
From 1 2 3 4
1 0 10 0 40
2 0 0 0 0
3 50 0 0 20
4 0 50 0 0

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