Unit 1-automation of assembly lines

LOW COST AUTOMATION
Prepared by
Dr.M. Joemax Agu, M.E, Ph.D,

UNIT-1-AUTOMATION OF ASSEMBLY
LINES

Concept of Automation
Automation can be defined as the
technology by which a process or
procedure is accomplished without
human assistance.
It is implemented using a
program of instructions
combined with a control system
that executes the instructions.

To automate a process, power
is required, both to drive the
process itself and to operate
the program and control
system.
It was in the context of
manufacturing that the term was
originally coined by an
engineering manager at Ford
Motor Company in 1946 to
describe the variety of automatic
transfer devices and feed
mechanisms that had been
installed in Ford’s production
plants

What is Low Cost
Automation ?
It is a technology that creates some degree of
automation around the existing equipment,
tool, methods, and people, using mostly
standard components available in the market.

Terms automation and
mechanization are often
compared and sometimes
confused.

Mechanization
• Mechanization refers to the use of machinery
(usually powered) to assist or replace human
workers in performing physical tasks, but human
workers are still required to accomplish the
cognitive and sensory elements of the tasks.

Automation
Automation
Refers to the use of
mechanized equipment that
performs the physical tasks
without the need for oversight
by a human worker.

The position of automation and control technologies in the larger
production system is shown in Figure

Types of Automation
• Fixed Automation
• Programmable Automation
• Flexible Automation

Fixed Automation • sequence of processing (or
assembly) operations is
fixed by the equipment
configuration.
• The operations in the
sequence are usually
simple.
• Integration and coordination of many such operations into one
piece of equipment that makes the system complex.
• Typical features are

• The economic justification for fixed automation is
found in products with very high demand rates and
volumes.
• The high initial cost of the equipment can be
spread over a very large number of units, thus
making the unit cost attractive compared to
alternative methods of production.
• Examples : Mechanized assembly and machining
transfer lines.

Programmable Automation
In this the production equipment is designed with the capability
to change the sequence of operations to accommodate different
product configurations.

• operation sequence is controlled by a program
• Set of Instructions
• New programs can be prepared and entered
into the equipment to produce new products.
• Some of the features that characterize
programmable automation are:
a. High investment in general-purpose equipment;
b. Low production rates relative to fixed automation;
c. Flexibility to deal with changes in product configuration; and
d. Most suitable for batch production.
Automated production systems that are programmable are used
in low and medium volume production.

• The parts or products are typically made in
batches.
• To produce each new batch of a different product,
the system must be reprogrammed with the set of
machine instructions that correspond to the new
product.
• The physical setup of the machine must also be
changed over:
• Tools must be loaded,
• Fixtures must be attached to the machine table
also be changed machine settings must be
entered.

Flexible Automation
NDT
• Extension of programmable automation.
• A flexible automated system is one that is capable of producing a
variety of products (or parts) with virtually no time lost for
changeovers from one product to the next.
• There is no production time lost while
reprogramming the system and altering the physical setup (tooling,
fixtures, and machine
setting).

Features of Flexible Automation
1. High investment for a custom-
engineered system.
2. Continuous production of variable
mixtures of products.
3. Medium production rates.
4. Flexibility to deal with product design
variations.
Essential features that distinguish flexible automation from
programmable automation
1. The capacity to change part programs with no lost production
time; and
2. The capability to changeover the physical setup, again with no
lost production time.

Concept of Automation in Industry
• Automated manufacturing systems operate in
the factory of physical product.
• Processing, assembly, inspection and material
handling
• Reduced level of human participation
compared with the corresponding manual
process.
• In some highly automated systems, there is
virtually no human participation.

Examples of Automated
Manufacturing System
• Automated machine tools that process parts
• Transfer lines that perform a series of machining
operations
• Automated assembly systems
• Manufacturing systems that use industrial robots
to perform processing or assembly operations
• Automatic material handling and storage systems
to integrate manufacturing operations
• Automatic inspection systems for quality control.

• It may turn out that automation of the process
is unnecessary or cannot be cost justified after
it has been simplified.
• If automation seems a feasible solution to
improving productivity, quality, or other
measure of performance, then the following
ten strategies provide a road map to search
for these improvements.

1. Specialization of operations
2. Combined operations
3. Simultaneous operations
4. Integration of operations
5. Increased flexibility
6. Improved material handling and
storage
7. On-line inspection
8. Process control and optimization
9. Plant operations control
10.Computer-integrated
manufacturing (CIM)

Specialization of operations
•use of special-purpose equipment
designed to perform one operation with
the greatest possible efficiency.
•concept of labor specialization

Combined operations
•Production occurs as a sequence of
operations.
•The strategy of combined operations
involves reducing the number of distinct
production machines or workstations
through which the part must be routed.
Simultaneous operations
•simultaneously perform the
operations that are
combined at one
workstation.
• In effect, two or more
processing (or assembly)
operations are being
performed simultaneously
on the same workpart, thus
reducing total processing
time.

Integration of operations
•Another strategy is to link several
workstations together into a single
integrated mechanism, using
automated work handling devices
to transfer parts between stations.
• In effect, this reduces the number
of separate machines through
which the product must be
scheduled.
Increased flexibility •This strategy attempts to achieve
maximum utilization of equipment
for job shop and medium volume
situations by using the same
equipment for a variety of parts or
products.
•Prime objectives are to reduce
setup time and programming time
for the production machine.

Improved material handling and
storage
• A great opportunity for reducing nonproductive time exists in the
use of automated material handling and storage systems.
• Typical benefits include reduced work-in-process and shorter
manufacturing lead times.
Inspection for quality of work is
traditionally performed after the
process is completed.
Incorporating inspection into the
manufacturing process permits
corrections to the process as the
product is being made.
This reduces scrap and brings the
overall quality of product closer to the
nominal specifications intended by the
designer.

Process control and optimization
•Intended to operate the individual
processes and associated equipment more
efficiently.
•By this strategy, the individual process
times can be reduced and product quality
improved.
Plant operations control
•Whereas the previous strategy was concerned with the control
of the individual manufacturing process, this strategy is
concerned with control at the plant level.
• It attempts to manage and coordinate the aggregate
operations in the plant more efficiently.
•Its implementation usually involves a high level of computer
networking within the factory.

BALANCING OF ASSEMBLY LINES
USING AVAILABLE ALGORITHMS
Assembly Line Balancing (ALB) is the term commonly used to
refer to the decision process of assigning tasks to workstations in
a serial production system.
The task consists of elemental operations required to convert raw
material in to finished goods.

•Most manufactured consumer products are assembled.
•Each product consists of multiple components joined together
by various assembly processes.
•These kinds of products are usually made on a manual
assembly line.

Factors favoring the use of manual assembly lines
• Demand for the product is high or medium
• The products made on the line are identical or similar
• The total work required to assemble the product can be
divided into small work elements
• It is technologically impossible or economically infeasible to
automate the assembly operations.

Additional factors One Line
• Specialization of Labor-. Each worker becomes a Specialist
• Inter Changeable parts- Manufactured to sufficiently close
tolerances
•Work Flow Principle- Which involves moving the work to the
worker rather than vice versa. Each work unit flows smoothly
through the production line, traveling the minimum distance
between stations.
•Line Pacing- (Cycle Time) Pacing is generally implemented by
means of a mechanized conveyor.

Fundamentals of Manual Assembly
Lines
•Sequence of workstations where assembly tasks are performed by
human workers
•Products assembled as they move on the go.
•Each portion worker works on a part of the total work on the unit.
• Launch Base Parts on Beginning Line
• Base part travels through successive stations and workers add
components that progressively build the product.
•Material transport line-move the base parts along the line as they
are gradually transformed into final products.
• Fast working stations are ultimately limited by slowest station.

• When the workers stand, they
can move about the station area
to perform their assigned task.
This is common for assembly of
large products such as cars,
trucks, and major appliances.
• The product is typically moved by
a conveyor at constant velocity
through the station.
• The worker begins the assembly task near the upstream side of
the station and moves along with the work unit until the task is
completed, then walks back to the next work unit and repeats
the cycle.

Smaller assembled products
(such as small appliances,
electronic devices, and
subassemblies used on larger
products), the workstations are
usually designed to allow the
workers to sit while they perform
their tasks.
This is more comfortable and less fatiguing for the workers
and is generally more conducive to precision and accuracy in
the assembly task

Work Transport Systems
MANUAL- Passed from station to station by the workers
themselves
Two problems result from this mode of operation:
starving and blocking.

Starving is the situation in which
the assembly operator has
completed the assigned task on the
current work unit, but the next unit
has not yet arrived at the station.
The worker is thus starved for
work.
Blocking
means that the operator has
completed the assigned task on the
current work unit but cannot pass
the unit to the downstream station
because that worker is not yet
ready to receive it. The operator is
therefore blocked from working.

MECHANIZED
• Power conveyors and material handling
equipments were utilized
• Classified into three categories
1. Continuous Transport System
2. Synchronous Transport System
3. Asynchronous Transport System

Line Pacing
• A manual assembly line operates at a certain cycle time that is
established to achieve the required production rate of the line.
• On average each worker must complete the assigned task at
his/her station within the cycle time, or else the required
production rate will not be achieved.
• This pacing of the workers is one of the reasons why a manual
assembly line is successful.
• Pacing provides a discipline for the assembly line workers that
more or less guarantees a certain production rate.

Three alternative Levels of Pacing
(1)rigid pacing, Worker is allowed only a fixed time
(2) pacng with margin, the worker is allowed to complete the
task at the station within a specified time range.
The maximum time of the range is longer than the cycle time, so
that a worker is permitted to take more time if a problem occurs
or if the task time required for a particular work unit is longer
than the average
(3) no pacing, meaning that no time limit exists within which the
task at the station must be finished. This case can occur when
(1) manual work transport is used on the line,
(2) work units can be removed from the conveyor, allowing the
worker to take as much time as desired to complete a given
unit, or
(3) an asynchronous conveyor is used and the worker controls
the release of each work unit from the station.

Single model line
Produces only one product in large quantities.
Every work unit is identical, so the task performed at each
station is the same for all products.
This line type is intended for products with high demand.

Batch-model and mixed-model line
BATCH MODEL
• Produces each product in
batches.
• Workstations are set up to
produce the required
quantity of the first product,
then the stations are
reconfigured to produce the
next product, and so on.
MIXED MODEL
• A mixed-model line also
produces more than one
model; however, the
models are not produced in
batches; instead, they are
made simultaneously on the
same line.
• While one station is working
on one model, the next
station is processing a
different model.

Analysis of Single Mode Assembly
Lines
Cycle Time and Workload Analysis
Hourly Production Rate is given by

Total Cycle time
Tc = cycle time of the line,
min/cycle;
Rp = required production rate
The constant 60 converts the
hourly production rate to a cycle
time in minutes; and E = line
efficiency.
Typical values of E for a manual
assembly line are in the range
0.90–0.98.
The cycle time Tc establishes the ideal cycle rate for the
line

work content time (Twc)
•The total time of all work elements that must be performed
on the line to make one unit of product.
•It represents the total amount of work that is to be accomplished
on the product by the assembly line.
•It is useful to compute a theoretical minimum number of workers
that will be required on the assembly line to produce a product
with known Twc and specified production rate Rp.

Repositioning losses. Some time will be lost at each station for
repositioning of the work unit or the worker. Thus, the time available
per worker to perform assembly is less than Tc.
The line balancing problem. It is virtually impossible to divide the
work content time evenly among all workstations. Some stations are
bound to have an amount of work that requires less time than Tc.
This tends to increase the number of workers.
Procedure for re positioning time calculation
• The repositioning time Tr must be subtracted from the cycle
time Tc to obtain the available time remaining to perform the
actual assembly task at each workstation.
• The time to perform the assigned task at each station is called
the service time.
• It is symbolized Tsi, where i is used to identify station, i = 1, 2,c,
n.

BOTTLENECK STATION
There will be at least one station at which Tsi is maximum.
This is referred to as the bottleneck station because it
establishes the cycle time
REPOSITIONING EFFICIENCY

MODEL OF LINE BALANCING PROBLEM

Minimum Rational Work Elements.
A minimum rational work element is a small amount of work that
has a specific limited objective, such as adding a component to
the base part, joining two components, or performing some
other small portion of the total work content.

Precedence Diagram
•For example, to create a threaded hole, the hole must be drilled
before it can be tapped.
• A machine screw that will use the tapped hole to attach a mating
component cannot be
fastened before the hole has been drilled and tapped.
• These technological requirements on the work sequence are
called precedence constraints. They complicate the line
balancing problem.

The total work content time is the sum of the work element times
0.2 0.4 0.7 0.1 0.3 0.11 0.32 0.6 0.27 0.38 0.5 0.12wcT            
= 4 min

(b) Given the annual demand, the hourly production rate is
(c) The corresponding cycle time Tc with an uptime efficiency of 96%
is
(d) The theoretical minimum number of workers is given by
Equation
(e) The available service time against which the line must be
balanced is
Ts=Tc-Tr=1.08-0.08=1.00min

Measures of Line Balance Efficiency
• Measures must be defined to indicate how good a given line
balancing solution is.
• One possible measure is balance efficiency, which is the work
content time divided by the total available service time on the
line:
Eb = balance efficiency, often expressed as a percent;
Ts = the maximum available
service time on the line (Max)Tsi, min/cycle; and w = number of
workers.

Worker Requirements.
Line Balancing Algorithms
The objective in line balancing is to distribute the total workload
on the assembly line as evenly as possible among the workers.

LARGEST CANDIDATE RULE
PRECEDENCE DIAGRAM

STEP 1:
work elements are arranged in descending order according to their Tek
values

Minimum No of work stations
min
wc
c
T
n
T

min
4
3.7 4
1.08
n   

(1)Assign elements to the worker at the first workstation by starting
at the top of the list and selecting the first element that satisfies
precedence requirements and does not cause the total sum of
Tek at that station to exceed the allowable Ts; when an element is
selected for assignment to the station, start back at the top of the
list for subsequent assignments;
(2) when no more elements can be assigned without exceeding Ts,
then proceed to the next station;
(3) repeat steps 1 and and 2 for as many additional stations as
necessary until all elements have been assigned.

Work Elements Assigned to Stations According to the Largest
Candidate Rule
WORK STATION ELEMENTS TEST
TIME
STATION TIME IDLE TIME
I 2 0.4
5 0.3
1 0.2 1.00-1
4 0.1 1.0 0
II 3 0.7 1.00-0.8
6 0.11 0.81 0.2
III 8 0.6 1.00-0.98
10 0.38 0.98 0.02
IV 7 0.32 1.00-0.59
9 0.27 0.59 0.49
V 11 0.5 1.00-0.62
12 0.12 0.62 0.38

Balance Delay min
min
100c wc
c
n T T
BD
n T
  
  
 

Kilbridge and Wester Method
•This method has received considerable attention since its
introduction in 1961 and has been applied with apparent success to
several large line balancing problems in industry.
• It is a heuristic procedure that selects work elements for
assignment to stations according to their position in the
precedence diagram.
•In the Kilbridge and Wester method, work elements in the
precedence diagram are arranged into columns, as shown in Figure .
• The elements can then be organized into a list according to their
columns, with the elements in the first column listed first.
• Such a list of elements has been developed for the example
problem in Table .

KILBRIDGE AND WESTER METHOD
PRECEDENCE DIAGRAM

Steps to follow
1. Work elements in precedence diagram are
arranged to columns.
2. Work elements are allocated to the stations
according to their columns with elements in
the first column listed first.

Ranked Positional Weights Method
• In this method, a ranked positional weight value
(call it RPW for short) is computed for each
element.
• The RPW takes into account both the Tek value
and its position in the precedence diagram.
• Specifically, RPW k is calculated by summing Tek
and all other times for elements that follow Tek in
the arrow chain of the precedence diagram.
• Elements are compiled into a list according to
their RPW value, and the algorithm proceeds
using the same three steps as before.

RANKED POSITION METHOD
PRECEDENCE DIAGRAM

TRANSFER LINE MONITORING SYSTEM
(TLMS)
• Each processing operation is performed at a
workstation, and the stations are physically integrated
by means of a mechanized work transport system to
form an automated production line.
• Machining (milling, drilling, and similar rotating cutter
operations) is commonly performed on these
production lines, in which case the term transfer line or
transfer machine is used.
• Other applications of automated production lines
include robotic spot welding in automobile final
assembly plants, sheet metal pressworking, and
electroplating of metals.

WORKPART TRANSPORT
The transfer mechanism of the automated
flow line must not only move the partially
completed workparts or assemblies between
adjacent stations, it must also orient and locate
the parts in the correct position for processing
at each station.
The general methods of transporting
workpieces on flow lines can be classified into
the following three categories:
1. Continuous transfer
2. Intermittent or synchronous transfer
3. Asynchronous or power-and-free

ALSO…
The most appropriate type of transport system for a
given application depends on such factors as:
The types of operation to be performed
The number of stations on the line
The weight and size of the work parts
Whether manual stations are included on the line
Production rate requirements
Balancing the various process times on the line

1) Continuous transfer
The workparts are moved continuously at Constant
speed.
This requires the workheads to move during
processing in order to maintain continuous registration
with the workpart.
For some types of operations, this movement of the
workheads during processing is not feasible, It would
be difficult for example, to use this type of system on a
machining transfer line because of inertia problems
due to the size and weight of the workheads.
Examples of its use are
In beverage bottling operations,
Packaging,

2) Intermittent transfer
As the name suggests, in this method the workpieces
are transported with an intermittent or discontinuous
motion.
The workstations are fixed in position and the parts are
moved between stations and then registered at the
proper locations for processing.
All workparts are transported at the same time and, for
this reason, the term "synchronous transfer system" is
also used to describe this method of workpart transport
.

3) Asynchronous transfer
This system of transfer, also referred to as a "power-and-free
system,“
It allows each workpart to move to the next station when
processing at the current station has been completed.
Each part moves independently of other parts. Hence, some
parts are being processed on the line at the same time that
others are being transported between stations.
In-process storage of workparts can be incorporated into the
asynchronous systems with relative ease.
Parallel stations or several series stations can be used for the
longer operations
Single stations can be used for the shorter operations.
A disadvantage of the power and-free systems is that the cycle
rates are generally slower than for the other types.

Transfer mechanisms-
There are various types of transfer mechanisms
used to move parts between stations.
These mechanisms can be grouped into two
types:
# Linear travel for in- line machines,
# Rotary motion for dial indexing machines.

Linear transfer System
We will explain the operation of three of the typical
mechanisms; The walking beam transfer bar
system
The powered roller conveyor system, and
The chain-drive conveyor system.

The walking beam transfer bar system
The work-parts are lifted up from their workstation
locations by a transfer bar and moved one position
ahead, to the next station.
The transfer bar then lowers the pans into nests which
position them more accurately for processing.
For speed and accuracy, the motion of the beam is
most often generated by a rotating camshaft powered
by an electric motor or a roller movement in a profile
powered by hydraulic cylinder

Powered roller conveyor
system
This type of system is used in general stock
handling systems as well as in automated flow
lines.
The conveyor can be used to move pans or pallets
possessing flat riding surfaces.
The rollers can be powered by either of two
mechanisms.
A belt drive
A chain drive
Powered roller conveyors are versatile transfer
systems
because they can be used to divert work

Chain-drive conveyor system
Either a chain or a flexible steel belt is used to transport
the work carriers.
The chain is driven by pulleys in either an “over-and-
under“ config, in which the pulleys turn about a horizontal
axis, or an “around-the-corner“ configuration, in which
the pulleys rotate about a vertical axis.

Rotary transfer mechanisms
There are several methods used to index a
circular table or dial at various equal angular
positions corresponding to workstation locations.

Rack and pinion
This mechanism is simple but is not considered
especially suited to the high-speed operation
often associated with indexing machines.
It uses a piston to drive the rack, which causes
the pinion gear and attached indexing table to
rotate, A clutch or other device is used to provide
rotation in the desired direction.

Ratchet and pawl:
A ratchet is a device that allows linear or rotary motion in
only one direction, while preventing motion in the
opposite direction.
Ratchets consist of a gearwheel and a pivoting spring
loaded finger called a pawl that engages the teeth.
Either the teeth, or the pawl, are slanted at an angle, so
that when the teeth are moving in one direction, the pawl
slides up and over each tooth in turn, with the spring
forcing it back with a 'click' into the depression before the
next tooth.
When the teeth are moving in the other direction, the
angle of the pawl causes it to catch against a tooth and
stop further motion in that direction.

Geneva mechanism:
The Geneva mechanism uses a continuously
rotating driver to index the table,
If the driven member has six slots for a six-station
dial indexing machine, each turn of the driver will
cause the table to advance one-sixth of a turn.
The driver only causes movement of the table
through a portion of its rotation.
For a six-slotted driven member, 120° of a complete
rotation of the driver is used to index the table. The
other 240° is dwell. For a four-slotted driven
member, the ratio would be 90° for index and 270°
for dwell. The usual number of indexings per
revolution of the table is four, five, six, and eight.

CONTROL FUNCTIONS
Controlling an automated flow line is a complex problem,
owing to the sheer number of sequential steps that must
be carried out. There are three main functions that are
utilized to control the operation of an automatic transfer
system.
The first of there is an operational requirement, the
second is a safety requirement, and the third is dedicated
to improving quality.
Sequence control.
Safety monitoring
Quality monitoring
Instantaneous control
Memory control

Sequence control.
The purpose of this function is to coordinate the
sequence of actions of the transfer system and its
workstations. The various activities of the automated flow
line must be carried out with split-second timing and
accuracy. Sequence control is basic to the operation of
the flow line
Safety monitoring:
This function ensures that the transfer system does not
operate in an unsafe or hazardous condition. Sensing
devices may be added to make certain that the cutting
tool status is satisfactory to continue to process the
workpart in the case of a machining-type transfer line.
Other checks might include monitoring certain critical
steps in the sequence control function to make sure that
these steps have all been performed and in the correct

Conventional thinking on the control of the line has been
to stop operation when a malfunction occurred. While
there are certain malfunctions representing unsafe
conditions that demand shutdown of the line, there are
other situations where stoppage of the line is not
required and perhaps not even desirable. There are
alternative control strategies
1.Instantaneous control and
2. Memory control.

Instantaneous control:
This mode of control stops the operation of the flow line
immediately when a malfunction is detected. It is relatively
simple, inexpensive, and trouble-free. Diagnostic features are
often added to the system to aid in identifying the location and
cause of the trouble to the operator so that repairs can be
quickly made. However, stopping the machine results in loss
of production from the entire line, and this is the system's
biggest drawback.
Memory control:
In contrast to instantaneous control, the memory system is
designed to keep the machine operating. It works to control
quality and/or protect the machine by preventing subsequent
stations from processing the particular workpart and by
segregating the part as defective at the end of the line. The
premise upon which memory-type control is based is that the
failures which occur at the stations will be random and
infrequent. If, however, the station failures result from cause
and tend to repeat, the memory system will not improve
production but, rather, degrade it. The flow line will continue to
operate, with the consequence that bad parts will continue to

Buffer Storage
It is not uncommon for production flow lines to include
storage zones for collecting banks of workparts along
the line.
One example of the use of storage zones would be two
intermittent transfer systems, each without any storage
capacity, linked together with a workpart inventory area.
It is possible to connect three, four, or even more lines
in this manner. Another example of workpart storage on
flow lines is the asynchronous transfer line.
With this system, it is possible to provide a bank of
workparts for every station on the line.

Analysis of Transfer Lines
• There are a few assumptions that we will
have to make about the operation of the
Transfer line & rotary indexing machines
• The workstations perform operations such
as machining & not assembly.
• Processing times at each station are
constant though they may not be equal.
• There is synchronous transfer of parts.
No internal storage of buffers.

Unit 1-automation of assembly lines

Unit 1-automation of assembly lines

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Unit 1-automation of assembly lines

Similar to Unit 1-automation of assembly lines (20)

Recently uploaded

Recently uploaded (20)

Unit 1-automation of assembly lines