Post on 03-Jun-2018
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Assembly
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1. Fundamentals of Automated Production Lines
2. Applications of Automated Production Lines
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Automated Production Lines
High production of parts requiring multipleprocessing operations
Fixed automation
Applications:
Transfer lines used for machining
Robotic spot welding lines in automotive finalassembly
Sheet metal stamping
Electroplating of metals
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Where to Use Automated ProductionLines High product demand
Requires large production quantities
Stable product design Difficult to change the sequence and content of
processing operations once the line is built
Long product life
At least several years Multiple operations required on product
The different operations are assigned to differentworkstations in the line
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Benefits of Automated ProductionLines Low direct labor content
Low product cost
High production rates
Production lead time and work-in-process areminimized
Factory floor space is minimized
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Automated Production Line - Defined
Fixed-routing manufacturing system that consistsof multiple workstations linked together by a
material handling system to transfer parts fromone station to the next
Slowest workstation sets the pace of the line Workpart transfer:
Palletized transfer line Uses pallet fixtures to hold and move workpartsbetween stations
Free transfer line
Part geometry allows transfer without pallet fixtures
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Automated Production Line
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General configuration of an automated production line consisting ofn automated workstations that perform processing operations
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System Configurations
In-line - straight line arrangement ofworkstations
Segmented in-line two or more straight linesegments, usually perpendicular to each other
Rotary indexing machine (e.g., dial indexing
machine)
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Segmented In-Line Configurations
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L-shaped layout
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Segmented In-Line Configurations
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U-shaped layout
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Segmented In-Line Configurations
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Rectangular configuration
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Two Machining Transfer Lines
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Rotary Indexing Machine
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Workpart Transfer Mechanisms Linear transfer systems:
Continuous motion not common for automated
systems Synchronous motion intermittent motion, all
parts move simultaneously Asynchronous motion intermittent motion,
parts move independently Rotary indexing mechanisms:
Geneva mechanism Others
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Belt-Driven Linear Transfer System
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Side view of chain or steel belt-driven conveyor (over
and under type) for linear transfer using work carriers
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Walking Beam Transfer System
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Walking Beam Transfer System
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Geneva Mechanism with Six Slots
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Cam Mechanism to Drive Dial IndexingTable
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Storage Buffers in Production LinesA location in the sequence of workstations where
parts can be collected and temporarily stored
before proceeding to subsequent downstreamstations Reasons for using storage buffers:
To reduce effect of station breakdowns To provide a bank of parts to supply the line
To provide a place to put the output of the line To allow curing time or other required delay To smooth cycle time variations To store parts between stages with different
production rates
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Storage Buffer
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Storage buffer between two stages of a production line
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Control Functions in an AutomatedProduction Line Sequence control
To coordinate the sequence of actions of the
transfer system and workstations
Safety monitoring
To avoid hazardous operation for workers andequipment
Quality control
To detect and possibly reject defective work unitsproduced on the line
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Applications of Automated ProductionLines Transfer lines for machining
Synchronous or asynchronous workpart transport
Transport with or without pallet fixtures,depending on part geometry
Various monitoring and control features available
Rotary transfer machines for machining Variations include center column machine andtrunnion machine
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System Design Considerations Building block approach: machine tool companies
specialize in transfer lines and indexing machines
User contracts for custom-engineered line Standard modules such as workheads, feed units,
transfer mechanisms, and bases
Called a unitized production line
Link line: uses standard machine tools connected byspecialized handling system
Specialized processes often engineered by the usercompany
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Standard Feed Units used with In-Lineor Rotary Transfer Machines
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(a) Horizontal feed drive unit, (b) angular feed drive
unit, and (c) vertical column feed drive unit
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Standard Milling Head
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Milling head unit that attaches to one of the feed drive
units in the previous slide
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Rotary Transfer Machine (Plan View)
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Center Column Machine (Plan View )
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Analysis of Transfer Lines
Three problem areas must be considered:
1. Line balancing
To divide the total work load among workstationsas evenly as possible
2. Processing technology
Theory and principles about the manufacturing
or assembly processes used on the line
3. System reliability - two cases:
Transfer lines with no internal parts storage
Transfer lines with internal storage buffers
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Lines with No Storage Buffers
As the number of workstations increases
Line efficiency and production rate are adversely
affected
As reliability of individual workstationsdecreases
Line efficiency and production rate are adverselyaffected
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Lines with Storage Buffers If E
0and E
are nearly equal
Then little advantage is gained by adding a storage
buffer If E
is much greater than E
0
Then adding a storage buffer may improve lineperformance significantly
Storage buffers should be located so that productionrates of the stages are about equal
During operation, if any buffers are always empty oralways full, then the buffer is serving little purpose
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Lines with Storage Buffers
The maximum possible efficiency is achieved by:
Setting the number of stages = number of stations
Using large buffer capacities
The law of diminishing returns operates inmulti-stage automated lines:
As the number of storage buffers is increased, lineefficiency improves at an ever-decreasing rate
As storage buffer capacity is increased, lineefficiency improves at an ever-decreasing rate
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1. Fundamentals of Automated Assembly Systems
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Automated Assembly - Defined The use of mechanized and automated devices to
perform the various assembly tasks in an
assembly line or cell Fixed automation usually
Most automated assembly systems are designed toperform a fixed sequence of assembly steps on aspecific product that is produced in very largequantities
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Automated Assembly - Application
Characteristics Where is automated assembly appropriate:
High product demand
Stable product design
The assembly consists of no more than a limitednumber of components
The product is designed for automated assembly
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Typical Products Alarm clocks
Ball bearings
Ball point pens Cigarette lighters
Door mechanisms
Gear boxes
Light bulbs
Locks
Mechanical pencils PCB assemblies
Small electric motors
Wrist watches
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Assembly Processes in Automated
Assembly Adhesive bonding
Insertion of components
Placement of components Riveting
Screw fastening
Snap fitting
Soldering
Spot welding Stapling
Stitching
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System Configurations In-line assembly machine
Dial indexing machine
Carousel assembly system
Single-station assembly cell
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In-Line Assembly Machine A series of automatic workstations located along and in-line transfer system
Either synchronous or asynchronous work transfer used
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Dial Indexing Machine Base parts are loaded onto
fixtures or nests attached to acircular dial table, and
components are added atworkstations located aroundthe periphery of the dial as itindexes from station to station
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Dial indexing assembly machine
(Bodine Corp.)
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Carousel Assembly System A hybrid between circular work flow of dial indexing
machine and straight work flow of in-line system
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Single-Station Assembly Cell Assembly operations are performed on a base part at a single location
A robot is sometimes used as the assembly machine
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Multi-Station vs. Single-Station Multi-station assembly machine or line
Faster cycle rate
High production quantities
More operations possible
More components per assembly
Single-station assembly cell Suited to robotic assembly
Intended for lower production quantities
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Parts Delivery at Workstations Typical parts delivery system at a workstation
consists of the following hardware components:
Hopper - container for parts Parts feeder - removes parts from hopper
Selector and/or orientor - to assure part is inproper orientation for assembly at workhead
Feed track - moves parts to assembly workhead
Escapement and placement device - removes partsfrom feed track and places them at station
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Parts Delivery System at Station
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Vibratory Bowl Feeder Most versatile of hopper feeders for small parts
Consists of bowl and helical track
Parts are poured into bowl
Helical track moves part from bottom of bowl tooutlet
Vibration applied by electromagnetic base Oscillation of bowl is constrained so that partsclimb upward along helical track
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Vibratory Bowl Feeder
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Vibratory Bowl Feeder
Photo courtesy Syntron Inc.
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Selector and/or Orientor Purpose - to establish the proper orientation of
the components for the assembly workhead
Selector Acts as a filter
Only parts in proper orientation are allowed topass through to feed track
Orientor
Allows properly oriented parts to pass
Reorients parts that are not properly oriented
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Parts Selection and Orientation
a) Selectorb) Orientor
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Feed Track Moves parts from hopper to assembly workhead
Categories:
Gravity - hopper and feeder are located at higherelevation than workhead
Powered - uses air or vibration to move partstoward workhead
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Escapement and Placement Devices
Escapement device Removes parts from feed track at time intervals
that are consistent with the cycle time of theassembly workhead
Placement device Physically places the parts in the correct location
at the assembly workstation Escapement and placement devices aresometimes the same device, sometimes differentdevices
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Escapement and Placement Devices
(a) Horizontal and (b) vertical devices for placement ofparts onto dial-indexing table
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Escapement and Placement Devices
Escapement of rivet-shaped parts actuated by workcarriers
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Escapement and Placement Devices
Two types of pick-and-place mechanisms fortransferring base parts from feeders to work carriers
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Analysis of Assembly Systems The parts delivery system at each station must
deliver components to the assembly operation at a
net rate that is greater than or equal to the cycle rateof the assembly workhead Otherwise, assembly system performance is limited by
the parts delivery system rather than the assemblyprocess technology
Component quality has an important effect onsystem performance - poor quality means Jams at stations that stop the entire assembly system Assembly of defective components in the product
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Analysis of Assembly Systems As the number of stations increases, uptime
efficiency and production rate are adversely
affected due to parts quality and stationreliability effects The cycle time of a multi-station assembly
system is determined by its slowest station
By comparison with a multi-station assemblysystem, a single-station assembly cell with thesame number of assembly tasks has a lowerproduction rate but a higher uptime efficiency
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Analysis of Assembly Systems Multi-station assembly systems are appropriate for high
production applications and long production runs By comparison, single-station assembly cells have a
longer cycle time and are more appropriate for mid-range quantities
Storage buffers should be used on partially automatedproduction lines to isolate the manual stations from
breakdowns at the automated stations An automated station should be substituted for a manualstation only if it has the effect of reducing cycle timesufficiently to offset negative effects of lower reliability
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