09 Automated Assembly

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Assembly


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1. Fundamentals of Automated Production Lines

2. Applications of Automated Production Lines

24/04/2014Manufacturing System

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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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U-shaped layout


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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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Manufacturing System

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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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(a) Horizontal and (b) vertical devices for placement ofparts onto dial-indexing table


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Escapement of rivet-shaped parts actuated by workcarriers


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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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09 Automated Assembly